Open access peer-reviewed chapter - ONLINE FIRST
Half-reaction potentials of the main low-temperature electrolysis paths [36].
Abstract
Low-temperature electrolysis driven by renewable energy sources has emerged as a vital route for sustainable chemical production, carbon cycle closure, and the realization of a circular economy. Central to the advancement of this technology is the development of efficient and stable electrocatalyst materials, which govern both the thermodynamics and kinetics of electrochemical reactions. The catalytic phase—specifically whether the material exists as a metal, oxide, or hydroxide—is decisive in determining key performance metrics such as activity, selectivity, stability, and product distribution. Each phase exhibits unique physicochemical attributes, including variations in crystal structure, electronic properties, and surface affinity, affecting adsorption behavior, charge transfer dynamics, and corrosion resistance. This chapter provides a detailed exploration of the roles of metal, oxide, and hydroxide phases in electrocatalysis, focusing on their mechanistic contributions in critical reactions like the electrochemical CO₂ reduction (ECR) and alkaline oxygen evolution reaction (OER). In addition to discussing the intrinsic properties of each phase, the chapter highlights the significance of phase evolution, particularly in situ transformations and induced transitions, as a promising strategy to enhance catalytic performance. These dynamic processes often lead to increased surface area and grain boundary density, which can substantially boost reactivity and durability. By combining structural insights with mechanistic understanding, this chapter aims to offer a cohesive framework for designing next-generation electrocatalysts optimized for high-performance electrolysis applications.
Keywords
- electrochemistry
- CO2 reduction
- low-temperature electrolysis
- electrocatalyst
- oxygen evolution reaction
- OER
- alkaline electrolysis
1. Introduction
Low-temperature electrolysis, particularly when powered by renewable energy sources, is rapidly emerging as a cornerstone technology in the transition to a circular and decarbonized economy. By facilitating the transformation of plentiful and readily accessible feedstocks—including water and captured carbon dioxide (CO2)—into chemical fuels and valuable industrial products, it provides a direct pathway to reduce greenhouse gas emissions, enhance energy security, and close the anthropogenic carbon cycle. The process is underpinned by two electrochemical reactions: the electrochemical reduction of carbon dioxide (ECR) at the cathode and the oxygen evolution reaction (OER) at the anode. Collectively, these elements facilitate the generation of storable and transportable energy carriers, including hydrogen and carbon-based fuels, thereby addressing the mounting demand for flexible, distributed energy systems [1, 2, 3].
In recent years, ECR has attracted significant attention as a method of storing excess renewable electricity in the form of chemical bonds. The process has the potential to yield a range of valuable products, including carbon monoxide (CO), formate, methane, ethanol, and other C2+ compounds, with the particular product depending strongly on the catalyst used. Among these, CO and formate are regarded as particularly promising due to their relatively high selectivity and favorable techno-economic profiles. More complex products, such as ethanol or hydrocarbons, offer high energy density and are therefore desirable for liquid fuel applications. However, their large-scale production remains challenging due to competing reaction pathways and low Faradaic efficiencies [4, 5, 6, 7]. In parallel, water electrolysis continues to serve as the most mature and direct route to green hydrogen production. In this process, the cathodic half-reaction, otherwise known as the hydrogen evolution reaction (HER), is relatively facile, while the anodic half-reaction, otherwise known as the OER, remains kinetically sluggish due to its complex four-electron mechanism [8]. Consequently, the OER is widely regarded as the limiting step in overall water-splitting efficiency and is a key focus of catalyst development efforts. The advancement of both ECR and OER is contingent on the design and implementation of effective electrocatalyst materials [9, 10, 11]. The catalyst’s properties determine the energy required to drive the reaction and also influence reaction kinetics, intermediate stabilization, product selectivity, and long-term system durability. With regard to the reduction of CO₂, the composition of the catalyst dictates the favored pathways. For example, copper uniquely facilitates C-C coupling and the formation of C₂ + products, while silver and bismuth favor simpler products such as CO and formate [12]. In the context of the OER, traditional benchmarks such as IrO₂ and RuO₂ offer excellent performance in acidic and alkaline environments. However, they are constrained by scarcity and cost, rendering their large-scale application unsustainable. This has given rise to a significant increase in the level of interest in transition metal oxides and hydroxides, particularly those based on nickel, iron, and cobalt, which have demonstrated competitive activity and are more abundant. However, these alternatives frequently exhibit limited durability under prolonged operation, undergoing structural transformations or dissolution under oxidative electrochemical conditions [13, 14, 15, 16].
The development of electrocatalysts capable of achieving high activity, selectivity, and stability simultaneously remains a central challenge in electrolysis research. Achieving product specificity in ECR is a particularly complex process due to the numerous competing multi-electron pathways, each of which is sensitive to changes in catalyst morphology, surface structure, and local reaction environment. It is imperative to consider stability, particularly in the context of OER catalysts, which are required to demonstrate resilience to harsh oxidative potentials, fluctuating pH levels, and corrosive electrolytes over the course of their operational lifetimes. A considerable number of materials that show great promise in laboratory settings often demonstrate significant degradation when subjected to industrial conditions. Moreover, the overall system efficiency is closely associated with the overpotential required to initiate and sustain the reactions. It is imperative to reduce these energy inputs while preserving elevated current densities to ensure economic viability and facilitate scale-up [17, 18, 19, 20, 21].
In order to address these interconnected challenges, it is necessary to develop a more profound mechanistic understanding of the behavior of catalysts under operating conditions. This includes phase transitions, active site restructuring, and interfacial dynamics. As electrochemical systems move toward practical deployment, these efforts will be instrumental in bridging the gap between fundamental materials science and applied electrochemical engineering. It is therefore vital to acknowledge the potential of low-temperature electrolysis to play a pivotal role in the development of a resilient, low-carbon energy infrastructure.
2. Fundamentals of electrocatalysis in electrolysis
The ECR is a complex, multistage process that encompasses the transfer of multiple electrons [1, 2, 3]. It involves several crucial steps, including CO2 adsorption, electron transfer, and product desorption occurring at the electrode’s surface. Extensive research has revealed that the current density, the specific electrochemical species involved, and the selectivity of the ECR are predominantly influenced by the choice of electrode material and the reduction potential applied [22, 23, 24]. The initial step of the ECR is the diffusion of CO2(g) over the catalyst layer, followed by one e-transfer for the formation of the •
The electrochemical CO2 reduction (ECR) process follows the Eley-Rideal mechanism, where only one species undergoes adsorption [29, 30]. Initial Tafel analysis data suggested that Eqs. (1) and (2) could be the possible rate-determining steps (RDS) for ECR. However, recent work by Deng et al. [31] has shown that the RDS for CO formation is equation Eq. (1), while the RDS is independent of the catalyst material used and the reaction environment. The Eq. (1) is a composite step that encompasses the crucial processes of CO2(g) diffusion over the catalyst layer and electron transfer. At lower current densities, the rate of electron transfer in Eq. (1) is the critical factor influencing the rate of ECR. At higher levels of polarization, of more than 200 mA cm−2, the diffusion of CO2(g), as seen in Eq. (1), toward the active surface of the catalyst becomes the limiting factor for the ECR rate. Given the strong correlation between the catalyst’s properties and the ECR performance, the Sabatier principle emerges as a crucial tool for predicting a catalyst’s activity and product selectivity [32]. It asserts that for high catalytic activity, the interactions between the catalyst and the reaction species should exhibit an intermediate intensity for the reaction to be favored. The parasitic hydrogen evolution reaction (HER) progresses at the cathode in parallel with the ECR. The generally accepted HER mechanism in alkaline and neutral media is exhibited below:
The splitting of a water molecule and the adsorption of hydrogen on the surface of the electrode or catalyst is described by the Volmer step, Eq. (5), which always consists of the initial step of the HER. This is then followed by the production of hydrogen through either an electrochemical process, the Heyrovsky step, Eq. (6), or a chemical process, as in a Tafel step, Eq. (7). Numerous studies have exhibited that at low η, lower than −0.15 V, the HER goes through the Heyrovsky step, while the Tafel step follows in parallel. However, at a high η of more than −0.25 V, the electrode is considered overwhelmed by Hads. The Tafel step becomes negligible, with the HER progressing through the Heyrovsky step, owing to its high rate constant [33, 34, 35]. The low thermodynamic potential of the HER, summarized in Table 1, and its faster overall kinetics strongly favor the reaction at the expense of ECR (Figure 1).
Figure 1.
Schematic representation of a typical electrolyzer, utilized for the cathodic CO2 valorization (ECR) and the anodic oxygen production (OER) at alkaline conditions.
| Product (Reaction) | Equation | Eo (V vs. SHE, 25°C) |
|---|---|---|
| Hydrogen (HER, acidic) | 2H+ + 2e− → H2 | 0 |
| Carbon monoxide (ECR) | CO2 + 2H+ + 2e− → CO + H2O | −0.104 |
| Formic acid (ECR) | CO2 + 2H+ + 2e− → HCOOH | −0.171 |
| Methanol (ECR) | CO2 + 6H+ + 6e− → CH3OH + H2O | 0.016 |
| Methane (ECR) | CO2 + 8H+ + 8e− → CH4 + 2H2O | 0.169 |
| Ethylene (ECR) | 2CO2 + 12H+ + 12e− → C2H4 + 4H2O | 0.085 |
| Oxygen (OER, alkaline) | 4OH− → O2 + 2H2O + 4e− | 0.401 |
| Hydrogen (HER, alkaline) | 2H2O + 2e− → H2 + 2OH− | −0.828 |
Table 1.
