Cooperative catalysis of Zn3(VO4)2/Ni(OH)2/rGO nanosheet arrays advancing highly active O2 reduction and water-splitting

Abstract

Electrocatalytic O₂ conversion and water-splitting hold great promise to enable the chemicals–electricity inter-transition in many renewable-energy initiatives. Enhancing the kinetics of the oxygen reduction reaction (ORR) is challenging. Here, we present that Zn₃(VO₄)₂/Ni(OH)₂/rGO (reduced graphene oxide) nanosheet arrays-a Zn₃(VO₄)₂/Ni(OH)₂ composite in the form of nanometre-thick nanosheets on an rGO substrate-serve as an efficient and stable electrocatalyst for the ORR in alkaline electrolytes. The thin-sheet structure and smaller free energy of Zn₃(VO₄)₂/Ni(OH)₂, as well as the excellent conductivity of the rGO substrate, enable a large electrochemically-active surface area and a high electron transport, contributing to the superior electrocatalytic oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). Furthermore, Zn₃(VO₄)₂/Ni(OH)₂/rGO and Zn₃(VO₄)₂/Ni(OH)₂ samples exhibit remarkable long-term water-splitting stability of 48 h. Density functional theory (DFT) calculations reveal the optimized intermediate affinity ability at the Ni(OH)₂ side, due to electrons transferring from Ni(OH)₂ to Zn₃(VO₄)₂. Additionally, the higher hybridization degree of density of states (DOS) boosts electron transfer in the electrocatalytic process. More broadly, this work provides new inspiration for the construction of a novel noble metal-free electrocatalyst that could show great promise in energy electrocatalysis.