bluuebunny/crossref_metadata_2025 huggingface dataset:
In Situ TEM Study of the Coarsening of Carbon Black Supported Pt Nanoparticles in Hydrogen
Authors: Simonsen Søren Bredmose , Wang Yan , Jensen Jens Oluf , Zhang Wenjing
Published: February 2020

The control of sizes and shapes of nanostructures is of tremendous importance for the catalytic activity in electrochemistry and in catalysis more generally. However, due to relatively large surface free energies, nanostructures often sinter to form coarser and more stable structures that may not have the intended physicochemical properties.

Pt is known to be a very active catalyst in several chemical reactions and for example as carbon supported nanoparticles in fuel cells.

The presentation focusses on coarsening mechanisms of Pt nanoparticles supported on carbon black during exposure to hydrogen. By means of in situ transmission electron microscopy (TEM), Pt nanoparticle coarsening was monitored in 6 mbar 20 % H2/Ar while ramping up the temperature to ca. 900 °C. Time-resolved TEM images directly reveal that separated ca. 3 nm sized Pt nanoparticles in the pure hydrogen environment are stable during constant temperature ramping by 10°C/min up to ca. 800 °C. The coarsening above this temperature is fully dominated by the particle migration and coalescence mechanism. This is contrary to supported Pt nanoparticles in oxygen, where the coarsening is fully dominated by Ostwald ripening. For agglomerated Pt nanoparticles, coalescence events were observed already at ca. 200 °C. The temperature-dependency of particle sizes and the observed migration distances are consistent with simple early models for the migration and coalescence.
A New Class of Fuel Cells Based on Ion Pair-Coordinated Proton Exchange Membranes
Authors: Kim Yu Seung , Lee Kwan-Soo , Purdy Geraldine M , Choe Yoong-Kee , Fujimoto Cy , Han Junyoung , Bae Chulsung
Published: February 2020

Low temperature proton exchange membrane (PEM) fuel cells that use perfluorinated sulfonic acid are at present being commercialized in fuel cell vehicles, but these cells can operate only at relatively low temperatures, ca. < 100°C, and high hydration levels. High temperature PEM fuel cells that use phosphoric acid-doped polybenzimidazole can operate effectively up to 180°C; however, these are difficult to operate below 140°C without suffering loss of phosphoric acid when exposed to water.1 In this presentation, we discuss a new class of fuel cells based on ion pair-coordinated proton exchange membranes.2

In the ion pair-coordinated proton exchange membranes, quaternary ammonium functionalized membranes, also known as anion exchange membranes, are doped with phosphoric acid. Due to the high basicity of the quaternary ammonium hydroxide, the acidic proton of phosphoric acid is completely deprotonated to form a strong ionic interaction between quaternary ammonium and biphosphate. Our density functional theory calculation indicated that the ion-pair interaction is 8.5 times greater than the conventional acid base interaction in the phosphoric acid doped polybenzimidazole. The strong interaction between the ion pair enables fuel cell operation at lower temperatures with substantially higher water partial pressure than are possible for high-temperature phosphoric acid doped polybenimidazole fuel cells. In this presentation, the chemical structural difference between this new system and the conventional phosphoric acid-doped polybenzimidazole system will be compared. The benefits and challenges of the new system in fuel cell operations will be further discussed.

Acknowledgment

This work was supported by the US Department of energy, Energy Efficiency and Renewable Energy, Fuel Cell Technology Office (Program Manager: Dimitrios Papageorgopoulos).

References

G. Bendlamudi Systematic Characterization of HT PEMFCs Containing PBI/H3PO4 Systems: Thermodynamic analysis and Experimental Investigations 104 (Logos Verlag Berlin GmbH, 2011).

Kwan-Soo Lee, Jacob S. Spendelow, Yoong-Kee Choe, Cy Fujimoto, and Yu Seung Kim Nature Energy, 1, 16120 (2016).
Performance Improvements in High-Temperature PEM Fuel Cells
Authors: Steenberg Thomas , Hjuler Hans A. , Jensen Jens Oluf , Li Qingfeng , Cleemann Lars Nilausen
Published: February 2020

The work presented here focuses on recent results obtained on degradation of PBI membranes used in membrane electrode assemblies (MEAs) for high temperature polymer electrolyte fuel cells (HTPEM) that operates in the temperature range 140-180 °C. The testing is done at 160 °C using either pure hydrogen or reformate of different compositions.

Pure platinum versus PtCo alloys have been studied. The latest developments show that it is possible to reduce the Pt loading, increase the platinum utilization and achieve a long lifetime. We have shown that cells based on a thermally cured membrane proved a degradation rate of as little as 0.5 μV/h over an extended period of time. This is, to the authors’ knowledge, lower than what is ever reported for HTPEM.

The degradation mechanisms over time have been studied using SEM and TEM characterization tools. It has been shown that the Pt nanocatalyst particles grow from approx. 3 to 9 nm over 17,000 hours on the cathode side, while the anode is far less affected.

The durability of HTPEM can now be considered similar to low temperature PEM as shown in Fig. 1. Here, more than 15,000 hours is demonstrated in single cells at 300 mA/cm2. The degradation rate is around 4 μV/h for approx. 13,000 hours.

