Study On Co-Ionic Solid Oxide Fuel Cell

Faced with the increasing shortage of non-renewable resources such as fossil energy,solving energy and environment problems has become the consensus of sustainable development of mankind.Solid Oxide Fuel Cell(SOFC),as a new electrochemical power generation device,has attracted much attention for its advantages of pollution-free,high efficiency,high reliability,and wide application.Co-ionic SOFC is a new type of electrolyte which can conduct oxygen ion and hydrogen proton simultaneously.Compared with oxygen ion SOFC,its operating temperature is lower,and its safety and stability are higher.Compared with proton SOFC,it uses more fuel types and has better carbon resistance.In this thesis,a combination of numerical simulation and experimental research is used to study co-ionic SOFC.The main research contents are as follows:1)A one-dimensional mathematical model is built to simulate the actual performance of co-ionic SOFC.The results show that when the total conductivity of electrolyte is the same as that of oxygen ion SOFC and proton SOFC,co-ionic SOFC has lower activation loss and concentration loss due to its unique conduction mechanism,so it has better actual performance.2)YSZ/BZCYYb doped electrolyte tablets,BZCYYb electrolyte strips and cells with BZCYYb as electrolyte were prepared and experimental studies were carried out.The results showed that the doped electrolyte tablets had poor compactness and low conductivity,but showed lower conduction activation energy;BZCYYb electrolyte has higher conductivity and lower conduction activation energy.The proton conductivity of BZCYYb electrolyte can be slightly increased by a small increase in water content in hydrogen atmosphere,but the increase of water content has little effect on activation energy.The maximum power density of SOFC cells with BZCYYb as electrolyte is 263m W/cm~2 at 700℃,and the performance decreases significantly with the decrease of temperature,mainly because the decrease of temperature leads to the increase of ohmic impedance and activation impedance of cell.3)Based on the experimental results,the one-dimensional mathematical model of co-ionic SOFC is improved and the parametric analysis is carried out.The research results show that the reversible voltage of cell is reduced slightly by increasing the temperature,but the ohmic loss of cell is greatly reduced,thus improving the actual output performance.Among the three support modes,the anode support has the best performance.In the range of high hydrogen concentration,the change of anode intake does not have a great impact on the performance.However,when the proportion of hydrogen in the anode intake component is reduced to 50%or less,the hydrogen pressure drops rapidly at high current density,which results in the deterioration of performance.The porosity and distortion factor of cell affect performance by affecting the gas transport.Higher porosity and lower distortion factor can significantly improve performance.4)Based on one-dimensional SOFC mathematical model,a two-dimensional segment model of co-ionic SOFC is constructed by adding material field.The research results show that:Under the two-dimensional model,the co-ionic SOFC has the best performance,with the output performance of 136.7%of oxygen ion SOFC and 146.4%of proton SOFC,which is due to the lower activation loss and concentration loss of co-ionic SOFC.At a stable operating voltage,the current density of the two-dimensional pieceway model gradually decreases along the flow path,which is due to the change of gas concentration in the flow path caused by the consumption of reactants and the generation of products.At this time,the change of substance concentration along the flow path is relatively uniform.Gas supply rate is an important factor in the SOFC reactor.Insufficient gas supply rate will make the SOFC lack fuel or oxygen and greatly reduce the power output.At the end of the flow channel,if the concentration of the reactant is reduced to an extremely low concentration,the current density will drop sharply.To sum up,in this thesis,co-ionic SOFC was studied by combining experimental research and numerical simulation,and a mathematical model of co-ionic SOFC was built.The conductivity of doped electrolyte and mixed ion electrolyte material BZCYYb was measured experimentally and applied to the model for analysis.The research content and results of this thesis have certain reference significance for the next research and application of co-ionic SOFC.