bluuebunny/crossref_metadata_2025_split huggingface dataset:
Injection Molding of Carbon Nanotube-Filled, Polymer Composite Bipolar Plates
Authors: Sander Meredith L , Pritts James T , Young Brian A , Santamaria Anthony D. , Hollinger Adam S 
Published: February 2020

Bipolar plates are one of the primary components of polymer electrolyte membrane fuel cells. These plates deliver reactants to electrodes, remove reaction byproducts, transfer heat, provide mechanical stability, and conduct electrical current. While graphite is the most commonly used material for fabrication of bipolar plates, the machining costs associated with graphite are a major drawback to mass production. In addition, graphite-based plates make the greatest contribution to the weight of the fuel cell stack. For this reason, electrically-conductive polymer composites have been explored as an alternative to the traditional metal alloys commonly used for fuel cell bipolar plates [1]. Polymer composites can reduce both the weight and cost of the bipolar plate, while still providing sufficient electrical properties.
In prior efforts, compression-molded, carbon fiber epoxy composites have shown promise to achieve the electrical conductivities needed for fuel cell bipolar plates [2]. While compression molding can be used for production of high volumes, injection molding is most ideal for the levels of mass production required for full scale commercialization of fuel cells. The main objective of this study is to investigate the suitability of injection molding polymer composites with sufficient electrical conductivities. Polymer composites based on nylon were developed for injection molding of bipolar plates. Carbon fiber was added to nylon at weight percentages ranging from 10 to 50%. The highest conductivity was obtained by direct injection molding. Results show that the percolation threshold for carbon fiber in nylon occurs around 25 wt%. Multi-walled carbon nanotubes were added to the direct injection-molded samples at weight percentages ranging from 2 to 4% to investigate the synergistic effects of adding multiple conductive fillers [3]. The addition of MWCNTs increases conductivities to United States Department of Energy technical targets for bipolar plate electrical conductivity (> 100 S/cm). Samples fabricated with MWCNTs and carbon fiber are shown to achieve up to 400% improvement in conductivity over samples with carbon fiber alone. The addition of carbon black as a third conductive filler, as well as the use of a polymer blend, may further increase electrical conductivity.
[1] Mighri F, Huneault MA and Champagne MF. (2004) Electrically conductive thermoplastic blends for injection and compression molding of bipolar plates in the fuel cell application. Polymer Engineering & Science 44: 1755-1765.
[2] Hwang IU, Yu HN, Kim SS, et al. (2008) Bipolar plate made of carbon fiber epoxy composite for polymer electrolyte membrane fuel cells. Journal of Power Sources 184: 90-94.
[3] Shen L, Wang FQ, Yang H, et al. (2011) The combined effects of carbon black and carbon fiber on the electrical properties of composites based on polyethylene or polyethylene/polypropylene blend. Polymer Testing 30: 442-448.

Figure 1
Mechanical Properties of Perfluorinated Sulfonic Acid Polymer Electrolytes and Their Effect on RH Cycling Durability
Authors: Okuyama Takumi , Watabe Hiroyuki , Hirai Takeshi , Saito Susumu , Shimohira Tetsuji 
Published: February 2020

Low resistive electrolyte membranes are important to improve fuel cell performance and they are indispensable for fuel cells, especially for automotive application, which are used under elevated temperature and low humidity conditions. There are some approaches to lowering membrane resistance in fuel cell operation. From a view point of the membrane design, increasing the ion-exchange capacity1, 2 and employing a thin membrane 3 are promising ways to decrease resistance. Although both are effective in improving fuel cell performance, they are not desirable in terms of mechanical durability in fuel cell operation. In reality, reinforced membranes made of perfluorinated sulfonic acid (PFSA) polymer and ePTFE have been widely used in fuel cell sytem3. However, relationship between mechanical properties of PFSA polymers and mechanical durability of unreinforced PFSA membranes is not yet well understood.
In this study, focusing on the backbone and cluster structure of the polymer, we synthesized PFSA polymer electrolytes with various mechanical properties and high proton conductivity as shown in Fig. 1, and investigated their mechanical properties and mechanical durability when used in a membrane electrode assembly. Various polymer properties were obtained, including work of fracture, ratio of yield stress to breaking stress, water uptake, and creep characteristics, which were compared with the results of RH cycling test. Though we couldn’t explain the results of RH cycling test using a single mechanical property, we found a clear relationship between a combination of four mechanical characteristics and the mechanical durability.

