High‐Performance Aqueous Supercapacitors Based on Biomass‐Derived Multiheteroatom Self‐Doped Porous Carbon Membranes

Porous carbons derived from widely accessible, renewable, and low‐cost biomass are being extensively pursued as biocompatible electrode materials for next‐generation supercapacitors (SCs), but their practical application is being largely restricted by insufficient performance related to their powdery status. Herein, a porous carbon membrane (denoted as lettuce‐derived carbon membrane [LCM]) is developed by direct and controllable carbonization of biomass lettuce. By taking the advantages of the inherent microstructure and composition of the lettuce, the as‐fabricated LCM electrode is endowed with a large specific surface area, interconnected hierarchical pores, and multiheteroatom (N, P, and S) doping. The benefits originating from the structure synergy provide this LCM electrode excellent electrochemical performance in an aqueous symmetric SC, exhibiting a high specific capacitance of 213.4 F g−1 at 0.2 A g−1, outstanding rate capability (78.6% capacitance retention at 10 A g−1), and superior cycling stability (96.9% capacitance retention after 100 000 cycles at 5 A g−1) and unit Coulombic efficiency. Notably, the LCM‐based SC delivers the highest energy density of 7.41 Wh kg−1 with a power density of 50.4 W kg−1 at 0.2 A g−1. This device‐compatible porous carbon membrane can be applied to other advanced energy‐storage and conversion devices with a high electrochemical performance.