(Invited) Crosslinked High Temperature Polymer Electrolyte Membranes
Authors: Kallitsis Joannis K. 
Published: February 2020

High temperature polymer electrolyte membranes containing basic units that are able to interact with strong protic acids providing ionically conductive composite membrane have shown respectable performance and long operational stability. Further increase of the operation temperature and even an increase on the obtained conductivity values would facilitate the construction of efficient systems providing both electricity and heat, increasing thus the total efficiency.
Initial attempts to stabilize the HTPEM electrolyte membranes through covalent crosslinking have proven that the operation temperature can be shifted up to 220oC 1,2. Different crosslinking methodologies have been tested to stabilize either PBI or aromatic polyethers bearing pyridine units3,4. In the present work we focused on the optimization of the crosslinking methodology using side double bonds and we also develop new crosslinking methodologies leading to wholly aromatic crosslinked structures. Different type of crosslinkers have been used, controlling thus the acid doping ability of the final membranes while the use of dopable crosslinkers that enable the high acid uptake and retention. Moreover, depending on the chemical structure of the crosslinked membranes, a significant increase of the conductivity values of the final acid doped composite membranes was obtained. High temperature operation as the one achieved here enables the use of liquid feed like methanol in a compact methanol reformer-high temperature PEM fuel Cell setup that is under construction and testing5.
References: 1. K.D. Papadimitriou, F. Paloukis, S.G. Neophytides, J.K. Kallitsis, “Cross-Linking of Side Chain Unsaturated Aromatic Polyethers for High Temperature Polymer Electrolyte Membrane Fuel Cell Applications” Macromolecules 44, 4942–4951 (2011)
2. C.I Morfopoulou, A.K. Andreopoulou, M.K. Daletou, S.G. Neophytides J.K. Kallitsis “Cross-linked high temperature polymer electrolytes through oxadiazole bond formation and their applications in HT PEM fuel cells” Journal of Materials Chemistry A: Materials for Energy and Sustainability1 (5) 1613-1622, (2013)
3. “Pyridine Containing Aromatic Polyether Membranes” J.K Kallitsis, A.K Andreopoulou, M. Daletou, S. Neophytides; in “Part I: Approaches to HTPEM Fuel Cells” of “High Temperature Polymer Electrolyte Fuel Cells - Approaches, Status and Perspectives” Springer International Publishing AG, Cham; Edited by J.O. Jensen, D. Aili, H.A. Hjuler, Q. Li, 2016.
4. K.D. Papadimitriou, M. Geormezi, S.G. Neophytides, J.K. Kallitsis “Covalent cross-linking in phosphoric acid of pyridine based aromatic polyethers bearing side double bonds for use in high temperature polymer electrolyte membrane fuel cells’ Journal of Membrane Science 433, 1–9 (2013)
5. G. Avgouropoulos, S. Schlicker, K.-P. Schelhaas, J. Papavasiliou , K.D. Papadimitriou, E. Theodorakopoulou, N. Gourdoupi, A. Machocki, T. Ioannides, J.K. Kallitsis, G. Kolb, S. Neophytides “Performance evaluation of a proof-of-concept 70W internal reformingmethanol fuel cell system. Journal of Power Sources, 307 875-882 (2016)
Acknowledgment: Financial support from the Fuel Cell and Hydrogen Joint Undertaking (FCH JU), program "Development of a Portable Internal Reforming Methanol High Temperature PEM Fuel Cell System" IRMFC-FCH-JU-325358 is acknowledged.