Temperature Polymer Electrolyte Membrane Fuel Cells Research Articles

Thermo-Mechanical Stability of Hydrocarbon-Based Pemion® Proton Exchange Membranes

Considering the environmental concerns about the disposal of perfluorosulfonic acid (PFSA) membranes as well as the growing interest in higher temperature operability of polymer electrolyte membrane fuel cells (PEMFCs), non-fluorinated hydrocarbon-based proton exchange membranes (PEMs) with aromatic backbones have become an increasingly active area of research. Low reactant cross-over, tunable electrochemical properties, and differentiated chemistries and potentially safer and cost-reducing synthesis procedures, are additional favourable features of hydrocarbon-based PEMs for prospective use in PEMFCs [1]. Vulnerable linking units, however, are known to be the main disadvantages of these polymers in the oxidative environment of fuel cells. During PEMFC operation, destructive radical species such as hydroxyl (HO•) are produced, causing polymer degradation and thinning in the membrane [2]. Recently, sulfo-phenylated polyphenylenes (sPPPs) have shown outstanding oxidative stability due to a polymer backbone comprising only aryl-aryl bonds, with mitigated chemical degradation in ex-situ and in-situ durability studies [3, 4]. Another concern is regarding the thermo-mechanical stability of PEMs. Thus, a systematic thermo-mechanical stability study is required to confirm the potential of sPPP-based PEMs to replace conventional PFSAs, especially for high temperature PEMFC, i.e., 110-120 °C.The present research objective is to assess the thermo-mechanical stability of a commercial reinforced hydrocarbon-based PEM, Pemion® (PF1-HLF8-15-X, 15 µm thick, reinforced), as well as a mechanically-reinforced PFSA-based reference membrane, across a wide range of temperature (30-120 °C) and relative humidity (RH) (10-90%) conditions that includes the crucial high temperature window of interest for future PEMFCs [6]. To this end, a comprehensive design of experiment yielded 19 tensile tests at various hygrothermal conditions with dynamic mechanical analyzer (DMA 850; TA Instruments) equipped with an external environmental chamber accessory (TA Instruments, RH Accessory). Important mechanical properties such as Young’s modulus, ultimate tensile stress, yield stress, maximum elongation at break, strain hardening, and modulus of resilience were extracted and discussed as well. Datapoints were fitted for empirical model development and mechanical properties were estimated for high temperature and RH conditions beyond the capability of the instrument. This method can be employed to assess if the mechanical properties of membrane materials can be retained at higher temperatures, regardless of polymer chemistry and type. Storage modulus and loss modulus were separately measured in a dynamic mode to observe the impact of temperature on the mechanical response of the hydrophobic backbone and hydrophilic ionic clusters, respectively.Overall, Pemion® demonstrates tough tensile properties in the stress-strain tests due to its sterically encumbered polyphenylene backbone (Figure 1a), whereas the reference PFSA (Figure 1b) shows elastomer-like behavior with much lower Young’s modulus, yield stress, and strain hardening (slope of the curve in the plastic deformation region). Figure 1c-f show the main viscoelastic properties extracted from the tensile tests at room (30 °C, 50% RH) and high temperature fuel cell conditions (110 °C, 50% RH). The modulus of elasticity and strain hardening of Pemion® membrane are almost temperature-independent, whereas these properties for the reinforced PFSA material undergo a significant decay at high-temperature ambience. Pemion® maintains good yielding strength even at high temperature and RH conditions (110-120 °C and 80% RH). Nevertheless, small mechanical stress values as low as 1 MPa can cause spontaneous yielding in the PFSA reference material above 110 °C. The modulus of resilience for the reinforced PFSA is also predicted to be zero at elevated hygrothermal conditions (i.e., 90 °C and 70% RH). This is interpreted as an approach to the material’s glass transition condition, where it loses its mechanical integrity and therefore, is potentially unsuitable for higher temperature PEMFC operation. Moreover, the dynamic mechanical thermal analysis revealed that Pemion® retains its robustness at hygrothermal ambience close to high-temperature PEMFCs, i.e., 110-120 °C and 40-50% RH, whereas the backbone of the PFSA material gradually loses its strength. Acknowledgements This project was financially supported by Natural Sciences and Engineering Research Council of Canada (NSERC), Ionomr Innovations Inc, Canada Foundation for Innovation (CFI), British Columbia Knowledge Development Fund (BCKDF), Western Economic Diversification Canada (WD), and Canada Research Chairs (CRC).

