| Direct carbon solid oxide fuel cell?DC-SOFC?is an efficient and clean power generation device,which can directly convert the chemical energy of solid carbon fuel into electrical energy,and it has the outstanding characteristics of all-solid,wide fuel selectivity,high safety and high energy conversion rate.However,as the electrochemical reaction of DC-SOFC involves multi-electron transfer process,multi-component and intermediate product generation,and the kinetic path is multiple,the battery performance declines with time,which seriously limits the industrialization process of DC-SOFC.This paper aims to realize the efficient and stable operation of DC-SOFC through the development of new biomass carbon fuel,the design of new SOFC structure,the development of efficient catalyst.The research content mainly includes the following two aspects:Firstly,the micro-tubular DC-SOFC was prepared by phase conversion technology,and the electrochemical performance of the battery fueled with the biochar derived from pepper straw was systematically investigated.The micro-tubular DC-SOFC powered with the pepper straw char shows the peak power density of 217m W·cm-2,which is comparable with that operated with hydrogen of 252 m W·cm-2 at850°C.It shows the great potential of pepper straw char in the application of DC-SOFC.The operation stability of the micro-tubular DC-SOFC fueled with pepper straw char at 850?,in which the weight of carbon fuel was 0.54 g and discharge current was 100 m A.Apparently,the single cell gives a high initial voltage of 0.65 V,a relatively stable discharging platform from beginning to end and the maximum discharge time was 21 h.Considering the overall reaction as a 4 electrons reaction(C is 44.4%calculated from Faraday's law with 0.54 g char as feedstock,which is obviously higher than that with other biomass fuels.Combined with the characterization results of carbon fuel,the pepper straw char contains naturally existed metal elements such as Ca,K and Mg,and there are few micropores on the particle of the biochar,which can effectively accelerate the Boudouard reaction rate and thus improve the battery performance.Based on the research findings,the present work is valuable for developing micro-tubular DC-SOFC into a safe,effective and environment friendly distributed power generation system for electrical power generation using local biomass as fuel.To further improve the electrochemical performance of DC-SOFC,four kinds of catalysts,including barium slag catalyst,barium-based catalyst,strontium slag catalyst and strontium-based catalyst,were prepared.The yields of barium-based catalyst and strontium-based catalyst were 30.3%and 40.8%,respectively.The SEM,EDS,XRD and XRF were used to characterize the phase composition and crystal structure of the four catalysts.The results show that a large number of metallic catalysts for the reverse Boudouard reaction are observed in the four catalysts.Moreover,the catalysts exhibit the porous structure after acid and alkali treatment,which is beneficial for the enhancement of the carbon gasification reaction.The catalysts were loaded into the solid carbon by the wet agglomeration technique.The electrochemical results suggest that the maximum power density of DC-SOFC fueled with 10 wt.%barium-based catalyst and 10 wt.%strontium-based catalyst loaded with activated carbon was 255 m W·cm-2 and 244 m W·cm-2 at 850?,higher than that of DC-SOFCs operated on barium slag and strontium slag catalysts,indicating the significance of pretreatment for improving the cell performance.In contrast,the maximum power density of DC-SOFC fueled with 5 wt.%Fe loaded with activated carbon and pure activated carbon were 195 m W·cm-2 and 178 m W·cm-2 at 850?,respectively.The operation stability of DC-SOFCs operated on various carbon fuels was performed under a constant current of 50 m A at 850°C.A long operation time of32.0 h was obtained from the single cell powered with 10 wt.%barium-based catalyst-loaded carbon fuel,whereas operation time of 31.8,28.9,25.8 and 25.9 h were observed in 10 wt.%strontium slag,10 wt.%barium slag and 5 wt.%Fe-loaded activated carbon fuel cells,respectively.The fuel utilization of DC-SOFC fueled with10 wt.%barium slag,10 wt.%barium-based catalyst,10 wt.%strontium slag and 10wt.%strontium-based catalyst loaded with activated carbon were 20.6%,25.6%,23.2%and 25.5%respectively,which were all higher than that of DC-SOFC fueled with pure activated carbon?15.9%?.The corresponding DC-SOFCs remained relatively stable during the operation.On the basis of the fuel utilization results,the conversion efficiency of DC-SOFC system can be obviously improved by loading the appropriate amount of metallic catalyst of the carbon gasification.In addition,the carbon gasification mechanism catalyzed by barium-based and strontium-based catalysts were also proposed on the basis of these properties.This study indicates that the designed barium-based and strontium-based catalysts-loaded activated carbon are expected to be an alternative carbon fuel for DC-SOFCs.More importantly,it can also provide a novel and green pathway for efficient utilization of industrial waste,and a new choice for solving environmental pollution and energy crisis.In conclusion,the present work has effectively improved the electrochemical performance and conversion efficiency of DC-SOFCs.In addition,it also provides the theoretical foundation and technical support for effective and stable operation of DC-SOFCs,and thus promotes the industrialization process of DC-SOFCs. |
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