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The oxygen evolution reaction (OER) is crucial for hydrogen production. However, OER with four‐electron transfer requires electrocatalysts to speed up its sluggish kinetics in alkaline solutions. Herein, amorphous CoV phosphate (denoted as CoV−Pi) nanosheets synthesized by a straightforward one‐step hydrothermal approach is reported, which provide a low overpotential of 320 mV at 10 mA cm−2, a small Tafel slope down to 48.8 mV dec−1 and long‐term durability over 80 h. The efficient activity is ascribed to the amorphous nanosheets structure, high electrochemically active surface area, enhanced surface wettability and the synergistic effect of the active metal atoms. This study significantly indicates that CoV−Pi is a promising alternative to replace expensive noble metal‐based catalysts for electrochemical water splitting. [ABSTRACT FROM AUTHOR]

Novel nickel nanotube arrays (NTAs) on foamed nickel (NF) are developed by a facile electrochemical dealloying method to achieve a high hydrogen evolution reaction. Meanwhile, three dimensional heterostructure NiFe layered-double-hydroxide (LDH)@Ni NTAs electrode materials with strong interfacial interaction are prepared on NF by coupling ultrathin NiFe LDHs with Ni NTAs by electrochemical deposition, which demonstrate an excellent catalytic performance for oxygen evolution compared with NiFe LDH. Ni NTAs/NF require an overpotential of 101 mV to force the current density of 10 mA cm−2 for hydrogen evolution reaction because of the unique NTAs structure and the active sites for water dissociation provided by Ni2+ on the Ni NTAs surface. NiFe LDH@Ni NTAs/NF exhibit a low overpotential of 191 mV at a current density of 10 mA cm−2 for oxygen evolution reaction due to the reliable electron transfer from the intermediate metallic Ni NTAs to the external the NiFe LDH layer and more active sites that are exposed by highly dispersed ultrathin NiFe LDH nanosheets. The development of self-supporting NiFe LDH@Ni NTAs and Ni NTAs electrodes for efficient overall water splitting in an integrated alkaline electrolyzer is achieved a current density of 10 mA cm−2 at 1.51 V, accompanying excellent long-term durability. Image 1 • NiFe LDH@Ni NTAs is prepared by electrochemical dealloying and coupling methods. • NiFe LDH@Ni NTAs increases the electron transfer rate and number of active sites. • NiFe LDH@Ni NTAs exhibits an excellent catalytic performance for OER. • The combination of Ni(OH) 2 and Ni on the surface of Ni NTAs promotes HER. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Co 3 O 4 @Fe-B-O/NF was synthesized by a facile immersion method. • Heterostructure tunes the electronic structure and provides more active sites. • Co 3 O 4 @Fe-B-O/NF shows excellent OER performance in both alkaline and neutral media. • Co 3 O 4 @Fe-B-O/NF anode exhibits great potential for overall water splitting and CO 2 RR. Developing highly efficient OER catalysts is essential for producing hydrogen from water electrolysis to compensate for conventional fossil fuel shortages. Here, the oxygen-vacancy-rich heterostructure grown on the Ni foam (NF) (Co 3 O 4 @Fe-B-O/NF) is fabricated. The synergistic effect between Co 3 O 4 and Fe-B-O has been proven effectively modulate the electronic structure and produce highly active interface sites, ultimately leading to enhanced electrocatalytic activity. Co 3 O 4 @Fe-B-O/NF requires an overpotential of 237 mV to drive 20 mA cm−2 in 1 M KOH, and 384 mV to drive 10 mA cm−2 in 0.1 M PBS, superior to most catalysts currently used. Moreover, Co 3 O 4 @Fe-B-O/NF as an oxygen evolution reaction (OER) electrode shows great potential in overall water splitting and CO 2 reduction reaction (CO 2 RR). This work may provide effective ideas for designing efficient oxide catalysts. [ABSTRACT FROM AUTHOR]

The Co 8 FeS 8 @CoFe–MOF/NF heterojunction array with abundant phase interface was formed on the surface of nickel foam (NF) via a simple solvothermal method for water and urea splitting. The designed Co 8 FeS 8 @CoFe–MOF/NF heterojunction electrocatalyst exhibits superior activity towards oxygen evolution reaction (OER), hydrogen evolution reaction (HER) and urea oxidation reaction (UOR), which only requires low overpotentials of 213 mV, 191 mV and 81 mV to reach a current density of 10 mA cm−2, respectively. Moreover, it shows low cell voltages of 1.62 V and 1.55 V at 10 mA cm−2 for overall water and urea splitting, respectively. [Display omitted] Designing efficient electrocatalysts to improve the overall water splitting and urea electrolysis efficiency for hydrogen generation can greatly solve the dilemma of energy shortage and environmental pollution. In this work, Co 8 FeS 8 @CoFe–MOF/NF heterojunction arrays were fabricated by embedding sulfides into the surface of metal-organic frameworks (MOFs) nanosheets as multifunctional electrocatalyst. The introduction of sulfide on CoFe–MOF/NF can not only adjust the electronic structure (electron-rich state) and change the surface properties (more hydrophilic), but also increase the active area to enhance the catalytic activity. The in situ Raman shows Co 8 FeS 8 @CoFe–MOF/NF is more easily to generate active species at low potentials and generates a higher content of active β-MOOH phase than CoFe–MOF/NF. Therefore, the Co 8 FeS 8 @CoFe–MOF/NF exhibits excellent oxygen evolution reaction (OER) performance with an overpotential of 213 mV at 10 mA cm−2. Furthermore, when used as a urea oxidation reaction (UOR), only an ultralow potential of 1.311 V at 10 mA cm−2. More importantly, the assembled two-electrode drives overall water splitting and urea electrolysis with cell voltages of 1.62 V and 1.55 V at 10 mA cm−2, respectively. This work provides insights into the preparation of electrocatalysts with multifunctional heterostructure arrays for hydrogen production. [ABSTRACT FROM AUTHOR]

