Nickel-cobalt phosphate/graphene foam as enhanced electrode for hybrid supercapacitor

Nickel-cobalt phosphate/graphene foam (40 mg) (NiCo(PO₄)₃/GF) composite was synthesized via a hydrothermal process and used as electrode material for supercapacitors. This work was done based on the fact that the electrochemical behavior of cobalt phosphate is similar to EDLC, while nickel phosphate is purely faradaic. Interestingly, the advantages of these two different mechanisms reflected on the results of NiCo(PO₄)₃/GF as an electrode for supercapacitor. The crystal structure, morphology and texture of the synthesized materials were studied with XRD, Raman spectrum, SEM and BET. The electrochemical performance of the produced sample was investigated by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) in 1 M KOH electrolyte. NiCo(PO₄)₃/GF_40 mg composite exhibited significantly improved specific capacity (86.4 mAh g⁻¹) much higher than pristine NiCo(PO₄)₃ (64 mAh g⁻¹) at 1 A g⁻¹ due to the synergistic effect between the conductive GF and NiCo(PO₄)₃. Furthermore, the hybrid supercapacitor device (NiCo(PO₄)₃//AC) fabricated achieved the highest energy density of 34.8 Wh kg⁻¹ and a power density of 377 W kg⁻¹ at a specific current of 0.5 A g⁻¹. The hybrid device also showed 95% of capacity retention after 10000 charge-discharge cycles at a specific current of 8 A g⁻¹ and 90% efficiency at floating time over 110 h at 5 A g⁻¹. These results make this composite to be a good candidate for electrochemical capacitors applications.