Amorphous Mo-Ta Oxide Nanotubes for Long-Term Stable Mo Oxide-Based Supercapacitors

With a large-scale usage of portable electric appliances, a high demand for increasingly high-density energy storage devices has emerged. MoO₃ has, in principle, a large potential as a negative electrode material in supercapacitive devices due to high charge densities that can be obtained from its reversible redox reactions. Nevertheless, the extremely poor electrochemical stability of MoO₃ in aqueous electrolytes prevents a practical use in high capacitance devices. In this work, we describe how to overcome this severe stability issue by forming amorphous molybdenum oxide/tantalum oxide nanotubes by anodic oxidation of a Mo-Ta alloy. The presence of a critical amount of Ta oxide (>20 at. %) prevents the electrochemical decay of the MoO₃ phase and thus yields an extremely high stability. Due to the protection provided by tantalum oxide, no capacitance losses are measureable after 10,000 charging/discharging cycles.