bluuebunny/crossref_metadata_2025 huggingface dataset:
A Study of the Effects of Ions in Aqueous Electrolyte on CO2 electrochemical Reduction to Efficiently Produce Formate
Authors: Zhang Qi , Shao Xiaolin , Liu Yuyu , Zhang Jiujun
Published: February 2020

It has early been known that the electrolyte cations and anions in aqueous can influence the electrochemical reduction of carbon dioxide (CO2) over the electrodes. This can be attributed to cation hydration and hydrolysis, and the specific adsorption of the anion, which occur near and on the cathode, respectively. In the experiment, we first found that the order of cations as to the effects on faradaic efficiencies (FEs) achieved when using SnO2/carbon paper electrode in the electrochemical reduction of CO2 to formate was found to be FENH4+ < FELi+ < FENa+ < FEK+ < FERb+ <FECs+ , whereas that of anions was FEHCO3- < FECl- < FEBr- < FEI-. From to Cs+, the pKa (Ka: dissociation constant) for cation hydrolysis decreases, and the pH near the cathode gets low, resulting in an increase in the local concentration of dissolved CO2. The consequences are an increase in cathode activity and FEs for HCOO- production. For anions, specific adsorption of the anion forms SnO2-X layer (X = NH4
+, Cl-, Br- and I-) on the surface of SnO2 electrode. Electron-transfer to CO2 may occur via the SnO2-X–C bond. It can be concluded that the stronger the adsorption of the anion to the electrode, the easilier transfer of electrons, the higher FE for formate of electrochemical reduction of CO2. Keywords: SnO2, electrolyte, cations, anions, electrochemical reduction of carbon dioxide
Effect of Praseodymium in Barrier Layer on the Performance of Perovskite Cathode in SOFCs
Authors: Wang Yudong , Zhou Xiao-Dong
Published: February 2020

Because of the large cathode polarization of solid oxide fuel cells (SOFCs) at intermediate operating temperatures, great efforts have been made in developing new cathode material and controlling the cathode microstructure to promote cell performance. The potential reaction and the mismatch of thermal expansion coefficient (TEC) between cathode and electrolyte requires a “barrier layer” inserted between them. Gadolinium doped ceria (GDC), owing to its good ionic conductivity and good match of TEC between cathode and electrolyte layer, is widely used as the barrier layer material. The barrier layer plays an important role in charge carrier transportation and electrochemical reaction at triple phase boundary. In this work, praseodymium and gadolinium co-doped ceria, Pr0.1Gd0.1Ce0.8O2-δ (PGCO), is used as a novel interlayer to optimize the cathode performance due to its better electronic conductivity than GDC and active Pr(III)/Pr(IV) couples in oxygen reduction reaction. Distribution of relaxation time is applied to analyze the mechanism of the enhanced performance.
(Invited) Fast Electrode Kinetics Enabled By New Triple-Conducting Oxides for Both Hydrogen Production and Power Generation Using Reversible Solid Oxide Proton-Conducting Electrochemical Cells
Authors: Ding Dong , Ding Hanping
Published: February 2020

Reversible solid oxide proton conducting electrochemical cells (rSO-PCEC)can alleviate the stress of grid shaving, providing an alternative energy storage pathway with high energy efficiency, especially when reduced operating temperature can bring in benefits of enabling less-expensive interconnect materials and mitigated degradation rate. Economically competitive rSO-PCEC systems have distinct advantages over conventional oxygen-ion conducting ceramic electrochemical cells, but further technology development and widespread market acceptance will require continuous innovation of materials in order to improve cell performance, enhance system lifetime and reduce cost. It is more crucial when electrode kinetics becomes sluggish and dominant with reduced temperatures. At Idaho National Laboratory, our focus is to address these material issues to facilitate maturation of rSO-PCEC technology at 400-600oC. Specifically, we highlight our advancement of rSO-PCEC with novel triple conducting electrode materials as steam electrode. Investigation on material properties including electrical, electrochemical and electrocatalytic activity are discussed.
High-Performance and Durable Reversible Fuel Cells Based on Proton Conductors
Authors: Zhou Yucun , Chen Yu , Zhang Weilin , Liu Meilin
Published: February 2020

A reversible fuel cell (RFC) can operate both in a fuel cell mode (to convert chemical fuels to electricity) and in an electrolysis mode (to produce hydrogen and carbon-containing fuels from electrolysis of water and carbon dioxide, respectively). RFCs have potential to be one of the most efficient and low-cost options for co-located energy storage and power generation. To date, oxide ion conductors (such as zirconia-based electrolytes) have been widely studied for RFCs. In comparison, RFCs based on proton conductors have several advantages, including operation at intermediate temperatures (400–600 °C), simplified system design, reduced cost, and enhanced durability due to the generation ‘dry’ hydrogen in the negative electrode compartment. In this presentation, we will report our recent progress in the development of high-performance and durable RFCs based on proton conductors. When operated in the fuel cell mode, the RFC achieves peak power densities of about 1.0 and 1.5 W cm-2 at 600 and 650 °C, respectively. When operated in both the fuel cell mode and the electrolysis mode, the RFC demonstrates a roundtrip efficiency of greater than 70% at 1 A cm-2 and 650 °C while maintain excellent stability (without obvious degradation in performance for continuous operation of more than 400 h).
(Invited) High Temperature Alkaline Electrolyte for Energy Conversion
Authors: Patil Kailash , Lattimer Judith , McCatty Steeve , Xu Hui
Published: February 2020

