bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of Acid Accelerators for an Off-Grid PEM Fuel Cell Power Station Utilizing Solid Sodium Borohydride for Hydrogen Storage
Authors: Hsu Lewis , Huang Mindy , Anderson Greg , Rubio Arthur , Kerber Maxwell , Putnam Michael , Phipps Alex
Published: February 2020

In rural areas, networkable environmental monitoring equipment is often used to provide continuous, real-time information without the need for a dedicated operator for maintenance or monitoring. However, power and energy availability are often controlling factors for operational lifetime when these systems are put on location. In these situations, batteries are often used as the main energy storage medium and require servicing or replacement when exhausted. This can lead high costs related to man-power and logistics to return and maintain the equipment at those locations.

Sodium borohydride hydrolysis was once looked at as a promising way to store hydrogen for use in PEM fuel cells. Concerns regarding hydrogen storage capacity and recyclability of reaction products have prevented its use in larger transportation or energy storage applications. However, the energy density of sodium borohydride still makes the reaction suitable for specific applications where reuse is not needed. As such, present here a system utilizing solid sodium borohydride as a storage medium to meet on demand power needs of these types of systems. The system utilizes a PEM fuel cell integrated with an electro-mechanical system to control chemical metering and power management.

We have previously shown results from our initial testing with solid sodium borohydride using commercial-off-the-shelf tablets for generating hydrogen when added to a reaction vessel containing water. Conceptually, a tablet would be introduced to the reaction vessel whenever additional hydrogen gas would be required. Operating in this manner would require good stability and reproducibility over multiple tablet reaction events.

Initial testing showed good reaction rates when a cobalt catalyst was employed, either pre-doped into the solid tablet mixture or when the catalyst was pre-mixed with the water in the reaction vessel. Analysis of the gas mixture showed high quality hydrogen gas flows could be produced and sent to the PEM fuel cell for power production. However, concerns with the stability, safety, and handling of the catalyst have led to a need to identify a more green chemistry approach.

We present here an alternative approach using common mineral and organic acids as hydrolysis accelerators that could be considered a greener approach to hydrogen generation for remote power applications. These include hydrochloric acid, phosphoric acid, citric acid, and acetic acid. Initial testing shows good reproducibility over multiple hydrogen generation events and reasonable reaction control. A comparison of hydrogen yield and gas composition is also shown. Finally, cost comparison between these accelerators is performed in order to assess their suitability in practical application.
(Invited) A General Strategy to Synthesize High-Performance Open Nanoframe Structured Catalysts
Authors: Shen Pei Kang
Published: February 2020

Developing a novel catalyst for oxygen reduction reaction (ORR) for real world applications should be focused on not only optimizing its activity and stability, but also synthesizing it by a simple process and thus being capable for mass production cost effectively. By taking a reliable recipe and facile one-pot synthesis method, we fabricated a wide range of unique nanoframe structures with high complexity, including the octopod, polyhedral, and hierarchical nanoframe architectures. Specially, the octopod nanoframe architectures possess three-dimensional catalytic surfaces, favorable platinum atomic arrangement and beneficial high-index facets (HIFs), thus can serve as models of advanced catalysts. The PtCu octopod nanoframe catalyst achieved 20-fold enhancement in mass activity for ORR compared to the commercial platinum-carbon catalyst. More importantly, this nanoframe catalyst maintained its structure over storing for months, after rigorous electrochemical reactions, and heat-treatment process. We also demonstrated that the one-pot synthesis of high-performance octopod nanoframe catalysts can be easily scaled up in high quality.

Fig. 1.
Structural and compositional analysis of typical Pt-based nanoframe architectures.

Figure 1
Imaging Phosphoric Acid in HT-PEFC: What Has Been Learnt so Far?
Authors: Büchi Felix N , Eberhardt Sebastian H. , Halter Jonathan , Schmidt Thomas J.
Published: February 2020

Phosphoric acid used as the electrolyte in high temperature polymer electrolyte fuel cells (HT-PEFC) is not covalently bound to the membrane polymer. The interaction of phosphoric acid with the nitrogen of the pyridine group of the polybenzimidazole (PBI) polymer backbone [1] is limited to two acid molecules per PBI repeating unit. Consequently, the bulk of phosphoric acid is mobile and the acid concentration and distribution in/and between membrane, catalyst and gas diffusion layers (GDL) is varying, depending on the operating conditions of the fuel cell.

X-ray imaging technology, initially developed for imaging liquid water in the porous structures of LT-PEFC, has been adapted [2] for the imaging of phosphoric acid. Operando tomographic microscopy imaging has shown that acid migration to the anode due to the non-zero transference number of the hydrogen phosphate anion is an important process in acid redistribution [3]. The acid can invade the anode GDL, similar to the injection of water into the cathode GDL of LT-PEFC.

So far, not much has been known about the characteristics of the interaction of phosphoric acid with the porous structure of the gas diffusion layer. Ex-situ acid injection and withdrawal experiments at temperatures up to 160 °C are performed with concurrent tomographic imaging to understand the characteristics, as well as the similarities and differences to the wetting of GDLs with water.

