bluuebunny/crossref_metadata_2025 huggingface dataset:
Selection of Materials for Cascaded Thermoelectric Generators under Transient Thermal Loading
Authors: Fergus J. W.
Published: February 2020

Materials for thermoelectric devices should have a large Seebeck coefficient, high electrical conductivity and low thermal conductivity as indicated by the thermoelectric figure of merit (ZT). The figure of merit is temperature dependent, so multiple materials can be used in cascaded thermoelectric devices, in which each material is located according to its properties at the temperature expected at its location during operation. Numerical modeling has shown that the energy conversion efficiencies of materials with the same figures of merit but different electrical/thermal conductivities depend on the position of the materials in the device (i.e. hot or cold region). The differences in performance are larger under transient heating and cooling, but there are differences even under steady-state conditions. In this paper, results of numerical modeling of thermoelectric generators will be presented to demonstrate how strategic materials placement can be used to improve device performance.
High Performance Infiltrated Backbones for Cathode-Supported SOFC's
Authors: Gil Vanesa , Hansen Kent Kammer
Published: February 2020

The concept of using highly ionic conducting backbones with subsequent infiltration of electronically conducting particles has widely been used to develop alternative anode-supported SOFC´s. In this work, the idea was to develop infiltrated backbones as an alternative design based on cathode-supported SOFC. The cathodes are obtained by infiltrating LSM into a sintered either thick (300 μm) yttria stabilized zirconia (YSZ) backbone or a thin YSZ backbone (10-15 μm) integrated onto a thick (300 μm) porous strontium substituted lanthanum manganite (LSM) and YSZ composite.

Fabrication challenges, microstructural characterization and electrochemical testing are discussed. Data on polarization resistance, Rp, are obtained from impedance spectra recorded on quasi-symmetrical cells (YSZ backbones/YSZ/LSM-YSZ (screen printed)). The backbones are infiltrated with LSM and compared to a standard LSM-YSZ screen printed symmetrical cells. Samples with LSM/YSZ composite and YSZ backbones made with graphite+PMMA as pore formers exhibited comparable Rp values to the screen printed LSM/YSZ cathode. This route was chosen as the best to fabricate the cathode supported cells.

SEM micrograph of a cathode supported cell with infiltrated LSM nanoparticles is shown in Fig. 1.

Figure 1. Cross section of LSM infiltrated cathode supported cell.
Short Stack Performance Using Lower Temperature GDC-Based SOFC
Authors: Yoon Hee Sung , Blackburn Bryan M. , Wachsman Eric D.
Published: February 2020

Recently, the University of Maryland Energy Research Center and Redox Power Systems LLC developed a GDC electrolyte based solid oxide fuel cell (SOFC) for lower temperature operation using conventional ceramic processing. The fabrication process was integrated with tape casting, screen printing, coating, etc., yielding a cell of 10 cm x 10 cm size and an active area of about 80 cm2.

Initial results for single cell tests running on hydrogen and air at 650 oC included an open circuit voltage (OCV) of 0.85 V and a power of over 48 W at over 80 A. At an operating voltage of 0.7 V, the single cell power was about 35 W. For a two cell short stack, the initial results under similar conditions showed an OCV of 1.5 V and a peak power of more than 70 Watts at 650 °C.
Modelling and Measurements of Temperature Distributions inside MEA and Its Effects on Water Transport
Authors: Araki Takuto , Sugimoto Toshiki , Minegishi Yasuyuki , Higuchi Masaru
Published: February 2020

Polymer electrolyte fuel cell (PEFC) is one of the cleanest and most fuel saving energy conversion devices. For the optimal design of PEFC reaction layer, the understanding of coupled phenomena consists of heat and mass transport and electrochemical reaction is essential. For the understanding, the thin film micro sensor array has been developed and the temperature and water concentration distribution near reaction layer have been measured. Moreover, the multi-scale numerical simulation has been developed and conducted to realize the conjugated problem inside reaction layer of PEFC.
Combined Pore Network and Finite Volume Modelling of Water Movement in PEM Fuel Cell Porous Transport Layers
Authors: Pharoah Jon G. , Allen Jeff , Nishida Robert , Medici Ezequiel , Konduru Vinaykumar , Tajiri Kazuya
Published: February 2020

The effects of water transport in the porous transport layers (PTLs) of polymer electrolyte membrane (PEM) fuel cells are commonly studied using sub-scale pore network models or geometric models which generate effective properties that can be applied in computational fluid dynamics (CFD) models using a continuum approach at larger length scales. This approach is commonly uncoupled and uses a steady state approach, thereby approximating and averaging important details of water transport effects. To capture water transport in sub-scale CFD models requires extensive computer resources and is often very difficult to converge. In this work, a three-dimensional pore network model is implemented in the open-source, finite-volume CFD code, OpenFOAM. The model captures transient water transport through a network of pores using an experimentally determined pore size distribution. This model is directly coupled to a continuum model to directly capture the effect of liquid water on fuel cell performance. After a description of the method, results are compared with those from an in-house pore-network model for code verification. The method presents a novel approach which benefits from both pore-network modelling and CFD to investigate the subject of water transport in PEM fuel cells.
Modeling Thermal Transport in Heterogeneous Porous Media of PEM Fuel Cells Using Pore Network Model
Authors: Konduru Vinaykumar , Medici Ezequiel , Allen Jeffrey S
Published: February 2020

