bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrochemical Devices Based on Solid Acid Electrolytes for Conversion of Methane Derivatives
Authors: Wilson David Leon , Papandrew Alex , Zawodzinski Thomas A.
Published: February 2020

A boom in natural gas production in the United States presents opportunities for economically effective use of methane-derived molecules.  In contrast with methane gas, derivatives may exhibit advantages in volumetric energy density, ease of transport and versatility.  Electrochemical conversion of these species to electricity and other fuels is desirable, but depending on the system in question, catalyst stability, activity, and impurity intolerance, or alternately, the cost and durability of the electrolyte may be impediments to adoption

The solid-state proton conductor cesium dihydrogen phosphate (CsH2PO4 or CDP) has shown potential in electrochemical devices operating on fuels such as reformed NG or methanol. CDP undergoes a solid-solid phase transition at 228 °C and an associated increase in proton conductivity of more than three orders of magnitude (8.5 x 10-5 S cm-1 at 223 °C to 2.5 x 10-2 S cm-1 at 250 °C).  These systems have been shown to tolerate reformate streams in H2-air cells containing CO, H2S, NH3, CH3OH, C3H8 and CH4 of 20%, 100ppm, 100 ppm, 5%, 3% and 5% respectively, retaining 90-95% of pure H2 performance1. Solid acid fuel cells operated using methanol and an integrated steam reformer have also shown similar results2.  Recently, we showed that this material can also be used in an electrochemical hydrogen separation system using similar reformate streams3. 

In the majority of these earlier studies, platinum was used as the catalyst for both the hydrogen reduction and oxidation reactions. We have also demonstrated that unsupported nickel is an effective hydrogen evolution catalyst in solid acid hydrogen pump devices4.  Here, we have synthesized a suite of carbon-supported non-platinum catalysts (Pt, Pd, Ru, Ni and Cu) for implementation in electrodes.  We evaluate these materials as hydrogen oxidation and evolution catalysts in CDP-based devices for electricity and fuel production from the methane derivatives methanol and dimethyl ether.

This work is supported by the National Science Foundation through TN-SCORE (EPS-1004083).

References

1 C. R. I. Chisholm et al., Electrochem. Soc. Interface, 18, 53–59 (2009).

2 T. Uda, D. a. Boysen, C. R. I. Chisholm, and S. M. Haile, Electrochem. Solid-State Lett., 9, A261 (2006).

3 A. B. Papandrew et al., J. Electrochem. Soc., 161, F679–F685 (2014).

4 A. B. Papandrew, T.A. Zawodzinski Jr., J. Power Sources 245 (2014) 171.

Figure 1
On the Hydration of P2-Layered Sodium-Ion Cathode Materials in Aqueous Battery Applications
Authors: Frankforter Kevin Jerome , Anderson Marc Arlen , Tejedor M. Isabel
Published: February 2020

The high-performance seen in today’s lithium-ion and sodium-ion batteries is enabled by the use of organic alkyl-carbonate electrolytes mixtures which demonstrate high electrochemical stability. However, the use of these organic solvents has led to significant challenges related to their safety/flammability, in addition to stringent processing requirements during manufacturing to avoid contamination of the electrolyte with water. This has led to interest in utilizing lithium-ion and sodium-ion intercalation electrode material with aqueous-based electrolytes.

Recent work on the development of high-performance sodium-ion cathode materials has identified layered transition-metal oxides synthesized with a P2 stacking sequence demonstrate both high capacity and high capacity retention, which makes this class of intercalation compounds promising for use in battery applications.

Our work focuses on the consequences of utilizing P2-layered oxides in aqueous electrolytes; in particular, the vulnerability of these layered materials to hydration, in which water is incorporated into the layered structure. This phenomenon is not dissimilar to the weathering of many naturally occurring layered minerals such as Mica and Vermiculite. P2 compounds of multiple compositions will be studied using a variety of techniques including cycling results, x-ray diffraction, and thermo-gravimetric analysis in order to identify the onset of material hydration as well as the ramification of this phenomenon for aqueous battery applications.
Factors Controlling the Reduction Rate of Dye Cation in Dye-Sensitized Solar Cells
Authors: Mori Shogo , Ogawa Junichi , Koumura Nagatoshi , Kimura Mutsumi
Published: February 2020

In dye-sensitized solar cells, dye-cations are formed by the injection of photo-excited electron from dyes to metal oxide semiconductor. To obtain the electrons for external circuit, the dye cations must be reduced by oxidized species of redox couple in electrolyte solutions. However, the dye cations can be also reduced by the injected electrons in the semiconductor. To reduce the dye cations by the species but not by the injected electrons, typically dyes are designed to have more than 0.4 eV energy difference between the dye’s HOMO level and electrolyte’s redox potential. However, to obtain high open circuit voltage, the difference needs to be decreased. In order to reduce the difference, we need dyes that can be reduced with small energy difference. To understand the factors controlling the reduction kinetics, we measured the reduction rate for several dyes whose structures are systematically varied. For the dye having alkyl chains, we found that the alkyl chains slow the reduction kinetics for both the injected electrons in semiconductor and oxidized species in electrolyte. We also found the structure of donor parts affected on the reduction rate. We will discuss how these findings can be applied to design the dyes for highly efficient dye-sensitized solar cells.
(Invited) Metallated and Metal-Free Molecular Materials for Light/Electrical Energy Conversion
Authors: Wong Wai-Yeung
Published: February 2020

