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 (C _p) 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 C _p 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 C _p 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.