Alkaline electrolyte can enable to use non-precious metal catalysts for a variety of energy conversions. However, conventional polymer-based alkaline membranes generally have poor stability, particularly at elevated temperatures (> 80 ℃), thus limiting their viable applications. On the other hand, operating electrochemical cells at higher temperature can improve the electrode kinetics, simplify heat management, and increase the system efficiency. We have developed a high temperature alkaline system that uses molten hydroxides (e.g., lithium, sodium, or potassium hydroxide) impregnated into porous metal oxides. The attained hybrid alkaline electrolyte has demonstrated very high hydroxide ion (OH-) conductivity (> 0.5 S/cm) in a wide operating range (300-500 °C), depending on the category and ratio of each individual electrolyte. A key factor that influences the success of this technology is the microstructures of the porous oxide matrices. Their thickness, porosity, pore size and structure largely determine whether they can successfully retain molten hydroxides in their pores, particularly over extended period of time. We have thereby successfully used high temperature alkaline electrolyte for water electrolysis, the water electrolysis efficiency has been improved to nearly 90% at 500 °C. The strategies to further lower the temperature while retaining a similar performance has been discovered. Mitigation strategies have also been found to reduce the hot corrosion. In addition to water electrolysis, this high temperature alkaline electrolyte can also be used for both electrochemical synthesis of ammonia and direct ammonia fuel cells.
Electrochemical CO2 conversion into High Value Added Chemicals Using Solid Oxide Proton Conducting Membrane Reactors
Authors: Hua Bin , Wang Lu-Cun , Ding Dong
Published: February 2020

As an economical, safe and renewable carbon source, CO2 is an attractive C1 building block for making organic chemicals, materials and carbohydrates. The CO2 conversion for producing chemicals not only contributes to mitigating global climate changes caused by increasing CO2 emissions, but also provides a grand opportunity in exploring new concepts and processes for catalytic and industrial development. Unfortunately CO2 is not extensively used as a source of carbon in industrial practices, due largely to the thermodynamic stability of CO2. ­In most cases of those reported CO2 conversion technologies, the process energy is extremely intensive, and leads to more CO2 emissions in fact. At Idaho National Laboratory, we report our finding on CO2 conversion using an electrochemical proton conducting membrane reactor using steam or natural gas as hydrogen feedstock, to produce high value added chemicals. Technically we demonstrate a promising pathway toward sustainable CO2 conversion, and to guide selective catalyst discovery. Our mission is to leverage the heat and electricity from nuclear energy for integrated energy systems and to engage in the INL’s energy to molecule (E2M) initiative.
(Invited) Sensitized "Thermal" Cell
Authors: Matsushita Sachiko
Published: February 2020

Efficient and low-cost thermal energy-harvesting systems are needed to solve the global energy crisis. If we were able to extract electrical energy directly from the geothermal sources, then the night would be safe regardless of developed or underdeveloped countries; there is no problem in the treatment of radiation waste. Heat, called low quality energy, would become a great renewable energy.

As such a dream cell, we suggested sensitized thermal cells (STCs), that is a new green power generation system operate by heating without a cooling temperature part (Japanese Patent Application No. 2015-175037). The structure of STC imitates the dye-sensitized solar cells (DSSCs).

In DSSCs, electrons in dyes are photoexcited by light irradiation, and the excited electrons are injected into the conduction band of an electron transport material. The transported electrons reduced oxidant ions in electrolyte, and the reductant ions were oxidized by the photoexcited holes, and we can get photo-excited current. If thermally excited electrons in the semiconductor can generate the ion redox reactions, a novel heat-to-electron conversion system functioned without a temperature difference, named a “sensitized thermal cell”, can be obtained.

This concept was firstly demonstrated using β-FeSi2 as the semiconductor material, n-Si as the electron transfer material, and a cupper ion conductor (CUSICON) as the electrolyte (1). The cell exhibited an open circuit voltage of 0.67 V and a short circuit current of 9.1 μA cm-3 at 600 °C. The acquisition voltage continuously maintained this value for at least 35 h in nitrogen. The redox reactions of the electrolyte ions due to thermal excited charge carriers were demonstrated using XPS.

