Active Oxygen Evolution Reaction Catalysts Research Articles

Spectroscopic and Electrokinetic Evidence for a Bifunctional Mechanism of the Oxygen Evolution Reaction**

AbstractA bifunctional oxygen evolution reaction (OER) mechanism, in which the energetically demanding step of the attack of hydroxide on a metal oxo unit is facilitated by a hydrogen atom transfer to a second site, has the potential to circumvent the scaling relationship. However, the bifunctional mechanism has hitherto only been supported by theoretical computations. Here we describe an operando Raman spectroscopic and electrokinetic study of two highly active OER catalysts, FeOOH‐NiOOH and NiFe layered double hydroxide (LDH). The data support two distinct mechanisms for the two catalysts: FeOOH‐NiOOH operates by a bifunctional mechanism where the rate‐determining O−O bond forming step is the OH− attack on a Fe=O coupled with a hydrogen atom transfer to a NiIII‐O site, whereas NiFe LDH operates by a conventional mechanism of four consecutive proton‐coupled electron transfer steps. The experimental validation of the bifunctional mechanism enhances the understanding of OER catalysts.

Key activity descriptors of nickel-iron oxygen evolution electrocatalysts in the presence of alkali metal cations

Efficient oxygen evolution reaction (OER) electrocatalysts are pivotal for sustainable fuel production, where the Ni-Fe oxyhydroxide (OOH) is among the most active catalysts for alkaline OER. Electrolyte alkali metal cations have been shown to modify the activity and reaction intermediates, however, the exact mechanism is at question due to unexplained deviations from the cation size trend. Our X-ray absorption spectroelectrochemical results show that bigger cations shift the Ni2+/(3+δ)+ redox peak and OER activity to lower potentials (however, with typical discrepancies), following the order CsOH > NaOH ≈ KOH > RbOH > LiOH. Here, we find that the OER activity follows the variations in electrolyte pH rather than a specific cation, which accounts for differences both in basicity of the alkali hydroxides and other contributing anomalies. Our density functional theory-derived reactivity descriptors confirm that cations impose negligible effect on the Lewis acidity of Ni, Fe, and O lattice sites, thus strengthening the conclusions of an indirect pH effect.

Mechanistic Insights on Enhanced Activity of Cu-Deposited Fibrous Electrocatalyst for Oxygen Evolution Reaction

Water electrolysis is an ideal method for producing hydrogen, which is expected as a next-generation energy carrier. However, the sluggish reaction kinetics of the oxygen evolution reaction (OER) limits the overall energy efficiency.1,2 Therefore, designing efficient electrocatalyst for the OER is crucial and has been studied extensively for more than a few decades.3 Precious metal catalysts such as RuO2 and IrO2 exhibit high activity,4,5 but are expensive, and transition metals have been attracted as alternative catalysts.6 In this study, a fibrous Cu catalyst was synthesized as a highly active and low-cost OER catalyst. An electrospinning method was selected to synthesize a fibrous polymer substrate, which was subsequently coated with Cu by electroless deposition. We applied Cu, which is a low cost and has excellent electrical conductivity as an electrocatalyst. As a geometric structure, fiber shape was adopted to increase the specific surface area and improving the diffusion efficiency of the catalyst. We selected PVdF-HFP as catalyst support, to promote the diffusion of the ions in the electrolyte and enhance the activity as a catalyst by its ferroelectricity.In order to clarify the effect of geometric structure on the OER activity, Cu catalysts were synthesized by various methods, including drop-casting, impregnation, and electrospinning. It was found that the fibrous Cu catalyst exhibited the best OER activity amongst all the geometric structures tested in this study, probably due to the increased active surface area as well as better mass transport and diffusion. Furthermore, the effect of the dielectric properties of PVdF-HFP on the OER activity was clarified. The molecular orientation of PVdF-HFP was evaluated by infrared (IR) spectroscopy, which indicates that the stretching and annealing treatment can effectively increase its electric polarizability. Linear sweep voltammetry (LSV) confirmed that the fibrous Cu catalyst with stretching and annealing treatment showed superior OER activity compared to the pristine fibrous Cu catalyst, indicating the large electric polarizability also enhanced the OER.Based on these results, it was clarified that the improvement of the OER activity of the fibrous Cu catalyst was due to the following reasons; (i) improvement of mass transport by fibrous structure, and (ii) optimization of the OER reaction energetics by catalyst(Cu)-support(PVdF-HFP) interaction. Optimizing both geometry and electronic structure of the electrocatalyst provides a new design strategy to achieve improved activity towards oxygen evolution reaction.1 Seh, W. Z. et al., Science. 2017, 355, eaad4998.2 Fabbri, E. et al., Catal. Sci. Technol. 2014, 4, 3800–3821.3 Jiao, Y. et al., Chem. Soc. Rev. 2015, 44, 2060–2086.4 Lee, Y. et al., J. Phys. Chem. Lett. 2012, 3, 399–404.5 Paoli, A. E. et al., Chem. Sci., 2015, 6, 190–196.6 Hong, T. W. et al., Energy Environ. Sci. 2015, 8, 1404–1427.

