Design And Study Of Solid Oxide Fuel Cells For High Efficient Utilization Of Biomass Carbon Sources

Clean and efficient use of biomass is an important way to achieve the goal of carbon peaking and carbon neutrality,and is also the key to promoting the large-scale use of biomass resources in China.Direct carbon solid oxide fuel cell（DC-SOFC）is an all-solid-state energy conversion device that uses solid carbon as a fuel to produce electricity efficiently.The application of biomass as a carbon source in DC-SOFC is an ideal technology to realize clean and efficient utilization of biomass,and has received wide attention.However,the current application of biomass in DC-SOFC still suffers from low efficiency and insufficient output performance,which limits its large-scale application.This paper aims to improve the output performance,energy conversion efficiency and application prospect of the cell through three paths:screening biomass carbon source,optimizing biomass application method,and optimizing cell structure design.The pattern of influence of biochar composition and structure on the electro-CO cogeneration performance of DC-SOFC was investigated.The in-situ pyrolysis process and conversion mechanism of biomass in SOFC were investigated by using Camellia oleifera shell directly as fuel,and the technical feasibility of direct application of biomass carbon source in SOFC was assessed.To further improve the output performance of DC-SOFC from biomass carbon sources,a3-cell stack LSGM-supported tubular DC-SOFC was developed,and the prospect of developing it into a portable power supply was investigated.La_0.75Sr_0.25Cr_0.5Mn_0.5O_3-δ-Ce_0.8Gd_0.2O_1.9（LSCM-GDC）composite anode was studied for its application in DC-SOFC The electrochemical performance of DC-SOFC and its improvement by impregnation with Ni nanoparticles were investigated.The following main innovative results were achieved in this paper:（1）Three types of biochar were prepared by high-temperature pyrolysis using Camellia oleifera shell,Pomelo peel and Michelia alba leaf as raw materials.The electro-CO cogeneration performance of DC-SOFC using these three biochar as fuel was tested,and the mechanism of the Reverse Boudouard reaction activity of the biomass char on the electro-CO cogeneration performance was investigated.Camellia oleifera shell char naturally contains higher content of Reverse Boudouard reaction catalyst（K,Ca and other elements）,higher specific surface area,rich defect structure and higher carbon content,which gives it the highest Reverse Boudouard reaction activity and energy density.The test results showed that the higher the Reverse Boudouard reaction activity of biochar,the higher its electrical performance for DC-SOFC and the higher the CO content in the exhaust gas.The maximum power density of DC-SOFC using Camellia oleifera shell char as fuel reached 306.8m W·cm^-2at 800℃,which is close to that of H₂-fueled SOFC(336.2 m W·cm^-2).The CO content in the exhaust gas under constant current discharge test exceeded 80%.the energy conversion efficiency of DC-SOFC’s electricity-CO cogeneration using biochar as fuel is about twice as high as the conversion efficiency of electricity,which can be more than 80%.By comparing the performance of DC-SOFC for electricity-CO cogeneration using these three biomass charcoals as fuel,the mechanism of the Reverse Boudouard reaction activity of biomass charcoal on its performance for electricity-CO cogeneration application was summarized.（2）A SOFC directly loaded with Camellia oleifera shell biomass as fuel was designed,and the pyrolysis behavior of the biomass in the cell and the working mechanism of the cell were studied to evaluate its electrochemical output performance.By the time the temperature rises to 700℃,the biomass in the cell has largely pyrolyzed to biochar and only small amounts of cracked gas（CO and H₂）,which are beneficial to the cell output performance,are emitted.The maximum power density of DC-SOFC directly loaded with Camellia oleifera shell biomass was 306m W·cm^-2at 800℃,which was very close to that of DC-SOFC fueled by Camellia oleifera shell char(317 m W·cm^-2),which also verified that the biomass carbon source could be pyrolyzed to biochar in situ in DC-SOFC.The biochar formed by in situ pyrolysis has a lower bulk density,which gives it a higher resistance to sintering,resulting in a higher discharge stability of SOFCs directly loaded with biomass carbon sources as fuel.This research element demonstrates the feasibility and application potential of direct biomass as a carbon source for DC-SOFC.（3）DC-SOFC stack with three-stage tandem tubular LSGM support was prepared by dip-coating method,and its output performance was tested with Camellia oleifera shell char as fuel.The stack has an open circuit voltage of 3.14 V,a maximum output power of 2.65 W,and a volumetric power density of 605 m W·cm^-3,which is a substantial improvement compared to the existing YSZ stack.A 3-cell stack with an external anode was further designed and assembled to overcome the limitation of the cell size on its fuel loading capacity,and the carbon fuel loading capacity was enhanced to increase the discharge time from 1 h to 9 h.The potential of this all-solid biochar DC-SOFC stack with high energy density as a portable or distributed high-performance fuel cell is confirmed.（4）To address the problems of high cost of Ag-based anode and poor stability of Ni-based anode commonly used in DC-SOFC,the application of LSCM-GDC composite anode electrode with excellent stability and good performance in carbon containing fuel in DC-SOFC was investigated.By comparing the output performance of DC-SOFC with pure LSCM,LSCM-GDC and Ag-GDC as anodes,respectively,the mechanism of the catalytic activity of the anode on the open circuit voltage of the DC-SOFC was investigated,and the higher the anode performance,the higher the open circuit voltage of the DC-SOFC.The maximum power density of DC-SOFC with LSCM-GDC composite anode is 221 m W·cm^-2at 800℃,which is lower than that of 300 m W·cm^-2with Ag-GDC anode.The maximum power density of DC-SOFC was significantly increased to 425 m W·cm^-2by introducing Ni nanoparticles into the LSCM-GDC anode using ionic impregnation.The potential of the LSCM-GDC composite anode for DC-SOFC applications was confirmed.