bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiscale Model of Proton Transport in Perfluorosulfonic-Acid Membrane
Authors: Crothers Andrew Robert , Radke Clayton J. , Weber Adam Z
Published: February 2020

To optimize polymer-electrolyte-fuel-cell performance, it is critical to improve transport properties of the polymer membrane. The typical fuel-cell membrane is a perfluorosulfonic-acid ionomer that consists of a hydrophobic backbone with hydrophilic side chains terminated by a sulfonic acid group. The polymer phase separates into hydrophilic domains that are on the order of nanometers and enables water and proton transport around the surrounding hydrophobic matrix that provides structural integrity. Although there have been concerted efforts to use molecular-level theory and simulations to understand ion and water transport inside a single pore, there is a need to develop a robust multiscale methodology to bridge molecular descriptors through mesoscale structures to macroscopic properties. In this poster, we present a methodology for such an approach.

Building on previous multiscale modeling efforts1, we use a resistor-network paradigm to describe ionomers as a network of conductive nodes and throats. The effective network resistance is a function of the connectivity of the network and transport resistance between each neighboring node. We use common imaging methods to extract the network geometry from direct imaging of the ionomer2. Molecular theory and simulations are used to describe and calculate the proton conductivity in throats as a function of size. Kirchhoff's circuit laws are applied on each node in the system and the effective resistance across the membrane is determined for ion conduction. Once designed, a poroelastic model is used to change node and throat sizes and subsequent network connectivity with water content and swelling.

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 and by a National Science Foundation Graduate Research Fellowship under Grant No. DGE 1106400

Citations

[1] J. T. Gostick and A. Z. Weber, “Resistor-Network Modeling of Ionic Conduction in Polymer Electrolytes,” Electrochimica Acta.

[2] F. I. Allen, L. R. Comolli, A. Kusoglu, M. A. Modestino, A. M. Minor, and A. Z. Weber, “Morphology of Hydrated As-Cast Nafion Revealed through Cryo Electron Tomography,” ACS Macro Lett., vol. 4, no. 1, pp. 1–5, Jan. 2015.

Figure 1. 3D projection of pore-network generated from skeletonization of cryo-TEM tomography image of Nafion ionomer. The green cylinders show throats of the hydrophilic network connecting nodes, shown as red balls. The background is a cutaway of the network where blue is the hydrophilic domain and black the hydrophobic backbone.

Figure 1
Improved Performance of Alkaline Membrane Fuel Cells
Authors: Watanabe Shin , Kikkawa Yuki , Oda Kengo , Okamura Takaaki
Published: February 2020

We have been developing materials for Alkaline membrane fuel cells(AMFCs) for about 10 years. AMFC is one of the polymer electrolyte fuel cells (PEFCs) which uses anion exchange membrane and anion conductive ionomer as polymer electrolyte materials. AMFC has some advantages over proton-exchange membrane fuel cells(PEMFC) 1-2).

(1) The high pH environment of AMFC allows the use of non platinum catalysts.

(2) The kinetics of the ORR reaction is more facile in alkaline environment than in acidic environment.

  AMFC has been  attracting worldwide attentions, and the number of report is  increasing year by year.

  We have already demonstrated the relatively high AMFC performances with hydrogen fuel, and have confirmed several features specialized to AMFC, namely CO2 self-purging phenomena3), which could be a solution against serious CO2
problem in AMFC4-6), and the effective water transport from anode to cathode side, which prevent the lack of water needed for cathode reaction7).

  To make the AMFC being popular FC, there are some issues to be resolved.

a) Few low-cost non-Pt or non-precious metal catalysts are known.

b) Low power density.

c) Low durability of electrolyte materials.

  The  absence of  good HOR catalysts with non precious metal is an big issues for the people in this field. But, with the considerable efforts for the development of  electrolyte materials, the operating conditions and so on, some researchers have achieved the power density of  1W/cm2
8).

  Now, we are focusing on the durability of electrolyte materials. The corsslinking between polymer chains  is one of  an effective way to improve the durability of electrolyte materials. We have  investigated some aspects of crosslinking reagents, and have achieved some improvement on the durability of  electrolyte materials for AMFC.

References

H. A. Gasteiger , FC-EXPO 2008, Technical conference fc-10.

J. R. Varcoe, R. C. T. Slade, E. Lam How Yee, S. D. Poynton, D. J. Driscoll, D. C. Apperley, Chem.  Mater., 19, 2686 (2007)

L. A. Adams, S. D. Poynton, C. Tamain, R. C. T. Slade, J. R. Varcoe, ChemSusChem, 1, 79 (2008).

H. Yanagi, K. Fukuta, ECS transactions, 16, 257 (2008).

K. Fukuta, H. Inoue, S. Watanabe, H. Yanagi, ECS transactions, 1
9, 23 (2009).

H. Yanagi, S. Watanabe, K. Sadasue, T. Isomura, H. Inoue, K. Fukuta, Abstract of 216th ECS Meeting, #341 (2009).

T.Isomura, K.Fukuta, H.Yanagi, S.Ge and C.Y. Wang, Abstract of 219th ECS Meeting, #221 (2011).

Y. Wang, G. Wang, G. Li, B. Huang, J. Pan, Q.Liu, J. Han, L. xiao, J. Lu, L. Zhuang, Enegy Environ. Sci. 8,177(2015)
Adsorption Behavior of Nafion Ionomers on Au and Pt Surfaces
Authors: Masuda Takuya , Uosaki Kohei
Published: February 2020

Adsorption behavior of perfluorosulfonated ionomer, i.e., Nafion, on gold and platinum electrode surfaces was investigated by various techniques including cyclic voltammetry, electrochemical quartz crystal microbalance, and electrochemical atomic force microscopy in an aqueous solution containing Nafion as an only electrolyte without any other electrolyte. It was shown that Nafion acts as an aqueous electrolyte and electrochemical measurements can be performed in this solution.

