bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of a (La,Sr)2CoO4 Phase on the Oxygen Exchange Reaction of Dense and Porous (La,Sr)CoO3 Electrodes
Authors: Kawada Tatsuya , Yashiro Keiji , Hashimoto Shin-ichi , Amezawa Koji
Published: February 2020

Oxygen reduction reactions on a mixed conducting lanthanum cobaltite, (La,Sr)CoO3: LSC, have been widely investigated both from scientific interest and from the technological importance as a cathode of a solid oxide fuel cell. Since the reaction pathway is not simple in a practical porous electrode, model electrode approaches have been adopted by many researchers. However, the reaction mechanism and rate determining processes may not be always identical between model and porous electrodes, which can mislead the research and development.

The authors have been making efforts to improve oxygen reduction activity of LSC by utilizing the promotion effect of a co-existing Ruddlesden-Popper phase, (La,Sr)2CoO4 : LSC214, which was first observed at the surface of a dense ceramic LSC(1). The concept worked for a dense film electrode but not for a practical porous electrode except when the initial performance of LSC was somehow poor(2). The difference between dense and porous LSC may account for the results. The followings are what we found in the course of the research:

1. The oxygen exchange rate around on LSC was faster around the thermally precipitated LSC214 particles. (1)

2.Application of a porous LSC214 layer on a dense film LSC electrode showed increased reaction rate and decreased activation energy. (3)

3. Application of a porous LSC214 layer on a porous LSC electrode appeared to improve the performance when the base LSC layer had somehow large electrochemical resistance. (2)

4. Well-prepared LSC electrode showed the electrochemical resistance of about 0.5 ohm cm2 in air at 600˚C, and no further improvement was achieved by application of LSC214 layer on the electrode ore mixing LSC214 particles in the electrode.

5. Effective utilization length of a porous LSC electrode evaluated by the electrochemical impedance was thinner than expected from the surface reaction and bulk diffusion constants of dense ceramic LSC.

6. Surface reaction rate of a dense LSC decreased significantly with Sr segregation in the surface/sub-surface layers.

7. Strontium on the surface of LSC film appeared to be removed when it was in contact with porous LSC214 layer. Based on the above observations, the difference of dense and porous LSC electrodes will be discussed in terms of Sr segregation and in the role of LSC214.

References

(1) M. Sase, K. Yashiro, K. Sato, J. Mizusaki, T. Kawada, N. Sakai, K. Yamaji, T. Horita, H. Yokokawa, Solid State Ionics 178(35), 1843 (2008).

(2) K. Yashiro, T. Nakamura, M. Sase, F. Hermes, K. Sato, T. Kawada, J. Mizusaki, Electrochem. Solid State Lett. 12(9), B135-B137 (2009).

(3) T. Kawada, T. Tairako, K. Nagao, A. Unemoto, M. Sase, K. Yashiro, S. Hashimoto, and K. Amezawa, Proc. 16th Intern. Conf. Nanotechnology, Sendai, Japan, August 22-25, 2016
Microstructure Degradation of Solid Oxide Fuel Cells Aged in Stack after Long Operation Time up to 20 000h Using 3D Reconstructions by FIB Tomography
Authors: Zekri Atef , Knipper Martin , Parisi Jürgen , Plaggenborg Thorsten
Published: February 2020

Solid oxide fuel cells (SOFCs) are getting more importance with their promising future, due to their high-energy conversion efficiency, low-emissions and flexibility of usable fuel type. The performance and the lifetime of SOFCs are keenly dependent on electrode microstructure. In order to recognize the microstructural evolution and its degradation kinetics in SOFC cermet cathodes during long exposure time (up to 20 000 h) under realistic operating conditions ( T= 850 °C, J= 190-250 ), investigations on porous LSM/YSZ cathodes were conducted. The 3D-tomography technique (FIB/SEM) offers extensive data about the microstructures of various cathode aged during different operating times (2 500 h, 15 000 h and 20 000 h), which allows an exact quantification of particle size distribution, phase-connectivity, tortuosity factor and Triple Phase Boundary Length (TPBL). With the increasing operating time no significant 3D microstructural changes in the cathode were noticed in the obtained data. However, additional qualitative X-ray fluorescence measurement, indicate a clear presence of chrome contamination on aged cathodes, which may be the main degradation mechanism in the SOFC cathode.

Keywords: chrome poisoning, long operating time, particle size distribution, SOFC, triple phase boundary, SEM, XRF
Impact of Dislocations on Surface Reactivity of Ceria with Singe Atom Catalysts
Authors: Yildiz Bilge , Sun Lixin
Published: February 2020

Single-atom catalysts, where atomically dispersed transition metals are anchored at solid surfaces, are a new type of low price, high efficiency and nonflammable catalysts for water gas shift and CO2 methanation, where selective oxidation or reduction is needed. Ceria is one of the most promising support materials for these single-atom catalysts, because of its large oxygen capacity and high ionic mobility. The large amount of available lattice oxygen or oxygen vacancies in ceria is beneficial for selective oxidation and reduction, though the performance of pure ceria is limited by its poor surface exchange properties. Mixing or doping transition metals to ceria can activate the surface of ceria. In particular, transition metals anchored as isolated single atoms are found to be highly active. However, it is challenging to enhance the density of these single atoms due to the strong tendency of metal agglomeration. Having understood how dislocations in oxides can serve as traps for charged point defects in our previous studies, we have aimed here to assess whether we can stabilize single metal atoms at dislocations in ceria.

