High Temperature Polymer Electrolyte Fuel Research Articles

Single-Layer-Graphene and Electrochemical Exfoliated Graphene Oxide for HT-PEMFC

High-temperature proton exchange membrane fuel cell (HT-PEMFC) is promising with its low demand for hydrogen purity, simple water management, and high waste heat utilization [1][2]. Although polybenzimidazole (PBI), as a typical high-temperature fuel cell membrane, has been developed for a long period, it still has defects such as phosphoric acid leaching and insufficient mechanical properties under high acid doping level [3][4]. With its unique 2D hexagonal grid structure and its electron cloud arrangement, single-layer graphene (SLG) can block the passage of any atoms [5]. However, hydrogen protons can easily penetrate SLG through a unique intermediate state mechanism to make it have excellent proton conductivity [6]. SLG's high proton conductivity combined with its excellent mechanical properties and thermal conductivity make it an ideal material for blocking phosphoric acid leaching. The SLG prepared by the chemical vapor deposition (CVD) method was transferred to the surface of catalyst layer of electrodes by the wet chemical transfer method. Due to the rupture and incompleteness of the SLG during the transfer process, the coverage rate of the SLG on the electrode surface is about 55%. This incomplete coverage facilitates small quantities of phosphoric acid leaching from PBI membrane to electrodes, which increases the three-phase boundary area and improves the performance of the HT-PEMFC. After 70 hours of accelerated stress testing (AST), the peak power density of membrane-electrode-assembly (MEA) with SLG on both sides of the cathode and anode can reach 480 mW cm-2, while the peak power density of MEA based on pure PBI membrane is only 249 mW cm-2. The quantification of phosphoric acid in the electrode by Lab based X-ray micro-computed tomography and the Raman spectroscopic mapping of the MEA cross-section shows that SLG can mitigate the leaching of phosphoric acid in the PBI film and improve the durability of HT-PEMFC. Graphene oxide (GO) is a low-cost application of graphene. Its doping in the PBI membrane can also reduce the leaching of phosphoric acid through enhancing the interaction between phosphoric acid and the PBI membrane [7]. A reactor based on 3D printing was designed so that natural graphite flakes can be used for electrochemical exfoliation to achieve rapid, safe, environmentally friendly, and mass production of GO. The electrochemically exfoliated (E)GO is doped in the PBI membrane. The 0.5%, 1% and 2% EGO loadings in the PBI membrane increased the peak power density by 13.8%, 24.4% and 29.2%, respectively.[1] Y.-L. Ma, J.S. Wainright, M.H. Litt, R.F. Savinell, Conductivity of PBI Membranes for High-Temperature Polymer Electrolyte Fuel Cells, Journal of The Electrochemical Society. 151 (2004) A8. https://doi.org/10.1149/1.1630037/XML.[2] H. Su, S. Pasupathi, B. Bladergroen, V. Linkov, B.G. Pollet, Optimization of gas diffusion electrode for polybenzimidazole-based high temperature proton exchange membrane fuel cell: Evaluation of polymer binders in catalyst layer, International Journal of Hydrogen Energy. 38 (2013) 11370–11378. https://doi.org/10.1016/J.IJHYDENE.2013.06.107.[3] S. Galbiati, A. Baricci, A. Casalegno, R. Marchesi, Degradation in phosphoric acid doped polymer fuel cells : A 6000 h parametric investigation, International Journal of Hydrogen Energy. 38 (2013) 6469–6480. https://doi.org/10.1016/j.ijhydene.2013.03.012.[4] S.H. Eberhardt, F. Marone, M. Stampanoni, F.N. Büchi, T.J. Schmidt, Quantifying phosphoric acid in high-temperature polymer electrolyte fuel cell components by X-ray tomographic microscopy, Journal of Synchrotron Radiation. 21 (2014) 1319–1326. https://doi.org/10.1107/S1600577514016348.[5] S. Hu, M. Lozada-Hidalgo, F.C. Wang, A. Mishchenko, F. Schedin, R.R. Nair, E.W. Hill, D.W. Boukhvalov, M.I. Katsnelson, R.A.W. Dryfe, I. V. Grigorieva, H.A. Wu, A.K. Geim, Proton transport through one-atom-thick crystals, Nature. 516 (2014) 227–230. https://doi.org/10.1038/nature14015.[6] S.M. Holmes, P. Balakrishnan, V.S. Kalangi, X. Zhang, M. Lozada-Hidalgo, P.M. Ajayan, R.R. Nair, 2D Crystals Significantly Enhance the Performance of a Working Fuel Cell, Advanced Energy Materials. 7 (2017) 1–7. https://doi.org/10.1002/aenm.201601216.[7] J. Li, X. Zeng, T. Ren, E. van der Heide, The Preparation of Graphene Oxide and Its Derivatives and Their Application in Bio-Tribological Systems, Lubricants 2014, Vol. 2, Pages 137-161. 2 (2014) 137–161. https://doi.org/10.3390/LUBRICANTS2030137.

