Fuel Cell Catalyst Layers Research Articles

3D generation and reconstruction of the fuel cell catalyst layer using 2D images based on deep learning

The catalyst layer (CL) being the site of electrochemical reactions, is the core subunit of the membrane electrode assembly (MEA) in polymer electrolyte fuel cells (PEFCs). Thus, the porous structure of the CL has a significant influence on oxygen transfer resistance and affects the charge/discharge performance. In this study, the three-dimensional (3D) porous structure of the catalyst layer is reconstructed based on the deep convolutional generative adversarial network (DCGAN) deep learning method, utilizing focused ion beam scanning electron microscopy (FIB-SEM) microstructure graphs as training data. Each set of spatial-continuous microstructure graphs, generated by DCGAN with interpolation in latent space, is applied to build a unique 3D microstructure of the CL without the use of real FIB-SEM data. Meanwhile, distinct interpolation conditions in the DCGAN are discussed to optimize the ultimate structure by approaching the structural information to real data, including that of porosity, particle size distribution, and tortuosity. Moreover, the comparison of real and generated structural data reveal that the data generated by DCGAN shows an adjacency relationship with real data, indicating its potential applicability in the field of electrochemical simulation with reduced situational costs. • Application of DCGAN-based method in 3D microstructure generation of catalyst layer • Optimization of interpolation methods by morphology and mass transport properties • Reduction of the computation cost for catalyst layer design in PEFC

Integrated Cathode with In-Situ Grown Mnco2o4/Nc/Mno2 Catalyst Layer for Alkaline Liquid Fuel Cells

Integrated Cathode with In-Situ Grown Mnco2o4/Nc/Mno2 Catalyst Layer for Alkaline Liquid Fuel Cells

Integrated Cathode with In-Situ Grown Mnco2o4/Nc/Mno2 Catalyst Layer for Alkaline Liquid Fuel Cells

Integrated Cathode with In-Situ Grown Mnco2o4/Nc/Mno2 Catalyst Layer for Alkaline Liquid Fuel Cells

Integrated Cathode with In-Situ Grown Mnco2o4/Nc/Mno2 Catalyst Layer for Alkaline Liquid Fuel Cells

Integrated Cathode with In-Situ Grown Mnco2o4/Nc/Mno2 Catalyst Layer for Alkaline Liquid Fuel Cells

Mechanistic interactions in polymer electrolyte fuel cell catalyst layer degradation

Mechanistic understanding of the coupled performance-durability interactions resulting from the transient landscape of catalyst degradation is elucidated.

Ionomer Films Impact on The Structure, Flow Regime, and The Wettability of The Catalyst Layer of PEMFC

Percolation testing and contact angle measurements have been used to investigate the role of relative humidity on structure, mass transport, and wettability of a PEM fuel cell catalyst layer and membrane. Four samples were tested, two catalyst layers and two membranes. Structure and mass transport changes in the catalyst layers resulting from RH changes were studied in terms of percolation pressure. A clear change in the structure between low and high RH conditioning was observed. Relative humidity (RH) cycling also impacted percolation pressures with an indication of catalyst layer cracking. In addition, RH effect on wettability of both catalyst layers and membranes was studied by measuring contact angles of sessile drops.

Probing Ionomer Swelling and Water Content in Catalyst Layer during Operation Using Small Angle Neutron and X-Ray Scattering

In the fuel cell catalyst layers (CLs), the ionomer plays roles as a binder and a conductor for protons. It is now known that the ionomer not only forms aggregates between the catalyst agglomerates of the porous structure of the CLs, but it also forms a few nanometer thick thin film covering the surface of this catalyst. In this latter form, it modifies the specific activity of the catalyst by altering the structure and behavior of the electrochemical double layer, and it hinders the oxygen transport toward the catalytic sites. In addition, the nanostructure and functional transport properties of O2 and protons of the ionomer depends on its water content which increases with water activity. Especially, the ionomer must be sufficiently hydrated to enable proton transport from the membrane toward the active sites through the CLs and ensure a proper utilization of the electrochemical surface area. However, excess liquid water accumulation in the pores of the CL hinders oxygen diffusion and should be avoided. Therefore, it is necessary to understand the distribution and the quantity of water, being either within the ionomer or in the pores of the catalyst layers, during fuel cell operation to improve their design and constituents. Very recently, and based on our former experience, we pushed forward the in situ and operando Small Angle Scattering techniques to quantify the water content and ionomer swelling in fuel cell CLs during operation. In this work, we report the effect of the conditioning and operating conditions on the ionomer behavior (Figure - Comparison of SANS Spectra obtained in dry state, at 100%RH and during operation at 80%RH, showing the evolution of the ionomer peak related to its swelling). Figure 1

