A long-term stable aqueous aluminum battery electrode based on one-dimensional molybdenum-tantalum oxide nanotube...

Aluminum ion aqueous batteries (AIBs) are among the most promising candidates for high energy density devices due to the multivalent redox processes associated with Al³⁺ ion intercalation. However, only a few stable AIB electrode materials have been reported so far. MoO₃ is a very promising electrode material due to its octahedral layered crystal structure which can accommodate multivalent cation by intercalation. However, the poor electrochemical stability of MoO₃ and the sluggish intercalation kinetics of Al³⁺ ion in Mo oxides electrodes limit its practical application. In this work, we propose a strategy to overcome such shortcomings of MoO₃ by fabricating electrodes composed of self-ordered one-dimensional (1D) MoTaO_x nanotubes synthesized via electrochemical anodization of Mo-Ta alloy substrates. We show that this approach allows for direct incorporation of Ta in the Mo oxide nanotubes. The resulting MoTaO_x nanotubes, composed of octahedral MoO₃ and rhombohedral Mo₂Ta₂O₁₁ phases, exhibit remarkable electrochemical stability and Al-ion storage properties in aqueous electrolytes that are superior to that of pristine Mo oxide or other most efficient electrode materials reported to date. Such MoTaO_x nanotube-based electrodes can achieve a specific capacity of 1180 mA h cm^-3 (337 mA h g^-1, 141 μA h cm^-2) at 1.25 A cm^-3 (∼0.35 A g^-1, 0.15 mA cm^-2). More importantly, the capacity retention of such nanotube array electrodes remains above 83% of the initial capacity after 3000 cycles.