Electrodeposited Co0.85Se thin films as free-standing cathode materials for high-performance hybrid supercapacitors

Abstract In this study, Co0.85Se 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 Co0.85Se electrodeposition, the Co0.85Se electrode prepared at -0.7 V vs. Ag/AgCl showed the most excellent electrochemical properties among all the electrodeposited Co0.85Se electrodes, which can be ascribed to its monodispersed morphology with interconnected porous nature. Moreover, the HSC based on the optimized Co0.85Se 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 Co0.85Se thin film could be regarded as one of the promising free-standing cathode materials for high-performance HSCs.