Numerical Simulation Study On Performance Of High Temperature Proton Exchange Membrane Fuel Cell

In the past decades, many attentions have been paid to high temperature protonexchange membrane fuel cells (HT-PEMFCs) due to its several outstandingcharacteristics, such as fast electrochemical reaction kinetics, high tolerance to COpoisoning, simple water management, and good availability of waste heat. However,the previous major research of HT-PEMFC focused on the development of cellmaterials and improvement of electrochemical performance, and a few attentions werepaid to the water and thermal management of single cells, however, the practicallyimportant thermal and water management on the stack level was rarely investigated.In this study, a HT-PEMFC mathematical model is developed. The modelconsists of three modules: stack fluid module, single cell module and heat transfermodule. The stack fluid module includes a pipe network to calculate the gasdistribution within the intake and exhaust manifolds and cell channel. The single cellmodule calculates the electrochemical performance of each single cell through theresults of gas distribution in the stack fluid module. The heat transfer module analysesthe temperature distribution in stack.A base case is first calculated based on the developed mathematical model, andthe distributions of gases, temperature and electrochemical performance are discussed.Afterwards, the structural and operational parameters of HT-PEMFC stack areintroduced to study their effects on the performance non-uniformity. The resultsindicate that the increments of current density and number of single cells bothimprove the stack power, but enlarging the performance non-uniformity. A largermanifold diameter ideally improves the performance uniformity, and the same theorycan be applied to the design of single cell channels to achieve better distributions ofgases within the stack and single cells. Increasing the relative humidity (RH)effectively reduces the ohmic voltage losses of each cell, barely deteriorating theperformance uniformity. However, it is difficult to obtain a high RH in the hightemperature condition. Higher cathode intake stoichiometry ratio and pressure havepositive effects on the gas concentrations within the stack, improving theelectrochemical performance and output power, and scarcely influencing the non-uniformity. The challenge is that the air compressor might waste more stack power, which could reduce the system power.Moreover, the effect of arrangement of cooling plates on the stack performance isconsidered. The stack size is decreased by increasing the cell number between twoadjacent cooling plates. Increasing the cell number between two adjacent coolingplates leads to higher operation temperatures of HT-PEMFC, and the difference oftemperature among the cells gets larger. These factors result in the deterioration ofuniformity of gas distribution within the HT-PEMFC stack, directly generating a largedifference of output voltages among the cells. When the cell number between twoadjacent cooling plates increases to a certain value, some cells start running out ofreactants. This study has a certain theoretical guiding sense in the design of practicalHT-PEMFC stack, and the water and heat management as well.