Cohydrothermal carbonization of cellulose and organic matter from municipal sewage sludge for the controllable synthesis of N-doped porous carbon for supercapacitor electrodes

The municipal sewage sludge (MSS) was hydrolyzed at 230 °C for 60 min to obtain an organic-rich aqueous phase (AQ). The effects of the volume ratio of AQ on the structural characteristics and electrochemical performance of nitrogen-doped porous carbon materials (A-BCs), prepared by co-HTC with cellulose were investigated. Elemental analysis and XPS results indicated that both the yield and the nitrogen content of the A-BCs increased proportionally with the amount of AQ added. The optimal AQ fraction (20 v%) effectively synergized with KOH activation, significantly increasing the specific surface area of the resulting A-BC-0.2 to 2279.20 m²/g. The A-BC-0.2 electrode exhibited a specific capacitance of 298.65 F/g at a current density of 1.0 A/g in a three-electrode system with a 6 M KOH electrolyte, which was 30.4% greater than that of the sample without AQ (A-BC-0). Moreover, excessive AQ addition (>20 v%) inhibited pore development and induced the formation of an aliphatic carbon structure, thereby decreasing the SSA of A-BC-1.0 to 952.15 m²/g. This study provides a theoretical basis for the preparation of high-performance supercapacitor electrode materials on the basis of the resource utilization of sewage sludge.