Interconnected Mn-Doped Ni(OH)₂ Nanosheet Layer for Bifunctional Urea Oxidation and Hydrogen Evolution: The Relation between Current Drop and Urea Concentration during the Long-Term Operation

Abstract

Replacing oxygen evolution reaction with more thermodynamically easy reactions such as urea oxidation reaction (UOR) in water splitting has received increasing attention in recent years. In this study, Mn-doped Ni(OH)2 is synthesized on carbon paper as a bifunctional electrode for UOR and hydrogen evolution reaction (HER). This novel electrode delivers high activity and durability for both UOR and HER. Moreover, a positive correlation between the current density and urea concentration during the long-term operation is found for the first time, which provides theoretical support to explain the UOR current drops for long-time operation. The full electrolytic cell constructed by Mn-doped Ni(OH)2 achieves a working potential of 1.407 V at 10 mA cm–2, which is one of the best UOR-based water splitting systems reported so far. This study brings new knowledge in the mass-transfer-controlled anodic reaction process of urea, which promotes the electrolytic systems for both clean energy generation and waste reuse.