Thermal and mass transport in the porous transport layers (PTL) of polymer electrolyte membrane (PEM) fuel cells is studied using a pore network model. The solid phase of the PTL is modeled as a network of solid cylinders and the pore phase is modeled as a network of hollow tubes. The two networks are coupled together at the nodes. The network of pores and solid-cylinders are generated independently using Weibull probability distribution function. In the current work, a new formulation of the thermal transport has been developed which incorporates the effect of compression under the lands of bipolar plate on thermal transport. The parameters of PTL used to model compression are obtained from experimentally obtained thermal conductivity values reported in literature. In this paper, a description of the model along with the technique of determining the parameters for compression and the effect of solid phase distribution on the thermal and mass transport in the porous media of fuel cells will be presented.
Engineering the Activity and Stability of Pt-Alloy Cathode Fuel-Cell Electrocatalysts by Tuning the Pt-Pt Distance
Authors: Escudero-Escribano Maria , Malacrida Paolo , Vej-Hansen Ulrik Grønbjerg , Tripkovic Vladimir , Rossmeisl Jan , Stephens Ifan E. L. , Chorkendorff Ib
Published: February 2020

One of the main obstacles to the commercialisation of low-temperature fuel cells is the slow kinetics of the oxygen reduction reaction (ORR). In order to decrease the ORR overpotential and reduce the Pt loading we need to develop more active and stable electrocatalysts. A fruitful strategy for enhancing the cathode activity is to alloy Pt with transition metals [1-2]. However, alloys of Pt and late transition metals are typically unstable under fuel-cell conditions. Herein, we present experimental and theoretical studies showing the trends in activity and stability of novel cathode catalysts based on alloys of Pt and lanthanides.

Sputter-cleaned, polycrystalline Pt5Gd shows a five-fold increase in ORR activity [3], relative to Pt at 0.9 V in 0.1 M HClO4. The rest of the Pt5Ln (Ln = lanthanide) tested present at least a 3-fold enhancement in activity [4,5]. In all cases, a Pt overlayer with a thickness of few Pt layers is formed. Accordingly, the effect of alloying Pt is to impose strain onto the Pt overlayer [3,4]. It is likely that this strain would be relaxed by defects [6]. Moreover, the activity of the Pt5Ln catalysts vs. the Pt-Pt distance shows a volcano relationship (Fig. A) [5]. Pt5Ln electrocatalysts are highly stable, as shown in Fig. B [4]. We show, for the first time, that the Pt-Pt distance not only controls the activity, but also the stability of these catalysts [5].

[1] H.A. Gasteiger, S.S. Kocha, B. Sompalli, F.T. Wagner, Appl.
Catal. B
2005, 56, 9.

[2] I.E.L. Stephens, A.S. Bondarenko, U. Grønbjerg, J. Rossmeisl, I. Chorkendorff, Energy Environ. Sci. 2012, 5, 6744.

[3] M. Escudero-Escribano, et al. J. Am. Chem. Soc. 2012, 130, 16476.

[4] P. Malacrida, M. Escudero-Escribano, A. Verdaguer-Casadevall, I.E.L. Stephens, I. Chorkendorff, J. Mater. Chem. A
2014, 2, 4234.

[5] M. Escudero-Escribano, et al., in preparation, 2014.

[6] P. Strasser, et al. Nature Chem., 2010, 2, 454.

Fig. (A) ORR kinetic current density at 0.9 V vs. RHE as a function of the lattice parameter and the Pt-Pt distance for Pt5Ln and Pt. (B) Kinetic current density of Pt5Ln and Pt before and after a stability test consisting of 10 000 cycles between 0.6 V and 1.0 V vs. RHE in an O2-saturated 0.1 M HClO4 electrolyte.
Improving the Activity and Stability of PdSn Catalyst for Oxygen Reduction by Heat Treatment
Authors: Salomé Sónia , Oliveira M.C. , Savadogo Oumarou , Rego Rosa
Published: February 2020

The search for new efficient and inexpensive ORR electrocatalysts for cathodes of PEMFCs has been a fast-growing area of research over the past 10 years.

One of the most promising cathode systems are the Pd-based alloys, such as PdCo, PdCr, PdNi [1,2], PdFe [3] and PdP [4] that compete with platinum in terms of electrocatalytic activity.

A very important concern in the development of fuel cells is the electrochemical stability of the catalyst, which can affect the fuel cell lifetime. A few publications have described the ORR activity of PdSn alloys in acid media [5,6]. However, to the best of our knowledge, the effect of heat treatment on PdSn electrocatalyst activity and stability has not been yet investigated.

In this work, PdSn/C electrocatalysts for ORR have been synthesized by the sodium borohydride method with sensitizing (Sn2+/SnO2 or Sn4+) and activating pretreatment (Pd2+/Pd) of the carbon support Vulcan XC72. The electrocatalysts have been then heat treated at 300 ºC in a reducing atmosphere (3% hydrogen in nitrogen). The morphology, structure and composition of the catalysts as-prepared and subject to thermal treatment have been characterized by XRD, SEM/EDS and TEM. The activity of PdSn/C catalysts for ORR in acid media has been studied using a rotating disc electrode (RDE) and electrochemical impedance spectroscopy (EIS). Specific activity-time curves measured at a fixed potential have been used to study the long-term catalyst performance for more than 2 days. The PdSn/C catalysts prepared with heat treatment exhibited an enhanced activity and stability as compared to those synthesized without treatment.

