Enhanced electrochemical performance of eco-friendly Cr-doped ZnO/RGO nanocomposites for pioneering supercapacitor applications.

Herein, a straightforward, and mild synthetic co-precipitation method is used to prepare Cr-ZnO/RGO nanocomposite to be used in supercapacitor applications. First, the chromium (Cr) doping concentration in zinc oxide (ZnO) nanoparticles was systematically varied (2, 4, 6, 8, and 10%) to evaluate its influence on the electrochemical performance. The composite was constructed by combining reduced graphene oxide (RGO) with 8% Cr-ZnO, which showed the best redox potential among the compositions under investigation. The structural, morphological, compositional, and optical properties were characterized using the complementary analytical techniques. Cyclic voltammetry (CV) and EIS were used to assess electrochemical performance in 1M KOH. The optimized 8% Cr-doped ZnO/RGO nanocomposite exhibited a band gap of 3.59 eV. Electrochemical evaluation revealed a high specific capacitance of 703 F g-1 at a scan rate of 100 mVs-1. The CV profiles were quasi-rectangular in nature, indicating a combination of electric double-layer and pseudocapacitive charge storage. Furthermore, the electrode demonstrated 89% capacitance retention over 5,000 charge-discharge cycles with 99% Coulombic efficiency, confirming stable electrochemical behavior. EIS analysis revealed low internal resistance and enhanced charge transport with considerably reduced surface resistance (Ru) and solution resistance (Rp) values. The synergistic effect between the optimal chromium doping and integration with RGO was attributed to this improved efficiency. These results demonstrate that Cr-ZnO/RGO nanocomposites can be used as a promising electrode material in supercapacitor applications.