Pyrolysis-derived phosphorus-doped porous carbon from chestnut shell waste for supercapacitor and hydrogen generation applications

Abstract

This work reports a sustainable route for converting chestnut shell waste into a multifunctional porous carbon material through pyrolysis-assisted chemical activation and subsequent phosphorus functionalization, targeting applications in electrochemical energy storage and catalytic hydrogen generation. Chestnut shells were first transformed into activated carbon via KOH-assisted pyrolysis, followed by phosphoric acid treatment to introduce phosphorus-containing surface functionalities, yielding P-doped CSKOH. Comprehensive physicochemical characterization (BET, SEM, EDS, FTIR, Raman, and XPS) confirmed the successful development of a mesoporous carbon framework enriched with structural defects and oxygen-phosphorus surface groups. The specific surface areas of CSKOH and P-doped CSKOH were measured as 524 m2 g-1 and 331 m2 g-1 , respectively, with average pore diameters in the mesoporous range (7.61-8.89 nm), which are favorable for electrolyte ion transport and surface redox activity. When evaluated as an electrode material in 1 M H2SO4, the P-doped carbon exhibited a high specific capacitance of 244 F g-1 at 0.8 A g-1 and retained 95.2% of its initial capacitance after 1000 charge-discharge cycles, demonstrating excellent electrochemical stability and durability. These results highlight the effectiveness of the pyrolysis-derived hierarchical porous structure and phosphorus-induced surface chemistry in enhancing charge storage performance. Beyond energy storage, the same material was further explored as a metal-free catalyst for hydrogen generation via NaBH4 methanolysis. The P-doped carbon achieved a high hydrogen generation rate of 6835 mL min-1 g-1 at 30 degrees C, with complete NaBH4 conversion within 7 min. Kinetic analysis based on the Arrhenius equation yielded an activation energy of 37.27 kJ mol-1 , indicating a kinetically favorable reaction pathway. Although a gradual decrease in activity was observed upon reuse, the catalyst maintained notable performance even after five consecutive cycles. This study demonstrates that pyrolysisderived, phosphorus-doped biomass carbon can serve as a cost-effective and environmentally benign multifunctional material, offering strong potential for integrated applications in supercapacitor energy storage and hydrogen production technologies.