[1] Q. Li, J. O. Jensen, R. F. Savinell, and N. J. Bjerrum, Prog. Polym. Sci., 34, 449–477 (2009)

[2] S.H. Eberhardt, F. Marone, M. Stampanoni, F.N. Büchi, and T.J. Schmidt, J. Synchrotron Radiat., 21, 1319–1326 (2014)

[3] S.H. Eberhardt, M. Toulec, F. Marone, M. Stampanoni, F.N. Büchi, and T.J. Schmidt, J. Electrochem. Soc., 162, F310-F316 (2015)
N-Functionalised Polyketone Ion Exchange Membranes for Aemfcs
Authors: Nawn Graeme , Cavinato Gianni , Pace Giuseppe , Vezzù Keti , Bertasi Federico , Negro Enrico , Bach Delpeuch Antoine , Di Noto Vito
Published: February 2020

Anion-exchange membrane fuel cells (AEMFCs) provide significant advantages over their proton-exchange membrane counterparts. In the alkaline environment, the oxygen reduction reaction (ORR) is more facile, there is diminished fuel crossover, and a greater flexibility regarding fuel and catalyst choice. The membrane at the heart of AEMFCs not only facilitates the ion exchange but also separates the fuel feedstocks and acts as a support for the membrane-electrode assembly (MEA). However, to date there are still no membrane materials that satisfy all the needs (long-term stability in alkaline environment, high ionic conductivity, low swelling and good structural integrity) for use in AEMFCs and this remains one of the larger obstacles for further AEMFC development.

The amination and subsequent quarternisation of polyketone leads to a new family of ionomers containing N-substituted pyrrole moieties. The degree of amination can be controlled by manipulating reaction conditions, allowing the composition and resulting structural properties of the polymer to be tuned. Membrane fabrication results in thermally stable (TD > 250 oC), structurally robust polymer electrolytes that exhibit ionic conductivity ( > 10-3 S cm-1). These new solid-state ion conducting materials have the potential to be used in a variety of applications including AEMFCs.

Here we present an in-depth study focusing on the structure-property relationships of this new polypyrrole/polyketone polymer. A variety of analytical techniques are used to probe the thermal and structural properties of the polymers, these include high-resolution thermogravimetric analysis, modulated differential scanning calorimetry, dynamic mechanical analysis, vibrational, NMR and UV-Vis spectroscopies. In addition, broadband electrical spectroscopy is used to gauge the interplay between the structural properties and electrical response.

Figure 1
MgO-Templated Mesoporous Carbon As a Catalyst Support for Polymer Electrolyte Fuel Cells
Authors: Kamitaka Yuji , Takeshita Tomohiro , Suzuki Noritomo , Jinnouchi Ryosuke , Murata Hajime , Morimoto Yu
Published: February 2020

Catalyst poisoning by specific adsorption of the sulfonic acid anion of ionomers has been known as one of the main performance-limiting factors of PEFCs. In a recent study, it was reported that the catalyst poisoning can be suppressed by using a mesoporous carbon (mesoporous carbon nano-dendrites) as a cathode catalyst support [1]. Here, we present that a similar effect can be obtained by using a MgO-templated mesoporous carbon [2] having meso-pores the sizes of which are more-systematically controllable by changing the size of the MgO templates than for conventional carbon supports.

An MgO-templated carbon denoted as CNovel® was purchased from Toyo Tanso Inc. The mean diameter of its mesopores is ca. 5 nm (the template MgO size was 5 nm). The sample was graphitized by a heat treatment at 2,100 °C for improving the chemical stability under electrochemical conditions and was crushed by a bead mill to form secondary particles smaller than hundreds nm in size. The obtained powder was immersed in 1 M HNO3 at 80 °C for 1 h to introduce hydrophilic surface groups for facilitating Pt deposition. After thoroughly washing it with pure water, platinum nanoparticles were deposited in aqueous media by using hexahydroxy-platinate as a platinum source. The ORR activity of the prepared catalyst was evaluated by the thin-film RDE method (without ionomers) in aqueous media (0.1 M HClO4) and in MEAs prepared with a Nafion® ionomer (I/C=1.0). The results were compared those of Pt/Vulcan.

Figures 1a and 1b show that TEM images of the catalysts. Platinum particles of ca. 2 nm are observed on both the carbons. While Pt/Vulcan shows platinum particles only on the outer edge of the carbon particle, Pt/CNovel shows platinum particles not only on the outer edge but also on the mesopores inside the carbon particle. Figure 1c shows the I-V curves of MEAs using Pt/CNovel and Pt/Vulcan. Pt/CNovel exhibits higher cell-voltage than Pt/Vulcan in the low current density region. This result indicates that the former has a higher ORR activity than the latter as specifically indicated in the specific activities at 0.9 V shown in Figure 1d. The trend is, however, opposite in the RDE measurements while the specific activities for both samples by RDE are higher than those measured by the MEAs. These results indicate that the Pt/CNovel suffers less catalyst poisoning by the sulfonic acid anion than Pt/Vulcan in MEAs probably because the anion linked to the ionomer cannot reach the surfaces of the Pt nanoparticles inside the mesopores of CNovel while all Pt nanoparticles on Vulcan® can be reached by the ionomer.

References

[1] M. Hori, et al., 225th ECS Meeting Abstract, #1500 (2013)

[2] T. Morishita, et al., Carbon, 48, 2690 (2010)

Figure 1
Nanofibrous Electrodes with Tunable Electrodeposited Pt Morphologies with High ORR Activity and Durability
Authors: Ercolano Giorgio , Farina Filippo , Cavaliere Sara , Jones Deborah J. , Rozière Jacques
Published: February 2020

A new approach for the preparation of PEMFC cathode electrocatalysts based on thin layers of platinum deposited on a support instead of conventional Pt nanoparticles supported on carbon black could be achieved adopting various Pt deposition techniques including atomic layer deposition, electrochemical atomic layer epitaxy, self-terminated Pt electrodeposition, thermal dealloying, and galvanostatic displacement of Ni and Cu ions with Pt1,2. This morphology allows for a more effective utilisation of the highly priced noble metal, while increases the durability of the electrodes over time.