A Numerical Investigation on Thermal Gradients and Stresses in High Temperature PEM Fuel Cell During Start-up

The High Temperature Polymer Electrolyte Fuel Cell (HT-PEMFC) stacks using polybenzimidazole (PBI) based membranes have an inability to internally heat up at low temperatures to their nominal operating temperature (160°C–180°C) during the start-up process. Several strategies, such as direct electrical heating, coolant/gas channel heating, catalytic hydrogen-oxygen combustion, etc., are proposed in the literature to assist the heating for quick start-up situations. However, little knowledge exists on the transient thermomechanical stresses induced during the start-up heating process due to non-uniformity in heat supply and disparity in thermal properties of the cell components. The objective of the present research is to analyze the thermal gradients and thermal stresses developed in the HT-PEMFC structure during the start-up with various heating methods discussed in the literature, as well as during the cell operation by exploiting the Fluid-Structure Interaction (FSI) approach. The use of polyalkylene glycol (Fragoltherm S-15-A) based Heat Transfer Fluid (HTF) in the coolant channel has substantially improved the start-up time due to the high Nusselt number. However, a significant gradient in temperature distribution is observed during the preheating process, which resulted in great inhomogeneous stresses in the membrane, particularly in the in-plane direction. Interestingly, the degree of uniformity in membrane current density distribution during cell operation is increased. A detailed heat analysis in the cell showed that the heat generated in the cell due to electrochemical reactions is sufficient to raise the cell temperature from 120°C to operating temperature in a short time. Being subjected to a compressive stress of above 40 MPa, which is higher than the ultimate strength of a typical acid doped PBI membrane, the electrolyte is the most vulnerable component during the start-up. Hence, to inhibit the concomitant effect on cell performance and degradation, a novel start-up strategy should be implemented.

CrN/Cr-Coated Steel Plates for High-Temperature Polymer Electrolyte Fuel Cells: Performance and Durability

This paper investigates the general performance and durability performance of a high-temperature polymer electrolyte fuel cell (HT-PEFC) with CrN/Cr-coated SS316L as bipolar plates and compares this with the bare SS316L and graphite bipolar plates. Polarization curves are conducted every 200 h during the 1000 h durability tests for evaluating the overall performances of the HT-PEFCs with different types of bipolar plates. An electrochemical model based on polarization curves, combined with electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM), is used for understanding the degradation mechanisms at play. The CrN/Cr-coated SS316L bipolar plates show excellent corrosion resistance and performance in a real HT-PEFC. Thereby, the degradation rate decrease from ca. 16% of the highest output power with the bare metallic bipolar plates and graphite bipolar plates to almost zero with the CrN/Cr-coated steel bipolar plate.

Fuel Cell Electrode Characterization Using Neutron Scattering.

