bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Neutron Irradiation Effect on GaN-Based Materials
Authors: Zhang Ming-lan , Yang R X , Wang X L , Liu S F
Published: February 2020

For the predominant property, GaN becomes a promising material for ultraviolet/ blue light-emitting diode, solar blind ultraviolet photodetector, radiation resistant particle detectors, and high power high temperature electronic devices. Because of the radiation hardness of GaN, those devices have the potential to be used in outer space and other radiation environment. Irradiation induced defects play the main role in the reliability of GaN based devices. Recently, a strong effort by several groups was devoted to the analyses of electrical and optical properties of defects and their interaction by irradiating GaN with electrons, ions, neutrons and protons [1–4], which is very important for the devices operating at extreme harsh environment.

Positron annihilation spectroscopy (PAS) with a slow-positron beam is an efficient tool for the investigation of open-volume defects such as vacancies in semiconductors, at which they get trapped. In a vacancy the electron density is decreased which makes the positron lifetime longer and narrows the positron-electron momentum distribution. The latter can be observed by recording the Doppler broadening of the energy spectrum of the annihilation radiation. Especially the momentum distribution of the core electrons is sensitive to the chemical environment of an annihilation site. However, in the case of light elements such as O or N the annihilation probability with the core electrons is negligible.

The samples used in the present work were grown on C-plane sapphire substrates by metal organic chemical vapor deposition (MOCVD) with unintentionally doped and Si doped. A 20 nm low temperature GaN nucleation layer was initially grown, and 4 μm GaN film grown at 1050°C was followed. The sample was cut into small pieces with an area of about 10×10 mm2, and irradiated with 2MeV proton from heavy ion accelerator. The incident fluence is 1014, 1015, or 1016 cm-2, respectively.  Positron annihilation spectroscopy, XRD, and Raman spectra were measured.

Irradiation induced defect is vacancies which increased with incident proton. XRD result shows that the crystal-order was kept after proton irradiation. Raman spectra of the Si doped sample shows a “carrier removal” effect but there is not any change in the other spectra.

References:

Look D C, Reynolds D C, Hemsky J W, et al. Defect Donor and Acceptor in GaN, J. Phys. Rev. Lett., 1997, 79: 2273-2276.

Fang Z Q, Hemsky J W, Look D C, et al. Electron-irradiation-induced deep level in n-type GaN, Appl. Phys. Lett., 1998, 72: 448-449.

Auret F D, Goodmann S A, Koschnick F K, et al. Effect of heating rate on positive-temperature-coefficient-of-resistivity behavior of conductive composite thin films, Appl. Phys. Lett., 1998, 73: 3742-3744.

Auret F D, Goodmann S A, Koschnick F K, et al. Proton bombardment-induced electron traps in epitaxially grown n-GaN, Appl. Phys. Lett., 1999, 74: 407-409.
Effect of Rising Edge in Dynamic Stress with Various Duty Ratio in Amorphous Ingazno Thin Film Transistor
Authors: Lee Yeol-hyeong , Seok Su-jeong , Kim Byeong-Koo , Kim Sung-Ho , Lee Tae-Kuen , Kim Ohyun
Published: February 2020

Recently, many research explains the positive threshold voltage (V

th
) shift of oxide TFT as charge trapping at gate dielectric or interface of gate dielectric and channel layer. But mechanism of degradation of rising edge of dynamic stress has not been explained exactly.

 During all stresses, gate stress of 1 Hz with 50%, 20%, 10% and 1% duty ratio was applied at 120 ℃ and both drain voltage and source voltage were grounded. Gate voltage (VG
) was on-voltage (Von
) of 20 V and off-voltage (Voff
) of 0 V in unipolar positive stress, Von
of 0 V and Voff of -20 V in unipolar negative stress, and Von
of 20 V and Voff
of -20 V in bipolar stress (Fig.1). During illumination, samples were illuminated using a top LED. We defined Vth
 as gate voltage at 1 nA of drain current ID
at VDS
of 15V. We defined effective time as sum of Von
time in all stress including illumination

 Fig. 2 shows the ΔVth as function of time with 50%, 20% 10% and 1% duty ratio. In dark, positive unipolar gate stress was applied in fig. 2(a) and bipolar gate stress was applied in fig. 2(b). In illumination, positive unipolar gate stress was applied in fig. 2(c) and bipolar gate stress was applied in fig. 2(d). Fig. 3 shows the ΔVth at effective time of 2000s as reciprocal function of duty ratio for positive unipolar gate stress and bipolar gate stress. At same effective stress time, ΔVth was increase with decreasing duty ratio and ΔVth was larger in bipolar gate stress than in unipolar positive gate stress. Fig. 4 shows ΔVth at effective time of 2000s as reciprocal function of duty ratio under positive unipolar gate stress for illumination and dark. In dark, higher ΔVth was observed compared with illumination.

 In this study, we investigated relationship of ΔVth with various bias stress condition including positive unipolar, negative unipolar and bipolar gate stress and ambient including dark and illumination. We will explain positive bias temperature stress based on charge trapping and introduce new mechanism of additional positive ΔVth on rising edge of dynamic stress.

Figure 1
(Invited) Life-Cycle Net Energy Assessment of Large-Scale Hydrogen Production Via Photoelectrochemical Water Splitting
Authors: Greenblatt Jeffery Buyers , Sathre Roger , Sharp Ian D. , Ager Joel W. , Houle Frances A
Published: February 2020

The Joint Center for Artificial Photosynthesis (JCAP) aims to find a cost-effective method to produce fuels for transportation and feedstocks using only sunlight, water, and carbon dioxide as inputs. Development of such a technology offers the possibility of widespread sources of environmentally benign, energy rich chemicals across the globe.  Although still at an early stage, solar-driven water splitting to produce hydrogen is the most mature artificial solar-to-fuel conversion approach.  Moreover, there is sufficient information from photoelectrochemical (PEC) water-splitting prototypes designed and developed by JCAP and others to perform an assessment of whether large scale application of this approach would be advantageous from a net energy production point of view.