Investigation of Ageing Methods on Gas Diffusion Layers for HT-PEMFC Application

Gas diffusion layers (GDLs) are commonly used materials for polymer electrolyte membrane fuel cell (PEMFC) applications. Key role of the GDL is the distribution of reaction gases evenly from the bipolar plate to the catalyst layer and enabling the removal of product water. Especially challenging are elevated temperatures and acidic conditions for materials applied in high temperature (HT) PEMFCs. In this work, ex-situ ageing tests on GDLs were performed. First, the GDLs were aged in an electrochemical set-up in concentrated phosphoric acid (PA) at temperatures up to 160 °C. After ageing, the GDLs were analysed regarding their morphology and changes in elemental composition. The results show lower impact after ageing at constant potentials of 0.1 V, 0.8 V and OCV but a significant effect of increasing temperature and higher potential of 1.2 V as well as potential cycling. This is confirmed by morphological analysis.

Efficient high temperature PEMFC metallic stack with innovative two-phase liquid cooling

High temperature (HT) polymer electrolyte membrane fuel cells (PEMFCs) are highly beneficial for high power applications. They can be used in both stationary and portable power devices combining the advantages of the PEM type cells (flexibility in dynamic operation, compactness) and high temperature operation (elimination of fuel humidification and carbon monoxide clean up). This work focuses on the development, construction and testing of an efficient all-metallic HT-PEMFC stack with a power output of 1 kWe. The selection of the proper polymer electrolyte allowed the operation of the stack within the range of 160–190 °C. The Membrane-Electrode-Assemblies (MEA) and all components of the stack were designed and prepared in-house. The fuel cell stack characteristics and performance are affected by many parameters such as the materials, components’ design and proper assembly of the stack, as well as the operating conditions. The stack accomplished 50% electrical efficiency with power output of 1070 W and a power density of about 0.18 W/cm2 at 180 °C under pure H2 feed. The same performance was reached with reformate hydrogen feeds. The 1 kW electrical and 1 kW thermal power HT-PEMFC stack presented herein consists of thirty MEAs, metallic bipolar plates and an innovative cost-efficient internal pumpless two-phase equilibrium water-steam cooling. The effective design and construction of the latter secures temperature gradientless and isothermal operation of the stack and the production of high temperature superheated steam, which is an effective carrier of high-quality thermal energy with several commercial and industrial applications.

Investigation of Pt/Fe-N-C Hybrids Towards ORR in Acidic Environment

Polymer electrolyte membrane fuel cells (PEMFCs) are recognized as one of the renewable energy sources in portable, automobile, and stationary applications. Currently, both low temperature (LT) and high temperature (HT) PEMFCs use platinum group metal (PGM) based catalysts for oxygen reduction reaction (ORR) containing usually Pt nanoparticles on carbon black. To reduce the total cost of PEMFC stack, worldwide researchers have considerable attention to find an inexpensive alternative catalyst. Recently, metal-nitrogen-carbon (M-N-C) compounds such as Fe-N-Cs are the most promising PGM-free catalysts for ORR. However, they suffer from insufficient volumetric activity and electrochemical stability in PEMFCs. [1,2] Xiao et al. have proven an improved electrochemical stability of Pt-Fe-N-C electrocatalysts consisting of atomically dispersed Pt and Fe atoms or Pt-Fe alloy nanoparticles in comparison with Fe-N-C only. [3] Mechler et al. have reported that the addition of 1-2 wt.% Pt in hybrid Pt/Fe-N-C catalyst performs well with an increased stability in LT-PEMFCs. [4] Liao et al. have recently shown better ORR activity of Pt/Fe-N-C than Pt/C. [5] With the overriding goal of reducing LT- and HT-PEMFC production costs, Pt/Fe-N-C activity, selectivity and stability with systematically reducing the Pt-content has not been investigated yet. In this study, Pt/Fe-N-C hybrids are synthesized using PMF-011904 from Pajarito Powder (USA) as catalyst support and wet-chemically precipitated Pt nanoparticles with targeted Pt-contents of 40, 5, 1 and 0 wt.%. First, ICP mass spectrometry is used for Pt quantification along all catalysts, and transmission electron microscopy is carried out to investigate morphology and Pt nanoparticle diameter and distribution on the Fe-N-C catalyst. Second, ORR activity and selectivity is investigated by rotating ring disc electrode (RRDE) experiments in 0.1 mol L-1 HClO4, and electrochemical surface area of Pt is calculated by hydrogen underpotential deposition and CO stripping voltammetry. Last, accelerated stress testing (AST) is performed with 5,000 triangle potential cycles between 0.6–1.5 VRHE to evaluate the catalyst stability. Figure 1 shows the initial ORR curves during the RRDE experiments. The mass activities of 40, 5 and 1 wt.% Pt/Fe-N-C determined at 0.9 VRHE are 222.5 ± 41.2 A gPt -1, 170.8 ± 80.4 A gPt -1 and 49.0 ± 8.6 A gPt -1, respectively. Thus, the mass activity depends on Pt-content in the hybrid catalyst strongly. In addition, the other electrochemical characterization results are also going to be discussed in terms of catalyst selectivity, stability and the correlation with morphological aspects during the presentation. Figure 1 ORR curves in O2-saturated 0.1 mol L-1 HClO4 electrolyte with rotation speed of 1,600 rpm and scan rate of 5 mV s-1 (averaged results of three separate electrodes per each catalyst).[1] Y. He, S. Liu, C. Priest, Q.Shi , G. Wu, Chem. Soc. Rev. 2020, 11, 3484–3524.[2] T. Reshetenko, A. Serov, M. Odgaard, G. Randolf, L. Osmieri, A. Kulikovsky, Electrochem. Commun. 2020, 118, 106795.[3] F. Xiao, G.-L. Xu, C.-J. Sun, I. Hwang, M. Xu, H.-W. Wu, Z. Wei, X. Pan, K. Amine, M. Shao, Nano Energy 2020, 77, 10592.[4] A. K. Mechler, N. R. Sahraie, V. Armel, A. Zitolo, M. T. Sougrati, J. N. Schwämmlein, D. J. Jones, F. Jaouen, J. Electrochem. Soc. 2018, 165, F1084.[5] W. Liao, S. Zhou, Z. Wang, F. Liu, H. Pan, T. Xie, Q. Wang, ChemCatChem 2021, 13, 23, 4925-4930. Figure 1

