Valorization of pistachio shell biomass into potassium- and fluorine-doped porous carbon through pyrolysis for supercapacitor applications

Abstract

In this study, pistachio shell biomass was valorized into a high-performance porous carbon material through controlled pyrolysis followed by KOH chemical activation and subsequent potassium/fluorine (K/F) modification. The influence of dual K/F doping on the structural evolution, surface chemistry, and electrochemical behavior of pistachio shell-derived activated carbon (PSAC) was systematically investigated. XRD and Raman analyses revealed partial graphitization accompanied by increased defect density after K/F incorporation, as evidenced by the appearance of a broadened (002) diffraction peak at similar to 26 degrees in the XRD pattern and an increased Raman ID/IG ratio compared to pristine PSAC, while FTIR and XPS confirmed significant modification of surface functional groups and successful introduction of K, F, and oxygen-containing species. Textural characterization demonstrated that K/F doping induced pore widening and the development of a hierarchical pore structure, with a decrease in BET surface area from 483 to 383 m(2) g(-1) accompanied by a substantial increase in average pore radius from 1.65 to 3.94 nm. Electron microscopy analyses showed that K/F modification resulted in rougher, more heterogeneous surfaces and a more uniform layered morphology at the nanoscale. Electrochemical evaluation in aqueous electrolytes revealed that K/F-doped PSAC exhibited significantly enhanced charge-transfer kinetics, lower interfacial resistance, and improved ion diffusion compared to pristine PSAC. The modified electrode delivered a high specific capacitance of 188 F g(-1) at 0.5 A g(-1) and maintained excellent rate capability and cycling stability, retaining 88.2 % of its initial capacitance after 10 000 charge-discharge cycles. Kinetic analysis indicated that K/F doping strengthened diffusion-controlled charge storage without shifting the mechanism toward purely capacitive behavior. The results demonstrate that dual K/F modification effectively tailors the pyrolysis-derived carbon framework and surface chemistry, offering valuable insights into the design of biomass-derived carbons for advanced electrochemical energy storage applications.