A high-temperature phosphorization for synthesis of core-shell Ni-NixPy@C nanocomposite-immobilized sponge-like P-doped porous carbon with excellent supercapacitance performance

Abstract

To effectively enhance the overall electrochemical performance of supercapacitors, a high-temperature phosphorization strategy was developed to fabricate core-shell Ni-NixPy@C nanocomposite-immobilized sponge-like P-doped porous carbon (Ni-NixPy@C/P-HPC). The Ni-NixPy@C/P-HPC was successfully constructed by a cross-linking process and subsequent high-temperature calcination. During the pyrolysis process in N2 multiple steps, including phosphating metal ions to Ni-NixPy nanoparticles, forming core-shell Ni-NixPy@C nanocomposites, doping P element into carbon skeleton and immobilizing core-shell Ni-NixPy@C nanocomposites onto porous carbon, were achieved simultaneously. The Ni-NixPy@C/P-HPC was studied using various characterization techniques. The results revealed that the obtained material integrated the advantages of interconnected P-doped framework (fast ion transport), nickel and nickel phosphide species (high theoretical specific capacitance), and graphene-like shell (excellent electrical conductivity and effective protection for activate sites). Therefore, the as-prepared hybrid delivered the outstanding electrochemical performance with ultrahigh specific capacity of up to 1275 F g−1 at 1 A g−1 and an excellent cycling stability with 92.5% capacity retention after 5000 cycles. Besides, the asymmetric supercapacitor using Ni-NixPy@C/P-HPC-900 and activated carbon as the anode and cathode materials exhibited a high energy density of 49.4 W h kg−1 at 250 W kg−1, and remained as high as 30.6 W h kg−1 even at 5000 W kg−1. Our research will open up a new way to synthesize transition metal phosphide@carbon composites with excellent electrochemical properties.