Developing Next Generation High Performance Polymer Electrolyte Membrane Fuel Cells Using Metal Foam As Gas Diffusion Layer

In recent years, low-temperature polymer electrolyte membrane fuel cells (PEMFCs) have played an increasingly important role in zero emission strategy to halt climate change. The performance improvement is a particular focus of fuel cell research and development, with water management being one of the major areas of interest. Here we report the development of a novel metal foam gas diffusion layer (GDL) material with embedded gas flow channels. Owing to the porous nature of the gas channel walls, the membrane electrode assembly (MEA) performance is significantly improved as a result of enhanced mass transport. Unprecedented high power density of 2.09 W/cm2 was observed at 90% relative humidity, and 2.04 W/cm2 for 149% relative humidity, which are respectively 12% and 37% improvement over current state-of-the-art low temperature PEMFC performance. Furthermore, we demonstrated that with our metal foam GDL, it is possible to simplify the flow field design on the bipolar plate, leading to manufacturing cost reduction of the fuel cell components. The work provides new pathway to achieve both high performance and low cost for fuel cells, water electrolyzers and other related technologies.

Combined effect of channel to rib width ratio and gas diffusion layer deformation on high temperature – Polymer electrolyte membrane fuel cell performance

The present study investigates the combined influence of Channel to Rib Width (CRW) ratio and clamping pressure on the structure and performance of High Temperature-Polymer Electrolyte Membrane Fuel Cell (HT-PEMFC) using a three-dimensional numerical model developed previously. It also considers the impact of interfacial contact resistance between the Gas Diffusion Layer (GDL) and Bipolar Plate (BPP). The structural analysis of the single straight channel HT-PEMFC geometry shows that the von-Mises stress greatly increases in the GDL under the ribs as the CRW ratio increases resulting in considerably high deformation. The cell performance analysis depicts the significance of ohmic resistance and concentration polarization for different CRW ratios, particularly at higher operating current densities. However, in low to medium current density regions, the CRW ratio has little influence on cell performance. A substantial impact on the species, overpotential, and current distributions is observed. The findings also reveal that the CRW ratio significantly affects the temperature distribution in the cell.

Enhancing proton conductivity on polybenzimidazole (PBI) membrane doped acid

Abstract This study provides various condition for acid doped polybenzimidazole (PBI) membrane which giving the best proton conductivity result with respect to the High Temperature-Polymer Electrolyte Membrane Fuel Cell (HT-PEMFC). A highly phosphonated polymer membrane based on acid-base complex membrane system was introduced where phytic acid (PyA) was chosen as an acid doping instead of phosphoric acid (PA) due to its properties of having high phosphate group content and ability to participate in H bonding interactions with the functionalities in PBI matrix. By introducing this PBI/phytic acid membrane helped to overcome the issues arise from PBI/PA membrane system especially on acid leaching problem. In this study, a simple and cost effective technique on porous PBI membrane fabrication and acid doping condition were employed to search an optimum acid-doping level and to further improve the stability and durability of the membrane.

