Intermediate-Temperature Fuel Cells Research Articles

A Comparative Effect of CsH2PO4/ZrP2O7 Composite Electrolytes for Intermediate Temperature Fuel Cell

Solid acid composite CsH2PO4 (CDP)/ZrP2O7 were synthesized and characterised with different weight ratio of CDP, SDP and ZrO2. The characterisations of the Solid acid composite were observed the structural, thermal stability and conductivity in terms of X-ray diffraction (XRD) analysis, Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric analysis, Differential Thermal Analysis, and conductivity measurements. The amount of CDP and ZrP2O7 powder were used for pallet production. The composites powders were to form of pellets of 1mm thickness for conductivity measurement. ZrP2O7 in the composites has a large effect on the conductivity measurement and this material increased the temperature and time dependent conductivity of CDP by up to 4 orders of magnitude. The transition was identified in CDP/ZrP2O7 composites under atmospheric pressure. The thermal stability of the solid acid composites for dehydration, melting, and decomposition was investigated in the temperature range of 50 to 300 °C under environments with atmospheric humidification. Keywords: Composite Electrolytes, Conductivity, Thermal Analysis, Caesium Dihydrogen Phosphate, Pyrophosphates.

(Invited) Mixed Conduction in Ceramic Electrolytes For Intermediate-Temperature Fuel Cells and Electrolyzers

High-temperature fuel cells and electrolyzers (e.g., T > 700 ˚C) rely on oxide electrolytes such as stabilized cubic zirconia that conduct a single defect, oxygen vacancies. Intermediate-temperature electrochemical cells (e.g., T < 650 ˚C) utilize mixed conducting ceramic electrolytes, that conduct multiple defects. Operating at T < 600 ˚C facilitates lower-cost interconnect materials and balance-of-plant components, but the mixed conductor behavior can reduce fuel cell voltages and lower electrolyzer faradaic efficiencies. Predicting behavior of these mixed conductors, even at open-circuit voltage, requires modeling the coupled transport of the multiple conducting defects in the electrolyte. Detailed models of mixed conductors coupled to porous electrode models can simulate cell performance over a broad range of operating conditions. This presentation highlights models of two types of cells with mixed conducting oxide electrolytes. Firstly, gadolinium-doped ceria (GDC) primarily conducts oxygen vacancies but also some electrons via a reduced-ceria small polaron, but it performs well in intermediate temperature solid-oxide fuel cells [1]. Secondly, yttrium-doped barium zirconates (BZY) primarily conducts protons but also oxygen vacancies and small polarons, which contribute to electronic leakage. Variants of BZY electrolytes perform well in fuel cells and electrolyzers [2-4]. This paper focuses on cell-level models of these mixed-conductors and how to identify favorable regions for high performance in fuel cells and electrolyzers. Zhu, A. Ashar, R.J. Kee, R.J. Braun, G.S. Jackson, “Physics-based model to represent the membrane-electrode assemblies of solid-oxide fuel cells based on gadolinium-doped ceria,” J. Electrochem. Soc., Under revision, 2023.J. Kee, S. Ricote, H. Zhu, R.J. Braun, G. Carins, J.E. Persky, “Perspectives on technical challenges and scaling considerations for tubular protonic-ceramic electrolysis cells and stacks ,” J. Electrochem. Soc. 169:054525 (2022).Zhu, Y. Shin, S. Ricote, R.J. Kee, “Defect incorporation and transport in dense BaZr0.8Y0.2O3-d membranes and their impact on hydrogen separation and compression,” J. Electrochem. Soc., Under revision, 2023.Zhu, S. Ricote, R.J. Kee, “Thermodynamics, transport, and electrochemistry in proton-conducting ceramic electrolysis cells,” in High Temperature Electrolysis, W. Sitte and R. Merkle, Editors, IOP Publishing, 2023.

Enhanced MEA Performance for an Intermediate-Temperature Fuel Cell with a KH5(PO4)2-Doped Polybenzimidazole Membrane.

