Activation of the Pseudocapacitive Behavior of MXene/PANI for High‐Performance Ammonium‐Ion Batteries

Abstract The development of aqueous ammonium‐ion batteries (AAIBs) requires electrode materials that combine high NH ₄ ⁺ storage capacity with rapid and reversible ion transport. Herein, a metal‐vacancy MXene/polyaniline (Mo _4/3 CT _z /PANI) composite is reported, in which the pseudocapacitive response is synergistically activated by introducing 0.1 m H ₂ SO ₄ into 1 m (NH ₄ ) ₂ SO ₄ electrolyte. This proton‐assisted modulation enables rapid and reversible NH ₄ ⁺ /H ₃ O ⁺ co‐intercalation, in contrast to the negligible ion insertion observed in the absence of H ₂ SO ₄ . Combined experimental and density‐functional theory (DFT) analyses reveal that proton doping significantly improves the electronic conductivity of PANI and induces a reversible Mo ⁶⁺ /Mo ⁵⁺ redox transition during cycling, which dynamically modulates the NH ₄ ⁺ adsorption energy (from −4.155 to −4.567 eV), thus facilitating both intercalation and deintercalation of NH ₄ ⁺ . As a result, the composite achieves a high specific capacity of 245 mAh g ⁻¹ at 0.1 A g ⁻¹ , with excellent capacity retention of 84.2% after 11,000 cycles at 1.0 A g ⁻¹ . Furthermore, the MnO ₂ /CNTs||M:P = 5:1 full cell delivers a high energy density of 81.6 Wh kg ⁻¹ and a power density of 16 000 W kg ⁻¹ . This work highlights a promising strategy for advancing MXene‐based electrodes via proton‐enhanced ion storage mechanisms, paving the way for high‐performance AAIBs.