One-step microwave synthesis of self-supported NiCoMn medium-entropy alloy with long cycling stability for supercapacitors and oxygen evolution reaction

This work reports the preparation of NiCoMn medium-entropy alloys and Ag-Bi bimetallic alloys grown on nickel foam using the microwave method. X-ray diffraction confirms the single face-centered cubic phase organization of NiCoMn. Electrochemical analyses show that it has a high capacitance of 3206 F g–1 at 1 A g–1 and remarkable cycle stability (83.0 % retention over 70,000 cycles). The Ag-Bi alloys manifest a decent storage capacity of 2462.5 F g–1. To meet the demand for high energy density, the prepared NiCoMn and Ag-Bi are used as positive and negative electrodes to assemble an asymmetric supercapacitor, respectively. The energy density of 218.8 Wh kg–1 is exhibited when the operating voltage is set to 1.5. The NiCoMn alloys also show favorable oxygen evolution reaction catalytic activity, with a low overpotential (186.6 mV) at 10 mA cm–2 and a small Tafel slope (79.6 mV dec–1).