Surface Redox-Driven Charge Storage in Electrodeposited Iron-Cobaltite/Vertical Graphene Binder-Free Hybrid...

Binder-free and self-supported iron-cobaltite/vertical graphene nanosheets hybrid electrodes are fabricated through a controlled electrodeposition approach for high-performance aqueous supercapacitors. The deposition process enabled precise tuning of the microstructure while inducing cation redistribution between Co^{+ 2}/Co^{+ 3} and Fe^{+ 2}/Fe^{+ 3} states, thereby improving the electrochemical activity of the hybrid electrode. The synergistic interaction between Fe and Co redox centers accelerated faradaic redox reactions, leading to remarkably high specific capacitance. In addition, annealing induced structural ordering, abundant oxygen vacancies significantly enhanced charge-transport kinetics and promoted dominant surface-controlled pseudocapacitive behavior, resulting in superior rate capability and long-term cycling stability. A correlation between microstructure, cation redistribution, oxygen vacancies, and charge-storage performance is established. An asymmetric coin cell assembled using the iron-cobaltite/vertical graphene hybrid electrode as positive electrode and oxidized vertical graphene as the negative electrode operated stably over a wide potential window of 1.5 V. The device delivered an areal capacitance of 41 mF/cm² together with high energy and power densities of 115.2 Wh/kg and 1405.8 W/kg, respectively. In addition, the assembled device exhibited excellent cycling stability (∼94%) and coulombic efficiency (96%). These findings highlight the potential of electrodeposited iron-cobaltite/vertical graphene hybrid electrodes for advanced energy-storage applications.