At lower polarization, the reactions’ kinetics are mainly determined by the e-transfer. The function of a selective and efficient catalyst for the ECR is to successfully redirect the majority of the total current of the electrolyzer toward the ECR instead of the HER. It is worth noting that at a high current density of more than 300 mA cm−2, both the ECR, Eq. (4), and HER, Eq. (6), rates are primarily governed by species desorption, with additional limitations imposed by mass transfer of the reactants. Considering the significantly higher diffusion coefficient of H2, DH2, compared to the CO2 one, DCO2, and CO one, DCO [37], the faster mass transfer of the H2 will inevitably favor the HER at high current densities. At lower reaction rates, ECR is favored by the catalyst’s active centers so that the partial current density for the ECR, jCO, is always larger than that for HER, jH2. While at higher currents, due to the effect of mass-transfer limitations on the reactions’ species, HER takes over, imposing the opposite condition [38, 39, 40]. Three key figures of merit determine the preference for either ECR or HER. The Faradaic Efficiency,
The oxygen evolution reaction (OER) in alkaline media, found in Table 1, follows complex yet distinct mechanistic pathways as reaction pathways [41, 42]. The two primary mechanistic pathways have been identified for the OER in alkaline media as either the Adsorbate Evolution Mechanism (AEM) or the Lattice Oxygen Mechanism (LOM). The AEM is the traditional surface-mediated pathway where OER proceeds through proton-coupled electron transfers (PCETs) involving adsorbed intermediates [2, 43]. These steps typically occur on transition metal active sites (M), with oxygen forming via a sequence of reactions involving *OH, *O, and *OOH surface species, as seen below:
The AEM activity is closely tied to the binding energies of these intermediates. However, the adsorption energies of *OH and *OOH are linearly correlated, with a typical energy difference of ∼3.2 eV. This imposes a theoretical overpotential limit of ∼370 mV. To overcome this bottleneck, recent strategies focus on optimizing intermediate adsorption via doping, vacancy engineering (VO), strain modulation, and electronic structure tuning, according to the Sabatier principle [44]. In contrast, the LOM introduces an alternative pathway in which the lattice oxygen (Olat) of the catalyst itself participates in the OER. This mechanism circumvents the *OOH intermediate and breaks the linear scaling constraints of AEM, potentially enabling lower overpotential and faster kinetics, as seen:
While LOM offers the advantage of enhanced activity by overcoming the adsorption energy limitations of AEM, it may compromise catalyst stability due to irreversible lattice oxygen loss and the formation of oxygen vacancies. Nevertheless, it has been shown that tuning metal-oxygen co-valence can modulate lattice participation, with lower Tafel slopes (∼43 mV dec−1) serving as an experimental fingerprint for LOM pathways [45, 46].
Overall, it is evident that the catalyst material plays a pivotal role in shaping both the reaction pathway and the overall efficiency of the electrochemical process, with its properties directly influencing performance and selectivity.
3. Electrocatalytic phases
Catalyst-material phases—namely metals, oxides, and hydroxides—play crucial and often complementary roles in governing electrocatalytic performance in low-temperature electrolysis, especially for the ECR and the OER. These phases influence key factors such as electron conductivity, adsorption energetics, intermediate stabilization, and structural stability, which in turn define activity, selectivity, and durability [47].
3.1 Metal phases in electrocatalysis
Metallic phases serve as highly conductive active sites, promoting efficient electron transfer and the adsorption of reactants. Their electrocatalytic performance is fundamentally influenced by their intrinsic properties, including electronic structure, binding energies, and the position of the d-band center. The electronic structure dictates the distribution of electronic states in the vicinity of the Fermi level, which in turn affects the ability of the catalyst to adsorb and activate reactants. The binding energies of the key intermediates must be optimized to ensure their stability during the reaction while also allowing for the desorption of the product. A pivotal descriptor in this context is the d-band center, whose position relative to the Fermi level is indicative of the adsorption strength of reaction intermediates. Metals with a higher d-band center have been observed to bind adsorbates more strongly, which has the potential to enhance activation. However, this binding may also impede product release. These properties have been shown to influence the overall activity, selectivity, and stability of metal catalysts [48].
The selectivity of ECR is governed by the adsorption energies and reaction pathways of key intermediates on the catalyst surface. For instance, the formation of *COOH and *OCHO intermediates leads to CO and formate products, respectively. The binding strength of these intermediates is influenced by the electronic structure of the catalyst, particularly the d-band center. A higher d-band center is generally associated with enhanced adsorption, which can stabilize intermediates but concurrently impede product desorption. Conversely, a lower d-band center leads to weaker adsorption, facilitating desorption but potentially destabilizing intermediates. It is notable that copper (Cu) is distinguished by its capacity to yield multicarbon (C₂+) products, including ethylene and ethanol. This phenomenon is attributed to its moderate binding strength for *CO intermediates, which facilitates C-C coupling steps. The formation of C-C bonds is a critical step in the generation of C2+ products, and it requires a delicate balance in the adsorption energies of intermediates to proceed efficiently. Conversely, silver (Ag) and gold (Au) exhibit high selectivity toward CO production due to their weaker binding of *CO intermediates, which promotes desorption before further reduction can occur. Tin (Sn) has been observed to promote the formation of formate, a process that is believed to be the result of its strong affinity for the *OCHO intermediate. The aforementioned trends in product selectivity are closely tied to the metal-dependent adsorption energetics of intermediates such as *COOH, *CO, and *OCHO [49]. A key addition from Ringe et al. [50] is the recognition of the role played by electrochemical double-layer (EDL) effects and field-driven adsorption in ECR kinetics, particularly for metals like gold. Their multiscale modeling and experimental analysis demonstrated that the rate-limiting step for CO formation on Au shifts with overpotential, from *COOH to *CO at low overpotential to CO₂ adsorption at intermediate potentials, and eventually to CO₂ mass transport at high overpotential. This underscores the significance of EDL-induced surface charge effects on *CO₂ stabilization and the recognition that reaction kinetics are not solely dictated by thermodynamics or static binding energies but also by field-mediated interactions with dipolar intermediates. In a similar manner, the alloying of metals has been demonstrated to modulate the electronic structure and binding properties of the active surface, thereby exerting a consequential influence on ECR selectivity. For instance, Cu-Ag alloys have been demonstrated to enhance C2 product formation by stabilizing *CO and *OCCO intermediates while suppressing formate pathways. This synergistic effect is attributable to the electronic interactions between Cu and Ag atoms, which adjust the d-band center and, consequently, the adsorption energies of key intermediates. In the same context, Cu-Sn alloys have been observed to exhibit selectivity toward CO or formate production, depending on the composition. The incorporation of Sn into Cu modifies the electronic environment, affecting the binding strength of intermediates and altering reaction pathways. It is possible to design catalysts with tailored selectivity for desired ECR products by carefully controlling the alloy composition and structure [51, 52].
Transition metal materials in their metallic phases (e.g., Ni, Co, Fe, Cu, or their alloys) are typically characterized by high electrical conductivity and structural robustness. These properties enhance OER efficiency by lowering energy barriers and accelerating intermediate transformations (e.g., M–OH → M–O → M–OOH) [53, 54]. However, as OER catalysts, their direct activity is generally limited. Metallic phases frequently function as precursors or conductive supports, forming the backbone structure that undergoes in situ transformation into more catalytically surface-active oxide or oxy-hydroxide phases under OER operating conditions. This process maintains mechanical stability and prevents degradation, as evidenced by the NiFe/NiFeOx core-shell structure [55]. Transition metals dynamically shift oxidation states (e.g., Ni0 → Ni3+, Fe0 → Fe3+), optimizing adsorption energies of OER intermediates (*O, *OH, *OOH) and fine-tuning reaction pathways [56]. The combination of metals with differing oxidation states, such as NiFe alloys with Fe3+ and Ni0, has been shown to yield synergistic effects, thereby reducing the overpotential to 160 mV at 10 mA/cm2. This is achieved by leveraging Fe3+ for OER activity and Ni0 for charge transfer. In the context of OER, metallic surfaces oxidize to form active oxyhydroxides (e.g., NiOOH, CoOOH), with the metallic core ensuring the continuous supply of electrons to these catalytic sites [57]. Strategies such as doping (e.g., Fe into Ni) or hybridization with conductive supports further enhance performance by modifying electronic structures, stabilizing intermediates, and increasing surface area. Collectively, these mechanisms ensure the balance of conductivity, active site availability, and stability, thus enabling transition metal-based catalysts to demonstrate comparable OER efficiency to that of noble metal systems [58].
3.2 Oxide phases in electrocatalysis
Oxide phases, typically transition metal oxides (e.g., NiO, Co3O4, Cu2O), offer tunable redox chemistry and rich surface chemistry. Their electrocatalytic functionality is governed by a combination of their electronic conductivity and surface reactivity, both of which are highly dependent on their composition and structural features. Metal oxides exhibit a wide spectrum of electronic conductivities, ranging from insulating to semiconducting to metallic, rendering them versatile platforms for catalytic applications. Transition metal oxides exhibit high intrinsic conductivity, facilitating efficient charge transfer during reactions such as the ECR or the OER [59]. The surface reactivity of metal oxides is influenced by surface terminations, lattice defects, and the presence of hydroxyl groups, complementing their bulk properties. The surface features of the material under investigation create active sites that enhance the adsorption and activation of reactant molecules. It is noteworthy that oxygen vacancies can function as electron-rich sites, thereby promoting CO2 adsorption and facilitating the formation of key intermediates during reduction. Furthermore, the acid-base character of the oxide surface has been demonstrated to modulate the adsorption strength and stability of intermediates, thereby directing reaction pathways and influencing product selectivity. Collectively, these intrinsic and tunable properties render metal oxides as highly adaptable materials for electrocatalytic systems [60].
For the ECR, metal oxides fulfill a vital function by stabilizing key reaction intermediates, thereby significantly influencing both catalytic activity and product selectivity. In the context of reductive electrochemical conditions, metal oxides frequently undergo partial reduction, resulting in the generation of distinctive surface characteristics that diverge significantly from their metallic counterparts. These features include the formation of oxygen vacancies, the emergence of mixed-valence states, and the retention of metastable oxide phases. Each of these contributes to the catalytic behavior observed in oxide-containing electrocatalysts [61]. One of the most critical contributions of partially reduced metal oxides is the stabilization of key reaction intermediates through the presence of oxygen vacancies (VO). These electron-rich defects function as active adsorption sites, thereby facilitating the binding and activation of CO2 molecules. The enhancement of the formation and stabilization of intermediates such as *COOH and *OCHO is influenced by oxygen vacancies, which in turn impact the subsequent formation of CO and formate. To illustrate this point, consider the case of SnO2-based catalysts. The deliberate generation of oxygen vacancies in these catalysts has been shown to correlate with an enhancement in formate selectivity. This is due to the stabilization of the *OCHO intermediate, which occurs preferentially over competing pathways [62]. Similarly, ZnO surfaces have been demonstrated to exhibit high CO selectivity, even in their partially reduced states. This finding suggests that active oxide sites persist under operational conditions and contribute directly to catalytic performance [63].
Furthermore, partially reduced metal oxides often exhibit a mixture of oxidation states on their surfaces, as exemplified by oxide-derived copper catalysts that feature Cu0, Cu+, and Cu2+ species [64]. This heterogeneity creates a dynamic and flexible surface environment where various intermediates can be stabilized through different adsorption configurations. The presence of Cu + sites has been shown to be specifically correlated with enhanced C-C coupling, a critical step in the formation of multicarbon products such as ethylene and ethanol. In addition to stabilizing intermediates, the surface characteristics of partially reduced oxides have been shown to suppress competing reactions, notably the HER. The utilization of catalysts that exhibit a preference for the adsorption and conversion of CO2-derived species over protons has been demonstrated to enhance the Faradaic efficiency toward the formation of desired carbon-based products. The capacity of non- and partially reduced metal oxides to provide tailored active sites, facilitate multi-electron reaction pathways, and mitigate undesired side reactions positions them as highly effective and tunable materials for selective and efficient ECR.