Metallated and metal-free molecules have become a field of intense activities in the optoelectronic research. They hold great promise as versatile functional materials for use in energy interconversions. These include systems where light is transformed into electricity and vice versa. This lecture highlights the recent progress in the advances of numerous functional metal-organic and organic molecules with tunable photofunctional and electronic traits. Focus is placed on examining their potential as efficient emitters in light-emitting applications and semiconductors in photovoltaic cells (both organic and dye-sensitized solar cells) for solar power generation. The strategies based on structural modifications of the organic groups to tune the emission and photovoltaic properties of these materials will be presented and discussed.
(Invited) Solid-State Z-Scheme Photocatalysts for Overall Water-Splitting Under Visible Light
Authors: Irie Hiroshi
Published: February 2020

We fabricated an Ag-inserted hetero-junction photocatalyst for water-splitting under visible light, similar to a Z-scheme system but is not required for a redox mediator. In this system, Ag acts as a solid electron mediator for water-splitting. We selected ZnRh2O4 (Eg=1.2 eV) and AgSbO3 (Eg=2.5 eV) as H2- and O2-photocatalysts, respectively. Ag could be inserted between these photocatalysts using a thermal-decomposition reaction of Ag2O and following melt reaction of Ag. In short, commercially available powder of Ag2O and prepared powders of ZnRh2O4 and AgSbO3 were thoroughly mixed and heat-treated at 900oC, which is slightly lower than the melting temperature of Ag. Then, the obtained powder was washed with HNO3 aqueous solution to remove excess Ag, forming the solid-state photocatalyst, ZnRh2O4/Ag/Ag1-xSbO3-y. The Ag1-xSbO3-y and ZnRh2O4 particles were connected to each other with their particle sizes of ~1000 and ~200 nm. In this system, Ag acted as the solid-state electron mediator for the transfer of electrons from the conduction band of Ag1-xSbO3-y to the valence band of ZnRh2O4. Utilizing the constructed photocatalyst, the simultaneous liberation of H2 and O2 from pure water at a molar ratio of ~ 2:1 was achieved under irradiation with visible light at ~ 545 nm. Utilizing the same strategy by changing the O2-evolution photocatalyst, we recently succeeded in pure water-splitting under visible light up to 600 nm. Detailed investigations will be discussed at the conference.
(Invited) Energy and Electron Transfer in Plasmonic Metal-Semiconductor Composite Photocatalysts
Authors: Wu Nianqiang (Nick)
Published: February 2020

This talk deals with the plasmonic metal-semiconductor composites for photocatalytic hydrogen evolution. The plasmon-induced photocatalysis enhancement of metal-semiconductor composites can be realized via different processes: light absorption and light scattering, plasmonic hot electron transfer and resonance energy transfer. These processes are enabled by effective coupling between the plasmonic metal and the semiconductor, which is determined by the materials or/and structure of metal-semiconductor composites.
Examing Proton Coupled Electron Transfer, Oxygen Reduction, and Anion Diffusion Using a Hybrid Bilayer Membrane
Authors: Gewirth Andrew A. , Tse Edmund C. M. , Barile Christopher J.
Published: February 2020

In this talk, we report on our work synthesizing and characterizing Cu-based catalysts for the oxygen reduction reaction.  In particular we prepared the first synthetic Cu O2 reduction catalyst that forms a self-assembled monolayer (SAM) on Au surfaces. We embeded this Cu catalyst inside a hybrid bilayer membrane (HBM) by depositing a monolayer of lipid on the SAM. By incorporating an alkyl phosphate in the lipid layer, we develop the first HBM containing a reversible switch that gates proton transport to a molecular oxygen reduction reaction (ORR) catalyst. We envision that this strategy can give unique mechanistic insight not only to the ORR, but to all proton-coupled electron transfer (PCET) reactions.

We also use the hybrid bilayer membrane as an electrochemical platform to study anion diffusion through a lipid monolayer. We first append lipid on a self-assembled monolayer that contains a covalently-bound Cu(I)/(II) redox center. We then perform cyclic voltammetry using different anions in the bulk solution and extract thermodynamic and kinetic information about anion transport. We analyze the results using linear combinations of fundamental chemical trends, and determine that anion transport quantitatively correlates to polarity and basicity, a relationship we formalize as the lipid permeability parameter. In addition, we discuss how our findings can be interpreted according to the two leading mechanisms describing ion permeability through lipids. Our results demonstrate that anion transport in a HBM is best described by the solubility-diffusion mechanism, not the pore mechanism.
Indium Tin Oxide and Silicon Nanocrystal Nanocomposite Grown By Aerosol Assisted Chemical Vapour Deposition
Authors: O'Brien S , Linehan K , Doyle H , Kingsley A , Ashfield C , Frank B , Xie L , Leifer K , Thony P , Perraud S , Pemble M E , Povey I. M
Published: February 2020

Nanocomposite films were successfully grown by aerosol-assisted chemical vapour deposition (CVD) in a single deposition step using a mixture of Indium Tin neodecanoate and ligand stabilised silicon nanocrystals. Samples were analysed by HRTEM and silicon nanocrystals with a density of 1.2 × 1012 cm-2 were observed.  From the reconstructed 3D tomogram, the averaged distance between the nearest nanoparticles is 8.3 nm and the 3D density of nanoparticles is 1.6 × 1018 cm-3.  An animation of the 3D reconstruction is supplied in the supporting information. These data show the versatility of aerosol assisted CVD in achieving a nanocomposite with such a density of silicon nanocrystals, of carefully controlled size and shape, within a polycrystalline host matrix. Therefore, meeting the density and size distribution requirements of particle inclusion in active nanocomposites for photovoltaic structures
Liquid Crystals of Phthalocyanine-Fullerene Dyads Exhibiting Homeotropic Alignment and Spiranthes-like Supramolecular Structure Useful for Solar Cells
Authors: Watarai Ayumi , Ishikawa Aya , Ono Kenta , Yasutake Mikio , Ohta Kazuchika
Published: February 2020

