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The development of advanced coal-based functional nanomaterials is of great significance for clean and effective utilization of coal resources. Herein, we report novel coal-based ultra-fine carbon nanosheets (UCNSs) prepared by chemical oxidation of bituminous coal with a high yield of 40.0 wt%. UCNSs show a lamellar size of 10–20 nm, mainly composed of 63.5 at.% carbon, 5.1 at.% nitrogen, and 31.4 at.% oxygen. The structural merits of suitable size distribution, enriched functional groups, and highly conjugated core enable the UCNSs showing a tri-functional reinforcement for carbon nanofibers prepared by electrospinning and carbonization. Thanks to the strong cross-linking effect and formation of entire conductive networks, the UCNS-embedded carbon nanofiber fabrics show 32.6 and 1.5 times improved mechanical strength and electrical conductivity, respectively, than the one without UCNSs. What's more, the exposed edges of UCNSs act as active sites for ultrafast capacitive energy storage, leading to the free-standing fabric with significantly improved capacitance and rate performance (191.2 F g−1 at 1 A g−1, 113.5 F g−1 at 50 A g−1) for aqueous supercapacitors. This work may provide a new thought for high-efficient and high-value-added utilization of coal resources. Ultra-fine carbon nanosheets with a high yield of 40.0 wt% were prepared through liquid-phase oxidation of bituminous coal, showing tri-functional (mechanical/electrical/electrochemical) reinforcement for carbon nanofiber fabrics. [Display omitted] • Ultra-fine carbon nanosheets with a high yield of 40 wt% were prepared from coal. • The inlaid UCNSs show tri-functional reinforcement for carbon nanofiber fabrics. • Exposed edges enable an ultra-fast pseudocapacitive energy storage ability. [ABSTRACT FROM AUTHOR]

Preparing activated carbon with high volumetric performance in organic electrolyte is crucial for developing high-energy and miniaturized supercapacitors, but still challenging because high surface area and large pore size are required to effectively store large-sized organic electrolyte ions, which usually result in the low density. Herein, an ultrafast strategy is proposed to tailor the interconnected porous structure of activated carbon through introducing CO 2 at the end of homogeneous activation. The uniformly distributed potassium components in carbon matrix promote a robust catalytic etching by CO 2 , leading to precise tailoring of the ultramicropores (0.50–0.72 nm) to large micropores (0.81–1.14 nm) within only 2 min. The optimized sample with both high surface area and compaction density (2147 m2 g−1, 0.68 g cm−3) shows high gravimetric and volumetric capacitances (155 F g−1 and 106 F cm−3 at 1 A g−1) as well as good rate performance (102 F g−1 and 70 F cm−3 at 20 A g−1) in organic electrolyte. The symmetric supercapacitor achieves high energy densities of 35 Wh kg−1 and 24 Wh L−1 at 573 W kg−1 and 395 W L−1, respectively, indicating great potential of the ultrafast tailoring strategy for practical application. Introducing CO 2 at the end of homogeneous activation for only 2 min effectively tailors the porous structure of activated carbon, leading to high gravimetric and volumetric capacitance as well as robust kinetics for supercapacitors in organic electrolytes. [Display omitted] • An ultrafast strategy is developed to tailor porous structure of activated carbon. • The tailored porous structure enables both high surface area and density. • The sample shows outstanding capacitive performance in organic electrolyte. • Robust electrochemical kinetics is maintained at high electrode mass loadings. [ABSTRACT FROM AUTHOR]

Functional carbon dots with conjugated core and enriched oxygen-bearing functional groups are prepared in large-scale through mild oxidation of the solid-waste coal liquefaction residue, promoting the efficient and high-value-added utilization of coal resource. [Display omitted] • Coal liquefaction residue is mildly oxidized to prepare functional carbon dots. • Carbon dots (ca. 6.8 nm) show conjugated core and enriched functional groups. • The derived microporous carbon and carbon nanofiber show improved performance. Effective utilization of the solid-waste coal liquefaction residue (CLR) is important for the development of direct coal liquefaction technology, but remains big challenge due to the high ash of about 30 wt% in CLR. Herein, we propose a mild oxidation method to prepare functional carbon dots (CDs) using CLR as the carbon precursor and piranha solution (H 2 O 2 /H 2 SO 4) as the oxidant. Through catalytic hydrogenation, the highly conjugated structure of coal converts to weakly linked structure by aliphatic chains in CLR, leading to an improved oxidation reactivity. The highly reactive aliphatic chains are oxidized and cut during oxidation, leading to the formation of CDs with enriched oxygen-bearing functional groups at the edge sites and simultaneous removal of ash. To present the special properties of CDs, we prepare a microporous carbon with high-surface area and compaction density (1345 m2 g−1 and 0.86 g cm−3) through homogeneous activation of CDs, performing both high gravimetric and volumetric capacitance for supercapacitors. CDs are also used as the functional reinforcing phase for activated carbon nanofibers, enabling high surface area, improved mechanical property, good conductivity, and extremely high rate performance for supercapacitors. Our work provides a new avenue for high efficient and high value-added utilization of CLR. [ABSTRACT FROM AUTHOR]