To convince the STC's principle, we also focused on an organic perovskite. This material has been used in a sensitized solar cell, and recent calculations show that it can generate several thermally excited charges at temperatures over 60 °C. Thus, if this perovskite cell can generate electric power with both light irradiation and thermal excitation, the STC concept would be perfectly proven, and the device succeeds thanks to the careful analysis of the perovskite’s unstableness (2). The battery characteristics of the cell were convinced both light irradiation and thermal excitation above the phase transition temperature of the organic perovskite. And very recently, it was revelaed that Ag2S also could act as the sensitizer both by light and heat (3). These results clearly prove the concept of an STC.

In this presentation, we will also report the latest results of the STCs, especially focused on the termination process.

[References]

(1) S. Matsushita, A. Tsuruoka, E. Kobayashi, T. Isobe and A. Nakajima, Mater. Horiz., 2017, 4, 649–656.

(2) S. Matsushita, S. Sugawara, T. Isobe and A. Nakajima, ACS Appl. Energy Mater., 2019, 2, 13-18.

(3) Y. Inagawa, T. Isobe, A. Nakajima, and S. Matsushita, J. Phys. Chem. C, in press. DOI: 10.1021/acs.jpcc.9b01922
Plasmon-Enhanced Photofixation of Dinitrogen for Ammonia Synthesis Using Visible Light Responsive Hybrid Hollow Au-Ag2o Nanocages
Authors: Nazemi Mohammadreza , El-Sayed Mostafa
Published: February 2020

Photo(electro)catalytic N2 fixation with water under ambient conditions offers an ideal pathway for clean, sustainable, and decentralized ammonia production and might serve as a potential alternative to the capital and energy intensive Haber-Bosch process. To date, almost all photocatalysts for nitrogen reduction reaction (NRR) suffer from poor selectivity, low activity due to the difficulty in breaking the strong N2 triple bond, competition with the more favorable hydrogen evolution reaction (HER), and inefficient utilization of the solar spectrum. Here, a photo(electro)chemical setup is demonstrated using a hybrid plasmonic-semiconductor as an active photocatalyst under visible light. Hybrid hollow Au-Ag2O nanocages are utilized to convert atmospheric N2 to NH3 in a pure water system without using sacrificial reagents. The average NH3 production rate of 28.2 mg m-2 h-1 and the solar-to-ammonia (STA) conversion efficiency of 0.017% are achieved under one sun illumination. The apparent quantum efficiency of 1.2% for NH3 production is obtained with the monochromatic light source at 685 nm, which is among the highest ever-reported values for the photocatalytic NRR. The isotopic labeling experiments using 15N2 confirms that supplied N2 gas is the only source of NH3 formation in the system. This work showcases the application of plasmonic photocatalysis in the challenging multi-electron nitrogen fixation.
Photoelectrochemical Applications of SrNbO2n Thin Films Synthesized Via a Two-Step Process at Reduced Temperatures
Authors: Heinselman Karen , Hwang Shinjae , Laursen Anders B. , Talley Kevin , Young James L. , Dismukes Gerard Charles , Garfunkel Eric , Zakutayev Andriy
Published: February 2020

Oxynitride materials often exhibit a perovskite structure in which the oxygen and nitrogen occupy the same lattice sites. Such oxynitride perovskites, for example SrNbO2N with a favorable bandgap of 1.8 eV for tandems, are studied as photoanodes for photoelectrochemical (PEC) water splitting applications. These photoanodes are an essential component to the OER side of the water splitting cell. In literature, SrNbO2N PEC electrodes are often prepared using ammonolysis of deposited Sr2Nb2O7 oxide at high temperatures. To transform Sr2Nb2O7 into SrNbO2N, the ammonolysis temperature has to reach over 900 °C for the time period of minutes to hours. This often leads to intermixing and reactions between the layers in the thin film device stack.

In this presentation, PEC measurements of photocurrent are presented for SrNbO2N on n-Si in ferro/ferricyanide, at varying thicknesses and Sr:Nb ratios. For the deposition of these films, we show a two-step low-temperature synthesis approach to SrNbO2N on Si for tandem PEC applications. In the first step, combinatorial RF sputtering (sometimes with a nitrogen plasma cracker) is used to deposit Sr1+yNb1-yO2-xN1+x at ambient temperature with varying Sr:Nb and O:N ratios. In the second step, these films are annealed in a nitrogen atmosphere using Rapid Thermal Annealing (RTA). We surveyed a series of temperatures and times to determine the minimum temperatures needed to obtain highly crystalline SrNbO2N for PEC applications without reaction with the Si substrate. The resulting film morphology, crystalline structure, and other characterization across the combinatorial spread was characterized. Photocurrent was observed in these materials over a range of varying thicknesses and compositions using a solar simulator and a standard 3-electrode setup.
(Invited) In Situ x-Ray Diffraction during Processing Under Extreme Conditions
Authors: Toney Michael F
Published: February 2020

