Elucidating the sources of activity and stability of FeP electrocatalyst for hydrogen evolution reactions in acidic and alkaline media

In this study, we conduct comprehensive experimental and theoretical investigations on the hydrogen evolution reaction (HER) preformation of FeP electrode in acidic and alkaline solutions. Theoretically, bulk Fe-O bond is unfavorable, but surface Fe-O bond is favorable and plays a negative role for HER. The presence of oxygen bonds (native or formed during reaction) is the root source of the reduced HER activity. Surface treatment in 37% HCl solution removes the oxide layer and significantly improves the HER performance, especially in alkaline solution. After etching, the overpotentials in 0.5 M H 2 SO 4 are 79 and 95 mV at 10 and 20 mA cm −2 , respectively. The ones in 1 M KOH are 95 and 102 mV at 10 and 20 mA cm −2 , respectively. Long-term instability in alkaline solution is caused by the presence of oxygen in the electrolyte. Good stability can be realized by removing oxygen from the solution.