Catalyst Layer Structure Research Articles

MnO2 Nanowire Thin Mesh With Enhanced Mass Transfer as Hydroxide Exchange Membrane Fuel Cell Cathode

AbstractHydroxide exchange membrane fuel cells (HEMFCs) are promising due to the potential use of nonprecious metal catalysts. However, the performance of HEMFCs based on nonprecious catalysts is still unsatisfactory, and one reason for this is hindered mass transfer in the catalyst layer. In this study, we employ a hydrothermal method to grow in situ a MnO2 nanowire thin mesh (NTM) catalytic layer on the gas diffusion electrode. The HEMFC prepared with MnO2 NTM cathode achieves a peak power density of 425 mW cm−2, surpassing the performance of the HEMFC prepared using the traditional powder catalyst spraying method by four times. High‐frequency resistance and limiting current tests indicate that the MnO2 NTM reduces ohmic resistance and improves mass transfer, thereby enhancing the HEMFC performance. Furthermore, the peak power density of the HEMFC is increased to 626 mW cm−2 by depositing additional active Co3O4 nanoparticles on the MnO2 NTM. These findings demonstrate that an interconnected and porous catalyst layer structure is beneficial for improving mass transfer properties, which in turn enhances HEMFC performance.

Hierarchical Electrode Design for Highly Efficient and Stable Anion Exchange Membrane Water Electrolyzers

Anion exchange membrane water electrolyzer (AEMWE) is a promising technology for green hydrogen production to reduce carbon emissions in industrial and heavy-duty transportation sectors. AEMWE has the advantage of using nonplatinum group metal oxides for the anode oxygen evolution reaction (OER) and therefore lower the capital expenditure comparing to proton exchange membrane water electrolyzers (PEMWE). However, the commercialization and deployment of AEMWE in large scale is still limited by its durability. Herein, we study how electrode structure and the cell operating conditions affect the cell stability and performance. Catalyst layer structures, including porosity and tortuosity, were investigated and correlated with cell performance for better understanding and designing AEMWE. Durability of different catalyst layers were investigated and correlated with catalyst layer structure and ionomer stability. Electrode fabrication methods were found to have significant impact on the catalyst layer structure and therefore catalyst utilization. With a doctor blading method to fabricate the catalyst layer, electrodes were scaled up from 5 cm-2 to >25cm-2 with negligible voltage loss. With these findings, cell performance was improved towards <1.8V at 2A cm-2 and durability of >500h was achieved at 2A cm-2 for a 25 cm-2 cell in 0.5M KOH.

Evaluation of Reaction and Mass Transport Properties of Fuel Cell Catalyst Layers

Recently, polymer electrolyte fuel cell (PEFC), which are expected to be applied to heavy-duty vehicles with high environmental load, are required to further improve their output power. the output characteristics of PEFC depend on the structure of the catalyst layer, including the aggregation form of the carbon support and the ionomer coating state. The structure of the catalyst layer is also important. The catalyst layer structure is also determined by the composition of the catalyst ink that forms the structure and the agglomeration form of the particles. However, the correlation between each ink condition and output characteristics is difficult to understand directly because it involves complex factors of structure formation and transport reaction distribution. In this study, we fabricated various catalyst layer structures under various ink conditions with different compositions and fabrication processes, analyzed their output characteristics, and evaluated the correlation using machine learning as a learning model.In the cathode catalyst layer, oxygen, protons, and electrons move through voids, ionomer (electrolyte polymer), and carbon black (CB), respectively, and oxygen reduction reaction occurs on the Pt surface. Since the anodic reaction is sufficiently rapid compared to the cathodic reaction, the anodic reaction was neglected, and the inside of the battery was assumed to be isothermal and steady state. A 300 nm substrate aggregate was formed and filled into the computational domain, and the catalyst layer structure was fabricated by arranging the Pt catalyst and coating it with ionomer. The structure was simulated by varying the spatial probability density of the support arrangement. The structure was subdivided into blocks of primary particle size and transport calculations 1) were performed between adjacent blocks.The I/C ratio (weight ratio of ionomer to CB), platinum loading, and spatial probability density related to the arrangement of the CB support were varied, and the battery characteristics were determined by transport calculations for each structure using 100 structures that reproduced the coarse and dense structure of the catalyst layer. From the results of the transport calculations, the voltage at a current density of 0 A/cm2 and the current density for each 0.05 V between 0.6 and 0.85 V were associated with the images of the catalyst layer, and a dataset consisting of 399 cross-sectional images of the catalyst layer, each voltage and current density was created.CNN 2) was used for the machine learning model.Four hundred images were prepared for the study, of which 240 were used for training, 80 for validation, and 80 for testing. Adam was used for the optimization method, RMSE for the loss function, and Keras for implementation.Transport calculations were performed under conditions similar to current fuel cell operating conditions: temperature 80 ℃, RH 80 %, and supply oxygen partial pressure 20 kPa. In order to reproduce differences in the fabrication process, the spatial probability density associated with the arrangement of CB carriers was varied to fabricate structures with different aggregation morphologies.This calculation confirmed the voltage drop associated with the formation of aggregates, especially in the high current density region where mass transport is the rate-limiting factor. This is because oxygen transport was inhibited as the aggregates became larger in the aggregation area, and the high current density region inside the catalyst layer became localized.The voltage at a current density of 0 A/cm2 and the coefficient of determination (R2) between the production value of the transport calculation and the machine learning prediction at the current density at each voltage were all better than 0.8, confirming that the machine learning model we constructed can predict battery characteristics. In addition, the machine learning model was able to predict differences in battery characteristics where the I/C ratio and platinum loading were equal and only the coarseness and density of the structure differed.As described above, it is suggested that differences in the fabrication process can cause differences in battery characteristics, and a machine learning model was constructed to predict battery characteristics based on catalyst layer structure images where process differences are assumed.AcknowledgmentThis study was supported by NEDO program, Japan.

