bluuebunny/crossref_metadata_2025_split huggingface dataset:
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].
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[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.
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[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
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[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.
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

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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.