If liquid crystals of phthalocyanine-fullerene (Pc-C60) dyads would exhibit homeotropic alignment at r.t., they would be very useful for the application to solar cells. Hence, we have synthesized nine novel Pc-C60 dyads, (CnS)6PcCu-Cm-C60 (n = 14, 16, 18; m = 8, 10, 12), to investigate whether they would exhibit perfect homeotropic alignment at r.t. by changing lengths of the peripheral alkylthio chains (Cn) and the spacer chain (Cm) between Pc and C60. As a result, each of them exhibited a hexagonal ordered columnar (Colho) mesophase and the Colho mesophase for n = 14 and m = 8, 10, 12, showed perfect homeotropic alignment in a wide temperature region from r.t. to clearing point. Moreover, the Colho mesophases exhibited spiranthes-like supramolecular structure, which is compatible with one-dimensional nano-array expecting the high conversion efficiency of solar cells.
Aromatically π-Extended Porphyrins with Large Two-Photon Absorption Cross-Sections and Bright Phosphorescence
Authors: Vinogradov Sergei , Esipova Tatiana
Published: February 2020

The ability to form triplet excited states upon two-photon excitation is important for several applications of metalloporphyrins. Here we present two-photon absorption (2PA) properties of several platinum (II) porphyrins, focusing on the effect of aromatic π-extension and peripheral substitution on 2PA cross-sections. p-Extension of the tetrapyrrolic macrocycle by way of syn-fusion with two external aromatic fragments, such as in syn-dibenzo- (DBP) and syn-dinaphthoporphyrins (DNP), removes the center-of-inversion symmetry in the porphyrins macrocycle. As a result, DBPs and DNPs exhibit stronger 2PA into their one-photon-allowed states (e.g. Soret state) than fully-symmetrical non-extended Pt(II) porphyrins (D4h symmetry). However, much stronger absorbing 2PA-allowed states still lie above the Soret state and cannot be accessed directly due to the interfering linear absorption. 2PA near the Soret state increases dramatically (up to 50 fold) upon introduction of alkoxycarbonyl groups (CO2R) into the benzo rings in DBP. TDDFT/sum-over-states calculations reveal that in these porphyrins low-lying molecular orbitals spanning over CO2R groups via configuration form new 2PA-allowed states located just above the Soret state. Furthermore, computations predicted major stabilization of gerade-states in fully-symmetrical D4h Pt alkoxycarbonyltetrabenzoporphyrins. Measurements confirmed that e.g. in PtTBP(CO2Bu)8 2PA cross-section near 810 nm is ~900 GM. Combined with ultrafast intersystem crossing and exceptionally bright phosphorescence 2PA makes alkoxycarbonyl-substituted p-extended porphyrins very promising candidates for several 2P applications.
Maug Catalysis: A Tale of Ferryl Iron, Radicals and Long Distance Hopping
Authors: Wilmot Carrie M , Yukl Erik T , Davidson Victor L
Published: February 2020

Methylamine dehydrogenase (MADH) enables some methylotrophic/autotrophic bacteria to grow on methylamine as a sole source of carbon and energy. MADH catalysis depends on the cofactor tryptophan tryptophylquinone (TTQ) that is a posttranslational modification of two Trp residues in the MADH β-subunit. The maturation of MADH depends on four gene products located in the methylamine utilization (mau) gene cluster. One of these, mauG, encodes a c-type di-heme enzyme that completes synthesis of the TTQ cofactor. The potent oxidant is an unusual bis-Fe(IV) MauG species composed of a ferryl heme (Fe(IV)=O) with an oxidizing equivalent stored as Fe(IV) at the second heme, which has an unusual His, Tyr axial ligation. The bis-Fe(IV) oxidant is formally Fe(V) and equivalent to Compound I. Completion of TTQ to generate active MADH involves long-range electron transfer and a radical hopping mechanism to effect catalysis over a 40 Å distance. The MauG catalyzed reaction occurs in three discrete 2-electron events in a H2O2 or O2-dependent process. A crystal structure of MauG in complex with its protein substrate, a precursor form of MADH known as preMADH, has been solved. The crystals are catalytically active. The order of the 2-electron chemistry catalyzed by MauG was determined through a series of structures from crystals harvested after different amounts of time following crystallization. H2O2 to initiate the reaction was generated by the slow breakdown of polyethylene glycol used in crystallization. These in crystallo data are corroborated by mass spectrometry in solution experiments.
Structural Basis for Heme Transport By Hmut in Corynebacterium Glutamicum
Authors: Aono Shigetoshi
Published: February 2020

Heme can be used as an iron source by some pathogenic bacteria, which have the heme acquisition system(s) to uptake heme. The typical heme acquisition system comprises several heme-binding proteins and an ABC transporter. The ABC heme transporter, HmuT-HmuUV is conserved in Gram-positive and Gram-negative bacteria. In this heme transporter system, HmuT, HmuU, and HmuV act as a substrate (heme)-binding protein, a heme permease, and an ATP-binding protein, respectively.

 In this study, the crystal structure of the heme-binding protein HmuT (CgHmuT) from Gram-positive bacterium Corynebacterium glutamicum will be reported at 1.4 Å resolution. The overall structure of CgHmuT reveals a bi-lobed topology formed by an N- and C-terminal domain. A heme molecule coordinated by His141 and Tyr242 is bound in a cleft between the N- and C-terminal domains. Though the global fold of CgHmuT is similar to that of HmuT from Yersinia pestis (YpHmuT), the coordination structure of the heme is different from each other. While two heme molecules are bound to YpHmuT, CgHmuT binds a single heme molecule with His141 and Tyr242 as the axial ligands. 

