CEA LITEN

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.

In order to meet the cost and volume requirements of fuel cell (PEMFC) systems for heavy-duty vehicle applications, the fuel cell must operate under low-humidity, high-temperature conditions to reduce the reliance on bulky heat exchangers and humidifiers. The US Department of Energy is considering reducing the number of humidifiers by sharing them between several stacks1. The subsequent stage of the simplification process entails an examination of the consequences of the elimination of the humidifier. The aim of this study is therefore to analyse how the operating conditions influence the performance and durability of the fuel cell supplied with dry air.The Toyota Mirai is a perfect example of fuel cell operation in these conditions. However, this result was achieved thanks to significant work on the design of the fuel cell assembly and an operating temperature lower than that generally targeted for high-power applications2. In the literature, studies focus on the temperature issue, such as that by Y. Shao et al.3, which examines durability under low-humidity (7.5%) and high-temperature (99°C) operating cycles. However, there are few published studies on operation with completely dry air, and those that address it, such as that by K. Subin and P. K. Jithesh4, focus on low-temperature analyses.In our study, operating conditions representative of a high-power application were selected. Based on these reference conditions, pressure, air stoichiometry and temperature were varied in order to analyse the performance and operating stability of the fuel cell when supplied with dry air. These tests were carried out on two different membrane electrode assemblies (MEA), and accelerated stressed tests were applied to one of these MEA. This study was realized using a segmented cell, which made it possible to measure the evolution of the current distribution locally and to perform local electrochemical characterisations such as impedance spectroscopy.Experimental results show that it is possible to ensure stable operation of the cell with equivalent or even better performances when it is supplied with dry air than when it is supplied with moist air. To achieve such a result, it is necessary to adjust the operating conditions. For example, increasing the pressure allows dry operation by promoting air humidification with the water produced by the electrochemical reaction. Similarly, reducing the stoichiometry of the air can also improve the performance by reducing the drying out of the membrane. It is found that both MEAs tested do not have the same performance nor the same sensitivity to the dry air supply.(1) Kleen, G.; Gibbons, W. Heavy-Duty Fuel Cell System Cost – 2023; DOE Hydrogen Program Record; 24004; U.S. Department of Energy, 2024. https://www.hydrogen.energy.gov/docs/hydrogenprogramlibraries/pdfs/review24/24004-hd-fuel-cell-system-cost-2023.pdf?sfvrsn=70ff384f_3(2) Konno, N.; Mizuno, S.; Nakaji, H.; Ishikawa, Y. Development of Compact and High-Performance Fuel Cell Stack. SAE Int. J. Alt. Power. 2015, 4 (1), 123–129. https://doi.org/10.4271/2015-01-1175.(3) Shao, Y.; Xu, L.; Xu, L.; Zhang, X.; Wang, Z.; Zhao, G.; Hu, Z.; Li, J.; Ouyang, M. Water Management Issues during Load Cycling under High Temperature and Low Humidity Conditions Relevant for Heavy-Duty Applications of PEMFC. eTransportation 2023. https://doi.org/10.1016/j.ijhydene.2019.11.150(4) Subin, K.; Jithesh, P. K. Experimental Study on Self-Humidified Operation in PEM Fuel Cells. Sustainable Energy Technologies and Assessments 2018, 27, 17–22. https://doi.org/10.1016/j.seta.2018.03.004.

The aviation industry is facing one of its greatest challenges: how to reduce its CO2 emissions in the context of a constantly increasing air traffic. High Temperature Proton Exchange Membrane Fuel Cell (HT-PEMFCs) technology is of great interest for aviation, due to its easier thermal management, a simplified water management system and lower weight. However, the current Membrane Electrode Assembly (MEA) of HT-PEMFCs operating at 160°C are not at the expected level of performance. In this context, the NIMPHEA project aims to develop a new generation of HT MEAs at temperatures above 120°C to meet the demanding requirements of aviation fuel cells. HT-PEMFCs typically use phosphoric acid doped polybenzimidazole (PA-PBI). However, PA-PBI-based fuel cells have limited stability in the presence of water or at higher operating temperatures. In fact, they suffer from phosphoric acid loss. Recently, HT-PEMFCs based on quaternary ammonium bisphosphate Ion-Pair coordination (Ion-Pair) have shown better phosphoric acid retention in the temperature range of 80-200°C than PBI ones. In the frame of NIMPHEA project, we worked on the development of MEA based on Advent's Ion-Pair membrane technology for HT-PEMFCs. After optimizing the composition of both the cathode and anode active layers and the gas diffusion layer, we obtained a fuel cell with a nominal power density of 0.8 W/cm² at 180°C under H2/Air at 1 bar exceeding the performance of standard PBI based HT-PEMCs based MEA. This project has received funding from the Clean Hydrogen Joint Undertaking under grant agreement No 101101407. This Joint Undertaking receives support from the European Union’s Horizon Europe research and innovation program and Hydrogen Europe and Hydrogen Europe Research. The authors also thanks Advent technologies for their participation . Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union. Neither the European Union nor the granting authority can be held responsible for them. Figure 1