Strategies to Develop Earth‐Abundant Heterogeneous Oxygen Evolution Reaction Catalysts for pH‐Neutral or pH‐Near‐Neutral Electrolytes

The anodic oxygen evolution reaction (OER) is the bottleneck of water splitting to produce hydrogen due to its sluggish kinetics. In order to lower the energy cost, highly active and cost-efficient OER catalysts need to be used to overcome the OER reaction barrier, especially in neutral pH. Compared to alkaline or acidic electrolytes, pH-neutral or pH-near-neutral electrolytes are considered to be cheaper and safer, and water from rivers and the sea could be used directly under such conditions. However, OER under neutral pH is challenging compared to the OER catalysts for alkaline conditions. Therefore, OER catalysts for neutral or near-neutral pH have not been pursued significantly and, hence, there are limited advances in this area. Here, the progress made in the research and development of earth-abundant heterogeneous catalysts for OER in three pH-neutral or pH-near-neutral systems, namely, the phosphate system, the carbonate system, and the borate system, are systematically reviewed and summarized for the first time. Strategies to develop high-performance OER catalysts for neutral pH are reviewed and summarized. In addition, future challenges and opportunities in this field are discussed, which may shed some light on the future developments of earth-abundant heterogeneous catalysts for OER in neutral or near-neutral pH.

Boosting the oxygen evolution activity of copper foam containing trace Ni by intentionally supplementing Fe and forming nanowires in anodization

Oxygen evolution reaction (OER) is the bottleneck for realizing energy-efficient hydrogen production through water electrolysis in both acid and alkali. Alkaline OER electrocatalyzed by Ni and Co hydroxides are well known which showed unexpected enhancement with the addition of Fe. We found that the commercially procured Cu foam containing trace amount of Ni (~1.5 wt.%) upon anodization formed Cu(OH)2CuO nanowires with conceivable formation of Ni(OH)2 and experienced a notable enhancement in its OER activity. When sufficient amount of Fe was intentionally supplemented during anodization, OER activity of the same was further improved. Specifically, as a combined result of anodization in KOH and in Fe supplemented KOH, overpotential at 50 mA cm−2 was lowered by 153 mV. Such an activation also improved the kinetics of OER by lowering the Tafel slope by 100 mV dec−1. With these, it has been shown here that a moderately active OER catalyst i.e., Cu(OH)2CuO/Cu formed upon the anodization of Cu foam can be turned into a highly active catalyst just by utilizing the trace Ni that it already contains and intentionally supplementing sufficient amount of Fe.

State-of-the-Art Iridium-Based Catalysts for Acidic Water Electrolysis: A Minireview of Wet-Chemistry Synthesis Methods

With the increasing demand for clean hydrogen production, both as a fuel and an indispensable reagent for chemical industries, acidic water electrolysis has attracted considerable attention in academic and industrial research. Iridium is a well-accepted active and corrosion-resistant component of catalysts for oxygen evolution reaction (OER). However, its scarcity demands breakthroughs in catalyst preparation technologies to ensure its most efficient utilisation. This minireview focusses on the wet-chemistry synthetic methods of the most active and (potentially) durable iridium catalysts for acidic OER, selected from the recent publications in the open literature. The catalysts are classified by their synthesis methods, with authors’ opinion on their practicality. The review may also guide the selection of the state-of-the-art iridium catalysts for benchmarking purposes.

A Surface-Oxide-Rich Activation Layer (SOAL) on Ni2 Mo3 N for a Rapid and Durable Oxygen Evolution Reaction.

