Decoupling polymer, water and ion transport dynamics in ion-selective membranes for fuel cell applications

Ion conducting polymer membranes are designed for applications ranging from separation and dialysis, to energy conversion and storage technologies. A key application is in fuel cells, where the semi-permeable polymer membrane plays several roles. In a fuel cell, electrical power is generated from the electrochemical reaction between oxygen and hydrogen, catalysed by metal nanoparticles at the cathode and anode sites. The polymer membrane permits the selective transport of H+ or OH− to enable completion of the electrode half-reactions, plays a major role in the management of water that is necessary for the conduction process and is a product in the reactions, and provides a physical barrier against leakage across the cell. All of these functions must be optimised to enable high conduction efficiency under operational conditions, including high temperatures and aggressive chemical environments, while ensuring a long lifetime of the fuel cell. Polymer electrolyte membranes used in current devices only partially meet these stringent requirements, with ongoing research to assess and develop improved membranes for a more efficient operation and to help realise the transition to a hydrogen-fuelled energy economy. A key fundamental issue to achieving these goals is the need to understand and control the nature of the strongly coupled dynamical processes involving the polymer, water and ions, and their relationship to the conductivity, as a function of temperature and other environmental conditions. This can be achieved by using techniques that give access to information across a wide range of timescales. Given the complexity of the dynamical map in these systems, unravelling and disentangling the various processes involved can be accessed by applying the “serial decoupling” approach introduced by Angell and co-workers for ion-conducting glasses and polymers. Here we introduce this concept and propose how it can be applied to proton- and anion-conducting fuel cell membranes using two main classes of these materials as examples

Decoupling segmental relaxation and ionic conductivity for lithium-ion polymer electrolytes

International audienceThe use of polymer electrolytes instead of liquid organic systems is considered key for enhancing the safety of lithium batteries and may, in addition, enable the transition to high-energy lithium metal anodes. An intrinsic limitation, however, is their rather low ionic conductivity at ambient temperature. Nonetheless, it has been suggested that this might be overcome by decoupling the ion transport and the segmental relaxation of the coordinating polymer. Here, we provide an overview of the different approaches to achieve such decoupling, including a brief recapitulation of the segmental-relaxation dependent ion conduction mechanism, exemplarily focusing on the archetype of polymer electrolytes – polyethylene oxide (PEO). In fact, while the understanding of the underlying mechanisms has greatly improved within recent years, it remains rather challenging to outperform PEO-based electrolyte systems. Nonetheless, it is not impossible, as highlighted by several examples mentioned herein, especially in consideration of the extremely rich polymer chemistry and with respect to the substantial progress already achieved in designing tailored molecules with well-defined nanostructures

Decoupling segmental relaxation and ionic conductivity for lithium-ion polymer electrolytes

xi+316hlm.;26c

Disentangling water, ion and polymer dynamics in an anion exchange membrane

Semipermeable polymeric anion exchange membranes are essential for separation, filtration and energy conversion technologies including reverse electrodialysis systems that produce energy from salinity gradients, fuel cells to generate electrical power from the electrochemical reaction between hydrogen and oxygen, and water electrolyser systems that provide H2 fuel. Anion exchange membrane fuel cells and anion exchange membrane water electrolysers rely on the membrane to transport OH− ions between the cathode and anode in a process that involves cooperative interactions with H2O molecules and polymer dynamics. Understanding and controlling the interactions between the relaxation and diffusional processes pose a main scientific and critical membrane design challenge. Here quasi-elastic neutron scattering is applied over a wide range of timescales (100–103 ps) to disentangle the water, polymer relaxation and OH− diffusional dynamics in commercially available anion exchange membranes (Fumatech FAD-55) designed for selective anion transport across different technology platforms, using the concept of serial decoupling of relaxation and diffusional processes to analyse the data. Preliminary data are also reported for a laboratory-prepared anion exchange membrane especially designed for fuel cell applications

A Roadmap for Transforming Research to Invent the Batteries of the Future Designed within the European Large Scale Research Initiative BATTERY 2030+

This roadmap presents the transformational research ideas proposed by “BATTERY 2030+,” the European large-scale research initiative for future battery chemistries. A “chemistry-neutral” roadmap to advance battery research, particularly at low technology readiness levels, is outlined, with a time horizon of more than ten years. The roadmap is centered around six themes: 1) accelerated materials discovery platform, 2) battery interface genome, with the integration of smart functionalities such as 3) sensing and 4) self-healing processes. Beyond chemistry related aspects also include crosscutting research regarding 5) manufacturability and 6) recyclability. This roadmap should be seen as an enabling complement to the global battery roadmaps which focus on expected ultrahigh battery performance, especially for the future of transport. Batteries are used in many applications and are considered to be one technology necessary to reach the climate goals. Currently the market is dominated by lithium-ion batteries, which perform well, but despite new generations coming in the near future, they will soon approach their performance limits. Without major breakthroughs, battery performance and production requirements will not be sufficient to enable the building of a climate-neutral society. Through this “chemistry neutral” approach a generic toolbox transforming the way batteries are developed, designed and manufactured, will be created