Nafion did not adsorb on the gold surface at 0 V (vs. Ag/AgCl) and started to adsorb at 0.45 V in a lying-down configuration. The adsorbed amount increased as the potential was made more positive. In the potential range between 0.75 and 1.0 V, Nafion aggregated at the surface. Those aggregated Nafion desorbed from the surface by keeping the potential at 0 V.

Nafion also desorbed from the surface upon the gold oxide formation. When the gold oxide was reduced, Nafion re-adsorbed on the surface. Thus, adsorption behavior of Nafion is similar to that of the sulfate anion, implying that sulfonate groups of Nafion play an important role in adsorption of Nafion on gold surfaces.

In contrast, Nafion adsorbed on the platinum surface without any significant morphology change in the potential range between 0.1 and 0.8 V despite the fact that the adsorbed amount of the sulfate anion increases as the potential goes more positive. When the potential was kept at 1.1 V where the place-exchange oxide is formed, Nafion desorbed from the surface. Once the platinum oxide was reduced, Nafion re-adsorbed on the surface.

The interaction of fluorocarbon chains on a bare platinum surface and the desorption of Nafion upon the oxide formation were confirmed by surface x-ray scattering in an MEA-like configuration.

References:

  1) T. Masuda, K. Ikeda, K. Uosaki, Langmuir,
2013,
29, 2420.

  2) T. Masuda, H. Fukumitsu, T. Kondo, H. Naohara, K. Tamura, O. Sakata, K. Uosaki, J. Phys. Chem. Soc.,
2013,
117, 12168-12171.

  3) T. Masuda, F. Sonsudin, P. R. Singh, H. Naohara, K. Uosaki, J. Phys. Chem. Soc.,
2013,
117, 15704-15709.
Comparison of Electrocatalytic Properties of PtCo/Graphene Catalysts for Ethanol, Methanol and Borohydride Oxidation
Authors: Kepeniene Virginija , Tamasauskaite-Tamasiunaite Loreta , Antanaviciute Kornelija , Balciunaite Aldona , Norkus Eugenijus
Published: February 2020

In this study the graphene supported PtCocatalysts (denoted as PtCo/GR) with diferent molar ratios of Pt and Co were fabricated by means of the rapid microwave heating method with the aim to use them in an alkaline fuel cells, using ethanol, methanol and borohydride as fuel.The synthesized catalysts were examined by Transmission Electron Microscopy, X-ray Ddiffraction and Inductively Coupled Plasma Optical Emission Spectroscopy. The electrochemically active surface areas of the prepared catalysts were determined from the cyclic voltammograms of the different PtCo/GR catalysts recorded in a deaerated 0.5 M H2SO4 solution at a sweep rate of 50 mV s–1 by calculating the charge associated with the hydrogen adsorption (220 µg cm-2). The electrocatalytic activitiy of the synthesized catalysts was investigated towards the oxidation of ethanol, methanol and borohydride in an alkaline medium by means of cyclic voltammetry and chronoamperometry.

It was found that the PtCo/GR catalysts with an average particle size of ca. 1-3 nm were synthesized by means of microwave heating of Pt(IV) and Co(II) salts in ethylene glycol solutions. The synthesized PtCo/GRcatalysts with the different Pt:Co molar ratios show an enhanced activity towards the oxidation of H2 generated by catalytic hydrolysis of BH4
– and direct oxidation of BH4
– ions as well as methanol and ethanol oxidation as compared with that at the graphene supported bare Co and Pt catalysts. It should be noted that the electrocatalytic activity of the PtCo/GR catalysts depends on the molar ratio of Pt:Co in the catalysts and type of fuel.
Tailored DC/Sputtered Niobium Oxide Properties for PEM Electrolysis Application
Authors: Ion-Ebrasu Daniela , Enache Stanica , Rizoiu Alexandru , Filip Mihaela , Preda Silviu , Varlam Mihai , Fruth Victor , Stefanescu Ioan
Published: February 2020

The fast renewable energy source penetration is creating often mismatch in grid power demand, and is making the case for new energy storage solutions. Hydrogen-based energy conversion technology is considered the most tenable large and long-term scale alternative, and proton exchange membrane (PEM) water electrolysis is seen as one of the most efficient and simple ways to obtain high purity hydrogen [1]. An important drawback in these systems is represented by the oxygen evolution reaction (OER) that is strongly influenced by the catalysts stability against oxidation potential [2].

The aim of this work was to tailor the niobium oxide properties using DC-magnetron sputtering deposition, and to correlate its structure with their electrocatalytic activity toward the Oxygen Evolution Reaction for PEM Electrolyser applications. The influence of the working parameters (deposition pressure, sputtering power and thickness) towards catalysts structure is studied by Uv-Vis and FTIR spectroscopy, X-ray diffraction (XRD), SEM, Rutherford Back Scattering experiments, and four-points resistivity measurements. AC impedance measurements, and cycling voltammetry for electrochemical surface area (ECSA) determination is carried out. The Niobium oxides are deposited on various substrates from transparent (optical glass) for optical and electrical measurements, to highly conductive glassy carbon for compositional and electrochemical investigations.

[1] C. Rozain Caroline, P. Millet, Electrochimica Acta, 131 (2014) 160-167.

