Water Management in Anion Exchange Membrane Fuel Cells
Recently, anion exchange membrane fuel cells (AEMFCs) have received attention as an attractive alternative to the acidic proton exchange membrane fuel cells (PEMFCs) that dominate in vehicle applications. The main advantage with AEMFCs is the possibility to use non-platinum-group metal (PGM) catalysts and less expensive metal hardware, thanks to the high pH of the electrolyte, which dramatically reduces the cost per kilowatt of power in fuel cell devices. The distinctive water transport scenario, together with the high alkaline medium in AEMFCs, represents unique features of AEMFCs. The possibility to reach power densities almost equal those achieved in PEMFCs with membranes of similar thickness and while using non-PGM catalyzed cathodes has already been demonstrated. However, closing the remaining performance gaps will require innovative approaches to effective water management in AEMFCs. Whereas both PEMFCs and AEMFCs require effective water management solutions, AEMFCs pose greater challenges. As more water is produced and consumed per electron, they are more sensitive to dryout of the cathode and flooding of the anode. Practically viable solutions for AEMFC design will most likely require both advanced material design (to tune and control the water diffusivity and hydraulic permeability across the membrane and the hydrophobic/hydrophilic character of the gas diffusion and electrode layers on both sides) as well as innovative stack-level or system-level design (to provide additional routes for water transport from the anode to the cathode). The future development of efficient AEMFCs will thus require a thorough understanding of the intricate coupling between the multiphase flow and the electrochemistry inside the cell, to allow the subsequent transformation of such understanding into innovative engineering solutions for a variety of vehicle applications.
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