Engineering Defects In Hexagonal Boron Nitride To Advance Electrochemical Energy Storage In Supercapacitor Devices

Hexagonal boron nitride (h-BN), a wide-bandgap two-dimensional material, has recently garnered attention for energy storage applications due to its chemical inertness and thermal stability. However, its intrinsically low electrical conductivity and limited surface reactivity hinder its electrochemical performance in supercapacitor devices. This thesis explores a comprehensive defect-engineering approach to overcome these limitations by inducing structural and chemical modifications in h-BN through high-temperature annealing, high-energy ball milling, and transition metal doping, specifically with manganese (Mn). Systematic structural, optical, and electronic characterizations were conducted using X-ray diffraction (XRD), Raman, photoluminescence (PL), and electron paramagnetic resonance (EPR) spectroscopy. Results revealed that controlled nitrogen vacancy formation and carbon substitution enhanced defect density, leading to significant improvements in charge transport and pseudocapacitive behavior. Mn doping was successfully achieved through a multi-step synthesis involving mechanochemical activation, chemical doping, and thermal annealing. EPR confirmed the substitutional incorporation of Mn²⁺, and PL spectra showed defect-mediated blue emissions with increasing Mn content. Additionally, Tauc analysis revealed bandgap narrowing, indicating improved electronic conductivity. The investigation was extended to Mn-doped ZnO and Mn:ZnO-hBN nanocomposites, revealing a synergistic interaction that further enhanced electrochemical properties. Electrochemical tests conducted in symmetric two-electrode supercapacitor configurations demonstrated substantial performance improvements. Ball-milled nitrogen-deficient h-BN (NHBNbm) showed a 3× enhancement in specific capacitance, reaching ~615 F/g at 10 mV/s. Mn-doped h-BN samples heat-treated at 800 °C delivered the highest stability and specific capacitance of ~566 F/g at 1 A/g, with >92% capacitance retention over 5000 cycles. The Mn:ZnO-hBN nanocomposites exhibited the best overall performance, achieving a maximum specific capacitance of ~795 F/g, energy density of 110 Wh/kg, and power density of 41.8 kW/kg. These findings highlight the critical role of defect engineering and composite design in activating h-BN as a high-performance electrode material, paving the way for its practical implementation in next-generation supercapacitor