EPR-Guided Defect Engineerıng Of Fe-Doped Zno, Cigarette-Butt–Derived Activated Carbon, And Mxene For Supercapacitors

In this work, we aim to synthesize new materials that achieve high energy density and power density, thereby enhancing the electrochemical performance of supercapacitors. Herein, the focus is given on synthesizing three different materials that will offer EDLC, pseudocapacitive, and hybrid charge storage mechanisms to produce hybrid supercapacitors. Thus, three distinct materials, which are Fe-doped ZnO nanoparticles, Ti₃C₂Tₓ MXenes, and activated carbons derived from cigarette butts, were synthesized, and paramagnetic defect centers were investigated using EPR spectroscopy. The effect of paramagnetic defect centers on electrochemical performance was analyzed. Firstly, Fe-doped ZnO was synthesized via solid-state reaction to investigate the effect of calcination temperature and dopant concentration. Secondly, Ti₃C₂Tₓ MXene were synthesized by selectively etching Ti₃AlC₂ in either concentrated HF, HF/HCl and HF/H2SO4 mixtures, followed by delamination using LiCl. Finally, waste cigarette-butt were transformed into hierarchically porous carbons through inert-atmosphere carbonization and subsequent KOH activation. Comprehensive characterization, including XRD, Raman spectroscopy, SEM, TGA analysis, BET analysis, PL spectroscopy, and EPR spectroscopy. Symmetric and asymmetric supercapacitors were assembled using two-electrode setup. Electrochemical analyses showed that among all samples, The supercapacitor assembly designed with ball-milled sample oppose to vactivated carbon derived by cigarette-butts exhibits the highest performance, reaching 416 F/g, 74 Wh/kg, and 1123 W/kg, surpassing every other design tested under the same conditions. This improvement is attributable to the ball-milling process, as evidenced by the superior results of the ball-milled sample compared to the undoped samples. In symmetric supercapacitors, ZnO:Fe3 delivered the best results (323 F/g, 58 Wh/kg, 1,049 W/kg). Our findings highlight a sustainable pathway for converting waste into high-performance energy storage