Oxygen Vacancies Boosted Hydronium Intercalation: A Paradigm Shift in Aluminum-Based Batteries

In aqueous aluminum-ion batteries (AAIBs), the insertion/extraction chemistry of Al³⁺ often leads to poor kinetics, whereas the rapid diffusion kinetics of hydronium ions (H₃O⁺) may offer the solution. However, the presence of considerable Al³⁺ in the electrolyte hinders the insertion reaction of H₃O⁺. Herein, we report how oxygen-deficient α-MoO₃ nanosheets unlock selective H₃O⁺ insertion in a mild aluminum-ion electrolyte. The abundant oxygen defects impede the insertion of Al³⁺ due to excessively strong adsorption, while allowing H₃O⁺ to be inserted/diffused through the Grotthuss proton conduction mechanism. This research advances our understanding of the mechanism behind selective H₃O⁺ insertion in mild electrolytes.