 Intriguingly, CgHmuT binds a heme with two different orientations. Though the previously reported heme-binding proteins have the interaction between proteins and heme propionate groups in addition to axial ligation to iron, such interactions with heme propionates are absent in CgHmuT. The presence of two different conformations in CgHmuT might be due to a lack of specific interactions between the heme and protein except for the axial ligations.

 EPR spectroscopy reveals the heme in CgHmuT is a mixture of high-spin and low-spin states, indicating one of the axial ligand of the heme is in equilibrium between the ligated and unligated states. EPR spectra of wild-type, H141A-, and Y242A-CgHmuT suggest His141 will be reversibly dissociated/associated from/to the heme. The equilibrium between the six- and five-coordinate states in CgHmuT would be responsible for the regulation of heme-binding affinity to control the heme transport reaction between CgHmuT and HmuUV.

 The crystal structures of H141A and Y242A variants have also been determined in this study. Iwill discuss the molecular mechanism of heme recognition and heme transport by CgHmuT based on these structures.
Formation of Hydrogen-Bonded Supramolecular Assemblies Based on Functionalized Saddle-Distorted Porphyrins
Authors: Kojima Takahiko , Kajii Hiroki , Sankar Muniappan , Ishizuka Tomoya , Kotani Hiroaki , Yamada Yusuke , Fukuzumi S.
Published: February 2020

Supramolecular assemblies consisting of porphyrins have been intensively investigated in the light of promising photo-functionality including photoinduced electron transfer, photo-conducting materials, dye-sensitized solar cells, and guest inclusion toward the emergence of novel functions on the basis of unique spatial host-guest arrangements and interactions.

   Along this line, we have developed a series of supramolecular assemblies using the diprotonated form of saddle-distorted dodecaphenylporphyrin (H2DPP) through intermolecular π-π interaction, such as Porphyrin Nanochannels, which include electron-donating guest molecules.1 In this presentation, we present formation and characterization of supramolecular assemblies based on H2DPP derivatives having hydrogen-bonding functional groups and their metal complexes.

   Introduction of carboxyl groups or hydroxyl groups to the meso-phenyl groups of H2DPP as hydrogen-bonding sites allows us to construct robust and well-organized supramolecular assemblies. A diprotonated tetracarboxyl-DPP derivative (1, Fig. 1a), for example, formed two-dimensional hydrogen-bonding networks (Fig. 1b) to form a porphyrin nanochannel structure, which were reminiscent of that formed by [H4DPP2+]Cl2 and was persistent up to 150°C, in contrast to that of [H4DPP2+]Cl2.2 To expand the size of the nanochannels, we also introduced 4-carboxylphenyl groups at the 4-positions of the meso-phenyl groups of H4DPP2+.

   A Zn(II) complex of H2DPP derivatives having hydroxyl groups at the 4-positions of the meso-phenyl groups (2) was prepared to form a dimer bridged by 4,4’-bypyridine.3 The dimer was revealed to form intermolecular hydrogen-bonding network among the hydroxyl groups in the crystal.

In addition to the crystal structures, we will also mention adsorption of gaseous molecules such as N2 and CO2 with porous supramolecular assemblies of functionalized H2DPP derivatives in the solid state.

References

(a) R. Harada et al., Chem. Commun.
2005, 716. (b) T. Kojima et al., Chem.–Eur. J.
2007, 13, 8714. (c) T. Nakanishi et al., Chem. Mater.
2008, 21, 7492. (d) S. Fukuzumi et al., Coord. Chem. Rev.
2012, 256, 2488.

T. Ishizuka et al.
Chem. Commun.
2012, 48, 6481.

T. Ishizuka et al.
Dalton Trans.
2013, 42, 16073.

Figure 1
Self-Organization of Tetraazaporphyrin Derivatives in 2 and 3 Dimensions
Authors: Eichhorn S. Holger
Published: February 2020

Many applications of dyes, such as phthalocyanines (Pcs) and tetraazaporphyrins (TAPs), require specific supramolecular structures for the achievement of advanced properties. Most approaches towards nanostructured materials of Pcs and TAPs are based on their self-organizing properties that lead to many interesting properties but also highlighted some limitations. The work presented here describes new amphiphilic TAPs that form stable Langmuir and LB monolayers with a face-on orientation of the macrocycle and self-organize into columnar liquid crystaline structures. Both types of self-organized structures were successfully crosss-linked via cycloadditions of azide and acetylene groups with and without Cu catalyst. Surprisingly, the supramolecular structures of the self-organized structures were only marginally affected by the cross-linking processes.
Synthesis and Electrochemical Properties of Phthalocyanines Bearing Fc(CH2)ns- and Dodecyl Substituents in Non-Peripheral Positions
Authors: Lewtak Jan P , Swarts Jannie C
Published: February 2020

Phthalocyanines and their metal complexes1 gain constant attention due to their chemical, thermal and photochemical stability as well as numerous applications including catalysis, as ink-jet printing components, photosensitizers for photodynamic therapy of cancer, memory devices and liquid crystals. The introduction of a ferrocenyl moiety to the core of phthalocyanine macrocycle imparts a new redox active centre in addition to four existing macrocyclic centres. Non-peripherally substituted long alkyl chains contribute to the solubility of the macrocycle, assist in studying catalytic properties and, depending on the type of substituent, convey the possibility of possessing liquid crystal properties.