[2] V. K. Puthiyapura,, S. Pasupathi, S. Basu, X. W, H. Su, N. Varagunapandiyan, B. Pollet, K. Scott, Int. J. of. Hydrogen Energy, 38 (2013) 8605-8615.
PEM-Type Water Electrolysis/Fuel Cell Reversible Cell with Low PGM Catalyst Loadings
Authors: Ioroi Tsutomu , Yasuda Kazuaki
Published: February 2020

To utilize fluctuating renewable energy stably and effectively, large-scale energy storage systems such as Li-ion, redox-flow and Na-S batteries have been extensively studied.  Battery storage system have advantages of high efficiency in energy utilization and rapid response for energy demand, however initial system cost tend to be expensive.  Electrochemical hydrogen production and storage is recently attracting attentions as another practical technology because of high energy efficiency of electrochemical water splitting, relatively low technological barrier for large-scale storage, and ease of long-term energy storage and long-range transport without self-discharge. 

Regenerative fuel cell is an energy storage system using hydrogen as an energy medium.  In particular, reversible (unitized) regenerative fuel cells (RFCs) can be functioned both as water electrolyzer and fuel cell in the same electrochemical cell by switching the operation mode, so that much more compact and cheaper system could be realized.  In the PEM-type RFC, unsupported platinum/iridium-based catalysts are usually selected in terms of activity and stability for both operation modes.  Loading amount of platinum group metals (PGMs) of RFC is relatively high (typically >1 mg cm-2) compared to the fuel cell dedicated system due to stability issue at high potentials during OER.  Therefore, reducing PGM loadings without expense of performance and durability is high priority to meet the capital cost of the systems. 

To reduce the PGM loadings of oxygen electrode of RFC, we examined electro-conductive Magneli phase titanium oxides (in particular Ti4O7) as a catalyst support material [1,2].  High surface area oxide support was prepared by UV laser technique; TiO2 nano particles dispersed in an appropriate solvent (typically acetonitrile) are reduced by pulsed UV laser irradiation [3].  Pt, Ir, and Pt-Ir alloy nano particles were deposited on the oxide support, and their electrocatalytic activities were examined by rotating disk electrode and MEA.  Ti4O7-supported Pt catalyst showed 3 times larger electrochemical active area (ECA) than that of commercially available Pt black, and 2.9 and 2.4-fold mass activity was obtained for ORR@0.9V and OER@1.7V, respectively.  Initial ORR/OER cycle durability test was conducted for Pt/Ti4O7 catalyst MEA at 80oC between >1.8V for OER and <0.8V for ORR, and almost no performance loss was observed.  These results show titanium oxide based materials can be applied as RFC catalyst support, which leads to effective use and lowering PGM loading in the oxygen electrode.

References

1. G. Chen, S. Bare, T. Mallouk, J. Electrochem. Soc., 149, A1092 (2002).

2. T. Ioroi, T. Akita, M. Asahi, S. Yamazaki, Z. Siroma, N. Fujiwara, K. Yasuda, J. Power Sources, 223, 183 (2013).

3. T. Ioroi, H. Kageyama, T. Akita, K. Yasuda, Phys. Chem. Chem. Phys., 12, 7529 (2010).
Dual Nafion/Polyaniline Nanofibers Architecture for Applications in Fuel Cells Electrodes
Authors: Simotwo Silas , Kalra Vibha
Published: February 2020

We demonstrate a facile route for fabrication of nanostructured fuel cell cathode catalyst support via simultaneous co-electrospinning of electron and proton conducting materials. Solutions of Nafion and polyaniline (PANI) were electrospun simultaneously from two separate nozzles on a common substrate with the aim to develop co-percolating electron and proton conducting pathways. Owing to the lack of entanglements in Nafion and PANI solutions, PEO was used to aid in electrospinning of both solutions. The composition of the dual nanofiber mat was tailored by varying the relative solution concentrations and flow rates. SEM micrographs (fig.1 (a)) of the mats show three-dimensional porous non-woven morphology, which is ideal for facile gas transport and also for enhancement of the triple phase surfaces. Electrochemical impedance spectroscopy show presence of independent charge transfer channels in the composite fiber mats (fig.1 (b)). Equivalent circuits were used to decouple electrical conductivity from protonic conductivity. Electrical conductivity was also verified via current/voltage (I-V) curves. Dual fiber mat with a Nafion/PANI/PEO composition of 50/32/18 showed proton conductivity of 0.032 S/cm and electron conductivity of 0.042 S/cm. Such proton conductivity was shown to be higher than the pure Nafion (with 2wt% PEO as the carrier polymer) nanofiber mat. The dual fiber mat also showed the highest water intake capacity (presumably due to its high composition of the hydrophilic PEO), which we believe is responsible for its higher proton conductivity. Such dual fiber mats with percolating phases of both electron and proton conductors and a three dimensional through–connected inter-fiber pore structure (for gas transport) can serve as an excellent catalyst support for PEMFCs.

Figure 1 Nanofiber mat with a Nafion/PANi/PEO weight composition of 50/32/18 (a): SEM micrograph, Scale bar; 1µm, b) Nyquist plot  showing experimentally-obtained data and fitted impedance data obtained via an equivalent circuit.

Figure 1
Electrochemical Impedance Spectroscopy as a Diagnostic Tool for High-Temperature PEM Fuel Cells
Authors: Mack Florian , Laukenmann Ruben , Galbiati Samuele , Kerres Jochen A. , Zeis Roswitha
Published: February 2020

The high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC) continues to attract great interest as an alternative power source for stationary and auxiliary applications. The operating temperature of HT-PEMFCs ranging from 140 °C to 200 °C offers several advantages compared with low-temperature (<100 °C) PEMFCs such as higher tolerance to impurities like carbon monoxide (CO) and simplified water management. HT-PEMFCs based on phosphoric acid doped polybenzimidazole (PBI) membranes are so far the most promising candidates for practical high-temperature operation. For commercialization, however, the performance and long-term stability of the high-temperature membrane electrode assemblies (MEAs) still need significant improvement. To achieve this goal, suitable analytical tools to evaluate single cells and their components are critical for the MEA developers.

