Freestanding MoO3−x nanobelt/carbon nanotube films for Li-ion intercalation pseudocapacitors

Molybdenum trioxide (MoO 3 ) is known as a promising pseudocapacitive material, but low conductivity limits its applications. Hydrogenation is demonstrated to increase the conductivity of MoO 3 and hence improve its electrochemical performance. Hydrogenated MoO 3 (MoO 3− x ) shows enhanced conductivity based on, both first principle calculations and single nanobelt measurements. Freestanding MoO 3− x /carbon nanotubes (CNT) composite films have been fabricated and showed much improved electrochemical performance compared to composites of CNT and as-synthesized MoO 3 (MoO 3 /CNT). Electrodes showed a specific capacitance of 337   F/g (based on the mass of MoO 3− x ) and a high volumetric capacitance of 291   F/cm 3 (based on the whole electrode) with excellent rate capability. Also we confirmed that the improved intercalation kinetics and the increased intercalation pseudocapacitance could be attributed to the higher electronic conductivity of MoO 3− x , which results in better and faster intercalations of Li + ions. This electrochemical behavior implies that MoO 3− x can serve as a very good negative electrode with high capacitance at high mass loading levels.