Many materials are processed under extreme conditions to lock in desirable structural properties, such as metastable phases, appropriate morphologies, and defect concentrations, since these can result in wanted functionalities. Examples include splat cooling, rapid thermal processing (RTP), selective laser melting (SLM), and roll-to-roll (R2R) printing. Often the evolution of the crystalline phases that form during such extreme processing conditions are not known, and can take place through unexpected sequences, including the formation of metastable phases. Understating these phase sequences is important, since this can guide more optimal synthesis or reaction pathways, but can be challenging due to the extreme environments. We have developed X-ray diffraction and imaging approaches to following such phase and microstructure sequences in environments such as RTP (1,2,3), SLM (4,5), R2R printing (6) and hydrothermal growth (7). In this talk, I will describe our methodologies for these types of experiments and give examples of RTP used to form silver electrical contacts to silicon solar cells, hydrothermal growth of Mn-oxides and SLM of Ti-alloys.

D. Fields, Md.I. Ahmad, V.L. Pool, J. Yu, D.G. Van Campen, P.A. Parilla, M.F. Toney, M.F.A.M. van Hest, Nature Comm. 7, 11143 (2016).

VL Pool, B. Dou, DG Van Campen, TR Klein, FS Barnes, SE Shaheen, Md. I. Ahmad, M.F.A.M. van Hest, MF Toney, Nature Comms 8, 14075 (2017).

I. Ahmad, D.G. Van Campen, J.D. Fields, J. Yu, V.L. Pool, P.A. Parilla, D.S. Ginley, M.F.A.M. Van Hest, M.F. Toney, Rev. Sci. Instrum. 86, 013902 (2015).

P. Calta, J. Wang, A.M. Kiss, A.A. Martin, P.J. Depond, G.M. Guss, V. Thampy, A.Y. Fong, J. Nelson Weker, K.H. Stone, C.J. Tassone, M.J. Kramer, M.F. Toney, A. Van Buuren, M.J. Matthews, Rev. Sci. Instrum. 89, 055101 (2018).

“Dynamics of pore formation during laser powder bed fusion additive manufacturing”, A Martin, N Calta, S Khairallah, J Wang, P DePond, A Fong, V Thampy, G Guss, A Kiss, KH Stone, CJ Tassone, J Weker, MF Toney, T van Buuren, M Matthews, Nature Comms, in press.

X Gu, L Shaw, K Gu, MF Toney, Z Bao, Nature Comms 9, 534 (2018).

B-R Chen, W Sun, D.A. Kitchaev, J.S. Mangum, V. Thampy, L.M. Garten, D.S. Ginley, B.P. Gorman, K.H. Stone, G. Ceder, M.F. Toney, LT Schelhas, Nature Comms 9, 2553 (2018).
(Invited) Functional Defects By Design—a High-Throughput Approach to Energy Materials Discovery
Authors: Ganesh Panchapakesan
Published: February 2020

Defects and impurities introduce localized heterogeneities in solids and decisively control the behavior of a wide range of energy technologies. Fuel cell materials, especially proton conducting fuel cells, are a quintessential example in this regard. Designing and developing solid oxide materials that can selectively transport protons will enable us to develop the next generation proton conducting solid oxide fuel cells. Protons require less activation energy compared to oxygen ions which results in a lower operating temperature, higher operating efficiency and better material reliability. In this work [1,2,3,4] we focus obtaining fundamental insights on how properties of host material structure along with dopants, disorder and strain influences proton transport properties in solid oxides by coupling high-throughput computations with functional imaging, neutron spectroscopy and transport measurements.

We initially focus on the perovskite family of compounds (such as doped BaZrO3). We benchmark our calculations against a wide range of experimental measurements such as kelvin probe force microscopy (KPFM), inelastic neutron scattering (INS) and atom probe tomography (APT). To obtain better insights on why certain cubic perovskite/dopant combinations are better at conducting protons compared to others, we developed a high-throughput framework to perform ab initio calculations. The high-throughput framework can scale massively to tens of thousands of nodes to fully exploit the computational capability of the Oak Ridge Leadership Computing facility. We employ this approach to calculate proton transport properties in several cubic perovskite materials with different host atoms and dopants. The results obtained from these calculations enables us to obtain better insights on how material structure – such as atomic properties (electronegativity, ionic radius) and lattice properties (sub-lattice distortion) influences proton transport. The results obtained from this high-throughput analysis is being employed to develop a machine learning framework to predict structure-property correlations on a larger set of perovskites materials. Finally, we explore the role of disorder on proton transport by studying for example fluorite based lanthanum tungstate materials.

