Regulating electrolytic Fe0.5CoNiCuZn high entropy alloy electrodes for oxygen evolution reactions in alkaline solution

Abstract

• FeCoNiCuZn x HEAs are prepared by one-step electrochemical reduction of their oxides. • Use of ZnO as the precursor prevents the evaporation of Zn for preparation Zn-containing HEAs. • The composition and structure of HEAs can be easily controlled by adjusting the ingredient of oxide precursors. • Zn enhances the OER activity of FeCoNiCuZn x and the high entropy effect stabilize Zn in the HEAs. • The HEA(Zn0.8) exhibits the best OER activity and a good durability. The properties of high entropy alloys (HEAs) depend on their phase structures and compositions. However, it is difficult to control the composition of the HEAs that contain highly volatile metals by the conventional arc melting method. In this paper, homogeneous powdery face centered cubic (FCC) phase Fe 0.5 CoNiCuZn x HEAs were prepared by the electrolysis of metal oxides in molten Na 2 CO 3 -K 2 CO 3 using a stable Ni11Fe10Cu inert oxygen-evolution anode. The use of oxide precursors and relatively low synthetic temperature are beneficial to efficiently preparing HEAs that contain highly volatile elements such as Zn. Moreover, the microstructures and compositions of the electrolytic HEAs can be easily tailored by adjusting the components of oxide precursors, then further regulating its properties. Thus, the electrocatalytic activity of Fe 0.5 CoNiCuZn x HEAs towards oxygen evolution reactions (OER) was investigated in 1 M KOH. The results show that Zn promotes the OER activity of Fe 0.5 CoNiCuZn x HEAs, i.e., the HEA(Zn 0.8 ) shows the best OER activity exhibiting a low overpotential of 340 mV at 10 mA/cm 2 and excellent stability of 24 h. Hence, molten salt electrolysis not only provides a green approach to prepare Fe 0.5 CoNiCuZn x HEAs but also offers an effective way to regulate the structure of the alloys and thereby optimizes the electrocatalytic activities for water electrolysis.