The high operating temperature makes it possible to make commercial fuel cell systems using methanol (methanol-water mixtures) as fuel. The HTPEM cells can tolerate CO impurities up to more than 3 vol-% without significant losses. Several demonstration projects have been made, including a Fiat 500 equipped with a 5 kW methanol based fuel cell system. This car is in every day operation at a catering company in Denmark. Another project is a street sweeper with the same type and size of system as shown in Fig. 2.

Figure 1
Reaction Selectivity for Oxygen Reduction of N-Doped Graphene Nanoclusters
Authors: Matsuyama Haruyuki , Akaishi Akira , Nakamura Jun
Published: February 2020

Nitrogen-doped graphene exhibits high oxygen reduction reaction (ORR) activity [1]. Recently, it has been theoretically revealed that nitrogen atoms prefer to locate near the zigzag edge of graphene [2,3]. Therefore, many theoretical researchers have paied attention to the nitrogen atom existing at the graphene edge. In this study, we focus on nitrogen site-dependence of ORR activity for the graphene nanocluster having edges with finite sizes.

We investigated the ORR activity for the hexagonal nitrogen-doped graphene nanoclusters having zigzag or armchair edges, using first-principles calculations within the density functional theory. Electrocatalytic activities were evaluated on the basis of the computational hydrogen electrode model proposed by Nørskov et al. [4] In general, the ORR mainly proceeds in two pathways: For the two-electron pathway (2e-), oxygen molecule (O2) is reduced to hydrogen peroxide (H2O2), and for the direct four-electron pathway (4e-), the final product is water (H2O). H2O2 for the 2e- pathway might erode a carbon based electrocatalyst material itself, leading to low durability. Therefore, we also play up the selectivity for the 4e-pathway.

Fig.1(a) shows a model of the graphene nanocluster. The doping sites are denoted by blue circles with numbers. Numbers are allocated from the edge toward in-plane. A nitrogen atom is substituted in each doping site. Models are labeled as X-Y, where symbols X and Y denote doping sites of nitrogen atoms and reaction sites of ORR, respectively. Fig.1(b) shows the energy diagrams for the 4e- and the 2e- pathways for the model 5-6. The maximum potentials are 0.70 V and -0.42 V for the 4e- and the 2e- pathways, respectively. This means the 4e- pathway prefers to occur up to 0.70 V, and the 2e- pathway does not occur unless the backward voltage is applied. Therefore, the model 5-6 shows extremely high selectivity for the 4e- pathway. In almost all reaction sites, the maximum potentials for the 4e- pathway are higher than those for the 2e- pathway. It is noted that the high selectivity for the 4e- pathway is assured not just at the edge but inside the cluster. The effects of edge structures, cluster sizes, and doping configurations on the ORR activity will be discussed in the presentation

References:

[1] K. R. Lee, K. U. Lee, J. W. Lee, B. T. Ahn, S. I. Woo, Electrochem. Commun. 12, 1052 (2010).

[2] S. F. Hung, K. Terakura, T. Ozaki, T. Ikeda, M. Boero, M. Oshimaj, J. Ozaki, S. Miyata, Phys. Rev. B 80, 235410 (2009).

[3] Y. Uchida, S. Gomi, H. Matsuyama, A. Akaishi, J. Nakamura, J. Appl. Phys. 120, 214301 (2016).

[4] J. K. Nørskov, J. Rossmeisl, A. Logadottir, L. Lindqvist, J. Phys. Chem. B 108, 17886 (2004).

Fig.1. Model of the graphene nanocluster and doping sites of nitrogen atoms and free energy diagram for ORR for the model 5-6. Value of UMax are referenced to the standard hydrogen electrode (SHE).

Figure 1
(Invited) First Principles Studies of Nitrogen Electrochemistry and the Electrocatalytic Properties of Ultrathin (hydroxy)Oxide Films
Authors: Zeng Zhenhua , Chun Hee-Joon , Kubal Joseph , Chang Kee-Chul , Markovic Nenad M , Greeley Jeff
Published: February 2020

Advances in the theoretical understanding of interfacial electrochemistry have, over the past decade, permitted the extension of periodic Density Functional Theory studies, which have traditionally been applied to probe chemistry at gas/solid interfaces, to electrochemical systems where potential-dependent structural and chemical phase transformations occur at liquid/solid interfaces. Indeed, such techniques have been employed to study a surprisingly wide class of electrochemical processes, ranging from electrocatalysis to corrosion.

In this talk, we will discuss how these strategies can be applied to predict the detailed, atomic-scale properties of monolayer (hydroxy)oxide base metal films on precious metal and precious metal alloy substrates as a function of applied potential. We will describe the analysis of Moire patterns, variable oxidation states, and three-phase boundaries of these films, and we will demonstrate how these results may be used to predict the shape and oxidation states of supported two-dimensional nanoislands as a function of electrochemical conditions. We will next discuss how the three-phase boundaries may promote hydrogen evolution rates in alkaline environments, and we will close with some perspectives on the possibilities for electrocatalyst design offered by these systems.

