Lithium-Free Metal Fatty Acid-Based Electrolytes for Quasi-Solid-State Photosupercapacitors

Novel lithium-free gel metal fatty acid (M:FA, M = Co, Cu, and Fe) electrolytes were prepared for use in photosupercapacitor (PSC) applications. Cyclic voltammetry (CV) analysis revealed that the device using the Fe:FA gel electrolyte had a superior specific capacitance (Cp) of 644 Fg–1 at 1 mVs–1. However, for higher scan rates, the Cu:FA gel electrolyte-based PSC performed better compared to the other M:FA. Galvanostatic charge–discharge (GCD) experiments also provided values close to the moderate scan rates of CV experiments, with Cp values obtained from GCD measurements under 20 Ag–1 and illumination conditions being 318, 265, and 252 Fg–1 for Cu, Co, and Fe:FA, respectively. Besides, to assess cyclic stability, devices were tested at a voltage of 1 V and a current density of 60 Ag-1 for 10,000 cycles. The Cp retention was found to be 67%, 117%, and 55% of the original capacitance for Cu, Co, and Fe:FA PSCs, respectively, with almost 100% Coulombic efficiency for all PSCs. In line with all of these results, it was concluded that Cu and Fe:FA-based PSC devices combine high performance and durability with low cost and abundance in nature as an alternative to lithium-based electrolytes and shed light on future studies.