In addition to pristine metal oxides, composite heterostructured oxide-based catalysts have demonstrated considerable application potential as efficient ECR catalysts. A variety of metal-oxide interfaces are of significance in this regard, not only as structural foundations but also as contributors to the overall catalytic performance [65]. At these junctions, electronic and structural synergies arise that modify the adsorption energies of CO2 and its intermediates, enhance local electric fields, and tune the d-band center of the metallic phase. These interfacial phenomena create energetically favorable pathways for key reaction steps such as *COOH or *CO stabilization, C-C coupling, and proton-electron transfer [66]. Besides promoting direct catalytic activity through interfacial synergy, metal oxides serve a crucial function as catalyst supports for the ECR. Oxides like Cr2O3 and CeO2 offer excellent chemical and electrochemical stability under the reductive potentials typically applied during CO2 reduction. These materials are capable of maintaining their structural integrity and surface composition while enabling the uniform dispersion and anchoring of ECR active metallic nanoparticles (e.g., Ag) [67]. The stability of these supports under reaction conditions is essential for preventing nanoparticle aggregation and maintaining high electrochemical surface area throughout long-term operation.
Beyond their structural role, these oxides can also influence the local electronic environment at the metal-support interface. A characteristic example is the CeO2, known to possess oxygen storage capacity and a reversible Ce4+/Ce3+ redox couple, which enables it to participate in dynamic surface charge transfer processes during catalysis. This can influence the electronic density of deposited metal particles, leading to modified intermediate binding and potentially altered product selectivity [21]. These oxide-supported systems offer several strategic advantages: (i) improved dispersion of supported catalytic sites, (ii) enhanced CO2 adsorption at oxide-metal boundaries, and (iii) the suppression of side reactions (e.g., HER) through surface polarity tuning. In addition, these supports often contribute to a more favorable electrochemical environment by affecting local ion distributions and double-layer capacitance, both of which are known to impact ECR kinetics [68].
Transition metal oxides (TMOs) have been identified as a class of materials with considerable potential for use as OER catalysts, particularly within an alkaline environment. The appeal of these materials can be attributed to three key factors. Firstly, their structural diversity plays a significant role in their appeal, as do their tunable electronic properties. Secondly, their ability to host a variety of oxidation states is a crucial factor. Transition metal oxides (TMOs) have the capacity to adopt a variety of crystal structures, including spinel (e.g., Co3O4), perovskite (e.g., LaNiO3), and layered (e.g., NiO). These structures offer distinct catalytic sites and pathways for oxygen evolution. A significant development in the field of TMO-based OER catalysis is the emergence of mixed metal oxides, where the amalgamation of two or more transition metals results in a synergistic effect. For instance, NiFe oxides have repeatedly exhibited superior OER activity in comparison to their single-metal counterparts. The incorporation of Fe into NiO or Ni(OH)2 matrices has been demonstrated to increase the number of active sites while concomitantly modulating the electronic structure, thereby optimizing the adsorption energies of OER intermediates such as *OH, *O, and *OOH [69, 70, 71]. Similarly, the doping of other metals can introduce additional active sites, create oxygen vacancies, and enhance charge transfer. Cu-doped Co oxides have also demonstrated reduced overpotential and improved stability, attributed to lattice distortions and enhanced surface reactivity [72].
Defect engineering is another powerful strategy for boosting the OER performance of TMOs. Introducing oxygen vacancies, cation deficiencies, or lattice strain can significantly alter the electronic structure and increase the density of active sites [73]. For example, porous NiO/NiCo2O4 nanotubes with abundant oxygen vacancies have been shown to facilitate a four-electron OER pathway, achieving low Tafel slopes and high current densities [74]. The presence of defects not only enhances intrinsic activity but also improves conductivity, which is often a limiting factor for oxide catalysts. Morphology control, such as the synthesis of aerogels, nanowires, or hollow structures, further amplifies the catalytic performance by maximizing surface area and exposing more active facets. NiFe oxide aerogels, for instance, combine the benefits of high porosity and interconnected networks, leading to rapid mass transport and efficient charge separation [75]. Oxide phases offer a versatile platform for OER catalysis, with their performance tunable through compositional, structural, and morphological modifications. The ongoing development of mixed metal oxides, defect-rich materials, and hybrid structures continues to push the boundaries of OER efficiency and durability.
3.3 (Oxy)-hydroxide phases in electrocatalysis
Metal hydroxides represent a distinct and functionally versatile class of electrocatalytic materials, particularly in alkaline media, where they often serve as active phases or dynamic precursors to catalytically competent species. Their layered structures, rich in hydroxyl groups (-OH), enable reversible proton and electron transfer, thereby conferring remarkable electronic and chemical adaptability. These characteristics render them particularly pertinent in both the OER and the ECR contexts.
The emergence of hydroxide phases as critical components in ECR has been particularly pronounced in alkaline and near-neutral pH environments. The function of these elements extends beyond the provision of structural support, as they contribute directly to key aspects of the catalytic process, including intermediate stabilization, interfacial charge modulation, and promotion of multicarbon product pathways. These materials frequently manifest as surface layers or discrete domains in hybrid systems, exhibiting distinctive electrochemical and chemical properties that enhance both activity and selectivity. A pivotal mechanism through which hydroxide phases promote ECR is through the modification of the local pH near the catalyst surface. This effect is especially significant when hydroxide species are formed or accumulated in situ during electrochemical operation. As demonstrated in the research conducted by Xiao et al., the development of hydroxide-rich layers on Cd-based catalysts has been shown to significantly increase the local pH level. This, in turn, has been observed to impede the competing hydrogen evolution reaction (HER) and to encourage the formation of carbon monoxide (CO) with Faradaic efficiencies that exceed 99% across a wide range of potential ranges [76]. The catalytic enhancement can be mechanistically attributed to several factors. First, the elevated local pH favors the deprotonation and activation of CO2 molecules, facilitating the formation of key intermediates such as *COOH and *CO. These intermediates benefit from hydrogen bonding interactions with surface hydroxyls, which stabilize their adsorption and lower the energy barrier for subsequent reaction steps. In particular, *CO stabilization is crucial for efficient CO desorption or further reduction into multicarbon products on metal centers such as Cu. Secondly, hydroxide phases actively participate in forming dynamic and adaptive surface structures. Under ECR conditions, many metal catalysts can develop surface-reconstructed layers consisting of mixed metal-oxide-hydroxide domains. These layers serve as electron-rich interfaces, which alter the local electric field and improve the adsorption energetics of intermediates. For instance, in Cu-based catalysts, the presence of hydroxide has been linked to enhanced C-C coupling due to increased *CO coverage and stabilization of *OCCO intermediates—critical steps in the formation of C2 + products [77, 78]. Additionally, hydroxide-containing interfaces such as metal-hydroxide junctions have been shown to enhance charge redistribution and interfacial electric fields, tuning the binding energy of intermediates. These properties enable not only improved CO2 activation but also selective pathway steering by inhibiting proton adsorption and HER, enhancing the ECR. The structural and chemical flexibility of hydroxides under operating conditions allows them to function as dynamic catalytic components. They can regenerate or reconfigure during operation in response to potential changes, thereby maintaining active sites and suppressing deactivation phenomena observed in other oxide or metallic systems [79, 80, 81].
While oxide phases have traditionally been regarded as the primary OER catalysts, recent
Layered double hydroxides (LDHs) are recognized as highly effective pre-catalysts for the OER in alkaline water electrolyzers due to their unique structural and electronic properties. The layered structure of LDHs, composed of edge-sharing metal-hydroxide octahedra with intercalated anions, allows for significant compositional flexibility and the incorporation of multiple metal ions. This versatility enables LDHs to undergo dynamic surface reconstruction under OER conditions, transforming into catalytically active metal oxy-hydroxide phases such as NiOOH or FeOOH. To illustrate this point, consider the example of NiFe-LDHs, which can reconfigure into highly active NiFeOOH phases. This process results in low overpotential and enables expeditious redox cycling of the metal centers [90, 91]. Additionally, the high surface area of LDHs, especially when exfoliated into single-layer nanosheets, greatly increases the number of accessible active sites, leading to significantly enhanced OER activity compared to bulk materials and even surpassing benchmark catalysts like IrO2 [92, 93]. The compositional flexibility of LDHs also allows for synergistic interactions between different metal ions, such as Ni and Fe in NiFe-LDHs, where Ni promotes charge transfer and Fe optimizes the adsorption energies of OER intermediates. This synergy results in catalytic performance that is outstanding, with LDHs demonstrating low overpotential at high current densities. In addition, the hierarchical and porous architectures frequently observed in LDH-based materials enhance mass transport and stability, thereby ensuring efficient operation even at industrially relevant current densities. It is evident that the aforementioned characteristics collectively render LDHs a versatile and powerful platform for the development of next-generation OER catalysts in water electrolyzers [94].
Oxy-hydroxides are characterized by higher electrical conductivity than their oxide counterparts, owing to the presence of hydrated layers and proton intercalation. This facilitates rapid transport and efficient electron transfer during OER. The electronic and structural properties of oxyhydroxides can be further tuned through doping, defect engineering, and the creation of heterostructures. For example, Mo-doped NiFeOOH has been reported to follow a heterogeneous diatomic oxygen mechanism, achieving exceptional activity in alkaline media [95, 96, 97]. While oxyhydroxides are highly active in alkaline environments, their stability in acidic media remains a challenge due to the dissolution of transition metal ions. Overall, oxy-hydroxide phases are now widely recognized as the true active catalysts for OER, with their formation and stability being key determinants of long-term performance. The dynamic interplay between oxide and oxy-hydroxide phases underscores the importance of
4. Phase transitions and in situ catalyst evolution
Electrocatalytic systems frequently undergo dynamic phase transitions (Figure 2a) between metallic, oxide, and hydroxide states, thereby significantly influencing catalytic activity, selectivity, and stability. The electrochemical environment is a driving force behind these transformations and is fundamental to key processes such as water splitting, nitrogen reduction, and carbon conversion. The Pourbaix diagram (Figure 2b) provides a thermodynamic framework for predicting the stable phase of a material as a function of pH and electrode potential.
Figure 2.
