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The design of diatomic catalysts with uniformly dispersed metal atoms is expected to improve catalytic performance, which is conducive to the intensive comprehending of the synergistic mechanism between dual-metal sites for the oxygen evolution reaction (OER) at the atomic level. Herein, we design a strategy to immobilize bimetallic Fe-Co atoms onto nitrogen-doped graphene to obtain a diatomic catalyst (DA-FC-NG) with FeN3-CoN3 configuration. The DA-FC-NG shows excellent OER activity with a low overpotential (η10 = 268 mV), which is superior to commercial iridium dioxide catalysts. Theoretical calculations uncover that the excellent activity of DA-FC-NG is due to the interaction between Fe and Co diatoms, which causes charge rearrangement and induces the adsorption of intermediates on the Fe–O–Co bridge structure, thus improving the catalytic OER performance. This work is of great significance for the design of highly active diatomic catalysts to replace noble metal catalysts for energy-related applications. [ABSTRACT FROM AUTHOR]

As a four-electron transfer reaction, oxygen evolution reaction (OER) is limited by large overpotential and slow kinetics. Here, we in-situ synthesized two-dimensional (2D) Ni-Fe metal-organic framework nanosheets on nickel foam (NixFe-TPA/NF, TPA = terephthalic acid) for oxygen evolution in alkaline and alkaline seawater electrolytes. In 1 M KOH, Ni3Fe-TPA/NF shows a low overpotential (η10) of 189 mV at 10 mA·cm−2 and an ultra-low overpotential of only 260 mV at 500 mA·cm−2. In alkaline seawater, Ni3Fe-TPA/NF still provides impressive OER performance, with an η10 of 265 mV. In-situ Raman characterization results show that the phase transition occurs during the OER, and Ni3FeOOH with more oxygen vacancies is in-situ formed, reducing the OER energy barrier. Density functional theory (DFT) reveals that the synergy between Ni and Fe reduces the energy barrier and accelerates the rate-determining step. In addition, the ultra-thin 2D sheet structure and the close combination of Ni3FeOOH and highly conductive NF support ensure the high catalytic OER activity. Therefore, the surface reconstruction and structural modification strategy can be used to design and prepare high-performance OER electrocatalysts for energy-related applications. [ABSTRACT FROM AUTHOR]

It is well-known that Fe3+ impurities in the electrolyte can significantly promote the oxygen evolution reaction (OER) activity of Co-based and Ni-based electrocatalysts. However, it is not clear if they work for single-metal Fe-based catalysts. Here, we systematically investigate the influence of Fe3+ ions in the electrolyte on the OER activity of core-shell FeO x @C catalytic system. We find that the absorbed Fe3+ can induce the generation of surface oxygen vacancies and regulate the electronic structure of active sites, thus increasing the OER kinetics and decreasing the energy barrier. Combining with in-situ Raman and ex-situ X-ray photoelectron spectroscopy (XPS) analysis, we disclose that Fe4+ species is the active species for the OER and positively correlate the characteristic content of the high-valence Fe species and OER activity. Fe3+ impurities in the electrolyte can improve the OER activity of Fe-based catalysts, which can be oxidized into Fe4+ as the active species. [Display omitted] • FeO x @C-700 exhibits improved OER activity when dropping Fe3+ into the electrolyte. • Fe3+ impurities have synergistic effects with FeO x @C-700. • In-situ Raman and ex-situ XPS spectra reveal Fe4+ species during the OER. • Fe4+ favors the OER as the reactive species. [ABSTRACT FROM AUTHOR]

