bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparative Study of Electrocatalytic Activity Towards Borohydride Oxidation on Gold- or Platinum-Metal (Cu, Co, Ni) Deposited on the Titanium Surface Via Galvanic Displacement
Authors: Tamasauskaite-Tamasiunaite Loreta , Balciunaite Aldona , Zabielaite Ausrine , Stankeviciene Ina , Jagminiene Aldona , Kepeniene Virginija , Selskis Algirdas , Juskenas Remigijus , Norkus Eugenijus
Published: February 2020

Here we present comparative study of electrocatalytic activity of gold- or platinum-metal (Cu, Co, Ni) catalysts deposited on the titanium surface towards the oxidation of borohydride in alkaline medium. A simple and cost-effective galvanic displacement technique was used for preparation of nanostructured catalysts [1-4]. The morphology, structure and composition of the prepared nanostructured catalysts were examined using Field emission scanning electron microscopy, Energy dispersive X-ray spectroscopy, X-ray diffraction and inductively coupled optical emission spectroscopy. The borohydride oxidation kinetic was studied on the as-prepared catalysts by cyclic voltammetry and chronoamperometry. The electrocatalytic activity of catalysts was compared with that of bulk Au or Pt electrodes.

Well-adherent gold- or platinum-coated metal (Cu, Co, Ni) films with nm-scaled particles were formed on the surface of titanium. The electrocatalytic activity of the as-prepared nanostructured catalysts was compared on the basis of electrochemical data. It was found that the nanostructured gold- or platinum-metal (Cu, Co, Ni) catalysts deposited on the titanium surface via galvanic displacement exhibits an enhanced electrochemical activity towards the oxidation of borohydride as compared to that of bulk Au or Pt electrodes and seem to be promising anodic materials for direct borohydride fuel cells.

Acknowledgments

This research was funded by a Grant (No. ATE-08/2012) from the Research Council of Lithuania.

References

[1] L. Tamašauskaitë-Tamašiûnaitë, A. Balèiûnaitë, D. Šimkûnaitë, A. Selskis. J. Power Sources 202 (2012) 85-91.

[2] L. Tamašauskaitë-Tamašiûnaitë, A. Balèiûnaitë, R. Èekavièiûtë, A. Selskis. J. Electrochem. Soc. 159 (2012) B611-B618.

[3] L. Tamašauskaitë-Tamašiûnaitë, A. Balèiûnaitë, A. Zabielaitë, I. Stankevièienë, V. Kepenienë, A. Selskis, R. Juškënas, E. Norkus. J. Electroanal. Chem. 700 (2013) 1-7.

[4] L. Tamašauskaitë-Tamašiûnaitë, A. Jagminienë, A. Balèiûnaitë, A. Zabielaitë, J. Vaièiûnienë, A. Selskis, R. Juškënas, E. Norkus. Int. J. Hydrogen Energy 38 (2013) 14232-14241.
ECS Energy Technology Division Supramaniam Srinivasan Young Investigator Award Advanced Electrocatalysts for Oxygen Reduction Reaction
Authors: Shao Minhua
Published: February 2020

Low temperature fuel cells have great potential for both stationary and transportation applications and are expected to help address the energy and environmental problems that have become prevalent in our society. Despite their great promise, commercialization has been hindered by lower than predicted efficiencies and the high cost of Pt-based electrocatalysts in the electrodes. For more than five decades, the predominant work has being focused on the development of novel catalysts for the cathodic reaction (oxygen reduction reaction. ORR), which has sluggish kinetics and is responsible for the high overpotentials.1 One way to address the high cost and low activity problem associated with the conventional Pt catalysts is to increase the activity by optimizing the shape of constituent nanoparticles and thus maximizing the expression of facets most reactive towards ORR reaction.2 Another approach is to increase the utilization of expensive noble metal atoms by developing core-shell catalysts.3

In this talk, recent progress in developing advanced materials for ORR in my group will be presented, with an emphasis on core-shell catalysts4-8 and shape-controlled nanocrystals.9-11 The structural dependence of ORR activity on Pd and PtNi nanocrystals were investigated. The mechanisms for activity enhancement of these materials will also be discussed based on the results of density functional theory (DFT) calculations. Finally, the issues associated with the mass production of core-shell catalysts were analyzed.

References

Electrocatalysis in Fuel Cells: A Non- and Low- Platinum Approach; Shao, M., Ed.; Springer: London, 2013.

V. R. Stamenkovic, B. Fowler, B. S. Mun, G. Wang, P. N. Ross, C. A. Lucas and N. M. Markovic, Science 2007, 315, 493.

Adzic, R. R.; Zhang, J.; Sasaki, K.; Vukmirovic, M. B.; Shao, M.; Wang, J. X.; Nilekar, A. U.; Mavrikakis, M.; Valerio, J. A.; Uribe, F. Topics in Catalysis 2007, 46, (3-4), 249.

Shao, M. H.; Shoemaker, K.; Peles, A.; Kaneko, K.; Protsailo, L. J. Am. Chem. Soc. 2010, 132, (27), 9253.

Shao, M. H., et al. J. Phys. Chem. Lett. 2011, 2, 67

Humbert, M.; Smith, B.; Wang, Q.; Ehrlich, S.; Shao, M., Electrocatalysis 2012, 3 (3-4), 298.

Shao, M. H., et al. Chem. Commun. 2013, 49, 4030.

Shao, M. H., et al. Phys. Chem. Chem. Phys. 2013, 15, 15078.

Shao, M.; Yu, T.; Odell, J.; Jin, M.; Xia, Y. Chem
.
Commun. 2011, 47, 6566.

