Gradient composition design of FeCoCrMnNi high entropy alloys: An efficient and stable electrocatalyst for water splitting

FeCoCrMnNi high entropy alloys (HEAs) are synthesized on nickel form by pulse electrodeposition as an efficient and stable electrocatalyst for water splitting. Due to the gradient composition of metal elements, which enhance the synergistic effect for FeCoCrMnNi HEA, FeCoCrMnNi HEA shows excellent catalytic activities and stabilities on both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline electrolyte. For HER, FeCoCrMnNi exhibits a low overpotential of 168 mV at current density of 10 mA cm⁻² and a Tafel slope of 180 mV dec⁻¹. For OER, FeCoCrMnNi shows an overpotential of 231 mV at 10 mA cm⁻², which is much lower than that of commercial IrO₂ electrocatalyst (330 mV). Moreover, FeCoCrMnNi exhibits an extraordinary stability in the current-density (i-t) test for 100 h at 100 mA cm⁻², which results from the self-sacrificed leaching of Cr and high valence state of Mn exposes more electrocatalytic active sites on external surface. Therefore, the gradient composition design for high entropy alloys gives a new path to synthesize efficient and stable electrocatalysts for water splitting.