Publikationsliste Severin Vierrath

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Originalarbeiten in wissenschaftlichen Fachzeitschriften

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2020

• C. Klose, T. Saatkamp, A. Münchinger, L. Bohn, G. Titvinidze, M. Breitwieser, K.-D. Kreuer, S. Vierrath
  All-Hydrocarbon MEA for PEM Water Electrolysis Combining Low Hydrogen Crossover and High Efficiency
  2020 Adv Energy Mater, Seite: 1903995
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  Kurzfassung

  Hydrocarbon ionomers bear the potential to significantly lower the material cost and increase the efficiency of proton-exchange membrane water electrolyzers (PEMWE). However, no fully hydrocarbon membrane electrode assembly (MEA) with a performance comparable to Nafion-MEAs has been reported. PEMWE-MEAs are presented comprising sPPS as membrane and electrode binder reaching 3.5 A cm−2 at 1.8 V and thus clearly outperforming state-of-the-art Nafion-MEAs (N115 as membrane, 1.5 A cm−2 at 1.8 V) due to a significantly lower high frequency resistance (57 ± 4 mΩ cm² vs 161 ± 7 mΩ cm²). Additionally, pure sPPS-membranes show a three times lower gas crossover (<0.3 mA cm−2) than Nafion N115-membranes (>1.1 mA cm−2) in a fully humidified surrogate test. Furthermore, more than 80 h of continuous operation is shown for sPPS-MEAs in a preliminary durability test (constant current hold at 1 A cm−2 at 80 °C). These results rely on the unique transport properties of sulfonated poly(phenylene sulfone) (sPPS) that combines high proton conductivity with low gas crossover.
• F. Hegge, F. Lombeck, E. Cruz Ortiz, L. Bohn, M. von Holst, M. Kroschel, J. Hübner, M. Breitwieser, P. Strasser, S. Vierrath
  Efficient and Stable Low Iridium Loaded Anodes for PEM Water Electrolysis Made Possible by Nanofiber Interlayers
  2020 ACS Appl. Energy Mater, Band: 3, Nummer: 9, Seiten: 8276 - 8284
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  Kurzfassung

  Significant reduction of the precious metal catalyst loading is one of the key challenges for the commercialization of proton-exchange membrane water electrolyzers. In this work we combine IrOx nanofibers with a conventional nanoparticle-based IrOx anode catalyst layer. With this hybrid design we can reduce the iridium loading by more than 80% while maintaining performance. In spite of an ultralow overall catalyst loading of 0.2 mgIr/cm2, a cell with a hybrid layer shows similar performance compared to a state-of-the-art cell with a catalyst loading of 1.2 mgIr/cm2 and clearly outperforms identically loaded reference cells with pure IrOx nanoparticle and pure nanofiber anodes. The improved performance is attributed to a combination of good electric contact and high porosity of the IrOx nanofibers with high surface area of the IrOx nanoparticles. Besides the improved performance, the hybrid layer also shows better stability in a potential cycling and a 150 h constant current test compared to an identically loaded nanoparticle reference.
• E.C. Ortiz, F. Hegge, M. Breitwieser, S. Vierrath
  Improving the performance of proton exchange membrane water electrolyzers with low Ir-loaded anodes by adding PEDOT: PSS as electrically conductive binder
  2020 Rsc Adv, Band: 10, Nummer: 62, Seiten: 37329 - 37927
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  Kurzfassung

  Reducing the iridium catalyst loading in the anode of polymer electrolyte membrane electrolyzers is a major goal to bring down the cost. However, anodes with low Ir-loading can suffer from poor electrical connectivity and hence lower the efficiency of the electrolyzer. In this work, we replace parts of the Nafion binder in the anode with an electrically conductive polymer (poly-3,4-ethylenedioxythiophene and polystyrene sulfonate acid complex, PEDOT:PSS) to counter this effect. At the optimal 50 : 50 blend we achieve a 120 mV lower overpotential (2.02 V) at 3 A cm−2 compared to a pure Nafion reference (2.14 V). This corresponds to a 6% better efficiency. Ex situ resistivity measurements and high frequency resistance measurements indicate that the major cause for this improvement lies in the reduced electrical in-plane resistance due to the electrical conductivity of PEDOT:PSS.
• P. Veh, B. Britton, S. Holdcroft, R. Zengerle, S. Vierrath, M. Breitwieser
  Improving the water management in anion-exchange membrane fuel cells via ultra-thin, directly deposited solid polymer electrolyte
  2020 Rsc Adv, Band: 10, Seiten: 8645 - 8652
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  Kurzfassung

  Thin ionomer membranes are considered key to achieve high performances in anion exchange membrane fuel cells. However, the handling of unsupported anion exchange membranes with thicknesses below 15 μm is challenging. Typical pre-treatments of KOH-soaking, DI-water rinsing and/or wet assembly with sub-15 μm thin films are particularly problematic. In this work, we report configurations of membrane electrode assemblies with solid polymer electrolyte thicknesses equivalent to 3, 5 and 10 μm, made possible by direct coating of the ionomer onto gas diffusion electrodes (direct membrane deposition). The anion-conducting solid polymer electrolyte employed is hexamethyl-p-terphenyl poly(benzimidazolium) (HMT-PMBI), which is known for its high mechanical stability and low rate of gas crossover. By fabricating membrane-electrode-assemblies with PtRu/C anodes and Pt/C cathodes with a low precious metal loading of <0.3 mg cm−2, reproducible performances beyond 1 W cm−2 in H2/O2 atmosphere are achieved. The thin membranes enable excellent performance robustness towards changes in relative humidity, as well as low ionic resistances (<40 mOhm cm2).

2019

• B. Shanahan, T. Böhm, B. Britton, S. Holdcroft, R. Zengerle, S. Vierrath, S. Thiele, M. Breitwieser
  30 μm thin hexamethyl-p-terphenyl poly(benzimidazolium) anion exchange membrane for vanadium redox-flow batteries
  2019 Electrochem Commun, Band: 102, Seiten: 37 - 40
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  Kurzfassung

  We present the first results of an anion exchange ionomer membrane, hexamethyl-p-terphenyl poly(benzimidazolium) (HMT-PMBI), in a vanadium redox flow battery. Anion exchange membranes exhibit superior vanadium crossover suppression compared to proton exchange membranes due to the Gibbs–Donnan effect. HMT-PMBI was benchmarked against a similarly thin Nafion XL membrane which allowed us to compare differences based solely on chemical properties of the ionomer materials. We report cycling data of 45 cycles at a current density of 150 mA/cm2 with excellent coulombic efficiency of >99.4%, energy efficiency of 80.6–74.2% and a low ohmic resistance of 0.219–0.255 Ω cm2. In addition, a three times lower self-discharge rate is obtained for the HMT-PMBI membrane compared to Nafion XL. HMT-PMBI is therefore a potential alternative for PFSA based ionomers in VRFB applications.
• F. Hegge, J. Sharman, R. Moroni, S. Thiele, R. Zengerle, M. Breitwieser, S. Vierrath
  Impact of Carbon Support Corrosion on Performance Losses in Polymer Electrolyte Membrane Fuel Cells
  2019 J Electrochem Soc, Band: 166, Seiten: F956 - F962
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  Kurzfassung