One such basic tool is electrochemical impedance spectroscopy (EIS). The technique is highly versatile, and instruments are widely available in electrochemistry laboratories. Here we present the capability of EIS to analyse the performance of high-temperature MEAs for optimizing their composition and material selection. We investigated MEAs with various commercial catalysts, PTFE contents, acid doping levels, and acid base blend membranes. Polarization curves and impedance spectra were taken for all these individual cases. Depending on the operating condition and the MEA design, up to three semi-circles were observed in the HT-PEMFC Nyquist plot, which allows us to resolve the individual cell overpotentials due to membrane resistivity, hydrogen oxidation, oxygen reduction, and mass transport. Such rich information acquired with EIS helps reveal the underlying processes occurring in the MEA during fuel cell operation, which is essential for MEA design and optimization.
Impact of Organic Cation Adsorption on the Hydrogen Oxidation Reaction of Pt in Alkaline Fuel Cells
Authors: Chung Hoon T , Martinez Ulises , Chlistunoff Jerzy , Kim Yu Seung , Choe Yoong-Kee , Matanovic Ivana
Published: February 2020

Relatively poor hydrogen oxidation reaction (HOR) kinetics in alkaline membrane fuel cells compared with those in proton exchange membrane fuel cells can limit the cell performance [1]. In the previous work, we have compared the HOR kinetics of platinum electrocatalysts with two structurally different polymer electrolytes, i.e. benzyl trimethyl ammonium functionalized polyaromatic ionomer and phenyl tetramethyl guanidinium functionalized perfluorinated ionomer [2]. In this presentation, we will give further evidence on organic cation adsorption and their impact on HOR kinetics on Pt under high pH conditions. Direct observation of organic cation adsorption on the disk platinum electrode using surface enhanced FT-IR is closely related to the HOR activities. Computational calculations give further insight on cationic structural effect on adsorption kinetics. Mitigation strategy will be discussed in order to improve HOR kinetics of electrocatalysts in alkaline membrane fuel cells.  

Acknowledgements

US department of Energy Fuel Cell Technologies Program (Program Manager: Nancy Garland) supports this research through Fuel Cell Incubator Project.

References

W.C. Sheng, H.A. Gasteiger, Y. Shao-Horn, “Hydrogen Oxidation and Evolution Reaction Kinetics on Platinum: Acid vs Alkaline Electrolytes,” J. Electrochem. Soc., 157, B1529 (2010).

Sung-Dae Yim, Hoon T. Chung, Jerzy Chlistunoff, Dae-Sik Kim, Cy Fujimoto, Tae-Hyun Yang, Yu Seung Kim, “A Microelectrode Study of Interfacial Reactions at the Platinum-Alkaline Polymer Interface,” J. Electrochem. Soc., 162, F499 (2015).
Effective Nickel and Ruthenium Modified Palladium Anode Catalysts for Ethylene Glycol Oxidation in Alkaline Medium
Authors: Da Silva Rodrigo Garcia , De Andrade Adalgisa Rodrigues , Servat Karine , Morais Claudia , Napporn Teko W. , Kokoh Kouakou Boniface
Published: February 2020

As one of the attractive fuels in the direct alcohol fuel cell applications, the ethylene glycol electrooxidation was investigated in alkaline medium on Pd-based bimetallic catalysts (PdM/C, where M = Ni, Ru). These electrode materials were synthesized by polyol method, using ethylene glycol as both solvent and reducing agent. The resulted anode catalysts displayed effectiveness toward the oxidation of ethylene glycol. The latter molecule was also scrutinized as potential fuel which can be converted by cogeneration into energy (5.2 kWh kg-1) and particularly to added value product. Ex situ analytical measurements with liquid chromatography/Mass spectrometry provided evidences on the identification of glycolate as the main reaction product on the PdM/C anode materials (Figure 1).

Figure 1: Glycolate1 isolated and identified by LC-MS as the main compound issued from the ethylene glycol oxidation at the Pd-M/C (M = Ni and Ru) catalysts in alkaline medium.

The identification of some adsorbed intermediates and the final reaction products, was also supported by combining electrochemical (cyclic voltammetry, chronoamperometry) and in situ reflectance infrared spectroscopy experiments. The PdNi/C catalyst showed the highest intrinsic catalytic activity for the ethylene glycol oxidation. From FTIR experiments our findings gave evidences that the initial molecule skeleton was conserved and carbon monoxide was observed in a low amount.

Acknowledgements: Da Silva R.G. gratefully acknowledges FAPESP (2012/07464-0; 2013/25632-0) and CNPq for his fellowship.

L.M. da Palma, T.S. Almeida, V.L. Oliveira, G. Tremiliosi-Filho, E.R. Gonzalez, A.R. de Andrade, K. Servat, C. Morais, T.W. Napporn, K.B. Kokoh, RSC Adv., 4, 64476 (2014).

Figure 1
Inhibiting the Swelling Behavior of Nafion Membranes for PEM Water Electrolysis
Authors: Carmo Marcelo , Henkensmeier Dirk , Lüke Wiebke , Stolten Detlef
Published: February 2020

Nafion is a commercially available perfluorosulphonate (PFSA) polymer electrolyte membrane (PEM) commonly used in both PEM fuel cells and electrolyzers. Catalyst coated membranes (CCMs) are prepared by hot-pressing the catalyst layers on a hot and dry Nafion film[1]. In the electrolyser, the dry CCMs get in contact with liquid water, which swells the membrane. Because the CCM is clamped in the cell, this leads to formation of folds and wrinkles. Furthermore, when the membrane shows stronger in-plane swelling than the catalyst layer, this swelling can also lead to membrane-electrode delamination and formation of electrode cracks. Therefore, the large in-plane swelling of Nafion membranes is an unwanted feature.