The morphology and nature of the support material also plays a crucial role. Nanostructured 1D materials have attracted significant research attention due to the influence of their nanostructure and porosity on performance and durability of the PEMFC3. In this regard, electrospinning is a reliable and scalable technique for the preparation of nanofibers with controlled and uniform diameters and structures. Its versatility allows the production of organic, hybrid and inorganic nanofibres, as well as the possibility of creating different geometries, assemblies and architectures4.

We developed novel nanofibrous electrodes (NFE) based on 3D nanostructured networks of carbon nanofibers covered by Pt nanoislands, merging the advantage of Pt thin layers catalyst and a highly porous robust support. This was achieved by combining electrospinning and high overpotential pulsed Pt electrodeposition.

These catalysts are based on self-standing electrospun carbon nanofibers covered by platinum thin platinum nanoislands. NFEs are highly durable when compared to commercial standards and have a higher degree of platinum exploitation. Electrochemical active specific surface areas as high as 140 m2g-1
Pt with retention in the order of 70 % after accelerated stress testing are measured, making them a suitable alternative to currently available commercial catalyst.

1. S. M. Alia, Y. Yan, and B. Pivovar, Catal. Sci. Technol., 4, 3589–3600 (2014)

2. G. Ercolano, S. Cavaliere, D. Jones, and J. Rozière, ECS Trans., 69, 1237–1242 (2015).

3. S. Cavaliere et al., ChemElectroChem, 2, 1966–1973 (2015).

4. S. Subianto et al., in Electrospinning for Advanced Energy and Environmental Applications, vol. 1, p. 29–60 (2015).
(Invited) Ultra-Low EW Ionomers and Membranes for Fuel Cells
Authors: Yandrasits Michael , Lindell Matthew , Kurkowski Michael , Schaberg Mark S
Published: February 2020

Perfluorosulfonic acid (PFSA) ionomers have long been used to fabricate membranes for proton exchange membrane fuel cells (PEMFC). When used in combination with mechanical reinforcements and peroxide scavenging additives, this class of ionomers has demonstrated excellent durability and performance in both accelerated lab testing and in end-use applications.

Automotive traction applications, among others, have very demanding performance targets at relatively high temperature and low humidity, driven by the need to reduce overall system cost. In order to meet these targets, ionomers with increased proton conductivity are required. Under dry conditions, conductivities of commercial ionomers are insufficient to achieve several of the targets, as they are limited to equivalent weights (EWs) of about 700 g/mol. Not only are low EW PFSA ionomers difficult to polymerize, they also tend to become water soluble as the amount of the tetrafluoroethylene (TFE) co-monomer is reduced.

One strategy for achieving lower equivalent weight, while maintaining suitable TFE content, is a multi-acid side chain (MASC) approach. We have developed a synthetic process to use the 3M precursor polymer to prepare a new ionomer containing both bis(sulfonyl)imide and sulfonic acid groups in each sidechain, to form the perfluoro-imide acid (PFIA) ionomer. Both functional groups are strong acids, and their combination results in EWs in the range of 620-650 g/mol, with increased conductivity under all conditions, including low humidity. This approach has been extended to include multiple bis(sulfonyl)imide groups per side chain to form materials classified as perfluoro-ionene chain extended (PFICE) ionomers, with EWs as low as 440 g/mol.

Characterization of these new ionomers for conductivity, solubility, and performance will be presented, along with a discussion of the practical limits of the MASC approach. Like PFSA ionomers, the PFIA and PFICE ionomers require both mechanical reinforcement and stabilizing additives in order to fabricate a viable PEMFC membrane. Development of membrane design considerations will be presented.
Amino-Functionalized Mesoporous Silica Based Polyethersuflone-Polyvinylpyrrolidone Composite Membrane for Elevated Temperature Fuel Cells
Authors: Zhang Jin , Lu Shanfu , Zhu Haijin , Chen Kongfa , Liu Jian , Xiang Yan , Forsyth Maria , Jiang San Ping
Published: February 2020

Inorganic-organic nanostructured hybrid membranes of polyethersuflone (PES)-polyvinylpyrrolidone (PVP) were prepared with mesoporous silica materials. Hollow mesoporous silica is synthesized via cationic surface-assistant etching method, while amino-functionalized hollow mesoporous silica and amino-functionalized mesoporous silica spheres were synthesized via post-grafting strategy. After the addition of mesoporous silica and amino-functionalized mesoporous silica into the matrix of PA doped PES-PVP composite membranes, all composite membranes show similar PA uptake. However, the proton conductivity of the composite membranes increases significantly with the substantial decrease in the activation energy for proton diffusion, especially for the amino-functionalized hollow mesoporous silica material. That reason is most likely due to the facilitated proton transportation in the ordered mesoporous channels via the hydrogen bond between the –NH2 groups and H3PO4. Cell performance also confirms the superiority of the addition of inorganic fillers in PES-PVP membrane, and the highest peak power density at 180 oC was 480 mW cm-2 for NH2-HMS based composite membrane, which is 92.7 % higher than that of PA doped PES-PVP composite membrane at the identical condition. The results show promising application of NH2-HMS based PES-PVP composite membrane for elevated temperature proton exchange membrane fuel cells.