[1] O. Savadogo, K. Lee, K. Oishi, S. Mitsushima, N. Kamiya, K.-I. Ota, Electrochem. Commun. 6 (2004) 105

[2] K. Lee, O. Savadogo, A. Ishihara, S. Mitsushima, N. Kamiya, K.-i Ota, J. Electrochem. Soc. 153 (2006) A20

[3] M.-H. Shao, K. Sasaki, R. R. Adzic, J. Am. Chem. Soc. 128 (2006) 3526

[4] R. Rego, A. M. Ferraria, A.M. Botelho do Rego, M. Cristina Oliveira, Electrochimica Acta 87 (2013) 73

[5] Md. R. Miah, J. Masud, T. Ohsaka, Electrochimica Acta 56 (2010) 285

[6] J. Salvador-Pascual, J. A. Chávez-Carvayar, O. Solorza-Feria, ECS Transactions 15 (2008) 3

Acknowledgements

This work was supported by Fundação para a Ciência e a Tecnologia (FCT) and FEDER (contracts PTDC/QUI-QUI/110855/2009, PEst-OE/QUI/UI0616/2014) and COST Action MP1202 "Rational design of hybrid organic-inorganic interfaces". R. Rego acknowledges FCT for grant SFRH/BSAB/1337/2013.
Invited: Bipolar Membrane Fuel Cells Using Anion Conductive Multiblock Copolymers
Authors: Kohl Paul A , Ahlfield John M. , Liu Lisha
Published: February 2020

Anionic fuel cells are a possible route to overcoming fundamental issues with acid-based fuel cells. The issues include the high cost of platinum catalysts, complex water transport, and sluggish electrochemical reactions. In particular, a bipolar membrane composed of a cation conducting material and an anion conducting material has several additional advantages because each electrode can have an optimum pH, and water can be created at the cation/anion membrane interface close to where it is used at the air cathode.

Anion conductive multiblock copolymer membranes have shown promise for hydroxide conducting media. Anion conductive membranes have been synthesized with different block lengths and ion exchange capacities in order to maximize the ionic conductivity and understanding the relationship between chemical structures and water mobility in anion exchange membranes. The multiblock copolymers were synthesized by a polycondensation reaction between separately-prepared hydroxide-terminated oligomers and fluorine-terminated oligomers. The polymers were made ion conductive and hydroxide ion exchanged. The resulting anion conductive multiblock copolymers had higher conductivity than their random copolymer counterparts at the same IEC. The structure-property relationship of the ion conductive polymers, and bipolar membrane fuel cells constructed from them were characterized and will be reported.
Invited: Applications of DFT Calculations to Platinum Surface Electrochemistry
Authors: Jinnouchi Ryosuke , Kodama Kensaku , Toyoda Eishiro , Suzuki Takahisa , Hatanaka Tatsuya , Morimoto Yu
Published: February 2020

The current status of electronic structure calculations on electrocatalysis will be discussed in this presentation. After a quick review of atomistic modellings of electrified solid / liquid interfaces, a method combining density functional theory and a continuum electrolyte theory will be presented. It will be shown that this theory can give thermodynamic properties of electrochemical reactions, such as electro-oxidation, specific anion adsorptions, underpotential deposition of Cu and oxygen reduction reaction, on closed packed single crystal platinum surfaces within practically useful accuracies. When the method is applied to structures other than the closed packed surfaces, such as stepped platinum surfaces, difficulties arise in modellings and accuracies. Some prescriptions to overcome those problems also will be discussed.

[1] R. Jinnouchi and A. B. Anderson, Phys. Rev. B, 77, 245417 (2008).

[2] R. Jinnouchi and A. B. Anderson, J. Phys. Chem. C, 112, 8747 (2008).

[3] R. Jinnouchi, E. Toyoda, T. Hatanaka and Y. Morimoto, J. Phys. Chem. C, 114, 17557 (2010).

[4] R. Jinnouchi, T. Hatanaka, Y. Morimoto and M. Osawa, Phys. Chem. Chem. Phys., 14, 3208 (2012).

[5] R. Jinnouchi, T. Hatanaka, Y. Morimoto and M. Osawa, Electrochim. Acta, 101, 254 (2013).

[6] K. Kodama, A. Shinohara, N. Hasegawa, K. Shinozaki, R. Jinnouchi, T. Suzuki, T. Hatanaka and Y. Morimoto, ECS Trans., 58, 363 (2013).

[7] R. Jinnouchi, K. Kodama, T. Hatanaka and Y. Morimoto, Phys. Chem. Chem. Phys., 13, 21070 (2011).

[8] E. Toyoda, R. Jinnouchi, T. Ohsuna, T. Hatanaka, T. Aizawa, S. Otani, Y. Kido and Y. Morimoto, Angew. Chem. Int. Ed., 52, 4137 (2013).

[9] R. Jinnouchi, K. Kodama and Y. Morimoto, J. Electroanal. Chem.,716, 31 (2013).
Charles W.Tobias Young Investigator Award: Understanding Transport Phenomena in Polymer-Electrolyte Fuel Cells
Authors: Weber Adam Z.
Published: February 2020

One of the keys to optimizing polymer-electrolyte-fuel-cell performance is the understanding of transport phenomena. This is especially critical when liquid water exists in the cell as it can result in flooding and blockage of the electrocatalytic sites. In this award talk, transport phenomena in general will be discussed with a focus on efforts conducted at LBNL in terms of both modeling and advanced diagnostics. Thus, this talk will discuss the current macroscopic modeling approaches being undergone in terms of multiphase flow and fuel-cell behavior at low and subzero temperatures. In addition, diagnostic work on effective properties will be discussed. Topics to be explored in depth include transport in GDLs and catalyst-layer ionomer.

For GDLs, there has been a study on the effective properties including diffusivity, thermal conductivity, and adhesion force for GDLs that demonstrate different performance at low temperatures. Both modeling and experiments show that the key is water removal out of the anode to decrease the cathode flooding. Such removal is enhanced by decreasing adhesion force at the GDL/channel surface owing to structural hetergeities in fiber density.

For catalyst-layer ionomer, it will be shown how this could be an important issue for the observed increased mass-transport limitations for low Pt loadings. In this structure, confinement and substrate interactions dominate and result in increased transport resistance for the ionomer thin-film surrounding the catalyst sites. Ex-situ thin-film studies show how the morphology changes to more of a membrane interfacial-type behavior as the thickness decreases, thereby decreasing the water content in agreement with water-content measurements in catalyst layers. Mitigation of this issue is paramount to the future commercial viability of polymer-electrolyte fuel cells.