This work exhibits an effective approach to enhance the performance of membrane-electrode assembly (MEA) with KH5(PO4)2-doped PBI membrane, by adding phosphoric acid (PA) in the catalyst layer (CL). The ohmic resistance and single-cell performance of the MEA, treated with PA, are reduced by ~80% and improved by ~800%, respectively, compared to that of untreated MEA. Based on the MEA pretreated with PA, the influence of humidity and temperature on the resistance and the single-cell performance are investigated. Under humidified gas conditions, the ohmic resistance of MEA is reduced but the charge transfer resistance is slightly increased. Regarding the effect of temperature, the ohmic resistance of MEA becomes lower as the temperature elevates from 140 to 180 °C, but increases at 200 °C. The maximum peak power density presents at 180 °C and 20% RH with 454 mW cm−2. The peak power density is favored with temperature increase from 140 to 180 °C, but decreases with further increase to 200 °C. Moreover, when dry gas conditions are employed, the output performance is unstable, suggesting that humidification is necessary to inhibit degradation for a long-term stability test.

Properties and Applications of Metal Phosphates and Pyrophosphates as Proton Conductors.

We review the progress in metal phosphate structural chemistry focused on proton conductivity properties and applications. Attention is paid to structure–property relationships, which ultimately determine the potential use of metal phosphates and derivatives in devices relying on proton conduction. The origin of their conducting properties, including both intrinsic and extrinsic conductivity, is rationalized in terms of distinctive structural features and the presence of specific proton carriers or the factors involved in the formation of extended hydrogen-bond networks. To make the exposition of this large class of proton conductor materials more comprehensive, we group/combine metal phosphates by their metal oxidation state, starting with metal (IV) phosphates and pyrophosphates, considering historical rationales and taking into account the accumulated body of knowledge of these compounds. We highlight the main characteristics of super protonic CsH2PO4, its applicability, as well as the affordance of its composite derivatives. We finish by discussing relevant structure–conducting property correlations for divalent and trivalent metal phosphates. Overall, emphasis is placed on materials exhibiting outstanding properties for applications as electrolyte components or single electrolytes in Polymer Electrolyte Membrane Fuel Cells and Intermediate Temperature Fuel Cells.

Performance of an Intermediate-Temperature Fuel Cell with a CsH5(PO4)2-Doped Polybenzimidazole Membrane

CsH5(PO4)2-doped polybenzimidazole (PBI) membranes exhibit good proton conductivity and mechanical properties. However, their application in fuel cells is impeded by poor performance. In this study, a novel method is confirmed to greatly improve the performance of a fuel cell based on a CsH5(PO4)2-doped PBI membrane. By coating phosphoric acid (PA) on the surface of the catalytic layer of the gas diffusion electrode, the interfacial contact between the electrolyte membrane and catalytic layer is improved, thereby reducing the ohmic resistance and improving the fuel cell performance. The cell performance is improved by ∼700%. Moreover, the effects of humidity and temperature on the performance and resistance analysis of membrane electrode assembly with a CsH5(PO4)2—doped PBI membrane are studied. Testing under a temperature range of 160 °C–220 °C and humidity range from dry to 30% relative humidity, a maximum peak power density of 554 mW cm−2 is found at 200 °C and 20% relative humidity. A durability test of the membrane electrode assembly indicates that its performance remains stable in a humid atmosphere but gradually decreases in a dry atmosphere. This means for the long-term operation of the molten proton conductor electrolyte membrane, a humid atmosphere is necessary to inhibit the performance decay.

Synthesis and Characterizations of Barium Zirconate–Alkali Carbonate Composite Electrolytes for Intermediate Temperature Fuel Cells

Composite ionic conductors for intermediate temperature fuel cells (ITFC) were produced by a combination of yttrium-substituted barium zirconate (BaZr0.9Y0.1 O2.95, BZY) and eutectic compositions of alkali carbonates (Li2CO3, Na2CO3, and K2CO3, abbreviated L, N, K). These materials were characterized by X-ray diffraction, scanning electron microscopy, and impedance spectroscopy. The combination of BZY with alkali metal carbonate promotes the densification and enhances the ionic conductivity, which reaches 87 mS·cm−1 at 400 °C for the BZY–LNK40 composite. In addition, the increase of the conductivity as a function of hydrogen partial pressure suggests that protons are the main charge carriers. The results are interpreted in terms of the transfer of protons from the ceramic component to the carbonate phase in the interfacial region.

