W-doping induced abundant active sites in a 3D NiS2/MoO2 heterostructure as an efficient electrocatalyst for urea oxidation and hydrogen evolution reaction

Electrochemical water splitting, including the anodic oxygen evolution reaction (OER) and cathodic hydrogen evolution reaction (HER), has been considered an eco-friendly and sustainable hydrogen producing approach. However, due to the slow kinetics and large thermodynamic potential requirements of anodic OER, water splitting process still needs high energy consumption. In this aspect, replacing the OER by urea oxidation reaction (UOR) with low thermodynamic potentials can endow opportunity for less energy consumption for hydrogen production. At the same time, the electrochemical UOR offers a good access to treat urea-rich waste water. As the anodic UOR involves a 6e(-) transfer process, it needs high-performance and low-cost electrocatalysts to boost the efficiency. Herein, through W doping, we fabricated a 3D NiS2/MoO2 hybrid heterostructure grown on conductive carbon cloth (W-NiS2/MoO2@CC). Due to the W-induced abundant active sites, the as-fabricated WNiS2/MoO2@CC demonstrates excellent bifunctional catalytic activities toward UOR and HER with very low potentials of 1.3 V and 52 mV to drive 10 mA cm(-2), respectively. More importantly, benefiting from the combined merits of the hybrid heterojunction of NiS2 and MoO2, W-doping and the 3D porous structure grown on conductive carbon cloth support, the catalyst exhibits highly efficient catalytic performance towards a urea electrolytic cell (HER||UOR). Substantially, reduced cell voltage of 1.372 V is required to achieve a current density of 10 mA cm(-2), which is 230 mV lower than that of conventional water electrolysis. In the meantime, the catalyst shows excellent stability with ignorable degradation of current density for 24 h. This work provides an effective catalyst design strategy for energy-saving electrochemical H2 production.