Outstanding Oxygen Evolution Reaction Activity Research Articles

Facile synthesis of Co-Ni layered double hydroxides nanosheets wrapped on a prism-like metal-organic framework for efficient oxygen evolution reaction

The construction of low-cost oxygen evolution reaction (OER) electrocatalysts with high activity and good durability is a considerable challenge for facilitating the efficient utilization of green energy. Herein, the prism-like materials of institute lavoisier frameworks-88 (MIL-88) was first synthesized by a hydrothermal method. Then, Co-Ni layered double hydroxides (CoNi-LDHs) nanosheets were directly wrapped on the MIL-88 surface by electrodeposition to form core-shell MIL-88@CoNi-LDHs composites. Due to the distinct structure and synergistic effect between the MIL-88 core and CoNi-LDHs shell, it was found that MIL-88@CoNi-LDHs had outstanding OER activity with a small Tafel slope (45.55 mV dec-1), low overpotential (314 mV) at 10 mA cm−2, and superior durability. This study provides a prospective pathway to exploit highly efficient low-cost electrocatalysts for OER.

Partially crystallized Ni–Fe oxyhydroxides promotes oxygen evolution

The slow oxygen evolution reaction (OER) kinetics influences hydrogen production efficiency from water splitting. To break through the bottleneck of water splitting, it is urgent to develop efficient and economic electrocatalysts. Although NiFe-based catalysts exhibit outstanding OER activity, the complicated preparation process limits their large-scale synthesis and applications. Here, partially crystallized nickel-iron oxyhydroxides are synthesized by a facile sol-gel method. When the Fe/Ni mole ratio is 0.5:1, the NiFe0.5(OH)x catalyst shows superior OER performance with a low OER overpotential of 265 mV and good durability. Kinetic studies show that the energy barrier of NiFe0.5(OH)x is only 31.5 kJ mol−1, much smaller than those of Ni(OH)x (41.0 kJ mol−1) and Fe(OH)x (44.8 kJ mol−1). The synergistic action between Ni and Fe sites not only facilitates mass and charge transfer, but also promotes the formation of ∗OOH intermediate for the OER.

Facile Synthesis and Origin of Enhanced Electrochemical Oxygen Evolution Reaction Performance of 2H-Hexagonal Ba2CoMnO6-δ as a New Member in Double Perovskite Oxides.

Perovskite oxides have been considered promising oxygen evolution reaction (OER) electrocatalysts due to their high intrinsic activity. Yet, their poor long-term electrochemical and structural stability is still controversial. In this work, we apply an A-site management strategy to tune the activity and stability of a new hexagonal double perovskite oxide. We synthesized the previously inaccessible 2H-Ba2CoMnO6-δ (BCM) perovskite oxide via the universal sol-gel method followed by a novel air-quench method. The new 2H-BCM perovskite oxide exhibits outstanding OER activity with an overpotential of 288 mV at 10 mA cm-2 and excellent long-term stability without segregation or structural change. To understand the origin of outstanding OER performance of BCM, we substitute divalent Ba with trivalent La at the A-site and investigate crystal and electronic structure change. Fermi level and valence band analysis presents a decline in the work function with the Ba amount, suggesting a structure-oxygen vacancy-work function-activity relationship for Ba x La2-x CoMnO6-δ (x = 0, 0.5, 1, 1.5, 2) electrocatalysts. Our work suggests a novel production strategy to explore the single-phase new structures and develop enhanced OER catalysts.

Bimetallic co-doping engineering over nickel-based oxy-hydroxide enables high-performance electrocatalytic oxygen evolution

Enhancing the electrocatalytic oxygen evolution reaction (OER) performance is essential to realize practical energy-saving water electrolysis and CO2 electroreduction. Herein, we report a bimetallic co-doping engineering to design and fabricate nickel–cobalt-iron collaborative oxy-hydroxide on nickel foam that labeled as NiCoFeOxHy-NF. As expected, NiCoFeOxHy-NF exhibits an outstanding OER activity with current density of 10 mA cm−2 at 194 mV, Tafel slope of 53 mV dec−1, along with the robust long-term stability, which is significantly better than bimetallic NiCo and NiFe combinations. Comprehensive computational simulations and characterizations jointly unveil that the twisted ligand environment induced by heteroatoms ensures the balance strength between the metal–oxygen hybrid orbital states and the oxidized intermediates adsorption, thus lowering the oxygen cycling energy barriers for overcoming the sluggish OER kinetics. Moreover, a novel phase transition behavior is monitored by in-situ Raman spectra under OER operating conditions, which facilitates electron-mass transfer as well as boosts the exposure of activity sites. For practical applications, Ni2P-NF || NiCoFeOxHy-NF and Cu || NiCoFeOxHy-NF couples were constructed to realize high-efficiency water electrolysis and CO2 electrochemical reduction for the production of valuable H2 and C2H4, respectively. This work elucidates a novel mechanism by which bimetallic co-doping improves the electrocatalytic OER activity of nickel-based hydroxides.

