Zn-Co phosphide porous nanosheets derived from metal-organic-frameworks as battery-type positive electrodes for high-performance alkaline supercapacitors

Abstract Excellent electrode materials are often desired to improve the overall performance of supercapacitors and conversion components, especially electrode materials synthesized by anion replacement to achieve high electrochemical performance. Herein, a zinc–cobalt phosphide electrode material with excellent electrical conductivity is synthesized through a metal–organic framework (MOF)-derived method, followed by phosphating in a tube furnace. As a result, an exchange of phosphorus ions and oxygen ions occurs, yielding a high specific capacitance of 2115.5 F g-1 at 1 A g-1, as well as a superior rate capacity of 1086.5 F g-1 at 50 A g-1. After 7000 cycle tests, 80.3% of the initial specific capacitance is maintained. Phosphorus substitution leads to a narrowed band gap, resulting in outstanding electrical conductivity, as confirmed through density functional theory (DFT) calculations. Subsequently, the self-assembled Zn0.33Co0.67P//Bi2O3 alkaline supercapacitor exhibits a high energy density of 83.05 Wh kg-1 (248.9 F g-1 at 1 A g-1) at a power density of 775.02 W kg-1. Meanwhile, a capacitance retention of 84.6% after 8000 cycles at a current density of 5 A g-1 is obtained. The outstanding performances of the electrode material in terms of electrical conductivity and electrochemical activity provide a new method for the design of high energy density alkaline supercapacitors (SCs).