Electrochemical energy conversion and storage is key for the use of regenerative energies at large scale. A thorough understanding of the individual components, such as the ion conducting membrane and the electrode layers, can be obtained with scattering techniques on atomic to molecular length scales. The largely heterogeneous electrode layers of High-Temperature Polymer Electrolyte Fuel Cells are studied in this work with small- and wide-angle neutron scattering at the same time with the iMATERIA diffractometer at the spallation neutron source at J-PARC, opening a view on structural properties on atomic to mesoscopic length scales. Recent results on the proton mobility from the same samples measured with backscattering spectroscopy are put into relation with the structural findings.

Effects of Ammonia Impurities on the Hydrogen Flow in High and Low Temperature Polymer Electrolyte Fuel Cells

AbstractFuel cells are a promising technology to use as a source of electricity and heat for buildings, and as an electrical power source for electric motors propelling vehicles. They consume hydrogen as fuel and oxygen to produce electricity, heat and water. Conventional fuels, such as natural gas, methanol, or even gasoline are reformed to produce the hydrogen required by the fuel cells. During the reforming process, impurities are inevitably obtained in the hydrogen flow. One of them is ammonia (NH3) that can result in serious damage to the fuel cell operation. In this paper, the effects produced by different concentrations of NH3 present in the hydrogen flow on the membrane electrode assembly (MEA) performance are studied, differentiating between irreversible and recoverable damages. Strictly experimental, the study includes both low and high temperature polymer electrolyte fuel cells (PEFC). The NH3 poisoning effect is analyzed and quantified by comparing the polarization curves. After the poisoning stage, the cells are subjected to a regeneration process (feeding the cell with neat H2) with the aim of knowing the membrane's recovery capacity. The experimental results demonstrate that in low temperature (LT)‐PEFCs, the cell recovers its performance almost completely with a new exposure to neat H2, in spite of the damage previously caused by the presence of traces of NH3 in the anode feed stream. In contrast, in high temperature (HT)‐PEFCs, the cell suffers irreversible damage, even with short time exposure to NH3. The paper concludes with discussing the possible chemical interactions by which NH3 affects the cell performance.

Tailoring Different Molecular Weight Phenylene-Polybenzimidazole Membranes with Remarkable Oxidative Stability and Conductive Properties for High-Temperature Polymer Electrolyte Fuel Cells.

Polybenzimidazole (ph-PBI) polymer was synthesized with different molecular weights (MWs) and casted into conductive films for use in high-temperature fuel cells (FCs). A comprehensive study on the influence of polymer MW on membrane cast efficiency, chemical stability, thermal behavior, tensile strength, conductivity, FC performance, and durability was reported. The synthesized materials were characterized by different techniques, including, nuclear magnetic resonance spectroscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, impedance microscopy, and scanning electron microscopy. The results showed the importance of manufacturing ph-PBI membranes with controlled properties to achieve high efficiency FCs. High MW ph-PBI membrane (119 kDa) showed a slower rate of chemical degradation, remarkable mechanical properties, and an improved FC performance compared to low MW ph-PBI membrane (39 kDa), thanks to the architecture of high MW ph-PBI. A gain of 91% in proton conductivity with a 47% in FC power density was obtained for the ph-PBI membrane with MW 119 kDa.

Investigation of Activation Process of Membrane Electrode Assembly Obtained By Various Formulation Conditions for High-Temperature Polymer Electrolyte Fuel Cell