Coordination Engineering of Single‐Atom Iron Catalysts for Oxygen Evolution Reaction

AbstractDeveloping highly active oxygen evolution reaction (OER) catalyst is essential to improve the performance of a water electrolyzer, where single‐atom catalysts (SACs) have shown promising performance in recent years. However, while SACs with various coordination environment have become experimentally feasible, knowledge about the structure‐performance relationship of SACs is still very limited, especially for the emerging multiple p‐block element‐doped SACs substrates. Herein, by adjusting the coordination environment of single‐atom iron catalysts, 122 SACs with various substrates were designed for comprehensive analysis. Through spin‐polarized density functional theory calculations with van der Waals corrections, 52 stable single‐atom iron catalysts were identified. To analyze their OER performance, an OER volcano activity model was derived to predict their performance as the function of O* and HO* binding free energies. Interestingly, a Fe1B1C1N2‐pen structure was found to have an outstanding OER activity (with a theoretical overpotential of 0.40 V vs. reversible hydrogen electrode) due to its unique adsorption mode that strengthens HO‐bonding by forming the Fe−OH−B bond. Based on these results, the OER performance of 26 TM1/B1C1N2‐pen (TM=Ti−Zn, Zr−Cd, and Hf−Au) SACs were determined based on this unique coordination environment by B‐doping. Most importantly, this study shows that the OER performance of SACs can be significantly improved by tuning the coordination environment of an active metal center.

Triethanolamine-assisted synthesis of NiFe layered double hydroxide ultrathin nanosheets for efficient oxygen evolution reaction

Water electrolysis is a promising technique for producing high-quality hydrogen, the application of which is impeded by the sluggish oxygen evolution reaction (OER) process. In this study, ultrathin nickel–iron layered double hydroxide (NiFe LDH) nanosheets were successfully synthesized through a facile hydrothermal reaction with the assistance of triethanolamine (TEA). Morphological and structural characterizations revealed that the presence of TEA modified the morphology of NiFe LDH, facilitated the synthesis of high-purity NiFe LDH, improved the crystallinity of NiFe LDH and resulted in a slight decrease in specific surface area. X-ray photoelectron spectroscopy (XPS) analysis demonstrated the modulation of the electronic structure engendered by the addition of TEA, with nickel and iron appearing in high valence state in the resulting NiFe LDH nanosheets. The as-prepared NiFe LDH nanosheets possessed outstanding OER activity with fast kinetics, exhibiting a low overpotential of 261 mV to achieve a current density of 10 mA cm−2 and a small Tafel slope of 32.5 mV dec−1 in 1 M KOH. The excellent OER performance and rapid OER kinetics are mainly attributed to the high-valence Ni and Fe rather than the modification in the morphology and microstructure.

Hybrid perovskites as oxygen evolution electrocatalysts for high-performance anion exchange membrane water electrolyzers

Highly active and platinum group metal-free (PGM-free) oxygen evolution reaction (OER) electrocatalysts are essential for producing low-cost and clean hydrogen in anion exchange membrane water electrolyzers (AEMWEs). Thanks to the unique characteristics of perovskite oxides, which include low cost, tunable electronic structure and cation deficiency, high electronic conductivity, high durability, high specific catalytic activity, and environmental friendliness, they have been widely designed and employed as the OER electrocatalysts. Here, a set of novel hybrid perovskites, LaxSr4-xNiyFe3-yO10-δ (LxS4-xNyF3-y), were demonstrated, which consist of a single-layer perovskite phase (P phase) and two Ruddlesden–Popper perovskite phases (RP phases). These hybrid perovskites synergize the advantages of the P phase and RP phases, which improves the oxygen-ion diffusion rate, leading to enhanced OER activity. Furthermore, the concentration of each phase can be tuned by alternating the compositional stoichiometry. A relatively uniform distribution of the P phase and RP phases can maximize the interfacial area and achieve the highest oxygen-ion diffusion rate. L3S1N2F1, L2S2N1F2, and L2S2N1.5F1.5 exhibit outstanding OER activity, which achieve 10 mA/cm2 at a low overpotential of less than 360 mV in 1.0 M KOH. Additionally, herein, the hybrid perovskites are implemented as the anodes of AEMWEs, which deliver an exceptional current density of > 1.0 A/cm2 at 1.8 V.

