Dense porous carbon from chemical welding the oxidized coal liquefaction residue for enhanced volumetric performance supercapacitors

Coal liquefaction residue (CLR) has the advantage of high carbon content. Its conversion into high value-added carbon materials is of great significance for solid waste treatment. Herein, we prepare dense porous carbons (DPCs) by chemical welding and homogenous activation from the oxidized CLR (OCLR). With the extension of oxidation time for CLR, the OCLR shows a reduced particle size, an increased amount of edge sites, and an improved oxygen content. Moreover, oxidation etching removes numerous defects, leading to an enhanced conjugation degree of the OCLR. Therefore, the dense porous carbon obtained from small-sized OCLR (ca. 5 nm) exhibits abundant edge oxygen-bearing groups, good electrical conductivity, large specific surface area (1368 m2 g−1) and high compaction density (0.98 g cm−3). As supercapacitor electrode, it shows good gravimetric capacitance and enhanced volumetric capacitance of 268.5 F g−1 and 263.1 F cm−3 at 1 A g−1, respectively. The assembled symmetric supercapacitor displays an enhanced volumetric energy density of 8.26 W h L−1 at 124.9 W L−1, as well as excellent cycle stability. Our work provides a new idea for the efficient use of CLR. •Oxidized CLR (OCLR) has a small particle size, abundant edge sites and oxygen content.•Dense porous carbon (DPC) with both high surface and density prepared by OCLR•DPC shows excellent capacitive performance and cycle stability.•Exposed edges and defects enable a balance between ion transport and electron transport.