Recently, the polymer electrolyte membrane fuel cells (PEMFCs) have attracted the great attention as energy conversion devices for powertrain for the fuel cell electric vehicle and a residential combined heat and power system due to the zero-emission of harmful gas and high energy efficiency. To overcome of the drawbacks of perfluorosulfonic acid (PFSA) membrane and Pt poisoning by CO, the high-temperature PEMFC (HT-PEMFC) has been developing over decades, which has significant advantages as compared to low-temperature PEMFC (LT-PEMFC). For example, it has a much better fuel tolerance, enhanced the reaction kinetics and a simple water management [1,2]. However, the practical power density of membrane electrode assembly (MEA) for HT-PEMFC is much lower than that of LT-PEMFC because of the huge activation loss by acid poisoning [3–5]. Thus, a large amount of Pt is required in the electrode to ensure the sufficient power and long-term durability, which is a critical issue for HT-PEMFC. Therefore, one of the most critical issue for the HT-PEMFC is the decreasing the Pt amount in the electrode without sacrificing the MEA performance [5]. In addition, the fabrication of electrode using the advanced supported catalyst is the very important topic for revealing the improved catalytic activity into performance of MEA [2,5]. In this study, various formulation parameters for making the catalyst slurry using ball-milling were investigated to obtain the smooth electrode for MEA. The parameters are the presence of a viscosity agent, the solid content, and the amount of binder for the MEA of HT-PEMFC. When the viscosity agent is added in the 2.5 wt.% in the catalyst slurry, the slurry is very suitable for making a coated electrode on the gas diffusion layer (GDL). On the contrary, while when the amount of viscosity agent is increased over than 5 wt.%, the electrode is not completely dried. The optimum solid content of catalyst in the slurry was determined in the range of 12 wt.% because if the amount of catalyst exceeded the 14wt.%, the electrode is peeled off severely after drying. The open circuit voltage and performance of MEA under HT-PEMFC condition is depended significantly on the amount of polyvinylidene fluoride (PVDF) in the catalyst slurry. The voltage at a very small current density at 0.008A/cm2 of MEAs with different amount of PVDF was decreased from 0.775 to 0.735 V by increasing the 10wt.% to 30 wt.% of PVDF, which provide the increase of the activation overpotential by poisoning of phosphoric acid on the Pt catalyst. However, the performance of MEA at 0.6A/cm2 was maximized as 0.44 V at the 30wt.% of PVDF in the catalyst slurry, which suggests that the Ohmic overpotential decreased with increasing the PVDF amount. In summary, for maximizing the MEA performance under HT-PEMFC at 150℃, the various conditions for the manufulation of electrode was invesitgated. The amount of PVDF has a significant effect on the performance of MEA. [1] J. Zhang, Y. Xiang, S. Lu, and S. P. Jiang, Adv. Sustainable Syst. 2, 1700184 (2018). [2] D. J. You, D. H. Kim, J. R. De Liled, C. Li, S. G Lee, J. M. Kim, and C. Pak, Appl. Catal. A: General 562, 250–257 (2018). [3] R. E. Rosli, A. B. Sulong, W. R. W. Daud, M. A. Zulkifley, T. Husaini, M. I. Rosli, E. H. Majlan, and M. A. Haque, Int. J. Hydrogen Energy 42, 9293–9314 (2017). [4] A. Chandan, M. Hattenberger, A. El-kharouf, S. Du, A. Dhir, V. Self, B. G. Pollet, A. Ingram, and W. Bujalski, J. Power Sources 231, 264–278 (2013). [5] S.-W. Choi, J. O. Park, C. Pak, K.H. Choi, J.-C. Lee, and H. Chang, Polymers 5, 77–111 (2013).

Effect of Gas Humidification on Performance of High-Temperature Polymer Electrolyte Fuel Cells

Effect of Gas Humidification on Performance of High-Temperature Polymer Electrolyte Fuel Cells

Stochastic Analysis of the Gas Flow at the Gas Diffusion Layer/Channel Interface of a High-Temperature Polymer Electrolyte Fuel Cell

