bluuebunny/crossref_metadata_2025_split huggingface dataset:
Enthalpy Analysis and Heat Exchanger Sizing of an Air-Cooled Proton Exchange Membrane Fuel Cell System
Authors: Gao Xin 
Published: February 2020

Xin Gao
[1]
, Torsten Berning, Søren Knudsen Kær

Department of Energy Technology
Aalborg University
Pontoppidanstraede 111, 9220 Aalborg, Denmark
Proton exchange membrane fuel cells (PEMFC’s) are becoming increasingly popular for uninterrupted power supply especially in remote areas. In the case of telecom back-up operations, PEMFC systems are often placed in areas of extreme climates, e.g. in Norway or Canada where the temperatures drop below -20 °C in the winter which make liquid-cooled fuel cells impossible. In such cases, air-cooled fuel cell systems are deployed where the air that is fed to the fuel cell serves both as reactant supplier and coolant to remove the waste heat that is generated during fuel cell operation. In some cases the warmer exhaust air is used to pre-heat and also humidify the incoming colder and dryer air stream using an enthalpy wheel.
It is important to thermodynamically understand such a fuel cell system, and in this work the enthalpy streams and the humidity stream are followed throughout the fuel cell system in order to optimize the operating conditions and the performance of such a system. The adjustable parameters include the fan speed that determines the amount of air that is brought into the system, and the size and rotating speed of the rotating enthalpy wheel. In addition, computational fluid dynamics simulations have been carried out to better understand the distribution of the reactant air over the fuel cell stack and the resulting temperature distribution across the stack. These results suggest that the humidifying function of the current enthalpy wheel is negligible and a smaller enthalpy wheel or an ordinary heat exchanger can fulfill the heat recovery demand. Despite the fact that the air enters the stack at a cold temperature, even the forefront of the stack is at a much elevated and desired stack temperature with the help of supplying an acceptable amount of power to an electric stack heater. So a preheating of the air stream by the enthalpy wheel might be unnecessary during steady-state operation.

[1] Corresponding Author: xga@et.aau.dk
Analysing Gas-Liquid Flow in PEM Electrolyser Micro-Channels
Authors: Sadeghi Lafmejani Saeed , Olesen Anders Christian , Kær Søren Knudsen 
Published: February 2020

PEM water electrolysis is a key component for closing the loop of the renewable energy eco-system. These high response water electrolysers are particular suitable for fluctuating power sources. Conventional PEM water electrolysers are typically operated at a current density of around 1 A/cm2 and are fairly expensive. One means of increasing the hydrogen yield to cost ratio of such systems, is to increase the operating current density. However, at high current densities, management of heat transfer and fluid flow in the anode GDL and channel becomes crucial. This entails that further understanding of the gas-liquid flow in both the porous media and the channel is necessary for insuring proper oxygen, water and heat management of the electrolysis cell.
In this work, the vertical upward gas-liquid flow pattern in a 0.5×1×94 mm micro-channel is both numerically and experimentally analysed. A sheet of titanium felt is used as a permeable wall for permeation of air to the column of water similar to the phenomenon encountered in Oxygen Evolution Reaction (OER).
The transparent setup is operated in situ and the gas-liquid flow regimes are identified using a high-speed camera. The picture shows how the transparent cell is made which consists of a channel for the inlet air and a channel for the water-bubble flow. The transparent material is Plexiglas that is sealed with a sheet of silicon.
The conventional co-current gas-liquid two-phase flow patterns, such as bubbly flow, slug flow and annular flow, are observed in the present micro-channel. The phenomenon is also analysed numerically in 3D, unsteady, euler/euler multiphase method using the commercial software ANSYS FLUENT 17 and the results show good agreement with the experimental data.
Influence of each multiphase flow regime is described in the study as well as the recommendation for improving the performance. A well management of the multiphase flow regime along the whole micro-channel length can assure a proper distribution of water inside the titanium felt.