Membranes pour piles à combustible : structure et transport. Apport de la diffusion neutronique

Les membranes pour piles à combustibles sont des matériaux caractérisés par une ségrégation de phase hydrophobe-hydrophile à l’échelle nanométrique. L’amélioration des performances de ces membranes ionomères, en particulier l’optimisation de la conductivité protonique, est un enjeu important pour la mise sur le marché des piles à l’échelle industrielle. Elle passe nécessairement par une caractérisation microscopique de la structuration du polymère en fonction de son hydratation, et de ses propriétés, notamment les propriétés de transport. Nous montrons l’intérêt des techniques de la diffusion des neutrons dans ces systèmes. La diffusion des neutrons aux petits angles a été employée récemment pour déterminer les profils de concentration d’eau à travers une membrane au cours du fonctionnement d’une pile. La diffusion quasiélastique a permis, quant à elle, d’étudier les mécanismes de diffusion des molécules d’eau et de préciser un scénario de la mobilité moléculaire dans le Nafion, membrane de référence

Lithiation heterogeneities in full cells by combined neutron and synchrotron scattering techniques

International audienceOperando characterization techniques are key to understand the electrochemical processes that dictate batteryperformance and the concomitant materials transformations during cycling. In particular, synchrotron and neutrontechniques are increasingly employed as they provide unique insights into the chemical, morphological andstructural properties inside electrodes and electrolytes across multiple length scales with, potentially, hightime/spatial resolutions. Horse techniques such as XRD/NPD, as well as advanced methods such as coherentbragg imaging or ptychography, are constantly developed to better characterize the structure of crystalline batterymaterials e.g. phase transitions, strain, defects, etc… - extending the experimental limits towards high fidelity andhigh resolution data. However, the usual rules at Large Scale Facilities is to perform stand-alone experimentsproviding one type of information at one scale, therefore leading to a fragmented knowledge. Bridging scales andheterogeneous datasets is a challenge that require correlative data acquisition and analysis integrated inmultimodal multi-techniques workflows, an approach that is still in its infancy [1]. In this talk, we will presentcombined and/or coupled operando experiments performed on full batteries of different types, using both neutrons& X-rays, and/or both atomic scale and nanoscale techniques, including scattering computed tomography. We willfocus on lithiation heterogeneities at the scale of electrodes, in the depth and/or in 3D, revealed in different types ofmaterials as hierarchical composite anodes based on silicon nanodomains [2] or silicon nanowires [3], and layeredintercalation compounds such as LNO [4].References[1] Advanced Energy Materials, 2021, 2102694. D. Atkins, E. Capria, K. Edström, T. Famprikis, A. Grimaud, Q.Jacquet, M. Johnson, A. Matic, P. Norby, H. Reichert, J-P. Rueff, C. Villevieille, M. Wagemaker*, S. Lyonnard*.Accelerating Battery Characterization Using Neutron and Synchrotron Techniques: Toward a Multi-Modal andMulti-Scale Standardized Experimental Workflow. DOI:10.1002/aenm.2021026944][2] C. Berhaut et al, ACS Nano (2019), 13, 10, 11538-11551 ; C. Berhaut et al, Energy Storage Materials (2020), 29190-197 ; M. Mirolo et al, in preparation.[3] C. Keller et al, in preparation[4] Q. Jacquet et al, in preparatio

Neutrons for fuel cell membranes: Structure, sorption and transport properties

A molecular level understanding of structure and transport properties in fuel cell ionomer membranes is essential for designing new electrolytes with improved performance. Scattering techniques are suited tools for this purpose. In particular, neutron scattering, which has been extensively used in hydrogen-containing systems, is well adapted to investigate water-dependent complex polymeric morphologies. We report Small-Angle Neutron Scattering (SANS) studies on different types of fuel cell polymers: perfluorinated, radiation-grafted and sulfonated polyphosphazene membranes. We show that contrast variation methods can be efficiently employed to provide new insights on membrane microstructure and reveal ionic condensation effects. Neutrons have been used also as non-intrusive diagnosis tool to probe water properties and distribution inside membranes. Recently, in-situ neutronography and SANS experiments on operating fuel cells have been reported. In-plane cartography of water distribution at the surface of bipolar plates and water profiles across membrane thickness have been obtained and studied as a function of operating conditions. The last section of the article is devoted to the use of Quasi-Elastic Neutron Scattering to study water dynamics at molecular scale. We show that analysis with an appropriate sophisticated diffusion model allows to extract diffusion coefficients, characteristic times and length-scales of molecular motions. This quantitative information is fruitfully integrated in multi-scale modelling and usefully compared with numerical simulations. QENS also permits to compare alternative polymers and relate dynamical properties to chemical composition and membrane nanostructure

Gaussian model for localized translational motion. Application to water dynamics in Nafion

A model based on Gaussian statistics aimed at describing translational motion in confined media is presented. An example of application of this model to the study of water dynamics inside a ionic polymer membrane commonly used in fuel cells, the Nafion®, is shown