Investigation of Spray and Roll to Roll Coated Gas Diffusion Electrode Surface & Bulk Properties Using Microscopy and Spectroscopy

Further development of large-scale manufacturing capabilities for the most critical component in polymer electrolyte membrane fuel cells (PEMFC), the membrane electrode assembly (MEA) is needed. Advances in MEA manufacturing capabilities could reduce one of the major cost factors associated with MEA production, the platinum group metal (PGM) catalysts currently used at the cathode electrode for PEMFCs. While spray coating methods have been prevalently used at lab-scale for MEA fabrication, it is desirable to move towards roll-to-roll (R2R) techniques to enable scalable production. Gas diffusion electrode (GDE) based MEAs are easier to manufacture in a R2R fashion than catalyst coated membrane (CCM) based MEAs, since the catalyst layer is deposited directly on the gas diffusion media (GDM) without inducing the PEM swelling observed via other fabrication routes.1 Understanding interfacial properties of these electrodes is important for optimization of electrochemical performance and fabrication procedures employed for wide-scale manufacturing of PEM electrodes.Key surface properties such as surface morphology and surface chemistry, as well as the bulk electrode nanostructure and composition were analyzed for a variety of GDEs with catalyst layers (CLs) prepared by R2R and spray coating methods using X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Energy Dispersive Spectroscopy (EDS). The R2R-coated GDEs were fabricated using the slot die and microgravure coating methods on the same GDM substrate (Freudenberg H23C8) and they were made with both alcohol- and water-rich ink solvent ratios. The ultra-sonic spray coated GDEs were fabricated using both SGL 29BC and H23C8 GDM. In some cases, the spray coated GDEs had an additional amount of ionomer added, referred to as ionomer overlayer.2,3 The water-rich slot die R2R-coated GDE and the spray-coated GDE with an additional ionomer overlayer achieved the highest performance from this set of GDEs. Additionally, these GDEs showed the highest ionomer content measured by both XPS and SEM-EDS and shared a similar level of low surface roughness, implying the differences in composition and performance result from the different coating processes. Interestingly, STEM-EDS didn’t reveal a higher ionomer concentration in these samples, suggesting that these fabrication methods enrich the top surface layer without a significant impact on the bulk electrode. It was also found that the different microporous layer (MPL) surface properties inherent to a specific GDM influence the electrode morphological properties such as surface roughness as well as surface chemistry. The differences in MPL porosity lead to a unique surface ionomer enrichment degree and morphology at the CL surface that will interface with the membrane. These CL surface properties that are in contact with the membrane are hypothesized to be the reason for the improved performance metrics despite fabricating the GDE based MEAs under the same conditions. This work improved the knowledge of how a change in just one material component, or varying the fabrication process, can lead in some cases to vast differences and in others to subtle changes in initial performance, while also demonstrating the effectiveness of multiple characterization techniques towards identifying processing-property-performance trends. Mauger, S. A., Neyerlin, K. C., Yang-Neyerlin, A. C., More, K. L. & Ulsh, M. Gravure Coating for Roll-to-Roll Manufacturing of Proton-Exchange-Membrane Fuel Cell Catalyst Layers. Journal of The Electrochemical Society 165, F1012–F1018 (2018).Wang, M. et al. Impact of Microporous Layer Roughness on Gas-Diffusion-Electrode-Based Polymer Electrolyte Membrane Fuel Cell Performance. ACS Applied Energy Materials 2, 7757–7761 (2019).Mauger, S. A. et al. Fabrication of high-performance gas-diffusion-electrode based membrane-electrode assemblies. Journal of Power Sources 450, (2020).