• IrO 2 @SL-NiFe LDHs was synthesized by anchoring IrO 2 nanoparticles to SL-NiFe LDHs. • –NH 2 acted as a coordination site to control the growth of IrO 2 nanoparticles. • Formation of oxygen defects on SL-NiFe LDHs increased OER performance. • DFT results indicated that IrO 2 and SL-NiFe LDHs synergistically catalyze OER. A hybrid oxygen evolution catalyst, IrO 2 @single-layer NiFe layered double hydroxides (SL-NiFe LDHs), is successfully synthesized by anchoring highly dispersed IrO 2 nanoparticles to SL-NiFe LDHs nanosheets with oxygen vacancies. Typically, during the synthesis process, the functional group –NH 2 from the external anchor formamide acts as a coordination site to control the nucleation and growth of nanoparticles, which can ensure high dispersion without aggregation of IrO 2 on SL-NiFe LDHs. In addition, this reducing synthetic environment causes a large number of holes and grooves in the NiFe-LDHs nanosheets, which result in the formation of oxygen vacancies in the SL-NiFe LDHs. The loading of IrO 2 nanoparticles and the formation of oxygen vacancies endow IrO 2 @SL-NiFe LDHs with excellent performance for the oxygen evolution reaction (OER). IrO 2 @SL-NiFe LDHs nanosheets display outstanding OER performance with an overpotential of 270 mV at a current density of 10 mA cm−2 and good stability. Density functional theory (DFT) calculations indicate that the hybridization of IrO 2 and SL-NiFe LDHs accelerates the reaction step. Notably, the Ir sites at the edges are more conducive to the formation of oxygen, and the oxygen sites on SL-NiFe LDHs are more conducive to the cleavage of the O–H bond, thereby improving the OER activity. This work highlights a potential synthetic strategy that can combine nanoprecious metals with transition metals to prepare highly active electrocatalysts for efficient water oxidation reactions. [ABSTRACT FROM AUTHOR]

Hydrogen production from electrolyzed water is a mature technology and has great development prospects in terms of energy conversion and utilization. However, the kinetically sluggish oxygen-evolution reaction becomes the limiting step in the electrolysis of water. Copper-based materials have been reported as a good choice to catalyze the oxygen evolution reaction, but their performance is poor. We describe a Cu 2-x Se@CuO/copper foam core–shell structure from the in situ electrochemical oxidation of Cu 2 Se/copper foam to promote the oxygen-evolution reaction performance. The presence of a semi-metallic Cu 2-x Se core and nanostructured CuO shell at a current density of 10 mA cm−2 requires a low overpotential of 253 mV. The Tafel slope was only 73 mV dec−1. The preparation of Cu 2-x Se@CuO on three-dimensional copper foam facilitates the reaction. Image 1 • Cu 2-x Se@CuO core-shell structure forms by the in situ electrochemicall oxidation of Cu 2 Se. • A formation model for the core-shell structure catalyst is proposed. • The phase change of copper selenide is clearly explained in OER process. • The presence of semi-metallic Cu 2-x Se promotes the OER performance of CuO. [ABSTRACT FROM AUTHOR]

NiFe-layered double hydroxide (NiFe–OH) is one of the most promising candidate materials for the oxygen evolution reaction (OER) in an alkaline electrolyte. However, it is difficult to be oxidized into Ni3+FeOOH active species with high valence Ni under mild conditions; thus, the activity under mild conditions is inferior. We report here that NiFe–OH is converted to amorphous NiFeO x H y (a3-NiFe-OH) with easily oxidized electron-deficient Ni2+ after pre-oxidation in an alkaline solution boosts the OER performance under mild conditions. The amorphous structure of a3-NiFe-OH also enlarges the electrochemically active area to expose more active sites. It merely needs an overpotential of 350 mV at 10 mA cm−2 in 0.1 M KHCO 3 electrolyte. The corresponding Tafel slope is as low as 89 mV dec−1. This work affords a strategy for developing (near) neutral OER catalysts. [Display omitted] • NiFeO x H y with electron-deficient Ni2+ and amorphous structure was prepared. • The electron-deficient Ni2+ can easily be oxidized during oxygen evolution reaction. • The amorphous structure helps to expose more active sites. • NiFeO x H y exhibits enhanced oxygen evolution reaction activity in mild condition. [ABSTRACT FROM AUTHOR]