Ultrathin and Highly Crumpled/Porous CoP Nanosheet Arrays Anchored on Graphene Boosts the Capacitance and Their Synergistic Effect toward High-Performance Battery-Type Hybrid Supercapacitors

Constructing novel electrode materials with supernal specific capacitance and cycle stability is important for the practical applications of supercapacitors. Herein, ultrathin and highly crumpled CoP/reduced graphene oxide (rGO) nanosheet arrays are grown on nickel foam (NF) through a hydrothermal-phosphidation route. Benefitting from the synergistic effects of CoP with large specific capacity and rGO with high conductivity and ultrathin nanosheet arrays structure, CoP/rGO shows extraordinary electrochemical performance. The CoP/rGO electrode possesses a superior specific capacity of 1438.0 C g^-1 (3595.0 F g^-1) at 1 A g^-1, which is 3.43, 2.05, and 2.26 times larger than those of Co(OH)₂/rGO, Co₃O₄/rGO, and bare CoP. In particular, the CoP/rGO nanosheet arrays show the highest specific capacities among the monometallic phosphide-based nanostructures reported so far. The CoP/rGO retains 1198.9 C g^-1 (2997.2 F g^-1) at 10 A g^-1, revealing the outstanding rate capability of 83%. Theoretical calculations reveal that rGO can adequately reduce the absorption energy of OH^- on CoP, which makes CoP/rGO have strong adsorption capacity of OH^-, resulting in boosting electrochemical performance. A hybrid supercapacitor of CoP/rGO/NF//AC was designed, which presents a superior energy density of 43.2 Wh kg^-1 at a power density of 1010.5 W kg^-1. After 10 000 cycles, the CoP/rGO/NF//AC supercapacitor reveals excellent cycling durability with a capacitance retention of 89%. This work provides a new insight into the design of high-performance electrode materials by combining high capacitive metal phosphides with conductive carbon, which is of great significance for energy storage systems.