Anion exchange membrane fuel cells (AEMFCs) have received significant attention in recent years as a potentially lower cost electrochemical energy conversion device to conventional proton exchange membrane fuel cells (PEMFCs) [1]. Several major advancements have been demonstrated in the past few years, including power densities comparable to PEMFCs (~ 1.4 W/cm²) [2-3], anion exchange membranes with very high conductivity [4-5], and stability over 100’s of ours of operation [5]. These are all crucial steps towards the realization of commercially viable AEMFCs; however, there are more hurdles to overcome, specifically AEMFCs with low/no precious metal catalyst that are able to achieve high power densities over long term operation. Additionally, tolerance to carbon dioxide is a key factor in the potential success of AEMFCs, and an area that is relatively unexplored.

Water content and balance is a key contributor to many the challenges faced in AEMFCs [2,6]. The water (im)balance in AEMFCs – caused by the consumption of water at the cathode, generation of water at the anode (twice as large as at the PEMFC cathode), and the need for a significant amount of water in the membrane for effective hydroxide transport – is three times larger than PEMFCs. The need for adequate membrane hydration and reactant water at the cathode is at odds with the tendency for the anode and cathode layers to flood when excess water is provided in the gas stream. Ultimately the structure, thickness, porosity, components, and ratio of catalyst:support:ionomer all play a crucial role in maintaining this balance.

In this study the composition of the catalyst layer is fundamentally investigated, with the goal of decreasing precious metal catalyst loading without sacrificing performance. The ionomer:carbon:catalyst ratios are tuned to optimize water content and hydrophobic/hydrophilic microporous layers are incorporated to maintain the water capacity and water rejection in the catalyst layer and preserve the triple phase boundary. Catalyst layers are analyzed through their electrochemical surface area, hydroxide transport resistance, as well as kinetic and mass transport reaction overpotentials. Operando and ex situ cell images are taken using 2D & 3D neutron imaging of the water content and X-ray tomography. Finally, performance and stability of the catalyst layers with decreased platinum group metal (PGM) loading will be shown, demonstrating a significant increase in specific current and power over previous work.

References

1. R. Varcoe, P. Atanassov, D.R. Dekel, A.M. Herring, M.A. Hickner, P.A. Kohl, A.R. Kucernak, W.E. Mustain, K. Nijmeijer, K. Scott, T. Xu, L. Zhuang, Energy Environ. Sci. 7 (2014) 3135-3191.
2. J. Omasta, L. Wang, X. Peng, C.A. Lewis, J. R. Varoce, and W. E. Mustain, J. Power Sources (2017), http://dx.doi.org/10.1016/j.jpowsour.2017.05.006
3. Wang, J. J. Brink, Y. Liu, A. M. Herring, J. Ponce-González, D. K. Whellingan, and J.R. Varcoe, Energy Environ. Sci. 10 (2017) 2154-2167.
4. P. Pandey, A.M. Maes, H.N. Sarode, B.D. Peters, S. Lavina, K. Vezzu, Y. Yang, S.D. Poynton, J.R. Varcoe, S. Seifert, M.W. Liberatore, V. Di Noto, A.M. Herring, Phys. Chem. Chem. Phys. 17 (2015) 4367-4378.
5. S. Pivovar, "Advanced Ionomers & MEAs for Alkaline Membrane Fuel Cells" DOE Hydrogen and Fuel Cells Program Review. (2017).
6. Gottesfeld, D. R. Dekel, M. Page, C. Bae, Y. Yan, P. Zelenay, Y. S. Kim, J. Power Sources (2017), http://dx.doi.org/10.1016/j.jpowsour.2017.08.010