[1] “Defect Genome of Cubic Perovskites for Fuel Cell Applications”, Journal of Physical Chemistry C, 121, 26637 (2017)

[2] “The Influence of Local Distortions on Proton Mobility in Acceptor Doped Perovskites”, Chemistry of Materials, 2018, 30 (15), pp 4919–4925

[3]“The Influence of the Local Structure on Proton Transport in a Solid Oxide Proton Conductor La0.8Ba1.2GaO3.9”, J. Mat. Chem. A, 5, 15507 (2017)

[4] “Influence of Non-Stoichiometry on Proton Conductivity in Thin Film Yttrium-doped Barium Zirconate”, ACS Appl. Mater. Interfaces, 2018, 10 (5), pp 4816–4823
(Invited) Electrocat: Expediting PGM-Free Fuel Cell Catalyst and Electrode Development
Authors: Papageorgopoulos Dimitrios C , Thompson Simon T. , Myers Deborah J. , More Karren L. , Neyerlin K C , Zelenay Piotr
Published: February 2020

The development of platinum group metal-free (PGM)-free catalysts with comparable performance and durability to low- PGM catalysts would hasten the cost competitiveness of fuel cells with alternative technologies. Therefore, addressing electrocatalyst development represents the most pressing technical barrier in fuel cell deployment and in meeting the ultimate U.S. Department of Energy (DOE) automotive fuel cell system cost target of $30/kW.

ElectroCat (The Electrocatalysis Consortium), like other DOE Energy Materials Network (EMN) consortia, aligns research and development (R&D) activities at national laboratories and, through DOE-funded projects, facilitates access of academic and industry partners to the world-class capabilities and expertise at the national labs. These capabilities, such as (1) catalyst synthesis (including in particular high-throughput methods), (2) advanced characterization expertise, and (3) quantum chemical modeling address the salient knowledge gaps in PGM-free catalyst development: ascertaining the structure-function relationship, increasing active site density, improving electrode structure to maximize active site utilization and mitigate mass transport limitations, and improving durability. In the near-term, the consortium will work to develop PGM-free catalysts and electrodes to meet the 2025 DOE current density technical target of 0.044 A/cm2 at 0.9 VIR-free, analogous to the goal for low-PGM catalysts. In 2018, ElectroCat R&D efforts increased initial activity by 68% compared to the 2016 baseline of 16 mA/cm2. The presentation will highlight current R&D advancements, core national lab experimental and computational capabilities, as well as high-throughput and machine-learning approaches to expedite the development of PGM-free catalysts and electrodes.
(Invited) SCAN Meta-GGA: An Accurate, Efficient, and Physically Sound Density Functional for Materials Discovery and Design
Authors: Sun Jianwei
Published: February 2020

The accuracy and computational efficiency of the widely used Kohn-Sham density functional theory (DFT) are limited by the approximation to its exchange-correlation energy Exc. The earliest local density approximation (LDA) overestimates the strengths of all bonds near equilibrium (even the vdW bonds). By adding the electron density gradient to model Exc, generalized gradient approximations (GGAs) generally soften the bonds to give robust and overall more accurate descriptions, except for the vdW interaction which is largely lost. Further improvement for covalent, ionic, and hydrogen bonds can be obtained by the computationally more expensive hybrid GGAs, which mix GGAs with the nonlocal exact exchange. Meta-GGAs are still semilocal in computation and thus efficient. Compared to GGAs, they add the kinetic energy density that enables them to recognize and accordingly treat different bonds, which no LDA or GGA can [2]. In this talk, I will present an advance in DFT, the recently developed non-empirical strongly constrained and appropriately normed (SCAN) meta-GGA [1]. SCAN predicts accurate geometries and energies of diversely-bonded molecules and materials (including covalent, metallic, ionic, hydrogen, and van der Waals bonds), significantly improving over its predecessors, the GGAs that dominate materials computation, at comparable efficiency [2]. SCAN’s excellent performance on formation enthalpies and ground structure predictions, critical for materials discovery and design, will be highlighted [3]. I will further explain how SCAN was constructed [1], why it can improve over GGAs [2], and where it should fail [4]. At the end, efforts to improve SCAN via nonlocal corrections will be discussed.

[1] J. Sun, A. Ruzsinszky, and J.P. Perdew, Strongly constrained and appropriately normed semilocal density functional, PRL
115, 036402 (2015).

[2] J. Sun, R.C. Remsing, Y. Zhang, Z. Sun, A. Ruzsinszky, H. Peng, Z. Yang, A. Paul, U. Waghmare, X. Wu, M.L. Klein, and J.P. Perdew, Accurate First-principles structures and energies of diversely-bonded systems from an efficient density functional, Nat. Chem.
8, 831 (2016).

[3] Y. Zhang, D.A. Kitchaev, J. Yang, T. Chen, S.T. Dacek, R.A. Sarmiento-Perez, M.A.L. Margues, H. Peng, G. Ceder, J.P. Perdew, and J. Sun, Efficient first-principles prediction of solid stability: Towards chemical accuracy, NPJ Computational Materials
4, 9 (2018).

