Water Management in Proton-Exchange Membrane Fuel Cells (PEMFCs): The Role of Porous Layer Roughness

Abstract

Faced with climate change and energy crisis, the polymer electrolyte membrane fuel cells (PEMFCs) have emerged as ideal energy-conversion devices for portable, stationary, and automotive applications. In this thesis, we focus on investigating the role of surface roughness on the fluid transport and droplet impact behaviours in the porous components of a PEMFC. We start by examining the fluid transport characteristics at the interfacial region of microporous layer (MPL) and catalyst layer (CL), considering the effects of compression stress, porosity, and wettability. The results highlight the importance of considering porosity change in the compression process, where increasing compression stress significantly decreases the liquid saturation in the MPL and interfacial region. In the following, the surface roughness effects of gas diffusion layer (GDL) on liquid droplet removal inside a PEMFC flow channel are investigated. The influences of airflow rate on liquid movement are discussed, and the liquid removal efficiency subject to different surface roughness parameters is evaluated by droplet detachment time and elongation. In addition, the effects of surface relative roughness on fluid flow permeability are also probed. Finally, we experimentally examined the liquid droplet impact dynamics on rough surfaces with various topological parameters using the high-speed visualisation technique. The results highlight the significance of surface area ratio on droplet impact dynamics, where a higher surface area ratio promotes the impact outcome transition from bouncing to wetting. Moreover, we probed the effects of roughness wavelength on droplet impact outcomes. To conclude, this thesis elucidates the significance of roughness feature of the porous layers and provide valuable insights into selecting appropriate parameters for optimising the performance of PEMFCs.