Defective layered NiFe double hydroxides anchored on self-supported CoNi-nitrogen doped carbon nanotube composite as advanced electrocatalyst for oxygen evolution reaction

Oxygen evolution reaction (OER) is an essential process during electrochemical water-splitting. Due to its sluggish kinetics, low cost and highly efficient catalyst is invariably desired to decrease its overpotential for large-scale application. However, the overpotential of most advanced OER electrocatalysts is still more than 200 mV at the current density of 10 mA cm−2. In this work, we constructed active layered NiFe double hydroxides with cation defects on self-supported three-dimensional (3D) CoNi nitrogen-doped carbon nanotube composite substrate as integrated OER catalyst. Strikingly, electrochemical measurements showed that the optimized sample exhibited outstanding OER activity with low overpotentials of 178 and 268 mV at the current densities of 10 and 100 mA cm−2 in alkaline environment, alongside a good durability. The excellent OER performance was ascribed to the strongly synergistic effect of intrinsically active NiFe double hydroxide layers with abundant cation vacancies and 3D carbon nanotube composite substrate with good conductivity and various functional moieties, thus facilitating the electrocatalytic kinetic.

Accelerating electrochemical hydrogen production on binder-free electrodeposited V- doped Ni-Mo-P nanospheres

• V-doped Ni-Mo-P nanostructure was fabricated using electrochemical deposition. • Fabricated electrode exhibited outstanding electrocatalytic HER and OER activity. • Synergistic effect and high surface area was main reason for excellent performance. • Deposited electrode represented outstanding electrocatalytic durability. The emergence and fabrication of cost-effective and active electrodes in the overall water splitting process are one of the most critical challenges for hydrogen production. Here, firstly Ni-P electrodes were generated at different scan rates using the electrochemical deposition method, and then molybdenum was doped in Ni-P structure using the same method and vanadium using hydrothermal deposition method, and V-doped Ni-Mo-P electrode was generated. It was revealed that the synthesized electrode displays outstanding electrochemical properties for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). For reaching a current density of 10 mA cm −2 , the optimum sample needed only 65 mV in the HER process and only 261 mV of overpotential in the OER process. In addition, the electrocatalytic stability investigation disclosed that this electrode had excellent durability at the 100 mA cm −2 in HER and OER process after 10 h of electrolysis in which only less than 2 % increase in overpotential was observed, which indicates excellent electrocatalytic stability. Such outstanding electrocatalytic properties were mainly because of increasing the active surface area and the synergistic effect due to doping of molybdenum and vanadium in the electrode structure .

Tailoring B-site of lead-ruthenate pyrochlore for boosting acidic water oxidation activity and stability

Achieving highly active, stable and low cost oxygen evolution reaction (OER) catalysts is a significant challenge for promoting splitting water technology in acidic media. Herein, we report a low-temperature pyrolysis cation exchange resin (CER) strategy to synthesize lead-ruthenate pyrochlore (Pb2[Ru2−xPbx]O7-δ) catalyst with different contents of Pb substituted at B-site. We demonstrated temperature effectively influence the amount of Pb at B-site, further modulated the electronic states of Ru and the concentration of oxygen defects. Benefiting from rich oxygen defects, the representative PRPO-350 catalyst exhibits outstanding OER activity with a overpotential of 174 mV at 10 mA cm−2geo, a super-low Tafel slope of 28.8 mV dec-1 and excellent stability up to 150 h in acid water. DFT calculations have demonstrated that the such structure will lead to the O-2p orbital closing to the Fermi level, eventually boosts the OER activity.

Abundant Dislocation Layered Double Hydroxides Synthesis by Molten Salt with Bound Water Boosting Oxygen Evolution.