Here we report a prospective life-cycle net energy assessment of a hypothetical large-scale PEC-based hydrogen production facility, assuming energy output equivalent to 1 GW continuous annual average (610 metric tons of H2per day) [1]. We determine essential mass and energy flows required to support such production [2], and use heuristic methods to conduct a preliminary engineering design of the facility. We then develop and apply a parametric model describing system-wide energy flows associated with the production, utilization, and decommissioning of the facility. Based on these flows, we calculate and interpret life-cycle net energy metrics for the facility. We find that under base-case conditions (10% solar-to-hydrogen (STH) conversion and 10 year PEC cell life span) the energy payback time is 8.1 years, the energy return on energy invested (EROEI) is 1.7, and the life-cycle primary energy balance over the 40 years projected service life of the facility is +500 PJ. The most important model parameters affecting the net energy metrics are the STH conversion efficiency, the life span of the PEC cells, and the embodied energy of several components of the PEC cell. We discuss the sensitivities of these and other parameters, and highlight recent work indicating promising ways to improve the net energy metrics. Results suggest that a strong program of research into improved materials and methods to process the materials will have a high impact on the feasibility of this technology.

References:

R. Sathre, C. D. Scown, W. R. Morrow, J. C. Stevens, I. D. Sharp, J. W. Ager, K. Walczak, F. A. Houle, and J. B. Greenblatt, Energy Environ. Sci. 7, 3264 (2014).

P. Zhai, S. Haussener, J. Ager, R. Sathre, K. Walczak, J. Greenblatt, and T. McKone, Energy Environ. Sci. 6, 2380 (2013).

Figure 1
Electrodes for Protonic-Ceramic Membranes Used in Natural Gas-to-Chemicals Processing
Authors: Ricote Sandrine , Manerbino Anthony , Sullivan Neal P , Coors Grover
Published: February 2020

Electrodes used in natural gas-to-chemicals processing must demonstrate unique performance attributes in challenging high-temperature, reducing environments.  Materials must be stable, have high electronic conductivity, and be chemically inert to methane and other hydrocarbons. Ceramic-metal composites (cermets) made of nickel and the electrolyte material, used as the fuel-side electrodes in protonic ceramic fuel cell, are not suitable as their performance decreases rapidly due to chemical reaction with the natural gas fuel. This leads to carbon-deposit formation, poisoning at the Ni phase and eventual electrode fracture [1]. These issues motivated the development of coke-resistant electrodes and catalysts. The coking rate of copper at 800 °C is reported to be two orders of magnitude lower than that of Ni [2].  This study presents a detailed electrochemical characterization of Cu electrodes on BaCe0.2Zr0.7Y0.1O3-d proton-conducting ceramic electrolyte (BCZY27).

High-quality dense BCZY27 electrolytes with large grains were successfully prepared using solid-state reactive sintering [3-4]. Cu electrodes were deposited by various techniques such as sputtering and screen-printing/painting, resulting in electrodes with different thicknesses and microstructures, making it possible to understand the chemical and electrochemical mechanisms taking place at the electrodes. Impedance spectra were recorded on symmetric cells (electrode/BCZY27/electrode) over a wide temperature range (400 - 700 °C) and in various atmospheres (dry and moist H2, dry methane). Figure 1 displays the ASR of 500 nm sputtered porous Cu electrodes in dry and moist H2. With this electrode architecture, lower ASR are obtained in dry H2, while dense Cu electrodes lead to the opposite trend. Stability tests were also performed to quantify the degradation of the electrodes in hydrogen and methane at 700 °C by using both the ASR and the post-testing micrographs. In this work, the ASR of the various Cu electrodes are compared.

References:

1. C.M. Finnerty, N.J. Coe, R.H. Cunningham, R.M. Ormerod (1998) Catalysis Today
46 137.

2. P.R.S. Jackson, D.J. Young, D.L. Trimm (1986) J. Mater. Science
21 4376.

3  W.G. Coors (2011) “Co-ionic conduction in protonic ceramics of the solid solution, BaCexZr(1-x)Y(y-x)O3-d; part I: fabrication and microstructure, ceramic materials”, Book 3. Intech, Croatia.

4    S. Ricote, N. Bonanos, A. Manerbino, W.G. Coors (2012) Int. J. Hydrogen Energy
37 7954.

Figure 1
(Invited) Reversible Solid Oxide Fuel Cell Development at Versa Power Systems
Authors: Wood Anthony , He Hongpeng , Joia Tahir , Brown Casey Cloudless
Published: February 2020

Versa Power Systems (VPS) is a developer of Solid Oxide Fuel Cell (SOFC) technology focused on SOFC stack development for commercial applications.  In recent years VPS has been developing reversible SOFC (RSOFC) materials systems with a view to future commercial development of RSOFC stacks.  VPS has demonstrated significant technical improvements in RSOFC materials technology in a relatively short timeframe, and has begun to test these at the stack level.  This paper will provide an update of RSOFC activities including cell and stack testing in both steady-state electrolysis operation and operating with RSOFC cycles (fuel cell and electrolysis cycling).
Hydrogen Permeation through Dense BaCe0.8Y0.2O3-δ - Ce0.8Y0.2O2-δ Composite-Ceramic Membranes
Authors: Rosensteel Wade A , Ricote Sandrine , Sullivan Neal P
Published: February 2020