High Surface Area Pt/C Electrocatalyst Modification with Ionic Liquids for Improved Ionic Conductivity in Polymer Electrolyte Fuel Cell Catalyst Layer

Oxygen reduction reaction (ORR), specifically in technological case of platinum (Pt) electrocatalyst, is one of the determining factors for commercialization and mass production of affordable fuel cell electric vehicles. ORR takes place at the triple phase boundary of the Pt electrocatalyst, the ionomer (Nafion) or water, and oxygen gas. In order to maximize the electrochemical surface area (ECSA) of the Pt nanoparticles, they are dispersed on high surface area (HSA) carbon supports and a large portion of them are buried inside the micro (< 2nm) and mesopores (< 50nm). Because of the size exclusion, ionomer cannot penetrate pores below 20 nm and water acts as the proton conducting media in these pores1. In addition, the dense polytetrafluoroethylene (PTFE) backbone blocks the oxygen transport. Therefore, the interface design principle in this work for improving catalyst layer ORR performance is to infiltrate micropores with ionic liquids (ILs) to facilitate sufficient proton and oxygen delivery to the Pt active sites. Ionic strength of ILs is within the range of 2.77 – 5.3×103 mol.m- 3 which is up to 7 orders of magnitude higher than that of water1. Higher ionic strength of electrolyte in micropores will ensure that electric double layers are thin and they do not exclude protons from entering the pores as fuel cells typically operate at higher potentials than the potential of zero charge of Pt. We implemented three imidazolium-derived ILs including 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2mim]+[NTf2]-), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C4mim]+[NTf2]-), and 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide ([C4dmim]+[NTf2]-) to modify 40 wt.% Pt on HSA Ketjenblack EC-300J catalyst (Pt/C). Our RDE prescreening showed improved proton conduction and accessibility of the electrocatalyst in all Pt/C-Nafion-IL catalyst layers compared to that of Pt/C-Nafion making them great candidates for catalyst modification2. After optimization of ink recipe including IL to carbon and water to IPA ratios, the MEAs with 5cm2 active area were fabricated via decal transfer of anode and cathode catalyst layers on Nafion XL membrane. Figure 1a represents the fuel cell polarization curves of the IL-modified catalysts compared to the baseline Pt/C. Pt/C-[C4mim]+[NTf2]- shows the best performance and highest kinetic activity compared to the baseline and other two IL-modified catalyst layers. The open circuit voltages (OCVs) were 0.942, 0.933, 0.948, and 0.929 V for baseline Pt/C, Pt/C-([C2mim]+[NTf2]-), Pt/C-([C4mim]+[NTf2]-), and Pt/C-([C4dmim]+[NTf2]-), respectively. Electrochemical impedance spectroscopy (EIS) data was used for measuring cathode catalyst layer ionic conductivity (Figure 1b), as Nyquist spectra represents a 45° line in the high frequency range where real and imaginary parts are equal, followed by a straight 90° line. A physical impedance model obtained from Obermaier et al.3 was fitted to EIS data, specifically at high frequencies to get the catalyst layer’s ionic conductivity. All the modified catalysts showed improved ionic conduction compared to the baseline Pt/C. Conductivity values for catalyst layers of Pt/C, Pt/C-([C2mim]+[NTf2]-), Pt/C-([C4mim]+[NTf2]-), and Pt/C-([C4dmim]+[NTf2]-) with approximately 10μm thickness were 1.93, 3.95, 2.34, 2.04 S/m, respectively. Our fuel cell results show that high conductivity of ([C4mim]+[NTf2]-) along with its optimum chemical structure is responsible for improved performance across kinetic and ohmic regions compared to the baseline Pt/C. References Avid, A. & Zenyuk, I. V. “Confinement effects for nano-electrocatalysts for oxygen reduction reaction”. Curr. Opin. Electrochem. 25, 100634 (2021). Avid, A. & Zenyuk, I. V. Ionic Liquid Modified Pt/C Electrocatalysts for the Oxygen Reduction Reaction in Polymer Electrolyte Fuel Cells. ECS Meet. Abstr. MA2020-02, 2155 (2020). Obermaier, M., Bandarenka, A. S. & Lohri-Tymozhynsky, C. A Comprehensive Physical Impedance Model of Polymer Electrolyte Fuel Cell Cathodes in Oxygen-free Atmosphere. Sci. Rep. 8, 4933 (2018). Figure 1