 In this work, a facile and economical approach was developed to inhibit the in-plane swelling behavior of Nafion membranes. When first swollen on a fixed metal frame and afterwards dried in a fixed geometry, the Nafion film will memorize the wet shape and show reduced area swelling upon rehydration, providing outstanding benefits for CCM fabrication[2]. We expect that when using Nafion membranes with inhibited swelling behavior for CCM fabrication, the life time of PEM water electrolyzers shall be remarkably increased.

[1] M. Carmo, D. Fritz, J. Mergel and D. Stolten, International Journal of Hydrogen Energy, 38, 4901-4934 (2013) 

[2] S. Hink, D. Henkensmeier, J. H. Jang, H.‐J. Kim, J. Han, S.‐W. Nam, Macromol. Chem. Phys. 2015, DOI: 10.1002/macp.201500063.
Investigation of Mass Transport Losses in Polymer Electrolyte Electrolysis Cells
Authors: Suermann Michel , Schmidt Thomas J. , Büchi Felix N
Published: February 2020

Dynamically operable polymer electrolyte water electrolysis cells (PEEC) are also targeted at storing excess electric energy from renewable sources in hydrogen and oxygen in order to prevent curtailment [1].

In the energy storage application, efficiency of the processes is of particular concern not to waste precious renewable electricity. PEEC allow operation up to current densities around 5 A/cm2 and the losses increase accordingly. Similar as in fuel cells, different processes contribute to the voltage losses with increasing current. While the contribution of the ohmic overvoltage is well characterized and can easily determined by measuring the high frequency resistance of the cell [2], the catalytic and transport losses are more rarely investigated.

For determining the mass transport losses, also the catalytic losses need to be characterized, which needs careful analysis in particular when pressure varies over a wide range. The dependence of the transport losses is determined as function of the structures employed as current collectors, i.e. possible two phase phenomena in the porous structures as well as for different operating conditions with respect to pressure and temperature. The results show that over a wide range of current densities a quite significant part of the voltage losses can to be attributed to mass transport.

[1] C.J. Barnhart, et al., Energy Environ. Sci., 6, 2804-2810 (2013).

[2] C. Rozain, P. Millet, Electrochim. Acta, 131, 160-167 (2014)

Figure 1
Pt Electrocatalyst Supported on a 3D-Nanoporous Carbon Shows a High Performance in a High-Temperature Polymer Electrolyte Fuel Cell
Authors: Nakashima Naotoshi , Yang Zehui , Moriguchi Isamu
Published: February 2020

Considerable attention has been focused on the high-temperature PEFCs (> 100 oC), due to their benefiting PEFCs with higher carbon monoxide (CO) tolerance, faster electrochemical kinetics, and better water management than those of conventional PEFCs. However, the high-temperature PEFCs also suffer from their low durability in terms of carbon corrosion and platinum nanoparticles (Pt-NPs) aggregation resulting in the detachment of the Pt-NPs from the catalysts and loss in electrochemical surface area (ECSA) as well as the degradation of FC performance. Thus, enhancement in durability is highly demanded for the commercialization of the next-generation PEFCs.

    We have already reported that poly[2,2’-(2,6-pyridine)-5,5’-bibenzimidazole] (PyPBI) is an efficient dispersant for carbon supporting materials and provides the anchor sites for the Pt-nanoparticles (NPs) as well as creating the so-called three-phase boundary structure[1-7].

    In this paper, we used a 3D nanoporous carbon (NanoPC) with a high specific surface area of 1,037 m2/g as a carbon support for high-temperature polymer electrolyte fuel cell, and fabricated an electrocatalyst (NanoPC/PyPBI/Pt) having platinum nanoparticles of ca. ~2.2 nm diameter deposited on the NanoPC that was wrapped by poly[2,2’-(2,6-pyridine)-5,5’-bibenzimidazole] (PyPBI). Even after 10,000 start-up/shutdown cycles in the range of 1.0 to 1.5 V vs. RHE, the NanoPC/PyPBI/Pt showed almost no loss in electrochemical surface area (ECSA), which was much higher durability than those of a CB/PyPBI/Pt (~32%-loss), in which conventional CB was used in place of the NanoPC, and conventional CB/Pt (~46%-loss).

    FC performance of the assembled MEAs was evaluated at 120 ºC without any external humidification using a computer-controlled fuel cell test system. The polarization and the power density curves were measured under the atmospheric pressure by flowing dry hydrogen (flow rate; 100 mL/min) and dry air (flow rate; 200 mL/min) at the anode and the cathode, respectively.

    The power density of the NanoPC/PyPBI/Pt was 342 mW/cm2, which was higher than those of the CB/PyPBI/Pt (183 mW/cm2) and CB/Pt (115 mW/cm2).

The present study provides useful information for the preparation of an electrocatalyst with a high durability and performance in high temperature PEFCs.

  References

[1]     N. Nakashima et al., Small
2009,
5, 735-740.

[2]     N. Nakashima et al., J. Mater. Chem.
2011,
21, 1187-1190.

[3]     N. Nakashima et al, Scientific Reports, 2013, 3, article no. 1764.

[4]     N. Nakashima et al.,, ChemCatChem, 2014, 6, 567-571.

[5]     N. Nakashima et al, Scientific Reports, 2014, 4, article no.6295.

[6]     N. Nakashima et al., ChemPlusChem, 2014, 79, 400-405.

