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 hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, Ag/CoNiV-LDH/CoO electrocatalyst with hierarchical core-shell structure were synthesized by a novel “template-oriented - ion exchange - spontaneous redox” method, inspired by the excellent OER kinetics of cobalt oxides and high-valence metal layered double hydroxide (LDH), and the enhanced conductivity of metal nanoparticles for HER. Notably, it exhibits superior electrochemical activity with a low overpotential of 298 mV for OER at 100 mA cm-2 and 79 mV for 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 double built-in electric field (BEF), the optimized electronic structure and d-band center by the 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 catalyst surface can produce a new double BEF to drive OER. This study not only prepared OER/HER bifunctional electrocatalyst for high current density, but also revealed the in-situ electrochemical reconstruction of LDH structure and true active substance in OER process, thus guiding the exploration of the origin of catalytic activity and the design of industrial grade catalysts.