To this end, first, a wide range of charge states and configurations of Cu defects in a dislocation free ceria model are calculated to elucidate the defect chemistry for Cu ions in bulk ceria. The formation energies of these defects as a function of chemical potential of oxygen and the Fermi energy indicate that the most preferred Cu defect is Cu1+ interstitial. This finding differs from previous calculations in the literature where only a copper vacancy complex is calculated, but is consistent with reported experimental observations. Moreover, the equilibrium Cu defect concentration in ceria is negligible, indicating a low solubility of Cu in bulk ceria.

Second, an edge dislocation model in ceria was constructed. We found that the Cu defect formation energy at the edge dislocation core is 2 eV lower than that in the bulk, indicating a tendency for Cu to enrich at the dislocation compared to the bulk ceria (which has a very low solubility of Cu). More interestingly, and importantly, Cu has a lower oxidation state in the dislocation core than in the bulk. This lower oxidation state is more active for catalytic activity. Both the enrichment of Cu at the dislocation core and the more active oxidation state indicate that dislocations in ceria are beneficial for increasing surface electro-catalytic reaction kinetics with single atom catalysts.
(Invited) Triple Phase Boundary Reaction in a Mixed-Conducting SOFC Cathode
Authors: Amezawa Koji , Fujimaki Yoshinobu , Mizuno Keita , Kimura Yuta , Nakamura Takashi , Nitta Kiyofumi , Terada Yasuko , Iguchi Fumitada , Yugami Hiroo , Yashiro Keiji , Kawada Tatsuya
Published: February 2020

Solid oxide fuel cells (SOFCs) attract attentions as high-efficiency energy-conversion devices. In order to establish high-performance SOFCs, the slow electrode kinetics, which is often a main cause of the energy loss, should be improved. In present SOFCs, mixed ionic-electronic conducting (MIEC) oxides, such as (La,Sr)CoO3
-δ
and (La,Sr)(Co,Fe)O3
-δ
, are typically used as the cathode materials. In such an MIEC cathode, it is generally believed that electrochemical oxygen reduction reaction takes place mainly at the oxide surfaces (double phase boundary, DPB) and the contribution of the reaction at the electrode/electrolyte/gas interface (triple phase boundary, TPB) is insignificant. Therefore, researches on the kinetics of SOFC cathodic reaction have mostly concerned to investigate the surface reaction on the electrode oxides.

In our previous works, the reaction distributions in MIEC SOFC electrodes were experimentally evaluated by using operando micro X-ray absorption spectroscopy (operando μ-XAS) [1, 2]. For more quantitative and precise investigation of the reaction distribution, we proposed a patterned thin film electrode, which is a kind of the columnar electrode simplifying the microstructures of a porous electrode [2]. However, the patterned thin film electrode in our previous work did not have triple phase boundaries, and it was thus impossible to discuss the contribution of TPB reaction to the total reaction. In this work, a patterned thin film electrode having triple phase boundaries was fabricated. (La,Sr)CoO3-

d
(LSC) was chosen as the model MIEC oxide for SOFC cathodes. The reaction distribution in this new type of the patterned thin film electrode was experimentally determined by using operando μ-XAS, and the results were compared with ones obtained with the old type of the patterned thin film electrode without TPB. It was found the effective reaction area tended to shrink by the introduction of TPB to the patterned thin film electrode. This fact might suggest that the reaction at TPBs in SOFC cathodes is not negligible even when MIEC oxides are used as electrode materials.

References

[1] Y. Fujimaki, T. Nakamura, K. Nitta, Y. Terada, K. Yashiro, T. Kawada, K. Amezawa, to be sumitted.

[2] K. Amezawa, Y. Fujimaki, T. Nakamura, K. D. Bagarinao, K. Yamaji, K. Nitta, Y. Terada, F. Iguchi, K. Yashiro, H. Yugami, T. Kawada, Electrochem. Soc. Trans., 66(2), 129 (2015).
First-Principles Study on Oxygen Reduction Reaction over La1-xSrxCoO3-δ
Authors: Koyama Michihisa , Ishimoto Takayoshi
Published: February 2020

Electrode kinetics in solid oxide fuel cells are intensively studied to realize the highly efficient system in small- and large-scale applications. As the understandings become deeper, it is important to understand the atomistic-level kinetics of the electrode catalysis as well as to understand the essential nature of catalyst properties. Thus the application of computational chemistry to this issue will be an effective and important option. The author’s research group has theoretically investigated the oxygen reduction reaction kinetics over La1-xSrxCoO3-δ cathode by using density functional theory method and the Ni-YSZ anode by using both density functional theory method [2] and a microkinetic simulation [3]

State-of-the-art results will be introduced in the presentation.

Acknowledgements

Activities of INAMORI Frontier Research Center is supported by Kyocera Co. Ltd. The part of the research is supported by CREST, Japan Science and Technology Agency.

References

[1] T. Ishimoto, K. Sato, T. Tada, K. Amezawa, M. Koyama, ECS Trans., 68(1) (2015) 651.

[2]S.-x. Liu, T. Ishimoto, D. Monder, M. Koyama, J. Phys. Chem. C, 119 (2015) 27603-27608.

[3] H. Kohno, S. Liu, T. Ogura, T. Ishimoto, D. S. Monder, K. Karan, M. Koyama, ECS Trans., 57(1) (2013) 2821-2830.
(Invited) Understanding and Controlling Anionic Electrochemical Activity in High-Capacity Oxides for Next Generation Li-Ion Batteries
Authors: Meng Ying Shirley
Published: February 2020

Recently, anionic activity, such as oxygen redox reaction, has been discovered in the electrochemical processes of rechargeable lithium ion batteries, providing extra reversible capacity for certain transition-metal oxides. Consequently, a more complete understanding and precise controlling on anionic electrochemical activity in these high-capacity oxides have become a flourishing, yet challenging subject. This talk highlights (see the figure below): (1) key features of the anionic electrochemical activities; (2) computational and experimental tools to characterize and quantify the anionic activity; (3) design principles that correlate the chemical and structural compositions with high reversible capacity to accelerate the discovery of novel cathode oxides for next generation Li-ion batteries.

