Double built-in electric fields and surface reconstruction endow Ag/CoNiV-LDH/CoO with superior water splitting activity

Abstract

It is of great significance to design bifunctional electrocatalysts that promote both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Herein, an Ag/CoNiV-LDH/CoO electrocatalyst with a hierarchical core–shell structure was synthesized using a novel “template-oriented – ion exchange – spontaneous redox” method, inspired by the excellent OER kinetics of cobalt oxides and high-valence metal layered double hydroxides (LDHs), and the enhanced conductivity of metal nanoparticles for the HER. Notably, it exhibits superior electrochemical activity with a low overpotential of 298 mV for the OER at 100 mA cm⁻² and 79 mV for the HER at 10 mA cm⁻². The coupled cell requires only a small voltage of 1.51/1.60 V to drive overall water splitting (OWS) at 10/100 mA cm⁻². The superior performance is due to the accelerated charge transfer by the double built-in electric field (BEF), the optimized electronic structure and the d-band center provided by high-valence heteroatoms, the large specific surface area provided by the unique structure, and abundant cation and oxygen vacancies resulting from V-leaching. More importantly, in situ reconstruction of the catalyst surface can produce a new double BEF to drive the OER. This study not only prepared an OER/HER bifunctional electrocatalyst for high current density, but also revealed the in situ electrochemical reconstruction of an LDH structure and true active substance in the OER process, thus guiding the exploration of the origin of catalytic activity and the design of industrial-grade catalysts.