Gas diffusion layers (GDLs) play a significant role in the efficient operation of high-temperature polymer electrolyte fuel cells. They connect the electrodes to the gas channels of the bipolar plate by porous material with a meso-scale geometric structure. The electrodes must be sufficiently supplied by gases from the channels to operate fuel cells efficiently. Furthermore, reaction products must be transported in the other direction. The gas transport is simulated in the through-plane direction of the GDL, and its microstructure created by a stochastic model is equivalent to the structure of real GDL material. Continuum approaches in cell-scale simulations have model parameters for porous regions that can be taken from effective properties calculated from the meso-scale simulation results, as one feature of multi-scale simulations. Another significant issue in multi-scale simulations is the interface between two regions. The focus is on the gas flow at the interface between GDL and the gas channel, which is analyzed using statistical methods. Quantitative relationships between functionality and microstructure can be detected. With this approach, virtual GDL materials can possibly be designed with improved transport properties. The evaluation of the surface flow with stochastic methods offers substantiated benefits that are suitable for connecting the meso-scale to larger spatial scales.

Fabrication of Stable and Well‐connected Proton Path in Catalyst Layer for High Temperature Polymer Electrolyte Fuel Cells

AbstractIt is of importance to establish stable and well‐connected proton path in the catalyst layer to promote the fuel cell performance. Here, we describe a novel method to fabricate stable and efficient proton path for high temperature polymer electrolyte fuel cells (HT‐PEFCs), in which the ionic liquid is doped into the platinum electrocatalyst. The electrochemical results depict that ionic liquid doped electrocatalyst exhibits comparable electrochemical surface area (ESA) and enhanced durability indicating that ionic liquid negligibly affects the hydrogen adsorption/desorption process and protects the electrocatalyst from carbon corrosion. Interestingly, the catalyzing activity toward oxygen reduction reaction (ORR) of Pt electrocatalyst is boosted after doping with ionic liquid mainly due to the modified electronic structures of Pt atoms induced by nitrogen atoms from ionic liquid resulting in weak interaction between Pt atoms and intermediates. The fuel cell performance of ionic liquid doped electrocatalyst is much improved ascribed to the homogeneously dispersed ionic liquid on the surface of Pt electrocatalyst facilitating the fabrication of triple phase boundaries (TPBs) as a result of efficient proton conduction in the catalyst layer. The fuel cell performance only decreases 10 % after 100,000 potential cycles from 1.0 to 1.5 V versus RHE suggesting that ionic liquid forms a stable proton path in the catalyst layer. Thus, the ionic liquid doped Pt electrocatalyst is applicable for the real HT‐PEFC operation.

Design and experimental validation of an HT-PEFC stack with metallic BPP

This paper provides detailed insight into the design, construction, production and verification of a metallic bipolar plate for High Temperature Polymer Electrolyte Fuel Cell stacks. With a focusing on applications with power demands of 5–10 kW, the active cell area is set to a maximum of 100 cm2. The double-plate-concept allows for liquid cooling in the inner bipolar plate compartment. Due to the bipolar plate production by hydroforming of thin stainless steel foils the structure of the coolant compartment is dependent on the gas flow field design. To ensure proper cooling functionality a co-design is necessary. The flow field design, in conjunction with the flow configuration of the reactants (reformate, air) and coolant, considers the effects of hydrogen and oxygen depletion on current density distribution, as well as the temperature profile on carbon monoxide poisoning. These specifications are based on previously published results. For validation, a 5-cell stack with commercial Membrane Electrode Assemblies was operated at 160 °C and 0.2 A/cm2 and regularly interrupted for the polarization curve measurement. After 4700 h of continuous operation, the test was terminated due to a rapid voltage drop in one of the cells. In this paper, it is shown that novel metallic bipolar plates from thin metal sheets can be used for the long-term operation of High Temperature Polymer Electrolyte Fuel Cell stacks.