Figure 1
Thermostatics of Concentration Polarization and the Possible Effects of Surface Ad-Ions in SOFC Composite Cathodes
Authors: Teixeira Roberto Janny , de Paiva José Luís
Published: February 2020

In situations common to high-temperature SOFC (Solid-Oxide Fuel Cell) operation at steady-state, the dependence of the activity of oxide ions on the oxygen partial pressure (p_O2) becomes relatively unimportant for p_O2>0.15 bar. Nevertheless, one might question what would be the indirect effect (if any) of surface ad-ions on the evaluation of concentration polarization due to changes on the oxygen partial pressure near to the grain boundary between electronic, ionic, and gas phases. From thermostatics considerations and macroscale-continuum phenomenological equations it is shown that the definition of concentration polarization, as commonly found in the literature, may contain a series of limitations and, among these limitations, it is discussed the relative importance of oxygen surface ad-ions on the formation of concentration cells,when it is compared to the concentration gradients of “bulk” gas species in the porous channels of SOFC cathodes. This theoretical discussion about the influence of contact chemistry near the TPB (three-phase boundary) region indicates that concentration polarization could in fact either increase or decrease, depending on whether the chemical activity of oxide ions is affected by the local chemical activity of O2 near the gas/solid interface. In order to verify this, one needs to know how the differences of interfacial potential step and chemical activity relate to changes in the contact chemistry and space charge zone near this interface. Particularly, the evaluation of the potential step between the electronic conductor and the ion adsorbed layer requires the prescription of certain phenomenological parameters. In the present study, one of these parameters is the density of “active” surface sites near the TPB region, which represents just a fraction of the total surface site density available over the entire electrode phase. It is a fraction because only those sites sufficiently close to the TPB “hot spot” are considered “active” for the adsorption of charged species, which are then subsequently able to undergo electrochemical reduction at the TPB. So to calculate this density of “active” surface sites and thus the corresponding electrostatic potential step, a phenomenological governing equation for oxygen ad-ions on the electrode surface is proposed (i.e., in terms of surface coverage of ad-ions) to account for electrocatalytic and interfacial transport processes (i.e., competing surface diffusion and adsorption processes near the TPB “hot spot”) within a composite porous cathode.
Promoted Cr-Poisoning Resistance of La2NiO4+
δ-Coated PrBa0.5Sr0.5Co1.5Fe0.5O5+
δ Cathode for Intermediate Temperature Solid Oxide Fuel Cells
Authors: Li Jun , Li Jin , Pu Jian
Published: February 2020

Solid oxide fuel cell (SOFC) is considered a highly promising technology for clean power and heat generation.1 One critical component in SOFC stack is metallic interconnect, which works as an oxidant/fuel gases separator as well as an electricity conductor.2, 3 However, Fe-Cr based ferritic stainless steels, the most common interconnect alloys, have been reported to cause rapid performance degradation of SOFC cathodes.4 Cr species evaporating from chromia-forming alloys deposit on the cathode, which deteriorates the ORR activity of the cathode. In this study, Cr-poisoning effect on pure layered perovskite PrBa0.5Sr0.5Co1.5Fe0.5O5+
δ cathode and La2NiO4+
δ-coated PrBa0.5Sr0.5Co1.5Fe0.5O5+
δ cathode are investigated. After 20 h aged at 750°C in the presence of SUS430 interconnect and under cathodic current, the performance of pure PrBa0.5Sr0.5Co1.5Fe0.5O5+
δ cathode shows severe degradation, and BaCrO4 product is identified on the cathode surface. However, La2NiO4+
δ-coated PrBa0.5Sr0.5Co1.5Fe0.5O5+
δ cathode shows remarkable tolerance and resistance towards chromium, and the performance of cathode maintains stable during the test. The results indicate that the presence of La2NiO4+
δ coating not only improves the electrochemical performance, but also prevents the cathode from being poisoned by chromium.

References

1. Z. Shao and S. M. Haile, Nature, 431, 170 (2004).

2. J. W. Fergus, Materials Science and Engineering: A, 397, 271 (2005).

3. J. C. W. Mah, A. Muchtar, M. R. Somalu and M. J. Ghazali, Int. J. Hydrogen Energy (2016).

4. S. P. Jiang and X. Chen, Int. J. Hydrogen Energy, 39, 505 (2014).
Oxygen Reduction Reaction at Self-Assembled La-Sr-Co-O Composite PLD Films: Dependence on Temperature and pO2
Authors: Merkle Rotraut , Stämmler Sebastian , Maier Joachim
Published: February 2020

Several recent investigations indicated that hetero grain boundaries between perovskite La1-xSrxCoO3-
d (P) and Ruddlesden-Popper phase (La1-xSrx)2CoO4+
d (R) may exhibit an accelerated oxygen exchange surface reaction ("TPB effect"), see e.g. [1,2,3]. In the present work, compact La-Sr-Co-O composite films with different fractions of P and R are formed by self assembly on single crystalline YSZ substrates during pulsed laser deposition from a single PLD target [4,5]. The lateral grain size is about 50 nm, and characteristic morphologies can be assigned to the different crystalline phases. In addition to P and R two metastable phases were found: a Co-deficient perovskite phase La0.7Sr0.3Co0.9O3-
d, and a higher order Ruddlesden-Popper phase.

During the self-organized phase separation, different Sr contents are established in P and R, leading for most sample compositions to a Sr accumulation in R and corresponding depletion in P [4,5]. However, during the PLD process the thermodynamic Sr distribution (as determined in [6] for powder samples annealed at 1200 °C) is not fully reached.

