Improving hydrogen production activity of bifunctional CuCoFe-layered double hydroxides for electrocatalytic water splitting: Effects of valence state evolution and oxygen vacancies

The development of noble metal-free electrocatalysts is crucial for efficient water splitting via both hydrogen (HER) and oxygen evolution reaction (OER) in alkaline electrolyte. In this study, bifunctional CuCoFe layered double hydroxides grown in-situ on Ni foam (NF) have been prepared to achieve high-efficient water splitting. The CuCoFe LDHs need a low overpotential of 49 mV for HER and 255 mV for OER to deliver a current density of 10 mA·cm−2, which is superior to many reported LDH-based electrocatalysts. On the one hand, the Cu2+ ions induce distortions of structure units, which promotes the formation of oxygen vacancies and facilitates electron migration as well as charge transfer. On the other hand, excessive addition of Cu2+ ions can lead to a reduction in active sites due to the acceleration of Co2+ oxidation during preparation. This work presents an opportunity to regulate the structure of LDH-based electrocatalysts by the new approach of Cu-doping, resulting in enhanced control over valence state evolution and oxygen vacancies.