bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermal Engineering of GaN Semiconductor Devices
Authors: Graham Samuel 
Published: February 2020

The development of gallium nitride (GaN) on a variety of substrates from Si to diamond has been used to create a variety of devices for both RF and power electronics technologies. In general, GaN devices can accommodate faster switching speeds, higher junction temperatures, and high voltages, allowing for devices operating at higher power with increased efficiency in smaller form factors. However, the lattice mismatch between c-axis hexagonal GaN and other non-native substrates requires the use of buffer layers in order to grow high quality, relaxed GaN required for advanced devices. Such layers can add to the thermal resistance which impacts to overall device thermal performance and thus, device reliability. In addition, these interfacial layers impact the growth and residual stress in the GaN epitaxial layers that can limit the overall voltage limits of lateral HEMT devices.
In this work we use a variety of experimental techniques to measure the thermal boundary resistance (TBR) for GaN on Si, SiC, and diamond substrates. The impact of the structure of the interface on the overall TBR and thermal conductivity of the GaN layers grown by MOCVD will be discussed. In addition to the TBR, the overall stress in the devices caused by growth on the differing substrates, measured by Raman spectroscopy, will be presented. A unique superlattice structure used to reduce the stress in GaN layers on Si will also be highlighted. Finally, the electro-thermomechanical performance of GaN devices under DC and pulsed operation will be presented where the temperature of the devices was measured using Raman Spectroscopy while the mechanical deformation was measured by Scanning Joule Expansion Microscopy. Data will show that rapid heating and high tensile stresses near the drain side edge of the gate during pulsed operation is dependent on the bias conditions, the TBR, substrate material, and the mechanical properties of the device. Overall, challenges associated with the structure of GaN devices that must be overcome for effective thermally management will be presented.
Catalytic Design through Computational Modeling: Exploring the Electrochemical Oxidation of Glycerol By Nitroxyl Radical
Authors: Hickey David P , Matanovic Ivana , Schiedler David , Atanassov Plamen , Sigman Matthew S , Minteer Shelley D. 
Published: February 2020

Recently there has been an increased interest in the development of small molecule electrooxidation catalysts such as (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), for use in the anodic compartment of a biofuel cell. Some TEMPO derivatives are capable of electrochemically oxidizing short chain alcohols and various sugars to the corresponding aldehydes and carboxylic acids under physiological aqueous conditions. However, building libraries of such a catalyst is difficult due to the limited number of commercially available TEMPO derivatives and the lack of modular synthetic pathways to more complicated TEMPO structures. A promising alternative to the physical preparation of such libraries is the use of computational modeling to allow for in silico catalytic screening of a much wider range of TEMPO compounds.
We have developed a computational model based on simple geometry optimization and population analysis to probe the catalytic activity and oxidation potential of TEMPO-derived species. Redox potentials were calculated from the free energy cycle of TEMPO oxidation while the relative catalytic activity was modeled using multidimensional analysis involving the computed pKas of various protonation states of the hydroxylamine form of TEMPO along with the corresponding redox potentials. We will also discuss how analysis of the atomic polar tensor (APT) charge of TEMPO can provide insight into the factors that affect its redox potential.
Hydrogen Generation from the Hydrolysis of Sodium Hypophosphite Using CoB2O4 Catalyst for Fuel Cell Operation
Authors: Gorelishvili Giorgi , Nikoleishvili Paata , Tsutsumia Gigla , Kveselava Valentina , Kurtanidze Rusudan , Koiava Nana , Sharabidze Daviti 
Published: February 2020

The goal of the work involves a radically new approach – establishment of possibility of the use of sodium hypophosphite (NaH2PO2) as hydrogen source or the study of the process of its reforming; synthesis of corresponding catalysts and their testing for generation of hydrogen. It is well known that in the process of chemical nickel plating at 80-95 0C, in the course of an interaction between sodium hypophosphite and water the formed atomic hydrogen reduces nickel on the surface of the plated metal. Nickel plating with the participation of sodium hypophosphite is self-catalytic. Overall catalytic reaction of the interaction between hypophosphite and water may be presented as follows:
H2PO 2‾ + H2O → H2PO 3‾ + H2