Since the oxygen exchange activity of P strongly depends on the Sr content, the knowledge of the actual Sr distribution is required to calculate the correct reference activity for the composite films, i.e. the hypothetical activity in absence of a "TPB effect". At 600 °C, the effective surface rate constant k
q measured by impedance spectroscopy of the self-assembled composite films with an overall La:Sr ratio of 7:3 exceed this reference activity by half to one order of magnitude [7]. This corresponds to a strength of the TPB effect normalized to the triple phase density of 2-9×10-13 cm2/s. Furthermore, the Co-deficient perovskite phase exhibits an increase of k
q by about two orders of magnitude relative to La0.7Sr0.3CoO3-
d(cf. related findings in [8]). The present results are compared to literature, and possible reasons for the increased oxygen exchange activity at hetero grain boundaries are discussed.

[1] T. Kawada, M. Sase, M. Kudo, K. Yashiro, K. Sato, J. Mizusaki, N. Sakai, T. Horita, K. Yamaji, H. Yokokawa, Solid State Ionics 177 (2006) 3081

[2] E. J. Crumlin, E. Mutoro, S.-J. Ahn, G. J. la O’, D. N. Leonard, A. Borisevich, M. D. Biegalski, H. M. Christen, Y. Shao-Horn, J. Phys. Chem. Lett. 1 (2010) 3149

[3] W. Ma, J. J. Kim, N. Tsvetkov, T. Daio, Y. Kuru, Z. Cai, Y. Chen, K. Sasaki, H. L. Tuller, B. Yildiz, J. Mater. Chem. A 3 (2015) 207

[4] S. Stämmler, R. Merkle, B. Stuhlhofer, G. Logvenov, J. Maier, poster at SSI-19 in Kyoto, June 2013

[5] S. Stämmler, R. Merkle, B. Stuhlhofer, G. Logvenov, K. Hahn, P. A. van Aken, J. Maier, submitted (2016)

[6] S. Stämmler, R. Merkle, B. Stuhlhofer, G. Logvenov, J. Maier, ECS Transact. 68(1) (2015) 579

[7] S. Stämmler, R. Merkle, J. Maier, submitted (2016)

[8] A. Takeshita, S. Miyoshi, S. Yamaguchi, T. Kudo, Y. Sato, Solid State Ionics 262 (2014) 378
Electrochemical Analysis of Ni Infiltrated Nanoporous GDC Scaffold for Metal Supported SOFCs Anode
Authors: Lee Kunho , Lee Jaeseok , Kang Juhyun , Bae Joongmyeon
Published: February 2020

Metal-supported SOFCs have been investigated to overcome the disadvantages of ceramic-supported SOFCs, such as mechanical strength and sealing. In the case of ceramic-supported cells, the mechanical support is a brittle ceramic or cermet, and it contains expensive materials. However, metal-supported cells utilize ceramic layers that are only as thick as necessary for electrochemical functioning, thereby compensating for the disadvantages of ceramic-supported cells. The mechanical support is fabricated from inexpensive and robust metals, and the electrochemically active layers are applied directly to the metal support. In other words, metal-supported SOFCs can provide a reduced system cost, easy manufacturing, and operational advantages. These features make metal-supported SOFCs a very promising candidate for commercialization.

To improve productivity and accelerate the commercialization, the metal supported SOFCs have to be fabricated at low temperature under oxidized environment. In these days, some metal substrates which can withstand corrosion from ≤1000 °C already have been developed. However, the low fabrication temperature is insufficient for conventional sub-micron scaled NiO/YSZ or GDC to generate smooth electrical and ionic paths. Furthermore, the unsuitable anode can affect to interfaces; and as a result, it can cause decrease of electrical conduction.

Therefore, we have tried to apply a wet infiltration technique for anode fabrication. It can fabricate nanosize particles into a porous scaffold at relatively low temperatures and achieve higher performance electrode structures. Then, to substitute the conventional anode, a nanoporous GDC scaffold layer, and the Ni solution were selected as a scaffold and catalyst material, respectively. It is known that the GDC has high ionic conductivity and can be sintered at relatively low temperature. Therefore, it was considered that the GDC could be well matched with the requirements for anode of metal supported SOFC.

For investigating the electrochemical performance according to Ni amounts, the half-cell tests were carried out via solatron 1287/1260 device under 97%H2+3%H2O condition. Then, the appropriate Ni infiltrated GDC was applied to the metal-supported SOFC, and the electrochemical performance of infiltrated metal-supported SOFC single cell was measured via the solatron 1287/1260 device.
Assessment of Sulfur Poisoning of Ni/CGO-Based SOFC Anodes
Authors: Riegraf Matthias , Zekri Atef , Yurkiv Vitaliy , Costa Rémi , Schiller Guenter , Friedrich K. Andreas
Published: February 2020

The presence of fuel impurities, such as sulfur, siloxane and phosphorus, in biogas, diesel and natural gas can cause Solid Oxide Fuel Cell (SOFC) degradation due to surface poisoning of Ni-containing anodes. In this regard, Ni/CGO anodes were shown to display higher sulfur tolerance than Ni/YSZ anodes and a comparable high performance. In order to allow for a more profound understanding of the processes underlying sulfur poisoning, this study presents an extensive experimental investigation of commercial Ni/CGO-based SOFC operating on H2/H2O gas and reformate fuel mixtures with trace amounts of hydrogen sulfide (H2S).

