Ni 2 Se 3 -CuSe x Heterostructure as a Highly Efficient Bifunctional Electrocatalyst for Urea-Assisted Hydrogen Generation.

Coupling urea oxidation reaction (UOR) with hydrogen evolution reaction (HER) is an attractive alternative anode reaction for electrochemical hydrogen generation with low energy consumption. However, the development of highly efficient bifunctional electrocatalysts is still a challenge. In this work, Ni 2 Se 3 -CuSe x heterostructure was synthesized on copper foam (Ni 3 Se 2 @CuSe x /CF) by electrodeposition accompanied by a selenization process. Benefiting from the abundant active sites, faster reaction kinetics, and modulated electronic structure, the self-supporting Ni 3 Se 2 @CuSe x /CF electrode exhibited superior catalytic performance. Extremely low overpotentials of 120 and 140 mV were achieved at the current density of 100 mA cm -2 for HER/UOR, respectively. Respectively, in HER||UOR coupled electrolyzer for H 2 generation, the Ni 3 Se 2 @CuSe x /CF||Ni 3 Se 2 @CuSe x /CF delivered a low cell voltage of 1.49 V to reach a high current density of 100 mA cm -2 along with good stability, outperforming most of the other well-developed materials to date. The rational design of coupled heterostructure as bifunctional electrodes is a promising approach for energy-saving H 2 production.