Macromolecular model-based mechanistic insights into the molten salt electrolysis graphitization of woody biochar

Molten salt electrolysis graphitization provides an efficient pathway for the green transformation of biomass waste into high-crystallinity graphitized carbon. However, the intrinsic correlation between heteroatom removal and aromatic carbon skeleton rearrangement during electrochemical graphitization remains poorly understood at the molecular scale. In this study, woody biochar (WB) was used as a precursor to achieve its graphitization via molten salt electrolysis. The carbon framework reconstruction and heteroatom structure evolution before and after electrolysis were systematically analyzed. Using Python to assist in identifying transmission electron microscopy (TEM) lattice fringes, quantitatively determining the scale and distribution characteristics of aromatic layers. Combining X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and elemental analysis, the transformation behavior of heteroatom functional groups was further analyzed. Given this, representative molecular models of WB and its electrolysis products (C₂₁₇H₁₈₀N₂O₄₈S and C₂₃₂H₁₇₈O₁₀) were constructed for the first time to elucidate the mechanism of electrochemical graphitization transformation of biomass carbon. The results indicate that cathode polarization may promote the removal of heteroatom functional groups, reduce their disturbance to the ordering of the carbon skeleton, and facilitate the expansion and ordered stacking of aromatic units. The electric field may promote the activation and removal of heteroatoms by enhancing particle diffusion and local interactions within the molten salt system and by regulating the local electronic structure in the vicinity of the heteroatoms, thereby potentially driving the ordered rearrangement of the aromatic carbon skeleton. This study elucidates the mechanism of molten salt electrolysis graphitization of woody biochar at the molecular scale.