The development of high activity and strong resistance to seawater corrosion oxygen evolution reaction (OER) electrocatalysts for seawater electrolysis has broad application prospects. Herein, we prepare Co-doped FeNiOOH rosette-like nanoflowers on nickel foam (NF) with different Co dosages by one-step solvothermal method. The Co0.2-FeNiOOH/NF exhibits a low overpotential (η10) of 185 mV and Tafel slope of 30 mV dec−1 in 1 M KOH. Moreover, it shows a low η10 of 244 mV in alkaline seawater electrolyte. The remarkable OER performance of Co0.2-FeNiOOH/NF is ascribed to the fact that the introduction of Co regulates the morphology and electron structure of the material, which provides abundant active sites for the reaction and promotes charge transfer. In situ Raman results demonstrate that NiOOH and γ-FeOOH are the key active species for the OER. This study provides a feasible basis for seawater electrolysis over transition metal (oxy)hydroxides. [ABSTRACT FROM AUTHOR]

High-entropy materials (HEMs) have potential application value in electrocatalytic water splitting because of their unique alloy design concept and significant mixed entropy effect. Here, we synthesize a high-entropy Ni–Fe–Cr–Mn–Co (oxy)hydroxide on nickel foam (NF) by a solvothermal method. The flower-like structure of FeNiCrMnCoOOH/NF can provide abundant active sites, thus improving the oxygen evolution reaction (OER) activity. In 1 M KOH, the FeNiCrMnCoOOH/NF shows an ultra-low overpotential (η10) of 201 mV for the OER, superior to FeNiCrMnAlOOH/NF, FeNiCrMnCuOOH/NF, FeNiCrMnMoOOH/NF, and FeNiCrMnCeOOH/NF. In addition, it exhibits a low η10 of 223 mV in 0.5 M NaCl + 1 M KOH and excellent stability. Electrochemical impedance spectroscopy measurements indicate that the synergistic effect between multiple metals accelerates charge transfer, while in situ Raman measurements reveal that NiOOH is a key active species for the OER. This work is of great significance for the construction of high-entropy (oxy)hydroxides for seawater electrolysis. [ABSTRACT FROM AUTHOR]

Searching for highly active and durable oxygen evolution reaction (OER) electrocatalysts is the key to break through the bottleneck of overall water splitting. Here, we prepare Ni x Fe-BDC (H 2 BDC = terephthalic acid) nanorods with different Ni/Fe ratios by a facile solvothermal method for the OER. The optimal Ni 3 Fe-BDC exhibits a low overpotential (η 10) of 265 mV and a Tafel slope of 90 mV·dec−1 in 1 M KOH. Moreover, it shows a low η 10 of 280 mV and excellent stability in the mixture of 1 M NaCl and 1 M KOH, which has strong corrosion resistance to Cl− anions. The role of Fe3+ not only increases the charge transfer rate of Ni 3 Fe-BDC, but also affects the specific surface area of the catalyst with high electrochemical activity. Kinetic studies show that both Fe and Ni sites act as active centers, which catalyze synergistically to reduce the reaction kinetic energy barrier. Characterization results of the used Ni 3 Fe-BDC reveal that the in situ formed rod-like Ni 3 FeOOH is the active site for the OER. Ni 3 Fe-BDC shows low η 10 of 265 mV and 280 mV for the OER in 1 M KOH and in 1 M NaCl + 1 M KOH, respectively. In situ transformation of nanorod-like Ni 3 Fe-BDC MOF to Ni 3 FeOOH can efficiently remain the advantages of MOF, e.g. porous structure, high specific surface area and uniformly dispersed metal sites. [Display omitted] • Ni 3 Fe-BDC shows low η 10 of 265 mV for the OER in 1 M KOH. • Ni 3 Fe-BDC shows η 10 of only 280 mV for the OER in 1 M NaCl +1 M KOH. • Ni 3 Fe-BDC exhibits a low OER energy barrier of 13.7 kJ/mol. • The in-situ formed rod-like Ni 3 FeOOH serves as efficient active site for the OER. [ABSTRACT FROM AUTHOR]