Figure 1
Origins of Suppressed Swelling and Increased Mechanical Properties of Ultrathin Nafion
Authors: Stafford Christopher M. , Frieberg Bradley R. , Jeong Cheol , Rowe Brandon W. , Page Kirt A. , Soles Christopher L. 
Published: February 2020

We have previously shown1,2 that there is a suppression in both swelling and water diffusivity when Nafion is confined to thin and ultrathin films. We have also shown that the modulus of ultrathin Nafion films increases upon confinement3,4, as well as upon thermal annealing. Interestingly, we also observe a decrease in swelling and an increase in modulus for ultrathin films aged in high humidity environments. Similar behavior has been shown to occur in bulk Nafion films.5,6 Some researchers suggest that the root cause of such a decrease in swelling and increase in modulus is due to the formation of sulfonic anhydrides, while others suggest that it is due to internal hydrogen bonding of dehydrated sulfonic acids.
In this talk, we will present our measurements results on thin and ultrathin Nafion films. We apply polarization-modulation infrared reflection-absorption spectroscopy to study the kinetics of dehydration and formation of sulfonate species in thin Nafion films. We also employ cantilever bending during humidity-induced swelling to probe the mechanical properties of these films. Grazing-incidence small-angle x-ray scattering is used to elucidate changes in morphology upon annealing and/or aging. By combing the results from these techniques, we can paint a more holistic picture of the origins of suppressed swelling and increased mechanical properties in thin and ultrathin Nafion films.

S. A. Eastman, S. Kim, K. A. Page, B. W. Rowe, S. Kang, C. L. Soles, and K. G. Yager. Effect of Confinement on Structure, Water Solubility, and Water Transport in Nafion Thin Films, Macromolecules, 45, 7920-7930 (2016).

E. M. Davis, C. M. Stafford, and K. A. Page. Elucidating Water Transport Mechanisms in Nafion Thin Films, ACS Macro Letters, 3, 1029-1035 (2014).

K. A. Page, J. W. Shin, S. A. Eastman, B. W. Rowe, S. Kim, A. Kusoglu, K. G. Yager, and G. R. Stafford. In Situ Method for Measuring the Mechanical Properties of Nafion Thin Films during Hydration Cycles, ACS Applied Materials and Interfaces, 7, 17874-17883 (2015).

K. A. Page, A. Kusoglu, C. M. Stafford, S. Kim, R. J. Kline, and A. Z. Weber. Confinement-Driven Increase in Ionomer Thin-Film Modulus, Nano Letters, 14, 2299-2304 (2014).

F. M. Collette, C. Lorentz, G. Gebel, F. Thominette. Hygrothermal aging of Nafion, Journal of Membrane Science, 330, 21-29 (2009).

S. Shi, T. J. Dursch, C. Blake, R. Mukundan, R. L. Borup, A. Z. Weber, and A. Kusoglu. Impact of Hygrothermal Aging on Structure/Function Relationship of Perfluorosulfonic-Acid Membranes, Journal of Polymer Science B: Polymer Physics, 54, 570-581 (2016).
Investigation of CeO2/Graphene and Nb2O5/Graphene Supported Pt and PtCo Catalysts Towards Methanol and Ethanol Oxidation and Oxygen Reduction Reactions
Authors: Kepeniene Virginija , Stagniunaite Raminta , Tamasauskaite-Tamasiunaite Loreta , Selskis Algirdas , Norkus Eugenijus 
Published: February 2020

In this study the CeO2/graphene and Nb2O5/graphene supported Pt and PtCo catalysts denoted as PtCeO2/GR, PtNb2O5/GR, PtCoCeO2/GR and PtCoNb2O5/GR were prepared by polyol method using the simple and rapid microwave heating method. To obtain the catalysts, required amounts of CeO2/graphene or Nb2O5/graphene, H2PtCl6 and CoCl2 were heated in ethylene glycol at 170 oC for 30 min in the microwave reactor. It was found that Pt nanoparticles were successively deposited onto the surfaces of CeO2/graphene and Nb2O5/graphene. For comparison, the PtCo/graphene (PtCo/GR) and Pt/carbon (Pt/C) catalysts were prepared in the same manner. The composition and morphology of catalysts were detected by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), Field Emission Scanning Electron Microscopy (FESEM), and Transmission Electron Microscopy (TEM). The synthesized PtCeO2/GR, PtNb2O5/GR, PtCoCeO2/GR, PtCoNb2O5/GR, PtCo/GR and Pt/C catalysts were examined as electrocatalysts towards the electro-oxidation of methanol and ethanol, and the reduction of oxygen.
It has been found that the CeO2/GR or Nb2O5/GR supported Pt and PtCo catalysts show an enhanced electrocatalytic activity towards the oxidation of ethanol and methanol in an alkaline medium as compared with that of the Pt/C catalyst. Depending on catalysts composition, ethanol and methanol oxidation current densities were found to be ca. 3 – 12 times higher at the CeO2/GR and Nb2O5/GR catalysts, respectively, in comparison with those at the Pt/C catalyst.
In the case of oxygen reduction, the PtCoCeO2/GR and PtCoNb2O5/GR catalysts outperform the PtCeO2/GR, PtNb2O5/GR, PtCo/GR and Pt/C catalysts towards oxygen reduction and shows higher onset potential, as well as higher current density towards the oxygen reduction reaction as compared with those at the aforementioned catalysts.
Oxide-Coated Carbon Black for Cathode Catalyst Support
Authors: Nako Yuki , Sonoda Takashi , Itoh Tetsuya , Kinumoto Taro 
Published: February 2020

