Composition-Dependent Pseudocapacitive Behavior of MoO3–V2O5 Composite Thin Films in an Aprotic Electrolyte

Abstract Transition-metal oxide electrodes offer high theoretical capacitance for electrochemical energy storage. Yet, their practical application is fundamentally constrained by chemical instability in aqueous electrolytes, where high-valence metal centers undergo rapid hydrolytic dissolution. Here, we prepared MoO3–V2O5 composite thin films across different compositions. Structural characterization reveals a composition-dependent evolution from orthorhombic phases in the pure oxides to the coexistence of both the metal oxides in intermediate compositions. We employ an aprotic organic electrolyte (LiBF4 in propylene carbonate), which suppresses hydrolytic degradation pathways and enables stable operation over an expanded electrochemical window. Under these conditions, V2O5-rich thin-film electrodes exhibit pronounced pseudocapacitive behavior, delivering a specific capacitance of 25 F g–1 and capacitance retention of 89.7% at a current density of 1 A g–1 after 10,000 cycles along with a columbic efficiency of 98.4% in a symmetric device configuration. This work demonstrates a synergistic interaction between MoO3 and V2O5 phases, leading to enhanced charge storage behavior compared to the individual oxides.