If time permits, we will also discuss a new approach, based on a combination of DFT and kinetic Monte Carlo simulations, that permits direct simulation of polarization curves as a function of sweep rate and that rigorously predicts intrinsic reaction pathways for both electroreduction of nitrates and NO in acidic environments.
Preparation of Monodispersed Ultra-Small PtCu Alloy with Remarkable Electrocatalytic Performance
Authors: Cao Longsheng , Jiang Shangfeng , Qin Xiaoping , Shao Zhigang , Yi Baolian
Published: February 2020

Without the assisstance of sufactant, CuCl2 was reduced by NaBH4 to form Cu nanoparticles, which acted as second dispersant during the preparation of PtCu alloy. The obtained PtCu of 2.1nm was supported on Vulcan XC72. The PtCu/C showed lattice compression, Pt surface segregation, high ratio of non-oxidized Pt with high electronic binding energy. All those structure feature contributed to weak adsorption strength of OHads on Pt, which had benefit on ORR. According to half cell test, the area specific activity and mass activity of PtCu/C reached 6.6 and 3.8 times that of Pt/C at 0.9V vs. RHE. What's more, after degradation test of 10000 cycles, the superiority of PtCu/C towards Pt/C remained. At 100 mA/cm2 in single cell test, ultra-small PtCu/C displayed superior performance and stability. Besides, this method in this article can also be used to synthesize supported ultra-small alloy, such as PtCo and PtNi.

Figure 1
Advaced Core-Shell Nanostructures for Electrocatalysis
Authors: Wang Lei , Wang Chao
Published: February 2020

The electrocatalytic performance of Pt-alloy catalysts is usually limited by the lack of long-term durability, primarily due to leaching of the non-noble element under the harsh electrochemical conditions. We find that cobalt-platinum core-shell nanostructures could sustain high catalytic activity for the oxygen reduction reaction, demonstrating 8 times of improvement in catalytic activity versus commercial Pt catalysts and no more than 13% of loss after 30,000 potential cycles. The evolutions of nanoscale and surface structures over the course of extensive potential cycling were followed by combining electron microscopic elemental mapping and electrochemical studies of CO stripping. Atomistic simulations and density functional theory calculations suggest that the core-shell nanostructure could protect the non-noble metal from leaching under the “electrochemical annealing” conditions while maintaining the beneficial mechanisms of bimetallic systems for catalytic enhancement.
Phosphorus-Enhanced Oxygen Reduction Activity and Stability of Commercial Pt/C
Authors: Lu Bang-Au , Tian Na , Zhou Zhi-You , Sun Shi-Gang
Published: February 2020

In fuel cell technologies, the sluggish kinetics of oxygen reduction reaction (ORR) on the cathode is the main obstacle, and it is thus urgent to develop high-performance catalysts. Recently, the role of surface Pt-OH in the ORR has drawn much attention and the highly active ORR catalysts reported recently show much less surface Pt-OH coverage than pure Pt does. Previously, lots of work have focused on tuning the surface electronic structure of platinum-based catalysts, controlling its interaction with reactants, and thus affects the efficiency.

In this work, we report that Phosphorus adsorption of moderate coverage could substantially enhance the activity and stability of commercial carbon supported Pt electrocatalyst towards oxygen reduction reaction. Compared to pure Pt/C, P-decorated commercial Pt/C exhibited weakened oxygen affinity on the surface, and 8-times higher specific activity and 7-times higher mass activity at 0.9 V. Furthermore, compared to commercial Pt/C, we observed that the stability of phosphorus-decorating commercial Pt/C can be enhanced dramatically. The mass activity loss of phosphorus-decorating commercial Pt/C is only 10%, much smaller than that of Pt/C (51%) after 10,000 potential cycles between 0.6-1.0 V. This study may provide a strategic design of Pt-based efficient ORR catalysts for fuel cells.

Figure 1
Microwave Preparation and Electrocatalytic Activity of Nitrogen Doped Carbon Nanotubes Supported Ru85Se15 Nanoparticles
Authors: Li Hengyi , Cheng Xuan
Published: February 2020

The nitrogen doped carbon nanotubes (NCNTs) were prepared by chemical vapor deposition (CVD) using 900℃ or 950℃. The ruthenium selenide (Ru85Se15) nanoparticles supported on NCNTs were then synthesized through microwave assisted route. It was found that the amorphous Ru85Se15 nanoparticles were uniformly distributed on NCNTs with no apparent particle agglomeration being observed. The as-prepared Ru85Se15/NCNTs exhibited high electrocatalytic activity toward oxygen reduction reaction and relatively good stability. The half-wave potentials reached 0.57 ~ 0.58 V and nearly 50 mV degradation was observed upon 1400 cycles by voltammetry in 0.5 mol L-1 sulfate acid solutions.
The Dual Role of Graphene As a Catalyst Support and Protection Cap for Monolayer Pt Catalysts
Authors: Abdelhafiz Ali , Vitale Adam , Alamgir Faisal M
Published: February 2020

Production of cost-effective polymer electrolyte membrane (PEM) fuel cell materials has been of a great interest over the past decade. At the cathode side, the oxygen reductionreaction (ORR) is the key reaction, for which Pt remains the most widely used catalyst. In order to leapfrog the current limits to Pt use, three main targets have to be achieved. First, is an enhancement of the catalytic activity per Pt atom; second, is a reduction of Pt loading; and third is an increase the catalyst longevity. Here, we demonstrate the dual role of single graphene layer, both as a growth platform and as a protective cap for 2D Pt monolayers catalysts, where all three targets can be achieved.

