Pyrolysis Enzymolysis-Treated Pomelo Peel: Porous Carbon Materials with Fe−Nx Sites for High-Performance Supercapacitor and Efficient Oxygen Reduction Applications

Abstract

This paper proposes a different strategy for deriving carbon materials from biomass, abandoning traditional strong corrosive activators and using a top−down approach with a mild green enzyme targeted to degrade the pectin matrix in the inner layer of pomelo peel cotton wool, inducing a large number of nanopores on its surface. Meanwhile, the additional hydrophilic groups produced via an enzymatic treatment can be used to effectively anchor the metallic iron atoms and prepare porous carbon with uniformly dispersed Fe−Nx structures, in this case optimizing sample PPE−FeNPC−900’s specific surface area by up to 1435 m2 g−1. PPE−FeNPC−900 is used as the electrode material in a 6 M KOH electrolyte; it manifests a decent specific capacitance of 400 F g−1. The assembled symmetrical supercapacitor exhibits a high energy density of 12.8 Wh kg−1 at a 300 W kg−1 power density and excellent cycle stability. As a catalyst, it also exhibits a half−wave potential of 0.850 V (vs. RHE) and a diffusion-limited current of 5.79 mA cm−2 at 0.3 V (vs. RHE). It has a higher electron transfer number and a lower hydrogen peroxide yield compared to commercial Pt/C catalysts. The green, simple, and efficient strategy designed in this study converts abundant, low−cost waste biomass into high-value multifunctional carbon materials, which are critical for achieving multifunctional applications.