Direct Formic Acid Fuel Cell Anode Catalyst Layer: Enhanced Mass Transport with Increased Porosity

Batteries are the predominant portable power source, but are inefficient due to their limited charge capacity, lengthy recharging times, and exponential degradation. Direct formic acid fuel cells present a sustainable replacement to batteries with their instantaneous refueling times and high efficiency. However, small pore size (~20 nm) between the agglomerates in the anode catalyst layer and two-phase flow hinders the mass transport and reduces the cell performance. Therefore, enhancing the cell performance also requires the two-phase flow optimization of the liquid reactant (formic acid, HCOOH) and gaseous product (carbon dioxide, CO2). To accomplish this, pore-forming agent (magnesium oxide, MgO) was incorporated during the anode catalyst layer fabrication and subsequent removal leaving behind lager pores to improve the two-phase flow through the anode catalyst layer.In 2012, the addition and subsequent removal of pore-former (lithium carbonate, LiCO3), formed ~10 μm pores within the anode catalyst layer.[1] The optimal performance was found for pores formed from with 17.5 wt% LiCO3; however, the formic acid electrooxidation charge transfer activity was reduced, due to the size of the pore-former increased the separation of the agglomerates and reduced the connected electrochemical surface area.To avoid damaging the integrity of the anode catalyst layer, previous work to integrate a smaller pore-former MgO (~50 nm), into the anode catalyst layer was investigated. [2] Compared to an anode catalyst layer without pore-former, 25 wt% pore-former increased the electrochemical surface area and cell performance by 293% and 86%, respectfully. The present study aims to further explore varying wt% of pore-former with additional sonication of the catalyst/ionomer ink prior to fabrication. The uniformity and effect of agglomerate size vs. MgO addition will be explored by quantifying the viscosity of the catalyst ink. [3] Bauskar, A.S. and Rice, C.A., Impact of Anode Catalyst Layer Porosity on the Performance of a Direct Formic Acid Fuel cell. 2012, 62, 36-41.Lam, S., Bixby, M.M., and Rice, C.A., Optimization of Mass Transport within Direct Formic Acid Fuel Cell Catalyst Layer via Pore Formers.Khandavalli, S., Park, H.J., Kariuki, N.N., Myers, J.D., Stickel, J.J., Hurst, K., Neyerlin, C.K., Ulsh, M., and Mauger, A.S., Rheological Investigation on the Microstucture of Fuel Cell Catalyst Inks. 2018, 10, 50.

Ionic Liquid Composite Electrocatalysts for the Oxygen Reduction Reaction in PEM Fuel Cells

