Nickel-driven enhancement of charge storage in layered β-Co1-xNix(OH)2/graphite-reduced graphene oxide composite electrodes

Abstract

The composition-dependent charge-storage behavior of graphite-rGO electrodes containing β-Co 1-x Ni x (OH) 2 (x = 0.25, 0.50, and 0.75) was investigated in 6.0 M NaOH at a hydroxide mass loading of 35.7 mg cm −2 . Cyclic voltammetry indicated a quasi-reversible one-electron M(OH) 2 /MOOH process, while Raman spectroscopy supported reversible MOOH-like formation upon oxidation. Increasing Ni content enhanced stored charge, specific capacitance, electrochemical accessibility, and surface-controlled contributions. Laviron analysis, however, revealed non-monotonic apparent electron-transfer kinetics, with the highest rate constant for the equimolar composition. Combined Dunn, Trasatti, and impedance analyses attribute the superior Ni-rich response to more effective electroactive-region utilization and reduced resistive and ion-transport limitations rather than faster elementary electron transfer. Despite exhibiting the lowest BET area (∼1.0 m 2 g −1 ), β-Co 0.25 Ni 0.75 (OH) 2 showed the largest electrochemically estimated roughness factor and delivered 50 ± 5 F g −1 at 0.1 A g −1 , 5.6 ± 0.3 Wh kg −1 , 3.4 ± 0.2 kW kg −1 , ∼95–100% Coulombic efficiency, and ∼94% capacitance retention after 10,000 cycles. Post-cycling XRD and FT-IR revealed no persistent long-range structural or bonding changes.