A self-supported NiCo2O4/CuxO nanoforest with electronically modulated interfaces as an efficient electrocatalyst for overall water splitting

摘要

Developing non-precious metal catalysts capable of both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in an alkaline medium is of great significance in the electrocatalytic water-splitting industry. Herein, a novel nanoforest-like NiCo2O4/CuxO/Cu heterojunction with excellent overall water splitting activity and long-term stability is synthesized through the facile substrate etching and hydrothermal crystallization processes. The nanotree-like NiCo2O4/CuxO supported on Cu foam achieves a current density of 10 mA cm(-2) at small overpotential (eta(10) = 92 mV for the HER; eta(10) = 213 mV for the OER), which is significantly ahead of the corresponding pristine catalyst NiCo2O4/Cu (eta(10) = 295 mV for the HER; eta(10) = 349 mV for the OER) and CuxO/Cu (eta(10) = 309 mV for the HER; eta(10) = 347 mV for the OER). In addition, NiCo2O4/CuxO/Cu can work stably for more than 125 h, and the stability is superior to the noble metal catalysts (Pt/C and RuO2) at different potentials. The electrons transfer from Cu2O to NiCo2O4 with the formation of Cu-O bonds at the interface, making parts of the relatively inert Cu(i) into the active Cu(ii), introducing abundant new active sites. The hierarchical self-supported nanoforest-like structure enlarges the electrochemically active surface area and ensures the bonding strength of NiCo2O4/CuxO with the Cu skeleton, giving rise to excellent stability. The superb electrocatalytic performance and stability of NiCo2O4/CuxO/Cu makes it a promising bifunctional catalytic material for overall water splitting. This study provides new testimony of interface effects and the mechanism may inspire the extending design of more effective catalysts.