A High Voltage Symmetric Supercapacitor Comprising Concentrated NaCl: PVA Electrolyte and Partially Reduced Graphene Oxide Electrodes

Abstract Strategies to improve energy density in supercapacitors are mainly based on utilizing electrodes providing larger effective surfaces and electrolytes allowing op eration in wider voltage windows. Here, a water‐based, binder‐free, environmentally friendly, high voltage, and quasi‐solid‐state symmetric supercapacitor is presented comprising partially reduced graphene oxide active electrodes and concentrated NaCl: polyvinyl alcohol gel electrolyte. It is shown that the ionic diffusion through the electrode‐electrolyte interface is augmented by the partial reduction of the graphene oxide electrodes up to an optimum level. The safe operation voltage window is 4 V; the high field endurance is attributed to the ion‐saturated hydrogel electrolyte used. At a scan rate of 25 mV/s, the provided capacitance and stored energy are 0.1 F.cm −2 and 5.6 e −5 W.h.cm −2 , respectively. The optimized device retains ~90 % of its initial capacitance after 1000 charge‐discharge cycles; no meaningful sign of degradation is detected afterwards up to the 2000 cycles examined. These results place further emphasis on the potentials of the gel polymer electrolytes in the fabrication of environmentally friendly supercapacitors. Our findings are anticipated to accelerate improvements in the properties of the graphene‐based electrodes, particularly in conjunction with the proposed electrolyte.