Development of modified nanocatalysts for photo/electrochemical water splitting

: In this thesis, the synthesis, structural evolution, and performance of graphitic carbon nitride (g-C₃N₄, GCN) and its derivative nanohybrids were systematically investigated for photoelectrochemical water splitting aimed at green hydrogen production. Graphitic carbon nitride, characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR), exhibited complete condensation at approximately 574 °C through the multistep thermal polymerization of melamine via melam, melem, and melon intermediates. Under controlled polymerization conditions, ultrathin nanosheets were ultimately obtained, enabling the yellow GCN to achieve a large surface area (343.6 m² g⁻¹), small particle size (61.8 nm), and high photoelectrochemical efficiencies (ηSTH = 1.59%; ηABPE = 2.14%; ηIPCE = 4.10%). Supramolecular precursors derived from the melamine–barbituric acid–cyanuric acid complex produced porous morphologies with low charge transfer resistance (26.1 Ω) and improved hydrogen evolution kinetics (Tafel slope = 56.2 mV dec⁻¹, Faradaic efficiency = 76.2%). Moreover, GCN nanosheets hybridized with 15% copper-substituted M-type hexaferrite (CuFe₁₂O₁₉, MCF) demonstrated superior performance, with reduced charge transfer resistance (15.25 Ω), high stability (>96%), and hydrogen generation rates up to 0.793 mmol cm⁻² h⁻¹. In addition, a 5% ST/SB nanohybrid synthesized via solvothermal treatment followed by ball milling achieved a thermoelectric figure of merit of zT > 1.1, while also exhibiting dual electrocatalytic functionality with a Faradaic efficiency of 86% and a hydrogen production rate of 0.263 mmol cm⁻² h⁻¹. These findings clearly demonstrate that structural adaptation, supramolecular self-assembly, hybridization, and thermoelectric integration act synergistically to enable efficient water splitting for sustainable hydrogen generation.