Dilber Esra Yıldız, Öncü Akyildiz, Cengiz Bağcı
ABSTRACT Asymmetric hybrid supercapacitors integrating transition metal oxides with carbonaceous electrodes have attracted significant attention for advanced energy storage applications due to their ability to combine high energy density with rapid power delivery. In this study, an Al/Nb 2 O 5 cathode and a Cu/graphene oxide (GO) anode were fabricated via slurry casting and electrophoretic deposition (EPD), respectively, and assembled with a paper separator in aqueous potassium hydroxide (KOH) electrolytes of varying concentrations (1, 2, and 3 M). Structural and morphological analyses confirmed the orthorhombic phase of Nb 2 O 5 and the uniform deposition of GO films. Galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopy (EIS) measurements revealed a strong dependence of electrochemical performance on electrolyte concentration. The device operating in 2 M KOH exhibited the most favorable balance between energy and power densities, achieving a specific capacitance of 30.7 F g −1 , energy density of 36.5 Wh kg −1 , and power density of 295 W kg −1 , with a relaxation time constant of 0.634 ms. In contrast, 1 M KOH provided moderate energy storage capability, while 3 M KOH suffered from reduced capacitance due to increased viscosity and ion–ion interactions. Comparative analysis with literature data highlights the competitive performance of the Al/Nb 2 O 5 //Cu/GO configuration, particularly in terms of energy–power trade‐off. These findings underscore the critical role of electrolyte optimization and electrode design in advancing hybrid supercapacitors for sustainable energy storage applications.