(a) Schematic representation of the main phase transitions to be observed in redox reactions for the different material phases. (b) Generic Pourbaix diagram for a metal (M) indicating the various phase transitions induced by overpotential and pH. (c) ECR reaction pathway over metallic Cu. (d) ECR reaction pathway over metallic-Cu(OH)2 and its parallel non-Faradaic reduction to metallic-Cu; both figures (c and d) were reprinted after permission from Iijima et al. [98].
4.1 Phase transitions in CO2 reduction electrocatalysis
Phase transitions among metal, oxide, and hydroxide states play a crucial role in governing catalytic behavior during the ECR. These dynamic transformations, strongly influenced by parameters such as applied potential, electrolyte composition, and pH, can significantly alter the catalyst’s surface composition, electronic structure, and reactivity [99]. One of the most impactful transitions is the reduction of metal oxides and hydroxides to their metallic state (Figure 2c and d) under cathodic conditions. This process gives rise to oxide-derived metals (OD-Ms), a class of catalysts that exhibit distinct physicochemical properties compared to their pristine metallic counterparts. The formation typically begins with the electrochemical or thermal reduction of an oxide-based material, acting as the pre-catalyst [100]. This principle is applied to both pristine metal-oxide materials and composite oxide pre-catalysts. Leading to the formation of either single-phase OD-Ms or OD-metal alloys [101, 102]. This redox cycling results in the partial or complete removal of lattice oxygen, generating defects such as vacancies, dislocations, and grain boundaries. These structural features enhance the density of active sites and alter the local electronic environment, while residual subsurface oxygen or oxide species may persist and further influence catalytic behavior [103, 104]. The transformation is often incomplete due to kinetic limitations, particularly in thicker oxide layers or under mild reduction conditions. The result is a mixed-phase surface composed of metallic, oxide, and/or hydroxide domains. These interfacial regions create a heterogeneous and highly active catalytic landscape, enabling alternative reaction pathways and offering a broad spectrum of binding sites not present on clean metal surfaces. Oxide-derived metals possess several key characteristics that make them particularly effective for ECR. Their defect-rich morphology, high surface area, and high grain boundary (GB) concentration improve CO2 adsorption and intermediate stabilization, and overall, the ECR activity [105, 106]. The modified electronic structure—often reflected in shifts in the d-band center due to embedded oxygen species—alters the binding energies of crucial intermediates such as *COOH, *CO, and *OCHO, thus tuning both activity and product selectivity [107]. Furthermore, metal-oxide interfaces present in these materials contribute to intermediate stabilization via local electric fields and spatial confinement. Importantly, the partially reduced and defective surfaces also suppress the competing HER, thereby enhancing Faradaic efficiency for carbon-based products.
In addition to oxide-to-metal transitions, the reversible transformation between metal oxides and hydroxides plays an equally crucial role in tuning catalytic behavior for the ECR. The electrolyte pH has a significant influence on the stability and restructuring of these phases [81]. Under alkaline conditions, metal oxides readily convert to hydroxides due to the abundance of OH− ions, whereas acidic environments favor re-oxidation or de-hydroxylation back to oxide phases. These phase transitions significantly affect the surface speciation and electronic properties of the catalyst, directly impacting the adsorption energies of key intermediates and, consequently, the activity and selectivity of the ECR. Notably, the formation of hydroxide layers during ECR is not a passive or inert phenomenon but a dynamic, in situ process that creates highly reactive surface states [98]. Hydroxide-rich layers have been shown to elevate the local pH, suppress the competing HER, and stabilize critical intermediates such as *CO and *OCCO—key precursors in C-C coupling pathways. These effects collectively promote the formation of valuable multicarbon (C2+) products such as ethylene and ethanol, especially under alkaline electrolysis conditions. Hydroxide-derived metals (HD-Ms), obtained via electrochemical reduction of pre-formed metal hydroxides, exhibit catalytic properties distinct from their pristine metallic counterparts [108]. The reduction process introduces a high density of surface defects, such as vacancies, grain boundaries, and amorphous regions, that serve as catalytic hot spots. These structural features facilitate CO2 adsorption and activation, while residual hydroxyl or subsurface oxygen species can modulate the electronic structure, finely tuning the binding strength of reaction intermediates. This is particularly evident in copper-based systems, where surface-adsorbed hydroxyls (OHad) can either enhance *CO adsorption and C-C coupling when optimally present or hinder activity by blocking active sites and promoting HER if in excess [76]. The hydroxide-to-metal transformation, therefore, is not merely a preparative step but a functional transition that defines the catalyst’s performance. The structural and electronic complexity resulting from this transition enables enhanced selectivity toward C2+ products by facilitating multistep reaction pathways and intermediate stabilization [109].
4.2 Phase transitions in oxygen evolution reaction (OER)
The OER in water electrolysis requires efficient electrocatalysts to overcome its inherently sluggish kinetics. LDHs have emerged as promising pre-catalysts due to their ability to undergo in situ structural transformation into active metal oxy-hydroxide phases under OER conditions. LDHs, with their general formula [M2+1-xM3+x(OH)2][An−]x/n· mH2O, feature tunable metal cations (e.g., Ni, Fe, Co) and interlayer anions (e.g., NO3−, CO32−) that enable dynamic reconstruction during electrochemical activation. Under anodic potentials, LDHs transition from their as-synthesized α-phase to catalytically active γ-phase oxyhydroxides (MOOH), characterized by ∼8% lattice contraction and interlayer cation exchange (e.g., K+ replacing anions). This structural evolution enhances electrical conductivity and exposes redox-active metal sites, as observed in NiFe-LDHs that form γ-NiFeOOH with optimized Ni3+/Fe3+ coordination environments [110].
The phase transformation is driven by oxidative deprotonation and metal oxidation, facilitated by defects and dopants. For instance, Cr doping in FeCoNi hydroxides reduces the free energy barrier for M(OH)2 → MOOH conversion by 10–22%, enabling faster activation [111]. Similarly, oxygen vacancies in Sr.2–CaxFe2O6–δ perovskites boost conductivity by two orders of magnitude compared to defect-free analogs.
The effectiveness of LDHs as pre-catalysts originates from their layered structure, which ensures uniform distribution of metal cations and provides efficient ionic diffusion pathways. Dynamic interlayer anions such as NO3− disrupt the layered framework during electrochemical activation, generating structural disorder that produces highly defective interfaces. These defect-rich surfaces exhibit optimized electronic configurations and coordinative unsaturated sites, which directly boost catalytic performance by lowering activation barriers for intermediate adsorption [114]. Post-transformation, the resulting oxyhydroxides exhibit exceptional stability (e.g., FeCoNiCr hydroxide maintains 150-hour OER activity with a 224 mV overpotential) [111]. This
The dynamic transformation between metal oxides and oxyhydroxides plays a key role in determining the performance and stability of OER electrocatalysts. Under anodic potentials, oxides such as NiO and Co3O4 transform into active oxy-hydroxide phases (e.g., γ-NiOOH, CoOOH), which possess hydrated layered structures that facilitate efficient proton-coupled electron transfer and expose more active sites [115]. The stabilization of these oxy-hydroxide species can be enhanced through doping and strain engineering; for example, Fe incorporation in NiOOH improves redox cycling and durability, while interstitial Si doping in RuO2 suppresses unwanted lattice oxygen activity and enhances stability in acidic media [116]. Cation leaching and surface restructuring also play crucial roles. Controlled leaching, such as Mo from NiFe sulfides, can generate defect-rich, highly active surfaces and extend catalyst lifetime, but excessive leaching leads to structural degradation and loss of activity. Therefore, balancing reconstruction and leaching is key to achieving both high activity and long-term stability in OER catalysts. These findings underscore the importance of tuning oxide-hydroxide transformations and surface chemistry to design robust, efficient water-splitting electrocatalysts. These degradation pathways are exacerbated in acidic media, where lattice oxygen participation in OER (Mars-van Krevelen mechanism) induces crystalline phase collapse and irreversible surface amorphization [117].
4.3 Comparative analysis of phase interplay and stability
In the ECR, the stability and performance of catalysts are intricately linked to phase transformations occurring during operation, particularly in oxide-derived and hydroxide-transformed metal systems. Oxide-derived metals, such as copper, undergo partial reduction (e.g., Cu2O → Cu0) under cathodic conditions, creating highly defective surfaces enriched with grain boundaries and undercoordinated sites that enhance activity and C-C coupling efficiency. However, these features also introduce vulnerabilities, such as structural coarsening, surface atom migration, and residual oxide instability, which compromise long-term durability under sustained operation [118, 119, 120]. Phase transitions between hydroxides and metallic copper (e.g., Cu(OH)2 → Cu0) also yield catalytically favorable morphologies but can suffer from dynamic reconstruction and uncontrolled subsurface oxidation or re-oxidation, especially at fluctuating potentials. Additionally, electrolyte-driven restructuring, including carbonate formation or cation exchange (e.g., K+ or Na+ adsorption), can lead to loss of active phase, catalyst delamination, and suppression of multicarbon product pathways [121, 122].
To address these degradation pathways, recent strategies have focused on controlling redox transformations and interfacial composition. Pre-conditioning oxide catalysts under reducing potentials enables the formation of thermodynamically stabilized defect sites while minimizing over-reduction or collapse of active regions [123]. Doping approaches have been shown to modulate electronic structures and maintain surface roughness essential for C-C coupling while simultaneously mitigating agglomeration and phase collapse. Composite catalyst systems, particularly metal-oxide and metal-hydroxide hybrids (e.g., Cu-CeO2, Cu-Ni(OH)2), further enhance operational robustness by offering lattice strain buffering and dual-functionality in CO2 activation and proton management. These heterojunctions facilitate charge redistribution and stabilize reactive intermediates like *CO or *CHO through synergistic interfacial fields. Operando studies reveal that maintaining partial oxide features under bias—rather than a complete reduction—is critical for preserving selectivity toward C2 + products [124, 125, 126].
The interplay between oxide and oxy-hydroxide phases during OER directly impacts catalytic stability and degradation pathways. In operational conditions, catalysts are subject to dynamic structural transformations, including hydroxylation of metal oxides (e.g., NiO → γ-NiOOH) and sulfur-oxygen exchange in sulfides. These processes expose active sites and concomitantly trigger destabilizing processes, such as cation leaching and phase over-oxidation [127].
Strategies to stabilize active phases focus on modulating reconstruction pathways. Doping high-valent cations (e.g., Mo in NiFeOOH) strengthens metal-oxygen bonds, suppressing over-oxidation and maintaining γ-phase integrity under high potentials [128]. Similarly, strain engineering in perovskites like SrCo0.9Fe0.1O3-δ stabilizes metastable phases with optimal oxygen vacancy densities, enhancing conductivity while resisting segregation [129]. For layered double hydroxides (LDHs), Cr doping promotes homogeneous cation distribution, delaying phase separation during OER and enabling 150-hour stability [130]. These approaches highlight the balance required between activity-enhancing phase transitions and structural preservation, guiding the design of catalysts that reconcile high performance with operational durability [131, 132].
