Constructing lignin-derived hierarchical porous carbon/manganese dioxide composites with robust interfacial bonding for boosting supercapacitive performances

Carbon/transition metal oxide composites hold significant promise for energy storage applications; however, achieving precise control over the carbon structure to enhance the electrochemical activity of metal oxides remains a challenge. In this work, we utilized low-cost enzymatic lignin as a carbon source and harnessed the synergistic effects of magnesium oxide templates and potassium acetate activator to synthesize a lignin-derived hierarchical porous carbon (HPLC) characterized by a high specific surface area of 1704 ± 36 m²/g, well-ordered nanosheet structures, and hierarchical porosity. The comparative analysis demonstrated that HPLC exhibited superior pore anchoring and enhanced interfacial Mn-O-C bonding interactions with manganese dioxide compared to mesoporous carbon synthesized via magnesium oxide templating and microporous carbon derived from potassium acetate activation. This unique architecture significantly boosted the charge storage capacity of manganese dioxide. The composite showed remarkable electrochemical performance, achieving a specific capacitance of up to 567 F/g at a current density of 0.5 A/g, while also demonstrating excellent rate capability. An asymmetric capacitor constructed with the composite electrode delivered a high energy density of 47.22 Wh/kg and maintained a capacity retention of 85.2 % after 12,000 cycles at 2.0 A/g, illustrating its outstanding cycling stability. Analysis of the energy storage mechanism revealed that the capacity of this material was predominantly attributed to redox reactions involving manganese species induced by potassium ion insertion and extraction, as well as the double-layer capacitance arising from the adsorption and desorption of potassium ions. This work elucidates the crucial influence of carbon structure on the loading of metal oxides, providing a novel strategy for tuning carbon carrier structures aimed at developing high-performance carbon/metal composites.