[4] H. Peng, Z. Yang, J.P. Perdew, and J. Sun, Versatile van der Waals density functional based on a meta-generalized gradient approximation, PRX
6, 041005 (2016).
(Invited) Mn4+ r-Line Emission Intensity: The Ways of Its Enhancement
Authors: Brik Mikhail G. , Srivastava Alok M
Published: February 2020

Mn4+-based red phosphors are excellent materials to be used for making white LEDs with warm white light. They can be excited by the blue or ultraviolet light to produce red photoluminescence (PL), which is due to the parity and spin-forbidden 2Eg→4A2g transition. However, in many host materials, the intensity of the 2Eg→4A2g zero-phonon line (R-line) is very weak due to the presence of the inversion center of the crystallographic site occupied by the manganese ions. As a result, the red-shifted Stokes components dominate in the emission spectra of such hosts, but this leads to the decreased overlap of the PL spectra with human eye sensitivity curve and decreased intensity of the phosphor (lower lumen/Watt value). Therefore, finding the recipes of enhancement of the R-line intensity and production of brighter phosphors is an important scientific and technological task.

In the present work we establish the key parameters responsible for the energy and the intensity of the Mn4+ R-line. Thorough consideration and analysis of the optical spectra for a large number of the Mn4+-based phosphors allowed to draw the following conclusions:

The energetic position of the R-line is determined by the “Mn4+-ligand” bonding covalence. Most phosphors for the solid state lighting can be conditionally divided into fluorides and oxides (where the fluorine or oxygen ions are the Mn4+ nearest neighbors, respectively). In ionic fluorides, the Mn-F bonding covalence is weak, which shifts the R-line to higher energies, with the emission wavelength at about 620 nm. In covalent oxides, the stronger Mn-O bonding covalence lowers the energy of the 2Eg state, moving the emission to about 650 nm.

In the host crystals, where the Mn4+ ions are located at the sites without inversion center, the R-line intensity is higher compared with the crystals possessing inversion symmetry at the Mn4+ Absence of the inversion center relaxes the parity section rule, which enhances the R-line intensity. As a result, the phosphor luminosity is increased considerably. The inversion center can be removed by cation co-doping, when different cations in the second coordination sphere around the Mn4+ ion remove the inversion center.

As an example, a figure below shows the PL spectra of K2SiF6:Mn4+ and NaKSiF6:Mn4+. In the former case the ideal MnF6 octahedron with the inversion center does not allow for high R-line intensity. It the latter case structural disorder and mixed occupation at the K/Na site results in the presence of different cations in the second coordination sphere. As a result, the intensity of the R-line is increased by several times.

Therefore, to get the phosphors with increased luminosity one has to focus on the host materials without inversion center at the dopant sites. If, however, the inversion symmetry exists, it should be broken by additional co-doping that would produce structural disorder around the dopant.

Figure 1
(Invited) Conversion Materials and Performance in Laser Based Light Sources
Authors: Raukas Madis , Lenef Alan , Kelso John , Engl Moritz
Published: February 2020

We briefly review the rationale and basic principles behind light sources based on (solid state) lasers and luminescence conversion, along with main applications and market need considerations for such sources (examples: medical, information projection, automotive and general lighting). It is clear that the efficiency of high luminance laser pumped phosphor sources depends strongly on the performance of conversion material which is often pushed to optical and thermal limits. Critical materials characteristics and physical mechanisms that control overall source performance will be discussed, also the expected interplay of material characteristics and laser conversion performance. We have separated contributions from thermal and non-thermal quenching mechanisms, and point out the distinction between the true loss mechanisms (e.g. Auger-like or excited state absorption related) and the decline in converted light output due to increased transparency for the pump light (due to activator ground state depletion). The main challenges and roadblocks for improving both the converter materials as well as laser sources are considered and outlook on future discussed: where is the laser based lighting expected to continue from here?
Electrochemical Oxygen Atom Transfer Reactions
Authors: Manthiram Karthish
Published: February 2020

Epoxides are essential chemical intermediates for the manufacturing of textiles, plastics, and pharmaceuticals. Existing routes, including both wet chemical and thermochemical approaches, have the drawbacks of large carbon dioxide footprints, stoichiometric waste products, and hazardous reagents. We have developed a route through which olefins can be epoxidized at ambient conditions, using water as the oxygen atom source. At the cathode, hydrogen is generated. Overall, this reaction provides a means by which the oxidation reaction can go towards generating a valuable product rather than generating oxygen which is simply vented in a conventional water electrolyzer. We have developed mechanistic understanding of how water is oxidized, providing means by which the selectivity for epoxidation can be rationally improved.
Redox Control of Supramolecular Polymerization Using Electroactive Ureidopyrimidones
Authors: Smith Diane K. , Cedano Mario , Vuong Katrina
Published: February 2020

