Enhancing Energy Density in Aqueous Ammonium-Ion Supercapacitors via CuCo₂S₄@MoS₂ 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 CuCo₂S₄@MoS₂ core@shell heterostructures to enhance the capacity of electrode material. The double electric layer energy storage mechanism of the MoS₂ shell facilitates the storage and provision of a substantial ammonium source for NH₄ ⁺ insertion into CuCo₂S₄, thereby enhancing the electrochemical performance of AASCs. The density functional theory (DFT) calculations demonstrate that the CuCo₂S₄@MoS₂ core@shell heterostructures exhibit better affinity for NH₄ ⁺ and improved conductivity. Furthermore, the internal electric field at the heterojunction accelerates NH₄ ⁺ transfer, thereby enhancing the pseudocapacitive behavior of CuCo₂S₄. Owing to the abundant active sites and pronounced pseudo-capacitance, the CuCo₂S₄@MoS₂ electrode achieves a specific capacity of 2045 C g^-1 at 1 A g^-1. With activated carbon (AC) as the negative electrode, the fabricated CuCo₂S₄@MoS₂//AC AASC device attains a specific capacity of 591 C g^-1 and an energy density of 83.23 Wh kg^-1. This work presents a promising new strategy for the next generation of AASCs.