Characterization and Electrochemical Properties of 10 mol% Lutetium-Doped BaCO3 and its Composite Electrolyte for Intermediate Temperature Fuel Cells

Characterization and Electrochemical Properties of 10 mol% Lutetium-Doped BaCO3 and its Composite Electrolyte for Intermediate Temperature Fuel Cells

Development of 3-Dimensionally Ordered Microporous Polyimide Based Composite Membranes Apply on Non-Humidified Intermediate Temperature Fuel Cells

Polymer electrolyte fuel cells (PEFC) have been used as clean power generation systems for households and vehicles because of their high energy conversion efficiency and low emissions. Perfluorosulfonic acid (PFSA) polymers have been used as electrolyte membranes in PEFCs due to their high proton conductivity, excellent chemical stability and superior durability. However, the membranes require water which limits the operating temperature to be below 100 °C leading to a complex system of water management and low effective utilization of heat. So new kinds of electrolyte membranes which can be operated under non-humidified intermediate temperature (120- 200 °C) are required. To achieve this kind of fuel cell, we focused on a mixed electrolyte based on phosphoric acid (PA) and sulfonic acid group containing ionic liquids (ILs) in our previous studies1. The PA_IL mixed electrolyte not only showed higher thermal stabilities, but also higher electrochemical activities and higher durability of Pt catalyst comparing with pure PA or pure IL. In this study, in order to realize a composite membrane for fuel cell, 3-dimensionally ordered microporous polyimide (3-DOM PI) which has the properties of high porosity, uniform pore structure and high thermal stability was developed as a backbone for composite electrolyte membrane. Polyamic acid (20 wt.%, JFE chemical Co.) was mixed with silica particles (100 nm, 300 nm and 900 nm in diameters, respectively) to making a slurry. The slurry was applicate on a glass board. Then the slurry membrane was drying for polymerization at 320 °C. At last, the silica was removed by HF aqueous solution (10 wt.%) etching for 12 hours. The 3-DOM PI was washed by distilled water then drying at room temperature for 2 days. The composite membrane was composed by PA_IL mixed electrolyte and 3-DOM PI under vacuum condition for 10 min at 100 °C. Figure 1 showed the image of 3-DOM PI. From the SEM analysis, it was confirmed that the different uniform pore sizes of 3-DOM PI were successfully fabricated. The composite membranes were evaluated by the thermogravimetric analysis, the ionic conductivities analysis and the fuel cell polarization test under the non-humidified intermediate temperature. The hydrogen crossover was also evaluated by changing the pore size and thickness of composite membranes. The optimized pore size (nanoscale) and thickness (microscale) of composite membranes were discussed to be 100 nm and 25±3 μm, respectively. The maximum current density and power density at 180 °C are 1.8 A cm -2 and 450 mW cm -2, respectively. The durability of the composite membranes was observed for more than 280 h with a constant current. From the result in Fig. 2 a), the stability of MEA was not only confirmed by the stable OCV, maximum current density and the stability of cathode Pt catalyst from TEM analysis (Fig. 2 b) and c)). In this study, the PA_IL/3-DOM PI composite membrane for Non-humidified IT-FC was developed. Acknowledgement This research was partly supported by “Platform for Technology and Industry” of Tokyo Metropolitan Government. References Yu, S. Kikuchi, H.P. Peediyakkal, H. Munakata, K. Kanamura. ACS Appl. Mater. & Interfaces2019, 11, 14, 13761-13767 Figure 1

Molten Hydroxide Dual-Phase Membranes for Intermediate-Temperature Fuel Cells

Anion exchange membrane (AEM) fuel cells are sought after due to its enabled adoption of non-precious metals as electrocatalysts and enhanced reaction kinetics at high pH conditions[1]. Typical polymer membranes contain quaternary ammonium or phosphonium group polymers that conduct ions at temperature below 90°C[2], limiting their applications at elevated temperatures. Nevertheless, elevated temperature operations allow for improved electrode kinetics, system efficiency and simplified heat management. Hence, there is a need to develop hydroxide ion conducting membranes that are chemically and mechanically stable and can operate at intermediate temperature ranges (150 - 400°C) without compromising its ionic conductivity. Here we report a novel hydroxide-ceramic dual-phase (HCDP) membrane technology that utilizes molten alkaline hydroxides (e.g. sodium, potassium, and lithium) impregnated into the porous zirconia matrix[3]. When using air as oxidant, hydroxide ions react with from air to form carbonates leading to performance degradation of the fuel cell due to loss of ionic conductivity. The poisoning effects are rapid and severe, necessitating the use of pure oxygen instead of air as cathode feed. Our proposed technology overcomes the poisoning issue while air feed operation by shifting the chemical equilibrium of the undesired carbonate ions toward hydroxide and in the presence of water at elevated temperatures, thus releasing from the electrolyte in situ during fuel cell operation. This contribution will highlight our recent developments in this area. [1] Urquidi-Macdonald, M.; Sen, A.; Grimes, P.; Tewari, A.; Sambhy, V. NSF Report from Penn State. https://arxiv.org/pdf/physics/0504130[2] Hibino, T.; Kobayashi, K., Journal of Materials Chemistry A 2013, 1 (24), 7019-7022 [3] Cerón, MR.; Lai, SZ.; Amiri, A.; Monte, M.; Katta, S.; Kelly, JC.; Worsley, MA.; Merrill, MD.; Kim, S.; Campbell, PG.; Journal of Membrane Science 2018, 567, 191-198

