P-Doped NiCo2S4 nanotubes as battery-type electrodes for high-performance asymmetric supercapacitors

Abstract

NiCo₂S₄ is a promising electrode material for supercapacitors, due to its rich redox reactions and intrinsically high conductivity. Unfortunately, in most cases, NiCo₂S₄-based electrodes often suffer from low specific capacitance, low rate capability and fast capacitance fading. Herein, we have rationally designed P-doped NiCo₂S₄ nanotube arrays to improve the electrochemical performance through a phosphidation reaction. Characterization results demonstrate that the P element is successfully doped into NiCo₂S₄ nanotube arrays. Electrochemical results demonstrate that P-doped NiCo₂S₄ nanotube arrays exhibit better electrochemical performance than pristine NiCo₂S₄, e.g. higher specific capacitance (8.03 F cm⁻² at 2 mA cm⁻²), good cycling stability (87.5% capacitance retention after 5000 cycles), and lower charge transfer resistance. More importantly, we also assemble an asymmetric supercapacitor using P-doped NiCo₂S₄ nanotube arrays and activated carbon on carbon cloth, which delivers a maximum energy density of 42.1 W h kg⁻¹ at a power density of 750 W kg⁻¹. These results demonstrate that the as-fabricated P-doped NiCo₂S₄ nanotube arrays on carbon cloth show great potential as a battery-type electrode for high-performance supercapacitors.