Using iterative under potential deposition (UPD), monolayers layers of Pt catalyst are grown on top of a monolayer graphene sheet, supported on 50 nm (111) Au substrate. X-ray absorption spectroscopic (XAS) and transmission electron microscopy (TEM) analysis show that Pt monolayers growth is dictated by the graphene-teplated epitaxy. Intimate contact between Pt/graphene induces a localized compressive strain on Pt monolayers ranges 3-10% with an overall compressive strain of 3.5% according to extended x-ray absorption fine structure (EXAFS) analysis. In addition, cyclic voltammetry (CV) analysis shows Pt monolayers fully wetting ~100 mm2area of graphene under-layer with only a ~1 nm ultra-thin layer of Pt, while avoiding ripening as shown through TEM images. Atomic Force Microscopy (AFM) analysis demonstrates that Pt monolayers prefer to follow Frank-van der Merwe growth (i.e. layer-by-layer growth mode) rather than Volmer-Weber growth (i.e. island growth mode), where root mean square (rms) of surface roughness remains quite similar while increasing Pt loading is increased.

Pt/graphene hybrid catalysts show superior catalytic activity for ORR relative to the graphene-free counterparts. A combination of the graphene-imposed compressive strain and electron transfer, push the Pt d-band center up, lowering the overpotential needed for ORR to occur. The graphene/Pt hybrid also show superior activity towards ORR for all shallow Pt mass loadings relative to graphene-free cases, which can be attributed to the interface strain. Due to their intimate epitaxial contact, graphene and Pt, therefore, form a new hybrid catalyst that outperforms Pt. Furthermore, the graphene/Pt cap hybrid shows the graphene protecting Pt MLs from both dissolution and from ripening, with almost no Pt loss after 1000 fuel cell operating cycles. Our demonstration of a graphene-Pt hybrid opens the door for graphene/metal or metal/graphene architectures with potential applications in, and not limited to, energy, thermo-electric and electronics field.

Figure 1
Synthesizing Highly Active and Stable Electrocatalyst for PEMFC through Composite the Carbon-Titanium Dioxide
Authors: Ji Yunseong , Jeon Yukwon , Cho Yong il , Hwang Ho Jung , Jeon Oksung , Kwon Oh Chan , Kim Jeong Pil , Shul Yong Gun
Published: February 2020

Fuel cell is one of the most promising electrochemical energy conversion devices which withholds many advantages; high efficiency, high power density, rapid start up, any significant pollutant, etc. Especially, polymer electrolyte membrane fuel cell (PEMFC) has been shown a lot of attention due to its high power density and relatively good portability. Commonly, Pt/C catalyst used as PEMFC catalyst because it has high surface area, high electrical conductivity, and appropriate pore structure. However, carbon support materials suffer from degradation in a harsh operation conditions. Generally, carbon corrosion is occurred on the surface and it makes vacancies under the Pt nanoparticles. This mechanism gives rise to agglomeration and sinter of Pt particles via Ostwald ripening. Consequentially, carbon corrosion brings decreases of the electrochemical surface area (ECSA) and hinder long-term operations. Thus, electrochemically stable support materials need to be developed. Recently, some researchers focus on the metal oxide support as promising materials due to their excellent mechanical strength and inherently higher corrosion resistivity. In these alternative material candidates, TiO2 support shows an excellent durability under severe acidic condition, which provides the possibility to directly use as a support. However, hindrances such as low electrical conductivity, catalytic activity and surface area limits direct usage of TiO2 as a catalyst support. In order to improve these drawbacks, we designed the new catalyst. TiO2 nanofibers are prepared by electrospinning method and platinum nanoparticles are deposited on the support by microwave-assisted polyol method. Lastly, CNT was winded around the catalyst surface to boost up the electrical conductivity. The newly designed CNT-Pt/TiO2 nanocatalyst shows well made a 3D network. As a results, the CNTs are placed on the TiO2 surface as an electric conducting pathway. Furthermore, we found a modified Pt electronic structure that takes advantage of the strong synergetic interactions of TiO2 nanofibers, Pt nanoparticles and winded-CNT. This structure influences on a decrease of the d-band vacancy of Pt due to electron transfer from the support, resulting in an improved oxygen reduction reaction. Therefore, the CNT-Pt/TiO2 nanofiber composite shows superior performance and durability, which is definitely distinguishable at high temperature condition of 120 oC, RH 40% compare to the commercial Pt/C.
(Invited) Catalyst Design for Oxygen Reduction Reaction: Platinum Monometallic, Binary and Ternary Nanocatalyst
Authors: Baranton Stève , Lankiang Styven , Dru Delphine , Bigarré Jannick , Buvat Pierrick , Coutanceau Christophe
Published: February 2020

Improving design and/or reducing noble metal content in electrocatalysts for fuel cell electrodes while maintaining and/or increasing proton exchange membrane fuel cell (PEMFC) performance in terms of durability and power density are crucial challenges for PEMFC mass market applications.

The formation of platinum alloys with transition metals represents a promising way for improving the activity of Pt-based catalysts [1-3]. Pt based alloys have indeed often demonstrated higher electrocatalytic activity towards ORR than pure platinum.

On the other hand, the structure and morphology of the catalyst [4] also play very important roles in the electrocatalytic efficiency for ORR.

In this context, the present study aims at systematically comparing the catalytic activity and the selectivity towards the ORR of binary and ternary catalysts based on Pt, and Au in order to determine the effects of alloyed metals, in terms of kinetics and selectivity. For this purpose, monometallic Pt/C, binary PtxM1-x/C and ternary PtxAuyMz/C (with M a transition metal) nanocatalysts supported on carbon have been first synthesized by a wet chemical method allowing the synthesis of the whole range of alloys and comprehensively characterized. The morphologies, compositions and structures of the particles were characterized by physical methods (thermogravimetric analysis, transmission electron microscopy, X-ray diffraction, atomic absorption, X-ray photoelectron spectroscopy). Electrochemical active surface areas and surface compositions were estimated by cyclic voltammetry. Electrocatalytic activity and selectivity of catalysts were studied by rotating disc and rotating ring disc electrodes.