5. Conclusion
The ECR is highly sensitive to the structural and electronic properties of the catalyst, which are governed by dynamic phase transformations. Oxide-derived metals (O-DMs) have emerged as highly effective electrocatalysts due to their defect-rich surfaces and altered electronic structures resulting from oxide-to-metal reduction. These structural features stabilize key intermediates such as *CO and *OCCO, thereby promoting multicarbon (C2+) product formation. Subsurface oxygen residues and grain boundaries in O-DMs have been shown to shift the d-band center, thereby tuning the adsorption energies of intermediates and enhancing reaction selectivity. Furthermore, in situ studies demonstrate that such catalysts are not static but undergo dynamic restructuring under operating conditions, thereby continuously regenerating active sites. Furthermore, the integration of oxides such as CeO2 or ZnO within composites has been demonstrated to enhance CO2 activation through the introduction of synergistic effects and oxygen vacancies, thereby facilitating enhanced electron transfer. While contemporary strategies have considerably enhanced selectivity and activity, challenges persist in the domains of long-term stability control and atomic-level phase behavior comprehension.
The catalytic performance of transition metal-based materials for the OER is intricately linked to their phase composition and dynamic transformations under operating conditions. Metallic phases function as conductive precursors, thereby facilitating the formation of catalytically active surfaces. Oxide phases offer structural versatility and tunable electronic properties, with their performance further enhanced by defect engineering, morphology control, and compositional tuning. In conclusion, it is the oxy-hydroxide phases that are formed in situ during OER that host the most active sites and drive the reaction with the highest efficiency, particularly when doped synergistically with elements such as Fe or Cr.
Recent advances in in situ and in operando characterization have enhanced the understanding of dynamic phase transitions in electrocatalysts, enabling more rational and targeted design strategies. Recent research has focused on the use of doping, defect engineering, and strain modulation to direct surface reconstruction and optimize active site exposure and electronic structure. In future research, the focus should be on enhancing the stability of oxy-hydroxide phases, particularly in acidic environments. Future efforts should also focus on developing hybrid materials with tunable interfaces, leveraging computational modeling, and applying machine learning to predict and control phase behavior. The integration of real-time diagnostics to monitor structural evolution under operating conditions has the potential to further accelerate the development of efficient, stable, and earth-abundant catalysts, thereby advancing the deployment of sustainable electrochemical energy technologies.
References
- 1.
Laha S, Lee Y, Podjaski F, Weber D, Duppel V, Schoop LM, et al. Ruthenium oxide nanosheets for enhanced oxygen evolution catalysis in acidic medium. Advanced Energy Materials. 2019; 9 (15):1803795. DOI: 10.1002/aenm.201803795 - 2.
Grimaud A, Hong WT, Shao-Horn Y, Tarascon J-M. Anionic redox processes for electrochemical devices. Nature Materials. 2016; 15 (2):121-126. DOI: 10.1038/nmat4551 - 3.
Middleton RS, Carey JW, Currier RP, Hyman JD, Kang Q, Karra S, et al. Shale gas and non-aqueous fracturing fluids: Opportunities and challenges for supercritical CO2. Applied Energy. 2015; 147 :500-509. DOI: 10.1016/j.apenergy.2015.03.023 - 4.
Spurgeon JM, Kumar B. A comparative technoeconomic analysis of pathways for commercial electrochemical CO2 reduction to liquid products. Energy & Environmental Science. 2018; 11 (6):1536-1551. DOI: 10.1039/C8EE00097B - 5.
Verma S, Kim B, Jhong H-R“M”, Ma S, Kenis PJA. A gross-margin model for defining technoeconomic benchmarks in the electroreduction of CO2. ChemSusChem. 2016; 9 (15):1972-1979. DOI: 10.1002/cssc.201600394 - 6.
Dinh C-T, García de Arquer FP, Sinton D, Sargent EH, Rate H. Selective, and stable electroreduction of CO2 to CO in basic and neutral media. ACS Energy Letters. 2018; 3 (11):2835-2840. DOI: 10.1021/acsenergylett.8b01734 - 7.
Weng L-C, Bell AT, Weber AZ. A systematic analysis of Cu-based membrane-electrode assemblies for CO2 reduction through Multiphysics simulation. Energy & Environmental Science. 2020; 13 (10):3592-3606. DOI: 10.1039/D0EE01604G - 8.
King LA, Hubert MA, Capuano C, Manco J, Danilovic N, Valle E, et al. A non-precious metal hydrogen catalyst in a commercial polymer electrolyte membrane electrolyser. Nature Nanotechnology. 2019; 14 (11):1071-1074. DOI: 10.1038/s41565-019-0550-7 - 9.
García de Arquer FP, Dinh C-T, Ozden A, Wicks J, McCallum C, Kirmani AR, et al. CO2 electrolysis to multicarbon products at activities greater than 1 a Cm−2. Science. 2020; 367 (6478):661-666. DOI: 10.1126/science.aay4217 - 10.
Wang X, Wang Z, García de Arquer FP, Dinh C-T, Ozden A, Li YC, et al. Efficient electrically powered CO2-to-ethanol via suppression of deoxygenation. Natural Energy. 2020; 5 (6):478-486. DOI: 10.1038/s41560-020-0607-8 - 11.
Zhong M, Tran K, Min Y, Wang C, Wang Z, Dinh C-T, et al. Accelerated discovery of CO2 electrocatalysts using active machine learning. Nature. 2020; 581 (7807):178-183. DOI: 10.1038/s41586-020-2242-8 - 12.
Kortlever R, Shen J, Schouten KJP, Calle-Vallejo F, Koper MTM. Catalysts and reaction pathways for the electrochemical reduction of carbon dioxide. Journal of Physical Chemistry Letters. 2015; 6 (20):4073-4082. DOI: 10.1021/acs.jpclett.5b01559 - 13.
Trasatti S. Electrocatalysis by oxides — Attempt at a unifying approach. Journal of Electroanalytical Chemistry and Interfacial Electrochemistry. 1980; 111 (1):125-131. DOI: 10.1016/S0022-0728(80)80084-2 - 14.
Lee Y, Suntivich J, May KJ, Perry EE, Shao-Horn Y. Synthesis and activities of rutile IrO2 and RuO2 nanoparticles for oxygen evolution in acid and alkaline solutions. Journal of Physical Chemistry Letters. 2012; 3 (3):399-404. DOI: 10.1021/jz2016507 - 15.
Son YJ, Kawashima K, Wygant BR, Lam CH, Burrow JN, Celio H, et al. Anodized nickel foam for oxygen evolution reaction in Fe-free and Unpurified alkaline electrolytes at high current densities. ACS Nano. 2021; 15 (2):3468-3480. DOI: 10.1021/acsnano.0c10788 - 16.
Liang C, Zou P, Nairan A, Zhang Y, Liu J, Liu K, et al. Exceptional performance of hierarchical Ni–Fe oxyhydroxide@NiFe alloy nanowire Array electrocatalysts for large current density water splitting. Energy & Environmental Science. 2020; 13 (1):86-95. DOI: 10.1039/C9EE02388G - 17.
Bediako DK, Surendranath Y, Nocera DG. Mechanistic studies of the oxygen evolution reaction mediated by a nickel–borate thin film electrocatalyst. Journal of the American Chemical Society. 2013; 135 (9):3662-3674. DOI: 10.1021/ja3126432 - 18.
Trześniewski BJ, Diaz-Morales O, Vermaas DA, Longo A, Bras W, Koper MTM, et al. In situ observation of active oxygen species in Fe-containing Ni-based oxygen evolution catalysts: The effect of pH on electrochemical activity. Journal of the American Chemical Society. 2015; 137 (48):15112-15121. DOI: 10.1021/jacs.5b06814 - 19.
Görlin M, Ferreira de Araújo J, Schmies H, Bernsmeier D, Dresp S, Gliech M, et al. Tracking catalyst redox states and reaction dynamics in Ni–Fe Oxyhydroxide oxygen evolution reaction electrocatalysts: The role of catalyst support and electrolyte pH. Journal of the American Chemical Society. 2017; 139 (5):2070-2082. DOI: 10.1021/jacs.6b12250 - 20.
Nguyen TN, Chen Z, Zeraati AS, Shiran HS, Sadaf SM, Kibria MG, et al. Catalyst regeneration via chemical oxidation enables long-term electrochemical carbon dioxide reduction. Journal of the American Chemical Society. 2022; 144 (29):13254-13265. DOI: 10.1021/jacs.2c04081 - 21.
Stamatelos I, Scheepers F, Pasel J, Dinh C-T, Stolten D. Ternary Zn-Ce-Ag catalysts for selective and stable electrochemical CO2 reduction at large-scale. Applied Catalysis B: Environment and Energy. 2024; 353 :124062. DOI: 10.1016/j.apcatb.2024.124062 - 22.
Gupta K, Bersani M, Darr JA. Highly efficient electro-reduction of CO2 to formic acid by Nano-copper. Journal of Materials Chemistry A. 2016; 4 (36):13786-13794. DOI: 10.1039/C6TA04874A - 23.
Zhu S, Ren X, Li X, Niu X, Wang M, Xu S, et al. Core-Shell ZnO@Cu2O as catalyst to enhance the electrochemical reduction of carbon dioxide to C2 products. Catalysts. 2021; 11 (5):535. DOI: 10.3390/catal11050535 - 24.
Zhang T, Li Z, Zhang J, Wu J. Enhance CO2-to-C2+ products yield through spatial management of CO transport in Cu/ZnO tandem electrodes. Journal of Catalysis. 2020; 387 :163-169. DOI: 10.1016/j.jcat.2020.05.002 - 25.
Qin B, Li Y, Fu H, Wang H, Chen S, Liu Z, et al. Electrochemical reduction of CO2 into Tunable syngas production by regulating the crystal facets of earth-abundant Zn catalyst. ACS Applied Materials & Interfaces. 2018; 10 (24):20530-20539. DOI: 10.1021/acsami.8b04809 - 26.
Peterson AA, Nørskov JK. Activity descriptors for CO2 electroreduction to methane on transition-metal catalysts. Journal of Physical Chemistry Letters. 2012; 3 (2):251-258. DOI: 10.1021/jz201461p - 27.
Liu X, Xiao J, Peng H, Hong X, Chan K, Nørskov JK. Understanding trends in electrochemical carbon dioxide reduction rates. Nature Communications. 2017; 8 (1):15438. DOI: 10.1038/ncomms15438 - 28.
