Effects of molybdenum content and heat treatment on hydrogen evolution reaction properties and microstructure of FeCoCrNiMox high entropy alloys

Abstract

The preparation of efficient and long-lasting electrocatalysts with low cost is crucial for hydrogen production by water electrolysis . Here, a series of high-entropy alloys (HEAs) of FeCoCrNiMo x (x = 0, 0.5, 1, 1.5, and 2) were created by arc melting method and enhanced by heat treatment according to various schedules. The microstructure transitioned from the FCC phase to the FCC + σ phase and finally to the FCC + σ + μ phase with the increase of Mo content . The FeCoCrNiMo 1.5 HEAs performed superior catalytic properties , which could be further modified by solution and aging treatment. As-cast FeCoCrNiMo 1.5 alloy showed a HER overpotential of 344 mV at the current density of 10 mA/cm 2 . After age treated at 800°Cthe overpotential decreased to 260 mV. According to the findings of SEM and TEM , the electrocatalytic activity performance of FeCoCrNiMo 1.5 HEAs after aged at 800 °C might be related to the precipitation of micro/nano-scale FCC phases inside μ phases. This work demonstrates the feasibility of non-noble metal-based HEAs (excluding platinum group metals) for hydrogen evolution and proposes a possible way to further enhance the electrocatalytic performance through heat treatment.