The short-term poisoning behavior of high-performance electrolyte-supported Ni/CGO10-based cells was systematically investigated by means of transient voltage stability experiments and electrochemical impedance measurements for a wide range of operating conditions. The effects of temperature (800 – 950 °C) and current density (OCV – 0.75 A·cm‒2) on the extent of sulfur poisoning (1 – 20 ppm H2S) was evaluated. The poisoning behavior was shown to be completely reversible for short exposure times in all cases. By means of equivalent circuit modeling, the chemical capacitance of Ni/CGO10 anodes was demonstrated to be strongly dependent on temperature and gas phase composition reflecting a changing Ce3+/Ce4+ ratio in the CGO phase. Using a model reformate as fuel gas, it was shown that CO can still be electrochemically converted under sulfur exposure.

Furthermore, long-term experiments of 1000 h were conducted at 900 °C and 0.5 A·cm‒2 with and without sulfur exposure and the degradation progress was monitored by impedance spectroscopy. Moreover, comprehensive post-mortem analysis including FIB/SEM, TEM and XRF was carried out in order to identify the nature and location of the occurring microstructural changes.
(Invited) Research By Students That Were Inspired By Russ Kunz in High Temperature Pemfcs, DMFCs, Analysis for Polarization Loses and FC Durability
Authors: Fenton James M , Kunz H. Russell
Published: February 2020

After retiring from United Technologies Corporation Dr. H. Russell Kunz, started a new career inspiring graduate, post-doctoral students and young researchers to innovate in fuel cell research at the University of Connecticut. These young researchers with the help of Russ published 47 peer reviewed publications, a book “Experimental Methods and Data Analyses for Polymer Electrolyte Fuel Cells (PEMFCs)” and produced three patents. This historical presentation will be presented with slides taken from Russ Kunz’s presentations from 1997 until 2014. From 1997 to 2004, research at UConn was focused on catalysts for methanol oxidation in phosphoric acid and direct methanol proton exchange membrane fuel cells (DMFCs), and development of selective CO oxidation catalysts for PEMFCs. From 2003 to 2014 membranes with barrier layers for DMFCs and high temperature membranes for PEMFCs were developed and studied. From 2004 to 2014, gas diffusion layers and catalyst structures were being developed along with high temperature membranes into innovative proton exchange membrane-electrode assemblies (MEAs) that provided excellent ionic conductivity and good performance in an under-saturated environment (120 oC, 1 atm., 35%RH and 70 oC, 1 atm., dry). To optimize the performance of these MEAs techniques for analysis of polarization curves to evaluate polarization loses were developed using air, oxygen, oxygen/helium experiments and AC impedance. Ionomen (a company founded by Russ Kunz, Len Bonville and Jim Fenton) together students from UConn demonstrated MEA performance that greatly exceeded that of commercial MEAs in a four-cell full-scale stack that provided 288 watts at a current of 120 A while providing 116 oC hot water. From 2006 on finding the degradation mechanisms for membrane and catalysts layers were explored along with the performance of MEAs with lower equivalent weight PFSA in the catalyst layers. From 2006 to 2013 Russ Kunz played a pivitol role in the leadership of the U.S. Department of Energy (DOE) High Temperature Membrane Working Group (HTMWG). The HTMWG investigated membrane performance at elevated temperature/low relative humidity conditions. For the final three years of the project, Russ and the team at the Florida Solar Energy Center worked with six teams to develop membrane electrode assembly (MEA) fabrication methods for their respective membranes.
(Energy Technology Division Research Award Address) MEA & DM Characterization/Optimization for Low Pt Loadings and High Current Densities
Authors: Orfanidi Alin , Simon Christoph , Harzer Gregor S. , Madkikar Pankaj , El-Sayed Hany A , Gasteiger Hubert A.
Published: February 2020

The large-scale commercial viability of fuel cell electric vehicles (FCEVs) requires a reduction of the platinum-specific power density (gPt/kW) from currently ca. 0.3 gPt/kW to levels of ≤0.1 gPt/kW [1]. This can only be accomplished by improving fuel cell performance at high current density (≥2 A/cm2) with membrane electrode assemblies (MEAs) containing ultra-low anode and cathode platinum loadings (<0.1 mgPt/cm2).

Owing to the fast hydrogen oxidation kinetics on platinum [2], anode loadings of 0.05 mgPt/cm2 and below can be realized without significant MEA performance losses. On the other hand, large mass transport related voltage losses at high current density are observed when the cathode loadings are reduced to 0.05-0.10 mgPt/cm2, which can be influenced by catalyst and electrode design [3]. In addition to optimization of catalysts and MEAs, the high current density performance is also affected by the diffusion medium, namely by the choice of substrate and the composition/design of the micro-porous layer (MPL) [4].

In this presentation, we will discuss various options for electrode and MPL design, illustrating their impact in 5 cm2 single-cell differential-flow experiments. The measured voltage losses will be deconvoluted into kinetic losses based on data from H2/O2 measurements, into oxygen transport induced losses obtained from limiting current density measurements [5], and into contributions from the proton conduction resistance in the cathode electrode determined by AC impedance [6].

References

[1] O. Gröger, H. A. Gasteiger, J.-P. Suchsland, J. Electrochem.
Soc., 162, A2605 (2015).

[2] J. Durst, C. Simon, F. Hasché, H. A. Gasteiger, J. Electrochem.
Soc., 162, F190 (2015).

[3] A. Kongkanand, M. F. Mathias, J. Phys. Chem.
Lett., 7, 1127 (2016).

[4] J. M. Morgan, R. Datta, J. Power Sources, 251, 269 (2014).

[5] D. R. Baker, D. A. Caulk, K. C. Neyerlin, M. W. Murphy J. Electrochem. Soc., 156, B991 (2009).

[6] Y. Liu, C. Ji, W. Gu, D. R. Baker, J. Jorne, H. A. Gasteiger, J. Electrochem. Soc., 157, B1154 (2010).

