Low-cost high entropy alloy (HEA) for high-efficiency oxygen evolution reaction (OER)

Abstract

Oxygen evolution reaction (OER) is the key step involved both in water splitting devices as well as in rechargeable metal-air batteries and there is an urgent requirement for a highly stable and low-cost material for efficient OER. In this article, for the first time, electrocatalyst based on high entropy alloy (HEA) of FeCoNiZnGa has been reported for OER. Nano-crystalline high entropy alloys materials withdrew the attention of the research academia due to their emerging unique properties due to the cocktail effect and synergetic effect between the constituent elements. The existing materials (IrO 2 , RuO 2 , etc.) being utilized in the OER reaction contain precious metals. Thus, high entropy alloy made up of low-cost elements has been formulated and tested for the OER, which is found to be highly stable and more efficient. The formulation of nanocrystalline HEA (FeCoNiZnGa) utilized a unique recipe casting-cum-comminution (CCC). After electrochemical CV activation, transition metal oxides formation at the HEA surface helps in OER activities. HEA exhibits a low overpotential of 370 mV to achieve a current density of 10 mA cm -2 with a very small Tafel slope of 71 mV dec -1 and exceptional long term stability of electrolysis for over 10 h in 1 M KOH alkaline solution, which is extremely stable in comparison to the state-of-the-art OER electrocatalyst RuO 2 . Transmission electron microscopic (TEM) studies after 10 h of long term chronoamperometry testing confirmed high stability of HEA as no change in the crystal structure observed. Our work highlights the great potential of HEA towards oxygen evolution reaction which is primary reaction involved in water splitting.