  Corrosion of the carbon support leads to a severe decay in the performance of PEM fuel cells, mainly due to an increase in the oxygen transport resistance. To investigate the effect of degradation on oxygen transport, we cycled MEAs between 1−1.5 V and analyzed the electrode structure with FIB-SEM tomography at various ageing states. The tomography results show that the electrode structure changes over 1000 cycles in terms of thickness (7.8 to 6.5 μm), porosity (44 to 38%) and diffusivity (9 to 8 105 m2s−1). Limiting current measurements in the wet (hydrogen/air) and dry state (hydrogen pumping) allowed the pressure dependent and pressure independent mass transport resistances to be distinguished and to quantify the impact of product water. The pressure independent resistance increased from 24 to 41 sm−1. Considering the marginal contribution of the catalyst pore space resistance (3 to 4 sm−1) it is concluded that the largest portion of the increase (50%) is caused by an increased local mass transport resistance. This is due to a decrease of the electrode roughness factor (282 to 169). The limiting current under wet conditions shows that another 44% could stem from a change in the wetting behavior, while 6% remains unexplained.
• M. Solihul Mu’min, T. Böhm, R. Moroni, R. Zengerle, S. Thiele, S. Vierrath, M. Breitwieser
  Local hydration in ionomer composite membranes determined with confocal Raman microscopy
  2019 Journal of Membrane Science, Band: 585, Seiten: 126 - 135
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  Kurzfassung

  Water management in electrochemical energy applications like fuel cells has a crucial impact on performance, in particular on the ionic conduction of ionomer membranes. To strengthen the understanding of water management in such devices, we report a novel method for non-destructive measurements of the hydration of composite membranes based on confocal Raman microscopy. Composite membranes were produced by spray-coating of Nafion into a mesh of electrospun poly(vinylidene fluoride-co-hexafluoropropylene)/polyvinylpyrrolidone (PVDF-HFP/PVP) blend nanofibers. Hydration levels of several pure nanofiber meshes and nanofiber/Nafion composites were evaluated by linear least squares fitting of reference Raman spectra to hyperspectral images. We found that spectral contribution of water to nanofiber spectra depends on the PVDF-HFP/PVP ratio and is independent from fiber diameter. Further, we were able to reliably determine nanofiber polymer composition of single fibers based on Raman spectroscopy. Raman imaging of composite membranes was performed at ambient air and fully hydrated conditions to study the local hydration in PVDF-HFP/PVP/Nafion composites as well as in a Nafion XL membrane. 2D through-plane mappings revealed that the nanofiber hydration positively correlated with PVP content. In the Nafion XL membrane, the polytetrafluoroethylene-based reinforcement was verified as a hydrophobic layer sandwiched between Nafion ionomer, which showed a more than 10% reduced hydration compared to the outer Nafion layers. These results motivate the use of confocal Raman microscopy as a novel method to investigate the local water distribution in ionomer composite membranes that are widely used in electrochemical energy conversion.
• M. Bühler, P. Holzapfel, F. Hegge, M. Bierling, S. Vierrath, S. Thiele
  Optimization of porous transport electrodes for PEM water electrolysis
  2019 J Mater Chem A, Band: 165, Seite: F305
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  Kurzfassung

  In this study we investigate the potential of porous transport electrode (PTE) based membrane electrode assemblies (MEAs) for proton exchange membrane water electrolysis. The focus is on the overpotential determining anodic PTE for the oxygen evolution reaction. The influences of catalyst loading, ionomer content and porous titanium substrate on the polarization behavior are analyzed. The comparison of a porous fiber-sintered substrate with a powder-sintered substrate shows no significant differences in the kinetic and mass transport regions. Ohmic losses, however, are lower for fiber PTEs above a catalyst loading of 1.0 mgIrO2 cm−2. Variations of the Nafion content in the catalyst layer reveal changes of mass transport and ohmic losses and have an influence on the reproducibility. Varying the noble metal loading and therefore the thickness of the applied catalyst layer influences the kinetic region and ohmic resistance of the MEAs. The best compromise between reproducibility and performance is found for a loading of 1.4 mgIrO2 cm−2 and 9 wt% Nafion. The stable operation of the aforementioned PTE is shown in a 200 h durability test at 2 A cm−2.
• T. Boehm, R. Moroni, M. Breitwieser, S. Thiele, S. Vierrath
  Spatially Resolved Quantification of Ionomer Degradation in Fuel Cells by Confocal Raman Microscopy
  2019 J Electrochem Soc, Band: 166, Nummer: 7, Seiten: F3044 - F3051
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  Kurzfassung

  Ionomer membranes are crucial components of many electrochemical devices. In this work, confocal Raman microscopy is employed to characterize Nafion ionomers quantitatively in pristine status and after usage as a proton exchange membrane in a fuel cell. Confocal Raman microscopy allows non-destructive thickness and equivalent weight measurements of Nafion with a 95% confidence interval of ±13 g mol−1 at an equivalent weight of 1000 g mol−1, which is significantly more accurate than previously reported methods. Characterization can be performed at a spatial resolution better than 2 μm, providing insights into local membrane degradation after fuel cell operation. Membrane thinning to less than 40% of the initial thickness of Nafion NR-211 occurs after a 100 h open circuit voltage hold, accompanied by an anisotropic increase of the equivalent weight from 1035 g mol−1 to an average of 1200 g mol−1. Most pronounced increases are found close to the anode. Further, the characterization of a Nafion XL membrane shows that its microporous reinforcement is represented as increased equivalent weight with local heterogeneities within the membrane. These results show that confocal Raman microscopy is a valuable tool to investigate ionomers that are used as ion exchange membranes in electrochemical devices.

2018

• C. Klose, P. Trinke, T. Böhm, B. Bensmann, S. Vierrath, R. Hanke-Rauschenbach, S. Thiele
  Membrane Interlayer with Pt Recombination Particles for Reduction of the Anodic Hydrogen Content in PEM Water Electrolysis
  2018 J Electrochem Soc, Band: 165, Seiten: F1271 - F1277
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  Kurzfassung

  Polymer electrolyte membrane (PEM) water electrolysis is a key technology for sustainable hydrogen based energy supply. Gaspermeation through the PEM leads to hydrogen in oxygen at the anode side posing a safety hazard and therefore restricting theoperation window of PEM water electrolysis, especially when operating under pressure. In this work the hydrogen in oxygen contentat the anode is significantly reduced when a recombination interlayer is integrated into the membrane electrode assemblies (MEAs)compared to reference MEAs without interlayer. The recombination interlayer with a platinum loading of 0.02 mg cm−2is sprayedbetween two membranes that are coated with anode and cathode catalysts on the outside. The permeating H2and O2forms waterat the recombination interlayer, leading to higher gas purity and resolving safety issues. In case of the MEAs with interlayer alsoa constant current hold at 1 A cm−2for 245 h revealed only a slight increase of the hydrogen in oxygen content (below 140·10−6vol.% h−1) whereas for the reference MEAs without interlayer a stronger increase was observed (above 1250·10−6vol.% h−1).Furthermore, the long-term experiments showed no increased degradation rates compared to the reference MEAs.
• F. Hegge, R. Moroni, P. Trinke, B. Bensmann, R. Hanke-Rauschenbach, S. Thiele, S. Vierrath
  Three-dimensional microstructure analysis of a polymer electrolyte membrane water electrolyzer anode
  2018 J Power Sources, Band: 393, Seiten: 62 - 66
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  Kurzfassung

  The anode catalyst layer of a PEM water electrolyzer is reconstructed using a combination of FIB-SEM tomography and ionomer modeling. The pore space is infiltrated with silicone, enabling good discrimination between pores and IrRuOx catalyst material, while the ionomer cannot be imaged. The reconstructed volume of 29 μm × 24 μm x 7 μm contains catalyst particles with a median size of 0.5 μm and has a porosity of 55%. By modeling different ionomer contents inside the pore space, the impact on microstructural and transport parameters is investigated. At an ionomer content of 40–50% of the pore volume, all transport parameters are in a reasonable range, confirming experimental results from literature. At an ionomer content of 48% the catalyst layer has a porosity of 29%, a median pore size of 0.94 μm, a permeability of the pore space of and a mean ionomer film thickness of . The tortuosities of the ionomer and the pore space are calculated to 3.5 and 6.7 at the corresponding phase fractions of 26% and 29% respectively. The electrochemically active surface area estimated from the tomography () is considerably lower than literature values, indicating a roughness below FIB-SEM resolution.

