Surface-Induced Desolvation of Hydronium Ion Enables Anatase TiO₂ as an Efficient Anode for Proton Batteries

Hydrogen ion is an attractive charge carrier for energy storage due to its smallest radius. However, hydrogen ions usually exist in the form of hydronium ion (H₃O⁺) because of its high dehydration energy; the choice of electrode materials is thus greatly limited to open frameworks and layered structures with large ionic channels. Here, the desolvation of H₃O⁺ is achieved by using anatase TiO₂ as anodes, enabling the H⁺ intercalation with a strain-free characteristic. Density functional theory calculations show that the desolvation effects are dependent on the facets of anatase TiO₂. Anatase TiO₂ (001) surface, a highly reactive surface, impels the desolvation of H₃O⁺ into H⁺. When coupled with a MnO₂ cathode, the proton battery delivers a high specific energy of 143.2 Wh/kg at an ultrahigh specific power of 47.9 kW/kg. The modulation of the interactions between ions and electrodes opens new perspectives for battery optimizations.