Acknowledgement:

The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement #325327 (SMARTCat project) and from the ADEME (French Environment and Energy Management Agency) for its financial support through the EXALAME project.

[1] M.T. Paffet, J.G. Beery, S. Gottesfeld, J. Electrochem. Soc. 135 (1988) 1431–1436.

[2] C. Wang, M. Chi, D. Li, D. van der Vliet, G. Wang, Q. Lin, J. F. Mitchell, K. L. More, N. M. Markovic, V. R. Stamenkovic, ACS Catal. 1 (2011) 1355–1359.

[3] T. Toda, H. Igarashi, H. Uchida, M. Watanabe, J. Electrochem. Soc. 146 (1999) 3750–3756.

[4] D. Alloyeau, C. Mottet, C. Ricolleau, Nanoalloys, London: Springer-Verlag; 2012.
Optimization of Pt Catalyst for Anode/Cathode of PEMFC via Magnetron Sputtering
Authors: Ostroverkh Anna , Dubau Martin , Johanek Viktor , Kus Peter , Khalakhan Ivan , Vaclavu Michal , Fiala Roman , Ostroverkh Yevhenii , Matolin Vladimir
Published: February 2020

In this study, the performance of the thin film Pt catalyst with loading in the range of 1–200 µg/cm2 prepared by magnetron sputtering was investigated for both anode and cathode sides of a proton exchange membrane fuel cell (PEMFC) in H2/O2 and H2/air modes (see example of anode study in Fig.1). Standard microporous layers comprising carbon nanoparticles and Teflon PTFE and FEP supported gas diffusion layer, as well as their modifications by magnetron deposition of carbon in N2 atmosphere (leading to CNx) followed by plasma etching were used as substrates for Pt deposition (Fig.1 right).

The choice of CNx interlayer was motivated by the higher resistance of the CNx structure as compared to pure C which was determined by a mass-spectrometry analysis of PEMFC exhaust at different cell potentials. Benefits of lower absolute carbon etching rate and at least 0.25 V lower corrosion threshold were found for CNxon both sides of the PEMFC (see Fig. 2 for cathode results).

The anode catalysts with various Pt loadings on all the substrates were tested and compared with a standard state-of-the-art commercial Pt/C reference anode with respect to their efficiency for hydrogen oxidation reaction (HOR; see Fig. 1). Performance up to 1.3 W/cm2 in pure H2 and O2 was achieved for anodes containing Pt loading of 2–10 µg/cm2 on CNx substrate. It is comparable to the performance of a standard commercial Pt/C anode with loadings 200–400 µg/cm2.

The same experiments as for HOR were performed for and oxygen reduction reaction (ORR). In this саsе, cathodes with various Pt loadings were tested. The maximum performance up to 0.54 W/cm2 in pure H2 and O2 was found for cathodes with Pt loadings in the range of 20–100 µg/cm2. The Pt loading of 100 µg/cm2 was found as the limit thickness for the magnetron sputtered thin film, further increase of Pt content leads to efficiency decrease of PEMFC. When PEMFC is switched from H2/O2 to the H2/air, the power is decreased 2.0 to 2.2-times relative to the reference Pt/C powder electrodes and 2.8 to 3.0-times on thin film Pt electrodes.

We have also performed 450-hour durability tests in a pulsed regime of 30min open voltage + 30 min under 400 mA/cm2 load, as well as in the regime of stable 400 mA/cm2load for both anode and cathode sides of the PEMFC with Pt loadings of 2 µg/cm2 and 20 µg/cm2.

Based on our research, the PEMFC with best Pt utilization was found for MEA based on a combination of anode with 2 µg Pt per cm2 and cathode with 10 µg Pt per cm2, yielding the total power density 0.45 W/cm2 for as little as 12 µg/cm2 of total noble metal content.

Figure 1
A Study of Carbonate Formation Kinetics and Morphological Effects Observed on OH- Form of Pfaem When Exposed to Air Containing CO2
Authors: Divekar Ashutosh G , Park Andrew Michael , Owczarczyk Zbyslaw R. , Seifert Soenke , Pivovar Bryan S , Herring Andrew M
Published: February 2020

For AEMFC OH- form of membrane reacts with CO2 when exposed to air leading to loss in conductivity. The data published by Yanagi et.al.[1] suggest that OH species reacts to form Carbonate/bicarbonate in few minutes and after 2 h the membrane only consists of carbonate and bicarbonate. Although this is an important data to consider the reaction kinetics, morphological properties and equilibrium concentrations are still unknown at different environmental conditions. We have attempted to study the CO2 kinetics and its transient effect on conductivity, water-uptake (or lambda) and morphology when the OH- form of PFAEM membrane is exposed to air which has approx. 400 ppm of CO2. The kinetics was studied by exposing the membrane to controlled environment and titrating it using Warder and Winkler titration methods. We have studied transient change in small angle x-ray scattering patterns when the films are exposed to air at different conditions to study the change in d-spacing of the ionic domains. From SAXS analysis it can be concluded that the intensity of spectrum drops over time and the time of equilibration is higher at higher humidity. It takes few hours for the conductivity to drop to carbonate/bicarbonate level. Ultimately we want to understand the effect of CO2 on membrane from every aspect and possibly help us think about strategies to mitigate the problem.

