Oxygen Evolution Catalysis Research Articles

The role of SO42− in manipulating partial charge distribution to boost alkaline water oxidation in Co9S8/C–Ni(OH)2

Transition metal sulfides (TM sulfides) has long been regarded as highly promising materials for catalyzing oxygen evolution reaction (OER). The function of TM sulfides in OER occurs on TM oxyhydroxide and SO42−, which are formed through surface reconstruction under certain potentials. It is worth noting that the impact of SO42− on the local charge distribution among atoms, a crucial determinant of OER performance, has been insufficiently studied. This study aims to investigate the role of SO42− in mediating the partial redistribution of charges among Co, Ni and O atoms on a precatalyst Co9S8/C–Ni(OH)2 electrode. The electrode undergoes self-reconstruction to form a CoOOH/SO42−/NiOOH structure on its surface that is active for the OER. The results demonstrate that SO42− facilitates the local charge redistribution of active atoms, leading to optimized adsorption energy of OER intermediates and increased redox center of the material. Furthermore, SO42− serves as an electron mediator in the OER process under varying applied voltages. Consequently, CoOOH/SO42−/NiOOH achieves a Tafel slope of 56 mV dec−1, an overpotential of 250 mV, and maintains a high stability for over 100 h at a current density of 20 mA cm−2. Overall, this research provides valuable insights into catalytic reaction mechanisms and the design of efficient composite catalysts.

Electrochemical Synthesis of Core-Shell Nanoparticles by Seed-Mediated Selective Deposition

Conventional solvothermal synthesis of core–shell nanoparticles results in them being covered with surfactant molecules for size control and stabilization, undermining their practicality as electrocatalysts. Here, we report an electrochemical method for the synthesis of core–shell nanoparticles directly on electrodes, free of surfactants. By implementation of selective electrodeposition on gold cores, 1st-row transition metal shells were constructed with facile and precise thickness control. This type of metal-on-metal core–shell synthesis by purely electrochemical means is the first of its kind. The applicability of the nanoparticle decorated electrodes was demonstrated by alkaline oxygen evolution catalysis, during which the Au–Ni example displayed stable catalysis with low overpotential.