Optimizing the adsorption free energy and promoting the active phase transition to further enhance the oxygen evolution reaction (OER) activity remain significant challenges. The adsorption free energy can be optimized by modulating the electronic structure and adjusting the crystal configuration. Meanwhile, the transformation of the active phase can be promoted by introducing strain energy. The theoretical calculations are conducted to verify the rational envisage. However, it is still a great obstacle to introducing strain into the electrocatalysts and avoiding destruction. The stress field caused by dislocation can realize both of the above. Hence, the molten salt with the bound water method is proposed and the abundant dislocation layered double hydroxides (D-NiFe LDH) are constructed. The in situ characterizations further verify the dislocations significantly affect the generation of the active phase and the state of electronic structure. Consequently, the D-NiFe LDH exhibits outstanding OER activity and obtains 10mA cm-2 , only requiring 199mV overpotential with fabulous stability (100mA cm-2 more than 24h). The work paves a new avenue for the rational introduction dislocations to optimize the crystal configuration and boost the active phase formation, significantly enhancing the OER performance.

In situ coupling of lignin‐derived carbon‐encapsulated CoFe‐CoxN heterojunction for oxygen evolution reaction

AbstractExploring highly active and stable electrocatalysts for oxygen evolution reaction (OER) is crucial for developing water splitting and rechargeable metal‐air batteries. In this study, a hybrid electrocatalyst of CoFe alloy and CoxN heterojunction encapsulated and anchored in N‐doped carbon support (CoFe‐CoxN@NC) was in situ coupled via the pyrolysis of a novel coordination polymer derived from lignin biomacromolecule. CoFe‐CoxN@NC exhibited outstanding OER activity with a low overpotential of 270 mV at 10 mA cm−2 and stability with an increment of 20 mV, comparable to commercial Ir/C. DFT calculations showed that CoxN and N‐doped graphitic encapsulation can reduce the binding strength between *O and CoFe alloy, limit metal leaching and agglomeration, and improve electron transfer efficiency, considerably enhancing the OER activity and stability. In situ coupling approach for preparing alloy and nitride heterojunctions on N‐doped lignin‐derived carbon offers a promising and universal catalyst design for developing renewable energy conversion technologies.

Freestanding 2D NiFe Metal–Organic Framework Nanosheets: Facilitating Proton Transfer via Organic Ligands for Efficient Oxygen Evolution Reaction

The oxygen evolution reaction (OER) is crucial to electrochemical hydrogen production. However, designing and fabricating efficient electrocatalysts still remains challenging. By confinedly coordinating organic ligands with metal species in layered double hydroxides (LDHs), an innovative LDHs-assisted approach is developed to facilely synthesize freestanding bimetallic 2D metal-organic framework nanosheets (2D MOF NSs), preserving the metallic components and activities in OER. Furthermore, the research has demonstrated that the incorporation of carboxyl organic ligands coordinated with metal atoms as proton transfer mediators endow 2D MOF NSs with efficient proton transfer during the electrochemical OHads → Oads transition. These freestanding NiFe-2D MOF NSs require a small overpotential of 260mV for a current density of 10mAcm-2 . When this strategy is applied to LDH nanosheets grown on nickel foam, the overpotential can be reduced to 221mV. This outstanding OER activity supports the capability of multimetallic organic frameworks for the rational design of water oxidation electrocatalysts. This strategy provides a universal path to the synthesis of 2D MOF NSs that can be used as electrocatalysts directly.

Tuning the electronic structure of layered Co-based serpentine nanosheets for efficient oxygen evolution reaction

