Interface engineering of a hollow core-shell sulfur-doped Co2P@Ni2P heterojunction for efficient charge storage of hybrid supercapacitors

Transition metal phosphides (TMPs) are widely used as supercapacitor energy storage materials due to their abundant valence and high theoretical capacity, but their poor electrical conductivity and low active material utilization lead to low actual capacity and slow kinetics. Herein, we demonstrate the excellent electrochemical properties of sulfur-doped Co2[email protected]2P heterojunction materials prepared using a combination of hydrothermal, ion-exchange and low-temperature annealing approaches. For sulfur-doped Co2[email protected]2P, hollow core-shell microstructures increase the number of electroactive sites and provides a shortcut for electron transport, while sulfur doping promotes the transfer and rearrangement of interfacial charge from Co2P to Ni2P, optimizing the redox ability of the active component. In addition, the S doping and the highly electrochemically active nickel-cobalt phosphide synergistically accelerate the charge transfer, which leads to fast reaction kinetics. Therefore, the obtained S-Co2[email protected]2P exhibits an optimal specific capacity of 1200 C g−1 at 1 A g−1 and excellent rate performance. Furthermore, when combined with activated carbon (AC) for hybrid supercapacitor (HSC), the S-Co2[email protected]2P//AC device shows an excellent energy density of 41.5 Wh kg−1 and a high-capacity retention of 93 % after 15,000 cycles. This work provides a novel approach for the exploration of high-performance and stable phosphorus-based battery-like supercapacitor materials.