Enhancing Energy Density in Aqueous Ammonium-Ion Supercapacitors via CuCoS@MoS Core@Shell Heterostructure Design.

Aqueous ammonium-ion supercapacitors (AASCs) are recognized for their rapid charge-discharge capability, long cycle life, and excellent power density. However, they still confront the challenges of low energy density. To address the above issue, this work proposes a novel strategy involving the establishment of CuCoS@MoS core@shell heterostructures to enhance the capacity of electrode material. The double electric layer energy storage mechanism of the MoS shell facilitates the storage and provision of a substantial ammonium source for NH insertion into CuCoS, thereby enhancing the electrochemical performance of AASCs. The density functional theory (DFT) calculations demonstrate that the CuCoS@MoS core@shell heterostructures exhibit better affinity for NH and improved conductivity. Furthermore, the internal electric field at the heterojunction accelerates NH transfer, thereby enhancing the pseudocapacitive behavior of CuCoS. Owing to the abundant active sites and pronounced pseudo-capacitance, the CuCoS@MoS electrode achieves a specific capacity of 2045 C g at 1 A g. With activated carbon (AC) as the negative electrode, the fabricated CuCoS@MoS//AC AASC device attains a specific capacity of 591 C g and an energy density of 83.23 Wh kg. This work presents a promising new strategy for the next generation of AASCs.