Iridium on Conductive Support: Towards Low Iridium Anodes in PEM Electrolyzers

Commercialization of proton exchange membrane (PEM) electrolyzers for green hydrogen production have been recently achieved, but with a limited scale of low gigawatts (GW).1 Large-scale and sustainable deployment of PEM electrolyzers will face the challenges of scarcity and high cost of iridium (Ir) used in the anode to catalyze oxygen evolution reaction (OER). A 1 MW PEM electrolyzer stack currently uses ~0.4 kg of Ir based on an Ir loading of 1.5 mg/cm2, which contributes ~$60k cost per stack.2 Moreover, the Ir production has been about 8 tons/year in recent years.3 This can only support an annual production of 5 GW PEM electrolyzer if assuming 25% Ir is available for PEM electrolyzers with the same Ir loading. Therefore, lowering the Ir loading in PEM electrolyzers is urgently needed to meet the rapid expansion of the PEM electrolysis market.Several groups including Plug have developed supported Ir catalysts to lower the Ir loading by a factor of 5 without sacrifice in efficiency.4-8 However, all support used by far is non- or poorly electrically conductive. The conductivity of the electrodes relies solely on the surface IrOx, which sets stringent limits on the catalyst/electrode development, especially with low Ir contents. Here we first argue from fundamental aspects that the catalysts/electrodes with Ir on conductive support can be free of these limits. We further show that platinum (Pt) and titanium diboride (TiB2) powders are feasible candidates as conductive support for Ir-based OER catalysts. We demonstrated a TiB2 supported IrOx (IrOx/TiB2) catalyst synthesized via wet chemistry deposition without post heat treatment combines a mass activity towards OER with high conductivity. Its conductivity of ~30 S/cm2 is comparable to that of Vulcan carbon, and ~105 times that of the counterpart IrOx/W-TiO2 (W-TiO2 represents commercial tungsten doped TiO2 nanoparticles). Meanwhile, the IrOx/TiB2 catalyst shows a mass activity comparable to that of the counterpart IrOx/W-TiO2, twice that of commercial Ir black, and 50 times that of a commercial IrO2/TiO2 catalyst in acidic solution. Durability test showed that the Ir dissolution of the IrOx/TiB2 in acidic solution holding at 2 V for 100 hours is comparable to that of Ir black. Characterization of the IrOx/TiB2 showed small hydrous IrOx nanoparticles (1-2 nm) uniformly distributed on the surface of TiB2 nanoparticles (~58 nm) with an Ir content of ~33±7 wt%. Membrane electrode assembly evaluation on the IrOx/TiB2 catalyst is undergoing. The results will be reported and discussed. References (1) IEA, World Energy Outlook, 2022. https://iea.blob.core.windows.net/assets/830fe099-5530-48f2-a7c1-11f35d510983/WorldEnergyOutlook2022.pdf (accessed 2023-02-12).(2) Mittelsteadt, C. (Invited) Ir Strangelove: Or How I Learned to Stop Worrying and Embrace the PEM. ECS Meeting s 2022, MA2022-01, 1335-1335.(3) Seeking Alpha Home Page. https://seekingalpha.com/article/4399727-sibanye-should-benefit-from-hydrogen-wars-thanks-to-iridium-exposure (accessed 2023-02-12).(4) Böhm, D.; Beetz, M.; Gebauer, C.; Bernt, M.; Schröter, J.; Kornherr, M.; Zoller, F.; Bein, T.; Fattakhova-Rohlfing, D. Highly conductive titania supported iridium oxide nanoparticles with low overall iridium density as OER catalyst for large-scale PEM electrolysis. Applied Materials Today 2021, 24, 101134.(5) Pham, C. V.; Bühler, M.; Knöppel, J.; Bierling, M.; Seeberger, D.; Escalera-López, D.; Mayrhofer, K. J. J.; Cherevko, S.; Thiele, S. IrO2 coated TiO2 core-shell microparticles advance performance of low loading proton exchange membrane water electrolyzers. Appl. Catal. B‐Environ. 2020, 269, 118762.(6) Zhao, S.; Stocks, A.; Rasimick, B.; More, K.; Xu, H. Highly Active, Durable Dispersed Iridium Nanocatalysts for PEM Water Electrolyzers. J. Electrochem. Soc. 2018, 165, F82-F89.(7) Oakton, E.; Lebedev, D.; Povia, M.; Abbott, D. F.; Fabbri, E.; Fedorov, A.; Nachtegaal, M.; Copéret, C.; Schmidt, T. J. IrO2-TiO2: A high-surface-area, active, and stable electrocatalyst for the oxygen evolution reaction. ACS Catal. 2017, 7, 2346-2352.(8) Lewinski, K. A.; van der Vliet, D.; Luopa, S. M. NSTF advances for PEM electrolysis-the effect of alloying on activity of NSTF electrolyzer catalysts and performance of NSTF based PEM electrolyzers. ECS Trans 2015, 69, 893.

Construction of n-type homogeneous to improve interfacial carrier transfer for enhanced photoelectrocatalytic hydrolysis

Photoelectrocatalyzed hydrogen production plays an important role in the path to carbon neutrality. The construction of heterojunctions provides an ideal example of an oxygen precipitation reaction. In this work, the performance of the n-n type heterojunction CeBTC@FeBTC/NIF in the photoelectronically coupled catalytic oxygen evolution reaction (OER) reaction is presented. The efficient transfer of carriers between components enhances the catalytic activity. Besides, the construction of heterojunctions optimizes the energy level structure and increases the absorption of light, and the microstructure forms holes with a blackbody effect that also enhances light absorption. Consequently, CeBTC@FeBTC/NIF has excellent photoelectric coupling catalytic properties and requires an overpotential of only 300 mV to drive a current density of 100 mA cm−2 under illumination. More importantly, the n-n heterojunction was found to be effective in enhancing charge and photogenerated electron migration by examining the carrier density of each component and carrier diffusion at the interface.

Understanding the Super-Theoretical Capacity Behavior of VO2 in Aqueous Zn Batteries.

