Electrodeposited Co_0.85Se thin films as free-standing cathode materials for high-performance hybrid supercapacitors

In this study, Co_0.85Se thin film of monodispersed morphology with interconnected and opened porous structure was successfully prepared via a facile electrodeposition method and employed as a free-standing cathode material in hybrid supercapacitors (HSCs). After the optimization of the applied potential for Co_0.85Se electrodeposition, the Co_0.85Se electrode prepared at -0.7 V vs. Ag/AgCl showed the most excellent electrochemical properties among all the electrodeposited Co_0.85Se electrodes, which can be ascribed to its monodispersed morphology with interconnected porous nature. Moreover, the HSC based on the optimized Co_0.85Se cathode was delivered outstanding electrochemical behavior, especially with regards to an impressive specific capacity of 16.47 mAh g ^{− 1} and 12.21 mAh g ^{− 1} at the current density of 1 A g ^{− 1} and 8 A g ^{− 1}, respectively. Additionally, the HSC device exhibited the maximum energy density of 23.95 Wh kg⁻¹ at a power density of 800 W kg⁻¹. Most importantly, the capacitive retention of 97.1% was reached even after the floating test for 48 h, demonstrating its outstanding electrochemical stability. As a result, the electrodeposited Co_0.85Se thin film could be regarded as one of the promising free-standing cathode materials for high-performance HSCs.