Defect-rich Ni(OH)2/NiO regulated by WO3 as core–shell nanoarrays achieving energy-saving water-to-hydrogen conversion via urea electrolysis

Constructing low-cost, high-efficient, and stable electrocatalysts is crucial for large-scale and sustainable water-to-hydrogen conversion. Herein, the combination approaches of hydrothermal, annealing and electrodeposition have been used to fabricate a novel defect-rich electrocatalyst, Ni(OH)2/NiO-C/WO3 HAs, that is composed of WO3 core with Ni(OH)2/NiO shell hierarchical arrays (HAs), which exhibits relatively large specific surface area and thus exposing abundant defect sites. Additionally, both experimental and computational results reveal that the regulation of the electronic structure of W6+ contributes to inducing Ni centers to reform and transform into active species. The unique Ni(OH)2/NiO-C/WO3 HAs possess extraordinary activities with an ultralow overpotential of 53 mV for cathodic hydrogen evolution (HER), and the low potential of 1.340 V for anodic urea oxidation (UOR) at 10 mA cm−2. When employing Ni(OH)2/NiO-C/WO3 HAs as symmetric electrolyzer in a hybrid water electrolysis system, the cell voltage reduces to 1.370 V at 10 mA cm−2. Moreover, the electrolytic cell remains stable over 60 h at 20 mA cm−2, outperforming the commercial counterpart of Pt/C||IrO2. This study provides a promising pathway to design high-efficient electrocatalysts for energy-saving water-to-hydrogen conversion via urea electrolysis.