Shao, M.; Odell, J.; Humbert M.; Yu, T.; Xia, Y. J. Phys. Chem. C 2013, 117, 4172.

Choi, S-I.; Shao, M. H., et al., Nano Lett. 2013, 13, 3420.
Nanostructuring of Catalysts Based on Platinum or Platinum Alloy for PEM Fuel Cell Application
Authors: Lepesant Mathieu , Guillet Nicolas , Mailley Pascal
Published: February 2020

The catalysts-cost lowering is one of the conditions necessary to make PEMFC technology economically viable. The performances of these catalysts, usually made of platinum nanoparticles are limited by their specific surface area and activity. Catalysts nanostructuring greatly increases the active surface area and may also help at reducing platinum load by the use of smaller amounts of noble metal or partial substitution of platinum by non-noble metals. The use of nanostructures such as "core-shell", hollow particles, well-controlled morphology, or templated Pt nanoparticles, represent some of the advanced routes that were assayed to structure catalysts at the nanoscale. The study of these nanostructured materials would enable to better understand the influence of the nanoparticles morphology on the electrocatalytic properties. This shape the hopes of a significant decrease in the amount of precious metals required for optimal operation of PEM fuel cells. A number of different structures were synthesized and their performances were compared towards the reduction reaction of oxygen (the most limiting reaction in PEMFC). Electrochemical tests on rotating electrode and half-cell have been conducted; then nanostructured catalyst performances were compared with reference catalysts (carbon black supported Pt nanoparticles). The integration and testing of these structures have been carried out in complete fuel cell systems to study their performances and durability in real environment.
Perovskites As Electrocatalysts for Alkaline Water Electrolysis
Authors: Nikiforov Aleksey Valerievich , Puebla Ana Raquel de la Osa , Jensen Jens Oluf , Petrushina Irina Michailovna , Bjerrum Niels Janniksen
Published: February 2020

Water electrolysis is a promising technology for the production of hydrogen as a sustainable energy storage source, combined with solar or wind power.

In this work various electrocatalysts for the Oxygen Evolution Reaction (OER) electrode were synthesized and characterized by several techniques such as X-ray diffraction, electrical conductivity, scanning electron microscopy (SEM), energy dispersive microscopy (EDX) and rotating disk electrode.

The perovskites tested in this work were both produced by a ball-milling technique and by an auto-combustion synthesis, which appeared to be a fast and robust method for synthesis of perovskites with various chemical compositions1.

The electrochemical performance of the materials was tested through pellet pressing of the perovskite powders. This involved in some case a time consuming preparation process. Furthermore the technique should show the adequate reproducibility.2

In this work we show the development of the method, which was further used to compare the activity of various electrocatalysts (Figures 1,2).

The electrocatalytic activity of all prepared perovskites was tested in 1M KOH at 80 °C, using an ink consisting of potassium exchanged Nafion®. All tests were performed in the potential window 0-700 mV on a glassy carbon electrode. All the tested perovskites were characterized by their overpotential , measured current at 650 mV, obtained kinetic current and Tafel slopes.

It was also shown that this technique do not depend on the initial powder electric conductivity which varied by several orders of magnitude, as shown on Figure 3.

1 H. Nijjar, J. Lamonier, O. Mentr´e, J. Giraudon, H. Batis, Appl. Catal. B, 106, 149–159, 2011

2 J.O’M. Bockris and T. Otagawa J. Phys. Chem. 87:2960-2971, 1983.
ECS Research Award of the Energy Technology Division Membrane Electrode Assembly Fabrication from Membranes of the DOE High Temperature Membrane Working Group
Authors: Fenton James M. , Mohajeri Nahid , Rodgers Marianne P. , Brooker R. Paul , Slattery Darlene K. , Bonville Leonard J. , Kunz H. Russell
Published: February 2020

The Florida Solar Energy Center (FSEC) has led the U.S. Department of Energy (DOE) High Temperature Membrane Working Group (HTMWG) since 2006. The HTMWG investigates membrane performance at elevated temperature/low relative humidity conditions. For the final three years of the project, FSEC has worked with six teams to develop membrane electrode assembly (MEA) fabrication methods for their respective membranes. This presentation details the challenges associated with MEA fabrication of various membrane types, along with the performance results from several HTMWG membranes.

The MEA fabrication technique utilized by FSEC is to suspend the membrane vertically in front of a heated plate, and then spray catalyst-ink slurry onto the membrane. Following electrode application, the CCM is hot pressed to ensure good interfacial contact. Through these procedures, several challenges were identified. First, during electrode application, the membrane can swell due to the high solvent content in the ink and shrink due to the heat from the plate. These combined effects were shown to cause significant internal stresses in a hydrocarbon-based membrane with Teflon support. A second challenge was the ductility (either too high or low) of the membrane, leading to poor mechanical stability. Too high ductility rendered spraying ineffective, while too low ductility led to crack formation, either during spraying or hot pressing. An example is given of a membrane showing a series of pressure-induced cracks after hot pressing. A third challenge relates to the compatibility of the ionomer in the electrode with that in the membrane. For the majority of the teams, the same ionomer was utilized in the electrode, to provide consistency across the tests. However, due to differences in the membrane, the cell performance changed, even though the electrodes were the same. This suggests a performance limiting mechanism is operating at the membrane/catalyst interface.