Phosphoric Acid Diethylmethylammonium Trifluoromethanesulfonate-Based Electrolytes for Nonhumidified Intermediate Temperature Fuel Cells.

The present study reports a new series of electrolytes for nonhumidified intermediate temperature fuel cells (IT-FCs). This series of new mixed electrolytes, composed of phosphoric acid (PA) and diethylmethylammonium trifluoromethanesulfonate ([dema][TfO]), was designed as nonhumidified IT-FC electrolytes. The mixed electrolytes show a higher thermal stability than pure PA, which is dehydrated at ITs. The thermal stability of the mixed electrolytes could be explained by the interaction between the triflate group in [dema][TfO] and PA, as indicated by Fourier transform infrared and proton nuclear magnetic resonance (1H NMR) spectroscopies. On the other hand, the ionic conductivity and proton transference number of the mixed electrolytes were similar to those of the pure PA. However, the oxygen reduction reaction (ORR) activity of a platinum catalyst is significantly enhanced in the mixed electrolytes, which was due to the several orders of magnitude increase in oxygen solubility by the addition of [dema][TfO] to PA. Specifically, for the equimolar fraction mixed electrolyte, the diffusion coefficient and the solubility of oxygen were ca. 1.47 × 10-5 cm2 s-1 and ca. 1.28 mmol dm-3 at 150 °C, respectively. The addition of [dema][TfO] to PA could significantly enhance the ORR activity. Therefore, the PA_[dema][TfO] mixed electrolyte can be one of the solutions to develop nonhumidified intermediate FC electrolytes.

SrCe0.9Sm0.1O3-α Compounded with NaCl-KCl as a Composite Electrolyte for Intermediate Temperature Fuel Cell.

SrCeO3 and SrCe0.9Sm0.1O3-α were synthesized using a high-temperature solid-state reaction method using Sm2O3, SrCO3, CeO2 as precursors, then the SrCe0.9Sm0.1O3-α-NaCl-KCl composite electrolyte was fabricated by compounding SrCe0.9Sm0.1O3-α with NaCl-KCl and sintering it at a lower temperature (750 °C) than that of a single SrCeO3 material (1540 °C). The phase and microstructure of the samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The conductivities of the samples were measured in dry nitrogen atmosphere using electrochemical analyzer. The conductivities of the SrCeO3, SrCe0.9Sm0.1O3-α and SrCe0.9Sm0.1O3-α-NaCl-KCl at 700 °C were 2.09 × 10−5 S·cm−1, 1.82 × 10−3 S·cm−1 and 1.43 × 10−1 S·cm−1 respectively. The conductivities of SrCe0.9Sm0.1O3-α-NaCl-KCl composite electrolyte are four orders of magnitude higher than those of SrCeO3 and two orders of magnitude higher than those of SrCe0.9Sm0.1O3-α. The result of logσ ~ logpO2 plot indicates that SrCe0.9Sm0.1O3-α-NaCl-KCl is almost a pure ionic conductor. The electrolyte resistance and the polarization resistance of the H2/O2 fuel cell based on SrCe0.9Sm0.1O3-α-NaCl-KCl composite electrolyte under open-circuit condition were 1.0 Ω·cm2 and 0.2 Ω·cm2 respectively. Further, the obtained maximum power density at 700 °C was 182 mW·cm−2.