VO2 material, as a promising intercalation host, is widely investigated not only in aqueous lithium-ion batteries, but also in aqueous zinc-ion batteries (AZIBs) owing to its stable tunnel-like framework and multivalence of vanadium. Different from lithium-ion storage, VO2 can provide higher capacity when storing zinc ions, even exceeding its theoretical capacity (323mAhg-1), but the specific reason for this unconventional performance in AZIBs is still unclear. The present study proposes a catalytic oxygen evolution reaction (OER) coupled with an interface oxidation mechanism of VO2 during the initial charging to a high voltage. This coupling induces a phase transformation of VO2 into a high oxidation state of V5O12∙6H2O, enabling a nearly two-electron reaction and providing additional zinc storage sites to achieve super-theoretical capacity. Furthermore, it is demonstrated that these vanadium oxide cathodes (V2O3, VO2, and V2O5) will all undergo phase change after the first charge or short cycle. Notably, water molecules participate in the final formation of layered vanadium-based hydrate, highlighting their crucial role as "pillars" for stabilizing the structure. This work significantly enhances the understanding of vanadium-based oxide cathodes.

Tuning electronic structure of hedgehog-like nickel cobaltite via molybdenum-doping for enhanced electrocatalytic oxygen evolution catalysis

As a typical spinel oxide, nickel cobaltite (NiCo2O4) is considered to be a promising and reliable oxygen evolution reaction (OER) catalyst due to its abundant oxidation states and the synergistic effect of multiple metal species. However, the electrocatalytic OER performance of NiCo2O4 has always been limited by the low specific surface area and poor intrinsic conductivity of spinels. Herein, the hedgehog-like molybdenum-doped NiCo2O4 (Mo-NiCo2O4) catalyst was prepared as an efficient OER electrocatalyst via a facile hydrothermal method followed with high-temperature annealing. The Mo-NiCo2O4-0.075 with Mo doping concentration of ∼ 1.95 wt% exhibits excellent OER performance with a low overpotential of 265 mV at a current density of 10 mA·cm−2and a Tafel slope of 126.63 mV·dec-1, as well as excellent cyclingstability.The results demonstrated that the hedgehog-like structure provides Mo-NiCo2O4 with the high surface area and mesopores that enhance electrolyte diffusion and optimal active site exposure. The in-situ Raman spectra and density functional theory calculations show that the Mo cations doping improve the intrinsic conductivity of the NiCo2O4 while modulating the chemisorption of intermediates. Meanwhile, the energy barriers of *OH and O* formation decrease significantly after Mo doping, effectively facilitating water dissociation and optimizing the reaction kinetics.

Diatomic Fe-Co catalysts synergistically catalyze oxygen evolution reaction

Diatomic Fe-Co catalysts synergistically catalyze oxygen evolution reaction

Synthesis of flower-like NixFe1−x layered double hydroxides with enhanced oxygen evolution catalysis

In this work, the NixFe1-x LDHs (x = 0.25, 0.5, 0.75, 0.8) samples were prepared by hydrothermal method. The morphology of NixFe1-x LDHs can be controlled and porous NixFe1-x LDHs “nanoflowers” were obtained at x = 0.75. The XRD patterns showed that pure NixFe1-x LDHs were produced when the nickel and iron salts were at a fixed ratio. By tuning the conductivity of LDHs, the current density of NixFe1-x LDHs/ acetylene black (AB) obviously increased. The Ni0.75Fe0.25 LDHs/AB showed good OER performance with Tafel slope of 31 mV/dec and low overpotential of 262.2 mV at current density of 20 mA/cm2.

Enhancing solar energy conversion with nickel/iron oxyhydroxide-modified hematite photoanodes: The role of Fe species in alkaline electrolyte

Hematite photoanodes have shown potential for use in practical applications of photoelectrochemical (PEC) water splitting cells due to their abundance and stability, yet their efficiency needs to be improved. To optimize photoanode performance, co-catalysts such as amorphous nickel/iron oxyhydroxide layers are often deposited on the surface of hematite to enhance activity by catalyzing oxygen evolution. Recent studies have shown that the role of oxyhydroxide layers in changing PEC activity can vary depending on factors such as film morphology, co-catalyst layer thickness, and electrolyte composition. In this study, we investigate the effect of NiOOH and (Ni,Fe)OOH layers on the PEC activity of electrodeposited nanostructured hematite films. Our analysis of charge transfer and recombination rate constants determined from chronoamperometry and electrochemical impedance data suggests that the coatings' role is purely passivating, which is crucial for discontinuous electrodeposited films. Importantly, we show that the passivating properties of these coatings are enhanced by the presence of ppm concentrations of Fe in the electrolyte. We believe that our findings will be useful for further development of hematite photoanodes.