Acknowledgement

This research was partially funded by ImPACT Program of Council for Science, Technology and Innovation (Cabinet Office, Government of Japan).

References

S. Kinoshita, T. Tanuma, K. Yamada, S. Hommura, A. Watakabe, S. Saito, and T. Shimohira, 226th Meeting of The Electrochemical Society, 1195 (2014).

S. Kinoshita, T. Shimohira, A. Watakabe, S. Hommura, S. Saito, T. Tanuma, and K. Yamada, 26th PRiME, 2414 (2016).

B. Kienitz, J. Kolde, S. Priester, C. Baczkowski, and M. Crum., ECS Transactions, 41(1), 1521 (2011).

Figure 1
Effect of Cobalt Ion Exchange and Thermal Pretreatment of Ionomer Thin Films on Conductivity, Water Uptake and Swelling
Authors: Eskandari Hamideh , Ozhukil Kollath Vinayaraj , Karan Kunal 
Published: February 2020

It is known that Cobalt (Co) can leach out from the Pt-Co alloy catalysts causing degradation of long-term fuel cell performance. Although the fundamental mechanism of performance loss is not fully understood, it has been hypothesized that the Co ion interacts with the nanothin ionomer films in the fuel cell catalyst layer by exchanging with the protons and thereby adversely affecting the performance. However, the effect of Cobalt ion, specifically and the transport properties of nanothin fluorinated ionomers films, in general is not fully known.
We have studied the effect of cation(Cobalt) on spin-coated nanothin ionomers on its key properties – (i) proton conduction and water uptake which directly affects the electrochemical performance of fuel cell catalyst layers, and (ii) swelling behavior, which is an indicator of mechanical strength and thereby the durability of the ionomer. Electrochemical impedance spectroscopy (EIS) of films on interdigitated elecrodes for conductivity measurements, quartz crystal microbalance (QCM) for water uptake, and environmental ellipsometry for swelling measurement was employed, Quantification of exchanged Cobalt in nanothin films is non-trivial problem and we have used a set of x-ray techniques (EDX, XPS) for determination of cobalt in the cation exchanged films.
In this work conductivity of the different ionomer thin film (~ 30 nm) were tested before and after Cobalt exchange at different temperatures (30-80 °C) and humidity (40-90 % RH) conditions. It was seen that the conductivity of the ionomer thin films decreased after Cobalt exchanged but the proton conduction of some of the non-commercial ionomers is not as strongly affected by Co ion exchange as that of the state-of-the-art Nafion ionomer. We also investigated the effect of ionomer thin film pretreatment on the conductivity of the cobalt exchanged ionomer. It was found that the the samples annealed at 160 °C and then cation exchanged by exposure to cobalt solution showed less reduction in conductivity than unannealed cation exchanged ionomer films.
The presentation will share the details of the film preparation and characterization as well as the results for the conductivity, water uptake and swelling of the ionomer films.

Figure 1
Durability and Degradation of Direct Dimethyl Ether High Temperature Polymer Electrolyte Membrane Fuel Cells
Authors: Vassiliev Anton , Reumert Alexander Kappel , Jensen Jens Oluf , Aili David 
Published: February 2020