Here we present the synthesis of above compounds and the results of their electrochemical investigation. Our particular interest lies in the dependence of ferrocenyl redox properties on the electron withdrawing properties of phthalonitrile. It was found to be a function of the linker atom (S) or lack of thereof as well as the chain length (expressed as n above). The redox properties were probed utilising glassy carbon working electrode as well as gold electrode to immobilize sulphide species. Dodecyl chains attached to the core of macrocycle proved increasing solubility of compounds in organic solvents2 and also led to liquid crystalline properties.

References

1.   E. Fourie, J. C. Swarts, I. Chambrier, M. J. Cook, Dalton Trans., 1145-1154 (2009).

2.   J. C. Swarts, E. H. G. Langner, N. Krokeide-Hove, M. J. Cook, J. Mater. Chem., 11, 434-443 (2001).

Figure 1
Photoelectrochemical Oxygen Reduction Reaction Using Phthalocyanines
Authors: Ishii Kazuyuki
Published: February 2020

The oxygen reduction reaction (ORR) has attracted broad interest not only with respect to biological processes, such as cellular respiration, but also in terms of practical energy conversion, i.e. cathodic reactions in fuel cells. Because the use of light energy is one of the promising alternatives to platinum that is utilized as an efficient catalyst for the ORR, we have investigated the photoelectrochemical ORR using various phthalocyanines (Pcs, Figure 1). The cathodic current corresponding to the ORR significantly increases upon visible light irradiation of the thin film consisting of Pc and the polyvinylidene difluoride (PVDF) polymer coated onto an ITO electrode (Figure 2). Although a previous study suggests that the high photocurrent may originate from the initial electron transfer between the photoexcited Pc and O2 (Pc* + O2 → Pc+ + O2
-) followed by the hole-transport between Pcs, herein we propose a new mechanism that can explain the efficient photoelectrochemical ORR in the Pc/PVDF thin film. The dependence on the reduction potential of Pcs indicates that the electrochemical reduction of the photoexcited Pc is an initial process. Subsequently, the electron transfer from Pc- to O2, i.e. Pc- + O2 → Pc + O2
-, occurs. Based on the comparison between the ZnPc and MgPc derivatives whose excited triplet quantum yields are different, the high photocurrent mainly originates from the electrochemical reduction of Pcs in the lowest excited singlet state, while the reaction via the lowest excited triplet state contributes to an increase in photocurrent only when the electrode potential is below +0.2 V. This study will be useful for developing catalysts for the photoelectrochemical ORR.

(1) D. Schlettwein, M. Kaneko, A. Yamada, D. Wöhrle, N. I. Jaeger, J. Phys. Chem.
1991, 95, 1748-1755.

(2) D. Schlettwein, N. I. Jaeger, J. Phys. Chem.
1993, 97, 3333-3337.

Figure 1
Synthesis and Field-Effect Transistor Performance > of Thiophene Containing Phthalocyanine Analogues
Authors: Heeney Martin
Published: February 2020

Phthalocyanine derivatives show much potential as the active layer in organic field effect transistors, as well as the light absorbing component in organic solar cells. In an attempt to further improve the charge transporting properties, we have been developing phthalocyanine analogues in which the benzenoid ring system is replaced with electron rich heterocycles containing a chalcogen atom. In this talk I will discuss the synthesis of a range of porphyrazine derivatives incorporating thiophene, thienothiophene or selenophene. I will discuss the influence of the peripheral heterocycle on the optical and morphological properties, as well as on the performance in organic field effect transistor and organic solar cells.
Refractory Metal Coatings on High Creep Strength Steel for Oxyfuel Coal Combustion
Authors: Suni Ian Ivar , Falola Daniel , Muralidas Pooja , Wiltowski Tomasz
Published: February 2020

Oxyfuel coal combustion, where coal is burned in oxygen instead of air, offers the potential for simplified CO2 sequestration, since the flue contains little N2 and is mainly CO2.  However, the widespread use of flue gas recycling to dilute the pure oxygen feed stream exacerbates corrosion problems in the furnace and boiler tubes by increasing the concentrations of SO2, SO3, HCl, and H2O.  In addition, the dew point temperature is raised, making condensation of H2O, H2SO4 and H2SO3more likely during downtime.

P91 steel, which contains ~8.4% Cr, 0.9% Mo and 2.2% V, is are widely utilized for high temperature applications in the power industry due to its increased creep strength.  However, Cr-containing steels are susceptible to failure in H2O-containing oxidizing environments due to formation and volatilization of compounds such as CrO2(OH)2.  We report the formation of Ti and Zr diffusion coatings atop high creep strength steels to improve their corrosion resistance.  Ti coatings 10-30 µm thick can be formed on P91 steel by pack cementation at 1000°C in flowing Ar.  Similarly, Zr coatings 10-30 µm thick can be formed by pack cementation at 1080°C. 