Figure 1
Water Balance in Non-Humidified PEM Fuel Cell with Different Membrane Thicknesses
Authors: Pivac Ivan , Penga Zeljko , Barbir Frano
Published: February 2020

It is possible to design and operate a fuel cell with non-humidified reactant gases, by relying on water produced by electrochemical reaction inside the fuel cell. However, in order to do so there must be adequate water and heat management applied. For example, temperature distribution along the cathode channel must be such that relative humidity is maintained close to 100%. As water is produced on the cathode side there is a water concentration gradient across the mebrane, and in order to humidify hydrogen on the other side there must be back-diffusion flux greater than or at least equal to the electroosmotic drag. Membrane thickness, thus, plays an important role in realization of this concept.

A segmented fuel cell is designed such that each segment can be maintained at different pre-determined temperature. The temperatures of the segments along the cathode channel are selected by the help of Molliere h-x diagram such that relative humidity is maintained close to 100%. Operating conditions are selected such that the product water is sufficient to saturate the cathode exhaust without appearance of liquid water. Humidity measurements are taken between each segment on both anode and cathode sides. The anode and cathode exhaust streams are condensed so that water balance may be established.

The entire setup is modeled with FLUENT CFD package, and the experiments are conducted with two different mebrane thickness. Good agreement is achieved between the modeling and experimental results.

The results indicate that it is possible to establish the required temperature profile along the cathode channel and keep the cathode stream relatively well humidified without external humidification. Performance of such variable temperature fuel cell is better than the uniform temperature fuel cell. The thinner membrane results in better humidification of the hydrogen side, which is important especially at higher current densities, i.e., at higher electro-osmotic drags.

Figure 1
Investigation on the Improvement of PEM Fuel Cell Performance through Two Novel Flow Field Designs
Authors: Shen Shuiyun , Wang Chao , Zhang Qinglei , Zhang Junliang
Published: February 2020

To further improve the cell performance of a proton exchange membrane fuel cell (PEMFC), thus meeting the high requirement for its automotive and stationary application, great efforts have been made on the optimization of the flow field pattern[1,2]. In this work, two novel flow field patterns are proposed and the influences on the cell performance are investigated. Both two novel flow field designs lead to superior cell performance than the conventional flow field patterns do, and this can be attributed to their superiority in removing water at high current densities while increasing the flow velocity near the outlet. The velocity magnitude in flow fields is examined and compared through the computational fluid dynamics modeling.

Acknowledgements

This work was supported in part by National Natural Science Foundation of China (Grant No. 21373135 and 21533005) and Science Foundation of Ministry of Education of China ( Grant No. 413064).

References

[1] Soler, J., E. Hontanon, and L. Daza, Electrode permeability and flow-field configuration: influence on the performance of a PEMFC. Journal of Power Sources, 2003. 118(1): p. 172-178.

[2] Lee, B., K. Park, and H.-M. Kim, Numerical Optimization of Flow Field Pattern by Mass Transfer and Electrochemical Reaction Characteristics in Proton Exchange Membrane Fuel Cells. Int. J. Electrochem. Sci, 2013. 8: p. 219-234.
Gas Diffusion Media for Open-Cathode Fuel Cells in Atmospheric Flight
Authors: Atkinson Robert W. , Hazard Matthew W. , Rodgers Joseph A. , Stroman Richard O'Neil , Gould Benjamin D.
Published: February 2020

Operating a proton exchange membrane fuel cell (PEMFC) in a planar, open cathode configuration can enable significant reductions in overall device weight and system complexity compared to a conventional fuel cell stack. This decrease in device weight makes an array of open-cathode, planar fuel cells a compelling candidate power source for unmanned aerial vehicles. The flow of ambient air over vehicle-mounted cells can improve oxygen, waste heat, and water transport between the catalyst layer and bulk air. We previously studied the effect of environmental conditions on cell polarization and found that ambient temperature, relative humidity, altitude and air speed all influence cell temperature, which affects water balance and oxygen transport to the catalyst layer. In this work, we relate gas diffusion media (GDM) properties to cell polarization behavior in a broad range of anticipated flight conditions. We study the effect of gas diffusion layer thickness and porosity on cell polarization and discuss its influence on cell temperature, oxygen transport and water management. Similarly, we investigate the polytetrafluoroethylene (PTFE) content in the GDM and the influence of hydrophobicity on cell water management and performance in a broad range of anticipated flight conditions. We use cyclic voltammetry and AC impedance spectroscopy to characterize performance losses associated with GDM properties to guide GDM selection.
Development of Highly Active and Stable Compressive Pt Cathode Catalyst for Pemfcs
Authors: Kim Taekeun , Popov Branko N
Published: February 2020

Cathode durability, cost, and performance are some of the key issues preventing the commercialization of polymer electrolyte membrane fuel cells (PEMFCs) for automotive applications. The support degradation during start-up/ shut-down and the catalyst degradation during driving potential cycling limit overall cathode catalyst lifetime. The ultra-low Pt cathode catalyst development project at the University of South Carolina (USC) has developed highly-stable activated carbon composite supports (ACCS) as well as highly-active and stable compressive Pt lattice cathode catalysts, Pt*/ACCS (Pt* = Compressive Pt lattice catalyst) that retain their activity after accelerated stress tests (AST) to simulate start-up/shut-down and driving potential cycling [1-7].

The novel USC technology is based on a two-step patented process. In the first step, the following major constraint was addressed: the support should be chemically and electrochemically stable at high potentials, low pH, and high temperature. To accomplish these requirements, ACCS was synthesized with optimization of: (i) BET surface area, porosity, pore-size and distribution, (ii) hydrophilic/ hydrophobic ratio, (iii) structural properties (amorphous/ crystalline ratio), and (iv) Pt-support interaction through inclusion of active surface functional groups.