Notwithstanding these challenges, several cells showed significant progress towards DOE performance and durability targets, including a hydrocarbon-based membrane. One team was able to develop a membrane that exhibited several times-lower fluoride release than NRE 211. Another team’s fuel cell performance exceeded DOE targets, with further optimization possible. These results will be presented.
Surface Fermi Energy and Activity of Atomically Layered Pt/Ru Catalyst
Authors: Takmeel Qanit , Moghaddam Saeed
Published: February 2020

The development of bimetallic catalysts has played a significant role in the development of technologies such as catalytic reforming, fuel cell electrocatalysis, hydrodesulfurization, partial alkene oxidation, etc. The interest in the development of bimetallic catalysis for direct methanol fuel cells (DMFCs) has been over a four-decade-old exercise. Platinum has generally been alloyed with a plethora of other metals such as tin, cobalt, ruthenium etc. in order to attain better methanol deprotonation and reduced carbon monoxide poisoning of the catalyst. Here, to better understand the role of ruthenium in a bilayered Pt/Ru catalyst, we demonstrate its effect on the surface Fermi energy level and catalytic activity.

Using the atomic layer deposition (ALD) process, a number of samples were prepared and the effect of atomic layering of platinum on ruthenium on the surface catalytic activity was studied. The thickness of Pt was monitored by varying the number of Pt ALD cycles and catalytic activity was determined by cyclic voltammetry. In addition, copper underpotential deposition (Cu-UPD) was used to estimate the fractional coverage of Pt on the surface of Ru at different Pt ALD cycles. This is key to the understanding since it ensures that the studied surface involves only one metal. We found that for 10 ALD cycles of Pt, the surface of Ru was completely coated with Pt. Work function of the catalyst surface was estimated by Kelvin probe. A large variation in work function values for the sample with 5 Pt ALD layers suggests that there is significant islanding of Pt on Ru corroborating well with Cu-UPD results.

Our results show that by manipulating Fermi energy of Pt catalysts, optimum activity can be obtained. In addition, it is suggested that the common 50/50% alloying of metals is an unnecessary enterprise and comparable activity can be achieved by careful engineering of catalysts involving lower Pt loading.
In Situ STEM Observation of Pt Nanoparticles on Carbon Surface in the Air Condition
Authors: Hayashi Akari , Zhao Xiaojing , Sasaki Kazunari
Published: February 2020

Electrocataysts for PEFCs are most commonly composed of Pt nanoparticles on carbon supports. Even though such electrocatalysts are highly active, their durability is still a problem. Especially, carbon corrosion at high potential followed by Pt agglomeration is a major issue to be overcome. Against the carbon corrosion, graphitization of carbon surface is one of possible solutions. In our studies, so far, the surface of carbon black, such as Vulcan and Ketjen black, was graphitized though the simple heat treatment, and then further Pt nanoparticles were deposited on such heat-treated carbon. As a result, durability of such electrocatalysts was successfully increased. On the other hand, we have found that degradation mechanism cannot be explained only by agglomeration and growth of Pt particles, according to the TEM observation before and after the electrochemically accelerated durability tests. Therefore, in this study, an accelerated durability test is newly introduced by using in-situSTEM observation in the air condition to understand the degradation mechanism.

For our study, Hitachi 300 kV Cold-FE TEM (HF-3000) was used. Continuous SEM/STEM observation for 30 minutes was performed at 200 oC in the air condition. A standard catalyst, Pt on Vulcan carbon was first investigated, and still images of SEM made out of the movie are shown in Figure 1. As seen, Pt particles, whose size was about 2 nm, were initially well dispersed on carbon particles. They did not move around very much and were rather embedded into the carbon surface owing to carbon corrosion. Interestingly, in this case, TEM images themselves cannot give us information on degradation mechanism since the particle size is not much changed. Now, we have found that decreased PEFC performance is rather derived from the fact that embedded Pt particles lose their active sites.

On the other hand, Pt particles on graphitized carbon were more agglomerated, but not much embedded into the carbon surface. Since the durability of PEFC performance is higher with graphitized carbon, we believe embedded Pt is a major reason for degradation. Details of comparison with electrochemically accelerated test are also discussed.
Study of through Plane Cation Contamination in Polymer Electrolyte Fuel Cell
Authors: Uddin Md. Aman , Qi Jing , Wang Xiaofeng , Ozdemir M. Ozan , Khajeh Hosseini Dalasm Navvab , Bonville Leonard J. , Pasaogullari Ugur , Molter Trent
Published: February 2020

The effect of through plane cation contamination on PEFC was investigated using a multilayered membrane cell. The MEA, similar to Watanabe et al. (1, 2), was prepared using five layers of Nafion® 211 (~1 mil=25.4 μm thickness) membrane, and four Pt wires (electrodes) were placed between the membranes (Figure 1). Pt electrodes were used to monitor the through-plane potential that results from the permeation of hydrogen and oxygen from anode and cathode, respectively. 1.14 mM CaSO4 solution was injected into the air stream through a nebulizer at a rate of 65 μL/min, corresponding to a 5 ppm of CaSO4based on dry air. Both the anode and the cathode flow fields were made of aluminum alloy, T6061 and were gold-plated to prevent corrosion.

As shown in Figure 2, the electrode closest to the cathode showed the same potential to the cell voltage and all the other electrodes showed zero potential. At the electrode closest to cathode, the potential was dominated by oxygen permeated from cathode, and in the other electrodes, oxygen permeated from cathode was negligibly smaller than hydrogen permeation, and the electrode potential was dominated by hydrogen oxidation reaction. After 32 hours with pure air, there was enough oxygen permeation from the cathode to other layers of membrane to symbolize the membrane degradation.

Posttest analyses showed that in spite of the gold plating, the aluminum flow fields were corroded. Aluminum corrosion byproducts degraded the cell performance from the beginning of the test. When CaSO4 was injected with air, the cell performance degraded rapidly (Figure 2). Aluminum was deposited as Al2O3 or Al(OH)3on the flow field and GDE surfaces causing mass transport losses. No calcium/sulfur was detected in the deposit from EDX analysis. It might happen that the presence of calcium/sulfur in the deposit was below the detection limit of EDX.