The cathode catalyst layer (CCL) of the proton exchange membrane fuel cell (PEMFC) cathode requires a high amount of Pt to compensate for the sluggish oxygen reduction reaction (ORR) kinetics. Reducing the Pt loading in the CCL remains the major challenge in commercializing fuel cell devices. Recent developments enable up to 20-fold improvement in the activity of ORR electrocatalysts and facilitate a lower amount of Pt in the catalyst layer.1 However, these low-Pt-loaded cathodes show significant voltage losses at high current densities (HCD).2 These performance losses are associated with local oxygen transport resistances due to higher particle-particle distance and the interfacial resistance between Pt and PFSA-based ionomers.3 The interfacial resistance observed at the catalyst-ionomer interface is exacerbated with the thickness of the ionomer film on catalyst particles4 and specific adsorption of sulfonate groups.5 These challenges can be potentially addressed by modifying the catalyst-ionomer interface at fuel cell cathode. Protic and hydrophobic Ionic liquids (ILs) are known to enhance the ORR performance of state-of-the-art catalysts in half cell experiments.6 Our research group has previously shown that an ionic liquid interlayer on the Pt surface mitigates the specific adsorption of sulfonate groups. Despite remarkable half-cell performance of ionic liquid modified catalysts (100-150%), ionic liquid incorporated CCLs show only a modest improvement (10-15%).7 Inhomogeneous distribution of ionic liquids in the catalyst layer and potential loss of ionic liquids during fuel cell operation are possible reasons behind this discrepancy. The use of sulfonated polymerized ionic liquid block copolymer (SPILBCP) as an ionomer presents a novel method to incorporate ionic liquids in the catalyst layer. SPILBCP has sulfonated domains to enable proton conduction and ionic liquid domains to facilitate oxygen transport and mitigate sulfonate adsorption. In this work, we implement rotating disk electrode (RDE) techniques to analyze a polymeric ionic liquid block copolymer (SPILBCP) as an ionomer for the PEMFC cathode. We found that Pt/C catalyst films prepared using PILBCP show two-fold improvement over those prepared using Nafion, a state-of-the-art ionomer. We use the CO displacement technique to show that PILBCP thin films exhibit a lower degree of sulfonate adsorption than Nafion on a highly ordered Pt surface. Furthermore, thin films of SPILBCP and Nafion show comparable proton conductivity and oxygen permeability. These results support the recent finding showing up to two-fold improvement in the kinetic activity of PEMFCs using SPILBCP as a catalyst binder. 8 References Shao M, Chang Q, Dodelet JP, Chenitz R. Recent Advances in Electrocatalysts for Oxygen Reduction Reaction. Chem Rev. 2016;116(6):3594-3657. doi:10.1021/acs.chemrev.5b00462 Kongkanand A, Mathias MF. The Priority and Challenge of High-Power Performance of Low-Platinum Proton-Exchange Membrane Fuel Cells. J Phys Chem Lett. 2016;7(7):1127-1137. doi:10.1021/acs.jpclett.6b00216 Weber AZ, Kusoglu A. Unexplained transport resistances for low-loaded fuel-cell catalyst layers. J Mater Chem A. 2014;2(41):17207-17211. doi:10.1039/c4ta02952f Sasikumar G, Ihm JW, Ryu H. Dependence of optimum Nafion content in catalyst layer on platinum loading. J Power Sources. 2004;132(1-2):11-17. doi:10.1016/j.jpowsour.2003.12.060 Garrick TR, Moylan TE, Yarlagadda V, Kongkanand A. Characterizing electrolyte and platinum interface in PEM fuel cells using CO displacement. J Electrochem Soc. 2017;164(2):F60-F64. doi:10.1149/2.0551702jes Snyder J, Fujita T, Chen MW, Erlebacher J. Oxygen reduction in nanoporous metal-ionic liquid composite electrocatalysts. Nat Mater. 2010;9(11):904-907. doi:10.1038/nmat2878 Snyder J, Livi K, Erlebacher J. Oxygen reduction reaction performance of [MTBD][beti]-encapsulated nanoporous NiPt alloy nanoparticles. Adv Funct Mater. 2013;23(44):5494-5501. doi:10.1002/adfm.201301144 Li Y, Cleve T Van, Sun R, et al. Modifying the Electrocatalyst-Ionomer Interface via Sulfonated Poly ( Ionic Liquid ) Block Copolymers to Enable High-Performance Polymer Electrolyte Fuel Cells. 2020. Figure 1

Electrospray Deposition: A Breakthrough Technique for Proton Exchange Membrane Fuel Cell Catalyst Layer Fabrication

