NH 4 + Deprotonation at Interfaces Induced Reversible H 3 O + /NH 4 + Co-insertion/Extraction.

Ion insertions always involve electrode-electrolyte interface process, desolvation for instance, which determines the electrochemical kinetics. However, it's still a challenge to achieve fast ion insertion and investigate ion transformation at interface. Herein, the interface deprotonation of NH 4 + and the introduced dissociation of H 2 O molecules to provide sufficient H 3 O + to insert into materials' structure for fast energy storages are revealed. Lewis acidic ion-NH 4 + can, on one hand provide H 3 O + itself via deprotonation, and on the other hand hydrolyze with H 2 O molecules to produce H 3 O + . In situ attenuated total reflection-Fourier transform infrared ray method probed the interface accumulation and deprotonation of NH 4 + , and density functional theory calculations manifested that NH 4 + tend to thermodynamically adsorb on the surface of monoclinic VO 2 , and deprotonate to provide H 3 O + . In addition, the inserted NH 4 + has a positive effect for stabilizing the VO 2 (B) structure. Therefore, high specific capacity (>300 mAh g -1 ) and fast ionic insertion/extraction (<20 s) can be realized in VO 2 (B) anode. This interface derivation proposes a new path for designing proton ion insertion/extraction in mild electrolyte.