As low-cost and abundant catalysts, layered cobalt-based hydroxides that are composed of Co–OH octahedron slabs have promising prospect in electrocatalytic oxygen evolution reaction (OER). However, the layered hydrotalcite and brucite structure hydroxides usually possess inferior activity and poor stability. Herein, we developed layered cobalt-based serpentine nanosheets with a tuned electronic structure and stable active phase by using Ge–O and Si–O tetrahedron slabs to coordinate with Co–(O)OH octahedron slabs for efficient OER. Theoretical calculations reveal that Co–(O)OH octahedron slabs that coordinate with Ge–O tetrahedron slabs possess an optimal electronic structure and smaller reaction energy barriers for OER. Inspired by the calculations, the layered Co3Ge2O5(OH)4, Co3Si2O5(OH)4 and brucite Co(OH)2 nanosheets are synthesized. The coordination of Ge–O tetrahedron decreases the size and crystallinity of Co–(O)OH octahedron slabs, simultaneously enhancing the stability of Co–(O)OH octahedron slabs during OER, thus improving the activity and stability. As a result, Co3Ge2O5(OH)4 nanosheets present an outstanding OER activity (overpotential is 287 mV at 10 mA cm–1, lower than that of Co3Si2O5(OH)4 and Co(OH)2) and a remarkable stability for water splitting (working continuously more than 100 h without decay, much higher than that of Co(OH)2 (<36 h)). The solar driven water splitting process achieves a high Faradaic efficiency of 98.8%, and the solar-to-hydrogen energy conversion efficiency is 7.2%. Such a strategy of tuning the electronic structure of Co–O(OH) octahedron by coordination with a Ge–O tetrahedron offers an effective method for designing highly efficient Co-based electrocatalysts.

Reprogramming thermodynamic-limiting oxidation cycle in NiFe-based oxygen evolution electrocatalyst through Mo doping induced surface reconstruction

Engineering of robust nonprecious electrocatalysts toward anodic oxygen evolution reaction (OER) is of great significance for lowering the cost and energy consumption for renewable fuel production. Herein, we report NiFeMoOx nanosheets as high-performance OER electrocatalyst through promoting the thermodynamic-limiting oxidation cycle process in NiFe oxyhydroxide via high-valence Mo doping. The NiFeMoOx nanosheets are prepared by an elaborate in-situ solvothermal etching-depositing process with NiFe alloy framework as substrate and metal precursors. The resultant nanosheets exhibit outstanding alkaline OER activity, requires only 235/282/327 mV overpotentials to achieve current density of 10/100/300 mA cm−2, respectively, with a good long-term stability at 20 mA cm−2 for 72 h. Besides, the Tafel slope low to 28.1 mV dec−1 indicates a favorable OER kinetics. The superior catalytic activity of NiFeMoOx nanosheets should be attributed to the lower oxidation states of Ni and Fe induced by high-valence dopant, leading to easier surface reconstruction at low charge oxidation cycling during OER, thereby effectively reducing the overpotential. The synergy between the electronic effect among multimetallic sites and the unique morphology is expected to inspire the development of robust OER electrocatalyst for industrial application.

RETRACTED: Super-hydrophilic MgO/NiCo2S4 heterostructure for high-efficient oxygen evolution reaction in neutral electrolytes

Oxygen evolution reaction (OER) in pH-neutral electrolyte is considered more difficult for the additional adsorption and the dissociation process of H 2 O. Herein, by in-suit construction of the heterostructure between MgO and NiCo 2 S 4 on carbon cloth (CC), a novel MgO/NiCo 2 S 4 heterostructure on CC (MgO/NCS-CC) is successfully fabricated. Benefitting from the optimized electronic structure attributed to the construction of hetero-interface, and the intense adsorption of H 2 O on the surface of catalysts owing to the introduction of hydration-effect-promoting (HEP) element Mg, the MgO/NCS-CC exhibits outstanding OER activity with overpotential of 145 mV at the current density of 10 mA·cm −2 in pH-neutral electrolyte and can maintain stability over 40 h. Density-functional theory (DFT) also demonstrates that the MgO/NiCo 2 S 4 heterostructure can effectively adjust the electronic structure and enhance the adsorption of reactant, thus further optimizing Gibbs free energies and improving the activity for OER in pH-neutral electrolyte. A novel heterostructure between MgO and NiCo 2 S 4 on carbon cloth (MgO/NCS-CC) was successfully constructed. Benefiting from the enhancement of H 2 O adsorption by the introduction of hydration-effect-promoting (HEP) element Mg and the construction of the heterostructure, MgO/NCS-CC exhibits outstanding OER performance in pH-neutral electrolyte, which the overpotential of 145 mV at the current density of 10 mA·cm −2 is the lowest among the reported OER electrocatalysts in pH-neutral electrolyte. • The hydration-enhancing-effect element Mg effectively enhanced the adsorption of H 2 O on the surface of catalyst. • The unique electronic structure of the heterostructure is the intrinsic reason for the super OER performance. • The catalyst shows outstanding OER performances and excellent stability in pH-neutral condition. • DFT calculation further reveals the change of electronic structure and the enhancement of water adsorption of the catalyst.

