Synergistic Enhancement of Zinc‐Ion Hybrid Capacitors via Redox‐Active Doping and Sulfonated MXene‐Modified Polypyrrole Cathodes

Abstract Polypyrrole (PPy) has emerged as a promising cathode material for zinc‐ion hybrid capacitors (ZIHCs) owing to its facile synthesis, high chemical stability, and reversible doping/dedoping behavior. Redox‐active dopants can provide additional capacity, thereby improving the electrochemical performance of PPy‐based electrodes. Meanwhile, sulfonic acid‐functionalized Ti ₃ C ₂ T _x (S‐Ti ₃ C ₂ T _x ) is introduced as a substrate for PPy. The excellent flexibility and electrical conductivity of S‐Ti ₃ C ₂ T _x help to buffer the volume changes of PPy, enhancing its structural integrity. Moreover, the grafted −SO ₃ H groups on Ti ₃ C ₂ T _x serve as in situ proton reservoirs, maintaining a localized acidic microenvironment near the electrode surface. This feature is beneficial for suppressing the formation of zinc hydroxide sulfate byproducts to a certain extent. Density functional theory calculations reveal that the integration of redox‐active dopants and S‐Ti ₃ C ₂ T _x optimizes the electronic structure, resulting in improved conductivity of the composite electrode. As a result, the ZIHCs employing sodium hydroquinone sulfonate‐doped PPy/S‐Ti ₃ C ₂ T _x as the cathode delivers a high specific capacity of 192.4 mAh g ⁻¹ and an energy density of 153.9 Wh kg ⁻¹ at a scan rate of 2 mV s ⁻¹ . This work offers valuable insights into enhancing the electrochemical performance of conducting polymer‐based electrodes through the synergistic design of redox‐active dopants and functionalized MXene substrates.