This report presents hydrogen permeation measurements through dense composite-ceramic membranes. The high-temperature operation of ceramic hydrogen-separation membranes makes them suitable in many hydrogen-production applications, such as catalytic partial oxidation of methane (CPOX), steam reforming of methane, the gasification of carbonaceous materials, and methane dehydroaromatization (MDA). Hydrogen permeation is measured through BaCe0.8Y0.2O3-δ–Ce0.8Y0.2O2-δ (BCY-YDC) membranes fabricated by solid-state reactive sintering with 1 wt.-% NiO and standard ceramic-processing methods. Hydrogen gas is incorporated into the membrane as protonic defects; proton transport must be compensated by electron transport in order for protons to re-associate into hydrogen gas on the opposite side of the membrane. BCY serves as the proton conductor, and YDC serves as the electronic conductor.

For hydrogen-permeation testing, the composite-ceramic membranes are hermetically sealed inside of a ceramic manifolding assembly utilizing a spring-compression system with vermiculite seals. Hydrogen and helium (for leak detection) are fed to the permeant (feed) side of the membrane using high-precision mass flow controllers, while argon is fed to the permeate (sweep) side of the membrane. All gases are humidified using a room-temperature bubbler, which results in ~3 mol.-% steam. The permeate gas composition is continuously measured using a gas chromatograph calibrated for low levels of hydrogen, helium, nitrogen, and oxygen (balance argon).  The hydrogen-permeation rate is quantified through the hydrogen mole fraction measured in the permeate exhaust. 

Hydrogen permeation rates are measured as a function of temperature and the hydrogen partial-pressure gradient. The permeation rate is found to increase exponentially with increasing temperature, and linearly with an increasing hydrogen partial-pressure gradient. The hydrogen permeation rate through a BCY-YDC membrane over several days is shown in Figure 1. No degradation in performance is observed at 900 °C and a 0.1 atm hydrogen partial-pressure gradient. However, when the gradient is increased to 0.5 atm, the permeation rate is found to decrease over time. Following testing, grain-boundary fractures and metallic nano-particles are observed in scanning electron micrographs of the membrane. This, in addition to performance degradation, may indicate that the materials are not stable in highly reducing environments. However, X-ray diffraction patterns of the membrane after testing do not reveal the formation of tertiary phases.  

Figure 1: Hydrogen permeation through a BCY-YDC membrane at 900 °C with a 0.1 and a 0.5 atm hydrogen partial-pressure gradient.

Figure 1
(Invited) Defect-Rich CO2 Reduction Catalysts
Authors: Feng Xiaofeng , Kanan Matthew
Published: February 2020

The discovery of new structural motifs that promote high electro-reduction activity is essential for the development of electrochemical fuel synthesis. Polycrystalline Au is the most active bulk material for electrochemical CO2 reduction to CO and serves as a useful model system to evaluate new structures [1]. We recently developed a catalyst called oxide-derived Au that has even higher selectivity than bulk Au for CO2 reduction to CO at very low overpotentials [2]. Oxide-derived Au is a nanocrystalline material with a dense grain boundary network. Quantifying the effect of the grain boundaries in oxide-derived Au is challenging because extracting TEM samples from the oxide-derived Au films is inefficient. Here we describe the synthesis of grain-boundary rich Au catalysts by vapor deposition. The catalysts can be directly studied by TEM with minimal sample preparation. We compared the CO2 reduction activity of as-deposited catalysts to catalysts that were annealed at various temperatures. The annealing process has very little impact on the electrochemical surface area or the distribution of Au surface facets, as determined by Cu and Pb underpotential deposition studies. Annealing does, however, reduce the grain boundary density, which is quantified by counting boundaries in a large number of individual particles using TEM. In the low overpotential regime (–0.3 V to –0.4 V vs RHE), there is a linear correlation between grain boundary density and specific current density (surface area normalized) for CO2 reduction to CO. This quantitative correlation between defect density and catalytic activity suggests that grain boundary engineering is a fruitful avenue to explore for the development of practical CO2 reduction catalysts.

References:

(1) Hori, Y. In Modern Aspects of Electrochemistry; Vayenas, C. G., White, R. E., Gamboa-Aldeco, M. E., Eds.; Springer: New York, 2008; Vol. 42, p 89.

(2) Chen, Y.; Li, C. W.; Kanan, M. W. J. Am. Chem. Soc.
2012, 134, 19969−19972.
The Performance of Doped Mesoporous Carbon Electrodes as Electrochemical Capacitors in Optimized Alkaline Electrolyte
Authors: Chen Wenzhao , Li Jiadong , Xu Nengneng , Wang Qiang , Liu Yuyu , Qiao Jinli
Published: February 2020

Electric double layer capacitors (EDLCs) have attracted widespread attention in recent years owing to their ability to supply high power in short-term pulse and long cycling durability, which make them very good energy storage devices for applications such as hybrid power sources for electrical vehicles, portable electronic devices, uninterruptible power supply (UPS), and pulse laser techniques1-3. The electrical properties of a supercapacitor are mainly determined by the electrode material. Various materials are used in EDLCs such as carbon-based material, transition metal-oxides, and conductive polymers, in which mesoporous carbon are the most competitive electrode material for its high specific surface and low cost. In this paper, using simple template method with poly(ethyleneimine) (PEI) as sources of C, ferrous sulfate as precursor of sulfur and metal and, the nanoscale silica as sacrificial supports to create pores, N- and S- dual-doped mesoporous carbon materials are synthesized and successfully applied to EDLC with high specific capacity and cyclic stability
Cross-linked Anion Exchange Membranes Composed of Imidazolium Salt for Alkaline Fuel Cell
Authors: Song Feifei , Chen Shuli , Gao Ying , Liu Yuyu , Qiao Jinli
Published: February 2020