Acknowledgements: We gratefully acknowledge funding from the German Federal Ministry for Economic Affairs and Energy (BMWi) for the project “Optigaa2” (funding number 03ET6015E) in collaboration with Freudenberg as well as for the BMWi funded subcontracts with Greenerity GmbH and Umicore (project “HyMotion5-Brennstoffzellenstapel”).
(Invited) Polymer Electrolyte Membranes for Fuel Cells: An Overview of Where We Have Been
Authors: Zawodzinski Thomas A.
Published: February 2020

In this contribution, a review of the efforts to improve membranes for fuel cells will be presented. Several themes will be interwoven:

What we have measured over the years, the insight provided and what is missing in most studies of membranes.

A historical perspective on the time-sequential major membrane issues, including some resolution and some circumvention of these issues.

 Types of membranes used and their relative merits as applicable to specific requirements.

Our state of understanding of membrane processes.

The roles of experimental and computational studies of membranes.

This talk is dedicated to Russ Kunz who always engaged in discussions as a gentleman with appropriate skepticism and obvious enthusiasm.

Acknowledgements

We gratefully acknowledge the long support of this work by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy FCTO, DARPA and by the Office of Naval Research. We also thank 3M, DuPont and Dow for providing membranes.
(Invited) Advances in PEM and Phosphoric Acid Fuel Cells
Authors: Mustain William E , Bonville Leonard J. , Pasaogullari Ugur , Maric Radenka , Singh Prabhakar
Published: February 2020

After a long and very successful industrial career spanning over 4 decades, Russ Kunz joined the University of Connecticut in 1992 and was one of the most passionate and influential voices in energy and energy systems at the university. Russ not only was the principle investigator of numerous research projects and awards, he was also instrumental in the formation of the Connecticut Global Fuel Cell Center – since renamed the Center for Clean Energy Engineering – which remains today one of the premier academic facilities in the United States focusing on fuel cell technology. During his over 20 years at UConn, Russ contributed to a wide range of projects and touched the lives of young faculty and countless students. During this talk, we will share stories about Russ’ life and career at UConn, as well as discuss specific projects and concepts in recent years where he was an integral partner in our team. We will also discuss his influence on what we continue to do today.

More specifically, we will highly Russ’ contributions to electrolyte management in phosphoric acid fuel cells, and manipulation of physical and chemical properties in low temperature and high temperature PEM fuel cells.

Figure 1
(Invited) The Growing Importance of Hydrogen in Our Energy System and Extended Surface Electrocatalyst Development and Implementation
Authors: Alia Shaun M , Hurst Katherine , Mauger Scott A , Neyerlin K.C. , Kocha Shyam S. , Ngo Chilan , Shulda Sarah M , Pylypenko Svitlana , Pivovar Bryan S
Published: February 2020

Today represents a particularly exciting time, as our planet’s energy system is undergoing major changes due to dramatically decreasing renewable energy prices and increasing societal concerns over greenhouse gas emissions, criteria pollutants (arsenic, mercury, NOx, particulate matter), and climate change. These factors are pushing society towards deep decarbonization of our energy system, perhaps the most challenging issue facing the planet today. Unfortunately, wind and solar energy, while both promising generation sources, come with intermittency challenges and have limitations in their abilities to impact industrial and transportation sector demands where fossil fuel energy carriers based on chemical bonds have provided the basis for historic energy demands. Hydrogen offers the potential to meet the multi-GW demand for both grid-balancing and input into the industrial and transportation sectors, as shown schematically in Figure 1. In such an energy system, hydrogen acts as an energy carrying intermediate that parallels electrons (electricity) within the energy system. Such an energy system allows all of society’s demands to be met with greatly reduced environmental impact.

Fuel cells for transportation and power generation are key enabling technologies for this future. However, the commercial viability of such systems is limited by cost, performance and durability with catalysts and electrodes being of central concern.

Our team has investigated extended surface catalysts as a novel platform for increased performance and durability at lower cost. This presentation will highlight the advances of our team in the synthesis of extended surface electrocatalysts with a focus on PtNi nanowires (NWs). While these materials have shown great promise in ex-situ (rotating disc electrode) studies, performance in-situ (fuel cell tests) has not yet reflected the performance potential seen in these ex-situ tests. In large part we attribute this to challenges in electrode fabrication and integration. This presentation will present results that focus on the differences between in-situ and ex-situ properties, quantification of performance losses in fuel cell tests, and our efforts to further improve performance and durability of such systems. These efforts parallel a number of different areas that Dr. Russ Kunz investigated throughout his career, and have benefitted from the knowledge basis Dr. Kunz contributed to throughout his career.

Figure 1: Illustrative future clean energy system in which hydrogen (water electrolysis) plays a key enabling role.

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(Invited) How Oxygen-Containing Intermediates and Surface Charge Regulate Oxygen Reduction Reaction of Platinum Electrocatalysts
Authors: Huang Jun , Zhang Jianbo
Published: February 2020

Oxygen-containing intermediates formed in oxygen reduction reaction (ORR) are widely believed to act as site-blockers. Recent experiments showing positive effects of O-containing intermediates throw doubt upon this prevailing understanding[1]. This situation calls for an overhaul of current understanding of mechanisms of the ORR. The theoretical challenge is how to consistently treat the formation of O-containing intermediates, surface charge on metal surface, ion and potential distribution in the solution, field-dependent behaviors of surficial water molecules, and thermodynamic relations and kinetics of the ORR. In the present article, a self-consistent framework bridging first-principles approaches and mean-field approaches, nanoscale and microscale, interface and bulk, is developed to address the above challenge. Model, parametrized with density functional theory results and rotating disk electrode data, sheds light on the potential-dependent Tafel slope and volcano shape of the activity versus binding energy of intermediate curve, focusing on the effects of surface charge and O-containing intermediates. Chemisorption of O-containing intermediates decreases surface charge density on metal surface, increases proton affinity at the interface, and brings positive effects to the ORR activity other than the negative effects of site-blocking.[2]

Reference:

[1] Gómez-Marín, A.M.; Rizo, R.; Feliu, J.M. Oxygen Reduction Reaction at Pt Single Crystals: A Critical Overview. Catal. Sci. Technol. 2014, 4, 1685-1698.