The oxygen evolution reaction (OER) is key to renewable energy technologies such as water electrolysis and metal-air batteries. However, the multiple steps associated with proton-coupled electron transfer result in sluggish OER kinetics and catalysts are required. Here we demonstrate that a novel nitride, Ni2 Mo3 N, is a highly active OER catalyst that outperforms the benchmark material RuO2 . Ni2 Mo3 N exhibits a current density of 10 mA cm-2 at a nominal overpotential of 270 mV in 0.1 m KOH with outstanding catalytic cyclability and durability. Structural characterization and computational studies reveal that the excellent activity stems from the formation of a surface-oxide-rich activation layer (SOAL). Secondary Mo atoms on the surface act as electron pumps that stabilize oxygen-containing species and facilitate the continuity of the reactions. This discovery will stimulate the further development of ternary nitrides with oxide surface layers as efficient OER catalysts for electrochemical energy devices.

A Surface‐Oxide‐Rich Activation Layer (SOAL) on Ni2Mo3N for a Rapid and Durable Oxygen Evolution Reaction

AbstractThe oxygen evolution reaction (OER) is key to renewable energy technologies such as water electrolysis and metal–air batteries. However, the multiple steps associated with proton‐coupled electron transfer result in sluggish OER kinetics and catalysts are required. Here we demonstrate that a novel nitride, Ni2Mo3N, is a highly active OER catalyst that outperforms the benchmark material RuO2. Ni2Mo3N exhibits a current density of 10 mA cm−2 at a nominal overpotential of 270 mV in 0.1 m KOH with outstanding catalytic cyclability and durability. Structural characterization and computational studies reveal that the excellent activity stems from the formation of a surface‐oxide‐rich activation layer (SOAL). Secondary Mo atoms on the surface act as electron pumps that stabilize oxygen‐containing species and facilitate the continuity of the reactions. This discovery will stimulate the further development of ternary nitrides with oxide surface layers as efficient OER catalysts for electrochemical energy devices.

Hydrophilic Ni(OH)2@CoB nano-chains with shell-core structure as an efficient catalyst for oxygen evolution reaction

Enormously active and cost-effective electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are the critical components to produce hydrogen via water splitting using the electricity produced from renewable energy sources. Herein, inspired by the highly electric conductivity of CoB, shell-core structured Ni(OH)2@CoB nano-chains are synthesized as highly active OER catalyst with the assistance of the magnetic field. In the shell-core structured Ni(OH)2@CoB nano-chains, Ni(OH)2 nanoflakes were directly grown onto CoB nano-chains via a facile and wet chemical method. Ni(OH)2 in nanoflake form can provide more available active sites on the surface for electrochemical reaction that is evidenced by high BET surface area (648.9 m2 g−1). At the current density of 10 mA cm−2, the overpotentials of OER occurred on Ni(OH)2@CoB is 320 mV. The obtained Ni(OH)2@CoB also shows very good OER durability without any observable decline for 12 h. The high OER catalytic performance combined with its low-cost makes the Ni(OH)2@CoB nano-chains promising OER catalyst for water splitting in alkaline media.

Covalency competition dominates the water oxidation structure–activity relationship on spinel oxides

Spinel oxides have attracted growing interest over the years for catalysing the oxygen evolution reaction (OER) due to their efficiency and cost-effectiveness, but fundamental understanding of their structure–property relationships remains elusive. Here we demonstrate that the OER activity on spinel oxides is intrinsically dominated by the covalency competition between tetrahedral and octahedral sites. The competition fabricates an asymmetric MT−O−MO backbone where the bond with weaker metal–oxygen covalency determines the exposure of cation sites and therefore the activity. Driven by this finding, a dataset with more than 300 spinel oxides is computed and used to train a machine-learning model for screening the covalency competition in spinel oxides, with a mean absolute error of 0.05 eV. [Mn]T[Al0.5Mn1.5]OO4 is predicted to be a highly active OER catalyst and subsequent experimental results confirm its superior activity. This work sets mechanistic principles of spinel oxides for water oxidation, which may be extendable to other applications. Spinel oxides have attracted interest as water oxidation catalysts due to their efficiency and cost-effectiveness. Now, the covalency competition between tetrahedral and octahedral sites is shown to dominate the OER activity on spinel oxides, and the design principle is used to predict and confirm the superior activity of [Mn]T[Al0.5Mn1.5]OO4.

