Proportion of MEA Design by Considering the Current Density Distribution

摘要

Most designers of polymer electrolyte fuel cells (PEFCs) supply the fuel cell with humidified gas to prevent the membrane from becoming dry. The steam generated by the electrochemical reaction is added to the humidified supply gas. The partial pressure of the steam in the cathode channel forces a supersaturated state. Additionally, because most PEFC designers also humidify the anode gas, the partial pressure of the steam in the anode gas channel is increased by the consumption of hydrogen from the electrochemical reaction, causing the gas channel near the anode outlet to reach a supersaturated state. These supersaturated states cause water management issues in the PEFC such as flooding and plugging where condensate blocks the pores of the gas-diffusion layer (GDL) and the gas channel, respectively. We have been examining the evaluation of a self-water management type of the membrane electrode assembly (MEA) since 2004. The self-water management MEA was developed by combining GDLs with different properties last year. A GDL with high drainage properties was positioned at the gas inlet, where the electrochemical reaction was active, and a GDL with high hydration properties was positioned at the gas outlet. The GDLs with different properties were arranged on the same cathode electrode, and this MEA with a segmented GDL was called the SGD. We examined the influence of the application on cell performance, when GDLs with different properties were combined and used. We used two kinds of GDL; one is produced from carbon paper and the other from carbon felt. As a result, the divided GDL use did not cause the decrease of the cell performance under the practical operating condition region. On the cathode side, the combination of the upper and lower GDL materials was changed to a felt-paper (SGD-FP) combination and a paper-felt (SGD-PF) combination. The cell performance of the SGD-PF was lower, when compared to that of the SGD-FP. This result was caused by a mismatch of the GDL; the paper was used where drainage was necessary, whereas felt was used where water was required. Moreover, the performances of both cells used the SGD-FP and the SGD-PF were lower than that of standard MEA used a non-divided carbon paper as GDL at the full humidifying condition [1]. Therefore, we should evaluate the SGD-FP under the condition of reducing the humidity of the cathode gas marginally. Finally, we aim to optimize the proportion of MEA design by considering the current density distribution.