Effect of water removal through the gas diffusion layer and flow field on proton exchange membrane fuel cell performance

• Main Author: Phillips, Ryan
• Language: English
• Published: University of British Columbia 2015
• Online Access: http://hdl.handle.net/2429/54995

The sustainable nature of fuel cells has attracted global attention, and major automotive companies are investing in their development. A proton exchange membrane fuel cell (PEMFC) combines hydrogen and oxygen to produce electricity, with only heat and water as by-products. The water produced in the reaction must be effectively removed to avoid flooding, whereby liquid water accumulates in the porous electrodes and blocks pathways for reactant diffusion. By impeding reactant transport, ineffective water management decreases cell performance. Hence, understanding water removal mechanisms in PEMFCs is critical in order to increase their performance and yield a viable alternative to present-day technologies. This study investigates the effects of water removal through the gas diffusion layer (GDL) and flow field of PEMFCs in order to elucidate the impact they have on output power performance. A novel technique is implemented to evaluate the joint influence of the inlet air flow rate (FR) and relative humidity (RH), which drive water removal processes. The technique consists of an in-situ experiment that assesses cell performance, in combination with a quasi in-situ experiment that captures the local rates of water removal through the GDL along the length of the flow field. Findings from the in-situ experiment indicate a positive effect of FR, a negative effect of RH, and an interaction between FR and RH. The highest performance results from a high air FR (stoichiometric value of 6 at 1 A/cm²) and 65% RH air input, resulting in a power density of 0.470 W/cm². Based on findings from the quasi in-situ experiment, diffusivity was extracted using a comprehensive model. The final effective water vapor diffusion coefficient of the studied GDL was 0.0481 cm²/s at 70°C. Results from the experiments were compared and the association between performance and water removal rates was analyzed. High in-situ performance is most likely to occur when the quasi in-situ water removal rates are above an in-situ water production rate at 1 A/cm². The results from the input conditions are discussed in relation to water removal characteristics and potential flooding of the electrodes. Ultimately, this thesis provides valuable insight into water management aspects of PEMFCs. === Applied Science, Faculty of === Engineering, School of (Okanagan) === Graduate