Dimethyl ether (DME) combines high energy density with low toxicity and good electro-oxidation kinetics due to the absence of carbon-carbon bonds. It has therefore been identified as an attractive fuel for various fuel cell types, including the high temperature polymer electrolyte membranes (HT-PEM) fuel cells utilizing phosphoric acid doped polybenzimidazole (PBI) membranes [1, 2].
The HT-PEMFC technology has been intensively developed during the last two decades, and recently lifetimes exceeding 9000 h with degradation rates as low as 0.5 μV h-1 have been achieved at 160 °C and 200 mA cm-2 with hydrogen and air [3]. This type of cell was originally developed for a direct methanol fueled system [4], but lifetimes exceeding a few hundred hours have yet not been reported in this mode. We recently demonstrated that this is, at least partly, due to severe chemical incompatibility between methanol and the phosphoric acid within the polymer membrane. It results in formation of organic phosphoric acid ester derivatives, which not only reduces the conductivity of the membrane but also promotes the acid loss [5].
This work presents durability studies of direct DME HT-PEM fuel cells, and extends to a discussion about the predominating degradation mechanisms responsible for the limited lifetimes. The cells were operated at a constant current load at 160 or 200 °C and periodically characterized by polarization curves and electrochemical impedance spectroscopy. Supported by studies on a model system of phosphoric acid and DME, a main degradation pathway is suggested, where methyl phosphates are formed within the membrane. In analogy with the direct methanol cells, this reduces the proton conductivity of the membrane and promotes the acid loss, which leads to gradually increasing internal resistance.
[1] J.O. Jensen, A. Vassiliev, M.I. Olsen, Q.F. Li, C. Pan, L.N. Cleemann, T. Steenberg, H.A. Hjuler, N.J. Bjerrum, J. Power Sources, 211 (2012) 173-176.
[2] J. Neutzler, G. Qian, K. Huang, B. Benicewicz, J. Power Sources, 216 (2012) 471-474.
[3] T. Søndergaard, L.N. Cleemann, H. Becker, D. Aili, T. Steenberg, H.A. Hjuler, L. Seerup, Q. Li, J.O. Jensen, J. Power Sources, 342 (2017) 570-578.
[4] J.S. Wainright, J.T. Wang, D. Weng, R.F. Savinell, M. Litt, J. Electrochem. Soc., 142 (1995) L121-L123.
[5] D. Aili, A. Vassiliev, J.O. Jensen, T.J. Schmidt, Q. Li, J. Power Sources, 279 (2015) 517-521
(Invited) The Effects of Water Binding and Morphology on Proton Transport in Polymer Membranes
Authors: Hickner Michael 
Published: February 2020

The effects of water binding and morphology will be reported in the context of designing new proton exchange membranes (PEMs). While much has been learned about the function of proton exchange membranes by studying perfluorosulfonic acid and sulfonated aromatic polymers, new generations of proton-conducting polymers for aqueous applications are being developed. Key to these advancements have been block copolymers and random copolymers with new sulfonic-acid bearing headgroups.
Sulfonated aromatic block copolymers are a known route to high-performing proton exchange membranes. Compared to their random sulfonated copolymer counterparts, the organization of the sulfonate groups in a concentrated ionic domain has demonstrable benefits to proton conductivity. However, the relative humidity effects on the specific headgroup chemistry still often lead to lower conductivity than desirable at low RH.
Using FTIR, we have explored the water binding in aromatic random copolymers with a number of new sulfonate groups. Our data shows that superacid groups on aromatic backbones can give comparable conductivities to perfluorosulfonic acid membranes. The interaction of these headgroups with water is one of the important factors for high proton conductivity – even though their morphologies can be much different than block copolymers or perfluorosulfonic acid materials.
This talk will discuss the morphology and water binding factors that influence the proton conductivity of a number of unique aromatic polymer-based proton exchange membranes.

Figure 1
Sputtered Pt3Y Thin Films As Cathode Catalysts with High Activity in PEMFC Measurements
Authors: Lindahl Niklas , Eriksson Björn , Grönbeck Henrik , Lindström Rakel Wreland , Lindbergh Göran , Lagergren Carina , Wickman Björn 
Published: February 2020

Proton exchange membrane fuel cells (PEMFCs) have the potential to become a vital part of sustainable energy systems, provided that cathode catalysts with higher activity and stability are developed. A very promising group of materials for the oxygen reduction reaction (ORR) is the group of alloys with platinum and rare earth elements.[1, 2].
We have recently showed that sputtered thin films of Pt3Y have specific activities for ORR up to seven times higher than polycrystalline Pt in rotating disk measurements, which is similar to that of bulk alloys.[3] In addition, sputtered thin films of Pt3Y with thicknesses about 3 nm show a mass activity more than an order of magnitude higher than state-of-the-art Pt nanoparticles.
However, in order to become realistic alternative catalysts these materials need to prove an increased activity also under real fuel cell conditions. By sputtering thin films of Pt3Y on gas diffusion layers (GDLs) we are able to construct full membrane electrode assemblies (MEAs) and evaluate these in single cell measurements.[4] The fuel cell measurements show that Pt3Y has a specific activity up to 2.5 times higher than pure Pt. Detailed characterization reveals important materials properties of the thin films and indicates that the catalyst structure of the films on GDL is not optimal. This suggests that even higher activities should be possible in the fuel cell if the electrode and catalyst structure is improved.
References

Escudero-Escribano, M., et al., Tuning the activity of Pt alloy electrocatalysts by means of the lanthanide contraction. Science, 2016. 352(6281): p. 73-76.