HFR was increased due to contamination. In the membrane layer close to the cathode, the HFR increase was more than 50% (Figure 3).

Acknowledgements

The authors gratefully acknowledge financial support from NSF (CBET-0748063), DOE-EERE through University of Hawaii-Hawaii Natural Energy Institute (DE-EE0000467).

References

1. S. Takaichi, H. Uchida and M. Watanabe, Electrochemistry communications,9, 8 (2007).

2. S. Takaichi, H. Uchida and M. Watanabe, J. Electrochem. Soc.,154, 12 (2007).
Thermal Contact Resistance Between Gas Diffusion Layer and Graphite Bipolar Plate: Modeling and Experiments
Authors: Sadeghifar Hamidreza , Bahrami Majid , Djilali Ned
Published: February 2020

An analytic, mechanistic robust model is developed to predict the thermal contact resistance (TCR) between fibrous porous media such as GDLs and flat surfaces. The model, which accounts for the salient and realistic geometrical parameters, mechanical deformation, and thermal spreading/constriction resistances, is successfully validated with new experimental data of the TCR between GDLs and graphite bipolar plates. Several parametric studies are performed to reveal the effect of fiber specifications such waviness and also GDL properties on the TCR. For instance, it is found that, interestingly enough, fiber length does not have any effect on TCR at constant porosity. From the parametric studies, the critical values of key parameters effective on TCR are also identified, which can be very useful in GDL manufacturing and fuel cell design in viewpoint of heat management. The presented model can be readily plugged into fuel cell models for simulations and modeling purposes. Overall, the model is developed in a general form to be also applicable, with only minor modifications, to other fibrous media such as fibrous catalyst layers, metal foams, and heat exchangers.
Influence of the Sintering of Electrocatalysts and Decrease of Proton Conductivity on the Current-Voltage Performance in the High-Temperature Proton Exchange Membrane Fuel Cells (HT-PEMFC)
Authors: Suzuki Ai , Miura Ryuji , Hatakeyama Nozomu , Miyamoto Akira , Oono Yuka , Hori Michio , Williams Mark
Published: February 2020

The relevance of the sintering of electrocatalysts and voltage drops of HT-PEMFC was theoretically evaluated under the non-humid conditions at 150 °C, 170 °C and 190 °C. The degree of agglomeration of electrocatalysts over time simulated by three-dimensional kinetic Monte Carlo method was compared and quantitatively agreed with experimentally measured Transmission Electron Microscopy (TEM) results. Agglomeration of electrocatalysts leads to the loss of the electrochemically active surface area. It was found to be occurred more severe as temperature increased. Decreasing rate of the proton conductivity was calculated based on the tortuosity of the proton pass. The more the phosphoric acid was evaporated, the more tortuous the proton path became. A theoretical breakdown of the voltage drops indicated that the deterioration of electrocatalysts impacted on the earlier several hundreds of hours. The decrease in the voltage at the latter stage was due to mainly the decrease in the proton conductivity.
Development of Novel High Efficiency Single-Layer Gas Diffusion Layers for Proton Exchange Membrane Fuel Cell
Authors: Lee Hung-Fan , Chen-Yang Yui Whei
Published: February 2020

Abstract

In this study, a series of single-layer gas diffusion layers(SL-GDL-Gx, x=1-3) for application in proton exchange membrane fuel cell (PEMFC) were successfully prepared by addition of various amount of graphene in a home-made composite-based single-layer gas diffusion layer (SL-GDL) prepared with a simple and inexpensive process. The surface morphologies of the as-prepared SL-GDL-Gx were characterized by scanning electron microscopy (SEM) and found that all the SL-GDLs had micro-porous layer (MPL)-like structures, in which the carbon black and VGCF powders were well-dispersed and covered on surface of the added graphene layers. The characteristics of the as-prepared SL-GDL-Gx, including electronic resistance, gas permeability, mechanical property, and hydrophobicity, were investigated. The fabrication of the SL-GDL-Gx–based membrane electrode assembly (MEA) for PEMFC was carried out by hot-pressing the assembly of NRE212 and the Pt catalyst coated SL-GDE-Gx electrodes. It was found that the best performance of the PEMFCs fabricated with SL-GDL-Gx measured at 80°C under the humidified H2/O2system was obtained from the one with SL-GDL-G3, which contained 5.0% of graphene, and was approximately 77.8% higher than that of the one fabricated with SL-GDL, and as efficient as that of the one fabricated with SGL 35BC, a commercial dual-layer GDL.

Acknowledgement

The authors gratefully acknowledge National Science Council, Taiwan, R.O.C and Chung Yuan Christian University for supporting the research work.

Table1.

SL-GDL-Gx
(x=1-3)
Graphene amount (wt%)

SL-GDL-G1
0.0

SL-GDL-G2
2.5

SL-GDL-G3
5.0
Enhanced Direct Oxidation of Formic Acid and Its Underlying Mechanism in the Ag-Pd Core-Shell Nanocatalyst: A First-Principles Study
Authors: Cho Jinwon , Lee Sangheon , Yoon Sung-Pil , Han Jonghee , Nam Suk Woo , Ham Hyung Chul
Published: February 2020