2017

• M. Breitwieser, C. Klose, A. Hartmann, A. Büchler, M. Klingele, S. Vierrath, R. Zengerle, S. Thiele
  Cerium Oxide Decorated Polymer Nanofibers as Effective Membrane Reinforcement for Durable, High-Performance Fuel Cells
  2017 Adv Energy Mater, Seite: 1602100
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  Kurzfassung

  High-power, durable composite fuel cell membranes are fabricated here by direct membrane deposition (DMD). Poly(vinylidene fluoride-co-hexafluo- ropropylene) (PVDF-HFP) nanofibers, decorated with CeO 2 nanoparticles are directly electrospun onto gas diffusion electrodes. The nanofiber mesh is impregnated by inkjet-printed Nafion ionomer dispersion. This results in 12 µm thin multicomponent composite membranes. The nanofibers provide membrane reinforcement, whereas the attached CeO 2 nanoparticles promote improved chemical membrane durability due to their radical scavenging properties. In a 100 h accelerated stress test under hot and dry conditions, the reinforced DMD fuel cell shows a more than three times lower voltage decay rate (0.39 mV h −1 ) compared to a comparably thin Gore membrane (1.36 mV h −1 ). The maximum power density of the DMD fuel cell drops by 9%, compared to 54% measured for the reference. Impedance spectroscopy reveals that ionic and mass transport resistance of the DMD fuel cell are unaffected by the accelerated stress test. This is in contrast to the reference, where a 90% increase of the mass transport resistance is measured. Energy dispersive X-ray spectroscopy reveals that no significant migration of cerium into the catalyst layers occurs during degradation. This proves that the PVDF- HFP backbone provides strong anchoring of CeO 2 in the membrane.
• C. Klose, M. Breitwieser, S. Vierrath, M. Klingele, H. Cho, A. Büchler, J. Kerres, S. Thiele
  Electrospun sulfonated poly(ether ketone) nanofibers as proton conductive reinforcement for durable Nafion composite membranes
  2017 J Power Sources, Band: 361, Seiten: 237 - 242
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  Kurzfassung

  We show that the combination of direct membrane deposition with proton conductive nanofiber reinforcement yields highly durable and high power density fuel cells. Sulfonated poly(ether ketone) (SPEK) was directly electrospun onto gas diffusion electrodes and then filled with Nafion by inkjet-printing resulting in a 12 μm thin membrane. The ionic membrane resistance (30 mΩ*cm2) was well below that of a directly deposited membrane reinforced with chemically inert (PVDF-HFP) nanofibers (47 mΩ*cm2) of comparable thickness. The power density of the fuel cell with SPEK reinforced membrane (2.04 W/cm2) is 30% higher than that of the PVDF-HFP reinforced reference sample (1.57 W/cm2). During humidity cycling and open circuit voltage (OCV) hold, the SPEK reinforced Nafion membrane showed no measurable degradation in terms of H2 crossover current density, thus fulfilling the target of 2 mA/cm2 of the DOE after degradation. The chemical accelerated stress test (100 h OCV hold at 90 °C, 30% RH, H2/air, 50/50 kPa) revealed a degradation rate of about 0.8 mV/h for the fuel cell with SPEK reinforced membrane, compared to 1.0 mV/h for the PVDF-HFP reinforced membrane.
• K. Lehmann, O. Yurchenko, A. Heilemann, S. Vierrath, L. Zielke, S. Thiele, A. Fischer, G. Urban
  High surface hierarchical carbon nanowalls synthesized by plasma deposition using an aromatic precursor
  2017 Carbon, Band: 118, Seiten: 578 - 587
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  Kurzfassung

  Hierarchical carbon nanowalls (CNW) are synthesized by plasma-enhanced chemical vapor deposition using p-xylene as a complex precursor. In contrast to ordinary CNW, synthesized with short-chained carbons, hierarchical CNW show a unique multi-scale pore structure, made up of micro- and mesopores connected by tubular macropores, offering higher surface area and surface accessibility. Their morphology, graphitic structure, surface area and accessibility are verified by transmission and scanning electron microscopy, gas sorption and impedance spectroscopy. Focused ion beam scanning electron microscopy tomography demonstrates the presence of macropores ensuring pore connectivity down to the substrate. Nitrogen/krypton physisorption confirms the micro- and mesoporous structure contributing extensively to the surface area. The impedance spectra are evaluated according to standard RC and transmission line models. The sample deposited for 60 min, with a structure height of 4.75 μm, features a volumetric capacitance of 2.6 F cm−3 and a response time of 25 ms. Hierarchical CNW exhibit a two to six times higher volumetric capacitance than CNW of similar proportions, reported in literature. Hierarchical CNW offer a promising way to realize high power and energy density requirements in electrochemical energy systems, like supercapacitors, due to their good conductivity, high surface area and open pore structure.
• M. Klingele, R. Moroni, S. Vierrath, S. Thiele
  Multiscale Tomography-Based Analysis of Fuel Cells: Towards a Fully Resolved Fuel Cell Reconstruction
  2017 J Electrochem Energy, Band: 15, Seite: 014701
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  Kurzfassung

  The microstructure of a fuel cell electrode largely determines the performance of the whole fuel cell system. In this regard, tomographic imaging is a valuable tool for the understanding and control of the electrode morphology. The distribution of pore- and feature-sizes within fuel cell electrodes covers several orders of magnitude, ranging from millimeters in the gas diffusion layer down to few nanometers in the catalyst layer. This obligates the application of various tomographic methods for imaging every aspect of a fuel cell. This perspective evaluates the capabilities, limits and challenges of each of these methods. Further it highlights and suggests efforts towards the integration of multiple tomographic methods into single multiscale datasets, a venture which aims at large scale, and morphologically fully resolved fuel cell reconstructions.
• M. Breitwieser, M. Klingele, S. Vierrath, R. Zengerle, S. Thiele
  Tailoring the membrane-electrode interface in PEM fuel cells: A review and perspective on novel engineering approaches
  2017 Adv Energy Mater, Seite: 1701257

2016

• M. Hagner, J. M. Fritz, P. Alknes, C. Scheuerlein, L. Zielke, S. Vierrath, S. Thiele, B. Bordini, A. Ballarino
  3D Analysis of the Porosity in MgB2 Wires Using FIB Nanotomography
  2016 Ieee T Appl Supercon, Band: 26, Seite: 6200305
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  Kurzfassung

