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

Abstract

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 ₂O molecules to provide sufficient H ₃O ⁺ to insert into materials′ structure for fast energy storages are revealed. Lewis acidic ion‐NH ₄ ⁺ can, on one hand provide H ₃O ⁺ itself via deprotonation, and on the other hand hydrolyze with H ₂O molecules to produce H ₃O ⁺. 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 ₃O ⁺. 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.