Investigation on Effect of Reducing Cathode Pt-Loading on Ohmic Overpotential in Catalyst Layer

To reduce the use of precious metals in polymer electrolyte fuel cells (PEFCs), it is necessary not only to develop high activity catalysts but also to design optimal membrane-electrode-assembly (MEA) structure. In the past two decades, it becomes well known that oxygen transport resistance near the catalyst surface is a critical issue when reducing cathode catalyst loading due to concentration of oxygen flux on a small catalyst surface area [1-3]. On the other hand, as well as the case of oxygen flux, small catalyst surface area also increases proton current density near the catalyst particles, which can cause larger overpotential due to proton migration (ohmic overpotential). This is likely to be more important for recent-trend catalyst layer structure which avoids direct coating of ionomer on the catalyst to improve catalyst activity, e.g., employing porous carbon for the catalyst support [4-5]. Such a structure of catalyst layer can cause large resistance especially at a low humidity condition where no proton conduction path through water film exists. In this study, we investigated the effect of reducing catalyst loading on ohmic overpotential in catalyst layers to discuss the impact of local proton resistance quantitatively.MEA samples were fabricated by a pulse spray method using commercial catalyst supported on porous carbon and solid carbon (TEC10E50E and TEC10V30E, TANAKA Kikinzoku Kogyo K.K.), respectively. Nafion D2020 was employed as an ionomer, and ionomer-carbon weight ratio (I/C) was varied. For each specification, MEAs with different Pt-loading on cathode were prepared with the value of ~0.05 mgPt/cm2 and ~0.2 mgPt/cm2, respectively. GORE-SELECT Membrane M788.12 was employed as a membrane. Humidity dependence of the cell performance was evaluated at a cell temperature of 80°C. To evaluate ohmic overpotential within the catalyst layer, the performance was evaluated varying oxygen partial pressure (p O2). Structures of catalyst layers were analyzed using a scanning electron microscope and a transmission electron microscope.Some of the evaluation results are shown below. Figure 1 shows the humidity dependence of the performance of the MEAs with different cathode catalyst loading at a high p O2 condition of 100 kPa, where the oxygen concentration overpotential can be ignored in a wide current density range. The performance of the low Pt-loading MEA shows large humidity dependence. One of the reasons of this is humidity dependence of the catalyst activity reflecting the humidity dependence of the electrochemical surface area. Additionally, the apparent Tafel slope is larger at lower humidity, which indicates the contribution of the ohmic overpotential at such a low current density. Figure 2 shows the performance at various p O2, where the current density is normalized by p O2. Assuming a reaction order equal to 1 for the oxygen reduction reaction, this p O2-normalized current should be identical at a certain electrode potential for the variation of p O2 when the proton resistance is enough small and spatial reaction-distribution within the catalyst layer can be assumed homogeneous. For the high humidity performance of solid carbon MEA presented in Fig. 2 (c), the p O2 normalized performance is almost identical for all the p O2 conditions, which supports that ohmic overpotential is not significant in this current density range. On the other hand, at the relative humidity of 40%, the normalized performance shows large deviations, which reflect the proton resistance contribution, for all of the samples. The low Pt-loading samples show relatively larger deviations, especially for the porous carbon MEA, which indicates the effect of the local proton resistance. Origin of these proton resistance will be discussed in conjunction with the structures of the catalyst support and catalyst layer.The results suggest that the local proton resistance in the vicinity of the catalyst particles causes overpotential large enough to suppress the cell performance. To investigate local proton transport character of developed catalyst, it should be useful to evaluate Pt-loading dependence of the ohmic overpotential.

Evaluation of Degradation Mechanisms of Polymer Electrolyte Fuel Cell Using DEM Simulation

Polymer electrolyte fuel cells (PEFCs), which have various advantages such as high power output, high conversion efficiency, and low operating temperature, are expected to be applied to heavy-duty vehicles with a high environmental impact, and further performance and durability improvements are required for practical use. Currently, the degradation of power generation performance due to long-term operation is an issue in the practical application of PEFCs and it is considered that one of the causes of this degradation is the corrosion of the carbon support. However, the dynamic process of catalyst layer structure change due to CB particle corrosion has not yet been clarified, and the relationship between power generation performance change and catalyst layer microstructure has not been linked. It is also considered difficult to do so experimentally with the current state of the art. In this study, we focused on analyzing the dynamic structural change behavior of the catalyst layer due to corrosion of the carbon support by using numerical model simulation. By using the catalyst layer created by the numerical model, we simulated the power generation reaction and to identify the factors that cause the degradation of power generation performance.Discrete element method (DEM) was used to calculate the structure of catalyst layer by using carbon support, which is a branch-like aggregate of carbon black (CB) particles. The aggregate arrangement was determined based on the translational and rotational equations of motion for individual aggregates, elasticity between particles, and viscous damping1). Based on previous studies2) 3), the carbon corrosion reaction caused by the reaction between the products of the carbon surface reaction and the platinum oxidation reaction is considered, reflecting localized carbon corrosion within the catalyst layer. Also, we hypothesized that the porosity increases due to the shrinkage of CB particles in the early stage of corrosion, followed by a decrease in porosity and thickness due to the separation of the sintered parts of the CB particles that compose the aggregates. Furthermore, in this model, the fastening pressure is related to the timing of the structural collapse of the catalyst layer. Therefore, in this study, we performed calculations considering the neck breakdown of the aggregate due to the fastening pressure. The particles were assumed to be non-porous carbon (Vulcan), and calculations were performed under the same initial conditions as actual carbon black: primary particle size of 30 nm and aggregate diameter of 400 nm. Ionomers were assumed to be uniformly coated and not change in volume during degradations. The power generation reactions considering transport and diffusion were simulated for the catalyst layer structures fabricated by DEM, and the factors that cause differences in power generation performance were evaluated for each catalyst layer structure. In this study, performance degradation due to aggregation and desorption of platinum was neglected because we focused only on the effects of structural changes.Dynamic degradation of the catalyst layer was calculated considering localized corrosion due to carbon oxidation and structural collapse due to fastening pressure.The results showed a significant change in the catalyst layer structure despite the small amount of carbon corrosion. It was also suggested that the fastening pressure affects the amount of carbon corrosion when structural collapse occurs.AcknowledgmentThis study was supported by New Energy and Industrial Technology Development Organization (NEDO).

Investigating Cathode Ionomer Content and Assembly Techniques for Anion Exchange Water Electrolysers