In the Internet of Things (IoT) era, the demand for cost-effective, flexible, wearable antennas and circuits has been growing. Accordingly, screen-printing techniques are becoming more popular due to their lower costs and high-volume manufacturing. This paper presents and investigates a full-screen-printed 1 × 4 Quasi-Yagi-Uda antenna array on a high-transparency flexible Zeonor thin-film substrate for emerging 26 GHz band (24.25–27.55 GHz) 5G applications. As part of this study, screen-printing implementation rules are developed by properly managing ink layer thickness on a transparent flexible Zeonor thin-film dielectric to achieve a decent antenna array performance. In addition, a screen-printing repeatability study has been carried out through a performance comparison of 24 antenna array samples manufactured by our research partner from CEA-Liten Grenoble. Despite the challenging antenna array screen printing at higher frequencies, the measured results show a good antenna performance as anticipated from the traditional subtractive printed circuit board (PCB) manufacturing process using standard substrates. It shows a wide-band matched input impedance from 22–28 GHz (i.e., 23% of relative band-width) and a maximum realized gain of 12.8 dB at 27 GHz.

Cation-disordered rocksalt lithium-rich compounds are promising materials for lithium-ion batteries as positive electrodes due to their potential low cost and high energy density. In this paper, we studied in detail redox processes of the composition Li2MnO2F using a combination of operando and ex situ X-ray absorption spectroscopy. Oxygen redox and manganese redox were deconvoluted during the first cycle by using a chemometric approach. We show a stepwise redox during charge with most of the manganese oxidized before 4.3 V, followed mainly by oxygen redox. In discharge, most of the reduction of Mn4+ occurs at high voltage above 4.3 V, but a non-negligible amount of Mn3+ is reduced to Mn2+ below 2 V, while oxygen redox occurs near 3 V with a strong hysteresis. The local order of the material is characterized by a strong Jahn–Teller deformation that disappears with the oxidation of Mn3+. The analysis of aged materials highlights that the capacity fade in the cathode material occurs in two stages: during the first few cycles, due to a decrease in oxygen redox activity and subsequently, due to a reduced manganese redox activity, linked with manganese reduction, O-loss, and probable cation-densification.

Lithium metal is being widely studied for next-generation batteries regarding these advantageous characteristics. Indeed, its ultrahigh theoretical capacity (3860 mAh.g-1) and its low electrochemical potential (-3.04 V vs. SHE) paves the way to the development of high-energy density batteries. However, the application of lithium metal in all-solid state batteries still suffers from many issues such as the thermodynamically instable Li metal/electrolyte interface, or the continuous lithium consumption1 leading to a rapid capacity fading of lithium metal batteries (LMBs). In addition, the unavoidable lithium dendrite formation represents a major cycle life issue as well as a safety hazard.2 In the recent years, lithium alloys have been regarded as promising alternatives to pure lithium metal.3 Indeed, it has been reported4 that the formation of a three-dimensional lithiophilic LixMy matrix promotes more homogeneous lithium plating and stripping behaviors. Such controlled phenomena could limit the dendrites’ growth during LMBs cycling. Therefore, replacing lithium metal by appropriate lithium alloys may lead to higher battery cycle life.In this work, a complete investigation on lab-made Li-rich alloys negative electrodes was carried out. First, their cycling mechanisms were studied in a symmetric configuration with a solid polymer electrolyte. We find that cycling Li-rich alloys cells leads to higher voltage values and noticeable peaking shapes in the first cycles, in comparison to cells built with a commercial lithium metal. Moreover, this voltage response at the early cycling stages brought our focus to the electrodes’ surfaces, especially their differences.To further study the surface composition of Li-rich alloys, advanced characterization methods such as X-ray Photoelectron Spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) were achieved. Quantitative data on Li-rich alloys’ surfaces exposed to dry room reveals the formation of a lithium carbonate (Li2CO3) rich layer. In contrast, the formed surface layer detected on commercial lithium metal is mainly composed of lithium hydroxide (LiOH). Furthermore, the different passivation layer compositions could be explained either by different surface reactivities due to alloying, or by different shaping processes between Li-alloys and commercial lithium metal. Both of these points have been addressed in this work.In this presentation, we will also discuss our extended investigations into surface degradation when exposed to various dew point environments in a dry room environment. Additionally, we examined their mechanical properties: tensile tests conducted on the studied Li-rich alloys demonstrate greater ductility compared to commercial lithium metal. These promising features may attract industry interest for improved storage solutions and manufacturing of thinner electrodes. Liu, J. et al. Pathways for practical high-energy long-cycling lithium metal batteries. Nat Energy 4, 180–186 (2019).Xu, W. et al. Lithium metal anodes for rechargeable batteries. Energy Environ. Sci. 7, 513–537 (2014).Lewis, J. A., Cavallaro, K. A., Liu, Y. & McDowell, M. T. The promise of alloy anodes for solid-state batteries. Joule 6, 1418–1430 (2022).Jia, W. et al. A dual-phase Li–Ca alloy with a patternable and lithiophilic 3D framework for improving lithium anode performance. J. Mater. Chem. A 7, 22377–22384 (2019). Figure 1

