Pulse electrodeposited FeCoNiMnW high entropy alloys as efficient and stable bifunctional electrocatalysts for acidic water splitting

High entropy alloys, possessing unique advantages of atomic scale synergy between multi-constituents, can be suitably designed to fulfill requirements of both activity and stability. Herein, a pulse current electrodeposition method is developed to grow a high entropy FeCoNiMnW alloy (H-FeCoNiMnW) in-situ on carbon papers to serve as an efficient robust bi-functional catalyst for acidic electrolytic water splitting. It exhibits an extraordinarily low overpotential of 15 mV and a serviceable overpotential of 512 mV for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, both at 10 mA cm−2. The H-FeCoNiMnW//H-FeCoNiMnW couple delivers a current density of 10 mA cm−1 at 1.76 V for overall water splitting, and exhibits outstanding stability, a less than 10% increase in cell voltages after a 6-day operation. Tungsten in H-FeCoNiMnW forms a surface protection oxide layer during the water splitting, rendering the outstanding catalytic stability of H-FeCoNiMnW in acidic media.