We have established that in the absence of nickel-ions in the hypophosphite solution, and with the use of so-called Raney nickel catalyst, an intensive separation of hydrogen is possible at high temperatures (80-95 0C), but at room temperature the process practically stops. Hence, by selection of corresponding catalyst the hydrogen production from hypophosphite solution and its use in fuel cell are possible. In the work the hydrogen evolution from aqueous solution of sodium hypophosphite was studied at 10-30 0C by CoB2O4 catalyst. In case of 2M NaH2PO2 solution hydrogen evolution rate was 3.4-3.6 ml sec-1 g-1, which was enough for 0.6 W H2–O2 fuel cell operation.
The designate project has been fulfilled by the support of Georgia National Science Foundation. Any idea in this publication is possessed by the authors and may not represent the opinion of “Georgia National Science Foundation"
Synthesis of VC-C Nanocomposite for Electrochemical Applications
Authors: Mahajan Mani , Singh K. , Pandey O. P. 
Published: February 2020

Carbon-coated vanadium carbide (VC-C) nanocomposite were synthesized by single-step chemical-reduction route in an autoclave at the temperature of 600oC. In this experiment, vanadium pentode (V2O5) was used as precursor, magnesium as reducing agent (Mg) and acetone as carbon source. The gases produced by the decomposition of acetone generate carbon and H2/CO2 gases at high temperature which further creates high pressure inside the autoclave. The processing parameters were optimized for the formation of single phase vanadium carbide (VC). The structure, morphology, and thermal stability of the obtained product were studied by XRD, TEM and TGA/DTA techniques, respectively. The N2 adsorption-desorption isotherm indicated the mesoporous structure of the VC. The electrochemical properties of the obtained C@VC were studied by the cyclic voltammetric studies.
Electrochemical Analysis for the Identification of Electrode Reaction in Ni-YSZ Anode as for Solid Oxide Fuel Cell
Authors: Im Ha-Ni , Lim Dae-Kwang , Lee Tae-Ryong , Yoo Young-Sung , Choi Mihwa , Song Sun-Ju 
Published: February 2020

The most widely studied anode for oxidation of hydrogen in solid oxide fuel cells (SOFCs) is the Ni/YSZ cermet. A detailed understanding of the rate-limiting steps in Ni-YSZ anodes is highly desirable from an optimization point of view. One of the most promising way of complex system is to define the reaction by impedance spectroscopy.
In principal, impedance measurement is comprised of electrolyte response, electrode response, and transport limitations for supply of reactants and removal of products. The electrolyte response is readily separated out as a series resistance, in simple geometries it can even be used to indicate the magnitude of the microscopic electrode contact area. For high temperature impedance model, transport restriction are believed to be negligible in typical setups. But anode with low resistance transport restrictions may contributes significantly.
The electrode reactions like charge-transfer reaction are suggested to occur in the vicinity of the active triple-phase boundary (TPB) line. The active TPB is defined as the line where the Ni network, the YSZ network, and open pores meet to form percolation paths for transport of electrons, oxide ions, and gas respectively. The reaction resistance related to any process occurring across the active TPB is coupled in parallel between Ni and YSZ.
This paper (i) brings forth a method of rationalizing impedance data and (ii) presents relevant data for the oxidation of hydrogen on Ni/YSZ cermet anodes produced by tape casting. In the analysis of the obtained impedance spectra, the distribution of relaxation times (DRT) was calculated in order to perform a pre-identification of the physico-chemical processes occurring in the cell. The impedance data are rationalized by fitting to a representative equivalent circuit, thus allowing the dependency of three processes on typical parameters to be derived.
Grain Boundary Engineering to Improve Ionic Conduction in Thin Films for Micro-SOFCs
Authors: Tarancón Albert , Morata Alex , Pla Dolors , Saranya Aruppukottai M. , Chiabrera Francesco , Garbayo Inigo , Cavallaro Andrea , Canales-Vázquez Jesús , Kilner John A. , Burriel Mónica 
Published: February 2020

New emerging disciplines are specifically devoted to study trivial and non-trivial effects resulting from working in the nanoscale, however, the implementation of these nanostructures in real devices is still a major challenge. Thin film deposition and silicon microtechnology is probably the most promising and straightforward combination for the reliable integration of nanomaterials in real devices. In particular, the implementation of pure ionic and mixed ionic/electronic conductors (MIECs) in thin film form allows the miniaturization of multiple solid state devices. A simple combination of three oxides properly integrated in silicon enables anode/electrolyte/cathode structures for the fabrication of solid oxide fuel cells (SOFCs). These micro-SOFCs represent a new family of micro-power generators that will drive a revolution in portable power generation [1].
In this lecture, we will talk about the implementation of novel nanoionics concepts in micro-SOFCs by using micro and nanofabrication technologies. We will put special attention on the contribution of grain boundaries to the mass transport properties in interface-dominated materials such as thin films. Grain boundary engineering will be presented as a powerful tool for reducing the resistance associated to electrolytes [2] and even control the intrinsic transport nature and performance of MIEC materials [3].