  Porosity is one of several current limiting mechanisms in MgB2 wires. We have compared the microstructural homogeneity and the porosity distribution in different ex situ and in situ MgB2 Powder-in-Tube (PIT) wires. The sub-micrometer structure was determined using Focused Ion Beam (FIB) nanotomography. The ex situ wires exhibit an isotropic microstructure, which has been quantified in terms of an identical tortuosity in transverse and longitudinal filament direction. The very homogenous microstructure in the new ex situ wire generation is probably one reason for its strongly improved critical current density. The in situ wire has an anisotropic microstructure with a lower tortuosity in the axial direction. The microstructural inhomogeneity of the in situ filaments makes microstructural characterization and the comparison between materials and superconducting properties particularly challenging.
• M. Klingele, B. Britton, M. Breitwieser, S. Vierrath, R. Zengerle, S. Holdcroft, S. Thiele
  A Completely Spray-Coated Membrane Electrode Assembly
  2016 Electrochem Commun, Band: 70, Seiten: 65 - 68
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  Kurzfassung

  We present a proton exchange membrane fuel cell (PEMFC) manufacturing route, in which a thin layer of polymer electrolyte solution is spray-coated on top of gas diffusion electrodes (GDEs) to work as a proton exchange membrane. Without the need for a pre-made membrane foil, this allows inexpensive, fast, large-scale fabrication of membrane-electrode assemblies (MEAs), with a spray-coater comprising the sole manufacturing device. In this work, a catalyst layer and a membrane layer are consecutively sprayed onto a fibrous gas diffusion layer with applied microporous layer as substrate. A fuel cell is then assembled by stacking anode and cathode half-cells with the membrane layers facing each other. The resultant fuel cell with a low catalyst loading of 0.1 mg Pt/cm2 on each anode and cathode side is tested with pure H2 and O2 supply at 80 °C cell temperature and 92% relative humidity at atmospheric pressure. The obtained peak power density is 1.29 W/cm2 at a current density of 3.25 A/cm2. By comparison, a lower peak power density of 0.93 W/cm2 at 2.2 A/cm2 is found for a Nafion NR211 catalyst coated membrane (CCM) reference, although equally thick membrane layers (approx. 25 μm), and identical catalyst layers and gas diffusion media were used. The superior performance of the fuel cell with spray-coated membrane can be explained by a decreased low frequency (mass transport) resistance, especially at high current densities, as determined by electrochemical impedance spectroscopy.
• M. Zeiger, S. Fleischmann, B. Krüner, A. Tolosa, S. Bechtel, M. Baltes, A. Schreiber, R. Moroni, S. Vierrath, S. Thiele, V. Presser
  Influence of carbon substrate on the electrochemical performance of carbon/manganese oxide hybrids in aqueous and organic electrolytes
  2016 Rsc Adv, Band: 6, Seiten: 107163 - 107
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  Kurzfassung

  Manganese oxide presents very promising electrochemical properties as an electrode material in supercapacitors, but there remain important open questions to guide further development of the complex manganese oxide/carbon/electrolyte system. Our work addresses specifically the influence of carbon ordering and the difference between outer and inner porosity of carbon particles for the application in aqueous 1 M Na2SO4 and 1 M LiClO4 in acetonitrile. Birnessite-type manganese oxide was hydrothermally hybridized on two kinds of carbon onions with only outer surface area and different electrical conductivity, and conventional activated carbon with a high inner porosity. Carbon onions with a high degree of carbon ordering, high conductivity, and high outer surface area were identified as the most promising material, yielding 179 F g−1. Pore blocking in activated carbon yields unfavorable electrochemical performances. The highest specific energy of 16.4 W h kg−1 was measured for a symmetric full-cell arrangement of manganese oxide coated high temperature carbon onions in the organic electrolyte. High stability during 10 000 cycles was achieved for asymmetric full-cells, which proved as a facile way to enhance the electrochemical performance stability.
• S. Vierrath, M. Breitwieser, M. Klingele, B. Britton, S. Holdcroft, R. Zengerle, S. Thiele
  The reasons for the high power density of fuel cells fabricated with directly deposited membranes
  2016 J. of Power Sources, Band: 326, Seiten: 170 - 175
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  Kurzfassung

  In a previous study, we reported that polymer electrolyte fuel cells prepared by direct membrane deposition (DMD) produced power densities in excess of 4 W/cm2. In this study, the underlying origins that give rise to these high power densities are investigated and reported. The membranes of high power, DMD-fabricated fuel cells are relatively thin (12 mm) compared to typical benchmark, commercially available membranes. Electrochemical impedance spectroscopy, at high current densities (2.2 A/cm2) reveals that mass transport resistance was half that of reference, catalyst-coated-membranes (CCM). This is attributed to an improved oxygen supply in the cathode catalyst layer by way of a reduced propensity of flooding, and which is facilitated by an enhancement in the back diffusion of water from cathode to anode through the thin directly deposited membrane. DMD-fabricated membrane-electrode-assemblies possess 50% reduction in ionic resistance (15 mUcm2) compared to conventional CCMs, with contributions of 9 mUcm2 for the membrane resistance and 6 mUcm2 for the contact resistance of the membrane and catalyst layer ionomer. The improved mass transport is responsible for 90% of the increase in power density of the DMD fuel cell, while the reduced ionic resistance accounts for a 10% of the improvement.
• L. Zielke, S. Vierrath, R. Moroni, A. Mondon, R. Zengerle, S. Thiele
  Three-dimensional Morphology of the Interface between Micro Porous Layer and Catalyst Layer in a Polymer Electrolyte Membrane Fuel Cell
  2016 Rsc Advances, Band: 6, Seiten: 80700 - 80705
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  Kurzfassung

  Interfaces between the different layers in proton exchange membrane fuel cells are expected to influence transport properties and therefore cell performance. So far the interface between micro porous layer (MPL) and catalyst layer (CL) was difficult to investigate due to its nanometer scale morphology. We apply focused ion beam scanning electron microscopy tomography with pore contrasting via atomic layer deposition to reconstruct a representative volume of 5.1 μm x 1.5 μm x 4.5 μm containing CL, MPL and their interface. We find that platinum in the CL results in brighter SEM image intensities, compared to the MPL. This allows i) estimating the extension of the interfacial region (530 nm), ii) evaluating Pt-content homogeneity in the CL and iii) calculating the individual roughnesses for the CL (102 nm) and for the MPL (129 nm). We further calculate porosity, pore sizes, and oxygen diffusivities. Thus, we find that the values of the parameters of the interfacial region are between those of the CL and the MPL, meaning that on the investigated scale, the interface is a homogeneous transitional region. A representativeness analysis shows that our reconstructed volume is sufficiently large concerning all calculated parameters.