Acknowledgements

This work was funded by the Assistant Secretary for Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, of the U. S. Department of Energy under contract number DE-AC02-05CH11231.
Invited: From PEM Fuel Cell Design to Biological Fuel Cells: The Status of Systems Development for Biological Fuel Cells
Authors: Rasmussen Michelle , Milton Ross D , Hickey David P , Reid Russ C. , Minteer Shelley D.
Published: February 2020

Over the last decade, the field of biological fuel cells has expanded almost exponentially. Much of the research was originally focused on understanding fundamental principles and showing bioelectrocatalysis in a variety of environments, with a variety of biocatalysts (microbes, enzymes, mitochondria), and a variety of electrode materials, but as fundamental electrocatalysis became known, there has been a push to develop biological fuel cell systems. This paper will discuss how different applications of biological fuel cells require different cell designs. Many portable power applications utilize cell designs similar to traditional fuel cells, but many implantable applications require new membraneless cell designs, flexible cell designs, and microscale cell designs. These new cell designs will be compared with more traditional PEM fuel cell designs.
Novel Dead-Ended Anode Design for Self-Regulating Humidification in an Air-Breathing H2-PEM Fuel Cell
Authors: Ferreira-Aparicio Paloma , Chaparro Antonio M.
Published: February 2020

Water management is a major engineering challenge for proton exchange membrane fuel cells (PEMFCs). Mass transport of hydrogen and/or oxygen is often hindered in flooded electrodes leading to a fuel cell current decrease and irreversible damages. Although optimal PEMFC operation is usually achieved with fully humidified flow-through anode and cathode streams, commercial and portable applications require simpler systems where the size, weight and complexity of the auxiliary systems are minimized. Therefore, dead-ended anode (DEA) operation is usually implemented for compact units. Feeding dry hydrogen with regulated pressure at the anode inlet presumably presents the advantage of requiring no excess hydrogen to be exhausted. In this way, only the stoichiometric amount would be consumed in the fuel cell. However, DEA operation mode usually results in a deterioration of cell performance if the accumulated gas-vapor mixture is not purged to remove liquid water and nitrogen from the anode flow field. Furthermore, this strategy may frustrate the main purpose of the dead-ended anode mode to increase hydrogen utilization while introducing parasitic loads to power the purge system.

A novel design of a PEMFC anode chamber has been implemented in an air-breathing fuel cell allowing for stable long-term operation under stoichiometric H2 consumption with 100% fuel utilization. The anode chamber consists of a perforated current collector and gas distribution plate in contact with the membrane-electrode assembly. The opposite face of this plate is covered by a gas-tight polymer film selectively permeable to water. This film is fixed to the external face of the anode gas distributor by a tailor-made methacrylate plate and allows for water exchange between the anode internal chamber and the external environment. This gas-tight water permeable film provides a suitable way for excess water removal from the anode. The present study analyzes in detail the operation of this novel design. Impedance spectroscopy and polarization hysteresis curves have been used to explore the cell behavior under several environmental conditions of temperature and relative humidity controlled inside of a climate chamber (Fig. 1). These results are evaluated in comparison with those obtained for a similar cell assembled with a conventional anode operating under continuous flow and dead-ended anode under periodical purge. The stable long-term operation of the 2 W-cell with this novel design ensures 100% efficiency in fuel utilization.

Acknowledgements

The authors gratefully acknowledge financial support from the Spanish Ministry of Economy and Competitiveness under project ELECTROFILM (MAT2011-271 51) and Comunidad de Madrid under DIVERCEL program (S2009/ENE-1475).

Fig. 1. Photograph of the experimental set-up showing the air-breathing fuel cell in the climatic chamber where measurements have been performed. Inset photograph: detail of the anode configuration in the novel H2-PEM fuel cell design.
Investigation of Impact of Carbon Surface Oxidation on Wettability of PEMFC Cathode Electrode
Authors: Takeuchi Norimitsu
Published: February 2020

The oxidation reaction on carbon in proton exchange membrane fuel cells (PEMFCs) electrodes has been reported as carbon corrosion recently under several fuel-cell operation procedures [1-4]. The influence of cell design factors for the membrane electrode assembly (MEA) and gas transport in the gas diffusion layer and the catalyst layer were often investigated at start up and partial hydrogen starvation. These results suggested that the coexistence of oxygen in the anode is critical for carbon corrosion on the positive electrode. Although the impact of carbon loss under ordinary fuel-cell operation is less than during startup / shutdown and partial hydrogen starvation situations, it is estimated to be large enough to affect long-term durability of PEMFC. CO2generation on Pt/C catalyst in a PEMFC occurs under potential dynamic condition such as cyclic voltammetry. They each suggested that platinum accelerated the oxidation of carbon supports under potential dynamic condition.

In order to elucidate the influence of platinum on carbon oxidation in more detail, carbon oxidation on Pt/C under potential dynamic model has been investigated. Four reactions were assigned as carbon oxidation reactions.

C + H2O → CO2 + 4H+ + 4e- (1)

C-C + H2O → C-COH + H+ + e- (2)

C-COH + H2O → C-COOH + 2H+ + 2e- (3)

C-COOH + Pt-OH → CO2 + Pt + COH + H+ + e- (4)

Carboxyl group and phenol group species were induced from graphite structure carbon on carbon surface through the electrochemical reactions with water.

High potential hold at 1.3V and potential cycling 0.1 V to 0.9 V were exposed to Pt/C catalyst under 0.1M H2SO4aq. in order to oxidize carbon surface. The carboxyl group and phenol group on carbon surface were measured before and after potential tests by Boehm method. Carbon groups were increased after 1.3V hold and potential cycling between 0.1 and 0.9V in Table 1. High potential hold caused high oxidation state carbon groups than lower potential cycling test. The increases in carbon groups on carbon surface is estimated to affect on the wettability on carbon surface and causes the suppress of PEFC performance.