[2] Huang, J.; Malek, A.; Zhang, J.; Eikerling, M.H. Non-Monotonic Surface Charging Behavior Of Platinum: A Paradigm Change. J. Phys. Chem. C 2016, 120, 13587–13595.

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(Invited) High Performance Pt-Based Octahedral Nanocatalysts in Fuel Cells
Authors: Huang Yu , Zhao Zipeng
Published: February 2020

Proton exchange membrane(PEM) fuel cells generate power by hydrogen oxidation reaction at anode and oxygen reduction reaction at cathode(ORR). They hold the potential for replacing internal combustion engine for powering automotive vehicle in future while producing zero emission. However, the broad application of PEM fuel cells has been limited by their high cost due to the Pt catalysts used on both anode and cathode. Platinum-nickel (Pt-Ni) octahedral based nanomaterials represent an emerging class of highly active catalysts for oxygen reduction reaction (ORR) in fuel cells, but suffered from stability. In this talk, we present our recent progress in creating alloy structures that can not only significantly enhance the catalytic activity of Pt-Ni based octahedral but also exhibit great stability in both RDE and MEA tests.
(Invited) Porous Electrode Engineering for Platinum Group Metal-Free Oxygen Reduction Reaction Catalysts
Authors: Komini Babu Siddharth , Ogawa Shohei , Chung Hoon T , Zelenay Piotr , Litster Shawn
Published: February 2020

As platinum group metal-free (PGM-free) catalysts make significant advances in their acidic oxygen reduction reaction activity when evaluated at low current, it is important to establish electrode designs capable of meeting automotive polymer electrolyte fuel cell (PEFC) demands for power density. Unfortunately, cathode-level transport losses can impose a tremendous penalty on PGM-free catalyst performance in PEFCs. The lower volumetric activity (A/m3) of PGM-free cathodes versus Pt/C cathodes requires cathodes thicknesses on the order of 0.1 mm, or roughly 10 times the thickness of Pt/C cathodes. That extreme thickness combined with hydrophilic, functionalized carbon surfaces, yields a cathode that is highly sensitive to liquid water flooding and large proton conduction Ohmic losses.

This talk will overview methods in the field developed for characterizing electrode-level losses in PGM-free electrodes and identifying the underlying mechanisms that hinder transport and limit high power density. The overview will include methods we have recently applied to Fe-N-C PGM-free catalysts synthesized from polyaniline and cyanimide (Fe-CM-PANI). As the figure illustrates, these methods include electrochemical measurements, nano-scale X-ray computed tomography (nano-CT) of 3D pore and ionomer morphology1, particle-scale simulation2, and PEFC simulation and optimization3. These studies are then subsequently applied to advancing electrode performance as well as guiding targets for future catalyst synthesis.

References

1. S. Komini Babu, H.T Chung, P. Zelenay, ACS Appl. Mater. Interfaces, 2016 8 (48), pp 32764–32777.

2. S. Ogawa, S. Komini Babu, H.T. Chung, P Zelenay, S Litster, ECS Trans 75 (14), pp 139-146.

3. S. Komini Babu, HT Chung, G Wu, P Zelenay, S Litster, ECS Trans. 64 (3), pp 281-292.

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(Invited) Imaging Techniques for Investigating Multiphase Transport Behaviour in Polymer Electrolyte Membrane Fuel Cells
Authors: Bazylak Aimy
Published: February 2020

The hydrogen polymer electrolyte membrane (PEM) fuel cell provides enormous potential for a future with clean energy. However, due to cost and inefficiency barriers, PEM fuel cells have not yet reached widespread commercial adoption. Mass transport limitations arising from liquid water flooding in low temperature PEM fuel cells and acid leaching in high temperature PEM fuel cells leads to inefficiencies. If these issues become resolved, smaller and more reliable devices could be produced at a lower cost. Mass transport limitations can be minimized through the development of optimized materials, which have tailored pore structures, connectivities, conductivities, and surface wettabilities. The porous materials in PEM fuel cells could be customized for mass transport with detailed information about their structure and the dominating mass transport mechanisms that result from these structures. In this talk, X-ray based visualization techniques, such as microcomputed tomography, synchrotron X-ray radiography, and neutron radiography, for investigating multiphase transport in PEM fuel cells will be discussed.
(Invited) Commercialization Road Map of Fuel Cell Commercial Vehicle (FCCV) at Telos Auto Power Systems Inc (TAPS)
Authors: Zhang Ruiming
Published: February 2020

In cope with increasing serious emission problems, Chinese government has officially launched a series policies and legislations to stimulate the development and deployment of zero emission vehicles (ZEV). Currently in China, ZEV is heading to a crossroad – the competition and choice among battery powered vehicle, hybrid system, and fuel cell powered vehicle. Leveraging strong commercialization capability on fuel cell system and well-defined supplier chain, Telos Auto Power Systems (TAPS) focuses on bringing FCCV, including metro bus and industrial truck, to China market. Aiming at being the leader of manufacturing power systems of FCCV in China, TAPS has formed a holistic strategy as below:

· Establish a multifunction platform of advanced fuel cell power systems in combination with battery (fuel cell and battery hybrid systems, FCBHS) for automotive applications;