The composition as a function of position for both Ti and Zr diffusion coatings is studied as a function of position by scanning electron microscopy (SEM) with energy dispersive x-ray spectroscopy (EDX).  This demonstrates formation of an inter-diffusion zone, with no sharp interface exists between coating and substrate, which may help limit delamination.  Results will also presented for thermogravimetric analysis (TGA) of both Ti and Zr coatings on P91 steel in gas mixtures that contains 5% N2, 70% CO2, 2% CO, 0.3% SO2, 21.7% H2O, 1% O2, and trace levels of HCl.
The Electrochemical Corrosion Behavior of High Strength Carbon Steel in H2S-Containing Alkaline Brines
Authors: Feng Ruishu , Beck Justin , Wolfe Ian , Cianni Rosemary , Ziomek-Moroz Margaret , Lvov Serguei N.
Published: February 2020

In-situ electrochemical measurements were performed during the corrosion tests of high-strength low-alloy steel, grade S-135, used as a drill pipe in oil and natural gas exploration, in 5 % mass NaCl(aq) solutions of pH 7.5, 10.5, and 12.3 at 85 °C. For each pH, four concentrations of H2S were investigated which corresponded to one dose of H2S gas at H2S partial pressure, P
H2S, equal to 0, 0.12 psi (0.83 kPa), 1.2 psi (8.3 kPa), and 10 psi (69 kPa), respectively. It was found that the corrosion process generally reached a steady state by 60 hours in a stirred solution. For P
H2S = 0 and 0.12 psi (0.83 kPa), the polarization resistance (R
pol) increased as pH increased from 7.5 to 12.3; however, R
pol at pH 10.5 were the lowest for P
H2S 1.2 psi (8.3 kPa) and 10 psi (69 kPa). The lower and moderate H2S concentrations (P
H2S 0.12 psi and 1.2 psi) were generally found to give larger R
pol values than without or high H2S levels (P
H2S 0 psi and 10 psi) at each pH. The corrosion rates were inversely proportional to R
pol and ranged on the orders of 0.001 to 0.1 mm/year. The change of pH had a larger effect on the corrosion rate than the change of H2S concentration. It is believed that higher pH suppressed the hydrogen reduction reaction by decreasing available proton sources and, therefore, resulted in higher R
pol. Besides pH, the corrosion rate was also affected by the nature of the corrosion product film on the surface. The corrosion films were predicted with Pourbaix diagrams and investigated with scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). With the pH increase from 7.5 to 12.3, the major products in the corrosion film generally changed from iron sulfides to iron oxides, which agreed with the Pourbaix diagrams. The morphology of the corrosion products was also believed to have influenced the protectiveness of the films. The change in R
pol and corrosion rate was consistent with the change in the electrochemical impedance spectroscopy (EIS) behavior. Two time constants were generally observed in the Bode plots and the plots of pH 10.5 tended to have the time constants at higher frequencies than pH 7.5 and 12.3.
Rebar Corrosion Due to Chlorides in the Presence of Different Cations
Authors: Sharma Krishneel Kumar , Deo Ravin N , Mamun Kabir A , Kumar Ajal
Published: February 2020

Recent attention on effects of climate change in the Pacific island countries (PIC’s) have focused on a multitude of areas which are at risk in the Pacific region. These include food security, flora and fauna, land accessibility, groundwater contamination and so on. These aspects are essential for sustainable development of the small island states in the Pacific region. One issue, which appears synonymous with climate change in the Pacific is sea-level rise. The rising sea level can have detrimental effects on civil infrastructure since its intrusion further inland can lead to deterioration of nearby civil metallic infrastructure due to corrosion. Since metropolisation of major PIC’s are mainly near the sea or along coast line, this presents a significant problem within the overall paradigm of sustainable development. In this regards, a study was undertaken to investigate the influences of different chloride salts (i.e. NaCl, KCl, MgCl2) on the corrosion of steel re-inforcing bars (rebar’s) in concrete mortars. This study is important to understand structural health conditions, especially for foundations in ground, and to understand the corrosion intensities in the presence of different cations, which can be significantly controlled by groundwater migration. The galvanostatic pulse technique was used to evaluate the effect of varying chloride contents of different salts on rebar corrosion. Results from this study are presented in an attempt to provide a conceptual model for understanding the interaction of aforementioned salts with metallic infrastructure. A holistic discussion is presented which are important for sustainable development in the PIC’s.
Atomistic Insights into the Interaction of Copper Oxide Surfaces with Chloride Ions in Aqueous Media
Authors: Narayanan Badri , Deshmukh Sanket , Ramanathan Shriram , Sankaranarayanan Subramanian K. R. S.
Published: February 2020

Corrosion of metals in aqueous environment, such as seawater, represents a technologically relevant electrochemical phenomenon involving complex chemical interactions at the metal-oxide/aqueous media interface. These interactions result in coupled electrochemical processes, such as, metal dissolution and reduction of agents in the environment. A fundamental understanding of these processes at the atomic level is an area of immense interest with applications not only in engineering, but also in catalysis and surface chemistry. To gain atomistic insights into such processes, we employ a model system consisting of copper oxide thin film on a copper substrate; the oxide film interacts with the chloride ions in the aqueous medium. Using extensive molecular dynamics simulations based on a reactive force field (ReaxFF), we systematically investigated the impact of (a) the stoichiometry of oxide film, and (b) solvation dynamics on the dissolution kinetics of Cu and adsorption of Cl on the Cu-oxide surface. Our MD simulations indicate that corrosion initiates via adsorption of Cl- ions on the Cu-oxide surface; these Cl- ions, in turn, bind with nearby Cu atoms causing dissociation of existing Cu-O bonds, and form soluble Cu-Cl complexes. These complexes dissolve in the aqueous media resulting in dissolution of Cu atoms and thinning of the oxide film. We found that upon increasing the oxygen content in the oxide film, the Cl- ion adsorption and Cu dissolution is severely impaired. For instance, increasing oxygen stoichiometry from 0.2 to 0.79 causes Cl-adsorption to drop by half. In other words, O-rich Cu-oxide films provide better corrosion resistance than O-deficient ones. Furthermore, our hydrogen-bond correlations show that water present in the aqueous media forms ordered layers on oxide films with high oxygen content; as the O-content is reduced, this order gets disrupted.

