Electrochemical boosting of kaolin-based electrodes through potassium/ fluorine co-doping nanoarchitectonics for advanced supercapacitors

Abstract

The limited electrochemical activity and low intrinsic conductivity of natural clay minerals restrict their application as electrode materials for energy storage. This study examines whether targeted surface and defect engineering, rather than surface area enlargement, effectively enhances the electrochemical performance of kaolin-based electrodes for supercapacitors. Potassium/fluorine (K/F) co-doped kaolin is synthesized via a mild hydrothermal-assisted activation route and evaluated in acidic (1 M H2SO4) and alkaline (1 M KOH) electrolytes. Structural and surface analyses confirm that K/F treatment induces controlled lattice disorder, partial amorphization, and defect-rich surface chemistry while preserving the kaolinite phase and without increasing surface area. Electrochemical behavior is investigated using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), electrochemical impedance spectroscopy (EIS), and both three-and two-electrode configurations. The K/F-doped kaolin shows significantly enhanced capacitive performance, delivering specific capacitances of 362.03 F g-1 (CV) and 407.42 F g-1 (GCD) in acidic electrolyte, along with good cycling stability (82% retention after 5000 cycles). Acidic electrolyte promotes dominant pseudocapacitive charge storage with an energy density of 12.05 Wh kg-1, whereas alkaline electrolyte favors electric double-layer capacitance and provides a high-power density of 2050.32 W kg-1. These findings demonstrate that K/F-induced defect engineering effectively tailors the electrolyte-dependent electrochemical response of kaolin-based electrodes for supercapacitor applications.