2015

• S. Vierrath, F. Güder, A. Menzel, M. Hagner, R. Zengerle, M. Zacharias, S. Thiele
  Enhancing the Quality of the Tomography of Nanoporous Materials for Better Understanding of Polymer Electrolyte Fuel Cell Materials
  2015 J Power Sources, Seiten: 413 - 417
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  Kurzfassung

  To investigate the nanostructure of polymer electrolyte fuel cell catalyst layers, focused ion beam - scanning electron microscopy (FIB-SEM) tomography is a common technique. However, as FIB-SEM tomography lacks of image contrast between the catalyst layer and its pores, state-of-the-art reconstruction methods by threshold cannot accurately distinguish between these two phases. We show that this inability leads to an underestimation of the porosity by a factor of nearly two, a reconstruction with channel-like artifacts and that these artifacts make it impossible to calculate reliable diffusivities. To overcome this problem, we fill the pores of the catalyst layer with ZnO via atomic layer deposition prior to tomography. By using atomic layer deposition, even smallest pores can be filled with ZnO, which exhibits a good contrast to the catalyst layer in SEM images. As a result, we present the porosity of the catalyst layer (65%) and its three-dimensional representation without typical reconstruction artifacts. Calculated O2 diffusivities (23.05 - 25.40 x 10-7 m2s-1) inside the catalyst layer are in good agreement with experimental values from the literature. Furthermore, filling with ZnO permits the identification of large Pt clusters inside the catalyst layer, which were estimated to reduce the catalyst surface area by 9%.
• S. Vierrath, L. Zielke, R. Moroni, A. Mondon, D. R. Wheeler, R. Zengerle, S. Thiele
  Morphology of nanoporous carbon-binder domains in Li-ion batteries—A FIB-SEM study
  2015 Electrochem Commun, Band: 60, Seiten: 176 - 179
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  Kurzfassung

  FIB-SEM tomography is used to reconstruct the carbon-binder domain (CBD) of a LiCoO2 battery cathode (3.9 × 5 × 2.3 μm3) with contrast enhancement by ZnO infiltration via atomic layer deposition. We calculate the porosity inside the CBD (57.6%), the cluster-size distribution with a peak at 54 nm, and the pore-size distribution with a peak at 64 nm. The tortuosities of the pore space (1.6–2.0) and the CBD (2.3–3.5) show a mild anisotropy, which is attributed to the fabrication process. A comparison to a modeled homogenous CBD reveals that clustering in the CBD decreases its electronic conductivity while increasing the ionic diffusivity. To account for the higher calculated diffusivity compared to experimental values from literature, a simple binder swelling model is implemented, suggesting a swelling of 75 vol%. The prevention of both clustering and swelling could increase the volume available for active material and therefore the energy density.

Vorträge

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2018

• S. Vierrath, M. Breitwieser, C. Klose, M. Klingele, S. Thiele
  Novel approaches to tailor the PEM|electrode interface for fuel cells with increased power density
  2018 innBW Wissenschaftlertreffen Stuttgart, 21.04.2018
• M. Breitwieser, S. Vierrath
  Neue Kompositmembranen und Mikrocharakterisierung: Die Gruppe „Elektrochemische Energiesysteme“ an IMTEK und Hahn-Schickard
  2018 Brennstoffzellenallianz Duisburg, 26. - 27. Juni 2018

2016

• C. Klose, M. Breitwieser, L. Zielke, S. Vierrath, H. Cho, S. Thiele, J. Kerres, R. Zengerle
  Long-life and high-power PEMFCs by combination of direct electrospinning and inkjet printing,
  2016 Statusworkshop der Baden-Württemberg Stiftung, Bad Herrenalb, 2016
• S. Thiele, S. Vierrath, R. Moroni, L. Zielke, R. Zengerle
  Multiple scales and interfaces in PEMFCs - a tomographic study
  2016 Electrocatalysis Workshop, Vancouver, February 2016.
• M. Breitwieser, M. Klingele, B. Britton, S. Vierrath, R. Zengerle, S. Holdcroft, S. Thiele
  Recent Progress in Low- and No- Pt loaded PEMFCs
  2016 Electrocatalysis Workshop, Vancouver, February 2016
• S. Vierrath, L. Zielke, R. Moroni, A. Mondon, R. Zengerle, S. Thiele
  ZnO Contrasted Nano Tomographies of Fuel Cell and Battery Components
  2016 MODVAL 13, Symposium for Fuel Cell and Battery Modeling and Experimental Validation, Lausanne, Schweiz (22.-23.03.2016)

2015

• S. Vierrath, F. Güder, A. Menzel, M. Hagner, R. Zengerle, M. Zacharias, S. Thiele
  Novel Approach in 3D-Reconstructions of PEMFC Catalyst Layers: Infiltration aided Segmentation
  2015 ModVal 12, Munzingen, Deutschland, 26.-27. März 2015
• L. Zielke, S. Vierrath, R. Moroni, R. Zengerle, S. Thiele
  Transport, Degradation and Multi-Scale Morphology in X-ray Tomographic Reconstructions of Battery Electrodes
  2015 Solid State Electrochemical Workshop 2015, Roggenburg, Germany, 06. – 09.09.2015

2014

• S. Vierrath, F. Güder, A. Menzel, R. Zengerle, M. Zacharias, S. Thiele
  Novel Approach in 3D-Reconstructions of PEMFC Catalyst Layer
  2014 97th Canadian Chemistry Conference and Exhibition”, Vancouver, Kanada, 01. - 05. Juni 2014

Konferenzbeiträge

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2020

• H. Nguyen, P. Heizmann, F. Lombeck, A. Belletti, B. Britton, S. Vierrath, M. Breitwieser
  Improving the Performance of All-Hydrocarbon PEM Fuel Cells Based on Pemion™ Ionomer
  2020 71st International Society of Electrochemistry, Belgrad, Serbia (Online), 30.08. – 04.09.2020
• M. Breitwieser, S. Vierrath
  One for all or one for each application? Recent advances in membrane & ionomer development for electrochemical energy converters
  2020 E3C Electrochemical Cell Concepts Colloquium Fraunhofer UMSICHT, 14.05.2020

2019

• B. Shanahan, T. Böhm, B. Britton, S. Holdcroft, S. Vierrath, S. Thiele, M. Breitwieser
  30 μm thin hexamethyl-p-terphenyl poly(benzimidazolium) anion exchange membrane for vanadium redox flow batteries
  2019 The International Flow Battery Forum, Lyon/France, 09 - 11 July 2019
• F. Hegge, E. Cruz Ortiz, S. Thiele, S. Vierrath
  Improving the performance of low loaded PEMWE electrodes
  2019 2nd International Conference on Electrolysis (ICE), Loen / Norway, 9. – 13. 06.2019
• T. Boehm, M. S. Mu’min, R. Moroni, S. Thiele, S. Vierrath, M. Breitwieser
  Resolving structure and properties in ionomer composite membranes with Confocal Raman Microscopy
  2019 Workshop on Ion Exchange Membranes for Energy Applications, Bad Zwischenahn, 25. -27.06. 2019
• T. Boehm, M. S. Mu’min, R. Moroni, S. Thiele, S. Vierrath, M. Breitwieser
  Resolving structure and properties in ionomer composite membranes with Confocal Raman Microscopy
  2019 FDFC 2019 - 8th International Conference on Fundamentals and Development of Fuel Cells Nantes/France, 12. – 14.02.2019
• P. Trinke, B. Bensmann, C. Klose, S. Vierrath, S. Thiele, R. Hanke-Rauschenbach
  System relevant Observation of Gas Crossover – Necessity of Mitigation Strategies
  2019 international Conference on Electrolysis, Leon (Norway), 09. - 13. 06.2019

