Heterogeneous Ni-Co phosphide/phosphate with a specific hollow sea-urchin-like structure for high-performance hybrid supercapacitor and alkaline zinc-metal battery applications.

Constructing well-defined nanostructures consisting of the multiple components with distinctive features are a promising but challenging strategy to develop advanced electroactive materials for energy storage applications. Herein, heterogeneous Ni-Co phosphide/phosphate with a specific hollow sea-urchin-like structure has been synthesized as advanced electroactive materials for both hybrid supercapacitor (HSC) and alkaline zinc-metal battery (AZB) applications. The heterogeneous Ni-Co phosphide/phosphate combines the merits of improved electrolyte interfacial property from the specific hollow sea-urchin-like structure, high electron-conductivity of phosphide, and better ion adsorption and solid diffusion property of phosphate. As a result, the Ni-Co phosphide/phosphate achieves a high capacity to 180.7 mA h g at 1 A g, excellent rate capability of 51% capacity retention when the specific current increases by 50 times, and stable cycling stability of 85% capacity retention when cycled for 1000 cycles. Ex situ test was conducted to investigate the formation mechanism for the hollow and sea-urchin-like structure, which can be ascribed to the anion exchange reaction between pre-formed hydroxide and CO ions. When used to assemble HSCs with reduced graphene oxide (RGO), the HSCs exhibit a high specific energy of 49.4 W h kg, an ultrahigh specific power to 11.7 kW kg, and an eminent cycling stability over 10,000 cycles. Meanwhile, NiCo-P/PO-based AZB also achieves both high-energy and high-power performance with the specific energy of 308.0 W h kg at 828.4 W kg and 117.4 W h kg at 30.8 kW kg. These results above suggest that heterogeneous Ni-Co phosphide/phosphate has great potential to be used as a candidate for both HSC and AZB applications.