Accelerated Electro-Conversion of a Nickel Coordination Complex for Hybrid Water Electrolysis

Electrocatalytic energy conversion relies on the dynamic transformation of electrode materials into "electrocatalytically active phases" under reaction conditions. Pre-catalysts, which undergo extensive structural and chemical changes during electrochemical activation, are particularly promising in this regard. In the context of electrocatalysis, coordination complexes with labile ligands offer a unique advantage, as they can rapidly reconstruct under electrochemical conditions. Herein, a hydrazine-coordinated Ni complex embedded in a conductive carbon nanotube matrix is presented as a pre-catalyst for urea-assisted hybrid water electrolysis, that transforms into highly active γ-NiOOH nanosheets on electrochemical activation, demonstrating exceptional urea electrooxidation performance, with a low Tafel slope of 21.6 mV dec^-1, a high turnover frequency (TOF) of 0.0728 s^-1, and stable operation over 40 h of continuous electrolysis, reflecting superior catalytic kinetics and excellent durability. In situ synchrotron X-ray absorption, Raman, and electrochemical impedance spectroscopy reveal the dynamic evolution of active sites, the underlying reaction mechanism, and the fate of the active species after prolonged electrolysis. The integration of this pre-catalyst into an anion-exchange membrane electrolyzer highlights its potential for practical application. This work showcases the transformative role of Ni-based coordination complexes as pre-catalysts, offering an innovative blueprint for the rational design of high-performance urea oxidation electrocatalysts.