Acknowledgement

Authors appreciated Dr. T. Abe and K. Miyazaki of Kyoto University for the discussion on this work.

References

L. M. Roen, C. H. Paik and T. D. Jarvi, Electrochem. Solid-State Lett.,
7, A19 (2004).

S. Maass, F. Finsterwlder, G. Frank, R. Jartmann and C. Merten, J. Power Sources, 176, 444 (2008).

N. Takeuchi and T. F. Fuller, J. Electrochem. Soc.,
155, B770 (2008).

N. Takeuchi and T. F. Fuller, ECS Transactions,
16 (2) 1563 (2008).
Study of the Constrained Expansion of Nafion within the Hardware of a PEMFC
Authors: Folgado María Antonia , Ferreira-Aparicio Paloma , Chaparro Antonio M.
Published: February 2020

Dimensional changes of Nafion polymer membranes occur by absorption of water giving rise to expansion in the three dimensions. For a standard Nafion membrane (NRE212, EW=1100), a change from a base dry state (5% water content) to a fully humidified state (50% water content) produces around 10% in-plane expansion at room temperature, whereas the thickness change may be up to 70% according to our measurements. Based on such Nafion expansion capability, the mounting of fuel cells can be carried out following two different strategies. One is performing first a humidification step and, then, mounting the membrane with the expanded dimensions. This strategy is mostly followed, but it may be problematic because handling humidified membranes difficults attaining fast and reproducible results, and in some cases it is incompatible with other processing steps. A second possibility is mounting dry membranes directly into the cell. Dry membranes are easily handled, and may be incorporated in a chain process without difficulty, like for deposition of catalyst layers or fuel cell mounting. On the other hand, mounting cells with dry membranes gives rise to their expansion inside the cell, under the constraint of the gas diffusion layer and the flow field plates. Such expansion yields necessarily different results than the unconstrained, free, expansion of Nafion.

In this communication a study is presented about the influence of Nafion expansion on the response of a proton exchange membrane fuel cell (PEMFC). First, the constrained expansion of the membrane is analyzed within the flow field of a cell, and compared with its free expansion. The study has been carried out by means of a specially designed cell that allows for the observation of morphology changes in cross section with optical microscopy. Minimal changes are observed in the morphology of the free expanded MEAs when clamping pressure and/or humidification is applied within the cell hardware (Fig. 1b). MEAs expanded within the cell hardware (Fig. 1a), however, lead to a zig-zag morphology.

In a second part, free and constrained expanded Nafion have been tested in single cells. The responses of both types of expansion have been analyzed by polarization curves (Fig. 1c), active area measurements, and impedance spectroscopy. First results indicate better behavior of free expanded Nafion, due to lower internal resistance of the cell. Durability issues under expansion-contraction cycles, and cell voltage cycles will also be analyzed.

Acknowledgements

This work is financed by the project ELECTROFILM, MAT2011-27151 from Ministry of Science and Innovation of Spain.

.
Quality Control Diagnostics for Mass Produced Fuel Cell Gas Diffusion Electrodes
Authors: Bender Guido , Ulsh Michael
Published: February 2020

With fuel cell systems striving into the market place at increasingly larger numbers, production methods need to begin to rely on cost effective methods to maximize yield and efficiency and minimize waste. The fuel cell industry has identified quality control as a critical barrier for continuous production of MEA components, i.e. membranes, electrodes, and GDLs. One of the critical manufacturing tasks is developing and deploying techniques to provide in-process measurement of fuel cell components for quality control, i.e. quality control (QC) diagnostics that allow for 100% areal inspection of moving fuel cell materials / components.

The National Renewable Energy Laboratory has developed a QC diagnostic method for gas diffusion electrodes that is applicable to roll-to-roll fuel cell materials during production. The experimental setup of this Infrared Reactive Impinged Flow (IR/RIF) method is shown in Figure 1. It provides three main functionalities: (i) gas supply and delivery, (ii) GDE material transport, and (iii) IR thermographic imaging. A non-flammable gas mixture that contains small amounts of hydrogen and oxygen (typically 2% and 1%, respectively) is impinged on a gas diffusion media in an ambient environment. The hydrogen reacts in an exothermic reaction at the platinum catalyst of the electrode with the oxygen. The resulting heat signature contains information about the homogeneity of the sample and is observed with an infrared sensing device.

Results will be presented that demonstrate the feasibility of the IR/RIF method using NREL’s industrial webline at 10 ft min-1and higher. Production defects were intentionally created in-house using various scratch and/or spray coating methods. Figure 2 shows a sample set consisting of 100% loading reduction defects placed at various locations. Defect sizes of this sample were 5 mm x 5 mm and 2 mm x 2 mm. Results will be discussed using false color temperature movies and images as well as raw and processed temperature data.

Figure 1: Schematic of Reactive Impinged Flow Method for detecting defects in the catalyst layer coating of a fuel cell gas diffusion electrode.

Figure 2: Example of GDE with catalyst loading defects: 100% loading reduction, 2 mm x 2 mm and 5 mm x 5 mm.

Figure 3: False color image of the sample’s heat signature with the sample moving at 10 ft min-1.

Figure 4: Temperature data along the dashed line in Figure 3 indicating the detection of two coating defects.