An ionomer is often used in catalyst layers to a) adhere catalysts to the membrane or transport layer, b) facilitate ionic conductivity for OH- species through catalyst layers, and c) achieve ideal catalyst dispersions in catalyst inks used in spraying methods[1]. The choice of ionomer plays a crucial role in determining ion conductivity, water management, and mechanical stability within the membrane electrode assembly of anion exchange membrane water electrolysers (AEMWEs). Therefore, optimizing ionomer properties is crucial to achieving high-performance AEMWEs with efficient hydroxide transport.Both low and high ionomer loadings can lead to challenges in charge transport resistance. At low loadings, poor electronic conductivity and reduced contact between the catalyst layer and the membrane surface can occur due to a rough electrode interface[2]. This can result in inefficient charge transfer kinetics and hinder the overall efficiency (Figure 1c). Conversely, high ionomer loadings can lead to increased charge transport resistance, attributed to decreased gas permeability to the catalyst surface. The excessive presence of ionomer within the catalyst layer can block gas-liquid transport pores inside catalyst aggregates, limiting mass transport of reactants to the active sites[2]. This phenomenon can impede gas diffusion and oxygen reduction kinetics, leading to decreased performance and lower efficiency in AEMWEs (Figure 1d). Achieving an optimal ionomer loading balance is therefore essential for promoting efficient charge transfer and gas transport processes (Figure 1e), ultimately enhancing the overall performance and durability of AEMWE devices. The use of a proton conducting ionomer such as Nafion seems counterintuitive for use within AEMWEs, its hydroxide conductivity is comparatively lower, potentially limiting electrolyser performance. However, compared to Nafion, OH- conductive binders (Sustainion and PiperION) typically yield poorer electrodes, with larger catalyst aggregates[3].Two anion exchange ionomers and one ion exchange ionomer are evaluated across a range of loadings, and two different cathode assembly techniques, Catalyst coated substrates (CCS) and catalyst coated membranes (CCM) (Figure 1a). Since different catalyst surfaces are observed to influence ionomer degradation differently[4], commercially available Pt/C was utilised as a catalyst to focus on ionomer content and fabrication techniques. To investigate the effect of using hydrophobic or hydrophilic ionomers on catalyst layer homogeneity, the content of Nafion, Sustainion, and PiperION ionomers in the catalyst layers was varied (Figure 1b). Electrochemical impedance spectroscopy was used to determine the trade-off between high and low ionomer contents, polarisation curves found the in-situ electrocatalytic performance and highlighted the best performing ionomer and fabrication technique. Scanning electron microscopy was used to highlight the differences in catalyst layer structures and homogeneity.[1] Volk et al. Nov. 2023, EES. Catal. 2(1). 109-137. DOI: 10.1039/D3EY00193H.[2] Zhao et al. Feb. 2023, Int. J. Hydrogen Energy. 48(13). 5266-5275. DOI: 10.1016/j.ijhydene.2022.11.057.[3] Jervis et al. Nov. 2017, J. Electrochem. Soc. 164(14). 1551-1555. DOI: 10.1149/2.0441714jes.[4] Li et al. Mar. 2019, ACS Appl. Mater. Interfaces. 11(10). 9696–9701. DOI: 10.1021/acsami.9b00711.Figure 1: Schematic illustrations of: a) Membrane electrode assembly fabrication techniques, catalyst coated membrane and catalyst coated substrate. b) The chemical structures of PiperION A5 by Versogen, Sustainion XA-9 by Dioxide Materials, and Nafion by Liquion. c) Catalyst layer with low ionomer loading. d) Catalyst layer with moderate ionomer loading. e) Catalyst layer with high ionomer loading. Figure 1

Effect of Carbon Additives on the Performance of Oxide-Based Cathode for PEFC

To further advance the adoption of PEFCs, there's a growing need for developing non-Pt catalysts. Among these, oxide catalysts have caught much attention due to their impressive resistance to corrosion in acidic conditions. However, the lack of electronic conductivity is a challenge, and it is considered that new design guidelines for catalyst layers different from existing Pt/C electrodes are needed. In the field of secondary batteries, it has been reported that the shape and amount of carbon materials used as conductive additives affect performance in electrodes using materials with poor conductivity. Based on these reports, the effects of adding carbon to the catalyst layer for PEFC electrode using oxide catalyst were investigated.Using an oxide catalyst with Zr as the active site[1, 2], we examined the effects of adding carbon of different shapes to oxide catalysts on electrode structure and power generation performance. The catalyst layer was prepared using a drop method. The IV performance was improved with the addition of carbon, and the catalyst layer with KB added showed higher current density at all potentials than CNT. Thus, it was revealed that the shape of conductive additives also affects the performance of electrodes in PEFCs. When the amount of catalyst layer coating was changed, IV performance improved by increasing the coating amount of the catalyst. From SEM images of cross-sections, it was found that catalyst layers with a higher coating amount had larger aggregates of catalyst particles, larger voids in the catalyst layer, and thicker membranes.To control the structure of the electrode, a spray coating method was used for the preparation of the catalyst layers. The catalyst layers were fabricated by varying the gun distance, discharge amount, and heater temperature during spray application. IV performance was highest under conditions with a large gun distance. From structural observations, it was found that with a large gun distance, the aggregates became smaller.To investigate the impact of spray coating conditions on catalyst layer structure, titania was used as the catalyst, and layers were produced by varying the discharge amount and heater temperature. Structures with smaller agglomerates were observed when the discharge amount was low. Similarly, smaller agglomerates were observed when the substrate temperature was higher. These results suggest that porous structures with suppressed particle agglomeration are more likely to form under conditions conducive to drying.

Connected Platinum–Based Catalysts and Carbon-Free Cathode Catalyst Layers for High-Performance PEFCs

The improvement of the activity and durability of Pt-based electrocatalysts for oxygen reduction reaction (ORR) is essential to realize the widespread uses of polymer electrolyte fuel cells (PEFCs). Our group has developed a carbon-free connected Pt1–Fe1 catalyst with a chemically ordered superlattice structure.1–7 This catalyst consists of a beaded nanonetwork (5–15 nm) by the connection of Pt1–Fe1 nanoparticles with high electrical conductivity, thus eliminating the need for a carbon support. The connected Pt1–Fe1 catalyst exhibits an ORR specific activity about 10 times higher than a commercial Pt/C catalyst. This catalyst with carbon-free and chemically ordered structures improves the durability against start/stop and load cycles.1,4 Furthermore, the carbon-free catalyst layer using the connected Pt1–Fe1 catalyst with a porous, hollow capsule structure has high porosity (> 80%) and thin thickness (~ 1 μm), which would be beneficial for oxygen transport.To advance connected nanoparticle catalysts, this study addressed structural control of connected Pt-based catalysts and carbon-free catalyst layers using the developed catalysts. Since Fe ions induce the Fenton reaction and accelerate the degradation of electrolyte polymers, carbon-free and iron-free connected Pt3–Co1 catalysts with chemically ordered structures (Figure 1a) were developed using our silica coating method.4 The investigation of the structural effects on ORR performances in 0.1 M HClO4 electrolyte solution indicated that higher ordered degrees of the connected Pt3–Co1 catalysts improved ORR specific activity and load cycle durability. The STEM-EDX line mapping results suggested that a highly ordered structure can greatly suppress metal leaching from the catalyst. Furthermore, as shown in Figure 1b, this study investigated the structural effects on fuel cell performances for the carbon-free cathode catalyst layers. Here, the connected Pt3–Co1 catalyst with a hollow capsule structure was used, and the structural parameters such as ionomer thickness on capsules, capsule size, etc. were controlled. This presentation will discuss the relationship between catalyst layer structures and fuel cell performances through electrochemical and oxygen transport analyses. The developed connected Pt-based catalysts and the findings obtained in this study will contribute greatly to the design of a carbon-free cathode catalyst layer to achieve enhanced PEFC performances. Acknowledgement: This presentation is based on results obtained from a project, JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO), Japan. References Kuroki, T. Yamaguchi et al., [1] Energy Environ. Sci., 8, 3545–3549 (2015). [2] J. Electrochem. Soc., 163, F927–F932 (2016). [3] ACS Appl. Energy Mater., 1, 324–330 (2018). [4] ACS Appl. Nano Mater., 3, 9912–9923 (2020). [5] ACS Appl. Energy Mater., 5, 13176–13188 (2022). [6] J. Chem. Eng. Jpn., 56, 2197946 (2023). [7] Jpn. J. Appl. Phys., 63, 048002 (2024). Figure 1