Simple and Complex Polymer Electrolyte Fuel Cell Stack Models: A Comparison

The High Temperature Polymer Electrolyte Fuel Cell (HT-PEFC) converts chemical energy to electricity and heat. Operating at around 160°C, the heart of a HT-PEFC is a phosphoric-acid-doped polybenzimidazole membrane, which exhibits good protonic conductivity. HT-PEFCs may readily operate with either hydrogen or reformate as fuel. As is the case with most fuel cells, HT-PEFCs are operated in stacks in order to increase the overall electric potential. However, there are few comprehensive models of HT-PEFC stack performance. The results of this research program are among the first to obtain performance calculations for HT-PEFC at the stack scale with experimental validation. HT-PEFC stacks designed at the Forschungszentrum Jülich are actively cooled with polyalkyline glycol liquid (oil) coolant, flowing in internal passages within the solid bi-polar plates, upon the surfaces of which a complex pattern consisting of straight and serpentine passages have been machined, in order to supply the air and fuel to the cell. Because of the elevated temperature, liquid water is not generally found in the gas channels or porous layers. Considerable experimental data have been previously gathered, in-house, for a 5-cell stack based on this design. Two high temperature polymer electrolyte fuel cell (HT-PEFC) models of a HT-PEFC stack are described in detail: (i) A detailed cell-level model where a set of conformal meshes are body-fitted to all the different parts of the stack. The code typically runs, in parallel, on 1000-2000 cores at the Jülich Supercomputer Centre; and, (ii) A coarse-grid stack model based on a ‘distributed resistance analogy’ whereby rate equations supplant local diffusion terms in selected locations and directions to reduce computational requirements. A multiply-shared space (MUSES) method is employed to obtain simultaneous solutions for concentration, heat and momentum for the different phases occupying the ‘same’ global space. Both (i) detailed and (ii) MUSES methods are implemented by instantiating 5 distinct meshes corresponding to (i) air, (ii) fuel, (iii) oil (fluid), and (iv) membrane electrode assembly, (v) bipolar plate (solid) regions, and obtaining solutions of the governing equations on these meshes. For both methods a solution is obtained simultaneously for the stack manifolds, cell manifolds (entrance regions) as well as the ‘core’ of the fuel cell stack. Thermal equilibrium between the 3 fluid phases is not presumed, a priori. In both methods, the electric field potential is expressed as the ideal (Nernst) potential less activation, ohmic, and transport losses. Individual cell potentiostatic boundary conditions are iteratively corrected until the desired overall galvanostatic condition is obtained for all cells in the stack. Both codes are developed in the modern open-source object-oriented library, OpenFOAM. The results of the two models are compared with each other in terms of local current density and species partial pressure distributions. Both models are then compared with experimental data. The results show that the coarse-grid stack model (ii) agrees well, both quantitatively and qualitatively, with the detailed model (i) and experimental results and calculations are performed in two orders of magnitude less computation time. However, neither the experimental results nor the stack model (ii) are able to resolve local extrema in the current density and species mole fraction values that are observed with the detailed model (i). These are due to complex flow regimes associated with the meandering channels and flow bypassing in the porous transport layers. Importantly, these lead to significant local extrema in the local current density and other parameters of significance. These are among the first fully-comprehensive physicochemicohydrodynamic models of a HT-PEFC stack which allows calculations to be performed simultaneously for all the fluid and solids in the manifolds, entrance regions and stack core, together with experimental validation.

Breaking through the Cracks: On the Mechanism of Phosphoric Acid Migration in High Temperature Polymer Electrolyte Fuel Cells

In high temperature polymer electrolyte fuel cells, at high current densities, phosphoric acid (PA) migrates toward the anode and invades catalyst, microporous and gas diffusion layers (GDL). This work studies this PA redistribution using synchrotron based operando X-Ray tomographic microscopy (XTM) and electrochemical impedance spectroscopy (EIS) during a current cycling protocol. It is shown that under reformate conditions, during the first 2 minutes after a positive current step, the cell voltage increases due to better wetting of the anode catalyst layer (CL). From 2 to 20 minutes, the cell voltage drops due to increasing mass transport losses in the microporous layer (MPL) and the GDL. At the anode, cracks in MPL and CL, both with widths up to 150 μm, are flooded within 2 minutes after a current density increase. Acid flooding is only observed for MPL cracks that overlap with CL cracks. The CL cracks therefore act as injection points for the flooding of the MPL cracks and the gas diffusion layer. No change in the PA content of any of the cathodic porous components was observed.