Keywords: Anionic exchange membrane, Carbonate,bicarbonate,carbon-dioxide, small angle x-ray scattering

Ref:

[1]Yanagi and Fukuta, ECS transactions,16(2008).

Figure 1
Structure and Performance of Fe-N-C PGM-Free Cathode Catalysts Derived By Polymerization-Pyrolysis and Sacrificial Support Method
Authors: Chen Yechuan , Gokhale Rohan Rajeev , Serov Alexey , Artyushkova Kateryna , Atanassov Plamen
Published: February 2020

Recently numerous metal-nitrogen-carbon type cathode electrocatalysts for fuel cell have been synthesized via different approaches [1]. Among these methods, sacrificial support method (SSM) has been developed at UNM group to prepare iron-nitrogen-carbon (Fe-N-C) platinum group metal free (PGM-free) catalysts for oxygen reduction reaction (ORR) [2-6]. Based on this method, we adopted polymerization pyrolysis (PP) to synthesize novel porous Fe-N-C ORR catalysts.

Pyrolyzing polymers has been widely investigated with different nitrogen contained candidate selection, such as polypyridine [7] and polyaniline [8]. However, it is the first time to synthesize ORR catalyst via pyrolyzing C-N-C backbone pyridine based polymers. By introducing ammonia persulfate into water with well dispersed 2-amino-6-methylpyridine (26AMP) or 2,6-diaminopyridine (26DAP) and silica, well nitrogen-carbon bonded polymers could be prepared. FTIR spectra show that there is no amino group absorption, indicating a thorough three dimensional polymerization. The followed pyrolysis with iron salt, HF washing and second ammonia processing lead to a final nanoporous composite.

These different PP catalysts all have good electrochemical performance. 26AMP based materials have high half-wave potentials in both base and acidic environment, no matter silica is used in polymerization (in situ) or just mixed with polymer before pyrolysis (ex situ). All four 26AMP and 26DAP based materials have competitive peroxide yield, achieving the 2% target of Department of Energy [https://energy.gov/eere/fuelcells/durability-working-group].

Figure 1
Interface-Controlled Synthesis of Platinum-Free Anode Catalyst for Fuel Cells Application
Authors: Ding Wei , Tao Sicheng , Wei Zidong
Published: February 2020

The ever-growing concerns about global warming and energy security demand the expansion of renewable energy sources as viable alternatives to fossil-fuel-based technologies. In all of these concepts, hydrogen is the key energy carrier and, despite several hurdles that still need to be overcome. Two reactions that will inevitably reign over the hydrogen economy are the HOR and its reverse, the HER. The HOR predominantly finds application in fuel cells, while the HER features in various electrolysers. However, the sluggish kinetics of HER and HOR in a basic environment causes high overpotential and associated large energy consumption, which greatly hinders practical application of alkaline electrolysis and alkaline fuel cell. As a typical example, though platinum (Pt) is generally believed as one of the best electrocatalysts for HER and HOR, its catalytic activity is about two orders of magnitude lower in alkaline environment compared with that in acidic electrolyte. Therefore, it is extremely crucial to synthesize a new HOR catalyst with low cost and high activity for HOR in alkaline environment to replace Pt in FCs.

The key to develop a highly active Pt-free HOR catalysts in alkaline environment is constructing a catalytic interface with suitable hydrogen (H) and hydroxyl (OH) binding energies (HBE). Such interface can promote the desorption of Had intermediate and depress adsorption of hydroxyl species. Herein, we report a synthetic method of Ru NPs with strong oxidation resistance and high activity for HOR in alkaline media, by using TiO2 to construct an interface with controlled H and OH binding energy. Our results show that the low-cost RuTiO2/C catalyst exihits an excellent HOR catalytic activity for HOR which is much better than that of Pt based catalysts. This opens a new way to tuning the catalyst interface for the preparation of high performance HEMFC anode catalysts.

Figure 1
Electrochemical De-Hydrogenation of Liquid MCH at Room Temperature
Authors: Badar Saifullah , Kanou Manabu , Nakata Yuki , Nam Hyunjeong , Zenitani Yuji
Published: February 2020

Hydrogen is a potential candidate for energy carrier role with high gravimetric energy density of 33kWh/kg. However, owing to its low volumetric energy density, 0.003kWh/l at STP, which is very small compared to common fuels, it poses logistical barriers in its widespread use. Conventional methods of hydrogen storage and transportation include compression up to pressures near ~80MPa or liquefaction by cooling down to temperatures below -253˚C. Another promising method of hydrogen storage is to chemically store in the form of organic hydrides. One such organic hydride is methyl-cyclo hexane (MCH), which is liquid at standard temperature and pressure and can be reversibly hydrogenated and de-hydrogenated for storage and extraction of hydrogen, respectively.

Extraction of hydrogen from MCH through dehydrogenation is an endothermic process (ΔH=204.8kJ/mol), so to favor hydrogen production the reaction is carried out at high temperatures. Conventionally, this is carried out in chemical plant sized reactors at temperatures near ~350˚C [1]. Maintaining such a high temperature in small scale energy devices increases the cost and complexity. Hence it is difficult to carry out dehydrogenation locally within the energy devices which utilize the thus extracted hydrogen. A low temperature (<120˚C) and low pressure (~1atm) dehydrogenation process able to be carried out in small scale devices can herald widespread use of MCH as a hydrogen carrier. This will promote hydrogen as a viable option to conventional fuels.