Rapid room-temperature synthesis of porous Sulfur-doped nickel-chromium-Layered Double Hydroxide for oxygen evolution catalysis in seawater splitting

Seawater splitting is a promising and sustainable technology for producing high-purity hydrogen, but its commercial application remains a major challenge due to the kinetically slow oxygen evolution reaction (OER) and severe corrosion in practical applications. In this work, we report a single-step approach to grow a highly porous Sulfur-doped nickel-chromium-Layered Double Hydroxide (S-doped NiCr-LDH) catalyst on Ni foam at room temperature. This rapid approach efficiently designs the surface of Ni foam into a porous S-doped NiCr-LDH layer with outstanding hydrophilic characteristics. The catalyst exhibits outstanding OER performance in alkaline freshwater and alkaline seawater electrolytes, requiring overpotentials of only 270 and 342 mV to achieve current densities of 100 mA cm−2, while also exhibiting an extremely long endurance of over 80 h. This simple OER catalyst preparation method could advance the development of hydrogen production from seawater splitting.

Effect of fluorine content in layered double hydroxide catalyzing oxygen evolution

Layered double hydroxides (LDHs) have been extensively studied in OER owing to their unique advantages. The mechanism of the effect of NH4F, a common and essential structural guide in the synthesis of LDH, on LDH is relatively ambiguous. Therefore, the solvothermal process synthesized a series of FeCoNi LDHs with different fluorine contents. Physical and chemical characterizations show that the fluorine content regulates the synthesis process, morphology, and electronic structure of the catalysts. The optimal catalyst required 196 mV overpotential to reach 10 mA cm-2, with a Tafel slope of 22 mV dec-1, and stable operation at a current density of 100 mA cm-2 for more than 120 h. XPS analysis demonstrated that the F- ions leached gradually during the OER reaction, promoting the formation of high-valent intermediates at the Co active site to enhance the catalyst activity. This work contributes to the subsequent study of LDH modification and NH4F.

Valence engineering via double exchange interaction in spinel oxides for enhanced oxygen evolution catalysis

The design of spinel-oxide-based catalysts with high activity and long-term durability for oxygen evolution reaction (OER) confronts grand challenges that may be well tackled by maneuvering the electronic structure of surface catalytic sites within spinel oxides. Herein, we harness a double exchange interaction (DEI) triggered by the synergistic effects of Schottky junction and oxygen vacancies (VO) to generate high proportions of octahedrally coordinated Ni3+ and Co2+ (highly active sites) in the edge-sharing [NixCo1−XO6] octahedra. Specifically, Schottky junction is formed between metallic Cu nanowires and semiconducting NiCo2O4 via a core-shell structure, and abundant VO sites are created in NiCo2O4 via H2 thermal treatment. As expected, the Cu@VO-NiCo2O4 electrocatalyst allows a significantly boosted OER performance, with a low overpotential of 214 mV at 10 mA cm-2 and a small Tafel slope of 64.9 mV dec-1, which outperforms the state-of-the-art RuO2 catalyst and most of reported Ni-Co based OER catalysts. Our work provides some inspirations for designing high-performance spinel-oxide-based electrocatalysts towards OER via DEI engineering.

Structurally-Distorted RuIr-Based Nanoframes for Long-Duration Oxygen Evolution Catalysis.

Oxygen evolution reaction (OER) plays a key role in proton exchange membrane water electrolysis (PEMWE), yet the electrocatalysts still suffer from the disadvantages of low activity and poor stability in acidic conditions. Here, a new class of CdRu2 IrOx nanoframes with distorted structure for acidic OER is successfully fabricated. Impressively, CdRu2 IrOx displays an ultralow overpotential of 189mV and an ultralong stability of 1500h at 10mA cm⁻2 toward OER in 0.5M H2 SO4 . Moreover, a PEMWE using the distorted CdRu2 IrOx can be steadily operated at 0.1 A cm⁻2 for 90h. Microstructural analyses and X-ray absorption spectroscopy (XAS) demonstrate that the synergy between Ru and Ir in CdRu2 IrOx induces the distortion of Ru-O, Ir-O, and Ru-M (M = Ru, Ir) bonds. In situ XAS indicates that the applied potential leads to the deformation octahedral structure of RuOx /IrOx and the formation of stable Ru5+ species for OER. Theoretical calculations also reveal that the distorted structures can reduce the energy barrier of rate-limiting step during OER. This work provides an efficient strategy for constructing structural distortion to achieve significant enhancement on the activity and stability of OER catalysts.