[7]     Nakashima et al., N., J. Mater. Chem. A
2014,
2, 18875-18880.
Characterization of Liquid Water Invasion in Gdls Using X-Ray Tomographic Microscopy
Authors: Lamibrac Adrien , Roth Jörg , Eller Jens , Marone Federica , Büchi Felix N
Published: February 2020

The accumulation of liquid water in the gas diffusion layer (GDL) of low temperature polymer electrolyte fuel cells (PEFC) results in increased mass transport limitations [1] and eventually in a significant potential and efficiency penalty. To achieve efficient water removal and maintain high performance, it is necessary to understand the morphological (porosity, pore and throat sizes) and chemical (surface tension) properties of the GDL, which control the water transport [2].

An ex-situ capillary pressure (pc) – saturation setup was developed in the framework of the IMPALA project [3] for imaging experiments using X-ray tomographic microscopy (XTM) at the Swiss Light Source synchrotron facility as it offers the advantage of well defined capillary pressure boundary conditions. This approach allows a quantitative analysis of the water transport through the GDL by linking the local saturation at the achieved pc levels with the microstructure of the invaded pores and throats.

Within the setup, a hydrophilic membrane implements a homogeneous boundary condition at the bottom of the GDL. At the top of the GDL either a hydrophobic membrane or a flow field was placed. While the hydrophobic membrane setup allows to study complete liquid wetting of the pore space, the flow field structure allows to implement an anisotropic compression simulating PEFC conditions and to study its consequences on water transport.

GDL samples of different suppliers have been tested. The breakthrough pressure, which corresponds to the capillary pressure when water reaches the opposite side of the injection surface, is a function of the materials. Correlation with the dry GDL microstructure shows that pore (and throat) size is the major controlling parameter. SGL 24BA shows a lower breakthrough pressure than Toray TGP-H060 due to larger throats and exhibits a stronger channel rib deviation of pore and throat sizes as well as of saturation.

References

[1] T. Rosen et al., Journal of the Electrochemical Society, 159 (2012) F536-F544.

[2] R. Flückiger et al., Electrochemica Acta, 56 (2011) 2254-2262.

[3] “IMprove Pemfc with Advanced water management and gas diffusion Layers for Automotive application” within the Fuel Cells and Hydrogen Joint Undertaking (FCHJU) initiative of the European Union. http://www.impala-project.eu

Figure 1: Capillary pressure saturation curves of Toray TGP-H060 and SGL 24 BA measured with the hydrophobic membrane setup (left) and the flow field setup (right). Compared to Toray TGP-H060 SGL 24BA shows a lower breakthrough pressure due to larger throats and exhibits a stronger channel rib deviation in saturation, as well as pore and throat sizes.

Figure 1
Influence of Thermal Conductivity and 2-D Temperature Distribution of Liquid Water Saturation
Authors: LaManna Jacob M , Hussey Daniel S , Jacobson David L , Mench Matthew M.
Published: February 2020

For use in automotive power, polymer electrolyte fuel cells are being pushed to ever higher levels of performance and efficiency. At these high performance levels, large thermal gradients can exist across the diffusion media. These large gradients can have a strong influence on water transport in the cell via phase-change-induced flow and thermally driven diffusion. The focus of this work is to elucidate the effects of diffusion media thermal conductivity on through-plane 2-D temperature and saturation distributions. Neutron imaging was conducted at the NIST Center for Neutron Research BT-2 neutron imaging facility and used to measure how saturation levels were influenced by the internal heat generation and temperature distributions. A custom 4.8 cm2 fuel cell with precision liquid coolant temperature control was used for the high resolution through-plane radiography. The precision liquid coolant ensures stable, high accuracy thermal boundary conditions for the analysis. Temperature distributions were computed in COMSOL using experimentally measured dry and wet thermal conductivity values for commercial diffusion media. These temperature distributions were then coupled to the measured saturation distributions from neutron imaging to determine the relationships between level of saturation and temperature gradient as shown in Figure 1. Data from this work will build upon an online database of benchmark data for the modeling community made available through this Department of Energy EERE supported program (Award Number DE-EE0000470). Additional funding provided by Department of Energy interagency agreement No. DEAI01-01EE50660.

Figure 1
Novel Gas Diffusion Layers with Patterned Wettability
Authors: Forner-Cuenca Antoni , Biesdorf Johannes , Gubler Lorenz , Schmidt Thomas J. , Boillat Pierre
Published: February 2020

Inside a polymer electrolyte fuel cell (PEFC), the water management is rather complex: on one hand, the membrane needs a certain hydration state in order to ensure a sufficient proton conductivity; on the other hand, excessive water leads to blocked gas pathways with increased mass transport losses. Liquid product water is transported by capillary forces [1] from the catalyst layer throughout the gas diffusion layer (GDL) towards the gas flow channels, in opposite direction of oxygen diffusion.

Under high current densities, the water production rate becomes high and the volume occupied by water can dramatically decrease the accessibility of oxygen resulting in mass transport limitations (so-called flooding). To address this issue, we are developing new GDLs with patterned wettability [2]. The idea is to define engineered hydrophilic pathways to force the transport of liquid water through them and vacate the rest of the volume for the transport of gases, decreasing the tortuosity.

The proposed synthetic method bears significant advantages compared to other reported approaches such us laser perforation [3] or local application of hydrophobic coating [4]: full flexibility in the pattern design without compromising the mechanical integrity, smaller hydrophilic regions can be defined (100 µm achieved) and the ratio between hydrophilicity and hydrophobicity can be tuned. Figure 1 shows the water preferentially accumulating in the hydrophilic regions.

In this talk, we will present details about the synthetic method together with ex-situ characterization results: chemical information based on energy dispersive x-ray (EDX) spectroscopy mapping (Figure 2) and water distribution with neutron radiography. Additionally, first operando results using the multicell setup [5] with pulsed gases analysis (PGA) will also be presented.

