Mingdong Zheng

Synthesis of hierarchical porous carbons for supercapacitors from coal tar pitch with nano-Fe2O3 as template and activation agent coupled with KOH activation

Hierarchical porous carbons (HPCs) for supercapacitors were synthesized from coal tar pitch using nano-sized γ-Fe2O3 as a template and activation agent coupled with KOH activation by conventional and microwave heating. The HPCs were characterized by scanning electron microscopy, transmission electron microscopy, N2 adsorption and X-ray diffraction techniques. The results show that the specific surface area (SBET) of HPCs is tunable, and increases from 761 m2 g−1 to 1330 m2 g−1 as the mass ratio of γ-Fe2O3 to the pitch increases in the mixture. The nano-sized γ-Fe2O3 is reduced to Fe3O4, FeO, Fe in the activation reaction step. The carbon dioxide generated from the oxidation reactions of carbon monoxide via γ-Fe2O3 reacts with carbon that is a kind of in situ physical activation, which results in the development of the porosity in HPCs. The large SBET in HPCs are due to the synergistic effects including γ-Fe2O3 template, KOH chemical activation, and physical activation resulting from the reactions of γ-Fe2O3 and KOH activation. Under optimum conditions with the mass of coal tar pitch, γ-Fe2O3, KOH at 4.2 g, 16.8 g and 6 g, the HPC made by conventional heating shows a high capacitance of 194 F g−1 in 6 M KOH aqueous electrolyte and an energy density of 20.3 Wh kg−1 in 1 M tetraethylammonia tetrafluoroborate in propylene carbonate electrolyte at a current density of 0.1 A g−1. This work may pave a new way to produce high performance HPCs for energy storage devices.

Removal of organic sulfur compounds from diesel by adsorption on carbon materials

Abstract Removal of organic sulfur compounds from diesel by adsorption on different carbon materials, including activated carbons (ACs), carbon aerogels, carbon nanotubes, and AC cloths, was reviewed. The effect of the textural and surface chemistry property of carbon on desulfurization performance, carbon surface modification, adsorption mechanism, and adsorbent regeneration and the effect of other components, including aromatics, additives, nitrogen compounds, and moisture, on adsorptive desulfurization of diesel fuel were also discussed in detail. Carbon materials showed very high selectivity for removing the dibenzothiophenes, especially for 4,6-dimethyldibenzothiophene, which is very difficult with hydrodesulfurization and other adsorbents. Both the textural and chemical properties of AC have an important impact on the adsorption of DBTs. Adsorption selectivity and capacity can be enhanced further by carbon surface modification. Considering the effect of diffusion hindrance and regeneration, mesoporous carbon is more suitable than microporous carbon with pore size <2 nm. It is necessary to eliminate the inhibiting effect of fuel additive and nitrogen compounds on the DBTs before carbon materials are used for desulfurization of real diesel fuel. In the end, some useful suggestions are also made.

Effect of microwave-treatment time on the properties of activated carbons for electrochemical capacitors

Abstract Activated carbons (ACs) made from petroleum coke by KOH activation were further treated by microwaves to investigate the effect of microwave-treatment time on the pore structure, the surface properties (functional groups) and the electrochemical properties of the as-made ACs for electrochemical capacitors (ECs). Results show that the specific capacitance and the equivalent series resistance of microwave-treated ACs become smaller with a decrease in the Brunauer-Emmett-Teller surface area and the total pore volume (vt) of the treated ACs. Compared with the AC sample heated at 1073 K for 1 h by a conventional heating method, the AC sample treated by microwaves at 700 W for only 7 min has a pore size distribution with a high (meso- and macropore volume)/vt ratio and a high carbonyl content, and exhibits a high energy density and powder density as an electrode of ECs. This has clearly shown that the microwave-treatment is a simple and efficient approach to obtain high-performance ACs for ECs.

The formation mechanism of CO2 and its conversion in the process of coal gasification under arc plasma conditions

The carbon dioxide (CO2) formation mechanism and co-conversion of CO2 with coal was investigated in the process of coal gasification in a steam medium at atmospheric pressure under arc plasma conditions in a tube-type setup. The arc plasma was diagnosed in situ by optical emission spectroscopy and the gas products were analysed by gas chromatography. CO2 yields are correlated with the quantitative emission peak intensity of the active species in plasma when the operating parameter is changed. The results show that the greater the emission peak intensity of the CH radicals, C2 radicals, OH radicals or O atoms, the smaller the CO2 yield is, which means that the CO2 formation process is inhibited by increasing the concentration of the mentioned active species under arc plasma conditions. On the basis of the diagnosis results, co-conversion of CO2 and coal in a steam medium under plasma conditions was carried out in the same setup and the results show that CO2 conversion reaches 88.6% while the concentration of CO + H2 reaches 87.4%; at the same time, coal conversion is in the range 54.7–68.7%, which proves that co-conversion of CO2 and coal in a steam medium under plasma conditions might be a prospective way to utilize CO2 and the production of synthesis gas.

Facile preparation of porous carbons from rice husk by microwave heating for supercapacitors

Porous carbons (PCs) including microporous and mesoporous carbons for supercapacitors were made from rice husk through zinc chloride (ZnCl2) activation in one-step by microwave heating with microwave power at 600 W at 20 min heating time. PCs were characterized by field emission scanning electron microscope, transmission electron microscope and x-ray diffraction. The pore structure parameters and surface chemistry of PCs were obtained by nitrogen adsorption, Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy. The results show that the average pore size of PCs increases from 2.02 nm to 5.99 nm, and the total pore volume of PCs increases from 0.75 cm3/g to 2.07 cm3/g with the mass ratio of ZnCl2/rice husk. The specific surface area of PCs passes through a maximum with the ZnCl2/rice husk mass ratio, and reaches 1727 m2/g at 3/1 of ZnCl2/rice husk mass ratio. At 4/1 of ZnCl2/rice husk mass ratio, the specific capacitance of PC (PC4/1) only decreases from 182 F/g to 171 F/g with the increase of discharge current density from 0.05 A/g to 2 A/g, possessing a capacitance retention up to 94.0% due to its low densities of surface functional groups, good conductivity and mesopore structure. The energy density of PC4/1 capacitor retains at 6.23 Wh/kg after 1000 cycles, showing perfect cycle stability. The results evidenced that microwave heating ZnCl2 activating rice husk at 20 min heating time in one-step is an efficient approach to the rapid preparation of low cost yet high performance PCs for supercapacitors.