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A Co-doped Ni-P-O film supported on nickel foam is successfully prepared. It exhibits high activity toward urea oxidation reaction (UOR) and hydrogen evolution reaction (HER). Regarding UOR, the onset potential of Ni-P-O is reduced by the introduction of Co and gradually decreases with the incremental of Co content in the film ascribed to the reduction of conversion potential of Ni2+/Ni3+. Concerning HER, the incorporated Co in Ni-P-O film not only increases the amounts of active sites, but also boost the synergetic effect on water dissociation and hydrogen desorption. Particularly, the optimum activity of Ni-P-O is achieved by the introduction of an 8% cobalt source (8% Co:Ni-P-O/NF), which offers the highest activity with the lowest overpotential of 94 mV and Tafel slope of 46.2 mV·dec−1. Furthermore, the efficiency of hydrogen generation is further improved by urea-assistance over the electrolyzer coupled with 8% Co:Ni-P-O/NF electrode. Only 1.481 V is needed to afford 20 mA·cm−2 in urea-mediated electrolysis cell, much lower than that for urea-free electrolyte with 1.689 V. [Display omitted] • A Co-doped Ni-P-O film is successfully electrodeposited on nickel foam. • The Co dopant induces charge redistribution and boosts the synergistic effect. • The Co dopant effectively boosts the performance of Ni-P-O toward HER and UOR. • The efficiency of hydrogen evolution was improved via urea-assisted electrolysis. [ABSTRACT FROM AUTHOR]

Increasing energy demands have accelerated the exploration of renewable energy, and H 2 is a promising substitute for nonrenewable energy sources. The electrocatalytic hydrogen evolution reaction (HER) is a convenient, stable, and eco-friendly route for producing hydrogen whose performance can be enhanced via the rational structure design of catalysts and the replacement of the anodic oxygen evolution reaction (OER) with the urea oxidation reaction (UOR). Herein, 3D hierarchically structured NiMo microrod arrays was constructed on Ni foam where ZnO served as core and support (NiMo@ZnO/NF), which showed a high activity when used as a bifunctional electrocatalyst for the HER and UOR. It only required potentials of −110 mV and 1.405 V to deliver a current density of 10 mA cm−2 towards HER and UOR, respectively. NiMo@ZnO/NF was used as both the anode and cathode to construct a symmetric electrolyzer that was used for water splitting and urea electrolysis. The cell voltage decreased from 1.718 V to 1.549 V at 10 mA cm−2 after substituting the OER with UOR. Finally, the coupled NiMo@ZnO/NF || NiMo@ZnO/NF system can be driven by an AA battery in an alkaline solution containing urea, which demonstrates a practical and effective method for producing hydrogen assisted by anodic urea oxidation. Image 1 • A 3D hierarchical structure with NiMo-based composite microrod arrays was prepared. • The composite electrode exhibited excellent performance toward HER and UOR. • The efficiency of hydrogen generation was enhanced via urea-assisted electrolysis. [ABSTRACT FROM AUTHOR]