In the second step, compressive Pt lattice catalyst (Pt*) was synthesized through a USC-developed annealing procedure that controls the particle size during annealing and forms several monolayers of Pt* by diffusing Co atoms into Pt which is deposited on ACCS support. The Pt*/ACCS shows high rated power density (0.174 gPt kW−1), excellent support stability (8 mV loss at 1.5 A cm−2), and enhanced catalyst durability (24 mV loss at 0.8 A cm−2) under AST conditions.

References

[1] T. Kim, B. N. Popov, Int. J. Hydrogen Energ., 41 (2016) 1828-1836.

[2] T. Kim, T. Xie, W. Jung, F. Gadala-Maria, P. Ganesan, B.N. Popov, J. Power Sources, 273 (2015) 761-774.

[3] W. Jung, T. Xie, T. Kim, P. Ganesan, B.N. Popov, Electrochim. Acta, 167 (2015) 1-12.

[4] T. Xie, W. Jung, T. Kim, P. Ganesan, B.N. Popov, J. Electrochem. Soc., 161 (2014) F1489-F1501.

[5] Á. Kriston, T. Xie, B. N. Popov, Electrochim. Acta, 121 (2014) 116-127.

[6] Á. Kriston, T. Xie, D. Gamliel, P. Ganesan, B. N. Popov, J. Power Sources, 243 (2013) 958-963.

[7] Á. Kriston, T. Xie, P. Ganesan, B. N. Popov, J. Electrochem. Soc., 160 (2013) F406-F412.

Figure 1
(Invited) Membrane Development and Transport Study for Redox Flow Batteries
Authors: Wang Wei
Published: February 2020

This presentation describes the membrane development and transport study at PNNL for the redox flow batteries. Several topics will be covered in the talk including the development of the PTFE/SiO2 porous separator and the research on the correlation between the Nafion membrane microstructure and the vanadium redox flow battery performance. The impact of the equivalent weight on the microstructure of the membrane and thus the performance of VRBs is systematically studied. By tailoring the equivalent weight and membrane thickness, the new membrane contains optimal pore geometry with extremely low vanadium-ion permeability was developed. In addition, its area resistance is comparable to, and its cost is significantly less than, the widely used Nafion 115 membrane. Excellent VRB single-cell performance (89.3% energy efficiency at 50mA∙cm-2) was achieved along with a stable cyclical capacity over prolonged cycling (>200 cycles). The chemical composition (Figure 1), pore geometry, transport properties and flow cell performance will be reported.

In addition, a detailed study on the ions transport behavior across the membrane and its impact on the redox flow battery performance will be presented, using vanadium redox flow battery as an example. In operando study on the vanadium ion crossover unveiled the mechanisms contributing to the battery capacity fading, as well as the state-of-charge changes along cycling. The studies were carried out on various membranes, such as cation exchange membrane and porous separators.

Figure 1.
19F MAS-NMR spectra measured at an 11.7 T magnetic field with a spinning speed of 13.5 kHz for NDM142, NDM220, and NDM221 membranes.  The circles and red line represents the experimental spectra and the fitted curve with deconvolution analysis, respectively (see text for details).  The asterisk (*) indicates MAS spinning side bands.

Figure 1
Stability and Efficiency Improvement of Sulfonated Poly(para-phenylene): Study of Random Co-Polymer for Proton Exchange Membrane for Fuel Cell
Authors: Skalski Thomas , Britton Benjamin , Peckham Timothy J , Holdcroft Steven
Published: February 2020

Sterically-encumbered, sulfonated poly(phenylene)s are an interesting group of hydrocarbon materials for use in low Pt-content catalyst layers because they potentially offer high conductivity, high thermo-oxidative stability, and appear less-prone to strong adsorption on Pt – a process that typically reduces the electroactive surface area. Frequently, polymers like poly(phenylene)s are randomly post-functionalized in order to introduce proton-conducting properties.(1-3) However, as randomly-functionalized materials are not ideal as proton conductors, a new synthetic route has been developed in order to obtain well-defined pre-functionalized monomers for the synthesis of sulfonated poly(phenylene)s. Using a variety of NMR pulse sequences, the isomers resulting from different couplings (e.g., meta-meta) of arylene moieties has been studied through an examination of several small molecule, model compounds. Furthermore, a series of random copolymers has been made in which the ionic content was varied by alteration of the monomer feed ratios. Finally, the properties (e.g., proton conductivity, chemical stability, fuel cell performance as membrane and catalyst ionomer) have been extensively studied.(4)

(1) Maier, G.; Meier-Haack, J. Advances in Polymer Science
2008, 216, 1

(2) Otsuki, T.; Kanaoka, N.; Iguchi, M.; Mitsuta, N.; Soma, H.; (Honda Motor Co., Ltd., Japan; JSR Corporation). Application: US, 2004, 13

(3) Fujimoto, C. H.; Hickner, M. A.; Cornelius, C. J.; Loy, D. A. Macromolecules
2005, 38, 5010

(4) T. J. G. Skalski, B. Britton, T. J. Peckham and S. Holdcroft, Journal of the American Chemical Society, 2015, 137, 12223

Figure 1
High Performance, High Catalyst-Efficiency Hydrocarbon Fuel Cells
Authors: Holdcroft Steven , Britton Benjamin , Skalski Thomas
Published: February 2020

While perfluorinated sulfonic acid (PFSA) membrane and ionomer materials such as Nafion® form the standard for high-performance proton-exchange membrane fuel cells (PEMFCs), the limited and difficult chemistry of perfluorinated materials hampers further material development to extended fuel cell performances and lifetimes, while the high cost of perfluorinated materials contributes to the cost barrier limiting the ubiquity adoption of fuel cells for energy generation. One method of reducing cost is the US Department of Energy target of 0.0625-0.125 mg PGM/cm2 as a catalyst loading. However, at low to ultra-low catalyst loadings, PFSAs exhibit a substantial increase in resistivity attributed to oxygen mass transport losses, particularly in the far Ohmic region of polarization data, causing disproportionate reductions to achievable power densities.