(High Temperature Materials Division Outstanding Achievement Award) Recent Advances in Intermediate-Temperature Fuel Cells: Surface Modification and In Situ/Operando Characterization

The performances of electrochemical systems are often limited by the charge and mass transfer along surfaces and across interfaces. Fundamental understanding of these electrochemical processes, especially the rate-limiting steps, is vital to achieving rational design of a new generation of intermediate-temperature fuel cells powered by a wide variety of readily available fuels. Also, surface modification has been successfully used to dramatically enhance electro-catalytic activity and durability of electrode materials. This presentation will highlight some recent advances in surface modifications and characterization of electrodes in energy storage and conversion systems. Surface enhanced Raman spectroscopy (SERS) has been used for probing and mapping new phases and reaction intermediates on electrode surfaces under or near operating conditions. It has also been demonstrated that SiO2 shell isolated Ag nanoparticles have excellent chemical and thermal robustness and stability for in situ SERS study of electrode materials under in situ or operando conditions, providing valuable information on reaction intermediates or structural changes that critically influence the performance and stability of the electrodes. Further, synchrotron-based X-ray absorption spectroscopy (XAS) and XPS have been used to characterize the local atomistic structure and oxidation state of electrode surfaces and interfaces, which may critically affect the activation or degradation processes of electrodes. These experimental studies, together with modeling and simulation, have helped us to gain important insights into the mechanisms of chemical and energy transformation, electro-catalytic reactions, and degradation processes, providing valuable guidelines for rational design of new electrode materials, surfaces, and interfaces with desired functionalities.

Visualization of the Diffusion Pathway of Protons in (NH4)2Si0.5Ti0.5P4O13 as an Electrolyte for Intermediate-Temperature Fuel Cells.

We demonstrate that (NH4)2Si0.5Ti0.5P4O13 is an excellent proton conductor. The crystallographic information concerning the hydrogen positions is unraveled from neutron-powder-diffraction (NPD) data for the first time. This study shows that all the hydrogen atoms are connected though H bonds, establishing a two-dimensional path between the [(Si0.5Ti0.5)P4O132-]n layers for proton diffusion across the crystal structure by breaking and reconstructing intermediate H-O═P bonds. This transient species probably reduces the potential energy of the H jump from an ammonium unit to the next neighboring NH4+ unit. Both theoretical and experimental results support an interstitial-proton-conduction mechanism. The proton conductivities of (NH4)2Si0.5Ti0.5P4O13 reach 0.0061 and 0.024 S cm-1 in humid air at 125 and 250 °C, respectively. This finding demonstrates that (NH4)2Si0.5Ti0.5P4O13 is a promising electrolyte material operating at 150-250 °C. This work opens up a new avenue for designing and fabricating high-performance inorganic electrolytes.

Solid Acid Proton Conductors: Insights into Proton Conduction Mechanisms and Advances in Electrode Architectures

Intermediate-temperature fuel cell (ITFC) systems have recently received significant interest for stationary distributed generation applications. As opposed to high-temperature (> 650 °C) solid-oxide fuel cells (SOFCs), intermediate-temperature systems (200-500 °C) may be capable of reaching cost targets by relaxing material re­quirements for interconnects and systems-level requirements for insulation, heat exchangers, and other balance-of-plant elements. ITFCs may operate on minimally-processed fossil fuels such as natural gas, rather than the ultra-purified hydrogen required for low-temperature (< 100 °C) polymer electrolyte membrane fuel cells (PEMFCs), a feature that could possibly accelerate adoption due to the existence of established distribution networks for these fuels. Various proton conducting solid acids of the general formula MHxXO4 (M = K, Cs, Nd; x = 0-2; X = S, P) have attracted considerable interest as electrolytes for ITFCs. We will present an overview of distinguishing structural features of these solid acids, temperature induced phase transitions, and comment on the varying mechanisms of proton conduction using studies from NMR, XRD, FT-IR, Raman microscopy, and AC impedance spectroscopy. The most promising candidate for solid acid fuel cells (SAFCs) is CsH2PO4 (CDP). The current state-of-the-art SAFC utilizes thin films of platinum nanoparticles on a porous framework of CDP electrolyte. Our methodology to improve Pt utilization, increase electrode surface area, and electrical interconnectivity was achieved by using carbon-based supports for the electrocatalyst and homogenizing framework with CDP. Using a combination of chemical functionalization of nanostructured carbon and infiltration of CDP, we fabricated nanocomposite electrodes that demonstrated vastly superior performance. For example, at 0.8V and 250 °C, a hydrogen-air SAFC using this new electrode architecture we found an improvement in power density by almost a factor of 2, with a decrease in Pt loading of a factor of 15. Furthermore, with Pt loadings of 0.18 mgPt cm-2 we observed peak power densities of in excess of 300 mW cm-2. We will present a detailed account of these effects, comment on improved stability and durability of these electrodes, and illustrate using a combination of SEM and TEM that nanoconfined CDP exists within the electrode. Finally, we will discuss future directions including advanced manufacturing enabled by the nanocomposite structure. Acknowledgements This work is supported by ARPA-E under Cooperative Agreement Number DE-AR0000499.