Hansen HA, Varley JB, Peterson AA, Nørskov JK. Understanding trends in the electrocatalysts activity of metals and enzymes for CO2 reduction to CO. Journal of Physical Chemistry Letters. 2013; 4 (3):388-392. DOI: 10.1021/jz3021155 - 29.
Cheng T, Xiao H, Goddard WAI. Reaction mechanisms for the electrochemical reduction of CO2 to CO and Formate on the Cu(100) surface at 298 K from quantum mechanics free energy calculations with explicit water. Journal of the American Chemical Society. 2016; 138 (42):13802-13805. DOI: 10.1021/jacs.6b08534 - 30.
Liang S, Huang L, Gao Y, Wang Q, Liu B. Electrochemical reduction of CO2 to CO over transition metal/N-doped carbon catalysts: The active sites and reaction mechanism. Advanced Science. 2021; 8 (24):2102886. DOI: 10.1002/advs.202102886 - 31.
Deng W, Zhang P, Seger B, Gong J. Unraveling the rate-limiting step of two-electron transfer electrochemical reduction of carbon dioxide. Nature Communications. 2022; 13 (1):803. DOI: 10.1038/s41467-022-28436-z - 32.
Kari J, Olsen JP, Jensen K, Badino SF, Krogh KBRM, Borch K, et al. Sabatier principle for interfacial (heterogeneous) enzyme catalysis. ACS Catalysis. 2018; 8 (12):11966-11972. DOI: 10.1021/acscatal.8b03547 - 33.
Ďurovič M, Hnát J, Bouzek K. Electrocatalysts for the hydrogen evolution reaction in alkaline and neutral media. A comparative review. Journal of Power Sources. 2021; 493 :229708. DOI: 10.1016/j.jpowsour.2021.229708 - 34.
Jakšić JM, Vojnović MV, Krstajić NV. Kinetic analysis of hydrogen evolution at Ni–Mo alloy electrodes. Electrochimica Acta. 2000; 45 (25):4151-4158. DOI: 10.1016/S0013-4686(00)00549-1 - 35.
Conway BE, Tilak BV. Interfacial processes involving electrocatalytic evolution and oxidation of H2, and the role of chemisorbed H. Electrochimica Acta. 2002; 47 (22):3571-3594. DOI: 10.1016/S0013-4686(02)00329-8 - 36.
Handoko AD, Wei F, Jenndy, Yeo BS, Seh ZW. Understanding heterogeneous electrocatalysts carbon dioxide reduction through operando techniques. Nature Catalysis. 2018; 1 (12):922-934. DOI: 10.1038/s41929-018-0182-6 - 37.
Marrero TR, Mason EA. Gaseous diffusion coefficients. Journal of Physical and Chemical Reference Data. 2009; 1 (1):3-118. DOI: 10.1063/1.3253094 - 38.
Casebolt DiDomenico R, Levine K, Reimanis L, Abruña HD, Hanrath T. Mechanistic insights into the formation of CO and C2 products in electrochemical CO2 reduction─the role of sequential charge transfer and chemical reactions. ACS Catalysis. 2023; 13 (7):4938-4948. DOI: 10.1021/acscatal.2c06043 - 39.
Zheng W, Wang D, Zhang Y, Zheng S, Yang B, Li Z, et al. Promoting industrial-level CO2 electroreduction kinetics via accelerating proton feeding on a metal-free aerogel electrocatalyst. Nano Energy. 2023; 105 :107980. DOI: 10.1016/j.nanoen.2022.107980 - 40.
Yang W, Xue Z, Yang J, Xian J, Liu Q, Fan Y, et al. Fe nanoparticles embedded in N-doped porous carbon for enhanced electrocatalysts CO2 reduction and Zn-CO2 battery. Chinese Journal of Catalysis. 2023; 48 :185-194. DOI: 10.1016/S1872-2067(23)64415-8 - 41.
Rossmeisl J, Qu Z-W, Zhu H, Kroes G-J, Nørskov JK. Electrolysis of water on oxide surfaces. Journal of Electroanalytical Chemistry. 2007; 607 (1):83-89. DOI: 10.1016/j.jelechem.2006.11.008 - 42.
Medford AJ, Vojvodic A, Hummelshøj JS, Voss J, Abild-Pedersen F, Studt F, et al. From the Sabatier principle to a predictive theory of transition-metal heterogeneous catalysis. Journal of Catalysis. 2015; 328 :36-42. DOI: 10.1016/j.jcat.2014.12.033 - 43.
Rong X, Parolin J, Kolpak AM. A fundamental relationship between reaction mechanism and stability in metal oxide catalysts for oxygen evolution. ACS Catalysis. 2016; 6 (2):1153-1158. DOI: 10.1021/acscatal.5b02432 - 44.
Fei H, Dong J, Feng Y, Allen CS, Wan C, Volosskiy B, et al. General synthesis and definitive structural identification of MN4C4 single-atom catalysts with Tunable electrocatalysts activities. Nature Catalysis. 2018; 1 (1):63-72. DOI: 10.1038/s41929-017-0008-y - 45.
Hwang J, Rao RR, Giordano L, Katayama Y, Yu Y, Shao-Horn Y. Perovskites in catalysis and Electrocatalysis. Science. 2017; 358 (6364):751-756. DOI: 10.1126/science.aam7092 - 46.
Mefford JT, Rong X, Abakumov AM, Hardin WG, Dai S, Kolpak AM, et al. Water electrolysis on La1−xSrxCoO3−δ perovskite electrocatalysts. Nature Communications. 2016; 7 (1):11053. DOI: 10.1038/ncomms11053 - 47.
Nolan M, Iwaszuk A, Lucid AK, Carey JJ, Fronzi M. Design of Novel visible light active photocatalyst materials: Surface modified TiO2. Advanced Materials. 2016; 28 (27):5425-5446. DOI: 10.1002/adma.201504894 - 48.
Liu K, Ma M, Wu L, Valenti M, Cardenas-Morcoso D, Hofmann JP, et al. Electronic effects determine the selectivity of planar Au–Cu bimetallic thin films for electrochemical CO2 reduction. ACS Applied Materials & Interfaces. 2019; 11 (18):16546-16555. DOI: 10.1021/acsami.9b01553 - 49.
Jeyachandran N, Yuan W, Giordano C. Cutting-edge electrocatalysts for CO2RR. Molecules. 2023; 28 (8):3504. DOI: 10.3390/molecules28083504 - 50.
Ringe S, Morales-Guio CG, Chen LD, Fields M, Jaramillo TF, Hahn C, et al. Double layer charging driven carbon dioxide adsorption limits the rate of electrochemical carbon dioxide reduction on gold. Nature Communications. 2020; 11 (1):33. DOI: 10.1038/s41467-019-13777-z - 51.
Mosali VSS, Bond AM, Zhang J. Alloying strategies for tuning product selectivity during electrochemical CO2 reduction over Cu. Nanoscale. 2022; 14 (42):15560-15585. DOI: 10.1039/D2NR03539A - 52.
Xu Y, Li C, Xiao Y, Wu C, Li Y, Li Y, et al. Tuning the selectivity of liquid products of CO2RR by Cu–Ag alloying. ACS Applied Materials & Interfaces. 2022; 14 (9):11567-11574. DOI: 10.1021/acsami.2c00593 - 53.
Wu Q, Gao Q, Wang X, Qi Y, Shen L, Tai X, et al. Boosting electrocatalysts performance via electronic structure regulation for acidic oxygen evolution. iScience. 2024; 27 (1):108738. DOI: 10.1016/j.isci.2023.108738 - 54.
Lee S, Shin Y, Yeom K, Shim J, Sung Y-E. An overview of design strategies and recent advancements in complex 3d transition metal-based electrocatalysts for alkaline oxygen evolution reaction. Advances in Industrial and Engineering Chemistry. 2025; 1 (1):2. DOI: 10.1007/s44405-025-00001-4 - 55.
Kim U, Mun J, Koo D, Seo J, Choi Y, Lee G, et al. Catalytic centers with multiple oxidation states: A strategy for breaking the overpotential ceiling from the linear scaling relation in oxygen evolution. Journal of Materials Chemistry A. 2022; 10 (43):23079-23086. DOI: 10.1039/D2TA05409D - 56.
Sun Y, Chen G, Xi S, Xu ZJ. Catalytically influential features in transition metal oxides. ACS Catalysis. 2021; 11 (22):13947-13954. DOI: 10.1021/acscatal.1c04393 - 57.
Marquez RA, Kalokowski E, Espinosa M, Bender JT, Son YJ, Kawashima K, et al. Transition metal incorporation: Electrochemical, structure, and chemical composition effects on nickel oxyhydroxide oxygen-evolution electrocatalysts. Energy & Environmental Science. 2024; 17 (5):2028-2045. DOI: 10.1039/D3EE03617K - 58.
Song F, Bai L, Moysiadou A, Lee S, Hu C, Liardet L, et al. Transition metal oxides as electrocatalysts for the oxygen evolution reaction in alkaline solutions: An application-inspired renaissance. Journal of the American Chemical Society. 2018; 140 (25):7748-7759. DOI: 10.1021/jacs.8b04546 - 59.
Stamatelos I, da Silva GTST, Ribeiro C, Shviro M. Exploring Heterostructures of D-block metal oxides coupled to ZnO for the electrochemical reduction of CO2. ACS Applied Energy Materials. 2023; 6 (22):11510-11520. DOI: 10.1021/acsaem.3c01791 - 60.
Whang HS, Lim J, Choi MS, Lee J, Lee H. Heterogeneous catalysts for catalytic CO2 conversion into value-added chemicals. BMC Chemical Engineering. 2019; 1 (1):9. DOI: 10.1186/s42480-019-0007-7 - 61.
Ma M, Trześniewski BJ, Xie J, Smith WA. Selective and efficient reduction of carbon dioxide to carbon monoxide on oxide-derived nanostructured silver electrocatalysts. Angewandte Chemie International Edition. 2016; 55 (33):9748-9752. DOI: 10.1002/anie.201604654 - 62.
Guo Z, Wang T, Liu H, Jia X, Zhang D, Wei L, et al. Electrochemical CO2 reduction on SnO: Insights into C1 product dynamic distribution and reaction mechanisms. ACS Catalysis. 2025; 15 (4):3173-3183. DOI: 10.1021/acscatal.4c07987 - 63.
Stamatelos I, Dinh C-T, Lehnert W, Shviro M. Zn-based catalysts for selective and stable electrochemical CO2 reduction at high current densities. ACS Applied Energy Materials. 2022; 5 (11):13928-13938. DOI: 10.1021/acsaem.2c02557 - 64.
