| The high value-added utilization of by-products produced in coal processing is an effective strategy to make the most of coal resources of our country and curb environmental pollution. However, by-products such as coal tar are mainly subjected to combustion with a small ratio of high value-added utilization. Therefore, development of a novel way to high value-added utilization of coal tar will bring a profound significance for sustainable development of our economy and society. Preparation of functional carbon materials from coal tar has unique advantages due to its high aromaticity and carbon content.In order to resolve a series of energy and environmental problems resulting from the application of traditional fossil fuel, the development of high-performance electrode materials for supercapacitors and lithium ion batteries has attracted extensive attention. Among all the energy-storing materials, porous carbons are most promising due to their high specific surface areas, large pore volumes, various pore structures, good electrical conductivity as well as their abundant sources. In the present work, coal tar was employed as the carbon precursor for the preparation of various porous carbons with different structures and morphologies and the electrochemical properties of these carbons as electrodes for supercapacitors and lithium ion batteries were investigated. The main results are summarized as follows:(1) Layer-structure hierarchical porous carbons were prepared by KOH activation of carbon-coated MgO layers with extracts of coal tar as the carbon precursor and Mg(OH)2nanosheet as the template. Results showed that the pore structures could be tuned by adjusting the mass ratio of KOH to carbon layers. When the mass ratio of KOH to the carbon layer was3, the prepared sample possessed layer structure composed of loosely packed nanosheets, high surface area (2649m2g-1), large pore volume (1.55cm3g-1) and large proportion of mesopores (53.5%). When used as the electrode material for supercapacitors, the porous carbon showed excellent electrochemical properties with a specific capacitance of329F g-1at a current density of0.1A g"1,79.9%retained ratio at5A g"1and92.4%retained ratio after5000cycles at1Ag-1.(2) Nitrogen-doped porous carbon nanosheets were prepared by pre-oxidation and carbonization using extracts of coal tar as the carbon source, melamine as the nitrogen source and porous MgO nanosheet as the template. The influences of carbonization temperature on porosity parameters, the types and amounts of the nitrogen functional groups in the porous carbons and their performance in lithium ion batteries were systematically investigated. Results showed that the sample synthesized at700℃possessed a high specific surface area of1209m2g-1, uniform mesoporous structure, a high nitrogen content of8.6wt.%and exhibited a specific capacity of nearly1000mAh g-1at a current density of100mA g"1.(3) A mixture of polyacrylonitrile (PAN) and coal tar was electrospun by the electrospinning technique and subsequently carbonized into porous carbon nano fibers. It was shown that with the increase of the mass ratio of coal tar to PAN, the specific surface areas of as-prepared samples decreased while their electrical conductivities increased. CNF-1(the mass ratio of coal tar to PAN is1) showed a balanced large specific capacitance (225F g-1at0.05A g-1), a high retained ratio (63.1%, from0.05A g-1to5A g-1) and excellent cycling stability after10000cycles (94.0%retained ratio at1A g-1). |
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