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Oxygen evolution reaction (OER) is the key anode reaction of electrolytic water. To improve the slow OER kinetics, we synthesize nanoflower‐like Co−Fe‐Cr−Mo‐Mn high‐entropy spinel (HES) nanosheets on nickel foam (NF) by one‐step solvothermal method, which exhibit an overpotential (η10) of only 188 mV at 10 mA cm−2, much lower than bimetallic CoFeOx/NF (233 mV), trimetallic CoFeCrOx/NF (211 mV), and tetrametallic CoFeCrMoOx/NF (200 mV). The OER overpotential decreases with the increase of the number of metals, indicating that the formation of HES has a positive effect on the improvement of electrocatalytic performance, since the synergistic effect between different metals enhances the charge transfer rate and decreases reaction barrier. In‐situ Raman spectra demonstrate that the formation of γ‐NiOOH on the HES surface is a crucial active species for the OER. This work demonstrates a simple and efficient synthesis method to prepare nanoflower‐like high‐entropy electrocatalysts for efficient OER electrocatalysis. [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]

The BiVO 4 was firstly prepared by modification's metal organic decomposition method followed by electrodepositing rGO and Cu 2 O on BiVO 4 to construct the rGO decorated BiVO 4 /Cu 2 O n-n heterojunction triadic photoanode for photoelectrochemical (PEC) water splitting. The structure and PEC properties of the photoanode were characterized and measured by various spectral analysis and three electrode system. The highest photocurrent density of the triadic photoanode achieves 2.2 mA/cm2 at 1.8 V (vs. RHE) that is closely 2 folds of single BiVO 4 photoanode. The photoanode has the highest IPCE value of 42.0% at 400 nm. The enhanced PEC properties come from the valid separation of the photogenerated electron-hole pair and enhancement of surface oxidation kinetics due to the formation of n-n heterojunction and rGO act as the role of electronic migration mediator accelerates charge carrier transfer, which has been demonstrated by calculated the decrease of charge transfer resistance at electrode/electrolyte interface and prolonging of charge carriers lifetimes. BiVO 4 /Cu 2 O/rGO (0.02C) photoanode achieves the higher photocurrent density of 2.2 mA/cm2 at 1.8 V vs. RHE. The enhancement is attributed to the efficient separation of the photoexcited electron-hole pairs and superior electrical conductivity of rGO. Image 1060707 • BiVO 4 /rGO/Cu 2 O photoanode was fabricated by facile electrochemical deposition. • The BiVO 4 /rGO/Cu 2 O photoanode is few reported in literature. • The photoanode achieves the photocurrent density of 2.2 mA/cm2 at 1.8 V vs RHE. • The enhancing mechanism is attributed to the heterojunction and decoration of rGO. [ABSTRACT FROM AUTHOR]

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 NiFe 0.5 (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 NiFe 0.5 (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. The OER energy barrier on NiFe 0.5 (OH) x is only 31.5 kJ mol−1, much lower than those on Ni(OH) x (41.0 kJ mol−1) and Fe(OH) x (44.8 kJ mol−1). [Display omitted] • Partially crystallized nickel-iron oxyhydroxides are synthesized by a facile sol-gel method. • The overpotential of NiFe 0.5 (OH) x is only 265 mV at 10 mA cm−2. • NiFe 0.5 (OH) x exhibits a low OER energy barrier of 31.5 kJ mol−1. • Synergy between Ni and Fe sites promotes charge transfer for the OER. [ABSTRACT FROM AUTHOR]