Formic acid is an excellent in situ source of hydrogen for fuel cells, for it offers high energy density and remains as a liquid at standard temperature and pressure. So far, there has been a lack of reports regarding the underlying mechanism in enhancing the direct oxidation of formic acid on the bimetallic nano-catalyst. In this study, using spin-polarized density functional theory we examine the reactivity and selectivity of Ag-Pd core shell catalyst toward direct oxidation of formic acid. We find that the ligand effect in Ag-Pd core shell catalyst plays an important role in determining direct oxidation of formic acid rather than the strain effect. In particular, the thinnest Pd shell catalyst can boost the hydrogen production from direct oxidation of formic acid at room temperature and this result provides possibilities for the development of fuel cell devices.
Atomistic Simulation Studies of TiO2 Nanosheets
Authors: Ngoepe Phuti Esrom , Matshaba Malili Gideon , Sayle Dean C
Published: February 2020

Studies on TiO2 nanosheets for energy storage and conversion, including anode in lithium ion batteries (LIB) and electrodes in dye solar cells respectively, are not as abundant as those of nanoparticle and nanoporous structures [1]. Such nanosheets are ideal owing to exposure of highly reactive surfaces, such as the anatase {001}facets, which can now be stabilised [2]. Electrochemical investigations reveal that the exposed (001) high-energy facets of the nanosheet result in enhanced rate capability which originates from both the shortened diffusion path and lowered insertion energy barriers on the active surface for Li+ ions [3]. Furthermore, the electrolyte/electrode contact is enhanced via hollow structures; and such features collectively allow for more efficient lithium diffusion in anodes of LIB. In addition to the anatase polymorph [4], TiO2–B [5] nanosheets have also been observed.

Generally, studies of nanostructures with the brookite structure are scarce since this polymorph is difficult to grow. Aggregations of nanoparticles with the brookite structure have been reported [6]. However, TiO2 nanosheets with the brookite and rutile components have been recently observed [7]. In order to understand such nano-architecture better, we present results of TiO2 simulated nanosheets, which were generated by amorphisation recrystallisation method [8]. Simulated X-ray diffractions of such structures allude to the presence of the brookite and rutile polymorphs. In addition analysis of their microstructures clearly show zigzag patterns associated with the brookite and straight tunnels related to twinned rutile polymorphs. The lithiated nanosheets of TiO2 were also investigated, and lithium ions were located well within the observed tunnels. The suitability of this TiO2polymorph and nano-architecture for lithium ion batteries electrodes, as compared to the bulk form, will be discussed.

References

[1] Su X., Wu Q-L., Zhan X., Wu J., Wei S. and Guo Z. (2012) J. Mater Sci. 47,2519.

[2] Yang H. G., Sun C. H., Qiao S. Z., Liu J. Z. Smith S. C. Cheng H. M. and Lu G. Q. (2008) Nature 453, 638.

[3] Knauth P. and Tuller H. L. (1999) J. Appl. Phys. 85, 897.

[4] Wei X., Liu J., Chua Y. Song J. and Liu X. (2011) Energy Environ. Sci. 4,2054.

[5] Liu S.,Jia H., Han L., Wang J., Gao P., Yang J. and Che S. (2012) Adv. Mater. 24,3201.

[6] Reddy M. A., Pralong V., Varadaraju U. V. and Raveau B. (2008), Electrochem. Solid-State Lett. 11, A132 – A134.

[7] Sussman M., Clouteau, Yasin A., Guo F., and Demopoulos G.P. (2013) Abstract #881, 224th ECS Meeting, © 2013 The Electrochemical Society.

[8] P.E.Ngoepe, R.R. Maphanga and D.C. Sayle, (2013), “Towards the Nanoscale”, Chapter 9 in Computational Approaches to Energy Materials, pp 261-290, edited by C.R.A. Catlow, A. Sokol and A. Welsch, John Wiley and Sons Ltd.
(Invited) Impact of Size Scale on Electro-Chemo-Mechanical Coupling Properties in MIECs: Bulk and Thin Film (Pr,Ce)O2-δ
Authors: Bishop Sean R. , Chen Di , Sheth Jay , Misture Scott , Sheldon Brian W. , Kim Jae Jin , Tuller Harry L.
Published: February 2020

Many oxides exhibit advantageous properties in energy conversion and storage applications, such as solid oxide fuel cells (SOFCs), heterogeneous catalysis, photoelectrochemical cells, and batteries, due in part to their high temperature stability, corrosion resistance, and dopant cation solubility, respectively. In particular, mixed ionic and electronic conducting oxides have been demonstrated to aid in increasing reaction kinetics at electrodes in SOFCs due to the simultaneous presence of electrons and oxygen vacancies. With changes in oxygen partial pressure and temperature during normal operation operation, the defect concentration and hence transport characteristics of MIEC oxides inevitably change. In addition, defects are often coupled to a significant lattice dilation, known as chemical expansion, which under some circumstances leads to mechanical failure. Furthermore, as length scales are reduced, the energetics for electron and vacancy formation have been shown to be modified. In this presentation, recent work examining the the interplay of electro-chemo-mechanical properties of bulk ceramic to thin film size scales will be discussed. This work was facilitated by using the model material system, (Pr,Ce)O2-δ (PCO), which, due to the ease of reduction of Pr from 4+ to 3+ valence, exhibits significant MIEC behavior at relatively high oxygen pressures (e.g. air). Impedance spectroscopy was used to study both the oxygen exchange resistance and oxygen content (via chemical capacitance) of cells consisting of PCO thin films deposited on yttria stabilized zirconia substrates. When compared to defect formation energies derived from a detailed thermogravimetric and conductivity model for bulk PCO, films were found to exhibit enhanced reducibility. This phenomenon was further verified using an in situ optical transmission measurement of films, coupled with chemical capacitance, which correlated the amount of absorbing Pr4+ centers to oxygen vacancy concentration. Additionally, oxygen exchange probed by optical transmission relaxation measurements on “bare” films exhibited slower kinetics as compared to corresponding electrochemical measurements. The role of metal electrodes as well as impurities in modifying oxygen exchange rate will be discussed, as well as new means to improve oxygen exchange of the aged “bare” film surface. Lastly, thermo-chemical expansion measurements of bulk and thin film PCO samples will be presented with discussion related to the atomistic role of individual point defects and defect association.
Comparative Iinvestigation of the High Temperature Corrosion Resistant Model and Commercial Fe-Cr-Al-RE Alloys with Different Chromium Content
Authors: Tsurtsumia Olga , Kutelia Elguja
Published: February 2020