The alkaline membrane fuel cells (AMFCs), which use the anion-exchange membranes(AEMs) as electrolytes have attracted considerable attention owing to their higher reaction kinetics, lower fuel crossover, reduced CO poisoning, and use of non-precious metal catalysts. 1 In the development of AMFCs, the AEMs are obviously the key issues to make a breakthrough in AMFC performances. However, the conductivity and stability of AAEMs are still far less than commercial membrane Nafion which has commonly been used to proton-exchange membrane fuel cells (PEMFCs).2

More recently, imidazolium-based AEMs are of interest due to the five-membered heterocyclic ring and π conjugated structure of the imidazolium cation, which is expected to have good stability in alkaline condition.3-4 We here report novel series of alkaline anion-exchange membranes: Chitosan / poly (3-methyl-1-vinylimidazolium chloride)-Co-(1-vinylpyrrolidone) membranes (Cs/PMViC-Co-VP)and PVA/ poly (3-methyl-1-vinylimidazolium chloride)-Co-(1-vinylpyrrolidone) (PVA/PMViC-Co-VP)membranes.

The membranes were prepared by a solution-casting method, where 1g chitosan (degree of deacetylation = 80.0-95.0,supplied by Sinopharm Chemical Reagent Co. Ltd. China) was dissolved in 50 mL of 2% aqueous solution of acetic acid. Meanwhile, PVA (99% hydrolyzed, average molecular weight Mw = 86,000-89,000; Aldrich) was fully dissolved in water to make a 10% solution at 70oC. Then PMViC-Co-VP (supplied by Aldrich) was mixed with the above chitosan solution and PVA solution, respectively. At last, 0.5 mg GA was added in two types of composite solutions for cross-linking reaction. Membranes were obtained with a thickness about 50-120 µm. The The hydroxyl ion conductivity of the obtained membrane is studied using AC impedance technique.
Analytical Modeling and Experimental Study of Thermal Conductivity of Catalyst Layer of Polymer Electrolyte Membrane (PEM) Fuel Cells
Authors: Ahadi Mohammad , Andisheh-Tadbir Mehdi , Tam Mickey , Stumper Jürgen , Bahrami Majid
Published: February 2020

In a PEM fuel cell, waste heat generation occurs due to: 1) reversible heat of the electrochemical reaction in catalyst layer, 2) irreversible heat due to losses caused by over-potential in catalyst layer, 3) latent heat due to phase change in cathode catalyst layer, and 4) joule heating in all of the fuel cell components including catalyst layer. The mentioned heat sources induce local temperature variations inside fuel cells, which, in turn, highly affect their drying, flooding, and degradation. Accordingly, detailed knowledge about the in situ temperature distribution in PEM fuel cells is essential for efficiently managing water and heat in these systems as well as for minimizing their degradation. A temperature distribution can be obtained through comprehensive structural models for thermal conductivity of different components. The thermal conductivity of PEM fuel cell gas diffusion layers (GDL) is well understood, and some experimental data on thermal conductivity of other components have been provided in literature. However, the thermal conductivity of the catalyst layer, where most of the heat generation modes occur, is still unknown. Accordingly, this work is concerned with structural modeling of this property through a unit cell approach. A detailed geometrical model is developed based on the real microstructural properties of the catalyst layer, and unit cells of various scales are developed. Then, the thermal conductivities of various unit cells are modeled in a mechanistic manner and are interconnected to and integrated with each other to yield the effective thermal conductivity of the whole catalyst layer. In addition to modeling, catalyst layers with different compositions are produced via precise micro-fabrication techniques, their thermal conductivity is tested by transient plane source and guarded heat flux methods, and the experimental values are used to tune and validate the model.
Effect of Ionomer Content and Relative Humidity on IT-PEMFC Performances at 120 oc
Authors: Cho Min Kyung , Park Hee-Young , Cha In Young , Lee So Young , Yoo Sung Jong , Kim Hyoung-Juhn , Han Jonghee , Nam Suk Woo , Sung Yung-Eun , Jang Jong Hyun
Published: February 2020

Due to its higher operating temperature (100 -120oC), intermediate temperature PEMFC (IT-PEMFC) is expected to provide improved heat and water management, CO tolerance, and electrode reaction kinetics. The previous researches regarding IT–PEMFCs have been focused on the material developments: proton exchange membranes and electrocatalysts, to achieve high performance and durability at elevated temperatures.

Maintaining hydration of membrane electrode assemblies (MEAs) to provide sufficient conductivity is one of the key issues in IT-PEMFC operation. When pressurized air feed is supplied with low humidity and high temperature, the sulfonated polymer membranes can be easily dried and, as a result, cell performances can be decreased severely. Therefore, the optimization of catalyst layer would be also very important, in order to achieve acceptable performances under unique operation conditions of IT-PEMFCs. However, there have been only reports regarding catalyst optimization of IT-PEMFC (1) (2). For conventional PEMFCs (~ 80oC), various groups have reported the effect of ionomer content (3), catalyst loading (4) and electrode thickness (5); but these results cannot be directly utilized to IT-PEMFCs that have much more severe drying problem.