Modulating interfacial electronic structure of CoNi LDH nanosheets with Ti3C2Tx MXene for enhancing water oxidation catalysis

Developing efficient nonprecious metal electrocatalysts is urgently needed to promote the sluggish kinetics of oxygen evolution reaction (OER). Transition metals-based layered double hydroxides (LDH) have been considered as highly active OER catalysts, while low conductivity and limited active site exposures hinder their further applications. Herein, CoNi LDH/Ti3C2Tx MXene is facilely constructed by using Ti3C2Tx coated nickel foam as support to load CoNi LDH through electrodeposition. Surprisingly, a significant enhancement in OER activity of pristine CoNi LDH is achieved due to the metallic conductivity and hydrophilic and electronegative surface of Ti3C2Tx. Importantly, CoNi LDH/Ti3C2Tx displays prominent OER performance and stability in alkaline medium, which exhibits a low overpotential of 257.4 mV to reach current density of 100 mA/cm2 and a small Tafel slope of 68 mV/dec. The experimental and calculated results demonstrate electron transfer from CoNi LDH to Ti3C2Tx plays a significant role in boosting OER activity by lowering the binding strength of intermediates.

Microkinetic Modeling of the Oxygen Evolution Reaction (OER) on Hydrous Iridium Oxide during Dynamic Operation

In an energy system which is based on intermittent renewable sources, efficient energy storage and conversion technologies are needed. Proton exchange membrane (PEM) electrolysis is a promising technology for the storage of electrical energy in the form of hydrogen. In PEM electrolyzers, the oxygen evolution reaction (OER) is seen as the bottleneck due to its high overpotential. To enhance the overall performance, highly active but stable OER catalysts are essential. Oxidized iridium shows good activity for the OER and is more stable compared to other materials such as ruthenium oxide[1]. It has been shown that electrochemically grown hydrous iridium oxide is particularly favorable[2]. A better understanding of the changes of its complex surface structure and chemistry during dynamic operations is crucial for practical applications and for obtaining deep insights in factors that affect its activity and stability.In the present work we investigate the surface states of hydrous iridium during the OER. For this purpose, we implement a dynamic physical model to simulate the formation of different types of intermediate states. A complete set of microkinetic equations is derived, solved and validated with cyclovoltammetric data (see figure 1). By solving the surface species balances dynamically, the phenomena that are observable in cyclovoltammetric, chronoamperometric and impedance spectroscopic experiments can be interpreted quantitatively[3].Applying this method onto hydrous iridium oxide we are able to study the degree of oxidation of the iridium atoms at the surface at various electrode potentials. In a wide potential region from 0.4 V vs RHE up to the OER potential range, the simulation predicts the amount of adsorbed -OH, -O, -OOH and -OO species, which determine the overall oxidation state of the iridium. The characteristic peaks and shoulders in the cyclovoltammogram are assigned to the single reaction steps. By comparing different mechanisms, a deep understanding of the predominant reaction pathway is gained. Furthermore, the quantification of microkinetic rate constants allows us to define rate determining reaction steps during the dynamic operation. With this study we confirm that the mechanism in figure 1, in which two parallel reaction pathways are present, can describe the experimental cyclovoltammogram quantitatively.[1] S. Cherevko et al., Oxygen and hydrogen evolution reactions on Ru, RuO 2 , Ir, and IrO 2 thin film electrodes in acidic and alkaline electrolytes: A comparative study on activity and stability, Catalysis Today 262 (2016) 170–180[2] S. Cherevko et al., Oxygen evolution activity and stability of iridium in acidic media. Part 2. –Electrochemically grown hydrous iridium oxide, Journal of Electroanalytical Chemistry 774 (2016) 102–110[3] U. Krewer et al., Impedance spectroscopic analysis of the electrochemical methanol oxidation kinetics, Journal of Electroanalytical Chemistry, 589 (2006) 148–159 Figure 1

Novel Scalable Production of Single-Layer Graphene Coated-Metal Nanoparticles for Water Splitting