Unlike conventional polymers, in which monomers are reacted to form strong covalent connections, supramolecular polymers are formed by linking monomers via weaker, non-covalent interactions such as H-bonds, ion-dipole interactions and so on. These imbue supramolecular polymers with unique properties since the linkages are readily broken, but also easily reformed as environmental conditions change. One particularly well-studied class of supramolecular polymers are based on the ureidopyrimidones, UPy’s, which dimerize via 4 strong, linear H-bonds in non-competitive solvents. Monomers for supramolecular polymerization can be made by linking together 2 or more UPy units with short covalent chains. Under dimerization conditions, the UPy’s link up to form longer polymeric chains. One of the useful attributes of such polymers is their self-healing ability. Application of heat or mechanical stress will readily break the monomers apart at the H-bonds, but, upon cooling or relief of stress, the bonds reform. The goal of this research is to see if electron transfer can be used as an alternative, more selective stimulus to break apart the UPy chains. As a first step in this direction, we have synthesized a known UPy monomer, 1, which is expected to polymerize at concentrations above ~20 mM in CH2Cl2. This can be verified by measuring the change in specific viscosity as a function of the concentration of 1. By adding simple UPy’s as chain terminators the degree of polymerization should decrease, with a corresponding decrease in the viscosity of solution. For this work, we plan to add our previously studied electroactive UPy’s, 2a and 2b. We have previously shown oxidation breaks apart the 2a and 2b dimers at mM concentrations in CH2Cl2. Thus, upon electrochemical oxidation, 2a or 2b will no longer be able to act as chain terminators and the linked UPy 1 should reform polymer chains. This can be detected by an increase in the viscosity of solution upon oxidation.

Figure 1
Single Cell Electrochemistry – Uptake of Bioinorganic Silver-Based Drugs
Authors: Sidambaram Prabhakar , Colleran John
Published: February 2020

Heterogeneity in a cell population is a universal phenomenon in all biological systems including whole tissues, and cell cultures.[1] Intra-tumour heterogeneity has been widely reported for decades from morphological perspectives, whereas phenotypic and genotypic heterogeneity has also been detected.[2] DNA platination is widely assumed as the central mode of action for most platinum anti-cancer drugs. This generalisation on the mode of action for conventional chemotherapy may actually impede effective drug development. Clinical approval for most novel anti-cancer drugs has been denied due to uncertainty in optimal usage, and the modes of action unclear.[3] For a better understanding of variations, from cell to cell, in response to metal-based drugs, single cell analysis is the key. Single cell experiments should provide critical information about the pathway and disease state, which will guide personalised medicine and therapeutic strategies. Electrochemistry is the foremost approach for studying the uptake of metal-based drugs in single cells. This strategy involves positioning a micro or nanoelectrodes inside or near the surface of a single cell for the electrochemical monitoring of individual cellular events.[4]

In this work, the aim is to exploit single cell electrochemical analysis, to study the uptake of silver-based bioinorganic drugs and to elucidate the mode of action. Single cell electrochemistry experiments were carried out using the platinum and platinum-black nanoelectrodes on human lung carcinoma (A549) cell lines. Speciation studies of the silver-phenanthroline bioinorganic drugs was examined using stripping voltammetry for metal detection, and the redox behaviour analysis by cyclic voltammetry for in vitro and single cell analysis.

[1] Andrew G. Ewing. et al., Anal. Chem. 2019, 91, 1, 588-621

[2] Glenn Deng. et al., Front Cell Dev Biol. 2016, 4: 116.

[3] Walter Berger. et al., ESMO Open. 2017, 2(3): e000239.

[4] Dechen Jiang. et al., ACS Sens. 2018, 3 (2), 242–250
Integration of Cyclodextrin-Mediated Surfaces with Electrochemical Flow Cell
Authors: Li Li , Merrill Mckenna , Panahi Zahra , Halpern Jeffrey M
Published: February 2020

Cyclodextrin (CD) is a widely used molecule in surface modification and chemical sensing. Cyclodextrin consists of a hydrophobic cavity and hydrophilic exterior, which can form host-guest inclusion complex with hydrophobic molecules. The host-guest complex can be used for recognition and detection. The working electrode surfaces are modified with adamantane or poly ethyl glycol (PEG) via thiol-based click chemistry, and further complexed with a CD intermediate to create our sensor surfaces. The modified surfaces are integrated with a flow cell, where solutions are pumped through multiple electrodes simultaneously. Flow cell allows us to reduce the required test volume and evaluate multiple surfaces simultaneously. We use Electrochemical Impedance Spectroscopy to measure changes in the surface. We will discuss appropriate equivalent circuit models to fit charge transfer resistance, capacitance, and Warburg impedance over multiple layers to achieve accuracy. Hydrophobic analytes such as cortisol and resveratrol are measured with flow cell and clear trend of capacitance/ impedance vs concentration is discovered. Our goal is to reproducibly monitor surface changes and measure hydrophobic analytes in unknown sample solutions.
Estimation of Molecular Orientation Using Water Drop Angle
Authors: Hirao Kohki , Murakami Takuya , Maeda Atsushi
Published: February 2020

In self-assembled monolayer, SAM, molecules are attracted each other to be closely packed. Such a structural feature causes the stable mechanical, chemical, and thermo-dynamical properties. In addition, recent preparation techniques allowed the direct electronic coupling between organic functionality and Si substrate. As the results, SAMs possess great potential in the fields of electrochemical sensors and molecular electronics. From the viewpoint of application, it is desirable to precisely estimate the molecular orientation in SAMs. In the present study, we propose the structural analysis using water drop angle.