2018

• F. Hegge, R. Moroni, E. Wright, J. Sharman, S. Thiele, S. Vierrath
  Catalyst Support Ageing of Polymer Electrolyte Fuel Cells Investigated with Tomography
  2018 69th Annual Meeting of the International Society of Electrochemistry (ISE), Bologna/Italy, 02. – 07.09.2018
• C. Klose, L. Bohn, M. Klingele, S. Thiele, R. Zengerle, M. Breitwieser, S. Vierrath
  Dynamic Quantification of Water Generation and Migration in Polymer Electrolyte Membrane Fuel Cells
  2018 69th annual meeting of the International Society of Electrochemistry, Bologna (Italy), 02. - 07.09.2018.
• C. Klose, L. Bohn, M. Klingele, S. Thiele, R. Zengerle, M. Breitwieser, S. Vierrath
  Dynamic Quantification of Water Generation and Migration in Polymer Electrolyte Membrane Fuel Cells
  2018 Gordon’s Research Conference on Fuel Cells, Smithfield (USA), 29.07. - 03.08.2018
• C. Klose, L. Bohn, M. Klingele, M. Breitwieser, S. Vierrath
  How engineering the PEM|CL interface influences the performance of PEMFCs
  2018 69th Annual Meeting of the International Society of Electrochemistry (ISE), Bologna/Italy, 02. – 07.09.2018
• C. Klose, L. Bohn, M. Klingele, M. Breitwieser, S. Vierrath
  Influence of the PEM|CL interface on performance and water management
  2018 Gordon Research Conference, Bryant University, Douglas Pike in Smithfield, RI, US., 29.07. – 03.08.2018
• S. Vierrath, M. Klingele, S. Thiele, R. Zengerle, M. Breitwieser
  Tailoring the membrane│electrode interface: a review and perspective of novel engineering approaches
  2018 69th Annual Meeting of the International Society of Electrochemistry (ISE), Bologna/Italy, 02. – 07.09.2018
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  Kurzfassung

  69th Annual Meeting of the International Society of Electrochemistry (ISE), Bologna/Italy, 02. – 07.09.2018

2017

• M. Buehler, S. Vierrath, C. Klose, F. Hegge, S. Thiele
  A Novel Fabrication Technique for Electrodes of PEM Water Electrolyzers
  2017 232nd ECS MEETING Oct. 1-5, 2017 | National Harbor, MD (greater Washington, DC area)
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  Kurzfassung

  In this work the improvement of material interfaces at electrodes for proton exchange membrane (PEM) water electrolyzers is addressed by a novel fabrication technique. In this approach the electrode and the membrane are directly deposited on the porous transport layers (PTLs), which serve as substrate for the electrodes. The aim is to stabilize and increase the oxygen and hydrogen evolution rate at high current densities leading to a reduction of the noble metal loading of the electrodes – and additionally to develop a cost effective novel fabrication technique applicable for the large scale industrial fabrication of electrodes for PEM water electrolyzers. The innovative manufacturing technique is described in this transaction, and current challenges regarding the coating of porous substrates in terms of parameter control, reliability and homogeneity are pointed out.
• S. Vierrath, M. Breitwieser, M. Bühler, C. Klose, R. Zengerle, S. Thiele
  Additive Fertigung für Brennstoffzellen und Elektrolyse
  2017 MST Kongress, München, 23. - 25.10.2017
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  Kurzfassung

  Bei der Wasserstoff-Elektrolyse wird Wasser mit Hilfe von Strom in Wasserstoff umgewandelt, der dann als Energieträger gespeichert werden kann. Bei der Brennstoffzelle wird dieser Prozess umgekehrt und somit Strom erzeugt. Zusammen bilden diese Systeme die Grundlage der zukünftigen Wasserstoffwirtschaft, in der große Energiemengen, z.B. aus erneuerbaren Quellen, flexibel gespeichert und abgerufen werden können. Die Brennstoffzelle ermöglicht zudem eine emissionslose Mobilität ohne Reichweitenbegrenzung oder lange Ladezeiten. Die Membran-Elektroden-Einheit bildet das Herzstück der Brennstoffzelle und der Elektrolysezelle. Darin ist die Membran nur für Wasserstoffionen durchlässig und sorgt so für kontrollierte Reaktionen in den beidseitig aufgebrachten Elektroden. Die Qualität dieser Membran-Elektroden-Einheit entscheidet maßgeblich über die Leistung und Alterungsverhalten in der späteren Anwendung. Klassischerweise werden die Elektroden und die Membran getrennt betrachtet und hergestellt – dabei hat die Grenzschicht einen beachtlichen Einfluss auf das Leistungsverhalten. Wir gehen mit additiver Fertigungstechnik neue Wege in der Herstellung: Statt die Membran in Folienprozessierung und die Elektroden im Sprüh-Abzieh-Verfahren herzustellen, können wir die gesamte Membran-Elektroden-Einheit nacheinander in einem Sprühprozess herstellen (Abb.1) [1]. Neben der Vereinfachung des Prozesses bildet die aufgesprühte Membran eine dreidimensionale Grenzfläche mit den Elektroden, statt der herkömmlichen 2D-Grenzfläche der Membranfolie. Die vergrößerte Grenzschicht und der verbesserte ionische Kontakt sorgen für eine 40% höhere Maximalleistung (Abb. 2a) und besseres Wassermanagement bei großen Strömen [2]. Dank additiver Fertigung ist zudem die gezielte ortsaufgelöste Aufbringung der Materialien möglich. So kann Material eingespart und auch die Membran-Elektroden-Einheit lokal optimiert werden, z.B. durch Anpassung des Katalysator- oder Ionomergehalts an das Reaktionsprofil. Neben der Leistung und dem Herstellungsprozess ist auch das Alterungsverhalten ein wichtiger Aspekt. Durch die Integration von Nanofasern und Nanopartikeln kann die mechanische und chemische Stabilität erheblich gesteigert werden (Abb. 2b) [3]. Dazu werden Nanofasern direkt auf die Elektrode gesponnen und anschließend mit Ionomer besprüht um eine Kompositmembran zu erhalten [4]. Die Nanopartikel können gezielt in eine Schicht, z.B. als Radikalfänger in der Membran, integriert werden.
• M. Breitwieser, S. Vierrath, C. Klose, M. Klingele, R. Zengerle, S. Thiele
  Direct Membrane Deposition (DMD): A novel and versatile fabrication technique for high performance fuel cells
  2017 7th International Conference on ”Fundamentals & Development of Fuel Cells” in Stuttgart, 31. Januar – 2. Februar 2017
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  Kurzfassung

  In the “Direct Membrane Deposition” (DMD) technique the conventional catalyst coated membrane (CCM) is replaced by two ionomer-coated gas diffusion electrodes (GDE). Assembling the ionomer-coated GDEs creates a fuel cell with a very thin membrane (12 μm) and improved interface between membrane and electrodes. Fuel cells fabricated with DMD showed record power densities of 4 W/cm² at 70°C, 300 kPa and with oxygen as fuel. The DMD approach also proved its suitability for medium temperature fuel cells: by incorporating TiO2 nanoparticles into the directly deposited membrane the fuel cell showed stable operation at 120°C with a power density of 2 W/cm² (300 kPa and oxygen at the cathode). Besides the increased power density, DMD bears the potential to simplify the membrane-electrode-assembly (MEA) fabrication process by successively spray-coating catalyst layer and membrane onto a gas diffusion layer. In very recent work, DMD was used to fabricate composite membranes by combining inkjet-printing of ionomer and with electrospun Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) reinforcing nanofibers. These 12 μm thin composite membranes provided excellent thermal stability and high electrochemical performance up to 120 °C operation temperature. By anchoring CeO2 nanoparticles to the PVDF-HFP nanofibers, the open circuit voltage (OCV) degradation rate (0.39 mV/h) was found to be 3 times lower than that of a comparably thin reference Gore membrane in an OCV accelerated stress test. This poster provides an overview about our DMD activities, its future potential and gives detailed information about the possible MEA architectures feasible with DMD.
• S. Vierrath, M. Breitwieser, C. Klose, M. Klingele, R. Zengerle, S. Thiele
  Direct Membrane Deposition (DMD): Improved Power Density, Water Management and Stability
  2017 7th International Conference on ”Fundamentals & Development of Fuel Cells” in Stuttgart, 31. Januar – 2. Februar 2017
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  Kurzfassung

