Study of optimal step-wise distributions of platinum and carbon loading in cathode catalyst layer of a proton exchange membrane fuel cell

Abstract

Proton exchange membrane fuel cells use hydrogen as fuel and directly convert the chemical energy into electricity. Electrochemical reaction rate is non-uniform inside the cell. So the step-wise non-uniform distributions of platinum and carbon loading in cathode catalyst layer are optimized to obtain higher cell output performance. The optimal distributions with and without constrains along gas flow direction, vertical flow direction and thickness direction are explored. Then, current density change is analyzed to obtain a group of parameter to be suited to more operation voltages. The results show that the parameters obtained and cell performance change under each optimization voltage is various. In the results with constrains, carbon distribution is better for cell performance improvement among these three directions. The best structure for increasing cell performance is the carbon distribution along Z-Axis. More platinum or carbon loading is good for cell performance, mainly because more loading can provide a larger electrochemical surface area and reduce oxygen transfer resistance. In the results without constrains, the platinum or carbon loading reaches to upper bound. Carbon distribution is more favorable to improve cell performance than platinum, and the current density can be improved at least 6.644 % compared with base case. For better output performance and considering operation voltage instability, the carbon loading obtained along Z-Axis at 0.5 V of optimization voltage can be used for catalyst layer fabrication.