Distribution of relaxation times as an accessible method to optimize the electrode structure of anion exchange membrane fuel cells

Recent significant progress in performance of anion exchange membrane fuel cells (AEMFCs) is proving this technology to be a meaningful low-cost alternative to commercial proton-conducting fuel cells. This progress has been largely driven by improved water management through electrode layer engineering. The plethora of membrane and ionomer chemistries makes the optimization of the electrode composition often unreproducible, leading to inaccurate performance comparisons. In this study we introduce the distribution of relaxation times (DRT) as an accessible and convenient tool to diagnose the limiting polarization processes in AEMFCs, which significantly simplifies the electrode optimization. To demonstrate the potential of DRT diagnosis, we fabricate cells with different anode electrode compositions simulating the effects of water transport limitations, such as anode flooding and cathode dry-out. The DRT separates and quantifies the contributions to the polarization resistance of the following processes: cathode and anode charge transfer, ion transport in the catalyst layer and gas diffusion. The anode catalyst layer optimization using information from the DRT has helped to increase the peak power density of the current cells from 550 to 690 mW/cm2. We foresee a large potential in using the DRT approach for the diagnosis and optimization of AEMFCs’ operational, structural, and compositional parameters.