Acknowledgments

The authors would like to acknowledge funding from the U.S. DOE Fuel Cell Technology Office under contract number DE-AC36-08GO28308. The authors would further like to thank D. Bittinat and J. Porter of Colorado School of Mines for participation in the early development stages of this method.
Stability of Pt/MWCNT Electrocatalyst during Startup and Shutdown Cycles: Voltage Degradation in PEM Fuel Cells
Authors: Hasché Frédéric , Aoun Nadia , Weber Philipp , Durst Julien , Kunz Ulrich , Turek Thomas , Gasteiger Hubert A.
Published: February 2020

Proton exchange membrane fuel cells (PEMFC) are interesting candidates for automotive applications. Today’s challenge is to increase the mass activity from pure platinum of currently 0.12 A/mgPt to 0.44 A/mgPt at 0.9 V (iR-free) vs. RHE, and to enhance the durability with a high stability in startup/shutdown (SU/SD) procedures.[1-3]

During SU/SD cycles, the cathode voltage of a PEMFC can increase up to 1.5 V vs. RHE which accelerates the carbon corrosion drastically. These huge carbon corrosion rates lead to a complete loss of the electrode structure, and therefore to a dramatic loss of performance. In order to reduce carbon corrosion, the chemically more stable multi walled carbon nanotubes (MWCNTs) can be used as catalyst support. The higher stability in comparison to conventional catalyst material was already demonstrated in rotating disk electrode (RDE) experiments.[4] Here, the electrocatalyst was tested with two different cycling protocols, (I) 0.5 to 1.0 V vs. RHE (10.000 cycles, 50 mV/s) and (II) 0.5 to 1.5 V vs. RHE (2.000 cycles, 50 mV/s) in deaerated electrolyte (0.1 M HClO4) at room temperature.

In this contribution, we present our recent results regarding the stability of Pt/MWCNTs under real hydrogen-air front experiments in 50 cm2 single cell. During this test, the anode side is successively flushed with hydrogen or air while the cathode side is continuously purged with air.

N. A., U. K. and T. T. acknowledge efzn for financial support.

Literature

[1] Department of Energy - Multi Year Research and Development Plan (2011), Table 3.4.13 Technical Targets: Electrocatalysts for Transportation Applications.

[2] Oezaslan, M.; Hasché, F.; Strasser, P., The Journal of Physical Chemistry Letters 2013, 4 (19), 3273-3291.

[3] Yu, P. T.; Gu, W.; Makharia, R.; Wagner, F. T.; Gasteiger, H. A., ECS Transactions 2006, 3 (1), 797-809.

[4] Hasché, F.; Oezaslan, M.; Strasser, P., Physical Chemistry Chemical Physics 2010, 12 (46), 15251-15258.
Effect of Au and Ru in Au@Pd and Ru@Pd Core@Shell Nanoparticles for Direct Formic Acid Fuel Cells
Authors: Hu Shuozhen , Scudiero Louis , Ha Su
Published: February 2020

The study of Pd-based core@shell bimetallic catalysts with Pd as the shell and another transition metal as the core has generated great interest in the field of PEM fuel cells because their electronic and chemical properties are completely different from pure Pd. As the anode catalyst in direct formic acid fuel cells (DFAFCs), an enhanced activity has been obtained for these Pd-based core@shell nanoparticles compare to pure Pd for formic acid oxidation [1,2]. However, there is a lack of understanding of how these added transition metals interact with Pd, namely by influencing their electronic structure and chemical property toward electrochemical oxidation of formic acid. It is important to fill this knowledge gap and find out a trend between the effect of the transition metals and the activity. This will help developing more efficient and less cost DFAFCs.

In this study, Au@Pd and Ru@Pd core@shell nanoparticles with same thickness of Pd are synthesized via a two-step process. Non-supported nanoparticles are used for TEM and X-ray photoelectron spectroscopy (XPS) analysis. TEM is used to characterize the structure and morphology of the nanoparticles. XPS is used to differentiate the chemical shifts due to charge transfer between Pd and Au (or Ru). XPS analysis shows a different binding energy shift for Pd peak of Au@Pd and Ru@Pd compare to that of pure Pd nanoparticles. In addition, a change of the XPS valence band shape and down-shift of the d-band center are also observed. This different binding energy shift indicates that Au and Ru core interact with Pd shell and significantly influence the electronic structure of Pd. Electrochemical measurements (cyclic voltammetry and chronoamperometry) are used to investigate the electrochemical activity of carbon supported Au@Pd and Ru@Pd core@shell nanoparticles toward formic acid oxidation. The Pd loading of the carbon supported samples is 40wt%. Based on CV results shown in Figure 1, Au@Pd shows the best activity toward formic acid oxidation, which is about twice higher than that of Pd/C. The relationship between the electronic perturbation and electrochemical activity will be elucidated in this paper. Furthermore, a real direct formic acid fuel cell test will be also operated with these Au@Pd and Ru@Pd core@shell nanoparticles under the various fuel cell operating conditions.

References

1. Zhang, M. M., Yan, Z. X., Xie, J. M., Electrochimica Acta, 2012,
77: p. 237-243.

2. Li, Y. J., Wang, Z. W., Chiu, C. Y., Ruan, L. Y., Yang, W. B., Yang, Y., Palmer, R. E., Huang, Y., Nanoscale 2012,4 (3): p. 845-851.

Figure 1: Cyclic voltammetry measurements for carbon supported Au@Pd, Ru@Pd, and Pd nanoparticles in 0.5 M formic acid with 0.5 M H2SO4. Scan rate 20 mV/s.
Performance Degradation of Polymer Electrolyte Membrane Fuel Cell through Fuel Starvation Induced by Anode Flooding
Authors: Jung Namgee , Kim Mansu , Eom KwangSup , Yoo Sung Jong , Kim Jin Young , Jang Jong Hyun , Kim Hyoung-Juhn , Cho EunAe
Published: February 2020