High-entropy FeCoNiMn (oxy)hydroxide as high-performance electrocatalyst for OER and boosting clean carrier production under quasi-industrial condition

Hydrogen is recognized as the most promising sustainable energy carrier. It is important to boost oxygen evolution reaction (OER) to produce more hydrogen. High-entropy compounds are a potential category of electrocatalysts for water splitting due to their outstanding reactivity and stability. Noble metal-free high-entropy FeCoNiMn (oxy)hydroxide was synthesized over a large area of 100 cm2 on nickel foam using a facile approach of one-step electrodeposition. High-entropy FeCoNiMnOOH led to outstanding OER activity with a low overpotential of 282 mV at current density of 100 mA cm−2 and showed excellent performance at room temperature as determined by the stability test for over 200 h at a high current density of 500 mA cm−2 in 1.0 M KOH. Under quasi-industrial condition of using 6.0 M KOH solution at 333 K, only 1.64 V was required to reach a high current density of 3000 mA cm−2. In addition, the high-entropy catalyst maintained its stability at a high current density of 1000 mA cm−2 for over 40 h, suggesting its suitability for practical application.

Amorphous Doping Promotes Utilization of Fe‐Doped Amorphous Zr(HPO4)2 for Superb Water Oxidation Electrocatalysis

AbstractDoping hetero‐atoms on the surface of host materials, namely effective doping with high atom utilization, is a promising strategy to optimize the activity of electrocatalysts for water electrolysis, especially for oxygen evolution reaction (OER). Herein, high utilization of doped atoms is successfully achieved in Fe‐doped 2D amorphous Zr(HPO4)2 nanosheets (amorphous Fe‐ZrP). Due to the unique amorphous surface with a large scale of coordinated unsaturated sites, a great quantity of Fe dopants with tunable electron density can anchor on the surface of the 2D amorphous Fe‐ZrP nanosheet. Benefitting from the ultrathin 2D structure and abundant Fe active sites on the amorphous surface, 2D amorphous Fe‐ZrP nanosheets exhibit outstanding OER activity, which is significantly superior to most OER electrocatalysts. This work offers new insights to promote doped atom utilization via amorphous doping for superb water splitting electrocatalysis.

Unraveling the Synergistic Effect of Heteroatomic Substitution and Vacancy Engineering in CoFe2O4 for Superior Electrocatalysis Performance.

Metal ion substitution and anion exchange are two effective strategies for regulating the electronic and geometric structure of spinel. However, the optimal location of foreign metallic cations and the exact role of these metals and anions remain elusive. Herein, CoFe2O4-based hollow nanospheres with outstanding oxygen evolution reaction activity are prepared by Cr3+ substitution and S2- exchange. X-ray absorption spectra and theoretical calculations reveal that Cr3+ can be precisely doped into octahedral (Oh) Fe sites and simultaneously induce Co vacancy, which can activate adjacent tetrahedral (Td) Fe3+. Furthermore, S2- exchange results in structure distortion of Td-Fe due to compressive strain effect. The change in the local geometry of Td-Fe causes the *OOH intermediate to deviate from the y-axis plane, thus enhancing the adsorption of the *OOH. The Co vacancy and S2- exchange can adjust the geometric and electronic structure of Td-Fe, thus activating the inert Td-Fe and improving the electrochemical performance.

Effect of Plating Variables on Oxygen Evolution Reaction of Ni–Zn–Fe Electrodes for Alkaline Water Electrolysis

In this study, we investigated the oxygen evolution reaction (OER) characteristics of Ni–Zn–Fe electrodes by varying plating current density and Ni:Fe ratio in a plating bath. The activity of the OER increased up to the plating current density of 160 mA/cm2, as the Fe content of the deposited electrode increased and electrochemical surface area (ECSA) increased after Zn dealloying. However, for the plated electrode with higher than 160 mA/cm2 of current density, the change in composition caused by underpotential deposition led to decreased activity due to decreasing Fe content and diminishing Zn dealloying. Moreover, when the Ni:Fe ratio in the plating bath was varied, outstanding OER activity was observed at Ni:Fe = 2:1. When the Fe content of the bath increased beyond this ratio, Fe could not restrain Ni oxidation and formed Fe oxides in OER reaction, and oxygen vacancy decreased. These caused a degradation of the OER activity.