Spatial analysis of CO poisoning in high temperature polymer electrolyte membrane fuel cells

The improved tolerance of the High Temperature-Polymer Electrolyte Membrane Fuel Cell (HT-PEMFC) to CO allows the use of reformate as an anode feed. However, the presence of several per cent of CO in the reformate, which is inevitable particularly in on-board reformation in automobiles, which otherwise demands complex systems to keep the CO level very low, will significantly lower the cell performance, especially when the HT-PEMFC is operated at 160 °C or below. In this study, a three-dimensional, non-isothermal numerical model is developed and applied to a single straight-channel HT-PEMFC geometry. The model is validated against the experimental data for a broad range of current densities at different CO concentration and operating temperatures. A significant spatial variation in current density distribution is observed in the membrane because the CO sorption is a spatially non-homogeneous process depending on local operating conditions and dilution of the H2 stream. To investigate the local spatial effects on HT-PEMFC operation, the model is applied to a real cell of size 49.4 cm2 with an 8-pass serpentine flow-field at the anode and the cathode. The membrane and anode catalyst layer are segmented into 5×5 array to investigate the spatial resolution of the polarization curves, H2 concentration, current density, and anode polarization loss. The simulation results show that the presence of CO in the anode feed reduces cell performance, however, the results reveal that uniformity in current density distribution in the membrane improves when the cell is operated in potentiostatic mode. The results are discussed in detail with the help of several line plots and multi-dimensional contours. The study also emphasizes on the importance of optimizing the reformate anode feed rate to improve cell performance.

Experimental and modelling studies of low temperature PEMFC performance

The performance of a PEMFC (Polymer Electrolyte Membrane Fuel Cell) is greatly influenced by the various operating variables like temperature, pressure, stoichiometry of reactants and humidity. The presented work deals with the experimental study of 30 cells low temperature PEM fuel cell stack employing Nafion®-212 membranes. Experimental results are discussed with polarization curves and compared with the steady state model results, developed in MATLAB. The model predicts increase PEMFC performance with increase in operating temperature, pressure and reactant humidity. The comparison shows good agreement between experimental and modeling results with deviations in the range of 7–15% only.

Effect of Surfactant for PTFE Binder Dispersion of Electrodes Prepared By Bar Coating Method in High Temperature Polymer Electrolyte Membrane Fuel Cell

Polymer electrolyte membrane fuel cells (PEMFCs) are one of the most promising energy devices for both mobile and stationary applications due to their high energy conversion efficiency and low environment pollution. However, there are some problems to be solved. PEMFCs operating at low temperatures (below 80℃) based on Nafion require humidification and have low CO tolerance. To overcome this problem, high-temperature PEMFCs that operate up to 180℃ are being studied. High temperature PEMFCs does not require humidification, which simplifies the system and is highly resistant to CO. It also has the advantage of using waste heat. However, the cell performance of high-temperature PEMFCs is still much lower than that of low-temperature PEMFCs and needs to be increased for practical applications The reason for this is slow Oxygen Reduction Reaction (ORR) and limited transport of protons and reactants, especially in the presence of phosphoric acid in the catalyst layer. In the high-temperature PEMFCs, phosphoric acid acts as a proton conduction as an electrolyte and is a necessary element for electrochemical reactions at the triple phase boundaries. Therefore, if the amount of phosphoric acid in the catalyst layer is too small, it exhibits low electrochemical activity. If it is too much, the pore inside the catalyst layer is blocked to restrict the movement of the fuel, thereby reducing the number of triple phase boundaries and reducing the performance. Therefore, the amount and distribution of phosphoric acid and the formation of structural network pores in the catalyst layer are important. Thus, several polymeric binders have been introduced to perform this role. Among them, PTFE is known as the most promising binder. PTFE has hydrophobicity and high chemical stability. However, PTFE easily agglomerates and sinks immediately in the solvent due to its high hydrophobicity. Therefore, if an electrode is made of a catalyst slurry that does not properly disperse PTFE, uniform PTFE distribution in the catalyst layer cannot be expected. So, in the catalyst layer, there may be more or less parts of the specific part than the desired PTFE content. Therefore, it is not only difficult to form a proper phosphoric acid distribution and structural network of the catalyst layer, but also may affect the reproducibility of electrode manufacturing. In this study, the catalytic electrode was prepared by introducing a surfactant to disperse PTFE in the preparation of catalyst slurry. Single cell test was carried out using membrane electrode assembly made from this electrode. And the electrochemical and structural characterizations were compared. The details will be discussed in presentation.

