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.