Dattila F, Garcı́a-Muelas R, López N. Active and selective ensembles in oxide-derived copper catalysts for CO2 reduction. ACS Energy Letters. 2020; 5 (10):3176-3184. DOI: 10.1021/acsenergylett.0c01777 - 65.
Onoh EU, Stamatelos I, Dubale AA, Pasel J, Ayalneh Tiruye G. Selective electro-reduction of CO2 into methane and formic acid using efficient bimetallic and bimetallic oxide electrocatalysts in liquid-fed Electrolyzers. Journal of Power Sources. 2025; 633 :236393. DOI: 10.1016/j.jpowsour.2025.236393 - 66.
He H, Xia D, Yu X, Wu J, Wang Y, Wang L, et al. Pd-SnO2 Interface enables synthesis of syngas with controllable H2/CO ratios by electrocatalysts reduction of CO2. Applied Catalysis B: Environmental. 2022; 312 :121392. DOI: 10.1016/j.apcatb.2022.121392 - 67.
Fu HQ, Liu J, Bedford NM, Wang Y, Sun JW, Zou Y, et al. Synergistic Cr2O3@Ag Heterostructure enhanced electrocatalysts CO2 reduction to CO. Advanced Materials. 2022; 34 (29):2202854. DOI: 10.1002/adma.202202854 - 68.
Yang Y, Guo M, Zhao F. Cr2O3 promoted In2O3 catalysts for CO2 hydrogenation to methanol. ChemPhysChem. 2024; 25 :e202300530. DOI: 10.1002/cphc.202300530 - 69.
Bao F, Kemppainen E, Dorbandt I, Xi F, Bors R, Maticiuc N, et al. Host, suppressor, and promoter—The roles of Ni and Fe on oxygen evolution reaction activity and stability of NiFe alloy thin films in alkaline media. ACS Catalysis. 2021; 11 (16):10537-10552. DOI: 10.1021/acscatal.1c01190 - 70.
Yu M, Moon G, Bill E, Tüysüz H. Optimizing Ni–Fe oxide electrocatalysts for oxygen evolution reaction by using hard templating as a toolbox. ACS Applied Energy Materials. 2019; 2 (2):1199-1209. DOI: 10.1021/acsaem.8b01769 - 71.
Avcı ÖN, Sementa L, Fortunelli A. Mechanisms of the oxygen evolution reaction on NiFe2 O4 and CoFe2 O4 inverse-spinel oxides. ACS Catalysis. 2022; 12 (15):9058-9073. DOI: 10.1021/acscatal.2c01534 - 72.
Jang MJ, Yang J, Lee J, Park YS, Jeong J, Park SM, et al. Superior performance and stability of anion exchange membrane water electrolysis: pH-controlled copper cobalt oxide nanoparticles for the oxygen evolution reaction. Journal of Materials Chemistry A. 2020; 8 (8):4290-4299. DOI: 10.1039/C9TA13137J - 73.
Mu G, Zeng Y, Zheng Y, Cao Y, Liu F, Liang S, et al. Oxygen vacancy defects engineering on Cu-doped Co3O4 for promoting effective COS hydrolysis. Green Energy & Environment. 2023; 8 (3):831-841. DOI: 10.1016/j.gee.2021.11.001 - 74.
Zhang L, Li Y, Peng J, Peng K. Bifunctional NiCo2O4 porous nanotubes electrocatalyst for overall water-splitting. Electrochimica Acta. 2019; 318 :762-769. DOI: 10.1016/j.electacta.2019.06.128 - 75.
Jiang B, Wan Z, Kang Y, Guo Y, Henzie J, Na J, et al. Auto-programmed synthesis of metallic aerogels: Core-Shell Cu@Fe@Ni aerogels for efficient oxygen evolution reaction. Nano Energy. 2021; 81 :105644. DOI: 10.1016/j.nanoen.2020.105644 - 76.
Xiao J, Liu S, Sui P-F, Xu C, Gong L, Zeng H, et al. In-situ generated hydroxides realize near-Unity CO selectivity for electrochemical CO2 reduction. Chemical Engineering Journal. 2022; 433 :133785. DOI: 10.1016/j.cej.2021.133785 - 77.
Dinh C-T, Burdyny T, Kibria MG, Seifitokaldani A, Gabardo CM, García de Arquer FP, et al. CO2 electroreduction to ethylene via hydroxide-mediated copper catalysis at an abrupt Interface. Science. 2018; 360 (6390):783-787. DOI: 10.1126/science.aas9100 - 78.
Lee JH, Jang W, Lee H, Oh D, Noh WY, Kim KY, et al. Tuning CuMgAl-layered double hydroxide nanostructures to achieve CH4 and C2+ product selectivity in CO2 electroreduction. Nano Letters. 2024; 24 (30):9322-9330. DOI: 10.1021/acs.nanolett.4c02233 - 79.
Senanayake SD, Stacchiola D, Evans J, Estrella M, Barrio L, Pérez M, et al. Probing the reaction intermediates for the water–gas shift over inverse CeOx/Au (1 1 1) catalysts. Journal of Catalysis. 2010; 271 (2):392-400. DOI: 10.1016/j.jcat.2010.02.024 - 80.
Henderson MA, Perkins CL, Engelhard MH, Thevuthasan S, Peden CHF. Redox properties of water on the oxidized and reduced surfaces of CeO2(111). Surface Science. 2003; 526 (1):1-18. DOI: 10.1016/S0039-6028(02)02657-2 - 81.
Sun M, Staykov A, Yamauchi M. Understanding the roles of hydroxide in CO2 electroreduction on a Cu electrode for achieving variable selectivity. ACS Catalysis. 2022; 12 (24):14856-14863. DOI: 10.1021/acscatal.2c03650 - 82.
Gao L, Cui X, Sewell CD, Li J, Lin Z. Recent advances in activating surface reconstruction for the high-efficiency oxygen evolution reaction. Chemical Society Reviews. 2021; 50 (15):8428-8469. DOI: 10.1039/D0CS00962H - 83.
Lee WH, Han MH, Ko Y-J, Min BK, Chae KH, Oh H-S. Electrode reconstruction strategy for oxygen evolution reaction: Maintaining Fe-CoOOH phase with intermediate-spin state during electrolysis. Nature Communications. 2022; 13 (1):605. DOI: 10.1038/s41467-022-28260-5 - 84.
He Z-D, Tesch R, Eslamibidgoli MJ, Eikerling MH, Kowalski PM. Low-spin state of Fe in Fe-doped NiOOH electrocatalysts. Nature Communications. 2023; 14 (1):3498. DOI: 10.1038/s41467-023-38978-5 - 85.
Chen JYC, Dang L, Liang H, Bi W, Gerken JB, Jin S, et al. Operando analysis of NiFe and Fe oxyhydroxide electrocatalysts for water oxidation: Detection of Fe4+ by Mössbauer spectroscopy. Journal of the American Chemical Society. 2015; 137 (48):15090-15093. DOI: 10.1021/jacs.5b10699 - 86.
Tsyganok A, Ghigna P, Minguzzi A, Naldoni A, Murzin V, Caliebe W, et al. Operando X-ray absorption spectroscopy (XAS) observation of Photoinduced oxidation in FeNi (oxy)hydroxide Overlayers on hematite (α-Fe2 O3) Photoanodes for solar water splitting. Langmuir. 2020; 36 (39):11564-11572. DOI: 10.1021/acs.langmuir.0c02065 - 87.
Aigul S, Enkhbayar E, Gaur A, Han H. Cr-doped tri-metallic Nano prism catalyst for efficient alkaline and seawater splitting. Journal of Crystal Growth. 2025; 649 :127928. DOI: 10.1016/j.jcrysgro.2024.127928 - 88.
Babu SP, Falch A. Recent developments on Cr-based electrocatalysts for the oxygen evolution reaction in alkaline media. ChemCatChem. 2022; 14 (15):e202200364. DOI: 10.1002/cctc.202200364 - 89.
Cao F, Li M, Hu Y, Wu X, Li X, Meng X, et al. Kinetically accelerated oxygen evolution reaction in metallic (oxy)hydroxides enabled by Cr-dopant and Heterostructure. Chemical Engineering Journal. 2023; 472 :144970. DOI: 10.1016/j.cej.2023.144970 - 90.
Zhou D, Li P, Lin X, McKinley A, Kuang Y, Liu W, et al. Layered double hydroxide-based electrocatalysts for the oxygen evolution reaction: Identification and tailoring of active sites, and Superaerophobic Nanoarray electrode assembly. Chemical Society Reviews. 2021; 50 (15):8790-8817. DOI: 10.1039/D1CS00186H - 91.
Lei H, Ma L, Wan Q, Tan S, Yang B, Wang Z, et al. Promoting surface reconstruction of NiFe layered double hydroxide for enhanced oxygen evolution. Advanced Energy Materials. 2022; 12 (48):2202522. DOI: 10.1002/aenm.202202522 - 92.
Wu L, Yu L, Xiao X, Zhang F, Song S, Chen S, et al. Recent advances in self-supported layered double hydroxides for oxygen evolution reaction. Research. 2020; 2020 . DOI: 10.34133/2020/3976278 - 93.
Song F, Hu X. Exfoliation of layered double hydroxides for enhanced oxygen evolution catalysis. Nature Communications. 2014; 5 (1):4477. DOI: 10.1038/ncomms5477 - 94.
Wan X, Song Y, Zhou H, Shao M. Layered double hydroxides for oxygen evolution reaction towards efficient hydrogen generation. Energy Material Advances. 2022; 2022 . DOI: 10.34133/2022/9842610 - 95.
Qu J, Dong Y, Zhang T, Zhao C, Wei L, Guan X. Impact of bimetallic synergies on Mo-doping NiFeOOH: Insights into enhanced OER activity and reconstructed electronic structure. Frontiers in Energy. 2024; 18 (6):850-862. DOI: 10.1007/s11708-024-0960-6 - 96.
He Z, Zhang J, Gong Z, Lei H, Zhou D, Zhang N, et al. Activating lattice oxygen in NiFe-based (oxy)hydroxide for water electrolysis. Nature Communications. 2022; 13 (1):2191. DOI: 10.1038/s41467-022-29875-4 - 97.
Krivina RA, Ou Y, Xu Q, Twight LP, Stovall TN, Boettcher SW. Oxygen Electrocatalysis on mixed-metal oxides/Oxyhydroxides: From fundamentals to membrane Electrolyzer technology. Accounts of Materials Research. 2021; 2 (7):548-558. DOI: 10.1021/accountsmr.1c00087 - 98.
