Nanostructured Ionomers and Membranes with Controlled Architectures for PEMFC – NSPEM

In this project, our objective is to create and develop proton conduction materials capable of replacing PFSA, both in the membrane and catalytic layers, for a viable application in a PEMFC. The project focuses on the synthesis and development of ionomers based on polyaryl ether bearing perfluorosulfonic acids. These materials contain significantly less fluorine than PFSA, and have the advantage of a very versatile architecture. The ionomers selected in this application are synthesized by polycondensation and their structure and architecture are modulated to obtain nanostructured materials with optimal proton conductivity and water uptake.
The membrane-electrode assemblies (MEA) are obtained by coating («spray coating«) the catalytic layer (solution of carbon, ionomer and platinum) directly on the membrane. The solutions for the active layers are prepared in a solvent or mixture of solvents with low-boiling points, typically a blend of alcohol / water.
The functional and structural properties of the materials are characterized at different relevant scales (macro and microscopic) and correlated with the performance of the cell. In particular, the morphology and nanostructure of the ionomers is studied according to the molecular architecture, the hydration, and the process conditions (membrane or catalytic layer). Operando studies are also carried out to evaluate the management of the water in the PEMFC in operation. Throughout the project three generations of ionomers are developed with improved properties.
The partners involved are international leaders in the field, with key skills in advanced material synthesis / characterization (LEPMI, CEA, Eras Labo, France), materials science / fuel cells (Simon Fraser University, Canada), and the fuel cells (Ballard, Canada).

We have developed ionomers with moderate ion exchange capacity and water absorption, and better performance in terms of conductivity and mechanical properties than Nafion. These ionomers have been incorporated into an MEA, either as a membrane (assembled with standard electrodes containing a PFSA ionomer, semi -aromatic cell), or as an ionomer in the electrode (assembled with a Nafion membrane, second semi cell). -aromatic), or in both compounds (all aromatic cell). A power density of 1080 mW / cm 2 was reached at 80 ° C, 100% RH (relative humidity) with an AME incorporating a poly (arylene ether sulfone) membrane carrying perfluorosulfonic functions and catalytic layers based on PFSA.
An accelerated aging test performed at 30% relative humidity, 90 ° C in the presence of H2 / Air, at open circuit potential demonstrated a durability of over 400 h, which is 4 times higher than that of Nafion 212.
The incorporation of the new ionomers into the catalytic layers has been successfully performed. The catalyst layers containing 20% by weight of sulfonated poly (arylene ether sulfone) as the ionomer were tested and showed, at high current densities and over a wide range of relative humidity, power densities comparable to those of MEAs based on PFSA. These results obtained during the first part of the project clearly demonstrate that NSPEM ionomers are very promising for PEMFC technology. From these results a second generation of ionomers was synthesized with a higher density of ion functions and conductivities much higher than the first generation. These materials being tested in fuel cells by our Canadian partners must far surpass the performance of the Nafion.

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The second generation of ionomers is being studied in fuel cells by our Canadian partners. Based on these results, we will design a third generation of polyphenylene ether type ionomers.
Additional to the applicative studies, we are currently carrying out a large study on the understanding of the relationships between the ionomer structure, the morphology of the membrane / catalytic layer and the mechanisms of transport. Thus during these studies we focus on:
1) the influence of the nature of the cation used during the membrane manufacturing and its impact on the morphology and therefore on its functional properties. 2) The nature of ionic function (sulfonic, sulfonimide) on transport properties (proton conductivity), and microstructure and morphology. We are studying the ionization and hydration phases in situ by infra-red spectroscopy at the synchrotron in order to highlight the differences in the organization of the hydrogen-bonding network at the molecular level.
3) The interactions between the different components of the catalytic layer (carbon, platinum, ionomer), which determine the complex morphology of the electrode by neutron scattering at small angles.
4) In order to complete the spectrum of structural and functional characterizations carried out on ex situ NSPEM membranes and electrodes, and battery tests performed in Canada, we have begun a study operando by the non-invasive technique of imaging and Neutron scattering The management of water in a semi-aromatic battery in operation has been measured under different operating conditions, and will be compared with the stack reference any PFSA. The accumulation / depletion of water in certain areas (channels or teeth, entry or exit of gases) can be obtained (under analysis).

