Stable α-MoO3 Electrode with a Widened Electrochemical Potential Window for Aqueous Electrochemical Capacitors

α-MoO 3 is a promising electrode material for electrocapacitive energy storage. However, it has poor stability in aqueous electrolytes due to dissolution in water. Here, we demonstrate that an α-MoO 3 electrode prepared using the electrochemical deposition method is stable over a wide potential window of 2.2 V in a neutral aqueous electrolyte. The improved stability of the α-MoO 3 electrode in water is attributable to enhanced electron conductivity, which minimizes the polarization-induced structural collapse, and the dense microstructure of the α-MoO 3 film electrode. The widened potential window is related to the electrocatalytic inactivity of the α-MoO 3 toward water electrolysis and the high overpotentials of the neutral electrolyte toward H 2 and O 2 evolution reactions. A symmetric supercapacitor cell fabricated with the electrochemically deposited α-MoO 3 electrode delivers a specific energy as high as ∼22 Wh/kg at a specific power of ∼301 W/kg. This work demonstrates that the electrochemical deposition method is a viable approach to fabricating α-MoO 3 electrodes for aqueous electrochemical energy storage.