During fast charging, metallic lithium can form on the negative graphite electrode, compromising both cycle life and safety. After deposition, plated lithium can re‐intercalate within graphite, be disconnected or chemically oxidized. To better understand these reactions and their kinetics, operando measurements on cells with electrochemical performances close to commercial ones are essential. Herein, a dedicated pouch‐cell design is developed to follow the dynamic of lithium using 7Li nuclear magnetic resonance (NMR) spectroscopy. These developments provide 7Li NMR spectra every 6 min leading to a good temporal resolution. The dynamics of lithium is investigated for various charging scenarios and temperatures within NMC 811/graphite pouch cells with industry‐standard electrodes. Introduction of an original method allows assessing the mass of plated lithium formed in operando mode, offering insights on the competition between graphite lithiation, plating, and reintercalation processes. Interestingly, the lithium deposition occurs mainly during the constant‐current step and early stage of the constant‐voltage (CV) step, and lithium reintercalation, oxidation, or disconnection during the subsequent CV hold, highlighting the interest of reducing the current during fast‐charge scenario. Comparison with three‐electrode monolayer pouch cells provides an onset of plating located between −100 and –150 mV versus Li.

Abstract The RNA exosome is a multiprotein complex essential for RNA maturation and degradation. In budding yeast, a nine-subunit protein complex (Exo9) associated with Rrp44 forms Exo10 in the cytoplasm and, in complex with Rrp6, Exo11 in the nucleus. Depending on its subcellular localization, the exosome interacts with different cofactors and RNA substrates. In the cytoplasm, Exo10 associates with the SKI complex via Ski7, while in the nucleus, Exo11 interacts with the TRAMP complex. Within the nucleolus, the exosome participates in ribosomal RNA (rRNA) processing, facilitated by Mtr4-dependent adaptors Utp18 and Nop53. In this manuscript, we have performed a comprehensive study that addresses the targeting mechanism and precise subcellular localization of all members of the Exo11 complex. We observed a high concentration of all Exo11 subunits in the nucleolus and identified the importins Srp1 (α) and Kap95 (β) as responsible for the nuclear import of Exo9 subunits. Notably, Exo9 subunits localization was not significantly disrupted in the simultaneous absence of NLS-containing subunits Rrp6 and Rrp44, suggesting redundant nuclear import pathways for Exo9. Additionally, we show evidence that Ski7 may play a role in the Exo9 retention in the cytoplasm. To explore the exosome sub-nucleolar localization, we compared Rrp43 with nuclear exosome cofactors and show that it is enriched in the same nucleolar region as Mtr4 and Nop53. In conclusion, our findings provide a detailed characterization of Exo11 distribution, highlight the primary nuclear import mechanisms for Exo9, and reveal the specific localization of the exosome within the granular component (GC) of the yeast nucleolus, suggesting a spatial regulation of the RNA processing pathway. Highlights – Comprehensive study of the localization of all exosome subunits in yeast. – Identification of karyopherins involved in exosome nuclear import. – Ski7 dependent cytoplasmic retention of exosome. – Yeast sub-nucleolar organization of exosome and its cofactors.

This article describes the development of a Safe-by-Design (SbD) module and its integration into an easy-to-use tool, named the Nano Exposure Quantifier-Safe-by-Design (NEQ-SbD) tool. The NEQ-SbD tool guides its user to lower the exposure to nanomaterials at the worksite where nanomaterials are manipulated or handled during a wide range of activities. This allows the tool user with an informed decision to assess airborne exposure and to select, compare, and identify appropriate risk management measures (RMM). The SbD module was developed using various information sources that can support and guide the SbD process, including the (i) RMM effectiveness based on analyses of an Exposure Control Efficacy Library (ECEL), (ii) RMM performance using a Computational Fluid Dynamics (CFD) model, (iii) e-cards based on a qualitative analysis of RMM information sources, and (iv) guidance for SbD strategy using an exposure directionality assessment. This information has been integrated in the user interface of the SbD module and NEQ-SbD tool to facilitate the SbD decision-making process. The SbD concept applied in the integrated NEQ-SbD tool introduces a comparison between a baseline exposure assessment and an (improved) SbD exposure assessment. The integrated NEQ-SbD tool consists of 4 modules including (i) a baseline exposure assessment, (ii) baseline results, (iii) SbD assessment, and (iv) SbD comparative results. The main purpose of the SbD module lies in guiding the user to the most sensitive (exposure) parameters and allowing a side-by-side comparison of potentially suitable RMMs. The integrated NEQ-SbD tool also offers a tiered approach and seamlessly shifts from a tier-1 to tier-2 uncertainty of an exposure assessment. The SbD module is illustrated using a worked example for the transfer of nano powders, showing the possibility of identifying SbD solutions for both safe-by-process and safe-by-material design purposes. The NEQ-SbD tool is a valuable tool for the SbD of nanomaterials and as a decision-making tool to support SbD risk management strategies that lead to minimizing health risks associated with occupational exposures.