The alloys of Fe-Cr-Al-RE system are the high temperature oxidation resistant materials and they are normally are intended to apply at the temperatures up to 1200OC. Usually the composition of the mentioned system is varied by the main elements values as well as RE’s and other alloying elements amount and the variety of the latter. The high temperature behavior of the Fe-Cr-Al-RE bulk alloys and the coatings with the chromium content of up to 25wt% and the Al that of up to 5wt% is investigated widely, whereas higher chromium content alloys of the mentioned system are barely studied.

The oxidation peculiarities of high (>40wt%) chromium content Fe-Cr-Al-RE model alloy with some minor additives were compared to that of the two commercial (Aluchrom YHf and PM2000) alloys of the same system. According to the experimental results the new material investigated exhibited the slowest oxidation rate (as it is shown in the Fig.1a) and the thinnest oxide scale formation comparatively to the other two alloys which makes it a quite promising high temperature oxidation resistant material [1-3].

The processes taking place on the surface of model alloy exposed to high temperatures are discussed and compared to those of the two commercial alloys. The attempt to disclose the ways differentiating the oxide scale formation on the investigated low and high chromium containing alloys of Fe-Cr-Al-RE system was made and the factors influencing the slower oxide development process for the model alloy were suggested.

The obtained kinetic data after the high temperature cyclic oxidation (120/15 minutes of heating up/cooling down cycling) in laboratory air at 1100OC during 2000 hours is compared for all the investigated tree alloys having either polished or rough surface conditions before the exposures at the elevated temperatures. Thus, the initial surface condition on the protective oxide scale growth kinetics was studied. Besides, the oxide scale growth rate dependence on the specimen thickness was studied as well for the alloys exposed at the same elevated temperatures during 1000 hours, where new model alloy has showed the outstanding priority comparing to the other two commercial alloys investigated (Fig. 1b). SEM analysis was applied for the evaluation of the oxidized specimens’ surfaces as well as their cross-sections. References

Tsurtsumia O., Kutelia E., Bulia B., Mikadze O., Materials Science Forum Vols. 595-598, 2008, (Trans Tech Publications) pp. 833-840

Tsurtsumia O., Kutelia E., Bakhtiyarov S., Proceed. Of 17th Int. Corrosion Congr. USA, Las Vegas, Nevada, October, 2008

Kutelia E., Tsurtsumia O., Eristavi B., Adanir H., Bakhtiyarov S., Journal on Engineering and Technology, 2006, Vol. 1, No. 4, pp. 61-71
Effect of Carbon Dioxide on the Cathodic Performance of Solid Oxide Fuel Cells
Authors: Cetin Deniz , Yu Yang , Luo Heng , Lin Xi , Ludwig Karl , Basu Soumendra Nath , Pal Uday Bhanu , Gopalan Srikanth
Published: February 2020

Solid oxide fuel cells (SOFCs) are ideally suited for environmentally benign conversion of chemical energy in hydrocarbons to electricity. While medium scale SOFC power systems in the hundreds of kWe have been demonstrated, larger scale application of such systems have been hobbled by still too high cost. In order to bring down the cost of these systems, manufacturing costs have to be decreased while the power densities have to be improved. Achieving these twin goals will require the reduction of operating temperatures of the cells. On a single cell level, the largest source of performance loss at lower operating temperatures occurs in the cathode. Thus many different groups are presently investigating a slew of new cathode materials. While the performance of the new cathode materials are impressive under controlled operating conditions, it is presently not clear whether they will stand up to the rigorous and punishing operating environments of actual fuel cell stacks. In particular the interfacial and bulk stability of the new generation of cathode materials such as strontium doped lanthanum cobaltites, strontium doped lanthanum cobaltites , and lanthanum nickelates when exposed to anodic gases such as carbon dioxide and water vapor is presently unknown. Exposure to at least trace amounts of anodic gases during the lifetime of the stack is a likely occurrence and could arise from back diffusion, pinholes in the electrolyte and/or interconnection, or compromised seals. Thus, it is important to have a clear understanding of the thermodynamic and kinetic stability of both the interfaces and the bulk of the cathode material under exposure to the aforementioned anodic gases. In this paper, we present results from a study that combines electrochemical and x-ray measurements of the impact of carbon dioxide exposure on strontium doped lanthanum cobalt iron oxide (LSCF), as a function of strontium dopant concentration, gas composition, and temperature. These are combined with computational studies of the stability of the LSCF cathode to carbon dioxide exposure. The longer term goal of this study is to identify cathode compositions which have long term stability to exposure to trace anode side gases.
Thermal Residual Stress and Biaxial Strength of (Y2O3)0.08(ZrO2)0.92 / (Sc2O3)0.1(CeO2)0.01(ZrO2)0.89 Multi-Layered Electrolytes for Intermediate Temperature Solid Oxide Fuel Cells
Authors: Chen Yan , Aman Amjad , Lugovy Mykola , Orlovskaya Nina , Wang Siwei , Huang Xinyu , Graule Thomas , Kuebler Jakob
Published: February 2020

