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Replacing the thermodynamically unfavorable oxygen evolution reaction (OER) with the low theoretical potential (−0.33 V) and safe by-product (N2/H2O) hydrazine oxidation reaction (HzOR) is an energy-saving way for hydrogen production. Nevertheless, the complexity of bifunctionality increases the difficulty of catalyst design. In this work, a hybrid of NiC2O4 and Nb2O5 is synthesized on nickel foam via a two-step low temperature reaction using Ni3S2 as a sacrificial template, named SNiC2O4–Nb2O5/NF. The experimental and theoretical calculation results illustrate that electrons are transferred from Ni to Nb, thus regulating the electronic structure of Ni. In the hybrid, Nb2O5 can effectively adsorb and split H2O, as well as downshift the d-band center of SNiC2O4, thereby optimizing the Volmer step. SNiC2O4–Nb2O5/NF achieves the properties for the hydrogen evolution reaction (HER: η20 = 155 mV) and the oxygen evolution reaction (OER: η20 = 293 mV). The addition of hydrazine to an alkaline electrolyte can decrease the cell voltage by 1.41 V when the current density is 20 mA cm−2, and achieve a high-speed hydrogen yield driven by an AA battery. This work puts forward an idea for the rational design of environmentally friendly and effective hybrid catalysts. [ABSTRACT FROM AUTHOR]

The interface Ni 0.85 Se/NiTe electrocatalyst achieves efficient oxygen evolution reaction and urea oxidation reaction with a large number of bubbles released from the catalyst surface, which benefits from accelerated electron transfer. [Display omitted] • Core-shell structure of Ni 0.85 Se/NiTe is built by interface engineering. • NiTe nanorods are vertically oriented on Ni foam via a one-step tellurization. • Ni 0.85 Se film is prepared through fast and safe deposition. • Ideal OER and UOR activity with low potential and high current density is obtained. The development of highly efficient oxygen evolution reaction (OER) and urea oxidation reaction (UOR) electrocatalysts with abundant resources is necessary for green hydrogen production. Ni-based compounds have received attention as the most promising earth-abundant electrocatalysts for OER and UOR, whereas some compounds in this main group, e.g., nickel selenides and tellurides, have received little attention. Herein, we demonstrate the interfacial engineered Ni 0.85 Se/NiTe array on Ni foam as a highly efficient catalyst for the OER, which exhibits an overpotential of 200 mV to obtain a current density of 10 mA cm−2 in alkaline solutions. Meanwhile, it exhibits a low potential of 1.301 V for the UOR at a current density of 100 mA cm−2. In particular, it even has the potential to be used in methanol oxidation reaction and ethanol oxidation reaction. The vertical NiTe array not only serves as the conductive substrate for highly improving the mass loading of Ni 0.85 Se, but also triggers the strong electron interaction between two components, leading to increased adsorption sites available for the intermediates formed in the OER and UOR on the Ni 0.85 Se surface. This study provides a broad avenue to construct hierarchical nanostructures as outstanding electrocatalysts for efficient OER and UOR. [ABSTRACT FROM AUTHOR]

Herein, we have synthesized successfully a three-dimensional/two dimensional (3D/2D) core–shell Cu2O@Fe–Ni3S2 nanoflower on copper foam at room temperature. Remarkably, by virtue of rich active sites and vacancies, large surface area, high conductivity and close contact with the electrolyte, the Cu2O@Fe–Ni3S2 catalyst exhibits superior stability and oxygen evolution reaction performance. [ABSTRACT FROM AUTHOR]

The efficiency of water electrolysis is greatly hindered by complex electron-proton transfer process of oxygen evolution reaction (OER). Exploiting cost-efficient OER electrocatalytic materials to improve the performance of overall water splitting is necessary. Partial chemical etching of iron foam (IF) with glacial acetic acid, using IF as the metal source and substrate, to form vertically aligned FeS/Fe 2 O 3 heterogeneous nanosheets on the IF (FeS/Fe 2 O 3 /IF) can obtain a hierarchical electrode to meet the above requirements. The nanosheets with heterogeneous interfaces in situ grown on IF can adjust electronic structure and expose more active sites, resulting in great improvement of catalytic activity and stability. FeS/Fe 2 O 3 /IF requires a small overpotential of 266.5 mV to attain 10 mA cm−2 and its Tafel slope is 51.17 mV dec−1. It is worth noting that FeS/Fe 2 O 3 /IF can work continuously for 50 h at high current density, which proves the strong stability during the OER process. The FeS/Fe 2 O 3 /IF has high electrocatalytic activity and stability, and can be used as a good candidate material for electrocatalytic OER in industrial manufacture. The FeS/Fe 2 O 3 nanosheets with heterogeneous interfaces in situ grown on porous conductive iron foam show highly efficient electrocatalytic oxygen evolution reaction activity and long-term stability. [Display omitted] • Porous conductive IF as both reactant and substrate improves catalytic activity and stability. • Nanosheets grown vertically on IF facilitate electrolyte diffusion and charge transfer. • Heterogeneous interfaces adjust electronic structure and expose more defects as active sites. • The FeS/Fe 2 O 3 /IF maintains the stability at 100 mA cm−2 for at least 50 h. [ABSTRACT FROM AUTHOR]

