Cr₂O₃ nanoparticles: a fascinating electrode material combining both surface-controlled and diffusion-limited redox reactions for aqueous supercapacitors

Chromium oxide has emerged as an attractive electrode material to construct high-performance supercapacitor. Despite some available reports on Cr₂O₃-based supercapacitors, the charge storage of Cr₂O₃ electrodes in alkaline electrolytes is far from being understood unlike those of other compounds of Ti, V, Mn, Fe, Co, Ni etc in periodic table of elements. Herein, the detail kinetics analyses of electrochemical behaviors of the electrode based on Cr₂O₃ nanoparticles in alkaline electrolyte were demonstrated in this work. We examine that there are both surface-controlled pseudocapacitance (with a contribution of 76%) and diffusion-limited redox reactions (with a contribution of 24%) for the charge storage in electrode based on Cr₂O₃ nanoparticles at a low sweep rate of 1 mV s⁻¹. The identifying pseudocapacitive contribution dominates the charge storage in electrode based on Cr₂O₃ nanoparticles at high sweep rates, reaching up to 96% at 50 mV s⁻¹. In addition, the assembled hybrid supercapacitor based on Cr₂O₃ nanoparticles as the positive electrode displays an operating voltage of 1.45 V, an energy density of 14.7 Wh kg⁻¹, and high stability of 3000 cycles. This work will contribute to the development of pseudocapacitive electrode materials for supercapacitors.