Single cathode material based on a vertically aligned MXene-ZnNi2S4-ZnNi2O4 nanoflake ensemble for multifunctional energy storage applications.

Aqueous energy storage devices are a subject of great interest due to their low cost and safety. Among them, ammonium-ion supercapacitors (AISCs) and zinc-ion and aluminum-ion batteries have attracted attention as next-generation energy storage systems. In this regard, single electrode materials capable of functioning in such varied aqueous energy storage systems are of utmost importance for meeting sustainable energy storage demands. This creates a challenge in designing suitable cathode materials that are stable and provide high electrochemical performance. In this regard, vertically aligned nanostructures can provide an open structure, ample electroactive sites, a large surface area, variable oxidation states, and high conductivity, thereby making them a suitable choice for the aforesaid applications. In this direction, a vertically arranged MXene-ZnNi2S4-ZnNi2O4 nanoflake ensemble grown over a graphite foil (MZNS) is considered a versatile electrode material for multivalent metal ion storage. This electrode exhibits a maximum specific capacitance of 329.1 F g-1 in the AISC. Subsequently, the Zn∥MZNS cell delivers a specific capacity of 139.6 mAh g-1, and the Al∥MZNS configuration achieves a specific capacity of 244 mAh g-1 with a remarkable capacity retention of 90% after 769 cycles. Such significant electrochemical performance achieved by the multifunctional MZNS cathode demonstrates its potential for developing next-generation energy storage systems.