Laboratoire d’Electrochimie et de Physico-chimie des Matériaux et des Interfaces

Freezing conditions pose a major challenge for Proton Exchange Membrane Fuel Cells (PEMFCs), particularly in automotive applications where fast, energy-efficient start-up is essential. Two critical issues arise: (i) internal mechanical degradation of the cells, induced by freeze/thaw cycling, and (ii) the difficulty of cold starting, which directly affects the durability and performance of the system. Ice formation in bipolar plates and catalytic layers leads to delamination and accelerated degradation of the membrane-electrode assembly (MEA), significantly reducing its lifespan [1]. Recent studies report a 2.4% loss in performance after only 3,000 freeze/thaw cycles [2], highlighting the urgent need to develop optimized cold start strategies that minimize energy costs, start-up time, and component degradation [3].To address these challenges, the PEPR Durasys PAC project proposes a collaborative approach aimed at providing concrete solutions. Within this framework, LEPMI and CEA have developed a methodology combining advanced experimentation and modeling to identify key drivers to improve and to validate robust strategies. In this article, we present more specifically the experimental results obtained, as well as the protocols implemented to characterize the degradation mechanisms under freeze/thaw cycles.Initial tests to investigate the impact of freeze/thaw cycles on PEMFCs are performed between - 20°C and +10°C. The freeze/thaw cycles (out of operation of the fuel cell) are repeated few hundred times. Electrochemical characterizations (during operation) are carried out after the break-in phase and during cycling to monitor any changes in performance: electrochemically active platinum surface area degradation, ionic resistance and mass transport increase thanks to polarization curve, Cycling Voltammetry and impedance spectroscopy measurements. High humidity conditions of 95/95RH are used to submerge the cell and exacerbate potential damage related to freezing/thawing. As shown in Figure 1, no significant cell performance degradation is observed after two hundred cycles. Freeze/thaw cycles are ongoing to go further in the aging study. Nevertheless, this unexpected result does not rule out the possibility of microstructural changes within the MEA and its components. In order to identify and characterize these potential degradations, post-mortem morphological analyses of MEAs are planned, targeting in particular interface delamination, membrane ruptures, and electrode alterations. In addition, an in-depth study of materials and interfaces is underway to elucidate the underlying mechanisms. A dedicated experimental platform will enable passive hydrothermal cycles (without active gases) to be carried out, both ex-situ and in-situ, in order to stress the components and MEAs. Physicochemical and morphological characterizations, such as X-ray microtomography and interface analysis, will be used to identify failures at the micrometric (delamination) and nanometric (electrode alteration) scales. In addition, the development of peeling methods will enable the quantification and characterization of interface properties. Finally, the properties of the materials, depending on temperature, relative humidity, and number of cycles, will be compared between MEAs aged under real-world and laboratory conditions.

As part of the DAEMOHYC project funded by the French government, we are developing alkaline anion exchange membrane electrolysis without platinum group materials, down to the 25cm2 single cell scale. Our consortium comprises five university laboratories and two industrial partners. Our strategy is to explore different ways of shaping materials, from the simplest, cheapest and most robust to the most performing, expensive and complex. For example, for the anode, we began by considering the use of simple activated stainless steel felts, without the use of ionomer [1]. We then textured these felts and decorated them with cobalt spinels by a combustion method using an amino acid ignition agent. The advantage of this shaping method is the robustness of the resulting electrodes and their good electronic conductivity, compared with electrodes obtained by ink deposition. The disadvantage is their low ionic conductivity, which essentially depends on the KOH concentration within the electrode. We have demonstrated that it is possible to increase the KOH concentration within the electrode thanks to the system architecture (dry cathode operation) and the good management of mass transport (PTL permeability), so as to maintain a pH gradient between the electrode and the feeding channels. Experimental studies combined with modeling work have enabled us to define stability domains for the various materials used, and to deduce optimal system control parameters (temperature, electrolyte pH, pressures, flow rates, clamping stress). In this presentation, we propose to take stock of the various advances made in the DAEMONHYC project in terms of materials, shaping, modeling and testing on the scale of the 25cm2 single cell. The idea is to share some insights that will help those involved in anion exchange membrane electrolysis to define their R&D strategy.The authors would like to thank the PEPR-H2 (ANR-22-PEHY-0010) for the financing support [1] Magnier, L., Cossard, G., Martin, V. et al. Fe–Ni-based alloys as highly active and low-cost oxygen evolution reaction catalyst in alkaline media. Nat. Mater. 23, 252–261 (2024) Figure 1

