Effect of Zn/Mn on the supercapacitor behavior of high-entropy FeCoNiCrZn/Mn alloy†

High-entropy alloys (HEAs) are emerging as potential electrode materials for energy storage owing to their unique multivalent transition states. Herein, we demonstrate the supercapacitor behavior of an HEA consisting of structural elements (earth abundant metals) iron, cobalt, nickel, chromium, and zinc (FeCoNiCrZn). The role of zinc as a replacement for manganese in FeCoNiCrZn/Mn was studied. The highest specific capacitance obtained was ∼556 F g⁻¹ at 5 mV s⁻¹ in an aqueous electrolyte. Further, an asymmetric liquid-state device was fabricated, which demonstrated the highest capacitance of 98 F g⁻¹ at 1 A g⁻¹ with a specific energy density of 34.8 W h kg⁻¹ at a specific power density of 800 W kg⁻¹. Detailed microscopy and spectroscopy analyses provided insights into the electrochemical behavior of individual elements in the HEA. Experimental observations were further supported by density functional theory (DFT) calculations, which showed d-band shifts in each individual element and the synergistic nature of the FeCoNiCrZn HEA compared to its individual nanoclusters.