8 mol % Y2O3-ZrO2 [YSZ] has been widely used as electrolyte material in SOFCs. (Sc2O3)0.1(CeO2)0.01(ZrO2)0.89 [SCSZ] has higher ionic conductivity in the intermediate temperature range (600oC - 800oC) compared to YSZ, but YSZ has better chemical and phase stability. In this work YSZ and SCSZ were used in developing layered electrolytes with a unique design to incorporate both materials, resulting in an electrolyte with enhanced ionic conductivity and improved robustness. The design involved placing SCSZ layers between two outer YSZ layers, so as to produce four- and six-layered electrolytes. Tape casting, lamination and pressureless sintering techniques were used in the development of the electrolytes. Due to the mismatch of the coefficient of thermal expansion between the two materials, thermal residual stresses arise between the layers. These stresses contribute to an enhancement of the ionic conductivity of the layered electrolytes. In addition, the compressive residual stress significantly affects the mechanical properties of layered electrolytes, and improves the electrochemical performance. Biaxial flexure strength was measured using ring-on-ring strength testing at room temperature and 800oC. A finite element method was employed to calculate the maximum principal stress at fracture. The results showed that the layered YSZ/SCSZ/YSZ electrolytes have improved flexure strength at both room temperature and 800 oC because of the appearance of compressive residual stresses in the outer YSZ layers of the electrolyte. The calculated compressive stress values were also verified using Weibull statistics of strength data measured at room temperature.
Effect of Dopant and Impurity Segregation on the Ionic Conductivity of Doped Ceria Electrolytes
Authors: Sulekar Soumitra S. , Peacock Bruce T. , Nino Juan C.
Published: February 2020

Doped ceria is a good electrolyte candidate for intermediate temperature solid oxide fuel cells (IT-SOFC) because of its enhanced ionic conductivity. Segregation of dopants and impurities at grain boundaries may degrade the performance of these materials. This grain boundary segregation can be mitigated through manipulation of processing conditions. Recent studies have shown that, at 550°C, Sm0.75Nd0.75CeO2-δ made by co-precipitation from nitrates followed by microwave sintering exhibits enhanced ionic conductivity (2.8 × 10-3 S·cm-1) as compared to the ball milled and conventionally sintered (1.9 × 10-3 S·cm-1) samples (1). Here we focus on the effects that the composition and processing have on the bulk and grain boundary contributions to ionic conductivity and gain a systematic understanding of the underlying processes. Scanning electron microscopy (SEM), electron energy dispersive spectroscopy (EDS) and electron backscattered diffraction (EBSD) studies indicate that the co-precipitated and microwave sintered samples exhibit smaller grain size, lower impurity content and less segregation at grain boundaries and triple point junctions as compared to conventional solid state processing route. These results are correlated with ionic conductivity data obtained from electrochemical impedance spectroscopy (EIS).

REFERENCES:

S. Omar, “Enhanced Ionic Conductivity of Ceria-Based Compounds for the Electrolyte Application in SOFCs”, Ph.D. Dissertation, University of Florida (2008).
On the Utility of Constant Phase Elements to Characterize Heterogeneous Ceramic Grain Boundaries
Authors: McNealy Benjamin E. , Hertz Joshua L.
Published: February 2020

Electrochemical impedance spectroscopy (EIS) is frequently used in conjunction with simple equivalent circuit models to quantify grain, grain boundary, and electrode properties in electrochemical cells involving ionic or mixed conducting ceramics. Constant phase elements (CPEs) are often used in the equivalent circuit to obtain a better fit of experimental data. However, the CPE is a mathematical abstraction with no clearly defined physical meaning, and its use remains poorly justified. Depression of the grain boundary impedance arc was previously shown to occur in samples with heterogeneous grain boundary conductivity [1]. Here, we use numerical modeling to investigate the utility of CPE-based equivalent circuit fitting in quantifying heterogeneous grain boundary conductivity and/or permittivity.

A 2D electrical model of a polycrystalline ceramic conductor with individually defined grain boundary properties was developed, allowing impedance spectra to be generated for arbitrary distributions of grain boundary conductivity and/or permittivity. For the present study, the relevant properties of each grain boundary were assigned randomly according to a specified distribution. Heterogeneous conductivity values followed a log-normal distribution, while heterogeneous permittivity values followed an exponential distribution with a maximum equal to the bulk grain permittivity. Simulated impedance spectra (Fig. 1) were produced by solving Poisson’s equation and fitted to an equivalent circuit consisting of two parallel R-CPE elements in series. Grain boundary conductivity and permittivity values were calculated from the circuit parameters Rgb
, Qgb
, and ngb
.

As expected, increasingly heterogeneous grain boundary properties correlated to increasingly depressed impedance arcs and reduced CPE exponent. When only the conductivity or the permittivity was heterogeneous, the spread of parameter values could be estimated from the CPE exponent. However, this was no longer possible when both parameters were heterogeneous. As one might hope, in all cases, the grain boundary conductivity determined from the CPE-based equivalent circuit was within ±30% of the actual mean grain boundary conductivity. Conversely, simple use of the CPE’s Qparameter as a capacitance results in severe error in calculating the mean grain boundary permittivity. A commonly used equivalent capacitance expression given by Brug [2] still caused the calculated permittivity to deviate by up to 60% from the actual mean value. However, a new empirical equation [3] allowed a more accurate estimate that differed from the mean by no more than 35% (Fig. 2). Recent extensions of this work to quantification of the impedance of the electrode–solid electrolyte interface will also be presented.

[1] J. Fleig, Solid State Ionics 131 (2000) 117–127.

[2] G.J. Brug et al., J. Electroanal. Chem. Interfacial Electrochem. 176 (1984) 275–295.

