Free-Standing α-MoO3/Ti3C2 MXene Hybrid Electrode in Water-in-Salt Electrolytes

Abstract

While transition-metal oxides such as α-MoO3 provide high capacity, their use is limited by modest electronic conductivity and electrochemical instability in aqueous electrolytes. Two-dimensional (2D) MXenes, offer metallic conductivity, but their capacitance is limited in aqueous electrolytes. Insertion of partially solvated cations into Ti3C2 MXene from lithium-based water-in-salt (WIS) electrolytes enables charge storage at positive potentials, allowing a wider potential window and higher capacitance. Herein, we demonstrate that α-MoO3/Ti3C2 hybrids combine the high capacity of α-MoO3 and conductivity of Ti3C2 in WIS (19.8 m LiCl) electrolyte in a wide 1.8 V voltage window. Cyclic voltammograms reveal multiple redox peaks from α-MoO3 in addition to the well-separated peaks of Ti3C2 in the hybrid electrode. This leads to a higher specific charge and a higher rate capability compared to a carbon and binder containing α-MoO3 electrode. These results demonstrate that the addition of MXene to less conductive oxides eliminates the need for conductive carbon additives and binders, leads to a larger amount of charge stored, and increases redox capacity at higher rates. In addition, MXene encapsulated α-MoO3 showed improved electrochemical stability, which was attributed to the suppressed dissolution of α-MoO3. The work suggests that oxide/MXene hybrids are promising for energy storage.