Self-Reconstructed Two-Dimensional Cluster-Based Co-Organic Layer Heterojunctions for Enhanced Oxygen Evolution Reactions.

When it comes to an efficient catalytic oxygen evolution reaction (OER) in the production of renewable energy and chemicals, the construction of heterogeneous structures is crucial to break the linear scalar relationship of a single catalyst. This heterogeneous structure construction helps creatively achieve high activity and stability. However, the synthesis process of heterogeneous crystalline materials is often complex and challenging to capture and reproduce, which limits their application. Here, the dynamic process of structural changes in Co-MOFs in alkali was captured by in situ powder X-ray diffraction, FT-IR spectroscopy, and Raman spectroscopy, and several self-reconfigured MOF heterogeneous materials with different structures were stably isolated. The created β-Co(OH)2/Co-MOF heterojunction structure facilitates rapid mass-charge transfer and exposure of active sites, which significantly enhanced OER activity. Experimental results show that this heterogeneous structure achieves a low overpotential of 333 mV at 10 mA cm-2. The findings provide new insights and directions for the search for highly reactive cobalt-based MOFs for sustainable energy technologies.

Studies on Electrochemical Performance of Flower-Like La4Mo7O27 Nanostructures towards Oxygen Evolution Reaction

Hydrogen production from water electrolysis demands modern and improved catalytic materials with increased electrocatalytic characteristics. A simple hydrothermal approach was used to prepare lanthanum molybdate (La4Mo7O27) nanoflowers. The X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques were used to characterise the physical structure and crystallinity of the prepared La4Mo7O27 nanoflowers. The SEM images reveal La4Mo7O27 was composed of nanoflowers. The prepared La4Mo7O27 nanoflowers were used as electrocatalyst to catalyse oxygen evolution reaction (OER) where it requires the overpotentials of 400 mV to generate hydrogen at the current density of 20 mA cm−2, which is less than that of commercially available bare nickel foam (450 mV).

Synergistic Co─Ir/Ru Composite Electrocatalysts Impart Efficient and Durable Oxygen Evolution Catalysis in Acid

AbstractExploring highly active and robust catalysts, which have low precious metal content, to boost the kinetically sluggish oxygen evolution reaction (OER) is a key concern for hydrogen production via proton exchange membrane water electrolysis (PEMWE). Here, rational engineering of the morphology and the local geometric ligand environment of Ir and Ru catalysts are presented by using defect‐rich, lanthanum‐ and lithium‐doped Co3O4 nanofiber (LLCF) as substrate that promotes the electrocatalytic OER. Two catalysts, IrCoOx@LLCF and RuCoOx@LLCF, achieve mass activities of 1013.5 A gIr−1 and 1911.4 A gRu−1 in 0.1 m HClO4 at 300 mV overpotential, respectively, which are 26 and 50 times higher than that of commercial IrO2 and RuO2. Operando X‐ray absorption spectroscopy unveils the reversible structure of IrCoOx during the OER and the suppression of over‐oxidation of Co and Ir, giving rise to high stability. Density functional theory calculations reveal that the local geometric ligand engineering optimizes the binding of oxygenated species to the active sites, resulting in strongly enhanced catalytic activity.

Tuning the electrocatalytic efficacy of nano-dumbbell shaped nickel selenide anchored cobalt telluride towards oxygen evolution

In the wake of environmental enigmas including global warming and the exhaustion of traditional hydrocarbon sediments, the usage of eco-friendly power generation is of paramount importance today. Alternatives to traditional fossil fuels such as hydrogen are clean, safe, and environmentally friendly. Moreover, hydrogen as a renewable energy source, as the only by product of burning hydrogen is water. Many electrochemical energy conversion methods rely on the oxygen evolution reaction (OER), but creating effectual, economical electrocatalysts for it has proven difficult. The multifunctional electrocatalyst, nickel selenide-anchored cobalt telluride, has been found to be effective in catalyzing oxygen evolution processes in alkaline medium. CoTe and NiSe, generated hydrothermally, exhibit promising electrocatalytic activity. However, their composite NiSe@CoTe, possesses higher OER durability. The presence of NiSe in the CoTe matrix responses a powerful OER responses due to the synergistic effect in alkaline environment. The NiSe@CoTe nanocomposite shows minimal Tafel value (39 mV/dec) and lower overpotential (247 mV) to attain a current density of 10 mA/cm2, whereas the pristine CoTe and NiSe needed higher overpotential to attain same current density. Following 16 h of utilizing the same catalyst, OER stability was maintained with 88 % current density retention.