(Invited) Computational and Experimental Characterization of PEFC Electrode Structures

In polymer electrolyte fuel cells (PEFCs) that demand high-efficiency and high-power-density for vehicle applications, elucidating the structure of the cathode catalyst layer is crucial to maximize the catalytic activity, proton conductivity, electric conductivity, and mass transport. Complex hierarchical primary particle, aggregate, and agglomerate structures of the cathode catalyst layer, which contains ionomer and platinum (Pt) catalysts supported on carbon particles, hinder the identification of bottlenecks in power generation. Particularly in recent years, emerging high-performance mesoporous carbon has introduced further complexity [1,2]. This advanced material is known to improve the catalytic activity by reducing the poisoning of Pt active sites. However, the gas transport resistance of mesoporous carbon remains unknown. Pt particles may be located both inside and outside the mesopores of the primary particles. The resistance to gas transport for Pt particles inside mesopores, which are less likely to be covered by ionomers that significantly hinder gas transport [3,4], is expected to be low. However, if Pt is located too deeply within the mesopores, or if the pores are submerged, the gas transport resistance could become substantial.Here, we elucidate impacts of ionomers and water on gas transport resistance in a catalyst layer composed of mesoporous and solid carbons by combined experiments and simulations. A pressure-independent gas transport resistance (Rother) can be determined from the limiting current of the hydrogen oxidation reaction (HOR) under various relative humidity (RH) conditions [3]. Separate ex-situ N2 and water adsorption isotherms of the catalyst layer powders allow for determining the volume ratio of ionomers within the mesopores and the RH-dependent water content in the catalyst layer, respectively. Moreover, computational simulations based on information from 3-D virtual models of the catalyst layers, reconstructed from 3-D transmission electron microscopy images and the isotherms, can reveal further details about the interactions between pore structure, Pt placement, ionomer distribution, and humidity. Our experiments have shown that at low RH, the mesoporous carbon exhibits a lower Rother than the solid carbon. However, as RH increases, Rother sharply increases, and the difference in Rother between mesoporous and solid carbons decreases. The experiments also displayed a hysteresis of RH-dependent Rother similar to that in the water adsorption isotherm. All these results suggest significant impacts of liquid water condensed in the mesopores. The simulations indicated that the lower Rother of mesoporous carbon at low RH can be reproduced by assuming that gas transport resistance at the ionomer/Pt interface is reduced in the mesopores, where Pt particles are not fully covered by ionomers owing to limited ionomer penetrations. The simulations also showed that Rother significantly increases, as observed in the experiments, when the mesopores are filled with liquid water. These findings suggest that optimizing the mesopore structure and distributions of Pt particles, ionomers, and water is crucial for enhancing power density.

Fitting Scattering Profiles of Perfluorinated Sulfonic Acid Ionomer Dispersions

Proton exchange membrane fuel cells (PEMFC) provide a path to wider adoption of hydrogen energy systems. This is because the energy density afforded by hydrogen makes PEMFC a strong candidate for the medium- and heavy-duty transportation sectors, where high allowable costs can reduce the barrier to adoption. As such, the focus of PEMFC research is toward greater efficiency and durability to reduce lifetime vehicle costs. To this end, high oxygen permeability ionomers (HOPI) are of interest, as the material has already been shown to increase mass activity in the cathode catalyst layer due to reduced anion poisoning from shorter side chains, in addition to enabling high power density through reduced oxygen transport resistance. While the performance of electrodes cast from HOPI and HOPI blended with commercial perfluorosulfonic acid (PFSA) has been documented, questions remain regarding the behavior of the novel ionomer in the dispersions and inks from which catalyst layers are fabricated. The literature on conventional PFSA ionomers devotes much attention to the effects of solvent media on interactions of ionomer backbone and side chains to form aggregates, motivated by the possible relationship between aggregates in dispersion and the structure of the cast catalyst layer, and thereby cell performance. In the present work, we probe the characteristic sizes and interactions among ionomer aggregates in dispersions by small angle x-ray scattering (SAXS). We report properties of aggregates in both HOPI and a commercial PFSA ionomer over a series of ionomer concentrations and at different ratios of water and propanol in the solvent medium. From these dispersions, aggregate spacings are estimated by fitting to the interference peak in the scattering intensity profile, and sizes are determined by form factor fitting. Next, series of blended HOPI and PFSA ionomer are prepared and studied by SAXS to understand the morphology of ionomer blends in solution. We further evaluate ionomer blends with different durations of ultrasonication, which can provide insight into the effect of sonication on ionomer blend aggregates during ink preparation.

Investigation of the Influence of Catalyst Layer and Carbon Structure for Cell Performance Using Reaction and Mass Transport Simulation of PEFC

The expectation of hydrogen is growing towards achieving a carbon-neutral society. In particular, further popularization of Polymer Electrolyte Fuel Cell (PEFC) is desired not only for passenger vehicles but also heavy duty vehicles. Therefore, high performance, high durability and cost reduction of the catalyst layer (CL) are becoming increasingly important. In recent years, research on mesoporous carbon (MPC) has become active [1, 2]. MPC exhibits high catalytic activity because this carbon is able to avoid sulfonic acid poisoning by reducing contact between the ionomer and Pt surface. However, it is disadvantage from the perspective of mass transport as it is necessary to supply oxygen and protons to the inside of the carbon support. Many studies have been conducted to balance sulfonic acid inhibition and mass transport of oxygen and protons of MPC. But it is still unclear which factors of the carbon structure play an important role for the performance and durability. Currently, carbon selection is being carried out by trial and error, and it is essential to provide design guidelines for CL and carbon structures to improve performance and durability.Our research group have developed a reaction and mass transport simulation within CL of PEFC and investigated the influence of CL structure for mass transport and cell performance [3, 4]. In this study, we have developed a model that takes into account the mass transport inside carbon support by extending the above CL scale model. Regarding the modeling of the internal carbon support, as reported in Chowdhury et al.'s research, the pore size distribution and surface wettability inside the carbon support are used to calculate the water uptake in the catalyst support, enabling the calculation of Electrochemical Surface Area (ECSA), proton conductivity, and gas diffusivity based on relative humidity (RH) [5]. By conducting such modeling, it became possible to simulate the polarization curve of CL using MPC. The calculated results, as reported in the studies by Ramaswamy [6] and Shinozaki [7], show that Pt utilization, proton conductivity, and gas diffusivity change depending on the RH inside the CL, and the polarization curve accurately match the experimental results.Furthermore, using this model, we simulated the effects of different MPC structures for FC performance. The relationship between carbon structures such as the ratio of Pt supported within the carbon interior and surface and depth from the carbon surface and cell performance will be reported in this presentation.Acknowledgements:This work is supported by the Junichi Miyamoto Hydrogen Research Award.