Greeley, J., et al., Alloys of platinum and early transition metals as oxygen reduction electrocatalysts. Nature Chemistry, 2009. 1(7): p. 552-556.

Lindahl, N., et al., High Specific and Mass Activity for the Oxygen Reduction Reaction for Thin Film Catalysts of Sputtered Pt3Y. Advanced Materials Interfaces, 2017. 4(13): p. 1700311.

Lindahl, N., et al., Fuel cell measurements with cathode catalysts of sputtered Pt3Y thin films. ChemSusChem, 2018. http://dx.doi.org/10.1002/cssc.201800023.

Caption. a) Electrochemical single cell characterization of Pt and Pt3Y sputtered catalysts in H2/O2, 80 °C, 1.5 bar absolute pressure, 100% RH, 20 mV s-1. Inset shows a schematic image of the atomic stucture of the Pt3Y. b) Bright-field TEM micrograph of as-sputtered Pt3Y thin film on GDL. The scale-bar is 50 nm.

Figure 1
(Invited) Addressing Interfacial Processes That Govern the Electrocatalyst Activity-Stability Balance
Authors: Snyder Joshua David 
Published: February 2020

The boundaries of functional materials development are continually being pushed where length scales down to the order of nanometers have introduced multi-functionality into the next generation of materials. The complex morphologies and compositional gradients that define these nanomaterials open pathways to new modes of instability, requiring strategies to address these instabilities and prolong the operational lifetime of these materials in real-world devices.
For complex, three-dimensional morphologies, the activity/stability balance begins to shift where an additional mechanism of performance degradation driven by the tendency to reduce the overall surface free energy of the system, results in material instability. It is critical that a more detailed fundamental understanding of the mechanisms of morphological and compositional instability and degradation in these topologically complex electrocatalytic materials be developed in order to propose strategies to improve their operational lifetime.
Here we will present an analysis of the mechanisms of material degradation for electrocatalysts with complex, three-dimensional nanoscale morphology with emphasis on operational conditions relevant for the oxygen reduction reaction (ORR). With a more fundamental understanding of the sources of structural evolution and performance metric degradation, we highlight the influence of the metal/electrolyte interface in governing both stability and activity. We will also present results of several mitigation strategies for the inherent instability of the three-dimensional morphology and their impact on electrocatalyst activity and selectivity.
Cathode Loading Impact on Voltage Cycling Induced PEMFC Degradation – a Voltage Loss Analysis
Authors: Harzer Gregor S. , Schwämmlein Jan Nicolas , Damjanović Ana Marija , Ghosh Sourov , Gasteiger Hubert A. 
Published: February 2020