Fuel cell technologies such as Proton Exchange Membrane Fuel Cells (PEMFCs) are amongst the most advantageous solutions for clean energy production due to their high efficiency, low maintenance cost and high energy density. To date, even though PEMFCs have been identified for decarbonized heavy mobility applications, massive efforts are still needed to make them competitive with the internal combustion engines, that presently govern the market [1]. A particular endeavor is currently to increase the temperature of operation from ca. 70-80°C to ca. 90-100°C, to meet the requirements of the heavy-duty mobility. Conceiving and fabricating catalyst materials that show high performance and durability in these conditions is still a big challenge, notably on the cathode side where the oxygen reduction reaction (ORR) proceeds.To that goal, it has been decided to alloy Pt to a 3d metal (Ni) to enhance the intrinsic ORR activity and to cap these PtNi nanoparticles by carbon to enhance their resistance to metal dissolution and particles sintering. Such carbon-capped PtNi nanoalloys catalysts (see Figure 1.A,B) have been elaborated using a novel and simple dry synthesis pathway [2] consisting of the blending of a commercial Pt/Gr.C catalyst (Pt nanoparticles supported on graphitized carbon black) with a Ni-chelate precursor, followed by heat-treatment [3]. This strategy enables both structure and composition flexibility for the alloyed PtNi nanoparticles and the surrounding carbon shell. The activations of these novel carbon-capped catalysts, either electrochemically, or chemically through suitable acid treatments, which are crucial steps to allow the accessibility of reactants to the catalytic sites, will be briefly presented. These materials demonstrate good activity and durability compared to commercial catalysts in a liquid electrolyte [4]. Furthermore, they have been integrated into a PEMFC differential single cell. The break-in procedure and polarization curves under different relative humidity and cell temperature conditions will be presented. After such necessary steps, the PtNi@C/Gr.C catalysts outperform the mother commercial benchmark (Pt/Gr.C), especially in dry and hot PEMFC conditions (Figure 1.C). Accelerated stress tests under various conditions have also been conducted, and the results, along with post mortem characterizations, will be discussed. Acknowledgement: This work was funded by the “France 2030” government investment plan managed by the French National Research Agency, under the reference “ANR-22-PEHY-0005” (PEMFC95).

Using confocal fluorescence microscopy in both hydrophilic and hydrophobic glass capillaries, this study explores (i) the influence of wall wettability on spontaneous emulsification at the oil/water interface and (ii) the mechanisms governing the interaction of water/oil microdroplets with solid surfaces, ultimately enhancing oil recovery during low-salinity water injection. Our findings reveal that microdroplet formation predominantly occurs on solid surfaces when they are hydrophilic, whereas in hydrophobic environments, droplets emerge at the water/oil interface, specifically within the thin film between the meniscus and the solid wall. The growth dynamics of these droplets follows distinct scaling laws depending on the wettability of the surface. Upon injection of low-salinity water, the apparent contact angle increases on hydrophilic walls but remains unchanged on hydrophobic walls. In both cases, however, the advancing meniscus leaves behind a residual oil film containing trapped water microdroplets. The mobility of these droplets whether sessile or not, depends on surface properties. Over time, they merge with the surrounding water, forming water patches within the residual oil film. As these patches expand and coalesce, they create a structure reminiscent of a two-dimensional foam. Ultimately, these patches continue to grow until the solid wall is fully exposed to the free water phase.

Des films polymères multicouches sont caractérisés par microscopies Raman et Infrarouge, offrant des détails sur leur structure, composition et vieillissement. La combinaison de ces deux techniques permet de comprendre les interactions entre polymères, les changements moléculaires et les réponses aux contraintes environnementales. Les sensibilités des techniques sont comparées pour différentes fonctions chimiques. La microscopie Raman offre une meilleure résolution spatiale pour les profils d’oxydation.