Hydrocarbon proton-exchange materials offer the potential for solutions to material issues inherent to PFSAs, with established, varied chemistry allowing for versatile material innovation. Properties such as lower fuel crossover and improved operation in desirable operational conditions such as reduced relative humidity (RH) or high temperature has been well established. Together with the lower cost of basic materials and the ability to recycle catalyst layers, these properties make the demonstration of high performance, fully hydrocarbon PEMFC operation significantly of interest to the field.

Here, hydrocarbon proton-exchange materials are shown that exhibit significant radical stability and high conductivities. Furthermore, these materials form thin membranes and are soluble in low-boiling, polar solvents necessary for incorporation as ionomer into catalyst inks that create high-quality catalyst layers. MEAs and catalyst layers were formed, incorporated into fuel cells, and characterized in situ by IV polarization, CV, CA, LSV, and EIS, and ex situ by mercury porosimetry and SEM. As ionomers, these exhibit reduced mass transport losses compared to PFSA ionomers, a result of substantially smaller increases to oxygen mass transport losses than PFSAs exhibit as catalyst layer loadings are decreased. As fully hydrocarbon fuel cells, improved interfaces lead to improved water transport and lower total resistivity attributable to membrane and ionomer congruency, thereby achieving higher power densities than directly comparable PFSA references using rigorously optimized conditions and catalyst loadings. These high-performance hydrocarbon proton-exchange materials may thereby represent a fully hydrocarbon alternative to PFSA materials for hydrogen fuel cells.
Development of Highly-Reliable Hydrocarbon-Based Membrane for Polymer Electrolyte Fuel Cells
Authors: Umeda Hiroaki , Adachi Shinya , Izuhara Daisuke
Published: February 2020

Toray had been developing highly-reliable hydrocarbon-based (HC) membrane for PEFC in NEDO FY2013-2014 Next Generation Project. Newly-developed HC membrane using newly-developed organic peroxide decomposition catalysts showed higher cell performance under high temperature and low humidity condition, and more than 5.2 times higher chemical durability, in comparison with the reinforced PFSA membrane NafionHPas a reference membrane. Consequently, newly-developed HCmembrane accomplished the FY2014 target of NEDO Project on both cell performance and chemical/mechanical durability.

Acknowledgement: This work was partially supported by the New Energy and Industrial Technology Development Organization (NEDO) of Japan.
Proton Exchange Membranes Based on Polymeric Ionic Liquids for Fuel Cell Applications
Authors: Ortiz Sainz De Aja Alfredo , Díaz Vejo Mariana , Ortiz Uribe Inmaculada
Published: February 2020

One of the most promising technologies for power generation are Proton Exchange Membrane Fuel Cells (PEMFCs). PEMFCs are electrochemical devices which convert directly the chemical energy of oxidation-reduction reactions into electrical energy. These electrochemical devices have high electric efficiency and low environmental impact [1].

Several authors are working in the upcoming commercialization of this technology. However, there are technical aspects that must be overcoming before their implementation. The proton exchange membrane, which is the key component of a PEMFC, needs a considerable improvement regarding its performance without external humidification [2]. This is of great importance because it allows working at temperatures above 80 ºC and eliminate the management of water.

Concerning this aspect, many authors are working incorporating ionic liquids as proton exchange components in PEMFCs. Ionic liquids, which are in liquid state at room temperature, have attractive properties for this application, such as thermal and electrochemical stability and high anhydrous conductivity.

There are several strategies in order to incorporate ionic liquids inside the proton exchange membrane. One of them deals with the polymerization of an ionic liquid monomer [3]. This option avoids the leak of the ionic component during the fuel cell operation.

In this work, membranes based on polymeric ionic liquids have been designed for their use as electrolytes without external humidification. For this purpose, the ionic liquids 1-(4-sulphobutyl)-3-vinylimidazolium trifluoromethanesulphonate [HSO3-BVIM][OTF], 1-sulfobutyl-3-metylimidazolium 2-sulfoethylmethacrylate [SBMIm][SEM] and 1-sulfobutyl-3-vinylimidazolium 2-sulfoethylmethacrylate [SBVIm][SEM] were polymerized under ultraviolet light. The ionic conductivity and fuel cell performance were tested without external humidification.

References

[1] Z. Wojnarowska, J. Knapik, M. Díaz, A. Ortiz, I. Ortiz, M. Paluch, Macromolecules, 2014, 14, 4056-4065.

[2] M. Díaz, A. Ortiz, I. Ortiz, J. membra. Sci., 2014, 469, 379-396

[3] D. Mecerreyes, Prog. Polym. Sci., 2011, 36, 1629-1648.