Graphitized Carbon: A Promising Stable Cathode Catalyst Support Material for Long Term PEMFC Applications.

Stability of cathode catalyst support material is one of the big challenges of polymer electrolyte membrane fuel cells (PEMFC) for long term applications. Traditional carbon black (CB) supports are not stable enough to prevent oxidation to CO2 under fuel cell operating conditions. The feasibility of a graphitized carbon (GC) as a cathode catalyst support for low temperature PEMFC is investigated herein. GC and CB supported Pt electrocatalysts were prepared via an already developed polyol process. The physical characterization of the prepared catalysts was performed using transmission electron microscope (TEM), X-ray Powder Diffraction (XRD) and inductively coupled plasma optical emission spectrometry (ICP-OES) analysis, and their electrochemical characterizations were conducted via cyclic voltammetry(CV), rotating disk electrode (RDE) and potential cycling, and eventually, the catalysts were processed using membrane electrode assemblies (MEA) for single cell performance tests. Electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SEM) have been used as MEA diagonostic tools. GC showed superior stability over CB in acid electrolyte under potential conditions. Single cell MEA performance of the GC-supported catalyst is comparable with the CB-supported catalyst. A correlation of MEA performance of the supported catalysts of different Brunauer–Emmett–Teller (BET) surface areas with the ionomer content was also established. GC was identified as a promising candidate for catalyst support in terms of both of the stability and the performance of fuel cell.

A Comparative Study of Ligand Modification to Pt Surface for Enhanced ORR Catalyst Activity and Durability

Last decade witnessed significant advances of polymer electrolyte membrane fuel cell (PEMFC) R&D and the exciting transition of such development into the commercialization of fuel cell vehicles. While the low temperature PEMFC represents the state-of-art technology for transportation applications, substantial challenges remain in finding better catalysts for oxygen reduction reaction (ORR), which accounts for the biggest loss of energy efficiency and the highest cost of material components of FC stacks. ORR involves multiple steps of proton coupled electron transfer processes and a “scaling” issue makes it difficult to optimize every elemental reaction step simultaneously. [1] In addition to the improvement of catalyst itself, engineering catalyst electrolyte interface properties may offer a separate venue to tackling the problem. One recent effort involves the modification of Pt catalyst surface with organic ligands and has demonstrated some successes in enhancing catalyst activity. The effect was mostly attributed to either the change of surface electronic structure of the catalyst or the protection of Pt active sites from poisoning by strong anion adsorption. [2-4] However, the impact of ligand modification on catalyst durability and the stability of the ligand itself on the catalyst surface have not been thoroughly investigated. In this study, we systematically examined a series of organic ligands with different structures and anchoring groups. Coupling material characterization with electrochemical analyses allowed us to assess both the catalyst durability and the ligand stability. Such a comparative study is expected to lead the development of design principles to further improve this technology towards MEA and FC stack applications. References (1) M. T. M. Koper, et al., J. of Electroanal. Chem., 2011, 660, 254-260 (2) Y. H. Chung, et al., J. Phys. Chem., Lett. 2013, 4, 1304-1309 (3) Z. Y. Zhou, et al., J. Phys. Chem., C, 2012, 116, 10592-10598 (4) D. Strmcnik, et al., Nature Chem., 2010, 2, 771

Control-oriented model of a membrane humidifier for fuel cell applications

Improving the humidification of polymer electrolyte membrane fuel-cells (PEMFC) is essential to optimize its performance and stability. Therefore, this paper presents an experimentally validated model of a low temperature PEMFC cathode humidifier for control/observation design purposes. A multi-input/multi-output non-linear fourth order model is derived, based on the mass and heat dynamics of circulating air. In order to validate the proposed model and methodology, experimental results are provided. Finally, a non-linear control strategy based on second order sliding mode is designed and analyzed in order to show suitability and usefulness of the approach.

Proton-Conducting SnP2O7 Electrolyte for Intermediate Temperature PEMFC Under Low Humidificatio