Graphene-coated metal nanoparticles (NPs) have attracted great attention owing to their unique structural, photochemical and electrochemical properties based on electron communication between graphene and metal NPs. The development of highly efficient and non-precious metal-based electrocatalysts for water splitting comprising hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is still a big challenge. The hybridization of nitrogen (N)-doped carbon and cost-effective transition metals is a promising approach to produce highly active catalysts for HER and OER. Herein, a highly controllable chemical vapor deposition method is designed for large-scale synthesis of nickel nanoparticle wrapped by single-layer N-doped graphene (Ni@SNG), where silica work as molecule sieve to tactfully assist single-layer graphene growth by depressing diffusion of carbon radicals. The Ni@SNG sample synthesized at 800 oC shows excellent activity for HER in alkaline solution with a low overpotential of 100 mV at 10 mA cm-2, which is close to state-of-the-art Pt/C catalyst. Furthermore, the Ni@SNG catalyst supported on nickel foil is developed as a magnetic adsorption binder-free electrode, which exhibits much improved performance on catalytic activity and stability than common Nafion binder-based electrode. Therefore, magnetism adsorption technique, taking full advantages of magnetic catalysts, will be a greatly promising approach to overcome high electron resistance and poor adhesive stability of polymer binder-based electrodes in actual applications. Figure 1

Enhanced Catalytic Activity and Stability of the Oxygen Evolution Reaction on Tetravalent Mixed Metal Oxide

The oxygen evolution reaction (OER) is a crucial energy conversion reaction for achieving a sustainable society. Highly active OER catalysts were reported in Fe–Co mixed oxides such as perovskite-t...

A pair of metal organic framework (MOF)-derived oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts for zinc-air batteries

Metal organic frameworks (MOFs) are amazing precursors for the development of functional catalysts due to their ability of being modified both structurally and in terms of composition. This work presents a pair of MOF - derived oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts for the advancement of zinc-air batteries. Zeolitic imidazolate frameworks (ZIF) are known as ideal materials to create doped carbons. Combining with a sacrificial tellurium template, we have developed a “pseudo-carbon nanotube” with a ZIF-8 that is doped with a mixture of zinc, cobalt, and iron. The resulting mixed-metal doped porous carbon nanotubes (CoFeZn@pCNT) show excellent catalytic activity for ORR with a half-way ORR potential (E1/2) of 0.87 V vs. RHE (reverse hydrogen electrode). Iridium-based catalysts are known as the best option for OER so far, but it is not viable for practical applications due to cost restrictions. Previous research into alternative catalysts has focused on metal oxides with first-row transition metals. Metal sulfides provide superior conductivity compared to metal oxides and are a new frontier in the search for affordable, active, and stable OER catalysts. By combining cobalt, iron, and nickel into a MOF structure (ZIF-67), followed by a sulfurization process, a MOF-derived mixed-metal sulfide catalyst (FeCoNi–S@ZIF) has been developed in this study. The resulting catalysts show an onset OER potential of 1.65 V vs. RHE at 10 mA cm−2 and exhibit remarkable stability for the operation of zinc-air batteries.

Core-Shell Structured NiFeSn@NiFe (Oxy)Hydroxide Nanospheres from an Electrochemical Strategy for Electrocatalytic Oxygen Evolution Reaction.

Efficient electrocatalysts for the oxygen evolution reaction (OER) are highly desirable because of the intrinsically sluggish kinetics of OER. Herein, core–shell structured nanospheres of NiFexSn@NiFe (oxy)hydroxide (denoted as NiFexSn‐A) are prepared as active OER catalysts by a facile electrochemical strategy, which includes electrodeposition of NiFexSn alloy nanospheres on carbon cloth (CC) and following anodization. The alloy core of NiFexSn could promote charge transfer, and the amorphous shell of NiFe (oxy)hydroxide is defect‐rich and nanoporous due to the selective electrochemical etching of Sn in alkaline medium. The optimized catalyst of NiFe0.5Sn‐A displays a remarkable OER performance with a low overpotential of 260 mV to reach the current density of 10 mA cm−2, a small Tafel slope of 50 mV dec−1, a high turnover frequency of 0.194 s−1 at an overpotential of 300 mV, and a robust durability. Further characterizations indicate that the superior OER performance of the core–shell structured NiFe0.5Sn‐A nanospheres might originate from abundant active sites and small charge transfer resistance. This work brings a new perspective to the design and synthesis of core–shell structured nanospheres for electrocatalysis through a facile electrochemical strategy.