In this study, the effect of ionomer content and relative humidity (RH) of inlet gas on single cell performance are examined under various RHs(10 ~ 35%). For this, MEAs were fabricated with ionomer content from 20 to 40 wt%. The cell performances were characterized through constant current operation and i-V polarization. In addition, impedance analysis was carried out in order to monitor the variation of ohmic resistances under various operating conditions. 

References

1.              Y. Song, H. Xu, Y. Wei, H. R. Kunz, L. J. Bonville and J. M. Fenton, Journal of Power Sources, 154, 138 (2006).

2.              H. Xu, H. R. Kunz, L. J. Bonville and J. M. Fenton, Journal of The Electrochemical Society, 154, B271 (2007).

3.              K.-H. Kim, K.-Y. Lee, H.-J. Kim, E. Cho, S.-Y. Lee, T.-H. Lim, S. P. Yoon, I. C. Hwang and J. H. Jang, International Journal of Hydrogen Energy, 35, 2119 (2010).

4.              S. H. Ahn, S. Jeon, H.-Y. Park, S.-K. Kim, H.-J. Kim, E. Cho, D. Henkensmeier, S. J. Yoo, S. W. Nam, T.-H. Lim and J. H. Jang, International Journal of Hydrogen Energy.

5.              J. W. Lim, Y. H. Cho, M. Ahn, D. Y. Chung, Y. H. Cho, N. Jung, Y. S. Kang, O. H. Kim, M. J. Lee, M. Kim and Y. E. Sung, Journal of the Electrochemical Society, 159, B378 (2012).
Surface Confinement of Oxygen in Carbon Supported Oxygen Reduction Catalysts
Authors: Chlistunoff Jerzy , Sansiñena José-María
Published: February 2020

In 2011, we reported an oxygen adsorption phenomenon for heat treated, Fe/polyaniline based oxygen reduction catalysts.1 We found that the extent of oxygen adsorption correlated with the surface density of the active sites (Fe-N4 (2+2)) and determined the thermodynamic as well as kinetic parameters associated with the adsorption process.1

         In our recent studies on oxygen reduction catalysis by macrocyclic complexes of transition metals such as porphyrins, phthalocyanines and corroles, we found the occurrence of similar phenomena. The surface confined oxygen can be easily detected by voltammetry, as its reduction produces a high reduction peak bearing typical “surface properties”, such as, e.g., the reduction current proportionality to the scan rate or the (approximate) axial symmetry (Fig. 1).

         In this work, we compare the surface confinement of oxygen in presence of numerous carbon supported catalysts and their mixtures and conclude that an essential condition for the surface confinement of oxygen is, among others, a graphitic (π-electronic) structure of the catalyst support. This conclusion explains the proportionality between the magnitude of the phenomenon and the density of the active sites in heat treated ORR catalysts,1 where the active sites are believed to be embedded in graphene planes.2,3

Acknowledgement

The financial support from the University of California (grant 12-LR-237440) is gratefully acknowledged.

References

1)       J. Chlistunoff, J. Phys. Chem. C, 115, 6496-6507 (2011).

2)       M. Lefèvre, J.-P. Dodelet, P. Bertrand, J. Phys. Chem. B, 106, 8705-8713 (2002).

3)       M. Lefèvre, E. Proietti, F. Jaouen, J.-P. Dodelet, Science, 324, 71-74 (2009).

Fig. 1. Cyclic voltammetry (100 mV s-1) of oxygen reduction catalyzed by carbon (XC72) supported cobalt phtalocyanine showing the predominantly surface character of the oxygen reduction peak. Catalyst ink composition: 46.5 mg XC72; 0.8 mg CoPC; 8 cm3 isopropanol; 55.9 μl 5% Nafion. Catalyst loading 0.1 mg (for XC72).

Figure 1
Selective Oxidation of Glycerol Using Au, Pd Mono and Bimetallic Nanoparticles Supported on Carbon Nanotube As Anode Catalysts in Anion Exchange Membrane Fuel Cells
Authors: Qi Ji , Chadderdon David J , Benipal Neeva , Qiu Yang , Han Xiaotong , Jiang Yibo , Li Wenzhen
Published: February 2020

PdAu bimetallic nanoparticles supported on carbon nanotube (CNT) is found to catalyze glycerol oxidation reaction more efficiently, providing higher yield to tartronate than mono-metallic gold supported on CNT. The reaction mechanism indicates that the re-adsorption and further oxidation of reaction intermediates in bulk eletrolytes on the Pd catalyst is the dominant factor leading to such differences. By lowering down the anode potential window (<0.7 V vs. RHE).of the anion exchange fuel cell, the C-C bond cleavage resulting from over-oxidation, which occurs more severely on Pd than Au, is successfully alleviated. The power density of the fuel cell is also increased by alloying PdAu due to enhanced reaction rate. During the 8 h reaction process, stable 50 mW cm-2 to 5 mW cm-2 can be generated with 67% yield of tartronate finally achieved using PdAu alloyed nanoparticles supported on CNT as anode catalyst.
Development and Characterization of Membrane and Catalyst Materials for the Cucl(aq)/HC(aq) Electrolytic Cell
Authors: Hall Derek M. , Lotfi Roghayyeh , Kim Soohyun , Lvov Serguei N.
Published: February 2020