Diethylmethylammonium Trifluoromethanesulfonate/Phosphoric Acid Mixture As Electrolyte for Non-Humidified Intermediate Temperature Fuel Cells

Polymer electrolyte fuel cells (PEFCs) have received more and more attention due to their high energy conversion efficiency and low emissions. Moreover, PEFCs have been used in wide range of applications, such as clean power generation systems for households and vehicles. Perfluorosulfonic acid (PFSA) polymers, such as Dupont’s Nafion®1have been used as electrolyte membranes in PEFCs for decades due to their high proton conductivity, excellent chemical stability and superior durability. However, the membranes require water to retain high proton conductivity, which limits the operating temperature to be below 100 °C, and needs a large humidification system. In order to realize more compact PEFC systems, new electrolytes applicable to intermediate temperature (IT), above 150 ºC, without humidification are needed. Under these conditions, phosphoric acid fuel cell (PAFC) has been applied, but the dehydration condensation of phosphoric acid (PA) still remains as a big problem to diminish its stable operation. Ionic liquids (ILs) have unique properties such as high ionic conductivity, high thermal stability, wide electrochemical potential window and non-volatility. Thus, they have been focused as candidate electrolytes for intermediate temperature fuel cells. In this study, we aimed to achieve the non-humidified intermediate temperature fuel cell by using 3-dimensionally ordered macroporous polyimide (3 DOM PI)/diethylmethylammonium trifluoromethanesulfonate (Dema-TfO)/phosphoric acid (PA) composite membrane. Dema-TfO was synthesized by direct neutralization of the N,N-diethylmethylamine and trifluoromethanesulfonic acid with 1 : 1 molar ratio followed by vacuum drying at 100 °C for 48 h, as a protic IL to prepare the composite membrane. Dema-TfO was added with different ratios of PA. 3 DOM PI was fabricated by using previous method2. 3 DOM PI/Dema-TfO/PA composite electrolyte membrane was then prepared by immersion of 3 DOM PI into the mixture of Dema-TfO and PA under vacuum at 100 °C. Figure 1 showed TG curves for the Dema-TfO/PA mixture. For comparison, the TG curves of Dema-TfO and PA were also provided. It was confirmed that Dema-TfO was thermally stable to 230 ℃. At 180 ℃, which is a target temperature of FC operation, the weight loss ratio of PA was as high as 6%. However, when the mixture was considered, 50 wt% PA in mixture, the loss weight ratio was same with the value of Dema-TfO which was less than 1.5%. Also the detection of 3 DOM PI/Dema-TfO/PA composite membrane showed thermally stable at 180 ℃. The thermally stable property indicated that interaction of mixture suppressed PA dehydration. The mechanism of interaction was explained by FT-IR and NMR analysis. From FT-IR results, the [P(OH)2] antisymmetric stretching in PA and the SO2 symmetric stretching in Dema-TfO showed peak shift when the two functional groups were in the Dema-TfO/PA mixture. On the other hand, in H1 NMR analysis of Dema-TfO/PA mixture, both of the weakened O-H bond in PA and enhanced N-H bond in Dema-TfO compared with pure PA and Dema-TfO could be explained by the interactions existing between phosphate groups and sulfonic groups from TfO-which were the same explanation with the FT-IR results. The proton ionic conductivities and proton transport number of Dema-TfO/PA mixture were measured, too. The oxidation reduction electrochemical polarization performances of Dema-TfO/PA mixture will be presented at the conference. According to our results, the Dema-TfO/PA mixture as electrolyte is one of the possible electrolytes to achieve the non-humidified intermediate temperature fuel cell. Acknowledgement This research was supported by “Platform for Technology and Industry” of Tokyo Metropolitan Government. References R. L. Coalson, W. G. Grot, US Patent 3, 1972, 684-747H. Munakata, D. Yamamoto, K. Kanamura, Journal of Power Sources 2008, 178, 596–602 Figure 1

