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Abstract

Pore structure engineering remains a critical challenge in the development of high-performance biocarbon materials, particularly for supercapacitor applications where an optimal balance of high specific surface area (SSA), tunable pore size distribution (PSD), and interconnected micro–mesoporous network is essential for effective ion adsorption and diffusion. Conventional activation methods, such as KOH or H₃PO₄ treatment, often suffer from poor control over PSD, high energy consumption, excessive chemical usage, and reliance on trial-and-error experimental design, limiting their tunability, scalability, and sustainability. This thesis introduces a systematic binary molten salt carbonization strategy to enhance and control the pore structure of biocarbon derived from chitin, an underutilized biomass waste. A novel ZnCl₂–CaCl₂ binary molten salt system is developed to achieve biocarbon with a hierarchical porous structure, high SSA (1671 m² g⁻¹), and rich heteroatom retention at 800 °C. These two salts show synergistic effects on enhancing SSA but play distinctively different roles in facilitating micropore and mesopore formation. Subsequently, a general strategy for binary molten salt selection is developed based on the understanding of salt accessibility and reactivity. CuCl₂ and ZnCl₂ serve as suitable primary salts and combined with various secondary salts such as CoCl₂ and CaCl₂ to fine-tune micropore-mesopore structure under different operating conditions. Notably, a ZnCl₂–CoCl₂ system achieved ultrahigh SSA (~2500 m² g⁻¹) at only 500 °C, and further guidance on secondary salt selection for pore tuning in ZnCl₂-based salt systems is proposed for low-temperature activation based on the mechanistic understanding of the roles of salt diffusion, transition and interactions with chitin for primary and secondary salts in controlling pore creation and development. Finally, the electrochemical characterization of fabricated biocarbon electrodes confirm excellent supercapacitor performance, including high specific capacitance, rate capability and long-term cyclic stability. Multivariable regression further quantitatively clarifies the contributions of micropore volume and mesopore fraction to specific capacitance and rate capability. Overall, this work offers a systematic and guided approach for tunable pore structure engineering in biocarbon, advancing the design of high-performance biocarbon for supercapacitors and adsorption-related applications (e.g., CO₂ capture). It marks a step forward from conventional and empirical fabrication methods towards organized and mechanism-driven process and material design.