[3] B.E. McNealy and J.L. Hertz (under review).
Determination of Non-Stoichiometry in Mixed Conducting Oxide Thin Films of Arbitrary Chemistry
Authors: Balaji Gopal Chirranjeevi , Shi Yezhou , Chueh William C , Haile Sossina M
Published: February 2020

The dependence of oxygen non-stoichiometry on oxygen partial pressure and temperature is critical to many of the applications of non-stoichiometric oxides in electrochemical energy conversion processes. It has been increasingly recognized that electrochemical methods, in particular, AC impedance spectroscopy, can be used to evaluate this non-stoichiometry. The method is particularly useful for determining the properties of thin films, for which conventional thermogravimetric methods are inapplicable. To date, analysis of the ACIS data to extract non-stoichiometry values has relied on application of various simplifying assumptions for the thermodynamic behavior, limiting the approach to oxides with ideal solution behavior. In this work, we determine the oxygen non-stoichiometry of cerium oxide, which displays non-ideal behavior under certain thermodynamic conditions. The chemical capacitance of single crystal, epitaxial thin films of cerium oxide deposited on yttria stabilized zirconia substrates is measured and related to the oxygen non-stoichiometry using thermodynamic principles. This work will demonstrate the validity of the chemical capacitance measurements to reliably extract non-stoichiometry of a generalized oxide system.
On the Role Played By Catalytic Metallic Additives on TiO2 for the Photoreduction of CO2
Authors: Andreu Teresa , Manzanares Marta , Fàbrega Cristian , Morante Joan Ramon
Published: February 2020

In photocatalytic processes, it is not only need to generate an electron-hole pair, but the electronic transfer must be efficient in the reaction process, involving multi-electronic redox reactions, occurring at the near vicinity at the surface of the semiconductor. All these factors need the surface engineering of the semiconductor to increase the overall efficiency of the process. The surface properties of TiO2 can be modified by the addition of some elements which give rise to a local lattice modification, introduce new potential catalysts issues and alter or vary the composition and bond ending of the last two nanometers layer being it essential and outstanding for the final photocatalytic properties.

In this contribution, we will present a comparative analysis among different potential additives such as magnesium, indium. More detailed surface analysis techniques have revealed significant changes at the outer part of the TiO2 material. XPS spectra, especially at the energy zone of oxygen and titanium, and corresponding to the last two nanometers, show significant evolution of the different detected bonds as the concentration of the additives is increased.

All these data have been correlated with the photocatalytic behavior for CO2 reduction as a function of the additive concentration below the limit of their solubility for avoiding segregation effects. A correlation between Ti+3 and adsorbed molecular oxygen concentration found in these outer layers will be discussed as well as their correlation with the total productivity rate, considering all the effective photogenerated electrons for the reduction of CO2 from the GC analysis of the products obtained, including CO, CH4 and C2 hydrocarbons. These findings confirm that the benefit introduced by the catalytic additive is mostly related to the “surface quality” and how it is lost as the concentration of additive is increased. Likewise, it is determined that the overall productivity is kinetically limited by a four-hole chemistry of the water oxidation reaction, like in the photoactivated water splitting process. Nevertheless, in spite of these limitative issues, significant increases, a factor of 3 o 4, can be achieved in the productivity of reduced CO2 if the concentration do not overcome some limits whereas the selectivity of the products becomes determined by the nature of the additive.
Enhancement of Photoaffinity and Charge Carrier Collection in Mixed Metal Oxides Photo-Anodes Implemented with Plasmonically Active Metal Nps
Authors: Solarska Renata , Bienkowski Krzysztof , Zoladek Sylwia , Kulesza Pawel J.
Published: February 2020

An effective solar light-driven water splitting in photo-electrochemical devices requires use of materials which combine both high photo-conversion efficiency and long term stability goals. For the latter reason the choice of the suitable systems is restricted to the semiconducting oxides that, in most cases, do not undergo photo-corrosion in aqueous solutions but which are also able to absorb efficiently the visible light. The low optical absorption coefficients near the fundamental band edge, which determine the extent of solar light absorption by many photo-anode materials, are the critical factors for a number of semiconductors characterized by an indirect optical transition. This is also the case of n-type semiconducting WO3 or Fe2O3 responding to the blue, respectively, green part of the solar spectrum for which the optical absorption depths exceed the minority charge carriers collection distances.Therefore, incoupling of light into semiconductor films by scattering from plasmonic nanostructures and/or resonant coupling of the plasmonic near field to the semiconductor, have a potential to improve the effectiveness of the photocurrent spectral response of the employed photoanode. The results regarding the improved light absorption and charge collection in doped and/or mixed semiconducting oxide photo-anodes will be presented.
Photoelectrochemical Water Splitting on Hydrogen Modified Titanium Oxide (HM-n-TiO2) Thin Film Electrode
Authors: Frites Mourad , Khan Shahed U.M
Published: February 2020

Hydrogen modified titanium oxide (HM-n-TiO2) thin films were synthesized by thermal oxidation of Ti metal substrate. The hydrogenation of n-TiO2 was carried out electrochemically under cathodic polarization at −1.6 V vs SCE in 2.5 KOH electrolyte under dark condition. The photoactivity of HM-n-TiO2 thin films was assessed by measuring the rate of the water splitting reaction under solar simulated light in terms of photocurrent density, J
p (mA cm-2). The HM-n-TiO2 photoelectrodes exhibited a fourfold enhancement in their photocatalytic activity compared to n-TiO2 prior to hydrogenation. The HM-n-TiO2 photoelectrodes were characterized using X-ray diffractions and the change in the valence band induced by the hydrogenation of n-TiO2 was examined by XPS measurements.