(Invited) Robust and Active Mixed-Conducting Electrodes for Intermediate-Temperature Fuel Cells

Intermediate-temperature solid oxide fuel cells have potential to be the cleanest and most efficient options for cost-effective utilization of a wide variety of fuels, from hydrogen to hydrocarbons, coal gas, and renewable fuels. They are ideally suited for distributed generation (which may be integrated with smart grids). To make these fuel cells economically competitive and commercially viable, however, several materials challenges must be overcome. One of them is the creation of durable, low-cost cathode materials and nanostructures of high electro-catalytic activity for oxygen reduction reaction at intermediate temperatures. Another challenge is the development of multi-functional anodes enabling efficient reforming of hydrocarbon fuels (e.g., methane) and directly operation on readily available fuels (e.g., natural gas) at intermediate temperatures. In this presentation, we will highlight an effective approach to fabrication of high-performance catalysts coated electrodes of dramatically enhanced electro-catalytic activity and durability, as schematically shown in Figure 1. The concept of modifying electrode surface through solution infiltration of a catalyst to create unique hybrid electrode structure (e.g., exsoluted nanoparticles on a conformal coating) are readily applicable to other electrochemical energy storage and conversion systems, including metal-air batteries, supercapacitors, and electrolyzers. Figure 1. Schematic for a high-performance cathode consists of the state-of-the-art cathode backbone (e.g., LSCF) and a durable catalyst (conformal coating and exsoluted nanoparticles) against various contaminants, making effective use of the best properties of two different materials (backbone and catalyst). Figure 1

(Invited) Robust and Active Mixed-Conducting Electrodes for Intermediate-Temperature Fuel Cells

Intermediate-temperature solid oxide fuel cells are ideally suited for distributed generation (which may be integrated with smart grids). To make these fuel cells economically competitive and commercially viable, however, several materials challenges must be overcome. One of them is the creation of durable, low-cost cathode materials and nanostructures of high electro-catalytic activity for oxygen reduction reaction at intermediate temperatures. Here we report our findings in the development of an effective approach to fabrication of high-performance catalyst-coated electrodes of dramatically enhanced electrocatalytic activity and durability. The concept of modifying electrode surface through solution infiltration of a catalyst to create unique hybrid electrode structures (e.g., exsoluted nanoparticles on a conformal coating) are readily applicable to other electrochemical energy storage and conversion systems, including metal-air batteries, supercapacitors, and electrolyzers.

Toward a New Generation of Intermediate-Temperature Fuel Cells

Solid oxide fuel cells (SOFCs) have potential to be the cleanest and most efficient option for direct conversion to electricity and heat of a wide variety of fuels, from hydrogen to hydrocarbons, coal gas, and bio-derived fuels. However, their commercialization hinges on rational design of novel materials of exceptional functionalities at lower temperatures to dramatically reduce the cost while enhancing performance and durability. To accomplish this goal, it is imperative to gain a fundamental understanding of the mechanisms of charge and mass transport along surfaces, across interfaces, and through porous electrodes in fuel cell systems. Further, new protocols must be developed to control materials structure, composition, and morphology over multiple length scales, thus producing nano-porous materials with more accessible surfaces of much higher functionalities and with shorter diffusion distances for greatly enhanced rate capabilities. Recently, we have fabricated and tested an electrode architecture derived from nanofibers of active cathode materials with enhanced electrochemical performance, multifunctional anodes with oriented porosity, nanostructured Sm-doped ceria electrolyte membranes with high ionic conductivity, and thin-film samples of proton and oxygen ion conducting electrolytes to study nanoionics effects at heterogeneous interfaces. This presentation will highlight the critical scientific challenges facing the development of a new generation of ITFCs, the latest developments in mixed-ion conducting electrolyte materials, nano-fiber-based cathodes, and catalytically-active anodes for internal reforming of methane at relatively low temperatures, and the perspectives for future-generation fuel cells that exploit nano-scale materials of significantly improved performance.