Recent developments in membrane and electrocatalyst characterization techniques for materials used in the CuCl(aq)/HCl(aq) electrolytic cell have significantly increased the amount of experimental data available in literature. Rotating disc electrode (RDE) and membrane conductivity cells capable of operating in highly concentrated HCl(aq) were developed to characterize the material performance of key MEA materials for this electrolytic cell. Specifically, exchange current density and transfer coefficient values for platinum and carbon as the electrocatalyst material for the anode reaction of this electrolytic cell were quantified in highly concentrated HCl(aq)1. Additionally, conductivity and permeability parameters of hot-pressed Nafion 117 were characterized for applications in highly concentrated HCl(aq) and CuCl(aq) solutions2. Though these fundamental properties are now available, there remained a need for a simple model to connect these properties appropriately to overall cell performance. While equilibrium thermodynamics of this electrolytic cell was carefully studied3, the cell electrode kinetics and transport in the membrane have not been modeled yet. Principles of non-equilibrium thermodynamics have the potential to incorporate membrane transport properties and electrochemical kinetic data together into a simple but useful model of this electrolytic cell. The use of linear phenomenological equations with phenomenological coefficients can be used to model the effects of permeability and conductivity on the ohmic resistance of the electrolytic cell. In addition to linear non-equilibrium processes, non-linear nonequilibrium thermodynamic expressions of the electrochemical reactions can be used to model the effects of electrocatalyst properties on the overall cell performance. As a result, suitable electrocatalysts and membrane materials were identified and their effects on the electrolytic cell performance were quantified in the form of a non-equilibrium thermodynamic model.

References:

1. D. M. Hall, E. G. LaRow, R. S. Schatz, J. R. Beck, and S. N. Lvov, J. Electrochem. Soc., 162, F108–F114 (2015).

2. R. Schatz, S. Kim, S. Khurana, M. Fedkin, and S. N. Lvov, ECS Trans., 50, 153–164 (2013).

3. D. M. Hall, N.N. Akinfiev, E. G. LaRow, R. S. Schatz, and S. N. Lvov,  Electrochim. Acta, 143, 70-82 (2014).
Energy Conversion Processes in Catalytic Electrolyte-Free Metal-Oxide Nanostructures
Authors: Hashemian Mohammad A , Karpov Eduard G
Published: February 2020

Over the past decade, a wide range of investigation has been carried out toward the development of high performance energy conversion devices. An interesting trend in the modern energy conversion research is an increased interest in electrolyte-free device concepts. In this presentation, we introduce a new type of device architecture based on an electrolyte-free catalytic metal-oxide nanostructure for conversion of chemical energy to electrical energy. In this device, a reaction-induced current is generated upon exposure of hydrogen and oxygen gases on a catalytic nanomesh metal (e.g. Pt, Rh) and a mesoporous oxide layer (TiO2). Interestingly, the reaction current kinetics revealed a new second mode of the reaction in addition to the usual catalytic oxidation of hydrogen to water. This mode induces a negative stationary reaction current at room temperature conditions. This production of negative current cannot be explained with any known mechanisms i.e thermal and hot electron. Instead, protons spillover from Pt to TiO2 substrate resulted in higher energy conversion efficiency compared to metal single-crystal systems. The number of charge carriers per one hydrogen molecule oxidized at Pt/TiO2 surface may reach 0.04 at room temperature, which is much higher than the values reported in pervious studies.
Electrochemical Performance of 100cm2 Class Direct Carbon-Molten Carbonate Fuel Cell (DC-MCFC)
Authors: Choi Sun Hee , Park Dong-nyeok , Ham Hyung Chul , Yoon Sung-Pil , Han Jonghee , Nam Suk Woo
Published: February 2020

One of major difficulties in developing direct carbon fuel cells is the high anode polarization in the carbon oxidation, which ultimately leads to the large loss of overall performance in direct carbon fuel cells. The molten carbonates (having the high ionic conductivity and good stability under CO2 environments) have been suggested to deal with this issue because they can facilitate the carbon oxidation by extending the electrochemical reaction sites from three phase boundary of anode to the bulk carbon surface. The molten carbonate fuel cell (MCFC) is the ideal choice for applying such molten carbonates into direct carbon fuel cells. Note that the molten carbonates such as Li2CO3 and K2CO3 are used in the electrolyte material in MCFC. However, the underlying mechanism in operating and developing MCFC-based direct carbon fuel cells is still unclear.

In this work, we present the effect of various operating parameters such as temperature, molten carbonate/carbon ratio and different Ni thin layers inserted between matrix (electrolyte support) and carbon green sheet on the electrochemical performance of 100cm2 class direct carbon - molten carbonate fuel cell (DC-MCFC). In addition, we attempt to understand the oxidation behavior of carbon in wet carbon anode (the composite of carbon and molten carbonates) of DC-MCFC. We find that in DC-MCFC, CO is produced via two electron transfer reaction [C (s) + CO3
-2 → CO2 (g) + CO (g) + 2e-] and is further oxidized with CO3
-2[CO(g) + CO3
-2 → 2CO2 (g) + 2e-] at CCV condition, indicating that CO is responsible for determining the DC-MCFC performance.
(Invited) Imaging and Quantitative Chemical Mapping of PEM-FC Catalyst Layers By Scanning Transmission X-Ray Microscopy
Authors: Hitchcock Adam P
Published: February 2020

Low temperature, hydrogen-fueled, proton exchange membrane fuel cell (PEM-FC) based engines are being developed rapidly for near-term implementation in mass production, personal automobiles. Materials and process research aiming to further optimize these systems is focused on understanding and controlling various degradation processes (carbon corrosion, Pt migration, cold start), and reducing cost by reducing or eliminating Pt  in the electro-catalyst, especially for the oxygen reduction reaction (ORR), and optimizing the nanoscale distribution of the cathode components. Soft X-ray scanning transmission X-ray microscopy (STXM) [1] is a powerful tool to study PEM-FC catalyst layers (membrane electrode assemblies, MEA). STXM provides spectroscopic identification and quantitative mapping of chemical components with 30 nm spatial resolution in both 2D projection and 3D spectro-tomography. For a given radiation dose, it provides much more chemical information than analytical transmission electron microscopy (TEM) and thus it has significant advantages for mapping ionomer in MEA cathodes [2, 3], which has proven to be a very challenging component to detect by TEM due to the high sensitivity of ionomer to radiation damage. This tutorial will describe the instrumentation, methodology and data analysis involved in applying STXM to PEM-FC catalyst layers, and illustrate its capabilities with results from recent   studies [4, 5].