Polymer electrolyte membrane fuel cell (PEMFC) stack in a fuel cell vehicle can be exposed to the flooding conditions induced by direct flow of condensed water into the electrodes through the cooled gas lines during winter. Therefore, the anode flooding was intentionally and repeatedly caused by introduction of the condensed water through the anode gas line during long-term operation, which resulted in considerable performance degradation of PEMFC. After the long-term durability test, the anode thickness was decreased, and the ratio of Pt to carbon in the anode was increased. In addition, the simulated and repeated fuel starvation situation in half-cell made the carbon surface of Pt/C catalyst severely oxidized due to induced high potential (> 1.5 VRHE). The cyclic voltammogram (CV) of the anode in the single cell after the long-term test under the anode flooding condition indicated similar feature of oxidized carbon surface like the CV in the half-cell. Therefore, it was concluded that the repeated fuel starvation by the anode flooding generated the severe carbon corrosion in the anode since the electrode potential locally rose up higher than 1.0 VRHE.
Development of Ir Nanocatalysts As CO2-Tolerant Anodes in Electrochemical Hydrogen Pumps for H2/CO2 Separation
Authors: Kim Soo Jin , Lee Byung-Seok , Park Hee-Young , Jung Young-Hoon , Choi Insoo , Cho Eun Ae , Kim Hyoung-Juhn , Henkensmeier Dirk , Nam Suk Woo , Kim Sung Hyun , Yoo Sung Jong , Jang Jong Hyun
Published: February 2020

Recently, various CO2 capture and storage (CCS) technologies have been actively researched and developed. As CO2 sources usually produce mixtures that contain other gases such as H2 and H2O, gas separation technologies are required to increase the efficiency of CCS processes, and the electrochemical hydrogen pump is expected to be effectively utilized for H2/CO2gas separation. Electrochemical hydrogen pumps will be suitable for the treatment of gas mixtures produced from coal gasification and steam-reforming processes, as well as the anode outlet gases from molten carbonate fuel cells integrated with fossil fuel power plants.

As electrocatalysts for electrochemical hydrogen pumps, carbon-supported Pt nanoparticles have been widely used for hydrogen compression [1] and hydrogen separation from gas mixtures [2, 3]. However, as Pt surfaces can be severely poisoned by the strong adsorption of CO molecules that are generated through the reverse water-gas shift reaction of CO2 and adsorbed hydrogen [4], the Pt catalyst in the anodes can be largely deactivated when H2/CO2gas mixtures are supplied to electrochemical hydrogen pumps.

In this study, we synthesized Ir-based nanocatalysts for the application of hydrogen separation from CO2-rich mixture gas and characterized them by XRD, XPS, TEM, and TGA. The electrochemical characteristics of Ir-based nanocatalysts were investigated by half-cell and single-cell tests, focusing on poisoning under CO2 atmosphere. The Ir-based catalyst demonstrated higher HOR/HER activity than the commercial Pt catalyst, and, by CO2 stripping analysis, it was confirmed that the CO poisoning under CO2 atmosphere was much smaller for Ir-based catalysts. As a result, enhanced hydrogen pump performances could be achieved with the anode feed of H2/CO2mixture.

References

[1] K. Onda, K. Ichihara, M. Nagahama, Y. Minamoto, T. Araki, J. Power Sources, 164, 1 (2007).

[2] B. Ibeh, C. Gardner, M. Ternan, Int. J. Hydrogen Energy, 32, 908 (2007).

[3] C.L. Gardner, M. Ternan, J. Power Sources, 835, 171 (2007) -841.

[4] N. Hoshi, T. Izuwra, Y. Hore, Electrochim. Acta, 40, 883 (1995) -887.
A Nonhumidified Fuel Cell Using Fluorohydrogenate Ionic Liquid - Polymer Composite Membrane: Advantages of the Use of Polyimide Membrane Supporting Material
Authors: Kiatkittikul Pisit , Nohira Toshiyuki , Hagiwara Rika
Published: February 2020

Operation at intermediate temperature (> 100 °C) without humidification offers several benefits for PEFCs such as reduction of expensive noble catalyst and simplicity of the unit. In the previous study, we reported a non-humidified fuel cell using a composite membrane of C2C1pyrr(FH)1.7F (C2C1pyrr = N-ethyl-N-methylpyrrolidinium) ionic liquid and HEMA (2-hydroxyethylmethacrylate) polymer with polytetrafluoroethylene (PTFE) as a membrane supporting material [1]. However, the single cell performance largely decreased when the operation temperature was elevated from 80 °C to 120 °C. The reason for this deterioration was revealed by the cross-sectional SEM images of the membrane electrode assemblies, showing that the composite membrane was softened and the composite electrolyte penetrated into gas diffusion electrodes (GDEs) to partially plug the gas channels in the gas diffusion layer.

In this study, to improve the mechanical properties of the membrane at elevated temperature, polyimide (PI) was used as a membrane supporting material instead of PTFE due to its higher mechanical strength and thermal deformation temperature. C2C1pyrr(FH)1.7F and HEMA monomer were mixed in the molar ratio of 8:2 and 9:1. Small amount of AIBN (2,2'-Azobis(isobutyronitrile)) was added as a radical initiator. PI (thickness: 16 and 30 μm, I.S.T) used as a porous supporting material was immersed in the mixed solution under vacuum for 1 h. Then, polymerization was conducted at 70 °C in Ar-filled oven for 12 h. Single cell tests were conducted under nonhumidified conditions at 25-120 °C. The GDEs with 1.0 mg Pt cm-2 were used for both the anode and cathode.

Fig. 1 shows i-V and i-p curves for a single cell using C2C1pyrr(FH)1.7F-HEMA (8:2) composite membrane with 16 μm PI supporting material operated at 25-120 °C under nonhumidified conditions. Contrary to the previous result in which PTFE was used as a supporting material, the single cell performance increases with the elevation of temperature. The maximum power density of 35 mW cm-
2 is observed at 120 °C. Fig. 2 shows cross-sectional SEM images of the membrane electrode assembly (MEA) for a single cell using C2C1pyrr(FH)1.7F-HEMA (8:2) composite membrane with 16 μm PI supporting material; (a) before single cell test, and (b) after single cell test at 25-120 °C. Yellow arrow indicates the membrane thickness. Comparing (a) with (b), there is no significant difference on membrane thickness, which means the previous problem of the penetration of composite electrolyte into the gas diffusion layer has been solved. Thus, the deterioration of cell performance does not occur even at over 80 °C.