Toward a New Generation of Intermediate-Temperature Fuel Cells

Solid oxide fuel cells (SOFCs) have potential to be the cleanest and most efficient option for direct conversion to electricity and heat of a wide variety of fuels, from hydrogen to hydrocarbons, coal gas, and bio-derived fuels. However, their commercialization hinges on rational design of novel materials of exceptional functionalities at lower temperatures to dramatically reduce the cost while enhancing performance and durability. To accomplish this goal, it is imperative to gain a fundamental understanding of the mechanisms of charge and mass transport along surfaces, across interfaces, and through porous electrodes in fuel cell systems. Further, new protocols must be developed to control materials structure, composition, and morphology over multiple length scales, thus producing nano-porous materials with more accessible surfaces of much higher functionalities and with shorter diffusion distances for greatly enhanced rate capabilities. Recently, we have fabricated and tested an electrode architecture derived from nanofibers of active cathode materials with enhanced electrochemical performance, nano-structured Sm-doped ceria electrolyte membranes with high ionic conductivity, and membrane samples of proton and oxygen ion conducting electrolytes to study nanoionics effects at heterogeneous interfaces.

(Invited) High Temperature Membrane Electrode Assemblies for Intermediate Temperature Fuel Cells: Past, Present, and Future

Fuel cells that operate between approximately 150 oC and 250 oC accrue certain advantages, most notably facilitated operation with low grade / low cost hydrogen sourced from carbon feedstocks, robust cathode performance in the presence of air contaminants, absence of balance of plant components for stack water management, high quality heat, and readily sourced materials of construction. Fuel cells running at these intermediate temperatures with phosphoric acid as the electrolyte currently hold the record for a commercial lifetime warrantee (1). Yet, lower temperature polymer electrolyte fuel cells (PEFC) operating at under 100 oC and comprised of a conductive membrane, electrodes, and gas diffusion layers offer the potential for low cost assembly at high volumes, especially if these components are made in roll-to-roll processes. The better of these two technologies would be a hybrid high temperature Membrane Electrode Assembly (MEA) based on phosphoric acid electrolyte. The first hybrid high temperature (HT) MEA made use of polybenzimidazole (PBI) as a membrane matrix for phosphoric acid and originated from the Case Western Reserve University team of Litt, Savinell and Wainright in the early 1990s as part of a research proposal to the Defense Advanced Research Projects Agency (DARPA). Their initial motivation was to develop a system that could overcome the limitations of direct methanol oxidation at under 100 oC (2). Although ultimately not viable for direct methanol oxidation, hydrogen oxidation with 1-2 % CO proved good enough to license the technology to PEMEAS, the company that developed the first commercial PBI HT MEA based on pre-formed membranes of PBI. However, using a preformed PBI membrane posed some limitations on acid content, and through the efforts of Calundann and Benicewicz, a second generation PBI membrane was invented (3). This new process identified a technique to polymerize PBI in the presence of polyphosphoric acid (PPA), and then hydrolyze the cast film to phosphoric acid (PA). The change of solvent from PPA to PA also radically changed the morphology of the PBI from a viscous solution into a tough second generation PBI plastic that held over 90 % by weight PA. This development also radically simplified the construction of HT MEAs by eliminating the acid soaking step. Due to the nature of these materials, new gas diffusion electrode architectures were developed and optimized to accommodate a membrane-electrode interface substantially different than that found in LT MEA assemblies. This electrode effort on roll coaters was awarded a Department of Energy Manufacturing R&D award (4). Ultimately, BASF purchased PEMEAS, as well as the electrode team at PEMEAS. In parallel to the development of the polybenzimidazole (PBI) system, Advent Technologies identified and developed a pyridine polymer based TPS® system also using PA imbibed into the membrane matrix. Advent’s TPS membranes operate over a wide temperature range from ~120 °C to greater than 200 °C. In 2014, Advent became the licensee of BASF’s PBI MEA and gas diffusion electrode technology. Advent develops, manufactures, and markets both the PBI and TPS MEAs. This presentation will present an overview of the commercial and technical history of developing HT MEAs, including some of the latest membrane advances like the third generation PBI MEAs, and cross-linked TPS MEAs operating at 210 oC, and conclude with future directions such as the application of HT MEAs in facilitating direct oxidation of dimethyl ether (DME). http://www.doosanfuelcell.com/en/main.doRobert F. Savinell and Jesse Wainright, "Overture: The Early History of PBI/Phosphoric acid membranes," in High Temperature Polymer Electrolyte Membrane Fuel Cells: Approaches, Status and Perspectives, edited by Qingfeng Li, David Aili, Hans Aage Hjuler and Jens Oluf Jensen, Spring International Publishing, 2016.For example, G. Calundann et al. US Patent 7,820,314.US Department of Energy Annual Merit Review, 2013.