Surface engineering CoP/Co3O4 heterojunction for high performance bi-functional water splitting electro-catalysis

In electrochemical water splitting process, integrating hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in the same electrolyte with same catalyst is highly beneficial for increasing the energy efficiency and reducing the fabrication cost. However, most of the catalysts towards OER are unstable in acidic solution while HER is of poor kinetics in alkaline solution, which hinders the scale-up application of electro-catalytic water splitting. In this work, a CoP/Co3O4 heterostructure is firstly fabricated and then the O and P defects are involved to it via surface engineering (s-CoP/Co3O4). The as-prepared material is employed as the catalyst towards electrochemical water splitting in alkaline environment. In alkaline HER, a current density of -10 mA·cm-2 can be achieved at an overpotential of 106 mV vs. RHE. In OER process, the overpotential of s-CoP/Co3O4 electrode is only 211 mV vs. RHE at 10 mA·cm-2 in 1 M KOH, and the corresponding Tafel slope is only 58.4 mV/dec, so that the s-CoP/Co3O4 electrode could be used as the bifunctional catalyst for alkaline water splitting. This project provides a simple and low-cost approach to fabricate a Co-based heterojunction electrode with unsaturated metal sites to improve the electro-catalytic activities towards water splitting.