Toward Superior Electrochemical Capacitance with Hierarchically Nanostructured Polypyrrole/MXene Hybrid Hydrogel...

Although the Ti₃C₂ MXene has demonstrated exceptional promise for supercapacitor applications, its practical implementation is limited by its inherent tendency of undergoing restacking and oxidation. Herein, we propose a facile self-assembly strategy of in situ polymerization to construct lignosulfonate (LS)-modified polypyrrole (PPy)/MXene hybrid hydrogels with a hierarchical porous structure. The formed PPy nanoparticles and coating layer effectively prevent MXene restacking and oxidation, while enhancing electrical conductivity and electrochemical activity. Furthermore, LS contributes redox-active quinone groups, further promoting electron and proton storage and exchange. The hierarchical heterostructure provides continuous ion-diffusion pathways and exposes abundant electroactive sites, yielding a remarkable specific capacitance of 663.7 F g^-1 at 0.2 A g^-1 with 81.2% capacitance retention and 95.3% Coulombic efficiency after 5000 cycles at 2 A g^-1. Assembled solid-state symmetric supercapacitors achieve an exceptional energy density of 29.3 W h kg^-1 at 200 W kg^-1 and maintain 12.4 W h kg^-1 at an ultrahigh power density of 3200 W kg^-1, alongside fairly good cycling stability (87.6% capacitance retention) and a Coulombic efficiency of 94.1% over 5000 cycles. These results highlight the multifunctionality of the LS component within the hybrid hydrogelssimultaneously stabilizing the structure, improving electrical conductivity, generating cross-links, and contributing toward pseudocapacitanceestablishing LS-modified PPy/MXene hybrid hydrogels as high-performance electrode materials for advanced supercapacitor applications.