Current fuel cells for transportation and residential applications use polymer electrolyte membrane fuel cells (PEMFCs) which require platinum catalysts and operate below 80 °C due to water management issues. However, PEMFCs operating at 100 °C or higher temperatures in anhydrous conditions do not need a humidifier, and do not suffer from water management issues created by the presence of liquid water. Excessive amount of liquid water in the electrode can flood the backing and catalysts layers at lower temperatures leading to poorer fuel cell performance. Furthermore, such intermediate temperature PEMFCs can solve the problem of carbon monoxide (CO) poisoning of the anode electrocatalyst leading to relaxation of the hydrogen fuel quality standards, thus lowering infrastructure costs. Finally, higher operating temperatures allow for simpler cooling systems in transportation applications, which results in smaller and lighter radiators. These advantages mean that a paradigm shift in fuel cells for transportation and residential applications can be achieved with an intermediate temperature proton conducting solid-electrolyte that can operate above 150 °C. Unfortunately, electrolyte membranes and ionomers developed so far do not have satisfactory conductivity and performance in the above temperature ranges, at low-humidity, or in non-humidified conditions. The further advancement of higher temperature PEMFCs relies on the development of membranes that possess the desired electrochemical and mechanical properties in dry (< 30% RH) and hot (> 100 oC) conditions. In this study, we have developed an organic/inorganic composite membrane using a SnP2O7 (TPP) inorganic conductor and evaluated the fuel cell performance under various conditions. Membrane electrode assemblies (MEA) were prepared from these membranes and gas diffusion electrodes (GDE) were optimized using either LANL ionomer dispersion or various commercial gas diffusion layer (GDL). A maximum power density (> 600mW/cm2 ) has been obtained for fuel cell operation at ≈ 220 oC under less than 2 % humidification condition.

Development of a Novel Sulfated Poly (ether sulfone) with Aliphatic Chain for High Temperature Fuel Cell

Polymer electrolyte membrane fuel cells (PEFCs) as one of fuel cell systems, offer a board range of benefits, including: (1) high efficiency, (2) clean process (no CO2 emission), (3) compact design1, and (4) quiet operation. As one of solutions to current technical problems, PEFC operation at high temperature (low humidity) has been considered as a promising system to reduce cost of PEFCs. High temperature PEFCs have some additional merits such as fast reaction kinetic, low activation energy for power generation and high CO catalyst poisoning tolerance2. These advantages make high temperature PEFCs very attractive. However, there are also some technical barriers to develop this attractive system. Especially, harsh environment such as high temperature and low humid condition are very severe for polymer electrolyte membranes (PEMs) as components of PEFCs. Sulfonated poly(ether sulfone)s (SPESs) have been commonly developed as hydrocarbon-type PEMs3,4for high temperature PEFCs, because of the high durability at high temperature condition. Several kinds of SPESs with different structures were investigated previously. However, most of them used only aromatic chain as backbone, which lead the membranes to be tough. In this research, we have investigated a series of copolymerized sulfated poly (ether sulfone) (SPES) with aliphatic chain for high temperature PEFCs. Sulfuric acid was attached to the hydroxyl group connected to the aliphatic main chain. The attached sulfuric acid would be able to move easily and work as a proton conductor because aliphatic unit is more flexible than aromatic unit. We evaluated the basic property of the aliphatic SPES as high temperature PEMs although chemical stability of the aliphatic unit is not higher than that of the aromatic unit. SPES shown in Figure 1 was prepared by sulfation of the hydroxyl group of aliphatic PES. Purification and protonation of the obtained SPES were carried out thoroughly by dialysis from SPES HCl aq. The structure of SPES was confirmed by 1H NMR. SPES films were prepared by cast method. SPES DMSO solution was cast on a petri dish and dried at 60 ˚C in vacuo overnight. The membrane showed hydrophobicity. This property indicated that it showed strong durability against water, which is necessary in fuel cell system. Thermal stability of PEMs is significantly required for high temperature PEFC operation. The obtained SPES was investigated by TGA/DSC experiment as shown in Figure 2. From the result of TGA, SPES had three stages of weight loss. The weight loss was assigned to the removing of water from 66 ˚C to 100 ˚C, thermal decomposition of sulfuric acid2from 176 ˚C to 343 ˚C and the thermal decomposition of the main chain from 343 ˚C to 600 ˚C. And DSC result indicated that no glass transition temperature was observed from SPES at operation temperature region for high temperature PEFC (<120 ˚C). In addition, the proton conductivity of SPES film was observed. The obtained proton conductivity was 0.3 mS/cm at 120 ˚C, 100%RH, which may be caused the high hydrophobic and long distance between sulfonic acid group. We introduce more sulfuric acid group in SPES, and the effect of the sulfuric acid amount and introduction position of sulfonic acid on the proton conductivity is discussed and an optimum condition for preparing MEA for high temperature PEFC is investigated. Reference T. Husaboe, J. A. Rittenhouse, M. D. Polanka, P. J. Litke, J. Hoke, AIAA Paper. DOI, 10, (2013).S. Bose, T. Kuila, T.X. Nguyen, N. H. Kim, K. T. Lau, J. H. Lee, Prog. Polym. Sci., 36, 813 (2011).Y. S. Ye, J. Rick, B. J. Hwang, Polymers, 4, 913 (2012).M. Ulbricht, Polymer, 47, 2217 (2006). Figure 1

