Photocatalysis-Assisted Co₃O₄/g-C₃N₄ p–n Junction All-Solid-State Supercapacitors: A Bridge between Energy Storage and Photocatalysis

Supercapacitors with the advantages of high power density and fast discharging rate have full applications in energy storage. However, the low energy density restricts their development. Conventional methods for improving energy density are mainly confined to doping atoms and hybridizing with other active materials. Herein, a Co₃O₄/g-C₃N₄ p–n junction with excellent capacity is developed and its application in an all-solid-state flexible device is demonstrated, whose capacity and energy density are considerably enhanced by simulated solar light irradiation. Under photoirradiation, the capacity is increased by 70.6% at the maximum current density of 26.6 mA cm⁻² and a power density of 16.0 kW kg⁻¹. The energy density is enhanced from 7.5 to 12.9 Wh kg⁻¹ with photoirradiation. The maximum energy density reaches 16.4 Wh kg⁻¹ at a power density of 6.4 kW kg⁻¹. It is uncovered that the lattice distortion of Co₃O₄, reduces defects of g-C₃N₄, and the facilitated photo-generated charge separation by the Co₃O₄/g-C₃N₄ p–n junction all make contributions to the promoted electrochemical storage performance. This work may provide a new strategy to enhance the energy density of supercapacitors and expand the application range of photocatalytic materials.