Nanostructure of HT-PEFC Electrodes Investigated with Scattering Methods

Small angle scattering with X-rays (SAXS) and neutrons (SANS) is used as a powerful tool to investigate different components of fuel cells or even groups such as membrane electrode assemblies (MEAs) (1,2). In particular, the structure of electrode layers and membrane electrode assemblies of High Temperature Polymer Electrolyte Fuel Cells (HT-PEFCs) is studied in this contribution with neutron and x-ray scattering (1). Electrode layers in different stages of preparation, pure and doped with different amounts of phosphoric acid have been studied with SAXS. Structural changes have been observed with the addition of phosphoric acid, which is used in this type of HT-PEFC as proton conducting electrolyte. Details of the phosphoric acid distribution and possible void distribution in electrode layers have been obtained with contrast variation experiments in small angle neutron scattering, where the different parts of the sample can be highlighted by exchanging hydrogen with deuterium, here in the phosphoric acid. An outlook will point at the strength of quasielastic neutron scattering experiments to shed light on the proton diffusion on different length scales in the range of 0.1-10 nm, as a microscopic equivalent to the macroscopic conductivity, and it will address the question of what can be retrieved from a multicomponent system such as the different parts of a fuel cell. M. Khaneft, O. Holderer, O. Ivanova, W. Lüke, E. Kentzinger, M.S. Appavou, R. Zorn, W. Lehnert, Fuel Cells 16 (2016), 406 – 413O. Holderer, O. Ivanova, B. Hopfenmüller, M. Zamponi, W. Maier, A. Majerus, W. Lehnert, M. Monkenbusch, R. Zorn, Int. J. Hydrogen Energy 39 (2014) 21657 – 21662

Influence of Different Side-groups and Cross-links on Phosphoric Acid Doped Radel-based Polysulfone Membranes for High Temperature Polymer Electrolyte Fuel Cells

In previous work we tested the potential of Radel based membranes for use in the high temperature polymer electrolyte fuel cell (HT PEMFC), using aminoyridine (AP) and imidazole (IM) as phosphoric acid (PA) binding and crosslinking group, respectively. In this work we developed the system further by comparing AP with hydroxypyridine (HP) and IM with oxydianiline (OX). The use of OX leads to reduced PA uptake, probably due to higher reactivity, increasing the density of crosslinks. HP leads to an increased PA uptake, clearly above 300wt% for HP-IM membranes. Conductivity correlates well with the PA uptake, and HP-IM membranes showed the highest ion conductivity, 18 mS/cm2 at 120°C and fully anhydrous conditions. The logarithmic value of the Young modulus, plotted against the PA uptake, shows a linear behavior, independent of the functional groups. In comparison to previous work, the slope is smaller, demonstrating that it is possible to shift the trade-off relation into a more beneficial range. In the fuel cell test, HP-IM membranes showed the best performance. Based on the peak power density, the HP-IM based system (294mW/cm2 at 800mA/cm2) showed a 2.5 times higher performance than the previously reported AP-IM based system.

