Understanding the Effect of Particle Size on Coal Oxidation Reaction Mechanism during Repeated Electrolysis Cycles

Coal electrolysis represents a paradigm shift from conventional high-emission applications by utilizing electrical current to decompose coal’s macromolecular structure into valuable chemical compounds. Despite technological advances, the relationship between particle size distribution and mechanistic pathways remains underexplored. This study systematically investigated particle size effects across three ranges (25–45, 45–75, and 75–106 μm) on charge consumption and structural evolution during repeated electrolysis cycles. Results demonstrated that 25–45 μm particles exhibited the highest charge consumption, indicating superior electrolysis performance. Ultimate analysis revealed increased carbon content and decreased oxygen content postelectrolysis across all sizes. Comprehensive characterization using Brunauer–Emmett–Teller (BET) surface area analysis, scanning electron microscopy (SEM), Raman spectroscopy, X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, and solid-state 13C nuclear magnetic resonance (NMR) provided mechanistic insights into structural transformations. BET and SEM analyses confirmed significant surface modifications including increased surface area, enhanced pore volume, and surface crack development. Raman and XRD revealed increased graphitic character and crystallinity with reduced structural defects. FTIR and NMR spectroscopy demonstrated substantial transformations in aliphatic and aromatic carbon groups. The most pronounced structural changes occurred in smaller particles, establishing 25–45 μm as the optimal particle size range for coal electrolysis applications.