  Klingele et al. showed never reached high power fuel cells by applying direct membrane deposition (DMD), excelling the peak power of a catalyst coated membrane (CCM) by a factor of 2.3. To understand the underlying reasons for their high power, we identify the reasons and quantify their impact by employing electrochemical impedance spectroscopy. As a result we show, that the main reasons for the high power of DMD fuel cells are (i) a 50% reduced high frequency resistance (26 mΩcm²) due to a thinner membrane (12μm) compared to state-of-the-art and (ii) a factor 2.2 reduced mass transport losses (0.12 Ωcm²) due to increased water back diffusion through the thin membrane. A comparison of DMD vs. CCM fuel cells at the maximum power point of the CCM shows that 91% of the DMD’s improvement can be attributed to reduced mass transport losses and only 9% are caused by the reduction of the ohmic resistances.
• S. Thiele, S. Vierrath, M. Breitwieser, M. Klingele, C. Klose, R. Moroni
  Direct membrane deposition (DMD) – a new way in membrane electrode assembly manufacturing
  2017 20th Topical Meeting of the International Society of Electrochemistry, Buenos Aires/Argentinien, 19-22 März 2017
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  Kurzfassung

  The membrane is one of the very central polymer electrolyte membrane fuel cell components. At the same time it must conduct protons and inhibit transport of electrons and cross-over of reactant gases. Additionally, degradation effects have to be small to ensure a long lifetime. While traditionally consisting of pure Nafion, up to date membranes contain nanofiber reinforcements and radical scavenger packages to decrease degradation effects. Thus, seminal membranes are multi-layer, multi-component structures. In the state of the art, membrane electrode assemblies (MEA) are manufactured as catalyst coated membranes (CCMs). To form a CCM, electrodes are deposited either by the decal method, or by another deposition method. In this talk we present a novel approach for MEA manufacturing. In the so called ‘direct membrane deposition’ (DMD) approach, liquid ionomer is deposited on the catalyst layers of two gas diffusion electrodes which are successively dried and pressed together to form an MEA. Interestingly, this approach enabled power densities more than two times higher than traditional CCM based approaches which are commercially available. Also this approach allows for a simple fabrication of thin multi-layer membranes and improves the water management. DMD applied to low Pt loading electrodes revealed very high power densities per gram Pt of up to 88 kW/g Pt. An analysis of the underlying reasons for the improved performance values revealed a small influence of membrane resistance but mainly an influence in mass transport and charge transfer phenomena. In this talk we highlight our latest developments in the field of DMD based manufacturing and give an insight on degradation and durability aspects.
• M. Breitwieser, C. Klose, M. Klingele, S. Vierrath, R. Zengerle, S. Thiele
  Direct membrane deposition (DMD): A versatile fabrication technique for PEMFC composite membranes
  2017 WE-Heraeus-Seminar, Bad Honnef, 02. – 05.07.2017
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  Kurzfassung

  The conventional catalyst coated membrane (CCM) can be substituted by two ionomer-coated gas diffusion electrodes (GDE). Assembling the ionomer-coated GDEs creates a fuel cell with a very thin, directly deposited membrane (12 μm) and improved interface between membrane and electrodes. This interface has significant impact onto the fuel cell performance. Besides the increased power density, DMD bears the potential to simplify the membrane-electrode-assembly (MEA) fabrication process by successively spray-coating catalyst layer and membrane onto a gas diffusion layer. In recent work, DMD was used to fabricate composite membranes by combining inkjet-printing of ionomer and with electrospun Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) reinforcing nanofibers [3,4]. The workflow for this type of novel composite membrane is graphically summarized in Figure 1. These 12 μm thin composite membranes provided high electrochemical performance up to 120 °C operation temperature. By anchoring CeO2 nanoparticles to the PVDF-HFP nanofibers, the OCV degradation rate (0.39 mV/h) was found to be 3 times lower than that of a comparably thin reference Gore membrane in an open circuit voltage accelerated stress test according to the US department of energy (DOE.
• M. Breitwieser, M. Klingele, S. Vierrath, C. Klose, R. Zengerle, S. Thiele
  Direct membrane deposition (DMD): A versatile technique for the production of novel fuel cell composite membranes
  2017 Fuel Cells | Workshop EMEA 2017, Bad Zwischenahn, 26. - 28.06.2017
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  Kurzfassung

  The conventional catalyst coated membrane (CCM) can be substituted by two ionomer-coated gas diffusion electrodes (GDE). Assembling the ionomer-coated GDEs creates a fuel cell with a very thin, directly deposited membrane (12 µm) and improved interface between membrane and electrodes. Fuel cells fabricated with direct membrane deposition (DMD) showed record power densities of 4 W/cm² at 70°C, 300 kPa and with oxygen as fuel. Besides the increased power density, DMD bears the potential to simplify the membrane-electrode-assembly (MEA) fabrication process by successively spray-coating catalyst layer and membrane onto a gas diffusion layer. In recent work, DMD was used to fabricate composite membranes by combining inkjet-printing of ionomer and with electrospun Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) reinforcing nanofibers. The workflow for this type of novel composite membrane is graphically summarized in Figure 1. These 12 µm thin composite membranes provided excellent thermal stability and high electrochemical performance up to 120 °C operation temperature. By anchoring CeO2 nanoparticles to the PVDF-HFP nanofibers, the open circuit voltage (OCV) degradation rate (0.39 mV/h) was found to be 3 times lower than that of a comparably thin reference Gore membrane in an open circuit voltage accelerated stress test according to the US department of energy (DOE).
• C. Klose, M. Bühler, S. Vierrath, N. Baumann, T. Lickert, A. Fallisch, S. Thiele
  Direct membrane deposition – a novel fabrication method for PEMWEs
  2017 International Conference on Electrolysis 2017, Copenhagen/Denmark, 12. - 15.06.2017
• S. Vierrath, M. Breitwieser, C. Klose, M. Klingele, S. Thiele
  Novel approaches to tailor the PEM|electrode interface for fuel cells with increased power density
  2017 7th Bonn Humboldt Award Winners’ Forum “Fundamental Concepts and Principles of Chemical Energy Conversion” Bonn, 11 - 15 October 2017
• M. Breitwieser, M. Klingele, S. Vierrath, R. Zengerle, S. Thiele
  Tailoring the membrane-electrode interface: A review and perspective of novel engineering approaches
  2017 Fuel Cells | Workshop EMEA 2017, Bad Zwischenahn, 26. - 28.06.2017
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  Kurzfassung

