Urea electrooxidation coupled with energy-saving H2 production using bimetallic sulfide heterojunctions

Abstract

The theoretical electrocatalytic potential for the urea oxidation reaction (UOR) is notably low at 0.37 V, positioning it as a promising alternative to hydrogen evolution reaction for traditional water electrolysis. In this study, we synthesized Ni_xS₆/MnS (NMS) heterojunction catalysts using a straightforward co-precipitation method. Initially, we prepared bimetallic hydroxides precursors (Ni/Mn(OH)₂), which were subsequently sulfurized to obtain the NMS heterojunctions. The formation of NMS heterojunctions could enhance charge transfer and improve electrical conductivity, significantly boosting the electrocatalytic UOR activity. The NMS heterojunctions facilitate electrocatalytic UOR at a low anodic potential of 0.7 V vs. Ag/AgCl, achieving a peak current density of 11.8 mA cm⁻², with effective electrochemical surface area and Tafel slope values of 6.23 mF cm⁻² and 78.3 mV dec⁻¹, respectively. Furthermore, when utilized as an anode for overall urea electrolysis within a dual-electrode system, the NMS heterojunctions obtained a higher current density of 13.2 mA cm⁻², double that of pure water electrolysis (6.1 mA cm⁻²). This work represents a significant advancement in employing nickel-based sulfide heterojunctions for catalyzing urea oxidation reaction.