Detailed analysis of Integrated Steam Ethanol Reformer and High Temperature Polymer Electrolyte Membrane Fuel Cell

Utilisation of hydrocarbon fuels as a source of hydrogen for Polymer Electrolyte Membrane Fuel Cell (PEMFC) is a possible solution for the demand for hydrogen infrastructure. Ethanol, which is considered to be a domestic and renewable fuel, is a potential source in this regard. Its use as a source of hydrogen production has received appreciations in recent years. For agriculture based countries such as India, China, Brazil, etc., where ethanol can be produced abundantly, this development serves as a boon to meet their future energy demands. This study presents the analysis of high-temperature PEMFC stack integration into a combined system with Steam Ethanol Reformer (SER). One dimensional mathematical model of the integrated system is developed. Performance of the system is studied methodically by varying the operating parameters such as temperature and steam to carbon ratio (S/C) of the SER, temperature of PEMFC and pressure of the system. In addition, the necessity of a Water Gas Shift (WGS) reactor to function as a carbon monoxide removal unit for pre-treating the reformate gas before it is fed to the high temperature PEMFC is also investigated in this study. The S/C ratio and reformer temperature do not affect the performance of the system considerably as long as the fuel processor unit contains WGS reactor along with the reformer. Inclusion of WGS reactor shows a positive influence on the performance of the fuel processor unit. A higher fuel cell temperature and pressure provides a higher voltage more prominently at higher current densities.

Effect of carbon dioxide on the contamination of low temperature and high temperature PEM (polymer electrolyte membrane) fuel cells. Influence of temperature, relative humidity and analysis of regeneration processes

An experimental investigation of the performance and contamination of low and high temperature PEMFCs (polymer electrolyte membrane fuel cells) operating with different concentrations of CO2 at the anode inlet is presented. 50 cm2 MEAs are used in the investigation: Nafion membranes with catalyst Pt loading 0.5 mg cm−2 for both anode and cathode for the low temperature cell, and Celtec P1000 PBI MEAs with catalyst loading 0.75 mg cm−2 in anode and 1 mg cm−2 in cathode for the high temperature cell. An analysis of the relative humidity influence in the contamination process for low temperature polymer electrolyte membrane fuel cells and the temperature effect for both low and high temperature operation range are also investigated in this work. The results show that the performance loss is larger than expected if only a dilution effect were considered, so that a real contamination process occurs in the cell when CO2 is fed to the anode, due to the RWGS (reverse water gas shift) reaction. This contamination effect is analysed and quantified by comparing the polarization curves of the contaminated cell with the ones corresponding to the cell operating with pure hydrogen, following the method described in section 2. The overpotentials for different current densities, CO2 concentrations, relative humidity, and cell temperatures are presented and discussed for both types of fuel cells. Two different regeneration processes (anode feeding with pure H2 and with air) are also presented and discussed. The analysis of the effectiveness of each regeneration strategy also supports that CO produced via the RWGS reaction is adsorbed onto the catalyst.

Enhancement of Oxygen Reduction and Mitigation of Ionomer Dry-Out Using Insoluble Heteropoly Acids in Intermediate Temperature Polymer-Electrolyte Membrane Fuel Cells

The use of Cs0.5H0.5PW12O40 insoluble salt as a superacid promoter in the catalyst layer of a polymer electrolyte membrane fuel cell (PEMFC) has been investigated. An increase of performance has been recorded at intermediate temperatures (110–130 °C) and under low relative humidity (R.H.). The promoter appears to mitigate the ionomer dry-out effects in the catalytic layer and produces an increase of the extent of the catalyst-electrolyte interface as demonstrated by cyclic voltammetry analysis. These effects are also corroborated by a significant decrease of polarization resistance at intermediate temperatures. Such characteristics have been demonstrated for a conventional membrane-electrode assembly based on a Pt-Co alloy and a Nafion 115 membrane.

