Constructing built-in electric field in oxygen vacancies-enriched FeO-FeSe heterojunctions supported on reduced graphene oxide for efficient overall water splitting.

Combining interfacial oxygen vacancy engineering with a built-in electric field (BEF) technique is an efficient way to build efficient and practical electrocatalytic water-splitting catalysts. In this study, a FeO-FeSe heterojunction catalyst with oxygen vacancies supported on reduced graphene oxide (rGO) was designed and successfully fabricated using a simple two-step hydrothermal method. Owing to the different Fermi levels of FeO and FeSe, a BEF was generated at the interface, which enhanced the separation of negative and positive charges, thus optimizing the adsorption of hydrogen/oxygen intermediates on the heterostructures and improving the activity of the catalyst. Experimental results show that FeO-FeSe/rGO/NF exhibits excellent hydrogen and oxygen evolution performances, with low overpotentials of 234/300 mV at 100 mA⋅cm. A water electrolyzer assembled with FeO-FeSe/rGO/NF as both the anode and cathode requires only a small potential of 1.78 V to reach a current density of 100 mA⋅cm. This study provides an innovative approach for constructing a catalyst with excellent electrocatalytic performance for overall water splitting.