H2 Production Efficiency in PEM Water Electrolysis Cells – Evaluating the Effect of the Electrode-Electrolyte Interface on O2 and H2 Crossover

PEM water electrolyzers (PEMWEs) are a promising candidate to store fluctuating renewable energy due to their wide current density operating regime. This flexibility is a significant advantage compared to alkaline water electrolysis. However, this flexibility in current density is also a challenge to fully understand local and interfacial effects at different operating conditions minding the different scales that have to be considered in PEMWEs – from the nanometer-sized ionomer thin film to millimeter-sized channel structures for water supply and gas removal.Gas crossover is a big challenge in PEMWEs. It does not just limit the operating regime due to possible formation of explosive gas mixtures on the anode side. 1 It also contributes significantly to the overall efficiency of the system by causing some hydrogen that was produced by the electrical energy input to not reach the cathode exhaust. Crossover hydrogen is lost to the anode exhaust and crossover oxygen chemically recombines with hydrogen, which is therewith also lost when considering the overall hydrogen production efficiency. 2 Compared to PEM fuel cells, gas crossover characteristics in PEMWEs under operation are diverging more from steady-state permeation data. 1, 3 This can be caused by operation dependent two-phase flow characteristics of liquid water and gaseous product. While the anode is actively flushed with liquid water as reactant supply, the cathode of a PEMWE also experiences two-phase operation; either due to being flushed with water additionally or caused by the significant electro-osmotic drag at high current densities leading to water droplet formation in the cathode catalyst layer. The exact environment of the electrode-electrolyte interface will dictate the crossover behavior at different operating points but it is not well understood.In this study we shed some light on the effect of the interfacial two-phase characteristics on the gas crossover behavior at different operating conditions. Hydrogen and oxygen steady-state permeation over PEMWE membranes is studied using a mass spectrometer at different single- and two-phase flow conditions that can be decoupled from the electrochemical gas production and electro-osmotic drag effects due to active hydrogen and oxygen gas supply. By a thorough parameter variation we are able to distinguish solubility, diffusivity and fugacity effects on the overall permeability of the active gases. We show that common pure gas-phase measurements lead to gas permeabilities that show a severalfold difference compared to the results from the two-phase measurements.By comparing such steady-state permeation with gas crossover characteristics at different operating points a better understanding of the electrode-electrolyte interface composition during PEMWE full cell operation can be achieved. While the exact interfacial characteristics depend on the catalyst layer and transport media structure, this experimental data shall serve as a starting point for revisiting the tuning of structural parameters in order to achieve PEMWEs with improved hydrogen production efficiencies. Such dynamic effects will be important in large-scale cells where the two-phase characteristics can change along the cell, additionally. Bernt, M.; Schröter, J.; Möckl, M.; Gasteiger, H. A., Analysis of Gas Permeation Phenomena in a PEM Water Electrolyzer Operated at High Pressure and High Current Density. J. Electrochem. Soc. 2020, 167.Schalenbach, M.; Carmo, M.; Fritz, D. L.; Mergel, J.; Stolten, D., Pressurized PEM water electrolysis: Efficiency and gas crossover. Int. J. Hydrogen Energy 2013, 38, 14921-14933.Trinke, P.; Haug, P.; Brauns, J.; Bensmann, B.; Hanke-Rauschenbach, R.; Turek, T., Hydrogen Crossover in PEM and Alkaline Water Electrolysis: Mechanisms, Direct Comparison and Mitigation Strategies. J. Electrochem. Soc. 2018, 165, F502-F513.

Understanding the Mechanism of Evaporation-Induced Islands during the Formation of Catalyst Layers and Their Influence on the Alkaline Oxidation Evolution Reaction

Advancements in anode development substantially reduce the cost and enhance the performance of water electrolysis. The strategic configuration of nano-sized catalyst materials on anode supports is a pivotal factor in the expansion of the production of catalyst layers and has a significant influence on their electrochemical performance [1–3]. Therefore, it is essential to understand the structure formation mechanisms during electrode fabrication. This contribution aims to explore the inherent drying mechanisms in the coating process and their subsequent influence on the morphological evolution of anodes, ultimately establishing a linkage between these morphological changes and electrochemical performance and stability metrics. The initial phase of the study involved a detailed characterization of commercial nickel cobalt oxide nanoparticles via advanced analytical techniques, including transmission electron microscopy and energy-dispersive X-ray spectroscopy [4]. Subsequently, a stable ink was formulated by dispersing the catalyst alongside a binder in a solvent, which was then uniformly applied to a conductive nickel plate utilizing an ultrasonic spray coater. Prior to application, the catalyst inks underwent optimization based on the Hansen solubility parameters of catalyst materials [5, 6] and subsequent visualization of their stability and dispersibility characteristics through transmittogram analysis [7]. The drying process of the coating was conducted at two distinct temperatures, 50 °C and 150 °C, to investigate the effect of temperature on solvent evaporation. Morphological and structural analyses of the anodes were subsequently performed using scanning electron microscopy (SEM), laser scanning microscopy (LSM), and atomic force microscopy (AFM), providing insight into the alterations induced by the drying process. The analyses conducted in this study elucidate significant modifications in the morphology of the layer structures attributable to variations in drying temperatures as illustrated in Figure 1. Specifically, lower temperature resulted in reduced evaporation rates that facilitated the formation of larger, isolated regions/islands on the anode support. These are indicative of a non-uniform coating distribution. In contrast, a higher temperature promoted rapid evaporation, resulting in a quite homogeneous distribution of smaller islands accompanied by the emergence of voids within the anode layer. Electrochemical analysis revealed that these morphological changes are of vital importance: they govern the wetting behaviour and the dynamics of bubble formation which are important for the electrochemical performance and durability of the catalyst layers. Moreover, the insights gleaned from this study are instrumental in identifying optimal configurations of catalyst layer structures, i.e., features that should be maintained during scale-up. In conclusion, this study significantly advances the field by revealing novel principles governing the design and optimization of electrode structures for the oxygen evolution reaction. In particular, the complicated relationship between drying temperatures and morphological evolution, which significantly influences electrochemical performance is explained.

