MoS ₂@Polyaniline for Aqueous Ammonium‐Ion Supercapacitors

Abstract

Ammonium‐ion aqueous supercapacitors are raising notable attention owing to their cost, safety, and environmental advantages, but the development of optimized electrode materials for ammonium‐ion storage still lacks behind expectations. To overcome current challenges, here, a sulfide‐based composite electrode based on MoS ₂ and polyaniline (MoS ₂@PANI) is proposed as an ammonium‐ion host. The optimized composite possesses specific capacitances above 450 F g ⁻¹ at 1 A g ⁻¹, and 86.3% capacitance retention after 5000 cycles in a three‐electrode configuration. PANI not only contributes to the electrochemical performance but also plays a key role in defining the final MoS ₂ architecture. Symmetric supercapacitors assembled with such electrodes display energy densities above 60 Wh kg ⁻¹ at a power density of 725 W kg ⁻¹. Compared with Li ⁺ and K ⁺ ions, the surface capacitive contribution in NH ₄ ⁺‐based devices is lower at every scan rate, which points to an effective generation/breaking of H‐bonds as the mechanism controlling the rate of NH ₄ ⁺ insertion/de‐insertion. This result is supported by density functional theory calculations, which also show that sulfur vacancies effectively enhance the NH ₄ ⁺ adsorption energy and improve the electrical conductivity of the whole composite. Overall, this work demonstrates the great potential of composite engineering in optimizing the performance of ammonium‐ion insertion electrodes.