MSc.Thesis Defense: Berfu Akgül
ELECTROCHEMICAL ANALYSIS OF VANADIUM DOPED ZINC SULFIDE
Berfu Akgül
Materials Science and Nano Engineering, MSc. Thesis, 2025
Thesis Jury
Prof. Dr. Emre Erdem,
Assoc. Prof. Dr. Feray Bakan Mısırlıoğlu
Assoc. Prof. Dr. Hülya Biçer
Date & Time: 21st July, 2025 – 5:00 PM
Place: FENS G032
Zoom Link: https://sabanciuniv.
Keywords : Cyclic voltammetry, defect engineering, electrochemical impedance, supercapacitor, vanadium doping, zinc sulfide
Abstract
This thesis investigates the structural, optical, and electrochemical properties of vanadium-doped zinc sulfide (ZnS:V) nanoparticles synthesized via precipitation synthesis for application as electrode materials in supercapacitors. ZnS, a wide bandgap semiconductor with limited intrinsic conductivity and capacitance, was doped with varying concentrations of vanadium (0.3–1%) to enhance its electrochemical performance. X-ray diffraction (XRD) analysis confirmed the cubic sphalerite structure with slight lattice distortions induced by vanadium incorporation, while UV–Vis spectroscopy revealed band gap modulation due to sp–d exchange interactions and the Burstein–Moss effect. Scanning transmission electron microscopy (STEM) demonstrated well-dispersed nanoparticles with spherical morphology, and electron paramagnetic resonance (EPR) spectroscopy detected characteristic signals indicating successful doping and defect formation. Photoluminescence (PL) analysis showed defect-related emissions, supporting the presence of intrinsic and dopant-induced states influencing carrier recombination. Electrochemical characterization was performed using cyclic voltammetry (CV), potentiostatic electrochemical impedance spectroscopy (PEIS), and galvanostatic charge–discharge (GCPL) techniques. CV and Dunn analysis revealed a substantial increase in both capacitive and diffusive contributions upon vanadium doping, attributed to enhanced redox activity and improved ion diffusion. PEIS results demonstrated a marked reduction in charge-transfer resistance and Warburg impedance in doped samples, indicating improved electronic conductivity and facile ion transport. Overall, vanadium doping significantly enhanced the specific capacitance, rate capability, and charge storage mechanisms of ZnS electrodes. This study highlights the potential of defect engineering and vanadium doping as effective strategies to enhance the electrochemical performance of ZnS-based electrodes for high-performance supercapacitor applications.