Proton exchange membrane fuel cell (PEMFC) based vehicles are on the verge of commercialization. However, significant hurdles for further market penetration of PEMFC vehicles are cost reductions by decreasing the amount of platinum catalysts while meeting long term durability targets. The durability of catalysts is usually estimated by accelerated stress tests (ASTs) using voltage cycling.[1] Generally, the electrochemically active surface area (ECSA) and mass activity of the cathode catalyst is analyzed over the course of 30000 voltage cycles, while effects of O2 mass transport related losses, especially for varying cathode catalyst loadings have not yet been systematically studied.
To better understand the influence of voltage cycling based ASTs on the development of mass transport resistances and on the extent to which they can be captured by currently available in situ diagnostics (ORR kinetics in H2/O2, cathode proton conduction resistance by impedance, oxygen transport resistance via limiting current measurements), we conducted a comprehensive voltage loss analysis on MEAs with high- and low-loaded cathodes (0.4 and 0.1 mgPt/cm2) over the course of ASTs conducted in H2/N2 (anode/cathode) at ambient pressure, 80 °C, and 100% RH, using different voltage cycling profiles: i) triangular wave (TW) and square wave (SW) cycles between 0.6 and 1.0 VRHE; ii) TW cycles between 0.6 and a lowered upper potential limit of 0.85 VRHE (TW-LUPL); and, iii) a combination of a triangular sweep between 0.6 and 1.0 VRHE with potential hold periods at the upper and lower potential (TW-H).
For all ASTs, the O2 transport resistance scaled inversely to the cathode electrode roughness factor (rf). Since the ECSA decreases in the course of potential cycling and two different loadings were used, a wide range of rf values with their corresponding pressure-independent O2 transport resistance was analyzed, proving its dependence on the available Pt surface area (Figure 1) as shown also by other researchers.[2] The pressure dependent transport resistance remained essentially constant. Furthermore, ex situ thickness measurements of catalyst layers showed no cathode thinning, indicating the absence of significant carbon corrosion. While 30000 TW or SW cycles dramatically decreased the H2/air performance for low- and high-loaded MEAs, only a negligible degradation in performance was observed when a lower upper potential limit of 0.85 VRHE was applied, providing a guideline to limit MEA degradation under automotive conditions.
Figure 1: Pressure independent O2 transport resistance vs the electrode’s roughness factor, rf, for high-loaded (0.4 mgPt/cm2, blue) and low-loaded (0.1 mgPt/cm2, orange) catalyst layers over the course of different voltage cycling ASTs.

Figure 1
Activity and Stability of Carbide Derived Carbon Supports in PEMFC Application
Authors: Sepp Silver , Nerut Jaak , Vaarmets Kersti , Kanarbik Rait , Tallo Indrek , Lust Enn 
Published: February 2020

Polymer electrolyte membrane fuel cells (PEMFCs) are regarded as a promising alternative energy conversion devices for both mobile and stationary applications. Main problems hindering the wide-scale commercialization of PEMFCs are high overpotential for oxygen electroreduction reaction (ORR) at the cathode decreasing the efficiency as well as the instability of porous carbon supports in fuel cell working conditions. Therefore, novel catalyst materials are being sought for PEMFC applications [1, 2]. Hierarchical microporous-mesoporous carbon supports were prepared from molybdenum carbide using the high temperature chlorination method. Prepared materials exhibited high specific surface area and large mesopore volume [3-4].
Thermogravimetric analysis, X-ray diffraction, low temperature nitrogen sorption and high resolution transmission electron microscopy methods were used to characterize the structure of the synthesized catalyst materials.
Prepared catalysts were used in the single cell measurements. Catalyst coated membrane method was used to prepare the MEAs using ultrasonic spaying technique. The polarization curves and chronopotentiometric measurements were conducted to evaluate the activity and stability of the catalyst materials synthesized. From cyclic voltammetry the electrochemically active surface area values were calculated and used to estimate the contact surface of platinum nanoparticles and Nafion electrolyte. The series resistance of electrolyte, polarization resistance and activation energy values have been calculated from electrochemical impedance spectroscopy data. It was established that prepared carbon materials with well-defined properties are excellent objects to study the impact of the catalyst support properties on the performance of a PEM fuel cell.
It was found that the novel synthesized catalyst materials are very stable and catalytically active towards ORR. Therefore, prepared materials are suitable for PEMFC applications.

Acknowledgements.

This work was supported by Estonian target research project IUT20-13, Personal Research Grant PUT1033, Estonian Centre of Excellence Project No. 2014-2020.4.01.15-0011.

References

S. Sepp, K. Vaarmets, J. Nerut, I. Tallo, E. Tee, H. Kurig, J. Aruväli, R. Kanarbik, E. Lust, Electrochim. Acta 2016, 203, 221−229.

S. Sepp, K. Vaarmets, J. Nerut, I. Tallo, E. Tee, H. Kurig, J. Aruväli, R. Kanarbik, E. Lust, J. Solid State Electrochem. 2016, 21(4), 1035–1043.

S. Sepp, E. Härk, P. Valk, K. Vaarmets, J. Nerut, R. Jäger, E. Lust, J. Solid State Electrochem. 2014, 18(5), 1223 – 1229.

E. Lust, K. Vaarmets, J. Nerut, I. Tallo, P. Valk, S. Sepp, E. Härk, Electrochim. Acta 2014, 140, 294-303.