Reference:

[1] P. Kiatkittikul, T. Nohira, R. Hagiwara, J. Power Sources, 2012, 220, 10.　

Acknowledgment: PI membrane supporting materials were provided from I.S.T Corporation.
Effect of Nanostructure of the Electrocatalyst Based on Carbon Nanotube for the Activation Overpotential for PEFC
Authors: Nagashima Akiyo , Fujigaya Tsuyohiko , Nakashima Naotoshi
Published: February 2020

Polymer electrolyte fuel cells (PEFC) are considered as one of the promising power sources for automobile and house in near future due to their high energy conversion efficiency and compactness. Recently high temperature PEFC using the polymer membrane doped with liquid phosphoric acid (PA) is attracting strong interest since it shows higher power density, CO poisoning on platinum (Pt) can be avoided and no cooling and humidifying devices are required. However, it was pointed the high temperature PEFC has poor durability due to leaching of PA from the membrane, which causes the deterioration of PEFC performance during long-term operation[1]. To overcome this issue, poly(vinylphosphonic acid) (PVPA) was used as the electrolyte instead of PA. We found the membrane doped with PVPA was free from the leaching of the electrolyte since PVPA is polymer and solid acid. Although this PEFC showed high durability, this catalyst had large overpotential in the area of low current density, probably because the poisoning of Pt by PVPA coating[2] or the lack of electrolyte in catalyst layers[3]. In this study, first we explored the new preparation method to avoid the Pt poisoning and investigated the catalytic performance by electrochemical techniques. And then, we increased the amount of acid in the electrolyte and compared the overpotential.

[1] M. Hori et al. J. Power Sources
2012, 210, 366.

[2] C. Roth et al. J. Phys. Chem. C
2013, 117, 6210.

[3] J.H. Jang et al. Int. J. Hyd. E.
2010, 35, 2119.
Comparison of Borohydride Oxidation on the Gold Crystallites Deposited on the Smooth and Fiber Cobalt Coatings
Authors: Tamasauskaite-Tamasiunaite Loreta , Lichusina Svetlana , Balciunaite Aldona , Simkunaite Dijana , Zabielaite Ausrine , Selskis Algirdas , Juskenas Remigijus , Norkus Eugenijus
Published: February 2020

In the present study the Co sublayers with different structures were used for the deposition of Au crystallites (denoted as Au(Co)/Ti). The smooth Co layer was deposited on the titanium surface via electroless deposition [1]. Cobalt coatings with a fiber structure were deposited from the electrolyte described in Ref. [2]. Au crystallites were deposited on the Co/Ti surface by immersion of Co/Ti into the 1 mM HAuCl4 + 0.1 M HCl solution at 25 oC for 0.5, 1 and 5 min, respectively [3].

The morphology, structure and composition of the prepared catalysts were examined by means of Field Emission Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, X-ray diffraction and Inductively Coupled Plasma Optical Emission Spectroscopy. Electrocatalytic activity of the prepared catalysts was investigated towards the oxidation of borohydride by means of cyclic voltammetry and chronoamperometry.

It was found that the gold particles deposited on the cobalt with a fiber and smooth structures show enhanced electrocatalytic activity towards the oxidation of borohydride in an alkaline medium as compared to that of bare Au and Co deposited on the Ti surface with smooth and fiber structures.

References

[1] A. Vaskelis, A. Jagminiene, I. Stankeviciene, E. Norkus. “Electroless deposition of cobalt alloys”. US patent 7,794,530 B2 (2010).

[2] E. Juzeliunas, S. Lichusina. Patent of the Republic of Lithuania No. 5481 26.03.2008.

[3] L. Tamasauskaitë-Tamasiunaite, A. Jagminiene, A. Balciunaite, A. Zabielaite, J. Vaiciuniene, A. Selskis, R. Juskenas, E. Norkus. Int. J. Hydrogen Energy 38 (2013) 14232-14241.
Electrocatalytic Oxidation of Formic Acid on Pd-Co/Omc Catalysts Prepared By the Polyol Method
Authors: Cazares-Ávila Eddy , Ruiz-Ruiz Edgar Jocsan , Hernández-Ramírez Aracely , Rodriguez-Varela F.J. , Morales-Acosta Diana
Published: February 2020

Direct formic acid fuel cells (DFAFC) have attracted considerable interest recently as portable power applications. This due to the lower crossover of the formic acid through the Nafion-based membrane, a higher kinetic activity and a higher voltage operation compared to direct methanol fuel cells. Pd-based catalysts possess superior performance in formic acid oxidation in DFAFC compared to Pt catalysts. Beside this, the addition of Co to Pd catalysts has been shown better tolerance of intermediates produced during formic acid oxidation that tend to poison it, which improves the catalytic activity and stability of the cell. However a poor dispersion state of Pd catalysts on the support is partially blamed for lowering catalyst activity in DFAFC. Thus in order to achieve a higher efficiency of the catalyst a well dispersed Pd-Co on the carbon support is mandatory. In this study, ordered mesoporous carbon (OMC) is evaluated as support to prepare Pd-based electro-catalyst (PdCo/OMC) for formic acid electro-oxidation in acid electrolyte. Pd-Co/OMC was synthesized by the polyol reduction method and characterized through XRD, EDS, TEM and electrochemical techniques. The results shown that the OMC support improves the catalytic activity of the Pd-Co anode, which has been attributed to the tailoring of the OMC support that facilitates the mass transfer process during the reaction.