High-performance solid-state symmetric supercapacitors based on porous Fe-Cr-O structures derived from stainless steel

This study presents the development of a solid symmetric supercapacitor using porous structured Fe-Cr-O oxide layers as both anode and cathode. The porous structures were obtained through a simple and efficient anodization method of stainless steel substrate. Further, an oxide layer containing Fe and Cr species was formed on the porous stainless steel mesh via a low-cost thermal oxidation process in an uncontrolled atmosphere. The prepared porous Fe-Cr-O structures delivered areal capacities of 172.66 and 155.77 mC·cm⁻² from cyclic voltammetry (CV) and galvanic charge-discharge (GCD) measurements, respectively, and retained 96.5% of their capacity after 10,000 cycles. Additionally, a solid-state symmetric supercapacitor assembled employing Fe-Cr-O electrodes and a gelatinous PVA/KOH polymer electrolyte exhibited an operating voltage of 2 V and a capacity of 31.33 mC.cm - ² at a scan rate of 5 mV s -1 , with 84.03% retention after 2000 cycles. The recorded energy density was 2.39 mWh cm - ² and the power density was 2669 mW cm - ². These performances reinforce the potential of porous Fe-Cr-O structures as electrode materials for the next generation of high-energy-density solid-state energy storage systems.