Nitrogen-Doped Carbon Aerogels Derived from Zn-MOF/Alginate Composites for Dual-Function CO2 Adsorption and Supercapacitors

Carbon aerogels are emerging as promising functional materials; however, their application in adsorption and energy storage is hindered by the inherently low density of active sites. Herein, ZIF-8/N-doped alginate-derived carbon aerogels (ZSCA) were synthesized via in situ growth of ZIF-8 on freeze-dried alginate aerogel precursors and subsequent treatment of pyrolysis and chemical activation for high-performance CO2 capture and supercapacitor applications. In this strategy, ZIF-8 served as a structural template, alginate provided a biomass-derived carbon source, polyethylenimine (PEI) acted as a nitrogen dopant and a costructure director, and potassium citrate functioned as the activating agent. The optimized ZSCA-550-1 (pyrolyzed at 550 °C with an activator-to-precursor mass ratio of 1:1) showed a high specific surface area of 811.34 m2/g, a micropore volume of 0.31 cm3/g, and a nitrogen content of 8.77 wt %. At 273.15 and 298.15 K (1 bar), ZSCA-550-1 achieved excellent CO2 adsorption capacities of 5.96 and 4.40 mmol/g, respectively, outperforming both SA-550-1 (2.79 mmol/g) and ZPC-550-1 (3.20 mmol/g). It also showed high CO2/N2 selectivity (35.0) and retained 94% capacity after 10 adsorption–desorption cycles. As a supercapacitor electrode, ZSCA-650-1 delivered 214 F/g at 1 A/g, with 88.6% capacitance retention over 5000 charge–discharge cycles at 10 A/g. This study introduces a sustainable strategy for the design and engineering of biomass-derived carbon aerogels with dual functionality in CO2 capture and electrochemical energy storage.