In this study, we have demonstrated the dehydrogenation of MCH at room temperature and pressure using polymer electrolyte membrane (PEM) based electrochemical cell. By applying a potential across the membrane electrode assembly (MEA), consisting of carbon supported catalyst electrode as anode and cathode, hydrogen evolution was observed at cathode side with the supply of MCH at the anode. Quinones have been used as reaction mediator to lower the electrode potential required for the dehydrogenation of liquid MCH to below the water electrolysis potential (1.23V). Formation of toluene as a dehydrogenation by-product at anode was also confirmed using gas chromatography mass spectrometry (GC-MS) analysis. Effect of temperature variation and anode reactant flow rate has been investigated.

References

F. Buonomo, D. Sanfilippo, F. Trifirò, in: G. Ertl, H. Knözinger, J. Weitkamp (Eds.), Handbook of Heterogeneous Catalysis, vol. 5, VCH, Weinheim, 1997, p. 2140
(Invited) From Discovery through to Commercialization: Federal Support
Authors: Madsen Lynnette D
Published: February 2020

As a Program Director at the National Science Foundation (NSF) working in the Mathematical and Physical Sciences Directorate, most efforts deal with supporting the discovery aspects of science – creating/revealing new materials or phenomena, improving the understanding of scientific underpinnings, and/or establishing new techniques and approaches. However, many NSF programmatic funding opportunities have an option to link to industrial partners through a mechanism called Grant Opportunities for Academic Liaison with Industry (GOALI). Also, there are centers across NSF that foster partnerships with industry; some include mandates to do so. The locus on going beyond discovery to applications at NSF lies within the Engineering Directorate, particularly in the Division of Industrial Innovation and Partnerships (IIP).

NSF is not alone in these undertakings; many Federal agencies have such efforts. The recently released 2016 National Academies report, Triennial Review of the National Nanotechnology Initiative (https://doi.org/10.17226/23603) summarizes many of these efforts to address technology transition. The Nanotechnology Innovation and Commercialization Ecosystem (NICE) Working Group chartered by the Nanoscale Science, Engineering, and Technology (NSET) Subcommittee (https://www.nano.gov/about-nni/working-groups) is interested in further identification of activities to improve technology exchange across the 20 Federal departments and independent agencies engaged in the National Nanotechnology Initiative (NNI).

This region between discovery and commercialization is often described in some circles as the Valley of Death – however, the National Institutes of Health discusses stages from basic science research through four translational phases: humans, patients, practice, and community where each occurs in conjunction with clinical trials. The assortment of programs available reflects the different agency missions, their attention to pinpointing specific hurdles in the process, and the importance of realizing economic benefits from the research. One example, the Small Business Technology Transfer (STTR) program, fosters technology transfer through cooperative R&D between research institutions and small businesses. Participating organizations include the Department of Defense (DOD), Department of Energy (DOE), Department of Health and Human Services (HHS), National Aeronautics and Space Administration (NASA) and NSF. Another example, Innovation Corps (I-Corps), teaches grantees to identify valuable product opportunities that can emerge from academic research, and offers entrepreneurship training facilitated by domain experts. Both NSF and NIH participate. These and other model programs will be discussed.
(Invited) Review of Advances in Solid Oxide Fuel Cells in the Past Four Decades
Authors: Singhal Subhash C
Published: February 2020

Solid oxide fuel cell (SOFC) technology has made significant progress in the past 40 years and is currently in the early commercialization stage. The progress of the technology can be seen through review of the papers and presentations at the biennial International Symposium on Solid Oxide Fuel Cells initiated in 1989. This paper highlights key advances in materials development, understanding of electrode reactions and chemical interactions, and design, performance, durability and operation of single cells, multi-cell stacks and power systems. Power generation systems built with various design solid oxide fuel cells are described and their operating experiences reviewed, as well as challenges in reducing cell and system costs are summarized.
(Invited) Enhancing Phase Stability and CO2 Tolerance of Ba0.5Sr0.5Co0.8Fe0.2O3-δ
Authors: Ivers-Tiffée Ellen , Almar Laura , Szász Julian , Meffert Matthias , Störmer Heike , Gerthsen Dagmar
Published: February 2020

High-temperature devices such as solid oxide fuel cells (SOFCs) and oxygen transport membranes (OTMs) require materials with high chemical, microstructural stability as well as high catalytic activity towards the oxygen reduction reaction. In its cubic phase the mixed ionic-electronic conductor Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) presents outstanding oxygen transport properties and exceedingly low cathode resistance [1]. However, the application in OTMs has been hampered by its degrading oxygen permeability in the relevant temperature range (600 – 800 °C). It was shown by our group [2], that the multivalent Co-cation prefers within this temperature range a higher valence which destabilizes the cubic structure favoring the hexagonal phase formation.

Various doping strategies with transition metals like, e.g., Y have shown beneficial effects with respect to stabilizing the cubic BSCF phase and preservation of the oxygen conductivity [3,4]. In this direction the effect of B-site partial substitution with Y, Ti or Nb has been studied thoroughly by our group using scanning electron microscopy (SEM) and analytical (scanning) transmission electron microscopy ((S)TEM) combined with energy dispersive X-ray spectroscopy (EDXS).

