Tailoring Molecular Structure of Coal Liquefaction Residue via Pyrolysis-Mechanochemistry: Structure–Activity Relationship Based on Multi-Scale Characterization and Density Functional Theory Calculations

The high-value utilization of coal liquefaction residue (CLR) is fundamentally constrained by the contradiction between its excessively condensed carbon framework and the scarcity of intrinsic active sites. To address this issue, an innovative pyrolysis-mechanochemical synergistic modification strategy was proposed. In this strategy, a weak-bond-rich aromatic framework was first constructed through demineralization-pyrolysis treatment, followed by mechanochemical activation via high-energy ball milling. By integrating multiscale characterization techniques (FT-IR, XPS, and 13 C NMR) with density functional theory (DFT) calculations, the molecular-level regulation mechanism of the synergistic process was systematically elucidated. The results demonstrated that the core of the synergistic effect lies in the mechanochemically induced “fracture-reconstruction” of the pyrolyzed carbon framework, driving the synchronous evolution of the carbon structure along two pathways. First, the cleavage of aliphatic bridge bonds and the dissociation of aromatic clusters generated abundant defects and edge-active sites. Second, the newly formed carbon dangling bonds underwent in situ oxidation, resulting in a significant increase in carbonyl functional groups. DFT calculations quantitatively revealed that oxygen-containing functional groups, aromatic edges, and defect sites act as nucleophilic reactive regions, while bond cleavage follows a distinct energy hierarchy. Process–structure–activity correlation experiments confirmed that the modified carbon anode achieved a current density of 23 mA cm –2 at 1.0 V RHE, with an ultralow charge transfer resistance ( R ct ) of 0.72 Ω. This study establishes a theoretical framework for the rational design and controllable preparation of CLR-derived functional carbon materials.