The Role of the Ionomer in the Catalyst Layer of Anion Exchange Membrane Water Electrolyzers

Anion exchange membrane water electrolyzers (AEMWE) have gained recent attention as a promising low temperature H2O electrolysis technology that combines the benefits of commercial liquid alkaline and proton exchange membrane water electrolyzers (PEMWE), while alleviating concerns over capital cost and materials criticality associated with these existing technologies.1,2 While AEMWEs have achieved significant performance advances in recent decades, overpotentials remain high relative to PEMWE counterparts,2 requiring AEMWE-specific catalyst layer design strategies to further advance this technology. Catalyst layers conventionally consist of catalyst particles which are co-deposited with an ion-conducting polymer or ionomer that is of the same chemistry as the ion-exchange polyelectrolyte phase.3 In PEMWEs, which are operated in pure water, this ionomer serves as the sole ion (H+) transport network through the catalyst layer. The ionomer further serves roles as a binding agent, adhering catalyst particles to the electrode, as well as an ink rheology agent.4 In contrast, AEMWEs often operate in dilute supporting electrolyte, raising questions about the role of the ionomer in AEMWE systems.In this work, we assess the specific roles of ionomers in supporting electrolyte fed AEMWEs using NiFe2O4, identified in our previous work as a strong candidate for a commercial alkaline oxygen evolution reaction (OER) catalyst, and PiperION TP85 from Versogen, a common commercially available AEM. Catalyst layers were constructed at variable ionomer contents (0 – 30 wt%) to investigate the role of the ionomer phase in supporting electrolyte-fed AEMWEs. Specifically, the role of the ionomer in catalyst structure and quality, catalyst adhesion, and ion transport were investigated via electrochemical and physical characterization of pristine and tested catalyst layers. Ex-situ scanning electron microscopy with energy dispersive x-ray spectroscopy (SEM-EDS), x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS) measurements were employed to provide insights into catalyst and ionomer loss mechanisms over 200 h durability tests at different ionomer contents. Voltage breakdown analyses were used to further investigate the effects of ionomer content on cell overpotentials. Electrochemical impedance spectroscopy (EIS) and Tafel analyses were utilized to decouple thermodynamic, Ohmic, kinetic, and catalyst layer resistance contributions to overpotentials for each ionomer content.The results show that intermediate ionomer contents (5-10 wt%) provide the highest cell current densities. Intermediate ionomer contents were found to a achieve a balance of catalyst adhesion, catalyst layer porosity, and catalyst layer homogeneity, leading to improved site accessibility and decreased cell overpotentials. Testing with Nafion (a non-anion conducting polymer) further demonstrated that the ionomer is not required for ion conduction in AEMWE catalyst layers under supporting-electrolyte operation and therefore that ionomers do not need to match the chemistry of the anion exchange membrane. Instead, we find that, for initial performance, the ionomer is crucial for catalyst layer structure and quality, and for long-term stability, the ionomer is crucial to provide catalyst adhesion for long-term durability.[1] IRENA Green Hydrogen Cost Reduction - Scaling up Electrolyzers to Meet the 1.5C Climate Goal 2020, [2] Alia, S. et al., Electrochem. Soc. Interface 2021, [3] Volk, E. K. et al., EES Catalysis 2024, [4] Khandavalli, S. et al., ACS Appl. Mater. Interfaces 2019

(Invited) Electrochemical Impedance Spectroscopy in Proton Exchange Membrane Water Electrolysis: Status, Features, Problems and Potentials

Proton exchange membrane water electrolysis (PEMWE) holds promise as an efficient and responsive technique for green hydrogen generation, vital for de-carbonization in diverse applications spanning from transportation, energy storage, to steel production, etc. Electrochemical impedance spectroscopy (EIS), as a non-invasive diagnostic tool, is increasingly being employed to differentiate processes and optimize performance of PEMWE.[1] This talk gives an overview of the status, features, problems and potentials of EIS in the study of PEMWE.Currently, the application of EIS in PEMWE remains in its early stages both in quantity and quality. There are less than 200 related journal papers, dwarfed by that in lithium-ion batteries (~700) and proton exchange membrane fuel cell (PEMFC, ~2300). Interpretations of the impedance spectra largely depend on visual inspection or fitting with empirical equivalent electric circuit models (EECM). Investigations using numerical and analytical frequency-domain model based on the physical processes in PEMWE are rather rare.Typical features in a spectrum for the anode and cathode catalyst in a 3-electrode setup generally include a depressed semi-circle, which is attributed to the charge transfer at high frequency end and surface adsorption at low frequency end in HER/OER reaction.[2-4] Occasionally, a small semi-circle at high frequency range may be observed, yet the origin is unclear.[5] In contrast, typical features in a spectrum for the catalyst layer in a 2-electrode setup include a straight line segment at high frequency range, a depressed semi-circle at medium frequency range and an arc at low frequency range. The straight line segment is a signature of the porous electrode. The depressed semi-circle corresponds to kinetic process. The arc at low frequency is related to mass transfer process. The characteristic frequency corresponding to surface adsorption may overlap with that of mass transfer in catalyst layer, and the arc at low frequency range is generally attributed to mass transfer rather than surface adsorption. [9-10] At high current density, the dynamic generation of bubbles may impair the quality of the EIS data or even invalidate the technique altogether.[11] Sometimes a small arc attributed to contact resistance/capacitance may be detected at the medium to high frequency range.Despite its easiness of use, EIS still grapple with problems or controversies in its application in PEMWE. Firstly, different from PEMFC, where electronic resistance in the catalyst layer is negligible, the electron resistance in the catalyst layer of PEMWE is comparable to the proton resistance. [12-13] Therefore, the intercept of the 45° line segment at high frequency range with the real axis under blocking or non-blocking conditions is affected by the electron resistance of the catalyst layer. Accordingly, analytical EIS model taking into account of both ionic and electronic resistivity should be used in the analysis.[14] Secondly, the combination of high electronic resistivity, the small thickness of the catalyst layer, the pore size jump between the catalyst layer and the porous transport layer (PTL), and the large deformation of the CL, causes significant 2D or 3D effects. Such effects are not yet considered in either analytical models or EECM.[15] Thirdly, while some groups reported inductive loops at low frequency range (0.1~10 Hz) with good repeatability for multiple types of catalyst and measurement setup[16-17], the majority of the impedance spectra in literature didn’t show such behavior. The conditions for the emergence and the underlying mechanism for such low frequency inductive loop remain largely unexplored.Lastly, there is a lacking of guideline for reporting EIS data and presenting the spectrum. Some normalization of the raw data in Ohm with apparent or effective area, catalyst loadings, flow rate per active area, etc., is needed to facilitate the understanding and comparison among the EIS data in literature. [9,10,17-23] The potential of EIS application in PEMWE can be further realized by upgrading its practice into the next stages. In experiment, measures to suppress the disturbance of bubbles are needed to extend the frequency range compliant with Kramer-Kronig transformation. Replacing PTL with gas diffusion layer (GDL) used in fuel cell may help to validate the power and limitation of the 1D analytical model that has considered the electronic resistance. In post-processing, the number and values of characteristic frequencies may be identified with the further development of distribution of relaxation time (DRT) method. In modeling, analytical and numerical EIS models taking into account the low electronic resistivity and 2D as well as 3D catalyst layer structure is needed to reveal the mechanism for the subtle features in the spectra.

