Dynamic Site Induced Self-Adaptive Adsorption on Bifunctional Catalysts for Highly Selective Oxidative Switching from Urea-to-Water Electrolysis

Abstract

The adsorption strength of hydroxide ions affects the catalytic activities of the oxygen evolution reaction (OER) and urea oxidation reaction (UOR). Inspired by the “for” loop function in computer programming, this work proposes a dynamic active site strategy to modulate “self-adaptive” adsorption of OH⁻ to achieve a continuous urea-to-water electrolysis for the first time, with a highly selective switching from UOR to OER. Specifically, MoO₄²⁻-doped NiCo-based layered double hydroxide (NiCo-LDH-MO) is developed as the UOR/OER bifunctional catalyst through the hydrothermal doping and electrochemical reconstruction of Prussian blue analogs. With the aid of density functional theory (DFT) calculation and the in situ characterizations, it suggests that OH⁻ is preferentially adsorbed on Co sites to generate CoOOH for UOR in the presence of urea, and then self-adaptively adsorbs on Ni sites to generate NiOOH for OER after the removal of urea. As a result, the reconstructed electrode exhibits remarkably low potentials of 1.27/1.36 V for UOR at 10/100 mA cm⁻², respectively, and only 347 mV overpotential for OER at 100 mA cm⁻². This work demonstrates a new pathway for the effective hydrogen and oxygen production from urea-contaminated water, such as human urine and industrial wastewater.