Improved hydrogen generation via a urea-assisted method over 3D hierarchical NiMo-based composite microrod arrays

Abstract

Increasing energy demands have accelerated the exploration of renewable energy, and H2 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.