In addition, the oxygen reduction reaction of pure and doped BSCF electrodes is investigated in oxygen-nitrogen mixtures (pO2 = 0.02 to 0.4 atm) as well as in CO2-atmospheres (0.1…1 vol. % CO2) using symmetrical SOFC cells with Ce0.9Gd0.1O2-δ (CGO) as electrolyte from 600 to 800 °C. Characterization by electrochemical impedance spectroscopy (EIS) combined with the distribution of relaxation times (DRT) reveals an enhanced tolerance of doped BSCF cathodes, in particular Y-doped, towards the adsorption-desorption of CO2 molecules. Channeling enhanced microanalysis (ALCHEMI) investigations on Y-doped BSCF demonstrate the coexistence of Y ions on both cation lattice sites with up to 55 % of the Y-ions located on the unintended A-lattice site [5,6].

Overall this study shows that enhancing the phase stability and the CO2 tolerance of BSCF by a rational substitution of the B-site is plausible while the high performance and its excellent oxygen transport properties are kept.

References:

[1] Z. Shao, S.M. Haile. Nature, 431 (2004) 170-173.

[2] P. Müller, M. Meffert, H. Störmer, D. Gerthsen. Microsc. Microanal., 19 (2013) 1595-1605.

[3] P. Haworth, S. Smart, J. Glasscock, J.C. Diniz da Costa. Sep. Purif. Technol., 94 (2012) 16-22.

[4] M. Meffert, L-S Unger, L. Grünewald, H. Störmer, S. F. Wagner, E. Ivers-Tiffée, D. Gerthsen. J. Mater. Sci., 52 (2017) 2705-2719.

[5] J. C. H. Spence and J. Taftø. J. Microsc., 130 (1983) 147-154.

[6] M. Meffert, H. Störmer, D. Gerthsen. Microsc. Microanal., 22 (2016) 113-121.
(Invited) Modeling Transport Processes in Perovskite-Based Mixed Ionic-Electronic Conducting Membranes
Authors: Kee Robert J. , Zhu Huayang
Published: February 2020

Although many mixed ionic-electronic conductors (MIEC) share crystallographically similar doped perovskite structures, wide ranges of particular materials offer a diverse range of practically useful applications. Broadly speaking, the MIEC materials may be dominantly oxygen-ion conductors or proton conductors. The present paper is primarily concerned with transport processes that are relevant for membrane applications. Such applications include fuel cells, electrolyzers, gas separations, membrane reactors, and electrochemical compressors. The presentation uses illustrative examples.

In practice gases must react at the membrane surfaces to incorporate or release ions or other charge-carrying defects. The mobile charge carrying defects can include oxygen vacancies, protons, and a variety of small polarons. The defect transport may be represented in terms of Nernst-Planck fluxes. An internal electrostatic-potential field must be developed maintain charge-neutrality within the membrane. The Nernst-Planck flux depends on gradients of defect concentrations, electrostatic potential, and hydrostatic stress.

Depending on the material and the application, the membrane may be polarized by applying an electric potential from an external circuit. Ideally, for most membrane applications, the defect transport is entirely ionic. However, electronic defects (typically small polarons) can effectively result in electrical “leakage” that frustrates polarization. Applications such fuel cells, electrolyzers, and electrochemical compressors require membrane polarization. Depending on the material’s effective electrical conductivity polarization may not be practical.

Local defect concentrations cause crystal-lattice-scale strain, which results in macroscopic stress through the membrane and its mechanical support structure. Such chemo-mechanical coupling can cause membrane distortion and potentially damaging high stresses.

Modeling membrane performance requires incorporating the Nernst-Planck fluxes into conservation equations. The rate of change in defect concentrations is balanced by the divergence of the Nernst-Planck fluxes. The local electrostatic fields may be determined in the context of a Poisson equation that effectively produces local electroneutrality. The resulting nonlinear, coupled, system of partial differential equations, generally called the Nernst-Planck-Poisson equations, may be solved computationally.
(Invited) Advances in Proton Ceramic Fuel Cells, Steam Electrolyzers, and Dehydrogenation Reactors Based on Materials and Process Optimizations
Authors: Norby Truls
Published: February 2020

Proton-conducting ceramics such as Y-doped BaZrO3-based perovskites form basis for hydrogen-fueled proton ceramic fuel cells (PCFCs) and proton ceramic electrolyzers (PCEs) for steam. Like the PCFC benefits from running undiluted hydrogen with superior fuel utilization without circulation, the PCEs produce directly dry hydrogen at the balanced total pressure of the electrolyzer while oxygen is diluted to lower pressure with the feed of steam, lowering the hazard of pressurized oxygen. The use of waste or renewable heat to generate and superheat the steam allows operation at high electrical efficiencies.

Operation at high steam pressures reduces p-type electronic conduction at the steam+oxygen electrode and the use of novel mixed proton-electron conducting double perovskites lowers the overpotential and hence p-type electronic conductivity further, altogether yielding acceptable faradayic efficiencies of the electrolyzer.

The presence of protons and significant protonic conduction in certain double perovskites in combination with their high electronic conductivity can be rationalized by recent results of studies of their structure and defect chemistry. 

Proton-conducting ceramics also offer unique opportunities for dehydrogenation of hydrocarbons including natural gas along different schemes and for different products, as suggested by Iwahara three decades ago. With materials and reactor design optimizations as well as process adaptions we now see emerging demonstrations of such use of proton-conducting ceramics.