Development of Low Cost High-Temperature Polymer Electrolyte Fuel Cell Membrane-Electrode-Assemblies for Combined Heat and Power Plants in Single Family Homes

High-temperature polymer electrolyte fuel cells (HT-PEFCs) are a suitable technology for decentralized small scale electricity and heat production. HT-PEFCs do not require hydrogen infrastructure and are characterized by a simpler and therefore less expensive system compared to available fuel cell systems. In combination with a reformer unit, HT-PEFC systems offer an efficiency gain over conventional combustion of hydrocarbons, such as natural gas. In near future, HT-PEFCs will be even more effective and efficient when renewable biofuels and hydrogen are widespread available. We present an efficient HT-PEFC based combined heat and power (µ-CHP) system for the provision of electrical energy and hot water in single family households (see Table 1). Due to the optimized design and layout of the fuel cell based µ-CHP system and the respective manufacturing processes of the catalysts and the membrane electrode assemblies (MEA), the demand for cost effective and greenhouse gas efficient energy at customer level is addressed. Major efforts were devoted to the establishment of scalable catalyst deposition methods, which enable a loss-free utilization of precious metals. By using appropriate multimetallic catalyst systems at anode and cathode, the precious metal loading was reduced by approx. 20% in comparison to commercially available electrodes without compromising performance (see Figure 1) [1]. Furthermore, by introducing post-preparation treatments, the stability of the catalysts was enhanced over commercial Pt/C. The activity and stability of the catalyst systems were evaluated ex situ by means of cyclic voltammetry and accelerated stress tests using a rotating disk electrode (RDE) setup. Furthermore, the catalyst systems were characterized in situ by means of polarization curves, continuous operation, accelerated stress tests and electrochemical impedance spectroscopy measurements at single cell, stack and at system level (see Figure 1). Acknowledgment Financial support was provided by The Climate and Energy Fund of the Austrian Federal Government and The Austrian Research Promotion Agency (FFG) through the program Energieforschung (e!Mission). [1] A. Schenk, C. Grimmer, M. Perchthaler, S. Weinberger, B. Pichler, C. Heinzl, C. Scheu, F.-A. Mautner, B. Bitschnau, V. Hacker, Platinum–cobalt catalysts for the oxygen reduction reaction in high temperature proton exchange membrane fuel cells – Long term behavior under ex-situ and in-situ conditions, J. Power Sources. 266 (2014) 313–322. Figure 1

Development of Low Cost High-Temperature Polymer Electrolyte Fuel Cell Membrane-Electrode-Assemblies for Combined Heat and Power Plants in Single Family Homes

The stationary use of high-temperature polymer electrolyte fuel cells allows the efficient decentralized production of electricity and heat at customer site. In order to reduce the production cost of such devices, platinum-cobalt based catalysts were synthesized directly at the surface of gas diffusion electrodes with a lower overall precious metal loading than comparable, commercially available state-of-the-art electrodes without impairing the overall fuel cell performance. The prepared membrane-electrode-assemblies showed high durability in single cell and stack tests.

Analysis of a High Temperature Polymer Electrolyte Fuel Cell Combined with an Organic Rankine Cycle System

Analysis of a High Temperature Polymer Electrolyte Fuel Cell Combined with an Organic Rankine Cycle System

Imaging Phosphoric Acid Migration in High Temperature Polymer Electrolyte Fuel Cells by X-Ray Tomographic Microscopy

High temperature polymer electrolyte fuel cells (HT-PEFC) exhibit extensive phosphoric acid electrolyte migration from cathode to anode under high current operation. In this work synchrotron based operando X-ray tomographic microscopy (XTM) was used to study the influence of current density, membrane material (DMAc film casted PBI and PPA-process membranes) and phosphoric acid loading on the extent of electrolyte migration.

Local Structure and Proton Transport in HT-PEFCs Measured with Neutron Scattering

The structural properties and proton transport processes of High Temperature Polymer Electrolyte Fuel Cells (HT-PEFCs) are studied on a broad range of length- and timescales with different neutron scattering techniques. We show structural properties of the proton conducting membrane and of the catalyst layer. Proton transport is measured with quasielastic neutron scattering techniques. The sensitivity of neutrons to individual isotopes, especially in the case of hydrogen and deuterium, makes neutron scattering a perfect tool for such studies. Complementary techniques such as transmission electron microscopy, PFG-NMR and X-ray scattering round up the picture of the different fuel cell components.