This Spotlight article presents the state-of-the-art of electrospray deposition technique applied to the fabrication of proton exchange membrane fuel cell (PEMFC) components, mainly focusing on catalyst layers in gas diffusion electrodes. The atomization of a suspension of particles over a substrate under the influence of a strong electric field results in the growth of a film with macroporous morphology and many interesting properties. This so-called electrospray deposition has reported many noteworthy beneficial effects for the fabrication of the catalyst layers of gas diffusion electrodes of PEMFCs. The electrosprayed catalyst layers prepared from suspensions of catalyst particles and ionomers present a dendritic macroporous morphology with superhydrophobic character that improves the water management inside the cell and increases the performance by ∼20% with respect to standard electrodes prepared by airbrushing. Other interesting effects observed with electrosprayed catalyst layers are increased catalyst utilization and water absorption capabilities of the ionomer, improved performance under nonhumidified conditions, and a reduction in catalyst degradation. In addition, the electrospray deposition decreases platinum losses during fabrication thanks to the attractive electrostatic forces between the ion mist and the substrate compared with regular ink-based spray methods.

Microstructure Investigation of Polymer Electrolyte Fuel Cell Catalyst Layers Containing Perfluorosulfonated Ionomer.

Perfluorosulfonated ionomers are the most successful ion-exchange membranes at an industrial scale. One recent, cutting-edge application of perfluorosulfonated ionomers is in polymer electrolyte fuel cells (PEFCs). In PEFCs, the ionomers are used as a component of the catalyst layer (CL) in addition to functioning as a proton-exchange membrane. In this study, the microstructures in the CLs of PEFCs were characterized by combined synchrotron X-ray scattering and transmission electron microscopy (TEM) analyses. The CL comprised a catalyst, a support, and an ionomer. Fractal dimensional analysis of the combined ultrasmall- and small-angle X-ray scattering profiles indicated that the carbon-black-supported Pt catalyst (Pt/CB) surface was covered with the ionomer in the CL. Anomalous X-ray scattering revealed that the Pt catalyst nanoparticles on the carbon surfaces were aggregated in the CLs. These findings are consistent with the ionomer/catalyst microstructures and ionomer coverage on the Pt/CB surface obtained from TEM observations.

Gas Diffusion Electrode Half Cells – a Powerful Tool for Fuel Cell Electrocatalyst Evaluation in Relevant Conditions

In aqueous rotating disk electrode (RDE) measurements, advanced catalyst materials show tremendous performance improvements in comparison to commercial Pt/C catalysts towards oxygen reduction reaction (ORR). However, these promising improvements cannot (yet) be transferred to realistic membrane electrode assembly (MEA). [1] These discrepancies can be explained by non-ideal catalyst layer composition, leading to mass transport limitations of either oxygen (which is transported through the pores) or protons (via the ionomer) to the active centers of the catalyst material. Mass transport phenomena in real catalyst layers are still under debate and hold huge potential to significantly improve catalyst performance.However, mass transport in realistic fuel cell catalyst layers cannot be assessed with RDE experiments, as they are limited to low current densities and idealized catalyst layers on solid substrate. Therefore, MEA experiments are usually employed to evaluate those phenomena. Yet, those investigations are time consuming, expensive (large quantities of catalyst needed, extended test equipment) and do not allow segregated investigation of either cathode or anode catalyst layer. Furthermore, comparison of different MEA studies can be challenging due to varying operating conditions. Therefore, techniques combining the advantages of RDE, namely simplicity and comparability, with the realistic operating ranges of MEA are urgently required to retrieve the potential of catalyst layer optimization.In this presentation half-cells using gas diffusion electrodes (GDE) are proposed as a new powerful experimental tool to enable high mass transport catalyst screening in relevant potential ranges and realistic electrode structures.On the example of a Pt loading study we show, that current densities of up to 2 A/cm² can be achieved [2]. In contrary to other formerly used methods [3], it is thereby possible to overcome mass transport limitations at relevant fuel cell operating potentials. Additionally, we demonstrate good compliance with MEA experiments, proving the method´s suitability for catalyst evaluation in realistic fuel cell potential ranges.Besides activity, also stability of the electrocatalyst is affected significantly by the catalyst layer structure. We present here a novel method, where a GDE half-cell is coupled to an inductively coupled plasma mass spectrometer (ICP-MS) to gain deeper insights into dissolution of electrocatalysts in realistic electrode structures [4]. With this unique online tool, we could measure Pt dissolution in realistic catalyst layers for the first time reported in literature. We show, how mass transport of dissolved Pt species influences net Pt dissolution and how Pt dissolution can also be detected through Nafion membranes. Besides that, also the mobility of Pt-ions through Nafion membranes is further investigated. Literature [1] Ly, A., et al. J. Power Sources, 2020. 478: 228516[2] Ehelebe, K., et al., J. Electrochem. Soc., 2019. 166(16): F1259-F1268,[3] Inaba, M., et al., Energy Environm. Sci., 2018. 11(4): 988-994,[4] Ehelebe, K. et al. submitted Figure 1

