Template-free preparation of layer-stacked hierarchical porous carbons from cheap pitch precursors for high-performance all-solid-state supercapacitors.

No abstract

A template-free strategy has always been attractive to design and fabricate advanced carbon materials with tunable nanostructures from cheap precursors. Herein, honeycomblike mesoporous carbons (HPCs) are prepared from pitch-based polymers through a self-assembly foaming strategy without using any templates. Rich mesopores specific in sizes of 2–5 nm and abundant open-ended honeycomblike holes endow a hierarchical pore-in-pore feature of HPCs and an ultrahigh specific surface area (3473 m2 g–1). With their superior structure, HPCs can deliver a high supercapacity of 339 F g–1 at a current density of 1 A g–1 in 6 M KOH aqueous electrolyte and retain 85.6% of the capacity even at a current density of 50 A g–1. Meanwhile, a supercapacitive cell assembled by two HPC electrodes yields a conspicuously ultrahigh energy density of 34.5 Wh kg–1 (12.8 Wh L–1) at a high power density of 679.4 W kg–1 (251.4 W L–1). This work provides a new method for the controllable synthesis of advanced carbon materials from pitch and presents further applications in flexible electrochemical supercapacitors.

Millimeter-sized activated carbon spheres are potential candidates for industrial-scale CO2 capture. Millimeter-sized sulfur-doped microporous activated carbon spheres were synthesized from poly­(styrene–divinylbenzene), a very cheap and easily operated resin product, in the present work and studied for CO2 uptake. A series of sulfur-doped spherical carbon materials were yielded through the sulfonation, oxidation, carbonization, and KOH activation of the polymer precursors. In addition to promoting the cross-linking of the polymer molecules, the sulfonic substituents directly introduced sulfur functional groups into the carbon materials after pyrolysis. The SCS-700 sample showed the best CO2 adsorption performance, whose sulfur content reached 0.69 wt %, and exhibited a high surface area of 1526 m2 g–1 and a large pore volume of 0.726 cm3 g–1. The adsorbent showed high CO2 uptake at both 25 °C (4.21 mmol g–1) and 50 °C (2.54 mmol g–1) under ambient pressure due to its abundant ultramicropores and a high proportion of oxidized sulfur functional groups. Thanks to its high microporous volume of 0.617 cm3 g–1, the CO2 performance at 8 bar was 10.66 mmol g–1 at 25 °C. The thermodynamics indicated the exothermic and spontaneous nature of the adsorption process, which was dominated by a physisorption mechanism. Furthermore, the CO2 uptake curves on a TGA analyzer were fitted with different kinetic models, and the fractional order model showed the best agreement with the experimental data. The recycling curve of SCS-700 exhibited excellent cyclic adsorption performance with no significant capacity loss even after ten adsorption–desorption cycles. It is suggested that this excellent CO2 uptake was due to the synergistic effect of the well-developed microporous structure and the oxidized sulfur-containing functional groups.