 

Acknowledgements

This research was supported by the Ministry of Education and Science under the project CTQ2012-31639 (MINECO, SPAIN-FEDER 2001-2013). Mariana Díaz also thanks MINECO for the FPU fellowship (AP2012-3721).
Proton-Conducting SnP2O7 Electrolyte for Intermediate Temperature PEMFC Under Low Humidificatio
Authors: Lee Kwan-Soo , Kim Yu Seung , Kreller Cortney R , Wilson Mahlon S. , Mukundan Rangachary
Published: February 2020

Current fuel cells for transportation and residential applications use polymer electrolyte membrane fuel cells (PEMFCs) which require platinum catalysts and operate below 80 °C due to water management issues. However, PEMFCs operating at 100 °C or higher temperatures in anhydrous conditions do not need a humidifier, and do not suffer from water management issues created by the presence of liquid water. Excessive amount of liquid water in the electrode can flood the backing and catalysts layers at lower temperatures leading to poorer fuel cell performance. Furthermore, such intermediate temperature PEMFCs can solve the problem of carbon monoxide (CO) poisoning of the anode electrocatalyst leading to relaxation of the hydrogen fuel quality standards, thus lowering infrastructure costs. Finally, higher operating temperatures allow for simpler cooling systems in transportation applications, which results in smaller and lighter radiators. These advantages mean that a paradigm shift in fuel cells for transportation and residential applications can be achieved with an intermediate temperature proton conducting solid-electrolyte that can operate above 150 °C.

Unfortunately, electrolyte membranes and ionomers developed so far do not have satisfactory conductivity and performance in the above temperature ranges, at low-humidity, or in non-humidified conditions. The further advancement of higher temperature PEMFCs relies on the development of membranes that possess the desired electrochemical and mechanical properties in dry (< 30% RH) and hot (> 100 oC) conditions.

In this study, we have developed an organic/inorganic composite membrane using a SnP2O7 (TPP) inorganic conductor and evaluated the fuel cell performance under various conditions. Membrane electrode assemblies (MEA) were prepared from these membranes and gas diffusion electrodes (GDE) were optimized using either LANL ionomer dispersion or various commercial gas diffusion layer (GDL). A maximum power density (> 600mW/cm2 ) has been obtained for fuel cell operation at ≈ 220 oC under less than 2 % humidification condition.
Enhancement of ORR Activity and Durability of Pt Single Crystal Electrodes Modified with Alkylamines
Authors: Saikawa Keiichiro , Nakamura Masashi , Hoshi Nagahiro
Published: February 2020

1. Purpose

 Fuel cell is high-efficiency and clean energy system. However, high overpotential of oxygen reduction reaction (ORR) and large Pt loading in electrocatalyst are grave issues for the general use.

 Miyake et al. reported that platinum nanoparticles modified with octylamine (OA) and alkylamine with pyrene group (PA) give higher activity and durability at the molar ratio OA/PA=7/3 compared with bare Pt nanoparticles [1]. However, the platinum nanoparticles are not shape controlled or well-defined. We have investigated surface structures which enhance the ORR activity and durability using Pt single crystal electrodes modified with OA/PA. The surfaces examined are Pt(100), Pt(110), Pt(111), Pt(331)=3(111)-(111) that has the highest ORR activity [2] and Pt(775)=7(111)-(111). In the notation of high index planes such as n(hkl)-(mno), the value of n, Miller indices (hkl) and (mno) show the number of terrace atomic rows, the structures of terrace and step, respectively.

 

2. Experimental

 Linear sweep voltammograms of the ORR were measured with rotating disk electrode (RDE). Potential was scanned from 0.05 V (RHE) to 1.0 V (RHE) at scanning rate 0.010 V s-1 and rotation rate 2000 rpm. The activity for the ORR was estimated using the specific activity at 0.90 V (RHE) j
k according to the Koutecky-Levich equation.

 Durability test was conducted using rectangular wave from 0.60 V step to 1.0 V.

 All the potentials were referred to RHE.

 

3. Result and Discussion

 The ORR activities of Pt(111) modified with OA/PA = 9/1, 8/2, 7/3 (molar ratio) were twice or three times higher than that of bare Pt(111). The ORR activity increases with the increase of the ratio of PA. The activity of Pt(775) = 7(111)-(111) modified with OA/PA=9/1 was also higher than that of bare Pt(775). Pt(100) and Pt(110) modified with OA/PA=9/1 gave lower ORR activity than bare electrodes. These results show that PA on wide (111) terrace enhances the ORR activity.

 The ORR activity of Pt(111) was enhanced after the durability test because active (110) type defects are formed on the surface. The ORR activity of Pt(111) modified with OA/PA was 1.8 mA/cm2 after 2000 cycles, higher than that of bare Pt(111) 1.0 mA/cm2. Adsorbed amines on wide (111) terrace preserved the high activity after the durability test. The activity after 2000 cycles decreased with the increase of the ratio of PA. This result differs from the previous study [1]. The ORR activity of Pt(775) modified with OA/PA was as high as that of bare Pt(775) after the durability test.  Durability of Pt(775) was not improved by OA/PA modification.

 

4. Acknowledgement

 This work was supported by New Energy Development Organization.