References:

[1] I. Garbayo, D. Pla, A. Morata, L. Fonseca, N. Sabaté and A. Tarancón, Full ceramic micro solid oxide fuel cells: towards more reliable MEMS power generators operating at high temperatures, Energy Environ. Sci. 7 (2014) 3617
[2] A. Chroneos, B. Yildiz, A. Tarancón, D. Parfitt, J. A. Kilner, Oxygen diffusion in solid oxide fuel cell cathode and electrolyte materials: mechanistic insights from atomistic simulations,Energy Environ. Sci. 4(2011) 2774
[3] A. M. Saranya, D. Pla, A. Morata, A. Cavallaro, J. Canales-Vázquez, J. A. Kilner, M. Burriel and A. Tarancón, Engineering mixed ionic electronic conduction in La0.8Sr0.2MnO3+

δ

nanostructures through fast grain boundary oxygen diffusivity, Adv. Energy. Mat (2015) 1500377
Multi-Layered Thin Film Y:BaZrO3 Electrolytes for Anode-Supported Protonic Ceramic Fuel Cells
Authors: Bae Kiho , Jang Dong Young , Noh Ho-Sung , Kim Hyun Joong , Hong Jongsup , Kim Byung-Kook , Yoon Kyung Joong , Son Ji-Won , Shim Joon Hyung 
Published: February 2020

Acceptor-doped barium zirconate electrolytes, represented as yttrium-doped barium zirconate (Y:BaZrO3 or BZY), are expected to allow ceramic fuel cells to be operated at intermediate temperatures in the range below 600 °C. This is because BZY conducts protons and exhibits a relatively high ionic conductivity with relatively small activation energy, especially compared to ceramics that conduct oxide ions, including yttria-stabilized zirconia (YSZ) and gadolinia-doped ceria (GDC). The bulk conductivity of BZY is greater than that of YSZ by about one order at 600 °C and by two orders at 400 °C and, unlike cerate-based materials, BZY was found to exhibit good phase stability (1). Thus, there have been numerous efforts to develop BZY-based protonic ceramic fuel cells (BZY-PCFCs). Although several studies have reported BZY-PCFCs to perform well, with outputs of 140 mW/cm2 and 180 mW/cm2 in the intermediate temperature regime at 400 °C (2) and 450 °C (3), respectively, both of these were achieved in the form of freestanding nanoscale membranes. For practical production and use, however, fabrication of the BZY electrolyte in anode-supported stacks would be more desirable. Yet, the performance of anode-supported BZY-PCFCs is not yet as good as that of solid-oxide fuel cells. To our knowledge, 170 W/cm2 is the greatest power output achieved with BZY-based fuel cells at 600 °C (4). An attempt to adopt a thin BZY electrolyte (4μm thickness) in anode-supported PCFCs has produced a power output of merely 110 W/cm2 at 600 °C (5), attributed to the prevalence of a relatively large ohmic resistance, which implies the presence of structural defects such as poor grain adhesion (5). After performing a series of experiments, we realized that the adoption of multiple anode support layers with multi-step sintering promotes the structural and mechanical stability of thin film BZY electrolytes. As a result, the power output has exceeded 700 mW/cm2 at 600 °C with an open circuit voltage over 1 V. At this presentation, we will share our recent experimental results and discuss the cell performance in relation with structural characteristics and composition.
1. K. D. Kreuer, Annu. Rev. Mater. Res., 33, 333 (2003).
2. J. H. Shim, J. S. Park, J. An, S. Kang, T. M. Gür, and F. B. Prinz, Chem. Mater., 21(14), 3290 (2009).
3. Y. B. Kim, T. M. Gür, S. Kang, H-J. Jung, R. Sinclair, and F. B. Prinz, Electrochem. Commun., 13(5), 403 (2011).
4. L. Bi , E. Fabbri , Z. Sun, and E. Traversa, Energy Environ. Sci., 4, 409 (2011).
5. D. Pergolesi, E. Fabbri, and E. Traversa, Electrochem
.
Commun., 12, 977 (2010).
Effect of Catalyst Layer and Fuel Utilization on the Durability of Direct Methane SOFC
Authors: Georges Samuel , Nóbrega Shayenne D. , Cheah Seng Kian , Steil M. C. , Bultel Yann , Rieu Mathilde , Viricelle Jean-Paul , Gelin Patrick 
Published: February 2020

