Characterization of Fuel Cell Catalyst Layers in a Gas Diffusion Electrode Setup (GDE)

Abstract

Although the performance of new catalyst materials for proton exchange membrane fuel cells (PEMFC) often show very promising results in ideal rotating disc electrode (RDE) environment, these results cannot always be transferred to applicable conditions in membrane electrode assemblies (MEAs). This is mainly attributed to differences in the catalyst layer (CL) structure, which hinders the transport of reactants and products for the oxygen reduction reaction (ORR). Therefore, the chemical structure and morphology of the CL have to be considered to improve the performance of these systems in fuel cells. However, due to the various possibilities in producing CLs, many experiments must be carried out until the optimum is reached. The interaction of Pt nanoparticles, carbon support, and ionomer creates a complex triple phase interface dependent on numerous parameters. Characteristics of the carbon support,[1] the Pt loading[2] or the ionomer content[3-5] leads to intensive research efforts and a considerable amount of time as many MEA experiments have to be performed for such studies.[6] To accelerate the screening of catalyst layers, the gas diffusion electrode (GDE) was recently proposed as a half-cell to study real catalyst layers.[7] As a proof of concept study, our group recently shown that catalyst layers with different Pt loading in GDE demonstrate similar ORR trends to MEA experiments.[7] Subsequently, GDEs from different laboratories were benchmarked with standardized electrochemical protocols obtaining reproducible results.[8] Most recently, advanced electrochemical characterization methods developed for MEA technique were established as a GDE method.[9] In the present work, we focus on main aspects of catalyst development, such as the morphology of catalyst layer formation and different catalyst materials, to gain fundamental insights into catalyst layer development. We tuned the porosity of real catalyst layers using different solvent compositions. The results show that low macroporosity leads to severe O2 mass transport limitations, whereas a better performance could be achieved for higher porosity. This allows a critical consideration of key parameters in MEA manufacturing, which has hot pressing as an indispensable step.This work demonstrates the importance of morphology and treatment of the catalyst layer and how substantially it affects the performance and mass transport in GDE setups to elucidate the optimal conditions for the accessibility of the triple phase interface.Literature[1] V. Yarlagadda, M. K. Carpenter, T. E. Moylan, R. S. Kukreja, R. Koestner, W. Gu, L. Thompson and A. Kongkanand, ACS Energy Lett. 2018, 3, 618-621.[2] J. P. Owejan, J. E. Owejan and W. Gu, J. Electrochem. Soc. 2013, 160, F824.[3] E. Antolini, L. Giorgi, A. Pozio and E. Passalacqua, J. Power Sources 1999, 77, 136-142.[4] K.-H. Kim, K.-Y. Lee, H.-J. Kim, E. Cho, S.-Y. Lee, T.-H. Lim, S. P. Yoon, I. C. Hwang and J. H. Jang, Int. J. Hydrogen Energy 2010, 35, 2119-2126.[5] G. Sasikumar, J. W. Ihm and H. Ryu, J. Power Sources 2004, 132, 11-17.[6] K. Ehelebe, D. Escalera-López and S. Cherevko, Current Opinion in Electrochemistry 2021, 29, 100832.[7] K. Ehelebe, D. Seeberger, M. T. Y. Paul, S. Thiele, K. J. J. Mayrhofer and S. Cherevko, J. Electrochem. Soc. 2019, 166, F1259-F1268.[8] K. Ehelebe, N. Schmitt, G. Sievers, A. W. Jensen, A. Hrnjić, P. Collantes Jiménez, P. Kaiser, M. Geuß, Y.-P. Ku, P. Jovanovič, K. J. J. Mayrhofer, B. Etzold, N. Hodnik, M. Escudero-Escribano, M. Arenz and S. Cherevko, ACS Energy Lett. 2022, 7, 816-826.[9] P. Kaiser, V. Lloret Segura, K. Ehelebe and S. Cherevko, ECS Meeting s 2022, MA2022-01, 2071.