Enhanced Energy Storage Capacity of TiO2 Atomic Layered Molybdenum Oxide–Sulfide Negatrode for an Aqueous Ammonium Ion Supercapacitor

Abstract

Ammonium ions (NH₄⁺) being the non-metallic charge carriers are deemed safe while enhancing the charge storage performance. To enable long term efficiency in energy storage systems, one needs to overcome the primary obstacle to ammonium storage, which is to develop materials with layered structures having enough interlayer separations as electrodes for hosting NH₄⁺ ions reversibly. To address the issues, herein, synthesis of a molybdenum oxide–sulfide composite with titanium oxide atomic layering was prepared to serve as active negative electrode (negatrode). The growth of MoS₂ nanosheet on hydrothermally grown MoO₃ nanosheets was confirmed from the low- and high-resolution imaging. The presence of uniform layer of TiO₂ over MoS₂/MoO₃ electrode was verified through imaging and compositional analysis. Thanks to its distinct nano-architecture and surface atomic layering, the constructed TiO₂/MoS₂/MoO₃ electrode was able to deliver specific capacitance of 624 F/g at a current density of 3 A/g. After 3000 charge–discharge cycles, the electrode’s retention was close to 86% at 5 A/g current density. The present results provide insights into the development of non-metal ion-electrolyte-based energy storage systems.