· Team up with prestigious vehicle and battery makers on FCBHS and FCCV forward engineering;

· Lead the efforts of supply chain integration and localization;

· Collect and utilize Big Data of FCCV end-to-end from manufacturing, daily usage, demonstration, to commercial operation, including operations of hydrogen infrastructure for further technology and business development.
(Invited) Integrating Theory and Experiment to Understand and Control Reaction Pathways
Authors: Toney Michael F
Published: February 2020

DuraMat - or the Durable Module Materials - Consortium is a Department of Energy (DOE) Energy Materials Network (EMN) that brings together national lab and university research infrastructure with the photovoltaic (PV) industries to discover, develop, de-risk, and enable the commercialization of new materials and designs for PV modules (1). One enabling aspect of DuraMat is to develop methodologies to understand reaction pathways and mechanisms in order to control the synthesis of novel functional materials. By coupling theory and experiments, we aim to accelerate materials discovery, characterization, scale-up, and commercial deployment. In this talk, I will describe several PV relevant examples where our coupled theory-experiment efforts have accelerated materials discovery, including transparent conducting spinel oxides (2), MnOx synthesis from solution, and the development of multifunctional coatings. Using novel materials discovered with this approach, DuraMat has the potential to develop modules with a levelized cost of electricity of less than 3 cents per kilowatt-hour.

(1) https://www.duramat.org/

(2) Y Shi et al., Chemistry of Materials 26, 1867–1873 (2014).
Metal- and Oxidant-Free Benzylic C-H/Aromatic C-H Cross Coupling Based on the Stabilized Cation Pool Method
Authors: Yoshida Jun-ichi , Hayashi Ryutaro , Shimizu Akihiro
Published: February 2020

The cation pool method serves as a nice tool in electroorganic synthesis. Organic cations are electrochemically generated and accumulated in solution at low temperatures. Reactions with subsequently added nucleophiles give the desired products. However, the cation pool method cannot be applied to highly unstable cations that decompose during the course of the electrolysis. To expand the scope of the cation pool method, we have developed the stabilized cation pool method, in which organic cations stabilized by suitable stabilizing agents are electrochemically generated and accumulated in solution. The reactions of the stabilized organic cations with subsequently added nucleophiles give the desired products.

In this paper we show that C−H/aromatic C−H cross-coupling can be achieved by the electrochemical generation and accumulation of stabilized benzyl cations followed by their reactions with subsequently added aromatic nucleophiles. Beznylaminosulfonium ions as stabilized benzyl cations are generated and accumulated in the electrochemical oxidation of toluene derivatives. In the next step, the reactions with subsequently added electron-rich aromatic compounds as nucleophiles give the corresponding cross-coupled product. The method has been successfully applied to the synthesis of TP27, an inhibitor of PTPase. The reactions of benzylaminosulfonium ions with other carbon nucleophiles such as acetylacetone, ketene silyl acetals, allyltrimethylsilane, and trimethylsilylacetylene will also be discussed in the presentation.
Electrocatalytic Alkene Difunctionalization
Authors: Fu Niankai , Sauer Gregory S. , Lin Song
Published: February 2020

Alkene difunctionalization represents one of the most efficient methods for the construction of highly functionalized products from simple and readily available starting materials. These transformations are usually promoted by a highly reactive electrophilic reagent (e.g., peracid, metal oxide, and hypervalent iodine), which engages the unactivated π electrons of the alkene to form two new vicinal chemical bonds in either a concerted or a stepwise fashion. The requirement for these highly reactive electrophiles can often lead to functional group compatibility issues, which may limit their broad use in late-stage synthesis. In addition, many of these reagents generate substantial amounts of byproducts upon reaction. Herein, we describe the development of alkene difunctionalization reactions via electrochemical generation of radical intermediates without the use of highly reactive oxidants or production of wasteful byproducts.
Asymmetric Synthesis of Substituted Piperidine Derivatives Based on the Indirect Cation Pool Method
Authors: Suga Seiji , Haisa Masahiro , Yoshioka Kazuki , Mitsudo Koichi
Published: February 2020

N-Acyliminium ions having a piperidine skeleton were attractive because the functionalized piperidines frequently show interesting biologically properties. The “indirect cation pool method” 1) is useful to prepare a solution of synthetically valuable N-acyliminium ions having a protecting group that is labile under acidic conditions, because organic cations can be generated and accumulated under neutral conditions. In this presentation we demonstrated utilities of highly enantiomerically enriched chiral N-Acyliminium ions bearing a piperidine skeleton, which are generated by the indirect cation pool method.

Almost enantiomerically pure chiral precursor 2 was prepared by using the enantioselective lithiation strategy using chiral diamine 1 (Scheme 1).2)
N-Acyliminium ion pool 3 was then irreversibly generated from 2 by the treatment of ArS(ArSSAr)+, which was generated by low temperature electrolysis (Scheme 2). The reaction of 3 with allylstannane gave trans isomer in high diastereomer and enantiomer ratios. In contrast, the coupling between 3 and allylmagnesium bromide afforded cis isomer in high stereoselectivity. As a result, we could selectively synthesized two

1) Suga, S.; Matsumoto, K.; Ueoka, K.; Yoshida, J. J. Am. Chem. Soc.
2006, 128, 7710-7711. Matsumoto, K.; Suga, S.; Yoshida, J. Org. Biomol. Chem.
2011, 9, 2586-2596.

2) Coldham, I.; O’Brien, P.; Patel, J. J.; Raimbault, S.; Sanderson, A. J.; Stead, D.; Whittaker, D. T. E. Tetrahedron: Asymmetry
2007, 18, 2113–2119.

Figure 1