 

5. References

[1] K. Miyabayashi, H. Nishihara, M. Miyake, Langmuir, 30, 2936 (2014)

[2] N. Hoshi, M. Nakamura, A. Hitotsuyanagi, Electrochim. Acta, 112, 899 (2013)
Effects of Transition Metal Doping in Pt/M-TiO2 (M = V, Cr, and Nb) on the Oxygen Reduction Reaction
Authors: Jung Sang-Mun , Kim Jun-Hyuk , Kim Yong-tae
Published: February 2020

High cost and low durability are unresolved issues that impede the commercialization of proton exchange membrane fuel cells (PEMFCs). To overcome these limitations, Pt/TiO2 is reported as an alternative electrocatalyst for enhancing the oxygen reduction reaction (ORR) activity and/or durability of the system. However, the low electrical conductivity of TiO2 is a drawback that may be addressed by doping. To date, most reports related to Pt/doped-TiO2 focus on changes in the catalyst activity caused by the Pt-TiO2 interaction (metal-support interaction), instead of the effect of doping itself; doping is merely considered to enhance the electrical conductivity of TiO2. In this study, we discuss the variation in the electronic fine structure of Pt caused by the dopant, and its correlation with the ORR activity. More extensive contraction of the Pt lattice in Pt/M-TiO2 (M = V, Cr, and Nb) relative to Pt/TiO2 and Pt/C leads to outstanding ORR specific activity of Pt/M-TiO2. Notably, a fourfold increase of the specific activity is achieved with Pt/V-TiO2 relative to Pt/C. Furthermore, an accelerated durability test (ADT) of Pt/V-TiO2 demonstrates that this system is three times more durable than conventional Pt/C due to the metal-support interaction.
Synthesis of Pt Catalysts Supported on W/Ta-Doped TiO2 As a Highly Durable Electrocatalyst for PEFCs
Authors: Ketpang Kriangsak , Kakinuma Katsuyoshi , Iiyama Akihiro , Uchida Makoto
Published: February 2020

One of the technical problems impeding commercial use of polymer electrolyte fuel cells (PEFCs) is the degradation of the carbon support under startup/shutdown (SU/SD) conditions, which leads to severe and eventually drastic reduction of the performance due to agglomeration, dissolution, or detachment of Pt nanoparticles. Thus, nanoceramic supports (NCSs) with both high electrical conductivity and durability under SU/SD operating conditions have been actively developed to replace the commercial carbon support.[1-6] Titanium dioxide (TiO2) doped with aliovalent cations is also a candidate as a high durability cathode NCS. We synthesized Pt catalysts supported on tantalum and tungsten-doped TiO2with unique microstructure, involving a fused-aggregated network, and evaluated the oxygen reduction reaction (ORR) activity and durability under SU/SD operation conditions.

We prepared the NCSs by a flame spray synthesis method. The morphology of the NCSs, which was investigated by use of transmission electron microscopy (TEM), had nanoparticles with a partially fused aggregated network structure, similar to that of carbon black (Fig. 1(a)(b)). The crystal structures of the NCSs included rutile and anatase. The surface areas, which were estimated using the Brunauer-Emmett-Teller (BET) technique, were greater than 30 m2g-1. The electrical conductivities, which were measured by use of the two-probe method, were as high as 10-4 S/cm at room temperature under a pressure of 19 MPa (Fig. 2). The NCSs were confirmed to be extremely stable in 1.0 M H2SO4 at 80 oC under air atmosphere. Pt nanoparticles, which were loaded on the NCSs by a colloidal method, were uniformly dispersed on the surface (Fig. 1(c)(d)). The Pt loadings were 19 wt% (Pt/Ta-TiO2) and 19.4 wt% (Pt/W-TiO2), determined by ICP-MS. Pt particle sizes were 4 nm (Pt/Ta-TiO2) and 10 nm (Pt/W-TiO2), determined by TEM. The ORR activity increased with increasing heat treatment temperature and reached that of a commercial carbon-supported Pt catalyst (c-Pt/CB). The durability of Pt/Ta-TiO2 under SU/SD conditions was superior to that of the c- Pt/CB.

Figure 1
A Successive One-Pot Synthesis of Au@Pt - q ML/C with Enhanced Ethanol Oxidation Activity in Alkaline Media
Authors: Wu Kuang-Heng , Wang Han , Jiang Bei , Cai Wen-Bin
Published: February 2020

Direct ethanol fuel cells raise the possibility for clean and high efficient energy utilization. Noble Pt-group metals are still essential for electrocatalysts related to such fuel cells. Yet, the high cost and limited reserve of Pt-group metals (especially Pt) as well as the sluggish oxidation kinetics of ethanol molecule call for facile synthesis of low-Pt-content efficient catalysts. Both experimental and simulated investigations suggested alcohol oxidation activity could be improved by coating a monolayer (ML) of Pt on Au [1]. To address the major challenge of scalable synthesis of practical carbon-supported catalysts, here we report a successive and convenient synthesis of Au@Pt-qML/C (qML: quasi-monolayer) using CO as the reducing and capping agents for Pt-qML deposition on Au/C [2]. The Au core with an average diameter of ca. 5 nm was first obtained by reducing HAuCl4 with NaBH4, and Pt-qML was later coated on Au surfaces in one pot through introducing CO and controlled amount of Pt(II). The Au core- Pt shell structure was examined through XRD, EDX, IR and electrochemical measurements. A remarkable enhancement towards ethanol oxidation reaction was obtained on the as-formed Au@Pt-ML/C as compared to that on the state-of-the art commercial Pt/C.

Acknowledgements
：Financial supports from NSFC (grant No. 21273046 and 21473039）and the 973 Program (No. 2015CB932303) of MOST are highly appreciated

References:

[1] M. Li, P. Liu, R.R. Adzic, J. Phys. Chem. Lett., 3, 3480 (2012).

[2] H. Wang, K. Jiang, Q.L. Chen, Z.X. Xie, W.B. Cai. Chem. Commun., 
52, 374 (2016).

Figure 1