The enhanced coalbed methane recovery using CO2 injection (CO2-ECBM) is widely proposed as a way of achieving the energy transition and reducing atmospheric CO2 in areas such as the Lorrain basin in France, where heavy industry is responsible for huge CO2 emissions and coal mines have been closed for more than a decade. This paper deals with the feasibility of extracting methane from the Lorraine basin using CO2-ECBM by comparing data from sorption isotherms, thermogravimetric analyses and breakthrough curves for two coal samples. One is bituminous (Box 18), from Folschviller (France) and is compared with another sub-bituminous (TH01) from La Houve (France), which is used as a reference because it was identified as a good candidate for CO2-ECBM in a previous research program. The quantities of adsorbed gases (CO2/CH4) obtained by sorption isotherms, thermogravimetry and CO2 breakthrough curves showed that Box 18 adsorbs more CO2 and CH4 than TH01 due to its higher porosity and good affinity for gases (CO2/CH4). Tόth model fits the experimental CH4 and CO2 adsorption isotherms better, reflecting the fact that the adsorption surface of the coals studied is heterogeneous. Adsorption enthalpies obtained by calorimetry indicated physisorption for gas-coal interactions, with higher values for CO2 than for CH4. Thermogravimetric analyses and breakthrough curves carried out at up to 50% relative humidity showed that the adsorption capacity of CO2 decreases with increasing temperature and the presence of water, respectively. The compilation of these experimental data explained the adsorption process of the studied coals and revealed their advantages for CO2-ECBM.

The ionic liquid tributyltetradecylphosphonium chloride ([P 4,4,4,14 ]Cl) forms micelles in water, with a very low CMC, below 1 wt%. The solution is macroscopically homogeneous, even large amounts of [P 4,4,4,14 ]Cl in water do not induce any phase separation. The ternary system [P 4,4,4,14 ]Cl/NaCl/H 2 O instead displays a LCST (Lower Critical Separation Temperature) behavior, being monophasic at low T and experiencing phase separation when T is increased. This phenomenon has been ascribed to the T -increased adsorption onto the micellar surface of these additional chloride ions. The lowering of the repulsive interactions between micelles finally allows coalescence and thus phase separation. In this work, we explore the impact of NaCl addition onto the phase separation, at fixed T . Specific chloride electrode allows the determination of chloride counterion adsorption for different samples in the phase diagram, all of them being single-phase. A simple theory based on the Poisson–Boltzmann equation and with charge regulation is proposed. The only fitted parameter is the chloride adsorption constant. It enables to model the different populations of ions in the solution and at the micelle surface in different conditions. Considering the effective charge of the micelles with respect to the ionic strength of the solution, it moreover provides a key element in the prediction of phase separation.

The temporal and spatial evolution of dispersed media is a fundamental problem in a wide range of physicochemical systems, such as emulsions, suspensions and aerosols. These systems are multiphasic and involve compounds of different densities. They are therefore subject to the influence of gravity which determines the sedimentation rate of their dispersed phase. This effect can be dominant and prevent a detailed study of the phenomena occurring between the constituents themselves, such as the coalescence of drops in emulsions, the evaporation of droplets or the flocculation in suspensions. In this context, the Centre National d’Etudes Spatiales (CNES) has recently supported the development of a new instrument to produce populations of droplets, a few micrometers in radius, under controlled conditions with the objective of allowing a detailed study of their properties in microgravity conditions. The principle of this instrument is to generate, by a fast compression/expansion of air, populations of water droplets and to track their evolution by optical scanning tomography in transmission mode within a volume of approximately 2 mm 3 . Parabolic flight experiments have shown the possibility to generate and accurately follow the evolution of populations of several hundred droplets for more than 20 s. The first experimental results show that it is possible to study their evaporation kinetics or their motion when imposing von Karman swirling flows. This work is part of the AEROSOL project of DECLIC-EVO supported by CNES and aims to help the understanding of cloud microphysics which remains a critical open problem in the context of global warming.

Some original poly(tetrasubstituted imidazole)s incorporating different units were synthesized and characterized. These materials were obtained via a cascade polycondensation process assisted by microwave irradiation that was developed by our team. This time, we integrated two well-known chromophore structures into the macromolecular backbone, which were benzothiadiazole (BTD) and diketopyrrolopyrrole (DKPP). These new polymers were fully characterized: their chemical structures were confirmed using NMR spectroscopy and their thermal, optical and electrochemical properties were investigated and compared with a reference polymer containing a phenyl spacer instead of the mentioned chromophore units. These materials were found to exhibit a large Stokes shift of up to 350 nm. Furthermore, a polymer presenting large absorption on the UV–visible range and an emission close to the near-infrared region was obtained by coupling the mentioned moieties. According to the established properties of this latter polymer, it presents a potential for applications in biological imaging or optoelectronic devices.