[1] U. Pasaogullari, et al., Int. J.Electrochem. Soc., 151 (2004), pp 399-406.

[2] P. Boillat, et al., European Patent Application EP15165515.6, (2015).

[3] D. Gerteisen, et al., J. Power Sources,177 (2008), pp 348-354.

[4] R. Koresawa, et al., J. Power Sources,271 (2014), pp 16-24.

[5] P. Oberholzer et al., Electrochem. Commun., 20 (2012), pp. 67-70.

Figure 1
Corrosion Resistant Electrospun Niobium Carbide Nanotube Supports for PEMFC Cathodes
Authors: Nabil-Moreau Yannick , Cavaliere Sara , Harkness Ian , Hards Graham , Sharman Jonathan , Jones Deborah Jacqueline , Rozière Jacques
Published: February 2020

Recent research has shown that metal carbides and nitrides can potentially present the required properties to replace the carbon blacks conventionally used as electrocatalyst supports in Proton Exchange Membrane Fuel Cells (PEMFC). Our aim is to associate these alternative compositions with controlled morphologies to design electronically conductive and chemically stable materials with the appropriate porosity.

Currently we are developing a range of synthesis routes leading to NbC based materials with different morphologies leading to high surface areas. For example, using a three step synthesis, we prepared hollow microspheres of niobium carbide with a surface area of 70 m2
g-1 and an electronic conductivity of 103 S m-1. Furthermore we are developing various syntheses leading to electrospun niobium carbide nanofibres with different porosities in order to study the influence of the morphology on surface area and electrochemical activity.

These various supports have been catalysed by deposition of platinum nanoparticles synthesised by a microwave assisted polyol method, and they have been evaluated as electrocatalyst support for the oxygen reduction reaction.

This contribution will describe the preparation of Pt on NbC-based supports and their chemical and electrochemical characterisation including cyclic corrosion tests to evaluate their stability over time compared with Pt on carbon.
Thermal & Humidity Stability of Mn4+ Doped Complex Fluoride Phosphors
Authors: Sista Srinivas P , Murphy James , Garcia-Santamaria Florencio , Setlur Anant A
Published: February 2020

Mn4+ doped complex fluoride based red phosphors have the potential to improve efficiency and color quality (CRI & R9) in LED lighting systems and enhance color gamut for LED displays. Owing to low absorption of Mn4+, high Mn4+ doping concentration is necessary to enable low CCT applications. One of the issues with Mn4+ doped phosphors is their high temperature and high humidity (HTHH) stability which is even more important for high Mn4+ doping. Here we will discuss the various post synthesis treatment techniques that help improve HTHH stability of Mn4+
 doped fluoride phosphors.
Cooperative and White Light Emission from Yb- and Yb,Er-Doped Y2Si2O7 Nanopowders
Authors: Di Bartolo Baldassare , Erdem Murat , Collins John , Sitt Bryan , Ligouri Joseph
Published: February 2020

We have investigated the luminescence properties of of Y2Si2O7 nanopowders doped with (1) Yb only and (2) Yb and Er.  Under 980 nm excitation of the Yb-only sample, the system exhibits a blue emission, which we attribute to cooperative emission from Yb pairs. When the air pressure in the sample holder is reduced to very low pressures, a broad band “white” emission, extending from the blue into the near IR, appears, and the blue Yb emission band disappears. In the Yb-Er doped system, no cooperative emission from Yb is observed, but the Er emission bands are observed throughout the visible region. These Er emissions result from upconversion processes through energy transfer or through a combination of energy transfer and excited state absorption. The broad band white light emission is also observed in this sample, and becomes the more favorable emission as the pressure is decreased and the pumping intensity increased.
Luminescence Quenching of [M]NbO4:Pr3+ [M=La, Lu, Gd] Under UV Excitation
Authors: Collins John , Labovitis Elena , Bettinelli Marco , Sutton Asa , Dauphinais Katrina
Published: February 2020

We report on the luminescence properties of three Pr3+-doped niobate systems (LaNbO4, LuNbO4, and LaNbO4) in the temperature range between 7K and 500K. These systems are d0 oxides that exhibit a metal-to-metal charge transfer state lying just below the conduction band. Pumping in the UV, the system exhibits the typical sharp line emission from the 3P0 and 1D2 levels of Pr3+. The emission intensities from these levels are temperature and host dependent, with the 1D2 emission showing strong quenching at higher temperatures. In addition to the Pr emission, we also observe broad-band emission from the niobate complex. Using results from steady state luminescence and kinetic studies, we discuss the flow of energy in these systems following uv excitation, and also consider the quenching mechanism of the luminescence from these systems.
Electrochemical and Catalytic Properties of Liver Microsomes Adsorbed to Magnetic Nanoparticles
Authors: Nerimetla Rajasekhara , Krishnan Sadagopan
Published: February 2020

Subcellular liver fractions (microsomes) act as an ideal in-vitro system to study the pharmacokinetics, drug metabolism and drug-drug interactions of new drugs. Therefore, developing microsomes based biosensors and bioreactors have immense significance in green drug metabolites, stereoselective chemical compound synthesis and drug sensing. Magnetic nanoparticles (MNP) have unique advantages such as large surface area and high loading capacity for enzymes/proteins which can enhance the electrochemical properties such as heterogeneous electrons transfer kinetics and catalysis.[1] Also our prior studies have shown edge plane pyrolytic graphite electrodes to exhibit good electron transfer kinetics and film stability when immobilized with microsomes.[2] In the present study, our objective was to use amine functionalized MNP to adsorb complex drug metabolizing microsomes on edge plane pyrolytic graphite electrodes without the need to isolate and purify enzymes to develop volume efficient bioreactors. The electrochemical properties and electrocatalytic conversion of a drug into its metabolite for the constructed bioelectrode will be discussed.              