STXM performed on BL 10ID1 at the Canadian Light Source  and on BL 5.3.2.2 at the Advanced Light Source.  Research supported by AFCC, NSERC, Canada Research Chairs, and the Catalyst Research for Polymer Electrolyte Fuel Cells (CaRPE-FC) network.

[1]  A.P. Hitchcock, Soft X-ray Imaging and Spectromicroscopy in Handbook on Nanoscopy, eds.G. Van Tendeloo, D. Van Dyck and S. J. Pennycook 2012.  (Wiley)

[2] D. Susac, V. Berejnov, A.P. Hitchcock, and J. Stumper, ECS Transactions 41 (2011) 629.

[3] D. Susac, V. Berejnov, A.P. Hitchcock and J. Stumper, ECS Transactions 50 (2012) 405

[4] A.P. Hitchcock,  et al., J. Power Sources 266 (2014) 66

[5] V. Lee, et al.  J. Power Sources 263 (2014) 163

Figure 1
(Invited) Modeling of and Novel Approaches to Water Management in Polymer Electrolyte Fuel Cells
Authors: Wang Chao-Yang
Published: February 2020

This lecture will discuss profound importance of water and thermal management in polymer electrolyte fuel cells. The science of water management in fuel cells will be scrutinized in two aspects: macroscopic phenomena and microscopic interfacial phenomena [1-4]. We shall review current advances in fundamental understanding and development of modeling tools for various length scales, as schematically summarized in Figure 1. In addition, we will discuss novel approaches to water management that have emerged most recently.

References

[1] C.Y. Wang, Chem. Rev., 104 (2005) 4727.

[2] P.K. Sinha, P.P. Mukherjee and C.Y. Wang, J. Mat. Chem., 17 (2007) 3089-3103.

[3] T. A. Trabold, J. P. Owejan, J. J. Gagliardo, D. L. Jacobson, D. S. Hussey, and M. Arif, Use of neutron imaging for proton exchange membrane fuel cell (PEMFC) performance analysis and design, in Handbook of Fuel Cells, Eds. W. Vielstich, A. Lamm and H. Gasteiger, Wiley and Sons Ltd., Vol.6, 2009.

[4] U. Pasaogullari and C.Y. Wang, Modeling and Diagnostics of Polymer Electrolyte Fuel Cells, in Modern Aspects of Electrochemistry, Springer, 2009.

Figure 1
(Invited) Combinatorial Study of Fundamental Electrocatalyst Performance - the Scanning Flow Cell Coupled to Online Analytics
Authors: Cherevko Serhiy , Schuppert Anna K. , Grote Jan-Philip , Geiger Simon , Zeradjanin Aleksandar R. , Keeley Gareth , Mayrhofer Karl J.J.
Published: February 2020

Continuous electrochemical flow reactors for efficient conversion of electrical energy into chemicals and vice versa, i.e. fuel cells and electrolyzers, become increasingly important for our energy sustainability and environmental concerns. One bottleneck for the commercialization are the electrocatalyst materials, which constitute the core of electrochemical energy conversion devices. While the optimization of kinetic activity of catalysts and efficiency of whole cells has been widely explored, the highly important stability of the materials and selectivity for reactions has often been neglected. In this presentation I will demonstrate how fundamental investigations of electrocatalyst activity, stability and selectivity can be performed online and in parallel, and what can be learned from these studies for large scale applications. The focus will be on the recent methodological developments from our group, in particular the scanning flow cell (SFC) coupled to online analytics, which also allows for combinatorial analysis. The potential of this approach will be demonstrated by results on the essential oxygen electrochemistry on noble metal catalysts as used in low-temperature fuel cells and electrolysers. 

1. Katsounaros, I.; Cherevko, S.; Zeradjanin, A.R.; Mayrhofer, K.J.J.; Oxygen Electrochemistry as a Cornerstone for Sustainable Energy Conversion; Angewandte Chemie – International Edition 2014, 53, 102 – 121.

2. Topalov, A.A.; Cherevko, S.; Zeradjanin, A.R.; Meier, J.C.; Katsounaros, I.; Mayrhofer, K.J.J.; Towards a comprehensive understanding of platinum dissolution in acidic media; Chemical Science, 2014, 5, 631-638.

3. Cherevko, S.; Topalov, A.A.; Zeradjanin, A.R.; Katsounaros, I.; Mayrhofer, K.J.J.; Gold dissolution: towards understanding of noble metal corrosion; RSC Advances 2013, 3, 16516-16527.
Anodic Olefin Coupling Reactions: Controlling the Reaction Pathways of Radical Cation Intermediates and Efforts Toward Artemisolide
Authors: Perkins Robert J , Moeller Kevin D
Published: February 2020

Intramolecular anodic olefin coupling reactions provide a useful method to quickly construct complex ring systems.  These reactions have been shown to be compatible with a range of nucleophiles to form a variety of cyclic compounds while conserving or increasing the functionality of the original substrate.

