Hydrothermally Synthesized Rare-Earth Oxides as Positive Electrodes for PVA/KOH Gel-Electrolyte Hybrid Supercapacitors

Abstract

Rare-earth metal oxides are an exciting group of pseudocapacitive materials, but there are limited comparative studies on their electrochemical performance and the further fabrication of gel-electrolyte-based energy-storage devices. In the present study, CeO2, La2O3, Y2O3, Sm2O3, and Pr2O3 were prepared via the hydrothermal method and then subsequently annealed to study their supercapacitor applications. A crystallinity study carried out using XRD confirmed the formation of crystalline oxide phases, while FESEM and N2 adsorption–desorption analyses revealed oxide-dependent structural, surface, and porosity characteristics. Maximum specific capacitance was exhibited for CeO2, while Y2O3 exhibited exceptional cycling stability. The optimal values obtained from the CeO2 electrode were used to assemble a hybrid supercapacitor device with a PVA/KOH gel electrolyte to evaluate its practical applicability. The device achieved an energy density of 20 Wh kg−1 at a power density of 1000 W kg−1 and maintained 100% capacitance retention after 2000 cycles. In summary, each oxide had distinct advantages; CeO2 showed the best overall electrochemical response, signifying its potential in solid-state hybrid supercapacitors.