Surface engineered CoP/CoO heterojunction for high-performance bi-functional water splitting electro-catalysis.

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