Facile synthesis of a NiMnFeCrCu high entropy alloy for electrocatalytic oxygen evolution reactions

Abstract

High entropy alloys (HEAs) are a new class of multiprincipal component alloys which can be potentially used for water splitting process as an alternative for nickel-based alloys and stainless steel for practical alkaline water electrolysis due to their excellent mechanical stability and catalytic activity toward the oxygen evolution reaction. In this study, NiMnFeCrCu HEA was synthesized using combined techniques of mechanical alloying and vacuum sintering, and its utility in oxygen evolution reaction was investigated. Phase composition and microstructural characterization were carried out using X-ray diffraction, scanning and transmission electron microscopy. Electrocatalytic properties were studied by an electrochemical workstation that incorporated linear sweep voltammetry, cyclic voltammetry (CV), and chronoamperometry. The experimental results showed that the HEA sample that was vacuum sintered at 1050 °C for 2 h (as referred to as R4) exhibited an overpotential of 310 mV under 100 cycles of CV activation. The R4 HEA alloy had a microhardness of 152 ± 6 HV and a compressive yield stress of 563 MPa. Hence the R4 HEA exhibited better combined properties of strength and activity than nickel-based alloys and stainless steel. This superior electrocatalytic properties could be attributed to the formation of an electrochemically active orthorhombic Mn3O4 species during CV activation which acted as active sites. This suggested NiMnFeCrCu HEA we synthesized possessed good electrocatalytic properties and adequate mechanical strength to function as a self-supported electrocatalyst for industrial scale practical water electrolysis application.