Among energy conversion systems, high temperature Fuel Cells are considered of great interest for delocalized, renewable and clean electricity and heat power production. The high operating temperature (500°C - 800°C) is likely to allow the use of various types of hydrocarbons instead of hydrogen as the fuel with high efficiency and flexibility. Theoretically, the fuel can be catalytically converted into hydrogen directly at the anodic side. Practically, the most important drawback is the formation of carbon deposits on the anode, poisoning the electrocatalytic activity of the electrode. Hence, one of the main current challenges remains the increase of the life-time of these systems (especially avoiding carbon deposition and anode pollution), and long term reliable operation with fuel flexibility. Such performances have not been achieved yet.
We recently demonstrated the fundamental importance of the fuel utilization on the carbon deposition limits. The quantity of steam released by the anode is directly proportional to the current density, and then to the fuel utilization UF. Below a given value of UF, the system does not produce enough steam to ensure the internal catalytic conversion of the hydrocarbon flux, resulting in irreversible degradation of the cell by carbon methane cracking. This observation and the deep understanding of the anode operation in methane allowed us to achieve long term operation with pure hydrocarbons without carbon deposition at the surface of conventional Ni-YSZ anodes. The thermodynamical limits of carbon deposition as a function of fuel utilization were also investigated.
Current developments and technological simplifications based on new principles of operation and original architectures designed in this finality will be presented. In particular the presentation will emphasize on the Gradual Internal Reforming and Electro-catalytic separation principles applied to the design of original anodic systems, and on the demonstration of the reliability of the systems in different pure hydrocarbons or carbon-based fuels (no H2O, CO2, O2 or carrier gas addition) [1-4]. The effect of the fuel utilization on the limits of carbon deposition will be discussed and the long term durability in pure dry methane will be demonstrated. The perspectives of direct operation of SOFC on waste fuels in order to decrease the amount of CO2 rejects in delocalized energy production systems will be discussed.
1. J-M. Klein et al., Journal of Power Sources 193, (2009) 331
2. S. D. Nobrega et al., Journal of Power Sources (2012) 156-159
4. S. Georges et al., ECS Transactions 57(1) (2013) 3023-3030
4. S.D. Nobrega et al., Journal of the Electrochemical Society, 161(3) (2014) F354-F359
5. J. Puig et al., Fuel Cells 14 (6) (2014) 1014-1021
6. K. Girona et al., Canadian Journal of Chemical Engineering 93 (2) (2015) 285-296
Development of Ceria-Based Microtubular Solid Oxide Fuel Cells
Authors: Sumi Hirofumi , Yamaguchi Toshiaki , Shimada Hiroyuki , Hamamoto Koichi , Suzuki Toshio 
Published: February 2020

Gadolinia-doped ceria (GDC) has higher oxide-ion conductivity than a conventional yttria-stabilized zirconica (YSZ). GDC is one of the most desirable materials as an electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs) operated below 600 °C. A nickel-GDC cermet anode has high catalytic and electrochemical activities against fuel oxidation in SOFCs. For example, direct butane utilization was successfully demonstrated for Ni-GDC anode-supported microtubular SOFCs. Furthermore, an La0.6Sr0.4Co0.2Fe0.8O3(LSCF)-GDC composite cathode shows high performance at intermediate temperature. We applied GDC materials to electrolyte, anode and cathode for microtubular SOFCs.
Development of Platinum-Niobium as a CO Tolerant Catalyst for PEFC Operating with CO Contaminated Hydrogen
Authors: Rocha Thairo A. , Colmati Flavio , Ciapina Eduardo Gonçalves , Linares José J , Gonzalez Ernesto Rafael 
Published: February 2020