A Fully Conjugated Covalent Organic Framework with Oxidative and Reductive Sites for Photocatalytic Carbon Dioxide Reduction with Water

AbstractConstructing a powerful photocatalytic system that can achieve the carbon dioxide (CO2) reduction half‐reaction and the water (H2O) oxidation half‐reaction simultaneously is a very challenging but meaningful task. Herein, a porous material with a crystalline topological network, named viCOF‐bpy‐Re, was rationally synthesized by incorporating rhenium complexes as reductive sites and triazine ring structures as oxidative sites via robust −C=C− bond linkages. The charge‐separation ability of viCOF‐bpy‐Re is promoted by low polarized π‐bridges between rhenium complexes and triazine ring units, and the efficient charge‐separation enables the photogenerated electron–hole pairs, followed by an intramolecular charge‐transfer process, to form photogenerated electrons involved in CO2 reduction and photogenerated holes that participate in H2O oxidation simultaneously. The viCOF‐bpy‐Re shows the highest catalytic photocatalytic carbon monoxide (CO) production rate (190.6 μmol g−1 h−1 with about 100 % selectivity) and oxygen (O2) evolution (90.2 μmol g−1 h−1) among all the porous catalysts in CO2 reduction with H2O as sacrificial agents. Therefore, a powerful photocatalytic system was successfully achieved, and this catalytic system exhibited excellent stability in the catalysis process for 50 hours. The structure–function relationship was confirmed by femtosecond transient absorption spectroscopy and density functional theory calculations.

Revealing the roles of surface treatments on hematite (α-Fe2O3) photoanode in the shift of the onset potential

In this study, we fabricated different types of Hematite (α-Fe2O3)-based photoanodes, treated with CeOx, FeOOH, and NiFeOx, and investigated the effect of each treatment on the onset potential shift. We revealed the Hematite films that were treated with either CeOx or FeOOH on the surface did not exhibit cathodic shifts of the onset potentials in photocurrent density–potential (J–V) curves, in which the significant improvements in charge transfer efficiencies were achieved, while charge separation efficiencies were not significantly enhanced. It means that the enhanced charge transfer efficiency resulting from the catalyzed oxygen evolution reaction did not significantly influence the shift of the turn-on voltage. On the other hand, we were able to observe the significant improvement of the photo-electrochemical performance of Hematite treated with NiFeOx, including the cathodic shift of the onset potential, which could be attributed to the enhancement of the charge separation efficiency, resulting from the Fermi level unpinning. Based on the results, we could believe that the cathodic shift of the onset potential was primarily due to the enhancement of the photovoltage.

Facet Engineering and Pore Design Boost Dynamic Fe Exchange in Oxygen Evolution Catalysis to Break the Activity-Stability Trade-Off.

The oxygen evolution reaction (OER) plays a vital role in renewable energy technologies, including in fuel cells, metal-air batteries, and water splitting; however, the currently available catalysts still suffer from unsatisfactory performance due to the sluggish OER kinetics. Herein, we developed a new catalyst with high efficiency in which the dynamic exchange mechanism of active Fe sites in the OER was regulated by crystal plane engineering and pore structure design. High-density nanoholes were created on cobalt hydroxide as the catalyst host, and then Fe species were filled inside the nanoholes. During the OER, the dynamic Fe was selectively and strongly adsorbed by the (101̅0) sites on the nanohole walls rather than the (0001) basal plane, and at the same time the space-confining effect of the nanohole slowed down the Fe diffusion from catalyst to electrolyte. As a result, a local high-flux Fe dynamic equilibrium inside the nanoholes for OER was achieved, as demonstrated by the Fe57 isotope labeled mass spectrometry, thereby delivering a high OER activity. The catalyst showed a remarkably low overpotential of 228 mV at a current density of 10 mA cm-2, which is among the best cobalt-based catalysts reported so far. This special protection strategy for Fe also greatly improved the catalytic stability, reducing the Fe leaching amount by 2 orders of magnitude compared with the pure Fe hydroxide catalyst and thus delivering a long-term stability of 130 h. An assembled Zn-air battery was stably cycled for 170 h with a low discharge/charge voltage difference of 0.72 V.