Iijima G, Inomata T, Yamaguchi H, Ito M, Masuda H. Role of a hydroxide layer on Cu electrodes in electrochemical CO2 reduction. ACS Catalysis. 2019; 9 (7):6305-6319. DOI: 10.1021/acscatal.9b00896 - 99.
Chen Y, Li CW, Kanan MW. Aqueous CO2 reduction at very low Overpotential on oxide-derived Au nanoparticles. Journal of the American Chemical Society. 2012; 134 (49):19969-19972. DOI: 10.1021/ja309317u - 100.
Löffler M, Mayrhofer KJJ, Katsounaros I. Oxide reduction precedes carbon dioxide reduction on oxide-derived copper electrodes. Journal of Physical Chemistry C. 2021; 125 (3):1833-1838. DOI: 10.1021/acs.jpcc.0c09107 - 101.
Mattarozzi F, van der Willige N, Gulino V, Keijzer C, van de Poll RCJ, Hensen EJM, et al. Oxide-derived silver nanowires for CO2 electrocatalysts reduction to CO. CheCatChem. 2023; 15 :e202300792. DOI: 10.1002/cctc.202300792 - 102.
Hu H, Tang Y, Hu Q, Wan P, Dai L, Yang XJ. In-situ grown Nanoporous Zn-Cu catalysts on Brass foils for enhanced electrochemical reduction of carbon dioxide. Applied Surface Science. 2018; 445 :281-286. DOI: 10.1016/j.apsusc.2018.03.146 - 103.
Eilert A, Cavalca F, Roberts FS, Osterwalder J, Liu C, Favaro M, et al. Subsurface oxygen in oxide-derived copper electrocatalysts for carbon dioxide reduction. Journal of Physical Chemistry Letters. 2017; 8 (1):285-290. DOI: 10.1021/acs.jpclett.6b02273 - 104.
Asiri AM, Gao J, Khan SB, Alamry KA, Marwani HM, Khan MSJ, et al. Revisiting the impact of morphology and oxidation state of Cu on CO2 reduction using electrochemical flow cell. Journal of Physical Chemistry Letters. 2022; 13 (1):345-351. DOI: 10.1021/acs.jpclett.1c03957 - 105.
Behnaz Varandili S, Stoian D, Vavra J, Rossi K, Pankhurst R, Guntern Y, et al. Elucidating the structure-dependent selectivity towards methane and ethanol of CuZn in the CO2 electroreduction using tailored Cu/ZnO Precatalysts. Chemical Science. 2021; 12 :14484-14493. DOI: 10.1039/D1SC04271H - 106.
Torelli DA, Francis SA, Crompton JC, Javier A, Thompson JR, Brunschwig BS, et al. Nickel–gallium-catalyzed electrochemical reduction of CO2 to highly reduced products at low overpotentials. ACS Catalysis. 2016; 6 (3):2100-2104. DOI: 10.1021/acscatal.5b02888 - 107.
Zhan C, Dattila F, Rettenmaier C, Herzog A, Herran M, Wagner T, et al. Key intermediates and Cu active sites for CO2 electroreduction to ethylene and ethanol. Nature Energy. 2024; 9 (12):1485-1496. DOI: 10.1038/s41560-024-01633-4 - 108.
Wei D, Wang Y, Dong C-L, Nga TT, Shi Y, Wang J, et al. Surface adsorbed hydroxyl: A double-edged sword in electrochemical CO2 reduction over oxide-derived copper. Angewandte Chemie International Edition. 2023; 62 (31):e202306876. DOI: 10.1002/anie.202306876 - 109.
Luo M, Wang Z, Li YC, Li J, Li F, Lum Y, et al. Hydroxide promotes carbon dioxide electroreduction to ethanol on copper via tuning of adsorbed hydrogen. Nature Communications. 2019; 10 (1):5814. DOI: 10.1038/s41467-019-13833-8 - 110.
Dionigi F, Zeng Z, Sinev I, Merzdorf T, Deshpande S, Lopez MB, et al. In-situ structure and catalytic mechanism of NiFe and CoFe layered double hydroxides during oxygen evolution. Nature Communications. 2020; 11 (1):2522. DOI: 10.1038/s41467-020-16237-1 - 111.
Wang Y, Liu S, Qin Y, Zhao Y, Liu L, Zhang D, et al. Chromium promotes phase transformation to active Oxyhydroxide for efficient oxygen evolution. ACS Catalysis. 2024; 14 (18):13759-13767. DOI: 10.1021/acscatal.4c03974 - 112.
Wang Y, Chen C, Xiong X, Skaanvik SA, Zhang Y, Bøjesen ED, et al. In situ tracking of water oxidation generated nanoscale dynamics in layered double hydroxides nanosheets. Journal of the American Chemical Society. 2024; 146 (25):17032-17040. DOI: 10.1021/jacs.4c01035 - 113.
Wang Z, Goddard WA, Xiao H. Potential-dependent transition of reaction mechanisms for oxygen evolution on layered double hydroxides. Nature Communications. 2023; 14 (1):4228. DOI: 10.1038/s41467-023-40011-8 - 114.
Gao MY, Sun CB, Lei H, Zeng JR, Zhang QB. Nitrate-induced and in situ electrochemical activation synthesis of oxygen deficiencies-rich nickel/nickel (oxy)hydroxide hybrid films for enhanced electrocatalysts water splitting. Nanoscale. 2018; 10 (37):17546-17551. DOI: 10.1039/C8NR06459H - 115.
Jiang Q, Wang S, Zhang C, Sheng Z, Zhang H, Feng R, et al. Active oxygen species mediate the iron-promoting Electrocatalysis of oxygen evolution reaction on metal Oxyhydroxides. Nature Communications. 2023; 14 (1):6826. DOI: 10.1038/s41467-023-42646-z - 116.
Ping X, Liu Y, Zheng L, Song Y, Guo L, Chen S, et al. Locking the lattice oxygen in RuO2 to stabilize highly active Ru sites in acidic water oxidation. Nature Communications. 2024; 15 (1):2501. DOI: 10.1038/s41467-024-46815-6 - 117.
Ferreira de Araújo J, Dionigi F, Merzdorf T, Oh H-S, Strasser P. Evidence of Mars-van-Krevelen mechanism in the electrochemical oxygen evolution on Ni-based catalysts. Angewandte Chemie International Edition. 2021; 60 (27):14981-14988. DOI: 10.1002/anie.202101698 - 118.
Arán-Ais RM, Scholten F, Kunze S, Rizo R, Roldan Cuenya B. The role of in situ generated morphological motifs and Cu(i) species in C2+ product selectivity during CO2 pulsed electroreduction. Nature Energy. 2020; 5 (4):317-325. DOI: 10.1038/s41560-020-0594-9 - 119.
Reichert MA, Piqué O, Parada AW, Katsounaros I, Calle-Vallejo F. Mechanistic insight into electrocatalytic glyoxal reduction on copper and its relation to CO2 reduction. Chemical Science. 2022; 13 (37):11205-11214. DOI: 10.1039/D2SC03527H - 120.
Cheng D, Zhao Z-J, Zhang G, Yang P, Li L, Gao H, et al. The nature of active sites for carbon dioxide electroreduction over oxide-derived copper catalysts. Nature Communications. 2021; 12 (1):395. DOI: 10.1038/s41467-020-20615-0 - 121.
Kim C, Bui JC, Luo X, Cooper JK, Kusoglu A, Weber AZ, et al. Tailored catalyst microenvironments for CO2 electroreduction to multicarbon products on copper using bilayer ionomer coatings. Nature Energy. 2021; 6 (11):1026-1034. DOI: 10.1038/s41560-021-00920-8 - 122.
Zeng J, Castellino M, Fontana M, Sacco A, Monti NBD, Chiodoni A, et al. Electrochemical reduction of CO2 with good efficiency on a nanostructured Cu-Al catalyst. Frontiers in Chemistry. 2022:10. DOI: 10.3389/fchem.2022.931767 - 123.
Li F, Thevenon A, Rosas-Hernández A, Wang Z, Li Y, Gabardo CM, et al. Molecular tuning of CO2-to-ethylene conversion. Nature. 2020; 577 (7791):509-513. DOI: 10.1038/s41586-019-1782-2 - 124.
Zong X, Zhang J, Zhang J, Luo W, Züttel A, Xiong Y. Synergistic Cu/CeO2 carbon nanofiber catalysts for efficient CO2 electroreduction. Electrochemistry Communications. 2020; 114 :106716. DOI: 10.1016/j.elecom.2020.106716 - 125.
Dongare S, Singh N, Bhunia H. Oxide-derived Cu-Zn nanoparticles supported on N-doped graphene for electrochemical reduction of CO2 to ethanol. Applied Surface Science. 2021; 556 :149790. DOI: 10.1016/j.apsusc.2021.149790 - 126.
You S, Xiao J, Liang S, Xie W, Zhang T, Li M, et al. Doping engineering of Cu-based catalysts for electrocatalysts CO2 reduction to multi-carbon products. Energy and Environmental Science. 2024; 17 (16):5795-5818. DOI: 10.1039/D4EE01325E - 127.
Knöppel J, Möckl M, Escalera-López D, Stojanovski K, Bierling M, Böhm T, et al. On the limitations in assessing stability of oxygen evolution catalysts using aqueous model electrochemical cells. Nature Communications. 2021; 12 (1):2231. DOI: 10.1038/s41467-021-22296-9 - 128.
Zhang D, Wu Q, Wu L, Cheng L, Huang K, Chen J, et al. Optimal electrocatalyst design strategies for acidic oxygen evolution. Advanced Science. 2024; 11 (38):2401975. DOI: 10.1002/advs.202401975 - 129.
Zhang C, Wang F, Batool M, Xiong B, Yang H. Phase transition of SrCo0.9Fe0.1O3 electrocatalysts and their effects on oxygen evolution reaction. SusMat. 2022; 2 (4):445-455. DOI: 10.1002/sus2.72 - 130.
Yin X, Hua Y, Gao Z. Two-dimensional materials for high-performance oxygen evolution reaction: Fundamentals, recent progress, and improving strategies. Renewables. 2023; 1 (2):190-226. DOI: 10.31635/renewables.023.202200003 - 131.
Zhang Y, Fu Q, Song B, Xu P. Regulation strategy of transition metal oxide-based electrocatalysts for enhanced oxygen evolution reaction. Accounts of Materials Research. 2022; 3 (10):1088-1100. DOI: 10.1021/accountsmr.2c00161 - 132.
Park W, Chung DY. Activity–stability relationships in oxygen evolution reaction. ACS Materials Au. 2025; 5 (1):1-10. DOI: 10.1021/acsmaterialsau.4c00086