Boosting oxygen evolution reaction by activation of lattice‐oxygen sites in layered Ruddlesden‐Popper oxide

AbstractEmerging anionic redox chemistry presents new opportunities for enhancing oxygen evolution reaction (OER) activity considering that lattice‐oxygen oxidation mechanism (LOM) could bypass thermodynamic limitation of conventional metal‐ion participation mechanism. Thus, finding an effective method to activate lattice‐oxygen in metal oxides is highly attractive for designing efficient OER electrocatalysts. Here, we discover that the lattice‐oxygen sites in Ruddlesden‐Popper (RP) crystal structure can be activated, leading to a new class of extremely active OER catalyst. As a proof‐of‐concept, the RP Sr3(Co0.8Fe0.1Nb0.1)2O7‐δ (RP‐SCFN) oxide exhibits outstanding OER activity (eg, 334 mV at 10 mA cm−2 in 0.1 M KOH), which is significantly higher than that of the simple SrCo0.8Fe0.1Nb0.1O3‐δ perovskite and benchmark RuO2. Combined density functional theory and X‐ray absorption spectroscopy studies demonstrate that RP‐SCFN follows the LOM under OER condition, and the activated lattice oxygen sites triggered by high covalency of metal‐oxygen bonds are the origin of the high catalytic activity.image

Engineering of the d-Band Center of Perovskite Cobaltite for Enhanced Electrocatalytic Oxygen Evolution.

Great efforts have been made to understand and upgrade the kinetically sluggish oxygen evolution reaction (OER). In this study, a series of V-doped LaCoO3 (V-LCO) OER electrocatalysts with optimized d-band centers are fabricated. When utilized as an electrode for the OER, as-formed LaCo0.8 V0.2 O3 (V-LCO-II) requires an overpotential of only 306 mV to drive a geometrical catalytic current density of 10 mA cm-2 . Furthermore, at a given overpotential of 350 mV, the OER current density of V-LCO-II is about 22 times that of pure LaCoO3 (LCO) nanoparticles. Tailoring of the d-band center by V doping facilitates the adsorption of OER intermediates and promotes the formation of amorphous active species on the surface of LCO through the exchange interaction between high-spin V4+ and low-spin Co2+ . This work may create new opportunities for developing other highly active OER catalysts through d-band center engineering.

Cation insertion to break the activity/stability relationship for highly active oxygen evolution reaction catalyst

The production of hydrogen at a large scale by the environmentally-friendly electrolysis process is currently hampered by the slow kinetics of the oxygen evolution reaction (OER). We report a solid electrocatalyst α-Li2IrO3 which upon oxidation/delithiation chemically reacts with water to form a hydrated birnessite phase, the OER activity of which is five times greater than its non-reacted counterpart. This reaction enlists a bulk redox process during which hydrated potassium ions from the alkaline electrolyte are inserted into the structure while water is oxidized and oxygen evolved. This singular charge balance process for which the electrocatalyst is solid but the reaction is homogeneous in nature allows stabilizing the surface of the catalyst while ensuring stable OER performances, thus breaking the activity/stability tradeoff normally encountered for OER catalysts.

Carbon cloth supported hierarchical core-shell NiCo2S4@CoNi-LDH nanoarrays as catalysts for efficient oxygen evolution reaction in alkaline solution

Hierarchical core-shell NiCo2S4@CoNi-LDH nanoarrays grown on carbon cloth (CC) with outstanding electrocatalytic activity for oxygen evolution reaction (OER) were successfully constructed by a three-step hydrothermal strategy. The as-prepared hierarchical core-shell NiCo2S4@CoNi-LDH nanoarrays were characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), energy dispersive spectrometry (EDS) and EDS mapping technologies. Electrochemical measurements showed that the OER catalytic activity of as-obtained NiCo2S4@CoNi-LDH catalyst could be tuned by the molar ratio of Co/Ni in CoNi-LDH. Experiments uncovered that NiCo2S4@Co1Ni4-LDH catalyst prepared at the Co/Ni molar ratio of 1:4 exhibited the strongest OER electrocatalytic activity. To deliver the current densities of 100 mA cm−2, the as-obtained NiCo2S4@Co1Ni4-LDH catalyst required the overpotential of 337 mV in 1.0 M KOH solution. After continuously catalyzing for 40 h, the voltage curve hardly waved, presenting excellent long-term stability. The present work is a useful attempt for constructing highly active and cost-effective OER catalyst.