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

A Mo4/3CTz/PANI composite with in situ grown PANI nanosheets forming a wrinkled structure is developed to stabilize interlayer spacing and enhance charge transport. Proton addition via H2SO4 activates pseudocapacitive behavior in both components by modulating Mo valence and improving PANI conductivity. This synergistic modulation lowers the NH4+ adsorption energy barrier and promotes its intercalation, thereby enabling efficient NH4+/H3O+ co‐storage. Abstract The development of aqueous ammonium‐ion batteries (AAIBs) requires electrode materials that combine high NH4+ storage capacity with rapid and reversible ion transport. Herein, a metal‐vacancy MXene/polyaniline (Mo4/3CTz/PANI) composite is reported, in which the pseudocapacitive response is synergistically activated by introducing 0.1 m H2SO4 into 1 m (NH4)2SO4 electrolyte. This proton‐assisted modulation enables rapid and reversible NH4+/H3O+ co‐intercalation, in contrast to the negligible ion insertion observed in the absence of H2SO4. Combined experimental and density‐functional theory (DFT) analyses reveal that proton doping significantly improves the electronic conductivity of PANI and induces a reversible Mo6+/Mo5+ redox transition during cycling, which dynamically modulates the NH4+ adsorption energy (from −4.155 to −4.567 eV), thus facilitating both intercalation and deintercalation of NH4+. 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 MnO2/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. A Mo 4/3 CT z /PANI composite with in situ grown PANI nanosheets forming a wrinkled structure is developed to stabilize interlayer spacing and enhance charge transport. Proton addition via H 2 SO 4 activates pseudocapacitive behavior in both components by modulating Mo valence and improving PANI conductivity. This synergistic modulation lowers the NH 4 + adsorption energy barrier and promotes its intercalation, thereby enabling efficient NH 4 + /H 3 O + co-storage. 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. Advanced Science, Volume 12, Issue 43, November 20, 2025.