Roe-shaped Ni3(PO4)2/RGO/Co3(PO4)2 (NRC) nanocomposite grown in situ on Co foam for superior supercapacitors

Abstract

A roe-shaped ternary nanocomposite, Ni₃(PO₄)₂/RGO/Co₃(PO₄)₂ (NRC), was grown in situ on cobalt foam (CoF). The synthesis and loading of NRC on the CoF was completed through a one-step hydrothermal process by immersing the CoF in an aqueous solution of GO and Ni²⁺ in the presence of H₂PO₄⁻, in which the CoF served as the support, reductant and Co source. Three interfaces of Co₃(PO₄)₂/CoF, RGO/Co₃(PO₄)₂, and Ni₃(PO₄)₂/RGO with strong interactions were constructed based on an in situ conversion reaction of Co to Co₃(PO₄)₂, a redox reaction between GO and the CoF, and the electrostatic attraction force of Ni²⁺ and GO, respectively. The as-synthesized NRC@CoF had a hierarchically porous structure, and directly acted as a supercapacitor electrode and delivered excellent electrochemical performances: a specific capacitance of 10 237.5 mF cm⁻² (1137.5 F g⁻¹) at 5 mA cm⁻² (0.56 A g⁻¹) with a capacity retention of 117.8% after 14 000 cycles. Furthermore, NRC@CoF-based asymmetric supercapacitors (ASCs) exhibited a specific capacitance of 4845.9 mF cm⁻² (115.4 F g⁻¹) at 5 mA cm⁻² (0.12 A g⁻¹), and a high energy density of 44.82 W h kg⁻¹ at a power density of 428.6 W kg⁻¹, as well as good cyclic stability (91.9% after 18 000 cycles).