Fe-assisted electrochemical graphitization and tubulation of woody biochar for energy storage: Multiscale mechanistic investigation and structural regulation

Molten salt electrolytic graphitization is an efficient and green pathway for the electrochemical conversion of biomass resources into high-value-added graphitized carbon. However, this process exhibits poor reaction kinetics and difficult structural modulation. In this paper, we report the process and mechanism of graphitization and tubulation of Fe-assisted molten salt CaCl₂ at low temperatures. Experimental results showed that Fe assistance significantly enhanced the graphitization rate, shortened the reaction time, and reduced the energy consumption. Fe also induced the evolution of the product morphology from a sheet structure to a tube–sheet hybrid structure. Experimental and simulated multiscale analyses revealed the kinetics of the Fe-promoted deoxygenation reaction and its pathway, as well as the mechanism of Fe-regulated directed growth of carbon rings to construct tube–sheet composite structures. The resulting graphitized carbon exhibited a specific capacity of 336.37 mAh·g⁻¹ (1 C) when used as a negative electrode for lithium-ion batteries. This electrochemically coupled Fe-catalyzed synergistic strategy provides a rational pathway for the high-value utilization of low-quality carbon-containing solid waste (e.g., woody biochar).