Innovative Anode Design Incorporating Sub-Catalyst Layer for Proton Exchange Membrane Water Electrolyzers with Ultra-Low Iridium Loading

Proton exchange membrane water electrolyzers (PEMWE) have garnered increasing attention in recent years due to their capability to produce clean, high-purity hydrogen. The optimization of the catalyst layer structure within these systems is critical, particularly in reducing the loading of platinum-group metal (PGM) anode catalysts. Under conditions of ultralow iridium loading, ion and mass transport are severely impeded, which hampers the kinetic performance of oxygen evolution reaction (OER) catalysts.In this study, we propose an innovative membrane electrode assembly (MEA) design for PEMWE, wherein an ultra-thin sub-catalyst layer is constructed atop the conventional catalyst layer. This sub-catalyst layer, fabricated via spray coating with an ultra-low iridium loading of less than 0.05 mg/cm², possesses a high surface area and is engineered to enhance the interfacial contact area between the catalyst layer and the porous transport layer. The integration of this sub-catalyst layer markedly reduces both kinetic and ohmic resistances, thereby lowering the overall overpotential.Our findings demonstrate that this novel approach results in a significant increase in the current density of the electrolyzer by 400 mA/cm² and a reduction in high-frequency resistance (HFR) by 35 mΩ cm², when compared to the conventional MEA structure. This study highlights the potential of the proposed MEA design to improve the efficiency and performance of PEMWE systems, contributing to the advancement of clean hydrogen production technologies.

Exploring the Impact of Cathode Ionomer Content on Alkaline Exchange Membrane Fuel Cells (AEMFCs) Using Inkjet Printing Technique

Hydrogen proton exchange membrane fuel cells (PEMFCs) typically rely on expensive platinum group metals (PGMs) as catalysts. A promising strategy to eliminate the need for PGM catalysts is to operate the cell under alkaline conditions. Non-PGM based AEMFCs have achieved power densities exceeding 1 W/cm2, and various commercial electrolytes, such as Tokuyama A201/A901/AS-4, FumaTech Fumasep, Ionomr Aemion, and Versogen PiperION, have been developed and are available for researchers to explore and enhance AEMFC performance. Unfortunately, AEMFCs using commercial materials have not yet demonstrated performance and stability comparable to PEMFCs even though their ion transport properties are similar. Therefore, there is a need to study the physical processes that are limiting the performance of these materials in AEMFC membrane electrode assemblies (MEAs).AEMFCs electrode performance is very sensitive to a myriad of factors with two key factors being: a) the fabrication method; and b) ionomer to catalyst ratio. Regarding the former, unlike in PEMFCs, the number of fabrication techniques studied to fabricate AEMFC electrodes in the literature has been limited with only a handful of studies utilizing techniques such as ultrasonic spray-coating and doctor blade to control the catalyst layer structure. The development of novel fabrication techniques would therefore help the development of these technologies and allow more systematic studies to be performed, such as a detailed analysis of the ionomer to catalyst ratio. Even though previous research already showed the sensitivity of AEMFC performance to variations in ionomer content [2,4-6,11,17], its influence at varying temperatures and with newly developed commercial materials has not been thoroughly investigated. Furthermore, its effect on cell stability has not received sufficient attention.In this work, inkjet printing is introduced as a novel fabrication method for AEMFC electrode fabrication and applied to fabricate low-loading PGM-based CCMs with varying and graded cathode ionomer loading for AEMFCs. The inkjet-printed CCMs were tested in operating AEMFCs with H2/O2 at 60 °C, demonstrating a cell power density of 0.53 W/cm2 with a total loading of 0.3 mgPt/cm2, one of the highest reported in the literature using commercial materials (see figure), along with high repeatability and stability. The effect of cathode ionomer content and grading was studied at 60 °C and 80 °C with 90% RH inlet gases. The optimal cathode ionomer content at the beginning of life was identified as 20 wt% under both conditions, but the cell experienced unstable performance over time at 80 °C, with a decrease in cell voltage during constant current holds. Adding more ionomer to the cathode decreased the rate of cell degradation, which we hypothesize is due to increased water retention. The graded cathode, with more ionomer close to the AEM, appears to be the best strategy to minimize the observed instability.[1] T. Reshetenko et al., Journal of Power Sources 375 (2018) 185–190.[2] R. B. Kaspar et al., Journal of the Electrochemical Society 162 (6) (2015) F483.[3] D. Yang et al., Chinese Journal of Catalysis 35 (7) (2014) 1091–1097.[4] D. Yang et al., Journal of Power Sources 267 (2014) 39–47.[5] A. Carlson et al., Electrochimica Acta 277 (2018) 151–160.[6] X. Xie et al., International Journal of Energy Research 43 (14) (2019) 8522–8535.[7] P. S. Khadke and U. Krewer, Electrochemistry Communications 51 (2015) 117–120.[8] B. Britton and S. Holdcroft, Journal of The Electrochemical Society 163 (5) (2016) F353.[9] J. Zhang et al., Cell Reports Physical Science 2 (3).[10] D. Sebastian et al., Catalysts 10 (11) (2020) 1353.[11] S. Kim et al., Electrochimica Acta 400 (2021) 139439.[12] I. Gatto et al., ChemElectroChem 10 (3) (2023) e202201052.[13] N. U. Saidin et al., Asia-Pacific Journal of Chemical Engineering e3024.21[14] V. M. Truong et al., Materials 12 (13) (2019) 2048.[15] T. Novalin et al., Journal of Power Sources 507 (2021) 230287.[16] Q. Wei, et al., Sustainable Energy & Fuels 6 (15) (2022) 3551–3564.[17] J. Hyun et al., Journal of Power Sources 573 (2023) 233161.[18] E. Sediva et al., Journal of Power Sources 558 (2023)232608. Figure 1

Coarse-Grained Molecular Dynamics Simulation on the Impact of the Primary Pores on the Distribution and Morphology of Ionomers within Catalyst Layers during the Drying Process