Traditional Polymer Electrolyte Fuel Cells (PEFC) are fed with hydrogen in the anode and oxygen in the cathode. This type of fuel cell is especially attractive because of the high efficiency at low temperature. However, the use of reformate hydrogen compromise cell performance due to the presence of traces of carbon monoxide (CO). This contaminant is adsorbed on the surface of Pt, blocking the sites necessary for the hydrogen oxidation reaction. In this context, to improve the CO tolerance of fuel cell anodes, several bimetallic Pt-based catalysts have been proposed. [1] Some studies reported in the literature have suggested the use of niobium (Nb) as the second element in bimetallic catalysts. [2] Thus, this study aims at analyzing the effect of the addition of Nb to Pt in order to develop a CO tolerant catalyst. Pt3Nb/C catalyst was prepared using a modified impregnation method, [1] physically and morphologically characterized and tested electrochemically in a single fuel cell operating on the traditional Nafion® membranes at 85 oC.
Figure 1 shows the ionic currents signal m/z = 44 obtained by on-line differential electrochemical mass spectrometry (DEMS) experiments, corresponding to CO2 formation. Lower CO oxidation overpotential is observed for the material with Nb, which is a consequence of the facilitated CO oxidation on Pt3Nb/C catalyst. Figures 2 and 3 show the results corresponding to performance of a single fuel cell operating on H2 or H2 + 100 ppm CO. As it can be seen, the Pt3Nb/C catalyst outperforms Pt/C 20%. The high CO tolerance of this material is usually explained by two distinct mechanisms: the bifunctional and electronic mechanisms. In the first, the Nb act as a source of oxygenated species, required for the electro-oxidation of CO to CO2 at overpotentials lower than that for pure Pt. The electronic effect can be discussed in terms of the changes of the position of the Pt 5d-band center induced by the presence of the second metal that modifies the CO adsorption energy, reducing the CO coverage on Pt, and leaving more free Pt sites available for H2 electro-oxidation. These effects will be discussed using on-line DEMS measurements and in situ X-ray absorption spectroscopy (XAS) analyses.

ACKNOWLEDGEMENTS

Authors thank FAPESP, CNPq and CAPES, Brazil, for the financial support.

REFERENCES

[1] Pereira, L. G. S., Paganin, V. A., Ticianelli, E. A. Electrochimica Acta, 54, 192 (2009).
[2] Rocha, T. A., Ibanhi, F., Colmati, F., Linares, J. J., Paganin, V. A., Gonzalez, E. R. Journal of Applied Electrochemistry, 43, 817 (2013).

Figure 1
Development of Alkaline Membranes and Alkaline Membrane Fuel Cells
Authors: Zhuang Lin 
Published: February 2020

In this invited keynote lecture, I will talk about the recent research progress on alkaline membranes and alkaline membrane fuel cells. The following topics will include:

High performance alkaline membranes and ionomers

Hydrogen oxidation reaction (HOR) catalysts in alkaline media

Nonprecious metal catalysts for oxygen oxidation reaction (ORR) in akaline media

Performance and challenge of alkaline membrane fuel cells.

References

Wang, Y., Wang, G., Li, G., Huang, B., Pan, J., Liu, Q., Han, J., Xiao, L., Lu, J. & Zhuang, L., Pt-Ru Catalyzed Hydrogen Oxidation in Alkaline Media: Oxophilic Effect or Electronic Effect? Energy Environ. Sci.
8, 177-181 (2015).

Pan, J., Chen, C., Li, Y., Wang, L., Tan, L., Li, G., Tang, X., Xiao, L., Lu, J. & Zhuang, L. Constructing Ionic Highway in Alkaline Polymer Electrolytes. Energy Environ. Sci.
7, 354-360 (2014).

Pan, J., Li, Y., Han, J., Li, G., Tan, L., Chen, C., Lu, J. & Zhuang, L. A Strategy for Disentangling the Conductivity-Stability Dilemma in Alkaline Polymer Electrolytes. Energy Environ. Sci.
6, 2912-2915 (2013).

Pan, J., Chen, C., Zhuang, L. & Lu, J. Designing advanced alkaline polymer electrolytes for fuel cell applications. Acc. Chem. Res.
45, 473-481 (2012).