Compared with defect-free FeO x , the ultrafine FeO x in the FeO x (0.03)@HG-110 with abundant surface defects shows lower energy barrier and higher OER activity. [Display omitted] • The FeO x (0.03)@HG-110 exhibits an OER overpotential as low as 342 mV at 10 mA cm−2. • The average particle size of FeOx is ca. 1.6 nm. • FeO x (0.03)@HG-110 possesses a low E a of 35.9 kJ mol−1. • The rate-determining step is *O → *OOH with the energy barriers of 0.79 eV. Development of earth-abundant and robust oxygen evolution reaction (OER) catalysts is imperative for cost-effective hydrogen production via water electrolysis. Herein, we report ultrafine iron (oxy)hydroxide nanoparticles with average particle size of 2.6 nm and abundant surface defects homogeneously supported on oleum-treated graphite (FeO x (n)@HG-T), providing abundant active sites for the OER. The optimal FeO x (0.03)@HG-110 exhibits high electrocatalytic OER activity and excellent stability. Electrochemical testing results and theoretical calculations reveal that the outstanding OER activity of FeO x (0.03)@HG-110 is due to its stronger charge transfer ability and lower OER energy barrier than defect-free FeO x nanoparticles. This work demonstrates that the OER performance of oxyhydroxide-based electrocatalysts can be improved by surface defect engineering. [ABSTRACT FROM AUTHOR]

Developing robust non-noble catalysts towards hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is vital for large-scale hydrogen production from electrochemical water splitting. Here, we synthesize Sn- and Fe-containing sulfides and oxyhydroxides anchored on nickel foam (SnFeS x O y /NF) using a solvothermal method, in which a heterostructure is generated between the sulfides and oxyhydroxides. The SnFeS x O y /NF exhibits low overpotentials of 85, 167, 249, and 324 mV at 10, 100, 500 and 1000 mA cm−2 for the HER, respectively, and a low overpotential of only 281 mV at 100 mA cm−2 for the OER. When it serves as both anode and cathode to assemble an electrolyzer, the cell voltage is only 1.69 V at 50 mA cm−2. The sulfides should be the efficient active species for the HER, while the oxyhydroxides are highly active for the OER. The unique sulfide/oxyhydroxide heterostructure facilitates charge transfer and lowers reaction barrier, thus promoting electrocatalytic processes. The heterostructure between sulfides and oxyhydroxides in the SnFeS x O y /NF facilitates charge transfer and lowers reaction barrier, thus promoting electrocatalytic HER and OER processes. [Display omitted] • SnFeS x O y /NF shows low HER overpotentials of 85 and 324 mV at 10 and 1000 mA cm−2, respectively. • SnFeS x O y /NF shows overpotential of only 281 mV at 100 mA cm−2 for the OER. • SnFeS x O y /NF-based electrolyzer needs 1.69 V to deliver 50 mA cm−2. • Heterostructure between sulfides and oxyhydroxides improves the electrocatalytic activity. [ABSTRACT FROM AUTHOR]

Oxygen evolution reaction (OER) is the core electrode reaction in energy-related technologies, such as electrolytic water, electrocatalytic carbon dioxide reduction, rechargeable metal-air batteries, and renewable fuel cells. Development of well-stocked, cost-effective, and high-performance OER electrocatalysts is the key to the improvement of energy efficiency and the large-scale commercial implementation of these technologies. Multicomponent transition metal oxides and (oxy)hydroxides are the most promising OER catalysts due to their low cost, adjustable structure, high electrocatalytic activity, and outstanding durability. In this review, a brief overview about the mechanisms of OER is first offered, accompanied with the theory and calculation criteria. Then, the latest advances in the rational design of the related OER electrocatalysts and the modulation of the electronic structure of active sites are comprehensively summarized. Specifically, various strategies (including element doping, defect engineering, and fabrication of binderless catalysts) used to improve the OER performance are detailedly discussed, emphasizing the structure—function relationships. Finally, the challenges and perspectives on this promising field are proposed. [ABSTRACT FROM AUTHOR]