Constructing efficient and stable bifunctional electrocatalysts for overall water splitting remains a challenge because of the sluggish reaction kinetics. Herein, the core-shell hybrids composed of Co(PO 3) 2 nanorod core and NiFe alloy shell in situ grown on nickel foam (NiFe/Co(PO 3) 2 @NF) are synthesized. Owing to the hierarchical palm-leaf-like structures and strong adhesion between NiFe alloys, Co(PO 3) 2 and substrates, the catalyst provides a large surface area and rapid charge transfer, which facilitates active sites exposure and conductivity enhancement. The interfacial effect in the NiFe/Co(PO 3) 2 core-shell structure modulates the electronic structure of the active sites around the boundary, thereby boosting the intrinsic activity. Benefiting from the stable structure, the durability of the catalyst is not impaired by the inevitable surface reconfiguration. The NiFe/Co(PO 3) 2 @NF electrode presents a low cell voltage of 1.63 V to achieve 10 mA cm−2 and manifests durability for up to 36 h at different current densities. The palm-leaf-like NiFe/Co(PO 3) 2 @NF electrocatalyst composed of nanorod arrays serves as bifunctional electrocatalyst for enhanced overall water splitting performance. [Display omitted] • Strong interaction between NiFe and Co(PO 3) 2 enhances the structural stability. • The core-shell structure accelerates the electron transfer. • The hierarchical palm-leaf-like structure helps to enlarge specific surface area. • The NiFe/Co(PO 3) 2 hybrids display outstanding overall water splitting activity. [ABSTRACT FROM AUTHOR]

In order to improve the application of transition metal materials in catalyzing overall water splitting, a self-supporting Prussian blue analogues-based hierarchical architecture with abundant active sites (PBA@MnO 2) is established for OER catalysis. Meanwhile, the corresponding nitrided derivatives (N-FeMnNi) are easily obtained for efficient HER catalysis. [Display omitted] • Facile hydrothermal method was used to obtain PBA@MnO 2 hierarchical structure. • Low OER overpotential of 238 mV for PBA@MnO 2 -150/30 in 1.0 M KOH was obtained. • Low HER overpotential of 101 mV for N-FeMnNi-130/10 in 1.0 M KOH was gained. • High durability was shown during long-term electrochemical test. • The hierarchical PBA and derivative catalyst was applied to full water splitting. Assembling a hierarchical well-defined Prussian blue analogues (PBA) construction is a useful way to take earth-abundant elements into application toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, we report a unique strategy for in-situ grafting three-dimensional (3D) MnFe-PBA cubes on the top of two-dimensional (2D) MnO 2 nanosheet arrays (PBA@MnO 2) via a facile two-step hydrothermal method with the participation of Ni foam (NF). After experiencing low-temperature pyrolysis in NH 3 /Ar atmosphere, the above catalysts are transformed into metal-nitride derivatives (N-FeMnNi). Remarkably, when operated in 1.0 M KOH aqueous solution, the as-obtained PBA@MnO 2 -150/30 (where 150 and 30 represent the hydrothermal temperature (°C) and the concentration of K 3 Fe(CN) 6 (mM) for preparation, respectively) shows the most outstanding OER activity, with an overpotential of 238 mV at 10 mA cm−2. Moreover, N-FeMnNi-130/10 requires an overpotential of 101 mV to reach 10 mA cm−2 for HER. As a result, the two samples are organized to establish a two-electrode cell, with a voltage of only 1.60 V needed to reach 10 mA cm−2. Meanwhile, it can stably work for 30 h without obvious current attenuation. This work provides a brand new perspective for the design of PBA electrocatalysts towards high-efficiency overall water splitting. [ABSTRACT FROM AUTHOR]