Phenolic Resin-based Microporous Carbons:Design, Preparation And Their Supercapacitance And CO₂ Sorption Performance

Microporous carbon materials have shown great potential application prospects in supercapacitor and carbon dioxide capture areas. Recent studies have found that the pore size and distribution of carbon materials matching the selected electrolyte ions is one of necessary conditions to keep the excellent capacitance for supercapacitors, and the abundant micropores and nitrogen functional groups could effectively improve the CO2 sorption performance of the microporous carbon materials. In this study, we reported two types of microporous carbons by using the phenolic resin as carbon source, and studied their supercapacitance and CO2 sorption performance.A series of microporous activated carbons(MACs) with tunable pore sizes were successfully obtained from the one-step pyrolysis of phenolic resin carboxylate, which were synthesized with 2, 4-dihydroxybenzoic acid and formaldehyde using the different alkali metal hydroxides as catalyst and activation agent, respectively. We realized control the micropore size precisely during the activation process. Nitrogen sorption test reveal that the micropore sizes were tuned from 0.63 to 0.76 nm with the increase of the activation ionic radius. Electrochemical measurements show that the most important factor affecting the supercapacitance of MACs is how well the micropore size matches the electrolyte ions. In KOH electrolyte, CsAC with suitable micropore size exhibits the best supercapacitive performance with a high specific capacitance of 221.6 F g-1, and good stability capability of 98 % after 10 000 galvanostatic charge/discharge cycles. In EMMIBF4 electrolyte, the supercapacitor could provide much higher energy density. The energy density of CsAC can reach 30.8 Wh kg-1 at 60 °C. CO2 sorption tests reflect that the micropore volume play a crucial role in CO2 sorption. The CO2 sorption capacity of CsAC can reach to 5.19 mmol g-1 at 25 °C and 1 bar, and CO2-over-N2 selectivity is up to 18:1, indicating its superior CO2 sorption performance.A series of N-doped microporous carbons(NMC-x) with uniform ultramicropores(ca. 0.50 nm) were successfully prepared by direct carbonization of K+ exchanged meta-aminophenol-formaldehyde resin. Characterization results show that as the activation temperature increases, the average micropore size of NMC-x increases from 0.50 to 0.58 nm, and the N content decreases from 1.3 to 3.8 at%. Electrochemical measurements display that the NMC-600 with highest N content delivered the highest specific capacitance value up to 195.4 F g-1, but the NMC-700 had the most optimal rate capability. These results demonstrate that heteroatom doping have a significant influence on the supercapacitance of the electrode materials. CO2 sorption measurements show that the NMC-x materials give very high CO2 sorption capacities at low partial pressure and impressive selectivity for CO2 over N2. The NMC-600 exhibits an unprecedented CO2 uptake of 1.67 mmol g-1 at 25 °C and 0.15 bar and a superior CO2-over-N2 selectivity(50:1).