| Coal is the most abundant and cheapest fossil energy resource on the earth, and is mainly used for coal-fired power generation. However, the conventional coal-fired electricity generation technology is a low efficiency and high emission process, and has a serious impact on the environment. As a new generation of power generation technique, solid oxide fuel cells (SOFCs) can directly convert coal to power cleanly and efficiently, which is of great practical significance to solve the problems of energy shortages and environmental pollution from fossil energy in China.The preparation technology of coal-derived carbon fuels suitable for SOFCs is an important part of the coal-based fuel cells power generation technology, and nowadays is one of the key factors in restricting the application process. Studying and clarifying the physicochemical properties and electrochemical performances of carbon fuels for fuel cells has an important significance for guiding the preparation of coal-derived carbon fuels. Structure of matter determines its property and performance. To gain a better understanding of the correlation between the structure and electrochemical performance of coal-derived carbon fuels as fuels for SO-CFCs, coal-derived carbon fuels are subjected to KOH treatment for structure modification in this paper. The influences of various physicochemical properties of coal-derived carbons on their Boudouard reactivity, and further the electrochemical performance of solid oxide-based carbon fuel cells (SO-CFCs) has been investigated.First, three kinds of activated coals with different specific surface areas were prepared by the way of KOH activation. It is found that carbon fuels with larger specific surface areas generally has higher Boudouard reactivity. Meanwhile, the properties including micropore surface areas, distribution of pore sizes, oxygen-containing functional groups and graphitization degrees are important factors affecting the Boudouard reactivity of carbon fuels. For the activated coal with specific surface area of 2067 m2 g-1 used as a fuel for SO-CFCs, the open circuit voltage (OCV) is 0.877 V and the peak power density (PPD) of the cell achieves 51 mW cm-2. In addition, the carbon availability of this carbon fuel is about 6 times of that of coal.Secondly, the industrial coal char was modified by the KOH activation for structure modification. After the process, the carbon microcrystals, micropore surface areas and oxygen-containing functional groups of the coal char are significantly improved. At the same time, the Boudouard reactivity is also greatly improved. The open circuit voltage of 0.97 V and the peak power density of 155 mW cm-2 are achieved by using the modified char as a fuel for SO-CFCs. Moreover, the carbon availability of the modified char is about 6 times of that of char. The result indicates that the structural modification of coal char plays an important role in the improvment of electrochemical performance of coal char-fueled SO-CFCs.Thirdly, the coal was pyrolyzed under 600 ℃ to obtain semi-char and the semi-char was further treated by the KOH activation. The result shows that semi-char has a better electrochemical performance than coal and coal char. The peak power density is up to 43.5 mW cm-2 and the carbon availability of the semi-char is almost 2.4 times of that of coal, when the semi-char is used as a SO-CFCs fuel. Therefore, the optimization of pyrolysis conditions is an important means to improve the performance of coal-derived carbon fuels.Briefly, the above results reveal that, the KOH treatment for structure modification of carbon fuels and the optimization of pyrolysis conditions of coal have a significant role in regulating the physicochemical properties and electrochemical performances of coal-derived carbon fuels. Carbon fuels, with smaller volumes of carbon microcrystals and more micropore surface areas and oxygen-containing functional groups, achieve higher Boudouard reactivity and electrochemical performances. |
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