Carbon black is an essential material for PEFC. Due to its specific surface area, conductivity, pore-making structure and stability for acidic environment, carbon black is so far the best choice as the catalyst support for cathode and anode. However, carbon black is being one of the critical elements which limit the lifetime of PEFC. Especially in cathode, oxidative degradation of carbon black support is resulting in the depression of catalyst activity.
In order to prevent carbon black support from its oxidative degradation, surface coating with silicon oxide (silica) on acetylene black was tried using sol-gel method. Nanometer-thick amorphous silica layer was formed on almost the whole surface on the acetylene black. Its effect on resistivity against oxidation, Pt supporting function and total behavior of the catalyst is to be discussed.
Resolving Active Sites and Porosity in PGM-Free Catalysts By Electron Microscopy
Authors: Cullen David A. , Sneed Brian , More Karren L. , Brewster James H , Odgaard Madeleine , Chung Hoon T , Zelenay Piotr 
Published: February 2020

Electrodes based on platinum group metal-free (PGM-free) catalysts are under development as an alternative to costly Pt-based cathodes for automotive fuel cell systems.[1,2] Novel PGM-free catalysts with much improved activity and durability must be developed in order to become competitive with their PGM nanoparticle counterparts for transportation applications. Analytical characterization by transmission electron microscopy plays an important role in identifying electrochemically active sites at the atomic scale as well as to exploring electrode morphology and porosity at the microscale.
In this work, a hybrid PGM-free catalyst developed at Los Alamos National Laboratory was studied by multiscale and multidimensional electron microscopy methods. This promising catalyst, branded CM-PANI-Fe-C, has been synthesized by heat-treating two nitrogen precursors, polyaniline (PANI) and cyanamide (CM). The catalyst is comprised of fibrous carbonaceous agglomerates intermixed with few-layer graphene sheets. Low voltage aberration-corrected scanning transmission electron microscopy (STEM) and atomic resolution electron energy loss spectroscopy (EELS) were utilized to identify single Fe atoms coordinated with nitrogen within the few-layer graphene sheets (Fig. 1a,b). These atomic features have been identified by modeling as a possible active site which exhibits high four-electron selectivity.
The thick electrode structures required to accommodate high non-PGM loadings also play a critical role in fuel cell performance. Hierarchal pore structures (spanning the micro to macro) are necessary for maintaining high mass transport through the thick electrodes. Complementary imaging and compositional mapping by energy dispersive X-ray spectroscopy (EDS) has been utilized to study the bulk electrode structures, as shown in Fig. 1c. These analytical studies will be extended to understand the role of different process parameters on catalyst and electrode structures at multiple length scales.
References

G. Wu, K. L. More, C. M. Johnston, P. Zelenay, Science 332 (2011) 443.

Z. Chen, D. Higgins, A. Yu, L. Zhang, J. Zhang, Energy Environ. Sci. 4 (2011) 3167.

Acknowledgements
Research sponsored by the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy (DOE), and through a user project supported by ORNL’s Center for Nanophase Materials Sciences (CNMS), which is a DOE Office of Science User Facility.

Figure 1
An Examination of Voltage Losses for the Hydrogen Oxidation and Reduction Reactions in an Alkaline Membrane Fuel Cell
Authors: Park Andrew Michael , Yang-Neyerlin Ami C. , Shiau Huai-Suen , Alia Shaun M , Weber Adam Z , Neyerlin K.C. , Pivovar Bryan S 
Published: February 2020