  The interface between the catalyst layer (CL) and the polymer electrolyte membrane (PEM) in a fuel cell has significant impact onto its electrochemical performance. In consequence, in the past years there have been growing research activities to engineer this interface in order to improve the performance of polymer electrolyte membrane fuel cells (PEMFCs). This talk summarizes these approaches and compares the various techniques. Based on the available fuel cell data in literature we provide a quantitative comparison of relative improvements caused by specially 3D-engineered PEM|CL interfaces. This allows to draw several conclusions: We show that the similar improvements of relevant electrochemical properties such as improved high and low frequency resistances as well as higher peak power density can be achieved by 3D PEM|CL interface engineering techniques. As an example, regardless if patterned membrane surfaces, ionomer gradients in the catalyst layer or direct membrane deposition techniques are used, comparable improvements of the fuel cell characteristics were reported. Second, for patterned membranes surfaces it was found that feature sizes of about 1-10 µm on the membrane surface seem to result in the most significant power density improvement. Finally it is shown that a re-engineered PEM│CL interface can also contribute to extend the durability of the MEA due to enhanced adhesion and contact between both functional layers.
• M. Breitwieser, M. Klingele, C. Klose, S. Vierrath, R. Zengerle, S. Thiele
  Tailoring the membrane/electrode interface - novel engineering approaches
  2017 EMEA Conference, Bad Zwischenahn, 26. - 28.06.2017
• F. Hegge, S. Vierrath, S. Ogawa, L. Zielke, M. Bühler, C. Klose, S. Litster, S. Thiele
  Tomography Aided Development of Membrane Electrode Assemblies for PEM Water Electrolysis
  2017 ECS Meeting, New Orleans/USA, 28.05. – 02.06.2017
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  Kurzfassung

  In polymer electrolyte membrane water electrolysis (PEMWE) the anode is crucial for the overall performance. State-of-the-art anodes comprise Ir, IrOx or IrRuOx, typically bound by an ionomer and can be TiOx supported [1]. Besides the material also the microstructure of the anode has an impact on the electrolyzer’s performance as it determines catalyst accessibility and species transport [2]. Optimizing the microstructure therefore offers a potential to increase cell efficiency. In our approach we use tomographic methods in order to establish a microstructure-performance relation for PEMWE anodes (see microstructure of a FuelCellsEtc PEMWE anode in Fig.1). We then apply our findings from the reconstructed anodes in order to develop improved membrane electrode assemblies (MEAs) for PEMWEs with novel manufacturing and design approaches. The experimental data will then be used as input for our theoretical models.

2016

• M. Breitwieser, M. Klingele, C. Klose, S. Vierrath, K. Holdcroft, S. M. Lyth, T. Bayer, B. Britton, S. Holdcroft, R. Zengerle, S. Thiele
  Direct membrane deposition (DMD): How to fabricate a high power DMD fuel cell in your lab
  2016 Gordon’s Research Conference on Fuel Cells, Stonehill College (USA), 07. - 12.08.2016
• M. Breitwieser, M. Klingele, S. Vierrath, R. Zengerle, S. Thiele
  Direkte Membrandeposition und 3D-Rekonstruktion elektro-chemischer Systeme: Aktivitäten der Porous Media Group
  2016 Fuel Cell Workshop Duisburg: „9. Workshop AiF-Brennstoffzellenallianz 2016“, Zentrum für Brennstoffzellentechnik Duisburg, 21. Juni 2016
• C. Klose, M. Breitwieser, M. Klingele, S. Vierrath, H. Cho, J. Kerres, R. Zengerle, S. Thiele
  Enhancing the ionic conductivity of directly deposited sulfonated poly(ether ketone)-Nafion composite membranes
  2016 Gordon’s Research Conference on Fuel Cells, Stonehill College (USA), 07.-12.08.2016.
• S. Vierrath, M. Breitwieser, M. Klingele, C. Klose, N. Wehkamp, R. Moroni, R. Zengerle, S. Thiele
  Polymer Electrolyte Fuel Cells Fabricated with Direct Membrane Deposition (DMD)
  2016 Prime 2016, Honolulu / Hawaii, 2-7 October 2016
• S. Vierrath, M. Breitwieser, M. Klingele, R. Zengerle, S. Thiele
  Reasons for the High Power Density of Direct Membrane Deposition Fuel Cells Revealed by Impedance Spectroscopy
  2016 MODVAL 13, Symposium for Fuel Cell and Battery Modeling and Experimental Validation, Lausanne, Schweiz (22.-23.03.2016) , Seite: 145
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  Kurzfassung

  Klingele et al. showed never reached high power fuel cells by applying direct membrane deposition (DMD), excelling the peak power of a catalyst coated membrane (CCM) by a factor of 2.3. [1] To understand the underlying reasons for their high power, we identify the reasons and quantify their impact by employing electrochemical impedance spectroscopy. As a result we show, that the main reasons for the high power of DMD fuel cells are (i) a 50% reduced high frequency resistance (26 mΩcm²) due to a thinner membrane (12µm) compared to state-of-the-art and (ii) a factor 2.2 reduced mass transport losses (0.12 Ωcm²) due to increased water back diffusion through the thin membrane (Figure 1a). A comparison of DMD vs. CCM fuel cells at the maximum power point of the CCM shows that 91% of the DMD’s improvement can be attributed to reduced mass transport losses and only 9% are caused by the reduction of the ohmic resistances (Figure 1b).
• C. Klose, M. Breitwieser, M. Klingele, S. Vierrath, H. Cho, J. Kerres, R. Zengerle, S. Thiele
  Simple fuel cell membrane fabrication by direct electrospinning and inkjet-printing
  2016 ELEN (Electrospinning for Energy), Montpellier (France), 22. - 24.06.2016

2015

• K. Lehmann, O. Yurchenko, S. Vierrath, S. Thiele, G. Urban
  High Surface Carbon Nanostructures with Improved Accessibility for Energy Applications
  2015 PacificChem, Honolulu, Hawaii, USA December 15 - 20, 2015
• S. Vierrath, M. Breitwieser, M. Klingele, R. Zengerle, S. Thiele
  Properties of a direct deposited membrane (DDM) Investigating the reasons for its high performance
  2015 EMEA Conference, Bad Zwischenahn (Germany), 22. - 24.06.2015
• C. Scheuerlein, M. Di Michiel, A. Rack, M. Hagner, S. Vierrath, L. Zielke, S. Thiele, R. Zengerle
  Tomographic characterisation of superconductors
  2015 Materials and Mechanisms of Superconductivity Conference, Geneva, 23.-28.08.2015

2014

• S. Vierrath, F. Güder, A. Menzel, M. Hagner, R. Zengerle, M. Zacharias, S. Thiele
  Enhanced FIB-SEM Reconstruction of PEMFC Catalysts Layers by Filling via Atomic Layer Deposition
  2014 Gordon’s Research Conference „Fuel Cells“, Bryant University Smithfield, RI, August 3-8, 2014.
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  Kurzfassung

  The bottleneck of FIB-SEM reconstruction of PEMFC catalyst layers is the segmentation, i.e. the physical interpretation of the raw SEM images. It is either extremely time-consuming when done manually, or incorrect when applying a threshold, as commonly done. We propose filling the catalyst layer via ALD prior to FIB-SEM reconstruction. In combination with threshold segmentation it is significantly faster and yields a more accurate reconstruction than state-of-the-art methods.
• S. Vierrath, J. Haußmann, H. Markötter, I. Manke, J. Scholta, R. Zengerle, S. Thiele
  Improving segmentation of PEMFC x-ray tomographies
  2014 ModVal 11, Winterthur, Schweiz, 17.-19. März 2014
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  Kurzfassung

  Proton exchange membrane fuel cell (PEMFC) performance strongly depends on morphology. Within the past years analysis by tomographic approaches has emerged as a valuable tool to assess morphology. Segmentation, the physical interpretation of 3D images, is a crucial step of tomography. In this study we compare different methods for segmentation of a gas diffusion layer/micro porous layer compound. We find that a mere threshold leads to erroneous segmentation and present a combined approach to overcome this problem.