Acknowledgements: We are grateful for the financial support by the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health under Award Number R15DK103386.

[1] S. Krishnan, and C.Walgama, Anal. Chem. 2013, 85, 11420−11426.

 

[2] C. Walgama, R. Nerimetla, N. F. Materer, D. Schildkraut, J. F. Elman, and S. Krishnan, Anal. Chem. http://dx.doi.org/10.1021/ac5044362
Bimetallic Iron and Nickel Nanoparticles for the Electrocatalytic Oxidation of Methanol and Ethanol for Fuel Cells
Authors: Candelaria Stephanie L , Bedford Nicholas , Greenlee Lauren F
Published: February 2020

The electrochemical oxidation of alternative fuels, such as methanol and ethanol, for alkaline fuel cells often relies on the use of precious metal catalysts. However, the scarcity and high cost of these Pt group metals (Pt, Pd, Au, etc.) leads to the search for earth-abundant alternatives with similar electrocatalytic properties. Among these, iron emerges as a promising candidate as it has already been shown to have high activity for a variety of reactions. However, the rapid formation of oxides severely limits the stability of the iron nanoparticles. The addition of a second metal, such as nickel, slows this oxidation and can also enhance catalytic activity of the nanoparticles. In this work, bimetallic iron-nickel nanoparticles are synthesized in aqueous conditions at room temperature and pressure. Slight changes in the synthesis leads to significant differences in the size, stability, and lifetime of the nanoparticles. Possible explanations for these differences are characterized through both ex situ and in situ experiments. During electrochemical measurements, these materials show two distinct regions where redox reactions are taking place, which may correspond to nickel and iron reacting separately. The effects of various testing parameters on the electrochemical behavior are also explored.
Electrochemical Kinetic Study on the a Yeast-Catalyzed Activity in Microbial Half Cell
Authors: Jeon Yang Bae , Tang Fusheng , Lee Jin Wook
Published: February 2020

Microbial biofuel cells produce electricity directly from organic fuels such as glucose sucrose, acetates and ethanol. In the present work, electrochemical characteristics of the yeast-catalyzed half cell against carbon cloth electrode with various yeasts and with immobilization are investigated experimentally. Three types of yeasts as anode catalyst are employed: (1) commercially available baker’s yeast (S. Cerevisiae); (2) wild type yeast cultured in our lab; and (3) respiration-free mutant yeast. Kinetic parameters for the three types of yeasts are obtained by Tafel analysis. Cyclic voltammetry (CV) techniques are applied to investigate the reversibility of the redox reactions. Open current potential (OCP) of each yeast is measured against a reference electrode to estimate the anodic potential. Electrochemical impedance spectroscopy (EIS) of the half-cell is conducted to estimate the resistivity of the electrode and the overall ohmic resistance. This fundamental kinetic study will be used to understand the activity of the yeast as a catalyst in microbial half cell as well as fuel cell.
Effect of High Energy Carbon Beam Irradiation on Carbon Nanotubes Modified Glassy Carbon and Its Application in Sensing of Deoxyguanosine
Authors: Goyal Rajendra N , Sharma Rosy , Gupta Pankaj
Published: February 2020

The effect of high energy carbon ion beam as the modification tool for the multiwalled carbon nanotubes (MWCNT) modified glassy carbon (GC) has been studied. The change in the morphology, length and diameter of the carbon nanotubes upon irradiation is analyzed using Raman spectroscopy, Atomic force microscopy and FE-SEM. The irradiated MWCNTs had a diameter in the range of 3-27 nm which is much lower in comparison to the diameter of the tubes present in the pristine state. All the bands in the Raman spectra, corresponding to the irradiated MWCNT, shifted towards higher wave numbers by 4-5 cm-1. The irradiated MWCNT/GCE has been further used as a sensor for the electrochemical investigation of deoxyguanosine and deoxyadenosine. A sharp oxidation peak with much enhanced peak current at ~930 mV, corresponding to the oxidation of deoxyguanosine, is observed at the irradiated sensor, whereas, no peak was observed at the bare GCE. A very small peak at ~ 975 mV is observed at MWCNT modified GCE. Thus, it can be concluded that irradiation leads to appreciable defects formation which promotes the electron transfer and leads to enhanced electrooxidation of deoxyguanosine on the irradiated sensor surface.

It was found that the peak potential of both deoxyguanosine and deoxyadenosine depends on the pH of the supporting electrolyte and shifted to more positive potentials with increase in pH. The linear relation between pH and the peak potential (Ep) can be expressed by the following equations:

Ep (Deoxyguanosine) = -52.96 pH + 1307.3       (R2 = 0.9928)                                          

Ep (Deoxyadenosine) = -49.94 pH + 1560.4       (R2 = 0.9990)                                           

From the linear current versus concentration relations, it can be seen that exposure of MWCNT to high energy carbon beam lead to ~ 7 times increase in sensitivity in the case of deoxyguanosine and ~ 2 times for deoxyadenosine. The limit of detection, calculated by 3σ/b where σ is the standard deviation of the blank solution and b is the slope of the calibration curve, is substantially changed on irradiation from 12 µM to 507 nM and 4.29 µM to 300 nM for deoxyguanosine and deoxyadenosine respectively.  The simultaneous determination of the two analytes was performed using the fabricated sensor and its practical utility was tested by analyzing DNA, extracted from herring sperm and MCF7 cell line, for the presence of deoxyguanosine and deoxyadenosine. The common biomolecules present in blood and urine did not interfere in the determination and the high stability and reproducibility of the sensor confirmed its successful application in real sample analysis.

Figure 1