Recent advances in highly conductive and base stable anion exchange membrane chemistries have enabled the widespread fabrication of alkaline membrane fuel cells (AMFC).(1) A significant limitation to AMFC commercialization, however, is the sluggish hydrogen oxidation reaction (HOR) kinetics of current anode catalysts. Much work has been performed to understand the fundamental limitations of HOR in an alkaline environment(2, 3) and to study the HOR in an alkaline membrane electrode assembly (MEA)(4). It is of significant interest to the AMFC community to continue studying the HOR reaction to understand the in-situsources of voltage losses, and to develop a diagnostic tool to test the kinetics of new/alternative catalysts in an alkaline MEA.
In this study, a series of MEAs were fabricated where the membrane (Tokuyama A201) and binder polymer (Tokuyama AS-4) are held constant, but where the catalyst content and composition are varied. A hydrogen pump technique was utilized where an external current source drives HOR on one electrode of the MEA and hydrogen evolution (HER) on the other. It should be noted that there is no traditional reference electrode in this system, as each electrode reaction contributes a significant overpotential. The polarization curves acquired from the hydrogen pump are analyzed for sources of voltage losses including mass transport, ohmic, and kinetic overpotentials. The causes of such losses will be discussed and presented with insight gained from modeling and experimental work. Exchange current densities of HOR and HER for both platinum on carbon and platinum ruthenium on carbon will also be presented, where all data was taken in an in-situalkaline MEA. The potential for hydrogen pump as a diagnostic method for future anode catalyst testing will also be included.
Figure 1. HOR and HER overpotentials for Pt/C electrodes between 0.119 and 0.8 mg/cm2 loading as a function of current density per Pt site, with the corresponding Butler-Volmer model fit
1. J. R. Varcoe, P. Atanassov, D. R. Dekel, A. M. Herring, M. A. Hickner, P. A. Kohl, A. R. Kucernak, W. E. Mustain, K. Nijmeijer, K. Scott, T. Xu and L. Zhuang, Energy & Environmental Science(2014).
2. J. Durst, A. Siebel, C. Simon, F. Hasche, J. Herranz and H. A. Gasteiger, Energy & Environmental Science, 7, 2255 (2014).
3. Y. Wang, G. Wang, G. Li, B. Huang, J. Pan, Q. Liu, J. Han, L. Xiao, J. Lu and L. Zhuang, Energy & Environmental Science, 8, 177 (2015).
4. M. D. Woodroof, J. A. Wittkopf, S. Gu and Y. S. Yan, Electrochemistry Communications, 61, 57 (2015).

Figure 1
Electrochemical Property of Ni-Ba(Zr,Y)O3 Anode for Direct Ammonia-Fueled SOFC
Authors: Miyazaki Kazunari , Okanishi Takeou , Muroyama Hiroki , Matsui Toshiaki , Eguchi Koichi 
Published: February 2020

Hydrogen carriers have attracted much attention as alternative fuels to hydrogen. This is because the hydrogen fuel has technological difficulties in transportation and storage, which impedes the wide application. Among various hydrogen carriers, ammonia is one of the promising candidates because of various advantages such as ease in liquefaction, high energy density, large hydrogen content, and zero emission of CO2during reforming or decomposition. In addition, the infrastructure for ammonia utilization has been established because ammonia has been used as a fertilizer and commodity chemicals worldwide.
In the case of solid oxide fuel cells (SOFCs) directly supplied with ammonia fuel, ammonia decomposes into hydrogen and nitrogen on the anode and subsequently hydrogen is electrochemically oxidized. Therefore, the anode materials for ammonia-fueled SOFCs need to be active for the electrochemical hydrogen oxidation as well as the catalytic ammonia decomposition. The mixture of nickel and Ba(Ce,Y)O3−δ
(BCY), which is one of the promising proton conductors, has been already reported as a highly active catalyst for ammonia decomposition[1].
In this study, then, the activity tests for ammonia decomposition were performed for various nickel catalysts supported on proton conductors. Ammonia decomposition proceeded at lower temperature over Ni−proton conductor cermets compared with the conventional anode of Ni−yttria-stabilized zirconia (YSZ) cermet. Ammonia decomposed completely over Ni−proton conductor cermets at ca. 600ºC, while a complete ammonia decomposition was accomplished over Ni−YSZ at higher temperature. In particular, the Ni−Ba(Zr,Y)O3−δ
(BZY) catalyst exhibited superior activity. In order to evaluate the anode performance of ammonia-fueled SOFC, a single anode-supported cell composed of Ni−BZY|BZY|Pt was fabricated. Electrochemical measurements were conducted at 600−700ºC by using ammonia or hydrogen as a fuel and oxygen as an oxidant. The partial pressure and flow rate of hydrogen in the hydrogen-containing fuel gas were controlled to be the same as those after the complete decomposition of ammonia in the ammonia-containing one. At each temperature, the open circuit voltages (OCVs) under both fuel gas flows were almost the same. From this result, it can be tentatively concluded that ammonia was oxidized via the two-step reaction on the anode as mentioned above. At 700ºC, the current density at the terminal voltage of 0.5 V under hydrogen and ammonia fuel conditions were 280 mA cm−2 and 250 mA cm−2, respectively. The difference in performance between ammonia and hydrogen-containing fuels was small. Consequently, the Ni−BZY catalyst is a promising anode for ammonia-fueled SOFCs.

