Phosphotungstic acid assisted growth of nickel hexacyanoferrate on Ni foam for binder-free supercapacitor electrode

•Ni foam was used as both Ni source and current collector.•Ni was oxidized by PTA to Ni2+ in the presence of K3Fe(CN)6.•Synthesized Ni-HCF nanocubes were uniformly distributed on Ni foam.•Ni-HCF/Ni foam demonstrates excellent electrochemical performances. The in-situ growth of nickel hexacyanoferrate nanocubes on Ni foam (Ni-HCF/Ni foam) was achieved with a one-step hydrothermal method with Ni foam as both the current collector and the nickel source. Phosphotungstic acid (PTA) acting as the oxidizing agent, oxidized elemental nickel to Ni2+ cations, which subsequently reacted with K3Fe(CN)6 to produce Ni3[Fe(CN)6]2 nanocubes. The prepared binder-free Ni-HCF/Ni foam was characterized with X-ray diffraction (XRD), X-ray photoelectronic spectroscopy (XPS) and field emission scanning electron microscopy (FE-SEM). The electrochemical performances of Ni-HCF/Ni foam were further investigated with cyclic voltammetry (CV) and galvanostastic charge/discharge technique (GCD). Ni-HCF/Ni foam exhibits areal capacitance of 7200 mF cm−2 (specific capacitance of 535.3F g−1) at 10 mA cm−2, high energy density and long cycling life. An asymmetrical supercapacitor (ASC) was assembled with Ni-HCF/Ni foam and activated carbon (AC) as the positive electrode and negative electrode, respectively. The ASC exhibits remarkable energy density of 5.89 W h m−2 at a high power density of 75 W m−2.