Organic/Inorganic Composite Membrane Using a Proton-Conducting SnP2O7 Electrolyte and PFSA Polymers for Intermediate Temperature PEMFC

Current fuel cells for transportation and residential applications use polymer electrolyte membrane fuel cells (PEMFCs) which require platinum catalysts and operate below 80 °C due to water management issues. However, PEMFCs operating at 100 °C or higher temperatures in anhydrous conditions do not need a humidifier, and do not suffer from water management issues created by the presence of liquid water. Excessive amount of liquid water in the electrode can flood the backing and catalysts layers at lower temperatures leading to poorer fuel cell performance. Furthermore, such intermediate temperature PEMFCs can solve the problem of carbon monoxide (CO) poisoning of the anode electrocatalyst leading to relaxation of the hydrogen fuel quality standards, thus lowering infrastructure costs. Finally, higher operating temperatures allow for simpler cooling systems in transportation applications, which results in smaller and lighter radiators. These advantages mean that a paradigm shift in fuel cells for transportation and residential applications can be achieved with an intermediate temperature proton conducting solid-electrolyte that can operate above 150 °C. Unfortunately, electrolyte membranes and ionomers developed so far do not have satisfactory conductivity and performance in the above temperature ranges, at low-humidity, or in non-humidified conditions. The further advancement of higher temperature PEMFCs this relies on the development of membranes that process the desired electrochemical and mechanical properties in dry (< 30% RH) hot (> 100 oC) conditions. In this study, we have developed an organic/inorganic composite membrane using a SnP2O7 (TPP) inorganic conductor and evaluated the fuel cell performance under various condition. Figure 1 illustrates the conductivity of this membrane under anhydrous conditions at various temperatures. The conductivity is a strong function of the % of TPP in the composite and reach as high as 0.1 S/cm at T ≥ 250oC using ≈ 90wt % TPP. Membrane electrode assemblies (MEA) were prepared from these membranes using either standard PEMFC Gas diffusion electrodes or Pt/C/TPP based electrodes painted into to the membrane. The performance of one of these MEAs is shown in Figure 2. A maximum power density of 300mW/cm2 (not shown) has been obtained for fuel cell operation at ≈ 250 oC and < 5 % relative humidity. While these preliminary results are promising, there are still challenges with low open circuit voltage (OCV) due to membrane porosity and high kinetic losses due to insufficient electrode morphology optimization. In this talk we will address these issues and discuss the progress made towards better performing intermediate temperature fuel cells. [1] Nagao et al., J Electrochem Soc, 2006 [2] Nagao et al. Electrochem Solid State Lett, 2006. Figure 1

Performance of a High Temperature Polymer Electrolyte Membrane Fuel Cell with Low Catalyst Loading Produced by Reactive Spray Deposition Technology

Traditional polymer electrolyte membrane fuel cells (PEMFCs) typically operate at temperatures around 80 °C. As a result of these low operating temperatures PEMFCs suffer from several performance issues such as problems with water and thermal management, poor electrochemical kinetics, and intolerance to poisons such as carbon monoxide. If the temperature can be increased to upwards of 200 °C the kinetics for the sluggish oxygen reduction reaction can be greatly improved and upwards of 1% carbon monoxide in the feed gas stream will not deteriorate cell performance. Additionally, water in the cell will exist primarily in the vapor phase helping mitigate the flooding of the electrodes. Finally, the greater discrepancy between the cell temperature and the surrounding environment enhances heat rejection and simplifies thermal management [1]. In the current work, gas diffusion electrodes (GDE) for a high temperature PEMFC are fabricated via Reactive Spray Deposition Technology (RSDT) [2,3]. This flame based deposition technique produces Pt nanoparticles through combustion of a precursor solution consisting of a metal organic compound (platinum(II) acetylacetonate) dissolved in a high enthalpy solvent (a mixture of xylene, acetone, and propane). The Pt catalyst is attached to a carbon support, Vulcan XC-72R in this case. This is accomplished by spraying a carbon based slurry, containing a PTFE binder, through secondary nozzles into the path of the Pt nanoparticles in the post luminous zone of the flame. In order to produce the GDE (5×5cm), the resulting spray from the RSDT process is directed at a gas diffusion layer substrate (SIGRACET® GDL25BC, 5×5cm). The resulting GDEs were then hot pressed to an ADVENT® membrane doped with 85wt% phosphoric acid to produce the 5×5cm single cell. A study of the effect of the binder to carbon ratio (PTFE/Vulcan XC-72R) on cell performance and structure was performed through the use of polarization scans, cyclic voltammetry, mercury porosimetry, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). PTFE/Vulcan XC-72R ratios ranging from 0.1 to 1 were studied. It was determined experimentally that the best performance resulted from a binder to carbon ratio of 0.9. This is believed to be due to the well-developed Pt nanoparticle distribution, small pores and uniform pore size distributions, and high electrochemical surface area. These experimental results will be coupled with a semi empirical model to mimic cell performance based on the catalyst agglomerate concept [4]. An attempt will be made to link the physical characteristics of the RSDT produced GDE to the appropriate parameters of the model to develop a firm understanding of the influence of the RSDT process parameters on catalyst structure and performance.