MoS₂ @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 MoS₂ and polyaniline (MoS₂ @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 MoS₂ 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 NH₄ ⁺ -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 NH₄ ⁺ insertion/de-insertion. This result is supported by density functional theory calculations, which also show that sulfur vacancies effectively enhance the NH₄ ⁺ 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.