Use of the Center for Nanoscale Materials was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

Figure Caption: Temporal evolution of the interface between the passive oxide layer (at different oxygen stoichiometry) and aqueous medium at selected times during our MD simulations of corrosion. For the sake of clarity, the adsorbed chloride ions are shown as big spheres (green), while the copper (tan), oxygen (red), and hydrogen (blue) atoms are shown are shown are small spheres.

Figure 1
Phthalocyanine Based Advanced Corrosion Resistant Coatings By LbL Technique
Authors: Yakut Yonca , Cebeci Fevzi Çakmak
Published: February 2020

Corrosion on metallic surfaces has been an ongoing and serious problem in the aeronautical industry. Advanced materials used for anticorrosive purposes contain heavy metals that damage the nature. Therefore, there is a need for improvement on environmental friendly coatings especially for the aeronautical industry.

In this study, anticorrosive thin film coatings are fabricated in order to prevent the metallic surfaces from the corrosive effect of singlet oxygen. Layer-by-layer (LbL) method is preferred as an alternative to literature. By the help of LbL it is possible to control the thickness and stability of the films. Oppositely charged materials (e.g polyelectrolytes) cover the surface of the substrate (glass, metal, Si-plate) by electrostatic attraction[1, 2]. Dip and spray LbL techniques are applied to obtain smooth and homogenous layers of polyelectrolytes and phthalocyanines[3]. The phthalocyanines have been embedded between the bilayers or tetralayers of thin multilayer films to get rid of corrosive effects of the highly reactive singlet oxygen by utilizing singlet oxygen reducing capability of these metal-centered compounds[4].

Electrochemical corrosion characterizations are performed to measure the corrosion resistance of the thin films. For this purpose, potentiodynamic polarization, Tafel, impedance and corrosion chamber tests are studied. Mechanical integrity of the films plays a great significance for demanding applications. Hardness/elastic modulus properties are analyzed to test the resistance of films. 

 

References:

1.    Decher, G., Hong, J. D., Schmitt, J., Buildup of Ultrathin Multilayer Films by a Self-Assembly Process .3. Consecutively Alternating Adsorption of Anionic and Cationic Polyelectrolytes on Charged Surfaces. Thin Solid Films, (1992). 210(1-2)(831-5).

2.    Decher, G., Fuzzy Nanoassemblies: Toward Layered Polymeric Multicomposites. Science, 1997. 277(5330): p. 1232-1237.

3.    El Harakeh, M., et al., Charge separation and photocurrent polarity-switching at CdS quantum dots assembly in polyelectrolyte interfaced with hole scavengers. Phys Chem Chem Phys, 2009. 11(28): p. 5962-73.

4.    Dumoulin, F., et al., Synthetic pathways to water-soluble phthalocyanines and close analogs. Coordination Chemistry Reviews, 2010. 254(23-24): p. 2792-2847.
Electrochemical Impedance Spectroscopy Investigations of Stainless Steels in Presence of Corrosion Inhibitors
Authors: Ribeiro Josimar , Moreira Roberta Rossi , Soares Thiago Freitas
Published: February 2020

The behavior of corrosion and corrosion inhibition of AISI 1010 carbon steel, AISI 316 stainless steel and UNS S31803 duplex steel was studied in sodium chloride solution (3.0 wt. %), in the absence and presence of benzimidazole and imidazole corrosion inhibitors. The chemical and morphological characterization of steels were performed using the techniques such as optical emission spectrometry,  optical microscopy, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). Electrochemical analysis were performed through the techniques of potentiodynamic polarization and electrochemical impedance spectroscopy. Metallographic, SEM and EDX analysis allowed to identify certain regions and elements present in the steel which provide corrosion occurring, such as inclusions.The electrochemical impedance results showed that the benzimidazole inhibition efficiencies were approximately 52%, 73% and 71%, respectively, for AISI 1010, AISI 316 and UNS S31803 steels. In the case of the imidazole was obtained efficiencies of about 96% for the AISI 1010 and AISI 316 steels and 85% for the UNS S31803 steel. Weight loss tests showed that for AISI 1010 steel, both benzimidazole and imidazole inhibit corrosion, and reduced the corrosion about 17% and 24%, respectively. In the analysis of the polarization curves in studies with seawater, it was observed that the inhibitors were lower efficient than in the middle chloride solution. The benzimidazole showed efficiencies of about 14%, 50% and 33% for AISI 1010, AISI 316 and UNS S31803 steels, respectively. In the case of Imidazole, it was observed that the inhibition efficiency of approximately 21%, 59% and 34% for the same steels, respectively. In all electrochemical analysis and weight loss test, imidazole proved to be the best inhibitor for the steels investigated.

Acknowledgments

FAPES, CAPES, FINEP, LMC and CNPq.
Assessing Concurrent Uniform Corrosion of Aluminum Alloys As a Function of Temperature, pH, Time, and Chloride Ion Concentration
Authors: Huang I-Wen
Published: February 2020

One of the greatest challenges for aircraft maintenance is localized corrosion induced fatigue and cracking, which is induced by aluminum alloys susceptibility to aggressive environment. Although pit growth kinetics was thoroughly investigated and nicely modeled by power law, the uniform corrosion impact on pit growth kinetics was ignored in the past, and therefore resulted in pit growth deviation from the ideal power law as indicated in a preliminary result. Uniform corrosion dissolved the surface material and thus induced reference plane recession and pit depth reduction. This non-trivial difference was proved to have a significant influence on pit growth modelling especially in high pH conditions.

