Nickel borate with a 3D hierarchical structure as a robust and efficient electrocatalyst for urea oxidation

Abstract

Water electrolysis has become a promising green and sustainable strategy for hydrogen fuel production. However, due to the slow kinetics of the oxygen evolution reaction (OER), large overpotentials are required to drive the overall reaction. In this work, we demonstrate an environmentally friendly and energy-saving strategy by the synergy of the urea oxidation reaction (UOR) with the hydrogen evolution reaction (HER) to replace the ordinary water hydrolysis. In order to further boost the UOR kinetics, nickel borate (Ni–B_i) is synthesized by a facile co-precipitation method, forming a nanosheet morphology and 3D hierarchical porous structure. The resulting Ni–B_i catalyst exhibits exceptionally high catalytic performance for the UOR, achieving a current density of 50 mA cm⁻² at 1.42 V vs. RHE, which is about 250 mV lower than that of the OER process. The two-electrode urea electrolytic cell composed of the Ni–B_i anode and a Pt cathode requires a small cell voltage of 1.66 V in order to reach a current density of 50 mA cm⁻² and is very stable. Overall, this work demonstrates a promising electrocatalyst system for efficient hydrogen production and simultaneous urea-containing wastewater treatment, providing valuable information for the development of advanced non-noble metal catalysts for the UOR.