1. Aromatic Copolymer/Nafion Blends Outperforming the Corresponding Pristine Ionomers, H-D Nguyen, J Jestin, L Porcar, C Iojoiu, S Lyonnard
ACS Appl. Energy Mater., 2018, 1 (2), pp 355–367
2. Fuel cell catalyst layers and membrane-electrode-assemblies containing multiblock poly(arylene ether sulfones) bearing perfluorosulfonic acid side chains, H-F Lee, M Killer, B Britton, Y Wu, H-D Nguyen, Cr Iojoiu, S Holdcroft, JES 165 ,10 , F891-F897, 2018
3. Sulfo-phenylated terphenylene copolymer membranes and ionomers Thomas J. G. Skalski, Michael Adamski, Benjamin Britton, Eric M. Schibli, Timothy J. Peckham, Thomas Weissbach Takashi Moshisuki, Sandrine Lyonnard, Barbara J. Frisken, and Steven Holdcroft, Chem Sus Chem doi: 10.1002/cssc.201801965 (2018)

Publication en cours de submission

4. Aromatic Multi-block Ionomers with Superacidic or Extensively Delocalized Anion Side Chains for PEMFC application: morphology and water interactions
H-D Nguyen, R Porihel, .T K L Nguyen, J-B Brubach, E Planes, P Soudant, P Judeinstein, L Porcar, S Lyonnard, C Iojoiu, J. Phys. Chem. C.
5. The cation : a simple way in controlling the microstructure and transport properties of a PEM, H-D Nguyen,.T K L Nguyen, E Planes, P Soudant, L Porcar, S Lyonnard, C Iojoiu, Electrohem Acta.

Conferences

1. Interplay in Single-Cation Conducting Polymers via Molecular Architecture Design, C Iojoiu, H-D Nguyen, S Lyonnard, G-T Kim, D Bresser, J-Y Sanchez, Solide State Ionic, 17-24 juin 2017, Padova, Italie (keynote)
2 Anion and cation influence on PEM microstructure and transport properties. C Iojou, H-D Nguyen T K L Nguyen, J-B Brubach, E Planes, P Soudant, P Judeinstein, L Porcar, S Lyonnard (communication orale) ISPE 16, 23-30 juin 2018, Yokohama, Japon
3. Structure-transport relationship in PFSA, aromatic and blend ionomers for PEMFC, S. Lyonnard, Q Berrod, S Hanot, S Mossa, H-D Nguyen, O Danyliv, L Assumma, C Iojoiu, Solid State Proton Conductors, 16-21 Sept 2018, Stowe, USA (keynote)

The proton exchange membrane fuel cell sector accounts for the largest share of world commercial demand for fuel cells, a sector that will increase considerably over the next 5 years. The technology manufacturers account for a disproportionally large share of this market but competition is growing. To remain competitive, fuel cell manufacturers must reduce materials costs. Much is focused on lowering Pt requirements, ultimately, removing them altogether. Nonetheless, complementary challenges exist that require a re-design of the materials that constitute the heart of the fuel cell, i.e., the membrane-electrode assembly. The current technical standard of choice for the proton exchange membrane (PEM) and for the solid electrolyte in the catalyst layer is the family of polymers known as perfluorosulfonic acid (PFSA) ionomers. Despite its ubiquitousness it is costly and requires the use of controlled and potentially-dangerous fluorous vinyl monomers, and it suffers from a loss of conductivity at low relative humidity and/or elevated temperatures. Alternative materials that do not possess perfluorinated polymer backbones are required for a long term solution to mass production of fuel cell devices. A solution to this problem also requires complementary examination and re-design of the catalyst layer. Within the catalyst layer a proton conducting polymer transfers protons between the nanocatalyst and the proton exchange membrane, and plays a critical role in fuel cell operation.

This proposal addresses the challenge of developing proton conducting media that do not require the use of polymer backbones and possess a much lower fluorine content, and which are sufficiently versatile to be viable candidates to replace existing perfluorinated materials in the membrane and catalyst layer. The proposal focuses on researching the synthesis and development of a class of materials known as the polyarylene ethers bearing fluorosulfonic acid. The proposal partners have materials science and fuel cell expertise with internationally-leading at LEPMI, CEA and Simon Fraser University and the fuel cell expertise at Automotive Fuel Cell Collaboration Corp.