The catalyst layer (CL) plays a crucial role in polymer electrolyte fuel cells (PEFCs) as it facilitates proton transport by coating the carbon surface with platinum (Pt) particles with the assistance of Nafion ionomers. Given the existence of complex pore structures of supported carbon and their potential impact on the distribution and morphological evolution of the ionomers in the CL of PEFCs, this area is essential while remaining underexplored. Herein, we employed the coarse-grained molecular dynamics (CGMD) simulation method to investigate the impact of the primary pores on the distribution and morphological evolution of ionomers from the Nafion ionomers solution to the Pt/C substrate surface during the drying process of the catalyst layer at the nanoscale. We aim to provide a comprehensive understanding of the behavior of ionomers in this process.To simulate the porous structure of the supported carbon, we employed carbon nanotubes (CNT) structure to represent the primary pores in the MD simulation. By varying the parameters, including the Nafion ionomers to carbon (I/C) ratio, the number and diameter of Pt particles, and the diameter of the CNT, the MD simulation was performed under different conditions. The MD analysis results demonstrated that the structure of the CNT had a significant impact on the distribution and morphology changes of Nafion ionomers during the drying process of the catalyst ink. In the early stage, a small fraction of Nafion ionomers were observed to adsorb directly onto the carbon substrate surface without any interaction with the Pt particles. Meanwhile, the majority of the Nafion ionomers were found to form cylindrical aggregates in the solution, which is attributed to the mutual attraction between the ionomers. During the drying process, the cylindrical Nafion ionomer aggregates were initially attracted to the surface of Pt particles on the carbon substrate due to their hydrophilic sulfonate group shells, undergoing a transformative unfolding upon contacting the carbon substrate. This shift to a lamellar structure is propelled by the hydrophobic attraction of the ionomer backbone and the hydrophilic affinity of the sulfonate groups. Moreover, it is noteworthy that Pt particles with a larger diameter enhance the adsorption of ionomer aggregates by offering a larger surface area during the drying process. Consequently, this leads to the formation of larger bare areas on the carbon substrate surface, even when using a solution with the same I/C ratio. As the drying process further progresses, the Nafion ionomers fully unfold, forming a layered structure on the hydrophobic carbon substrate surface, which finally results in a well-structured ionomer distribution. As the drying process nears completion, ionomer aggregates adhere to the surface of the carbon substrate and form ionomer layers. Specifically, as shown in Fig. 1-c, an adequate I/C ratio will result in the ionomers having a uniform and complete laminar distribution on the carbon substrate along with the edge of CNT. Besides, larger Pt particles resulted in a larger bare area of the carbon substrate (Fig. 1-a). Moreover, the thickness of the ionomer above the primary pore is significantly smaller than that on the surface of the carbon substrate (Fig. 1). These results highlight the significance of taking into account the porous structure when investigating ionomer behavior. The existence of CNT impacts the distribution and morphology of Nafion ionomers during the drying process of the catalyst layer.This study demonstrates the significant influence of the porous structure of primary pores on the distribution and morphological changes of Nafion ionomers in the catalyst layer. These findings offer valuable insights for the development of more effective catalyst inks and optimization of catalyst layer structures. The results also provide a theoretical foundation for enhancing the catalytic efficiency and proton transport performance of PEFCs.AcknowledgementsThe New Energy and Industrial Technology Development Organization (NEDO) of Japan supported this work under Grant number JPNP20003. The simulations were performed on the Supercomputer system 'AFI-NITY' at the Advanced Fluid Information Research Center, Institute of Fluid Science, Tohoku University. We want to express our sincere gratitude to W. Shirakawa for her invaluable assistance. Figure 1

(Invited) Advanced Analysis Technologies Developed in Nedo FC-Platform: From Innovative Material Developments to Solving Problems for Industrial Implementation

Polymer electrolyte fuel cells are a key device for hydrogen utilization towards achieving carbon neutrality. It is effective to expand it not only to FCVs, but also to heavy duty vehicles (HDVs) and other mobilities to expand the range of its use. In many countries around the world, application to trucks has become mainstream, and its application to trains and ships is also progressing. The specifications required for fuel cells for such heavy-duty usage are higher performance and durability than fuel cells for FCVs, making material development challenging. [1]Considering such background, NEDO is working with the industry to envision the fuel cell specifications that will be needed around 2030 and 2040. [2] By breaking the overall target down to each material target, we are making our research and development goals more concrete: the 2030 materials targets will require solutions to current complex and difficult challenges and the material development targets for 2040 are aggressive targets that may not be achieved by extending current material development. We have built and operate NEDO FC-platform to promote and support such challenging research and development. [3, 4] (Fig. 1)The materials analysis group in NEDO FC-Platform has four missions to contribute to achieving these goals: support for the development of innovative materials, database construction to promote materials informatics, advanced phenomenon analysis for simulator development, and advanced phenomenon analysis for solving industrial issues. Research institutes in Japan are working together to advance the sophistication of analysis technology.The figure below shows the portfolio of advanced analysis technology in NEDO FC -Platform. The development of fuel cells with a hierarchical structure requires multiscale analysis techniques. High-performance electron microscope and operando X-ray analysis technology to measure structure and dynamics at the atomic level, X-ray and neutron beam analysis technology to analyze catalyst layer structure and formation process, and visualization of reactions and changes in their distribution within the catalyst layer, and X-ray and neutron technology for elucidating mass transfer and phenomena at the cell level is progressing, and it is being applied to fuel cells provided by industry to verify their effectiveness. We are conducting verification and working to resolve issues.Furthermore, in the coming years, synchrotron radiation facilities, such as SPring-8 and NanoTerasu will be upgraded, and neutron facilities such as J-PARC and electron microscopes will become more sophisticated. We are also working on improving the performance of measurement hardware and innovating measurement technology through digitalization, and we will discuss our prospects. Acknowledgement This work is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO). References :[1] Cullen, D.A., Neyerlin, K.C., Ahluwalia, R.K. et al. New roads and challenges for fuel cells in heavy-duty transportation. Nat Energy 6, 462–474 (2021).[2] Technology Roadmap Hydrogen and Fuel Cells, https://www.nedo.go.jp/content/100973008.pdf[3] K. Amemiya, et. al., 242nd ECS meeting abstract.[4] N. Takeuchi, et. al., 244th ECS meeting abstract. Figure 1

Comparative Study of Different Polymeric Binders in Electrochemical CO Reduction.

Electrochemical reduction of carbon monoxide offers a possible route to produce valuable chemicals (such as acetate, ethanol or ethylene) from CO2 in two consecutive electrochemical reactions. Such deeply reduced products are formed via the transfer of 4-6 electrons per CO molecule. Assuming similar-sized CO2 and CO electrolyzers, 2-3-times larger current densities are required in the latter case to match the molar fluxes. Such high reaction rates can be ensured by tailoring the structure of the gas diffusion electrodes. Here, the structure of the cathode catalyst layer was systematically varied using different polymeric binders to achieve high reaction rates. Simple linear polymers, bearing the same backbone but different functional groups were compared to highlight the role of different structural motifs. The comparison was also extended to simple linear, partially fluorinated polymers. Interestingly, in some cases similar results were obtained as with the current state-of-the-art binders. Using different surface-wetting characterization techniques, we show that the hydrophobicity of the catalyst layer-provided by the binder- is a prerequisite for high-rate CO electrolysis. The validity of this notion was demonstrated by performing CO electrolysis experiments at high current density (1 A cm-2) for several hours using PVDF as the catalyst binder.