     Though a powerful synthetic tool, anodic olefin coupling reactions do not always proceed well.  Radical cations are very reactive intermediates and are thus susceptible to side reactions such as eliminations and polymerization.  When the desired intramolecular cyclization is relatively slow, these side reactions outcompete cyclized product formation entirely.  Two examples are provided in Scheme 1.1,2  In the first example, simultaneous formation of a 6-membered ring and a quaternary carbon using an allyl silane as a trapping nucleophile led to only elimination products along with other general decomposition.  The same problem presents itself in the second example, where the coupling of a furan and enol ether to form a 7-membered ring is too slow to compete with the elimination.

      To circumvent this problem, new methodology is being developed that incorporates an additional nucleophile into the electrolysis substrate to allow intramolecular trapping of both ends of the radical cation.3  By tethering an extra alcohol nucleophile to the end of an enol ether to quickly trap the radical cation, cationic decomposition pathways can be avoided, allowing for the desired cyclization occur (Scheme 2).

     In the talk to be presented, the development of this methodology will be discussed along with ongoing efforts to apply this methodology towards the synthesis of the 5:7:5-fused core skeleton of the natural product Artemisolide. 

References: 

1. Tinao-Wooldridge, L.V.;  Moeller, K.D.;  Hudson, C.M. J. Org. Chem.
1994, 59, 238

2. Redden, A.;  Moeller, K.D. Org. Lett.
2011, 13, 1678.

3. Redden, A.; Perkins, R.J.; Moeller, K.D. Angew. Chem. Int. Ed.
2013, 52, 12865.

Figure 1
Modeling Two-Phase Transport on the PEM Water Electrolyzer
Authors: Han Bo , Steen Stuart M. , Mo Jingke , Zhang Feng-Yuan
Published: February 2020

Understanding multi-phase and multi-component transport in a porous electrode plays a crucial role in optimizing the actual electrode structures and maintaining the performance of a polymer electrolyte membrane (PEM) water electrolyzer, which has attracted more attention for renewable energy storage and hydrogen production due to its higher efficiency/density and a more compact design. Since the electrode microstructure and transport mechanisms of a PEM water electrolyzer is quite complex, until recently, it has been very difficult to provide a comprehensive understanding of these mechanisms. Although some experiments and few simple numerical models have been carried out for investigating the two-phase  transport phenomena in a PEM water electrolyzer, many fundamental issues still remain, particularly concerning the effects of gas-liquid two-phase  transport inside porous liquid/gas diffusion layer (LGDL) with various surface wetting properties, pore structures on the electrolyzer performance.

In this study, a comprehensive two-phase transport model has been developed as an efficient numerical scheme for direct modeling the effects of two-phase  transport on the electrolyzer performance, particularly for liquid water and oxygen transport in the anode porous gas diffusion layer. The liquid water saturations are found to decrease significantly along the LGDL thickness direction with larger contact angles. But for smaller contact angles, the saturation values along the LGDL thickness direction are almost identical. Further numerical results for the gas-liquid two-phase transport behaviors and electrolyzer performance with effects of LGDL pore morphology will also be presented. Results obtained from the present model will provide fundamental understandings of gas-liquid transport behaviors in a porous electrode and can be employed as the useful information to design and optimize the electrode microstructure and improve the performance of PEM water electrolyzers.
Model-Based Regional Comparison of Autonomy and Battery Utilization of Energy Storage Integration with Solar Power
Authors: Lawder Matthew T , Subramanian Venkat R.
Published: February 2020

For intermittent renewable energy sources to be utilized beyond small penetration levels in the electric grid they must be coupled with some form of energy storage (see Figure 1). Solar power varies on two time scales. Solar trends vary seasonally, but instantaneous solar power can also vary on a minute-to minute basis because of cloud cover. This variability creates a need for a flexible form of energy storage.

We used a model-based approach to study the autonomy (the percentage of time the system meets demand) and battery utilization (amount of capacity used)  of a battery system tied to solar generation during yearly operation.1 Along with the variation in solar insolation seen throughout the year, we include a demand schedule which allows for different system load demands to be studied. Including demand allows for the study of different types of grid systems ranging from regional utility scale to Microgrid scale. In the study we look at Microgrid systems which include energy storage and distributed energy generation2 and include both islanded and grid-tied demand structures. Grid charging options have been incorporated into the study and allow for an economic analysis of battery utilization strategies.

We used an electrochemical and transport based battery model battery model for the energy storage aspect of the system.3 For the solar portion of the model we will assess both ideal insolation curves as well as site based insolation data. For the real-site data, several solar monitoring sites within the US were studied. The real data from solar sites was obtained through an NREL database and will offer a contrasting look at how much the coupled system can be affected on a daily and seasonal basis.4

Comparisons for solar charging versus grid charging will be studied from an autonomy, utilization, and economic stand-point. System wide metrics will be used to assess the system’s operation.

Acknowledgements

The authors acknowledge financial support from the Solar Energy Research Institute in India and the United States (SERIIUS), as well as, Washington University in St. Louis’ McDonnell Academy Global Energy and Environmental Partnership (MAGEEP).

References

1.             C. Protogeropoulos, B. J. Brinkworth, and R. H. Marshall,  International Journal of Energy Research,
21, (1997)

2.             R. H. Lasseter,  Journal of Energy Engineering-Asce,
133, (2007)

3.             S. Santhanagopalan, Q. Z. Guo, P. Ramadass, and R. E. White,  Journal of Power Sources,
156, 620(2006)

4.             National Renewable Energy Laboratory. (2013). Solar Resource Data. Available: http://www.nrel.gov/rredc/solar_data.html

Figure 1