pH-Modulated Upcycling of Black Liquor into N/O Co-Doped Hierarchical Porous Carbon via Green Templating-Activation Synergy for High-Performance Supercapacitors

Under the global acceleration of carbon neutrality initiatives, the green valorization of industrial waste has emerged as a critical pathway for establishing sustainable manufacturing systems. This study addresses the challenges of inefficient component regulation and restricted pore development in activated carbon derived from pulping black liquor (BL). We propose an innovative activation strategy utilizing magnesium basic carbonate (MBC) as a dual-functional template-activator. By integrating evaporation-induced self-assembly (EISA) with pH gradient fractionation technology, BL is converted into high-performance nitrogen-doped porous activated carbon. A hierarchical regulation system was established to synthesize three lignin-based activated carbons: alkaline, neutral, and acidic. Characterization reveals that AcidBLAC@MBC@N exhibits a unique lamellar porous architecture with a synergistic micro-mesoporous network (mesopore 78%). The optimized material demonstrates exceptional electrochemical performance: a specific capacitance of 305 F g⁻¹ at 0.5 A g⁻¹ and 98% capacitance retention after 10,000 cycles. This work circumvents energy-intensive pre-carbonization (> 800°C) and complex component separation steps in conventional processes. This strategy establishes an eco-efficient paradigm for black liquor valorization, offering a scalable solution for transforming industrial waste into advanced energy storage materials. The design principles may be extended to other biomass-derived systems, aligning with circular economy and carbon neutrality goals.