Fabrication Of Nickel-based Straight Pore Anode For High-temperature Fuel Cells And The Research Of Its Catalytic Mechanism For Coalbed Methane

Coalbed methane is a self-storage natural gas stored in coal seams and adjacent rock formations in an adsorbed or free state.As the most realistic and reliable supplemental resource for conventional natural gas in China,the development and utilization of coalbed methane has gradually become an important issue in the development of national resource and energy strategies.Coalbed methane will inevitably be mixed with air during the underground extraction process,resulting in a methane concentration of less than 30%in coalbed methane,which is also known as low concentration coalbed methane.Due to the low concentration of methane in low concentration coalbed methane and the presence of large amounts of air that cannot be directly burned,a large amount of low concentration coalbed methane is vented directly,resulting in significant environmental pollution and waste of resources.Adopting solid oxide fuel cell（SOFC）technology to convert and utilize low concentration coalbed methane can avoid the multi-stage energy conversion process of traditional methane power generation,and is a clean and efficient energy conversion technology that can promote safe production and energy conservation and emission reduction in coal mines,and is an important way to achieve the major strategic goals of"achieving carbon peaking and carbon neutrality".In view of the current research status of low concentration coalbed methane and the structural characteristics of solid oxide fuel cells,this thesis prepares a straight pores anode-supported solid oxide fuel cell through optimized phase conversion technology,and combines experimental tests,theoretical analysis and numerical simulations to investigate the key reaction mechanism and electrochemical performance evolution of the straight pores anode-supported solid oxide fuel cell when using low concentration coalbed methane.The main results obtained are as follows:（1）Based on the technology of stainless-steel mesh-assisted phase inversion,a straight pores anode-supported cell structure was constructed to reduce the gas transfer path and transfer resistance,solving the problem of concentration polarization faced by the conventional anode-supported configuration of solid oxide fuel cells when using low concentration coalbed methane.By adjusting the position of the stainless-steel mesh in the phase inversion process,the microstructure of the straight-pore anode support was investigated and the anode support with high porosity and high permeability was obtained.The dense skin layer formed by the phase inversion process can provide more active sites for the whole electrochemical reaction,which promotes the output performance of the single cell with peak power densities of 1022 m W cm^-2and 904 m W cm^-2 when fueled by hydrogen and low-concentration coalbed methane at750°C.The straight pore anode-supported single cell not only avoids the problems faced by conventional anode-supported cells when using low-concentration coalbed methane,but also improves the performance of the single cell.In addition,the relationship between O/C ratio and concentration polarization of the straight pore anode-supported single cell using low-concentration coalbed methane as fuel was investigated by changing the O/C ratio.The results show that at O/C ratios greater than0.5 in low concentration coalbed methane,the straight pore anode supported single cell will experience concentration polarization due to insufficient fuel supply.（2）The effects of O₂/CH₄ ratio in low concentration coalbed methane on the catalytic conversion efficiency,single-cell performance and lifetime on the anode surface were investigated.The results show that as the O₂/CH₄ ratio increases,the output performance of the single cell gradually decreases,and the peak power density of the single cell at 750°C decreases from 994 m W cm^-2 to 673 m W cm^-2.This is mainly due to the increase of oxygen partial pressure inside the anode,which consumes the hydrogen and carbon monoxide in the fuel and leads to the decrease of the electrochemical reaction rate on the anode side,which further leads to the decline of the cell output performance.Numerical simulation shows that the anode surface is the main chemical reaction site,and the wet and dry reforming of methane decreases gradually with the anode thickness direction.When the ratio of O₂/CH₄ in low concentration coalbed methane is less than 0.58 at 750°C,the carbon formation is generated from methane cracking and distributed on the anode surface.In addition,when the ratio of O₂/CH₄ is greater than 1.97,the Ni in the anode will be oxidized,which leads to the reduction of the anode active site and affects the catalytic reforming efficiency of the low concentration coalbed methane.（3）The effect of coal-based greenhouse gas CO₂ on the methane catalytic reaction efficiency,electrochemical performance and lifetime of the low concentration coalbed methane was investigated by blending coal-based greenhouse gas CO₂ into the low concentration coalbed methane.The results show that the highest output performance as well as conversion efficiency is obtained for a single cell with a peak power density of 1321.5 m W cm^-2 at 800°C and conversion rates of 50.03%and 74.48%for methane and CO₂,respectively,when 5%CO₂ is blended with low concentration coalbed methane.The reforming reaction rate of low concentration coalbed methane on the anode surface was calculated by constructing a two-dimensional numerical simulation.It was found that the dry reforming rate of methane and the reversible water-gas shift rate were significantly increased with increasing carbon dioxide content inside the anode,while the reaction rate of methane steam reforming was suppressed.The increased dry reforming rate of methane was the key factor to improve the methane utilization efficiency.By analyzing the carbon activity,it is found that the carbon activity from methane decomposition can be significantly suppressed with the introduction of CO2 content.The microstructure of the cell after long-term operation shows that there is no significant carbon formation on the anode surface,and the stability of the cell is significantly enhanced with the introduction of CO2 compared to the anode surface without CO2 involvement.（4）By optimizing the anode-electrolyte interface,constructing an anode functional layer to provide more active sites for the electrochemical reaction of the cell.Meanwhile,highly active nanocatalysts（Ni-Ce0.5Zr0.5O2-δ-Y2O3）were loaded by impregnation in the straight-pore anode microchannels to promote the efficiency of methane catalytic reforming reaction.The results showed that the peak power density of single cell was increased from 1021 m W cm-2 to 1248 m W cm-2 under hydrogen atmosphere at 750 °C and from 904 m W cm-2 to 992 m W cm-2 under low concentration coalbed methane atmosphere by the construction of anodic functional layer.In addition,the prepared catalysts are a continuous mesh structure,and Ni particles and Y2O3 are highly dispersed on the Ce0.5Zr0.5O2 carrier.Ni nanoparticles can improve the active sites of the catalyst,while Y2O3 can adjust the surface acidity of the catalyst,which is more favorable for the adsorption of low concentration coalbed methane on the catalyst surface.Through the optimization of the interface and the construction of the nanocatalysts,the peak power density of hydrogen-fueled single cell at 750 °C was 1501 m W cm-2,while the peak power density of low concentration coalbed methanefueled was 1208 m W cm-2.When the catalyst was over loaded in the anode,the active sites are reduced due to the agglomeration phenomenon during calcination.The loading of highly active nanocatalysts increased the conversion of methane from 23.59% to 43.22%,and also improved the coking resistance of the anode,which greatly improved the service life of the cell and enabled the long-term stable operation.The research results obtained in this thesis provide a theoretical and practical basis for the efficient and clean conversion and utilization of low-concentration coalbed methane by solid oxide fuel cells,and the further improvement of this technology will be conducive to the further development of the coal mine and the SOFC industry,ultimately realizing the clean and efficient utilization of coalbed methane.This thesis has 88 figures,4 tables and 222 references...