In this work, temperature and pH influence on uniform corrosion of 2024-T3, 6061-T6, and 7075-T6 aluminum alloys were reported through the free immersion test method. Extensive results performed in various pH (3 to 10), chloride concentration (0.01M to 1M), and temperatures (20⁰C to 80⁰C) from up to 1 month is reported to mimic real applications. A comparison with the weight loss experiment was demonstrated to provide a quantitative significance of pitting and uniform corrosion, respectively. Severity of uniform corrosion were measured and versus various pH, temperature, time, and chloride concentration. The key finding in this work was that uniform corrosion rate is oxygen-dependent with a dynamic influence of passivation. Therefore, to identify the contribution of oxygen and passivation (as affected by pH and temperature), experimental approaches including electrochemical impedance spectroscopy (EIS) and cathodic polarization were utilized. Furthermore, TEM images and electron diffraction were performed to assess the structure and morphology of the protective corrosion product driven by temperature. In addition, the Artificial Neural Network (ANN) modelling was employed to analyze the data obtained. A statistic-based model is able to recognize corrosion behavior pattern versus various conditions, therefore a prediction model can be generated according to the environmental inputs.

In summary, the ultimate goal of this study is to suggest an effective maintenance for high value DoD and industrial assets according to an experiment-based prediction model and to understand the impact of different environmental parameters. In this study, a successful uniform corrosion predictive model was developed within specified conditions, which has a significant modification over pit depth growth. Therefore, a predictive model based on lab experimental data is applicable and an efficient low cost maintenance is doable.
Silicon Effects on the Corrosion of Ferritic and Austenitic Chromia Forming Alloys in Wet and Dry CO2
Authors: Nguyen Thuan Dinh , Zhang Jianqiang , Young David John
Published: February 2020

Model alloys of Fe-9Cr, Fe-20Cr and Fe-20Ni-20Cr (wt.%) with Si (0.1, 0.2 and 0.5%) were reacted isothermally in dry Ar-20CO2 gas at 818 oC.  Silicon-free Fe-9Cr formed thick scales of FeO and FeCr2O4, Fe-20Cr formed thin scales of Cr2O3 alone, and Fe-20Ni-20Cr formed Fe3O4, FeCr2O4 and FeNi3. Silicon additions suppressed formation of iron oxides on Fe-9Cr and Fe-20Cr-20Ni, and dramatically slowed oxidation of all alloys. Scales on 0.2Si-alloys consisted of an outer layer of Cr2O3 and an inner layer of amorphous SiO2. Internal precipitation of chromium-rich carbides took place in all undoped alloys, but was suppressed in Si-bearing alloys. Wagner’s theory of alloy depletion is shown to provide a successful description of these phenomena.

Addition of water vapour to the gas makes it much more corrosive.  All silicon-free alloys underwent breakaway corrosion, developing thick iron-rich oxide scales and internal carbide precipitates.  Silicon additions to Fe-9Cr had no detectable effect on reaction in wet gas, but were beneficial in the higher chromium alloys.  Silicon additions substantially improved both oxidation and carburisation resistance in wet CO2, by forming a layer of silica beneath the chromia scale.

In both wet and dry gases, the silica layer acted as a barrier to carbon entry, and slowed outward metal diffusion, thus slowing scaling rates.  Silicon-bearing austenitic alloys underwent scale spallation on cooling from reaction in wet gas, but not after reaction in dry CO2.  No spallation was observed for ferritic alloys after reaction in either wet or dry CO2. The contributions of thermal and growth stresses to spallation, and of growth stresses to the onset of breakaway are discussed.
Hot Corrosion of SiC/BN/SiC Composites
Authors: Opila Elizabeth J. , Hagan Joseph
Published: February 2020

SiC fiber-reinforced SiC matrix composites with a BN interphase (SiC/BN/SiC) are proposed for hot-section turbine engine applications.  NaCl ingested into the engine in marine environments can react with sulfur impurities present in fuel forming molten sodium sulfate deposits resulting in hot corrosion.  Hot corrosion of bulk SiC has been investigated, however, the effects of BN on SiC corrosion, as well as an understanding of hot corrosion resistance of SiC fibers and SiC matrix materials produced by different processing routes has not been elucidated.

 In this study, Na2SO4-induced hot corrosion of model materials (i.e. bulk CVD or Hexoloy SiC with thin BN surface films) and SiC/BN/SiC composites was characterized in furnace studies at temperatures between 900 and 1150°C, for times up to 96 hours, and in O2 with 2.5 or 1000 ppm SO2.  Na2SO4 was applied to the surface of coupons prior to furnace exposure.  After exposure, the amount of corrosion was determined from weight change measurements.  Corrosion products were characterized by Scanning Electron Microscopy, Energy Dispersive Spectroscopy, and dissolution followed by Inductively Coupled Plasma Optical Emission Spectroscopy.   Thin film BN appeared to increase the hot corrosion attack of the model materials.  The composites exhibited more severe hot corrosion than the model materials, especially in matrix areas with initial porosity.  Sylramic fibers underwent more attack than Hi-Nicalon-S fibers.

 Ceramic matrix composites were also exposed in a Mach 0.3 Burner Rig at 950°C for times of 24 and 45 hours.  Simulated seawater (NaCl in deionized H2O) was injected into the burner rig, reacted with sulfur in the fuel to form Na2SO4 (8ppm) to induce hot corrosion.  Severe hot corrosion was observed under these conditions.  Microstructural and compositional characterization of the corrosion products is underway.

 Finally, solubility of relevant oxides in sodium sulfate will be determined as a function of Na2O activity at 900°C to elucidate the SO2 and SO3 partial pressure dependence of hot corrosion of silica- and boria- forming materials.