[1] J. Yang, A.F.S. Molouk, T. Okanishi, H. Muroyama, T. Matsui, K. Eguchi. ACS Appl. Mater. Inter., 7, 7406 (2015).
Electro-Chemo-Mechanical Studies of Perovskite-Structured Mixed Ionic-Electronic Conducting SrSn1-XFexO3-x/2+d
Authors: Kim Chang Sub , Bishop Sean R. , Perry Nicola H. , Tuller Harry L. 
Published: February 2020

High efficiency and fuel flexibility make solid oxide fuel cells (SOFCs) attractive for conversion of fuels to electricity. Reduced operating temperatures, desirable for reduced costs and extended operation, however result in significant losses in efficiency. This has been traced primarily to slow cathode surface reaction kinetics. In this work, we extended previous studies on the promising mixed ionic and electronic conducting perovskite-structured SrTi1-xFexO3-x/2+δ (STF) materials system whose exchange kinetics were correlated with the minority electron charge density by replacing Ti with Sn, due to its distinct band structure and higher electron mobility.
Oxygen nonstoichiometry and defect chemistry of the SrSn1-xFexO3-x/2+δ (SSF) system were examined by thermogravimetry as a function of oxygen partial pressure in the temperature range of 973-1273 K. Marginally higher reducibility was observed compared to corresponding compositions in STF system. The bulk electrical conductivity was measured in parallel to examine how changes in defect chemistry and electronic band structure associated with the substitution of Ti by Sn impact carrier density and ultimately electrode performance. Bulk chemical expansion was measured by dilatometry as a function of oxygen partial pressure while surface kinetics were examined by means of AC impedance spectroscopy. The electro-chemo-mechanical properties of SSF were found not to differ significantly from the corresponding composition in STF. Key thermodynamic and kinetic parameters for SrSn0.65Fe0.35O2.825+δ (SSF35) were derived including the reduction enthalpy, high electronic band gap, anion Frenkel enthalpy, oxygen vacancy migration energy, electron and hole mobilities. Though slightly shifted by Sn’s larger size, the defect equilibria and the cathode area specific resistance differed only in a limited way from those in STF. This was attributed to properties being largely dominated by Fe and not by the substitution of Ti with Sn.
Chromium Impurity Effects on SOFC Cathodes Using Half-Cell Measurements
Authors: Gong Yiwen , Zhu Yuexing , Wang Ruofan , Sun Zhihao , Pal Uday Bhanu , Basu Soumendra Nath , Gopalan Srikanth 
Published: February 2020

Solid oxide fuel cells (SOFCs) offer a clean, efficient and environmental-friendly technique to convert chemical energy to electricity . In order to achieve high performance at lower operating temperature, anode-supported planar solid oxide fuel cells are usually preferred. The lower operating temperature enables the deployment of metallic interconnects based on ferritic stainless steel. The leading candidate alloy is Crofer 22 APU which is a state-of-the-art material with good high-temperature stability, high electrical conductivity and low coefficient of thermal expansion. However, the chromia oxide scale that forms on the surface of the Crofer 22 APU alloy reacts with the oxygen and water vapor to form volatile chromium species, chromium trioxide, CrO3, and chromium oxyhydroxide, CrO2(OH)2which deposit on the electrochemically active regions of the cathode. In order to understand the mechanism of chromium poisoning in SOFCs, electrolyte-supported half-cells have been fabricated. 8mol%-yttria-stabilized-zirconia pellets are used as electrolyte by uniaxial pressing. Lanthanum strontium manganite is screen printed on both side of the YSZ pellet, and a silver wire is used as the reference electrode.
These half-cells have been tested at different temperatures with different humidity levels in the air, with and without contacting the Crofer 22 APU alloy. Galvanostatic current interruption (GCI) has been employed during the electrochemical test, and after the test, scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX) have been used to detect the composition near the TBPs.

Figure 1