Interpreting Ionic Conductivity for Polymer Electrolyte Fuel Cell Catalyst Layers with Electrochemical Impedance Spectroscopy and Transmission Line Modeling

A cathode catalyst layer containing optimally distributed ionomer is critical to reduce the platinum loading and increase its utilization in polymer electrolyte fuel cells. Here, electrochemical impedance spectroscopy (EIS) was used to measure effective ionic conductivity of pseudo catalyst layers (PCLs) at a relative humidity (RH) range of 50%–120%. These results are compared to previous work using the hydrogen pump (HP) method. EIS effective ionic conductivity results reported here are higher than those from the HP because in the HP set-up ionic pathways must be effectively connected through the PCL to be counted, whereas in the EIS measurement, ionomer segments that are in contact with the membrane but are not effectively connected all the way through the PCL can be detected. Double layer capacitances and effective ionic conductivities of Pt/C catalyst layers with various supports and ionomer to carbon (I/C) ratios were studied. High surface area carbon support resulted in a lower effective ionic conductivity compared to the graphitized carbon support due to worse ionomer dispersion. Effective ionic conductivities of Pt/C layers were compared to that of PCLs. On average, effective ionic conductivities of Pt/C layers were higher than PCLs because of possible carbon agglomeration within the PCLs.

Multicomponent, multiphase interactions in fuel-cell inks

Fuel-cell catalyst layers (CLs) are porous electrodes that are fabricated from CL inks: colloidal dispersions of catalyst particles and ion-conducting polymer (ionomer), dispersed in solvent(s). The complex interactions between the ink components ultimately dictate CL microstructure and electrochemical performance. To control the CL formation process and optimize fuel-cell performance, knowledge of these ink interactions is vital. In this review, we analyze data from ink-focused papers to elucidate how ink parameters (solvent type, ionomer-to-carbon ratio, etc.) impact ink interactions and CL performance. We then discuss these results in the context of the current understanding of two critical ink interactions: ionomer/solvent and ionomer/catalyst particle interactions. • Catalyst layer microstructure/performance controlled by ink interactions/parameters. • Regression analysis performed to analyze most sensitive parameters. • Ionomer-to-carbon ratio and ink solvent determine final catalyst layer properties. • Ionomer/particle and ionomer/solvent interactions are critical.

Toward Optimizing Electrospun Nanofiber Fuel Cell Catalyst Layers: Polymer–Particle Interactions and Spinnability

We investigate the effect of the poly(acrylic acid) (PAA) carrier polymer concentration on the microstructure and rheological properties of catalyst inks for electrospun polymer–electrolyte membran...

Toward Optimizing Electrospun Nanofiber Fuel Cell Catalyst Layers: Microstructure and Pt Accessibility

This work investigates how local ionomer/platinum (Pt) interactions and ionomer distribution in electrospun Pt/Vulcan nanofiber electrodes impact ionomer coverage, proton accessibility, and oxygen ...

