Enhancing Energy Density in Aqueous Ammonium-Ion Supercapacitors via CuCo2S4@MoS2 Core@Shell Heterostructure Design.

Abstract

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 83.23Wh kg-1. This work presents a promising new strategy for the next generation of AASCs.