Two-Phase Dynamics and Hysteresis in the PEM Fuel Cell Catalyst Layer with the Lattice-Boltzmann Method

In this work, a Lattice-Boltzmann-Method (LBM) model for simulating hysteresis in a proton exchange membrane fuel cell (PEMFC) electrode is presented. One of the main challenges hindering study of the cathode catalyst layer (CCL) in PEMFCs is the lack of understanding of two-phase transport and how it affects electrochemical performance. Previously, the microstructure details needed to build an accurate mesoscale model to examine such phenomena have eluded researchers; however, with advances in tomography and focused-ion-beam scanning-electron-microscopy (FIB-SEM), reconstruction of the complex porous media has become possible. Using LBM with these representations, the difficult problem of catalyst layer capillary hysteresis can be examined. In two-phase capillary hysteresis, both the equilibrium saturation position as well as its absolute value depends on the wetting history. Based on the models, it is ascertained that at lower capillary numbers, the liquid begins to undergo capillary fingering—only above a capillary pressure of 5 MPa, a regime change into stable displacement is observed. As capillary fingering does not lead to uniform removal of liquid, the prediction is that because high capillary pressures are needed to change to the regime of stable displacement, wicking is not as effective as the primary means of water removal.

Impact of Solvent on PFSA Properties from Dispersion to Cast Film

Perfluorosulfonic-acid (PFSA) ionomers are a critical part of proton-exchange-membrane (PEM) fuel-cell catalyst layers (CLs). They serve both to bind the catalyst particles together, lending mechanical support, and provide pathways for ion transport. The CL fabrication process has garnered significant attention in recent years, with research efforts focused on understanding the properties of the CL ink (colloidal dispersions of solvent(s), catalyst particles, and ionomer), and how those properties translate to the cast CL structure.1-2 The PFSA/solvent interaction is a crucial and complex piece of the larger multi-component interaction phenomena. Recent work has shown the strong impact of solvent composition on dispersion properties3 and structure,4 and eventual CL performance,1 but there is little understanding of how these initial (dispersion) and final (dried film) states are connected. How do different dispersion properties as a result of varying ionomer/solvent interactions control cast structure and behavior? Do these interactions persist upon drying? This information is vital to understand, predict, and control PFSA film and CL structure and properties, instead of relying on current empirical approaches to the formation process.In this presentation, we investigate these questions by studying the impact of solvent on PFSA properties over the course of film preparation. In-situ grazing incidence x-ray scattering (GISAXS)5 experiments on ionomer dispersions are systematically performed over a range of water to n-propanol composition to explore the evolution of film structure from dispersion to dried state. Dispersion properties (particle size, viscosity, structure) and film properties (structure, water uptake, conductivity, etc.) are evaluated within the context of the GISAXS data, connecting properties across the range of PFSA states, and lending insight into interaction/property relationships. These results provide important understanding of the impact of solvent during film and CL manufacturing processes, and reveal that final properties are a strong function of ionomer/solvent interactions in the dispersion state that persist long past formation and annealing.AcknowledgementsScattering work was conducted at the Advanced Light Source (ALS), beamline 7.3.3, which is supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy (Contract No. DE-AC02-05CH11231). This work was mainly funded under the Fuel Cell Performance and Durability Consortium (FC-PAD), by the Hydrogen and Fuel Cell Technologies Office (HFTO), of the office of the Energy Efficiency and Renewable Energy (EERE), of the U. S. Department of Energy under contract number DE-AC02-05CH11231. S.B. acknowledges support from the Graduate Research Fellowship Program by the National Science Foundation under Grant No. DGE 1752814.References Van Cleve, T.; Khandavalli, S.; Chowdhury, A.; Medina, S.; Pylypenko, S.; Wang, M.; More, K. L.; Kariuki, N.; Myers, D. J.; Weber, A. Z.; Mauger, S. A.; Ulsh, M.; Neyerlin, K. C. ACS Appl. Mater. Interfaces 2019, 11 (50), 46953-46964.Hatzell, K. B.; Dixit, M. B.; Berlinger, S. A.; Weber, A. Z. J. Mater. Chem. A 2017, 5 (39), 20527-20533.Berlinger, S. A.; McCloskey, B. D.; Weber, A. Z. J. Phys. Chem. B. 2018, 122 (31), 7790-7796.Welch, C.; Labouriau, A.; Hjelm, R.; Orler, B.; Johnston, C.; Kim, Y. S. ACS Macro. Lett. 2012, 1 (12), 1403-1407.Dudenas, P. J.; Kusoglu, A. Macromolecules 2019, 52 (20), 7779-7785.