To form hexadecyl-SAMs, hydrogen-terminated Si substrate was soaked in 1-hexadecene under UV light for 2 hours. UV light is capable of breaking Si-H bond homolytically, which yields the Si dangling bonds that can act as the starting point for radical chain propagation.

When a droplet is attached to SAM and the SAM surface is tilted little by little, the droplet will lunge forward and finally slide downward. The tilting angle when the droplet starts sliding is called ‘water drop angle’, WDA. We measured WDA by an original system, in which sample surface could be simultaneously tilted and rotated from 0 to 90 and from 0 to 360 degrees, respectively.

Figure 1(a) shows the typical measurement results for the hexadecyl-SAMs. WDAs were found to considerably change with the rotation angles. In addition, the period in the WDA change was nearly equal to 180 degrees. Here in-plane rotation angle was defined the orientation flat of the wafer, Si(111)<110>, as 0 degree. We believe that the periodic change is in relation to the molecular orientation. Namely, when a sample is tilted in the direction as shown in Fig. 1(b), a droplet is hooked by the SAM molecules, resulting in the large WDAs. On the other hand, in the case of Fig. 1(c), the friction between a droplet and the SAM surface is expected to be weak, corresponding to the small WDAs. The maximum WDAs for the hexadecyl-SAMs were observed at the rotation angles about 210 degrees. To justify these experimental results, it is extremely important to notice that the sterific hindrance between the (Si-C-)C-H bonds of the SAM molecules and the surrounding unreacted Si-H bonds should be minimum in six molecular orientation. As a result, the WDA reasonably exhibited the maximum value at the rotation angles of 210 degrees. In the ECS meeting, we will indicate that our measurement method is useful to estimate the orientation direction of the molecules covalently-bonded to the solid surface.

Figure 1
Electrocatalytic and Optoelectronic Characteristics of Exfoliated Two-Dimensional Titanium Nitride Ti4N3Tx mxene
Authors: Djire Abdoulaye , Zhang Hanyu , Liu Jun , Miller Elisa M. , Neale Nathan
Published: February 2020

A relatively new class of two-dimensional (2D) materials called MXenes have garnered tremendous interest in the field of energy storage and conversion. Thus far nearly all MXenes reported experimentally have been described as metals, with a lone report of a mixed-metal carbide phase exhibiting semiconducting character. Here, we report the optical, electrocatalytic and electrical properties of the 2D Ti4N3TxMXene (Tx= basal plane surface terminating groups) and show this material exhibits both metallic and semiconducting behavior. We provide complete structural characterization of exfoliated Ti4N3TxMXene and assign Tx= O and/or OH and find that this material is susceptible to surface oxidation. Optical experiments indicate that the exfoliated Ti4N3TxMXene forms a hybrid with a thin surface oxide layer resulting in visible light absorption at energies greater than ~2.0 eV and an excitation wavelength-dependent defect-state emission over a broad range centered at ~2.9 eV. As an electrocatalyst for the hydrogen evolution reaction, the exfoliated Ti4N3Txshows an overpotential of ~300 mV at –10 mA cm–2and a Tafel slope of ~190 mV/decade. Finally, we observe a clear semiconductor-to-metal transition at ~90 K from temperature-dependent transport measurements under 5 T magnetic field likely resulting from the thin oxide layer. These results unveil the intriguing optical, electrocatalytic, and electrical properties of this 2D Ti4N3TxMXene that expands the potential of these new 2D materials into electrocatalysis and (opto)electronic applications.
In Situ Spectrospecopy Investigation of the Surface-Interface Charge-Transfer Process over Tailored Nano-Structured Based PEC Fuel Cells for Solar Energy Harvesting and Conversions
Authors: Li Xinyong
Published: February 2020

Solar energy induced catalytic reactions allow solar energy to be used directly in sunlight-to-chemical energy conversions. Many scientific progress have been made in solar energy utilization and conversions, whereas, scientists from all over the world claimed that there are still many problems need to be further addressed including how to further enhance the solar energy utilization & conversion efficiency etc. The detail micro-interface process, redox mechanism, charge-carrier transfer behavior and active species actions need to be further studied. Following all of these concerns, series of multifunctional complex oxides with hetero-junctions have been well designed in our group towards solar energy utilization and conversion process via photo-induced chemical process, and different transient physical techniques including in situ EPR, in situ SPV and transient laser flash photolysis etc. have also been used to elucidate the interfacial photo-induced redox process and charge-carrier behaviors.

We found that hierarchical nanostructured assemblies can be engineered to tailor the properties of external fields modulated and/or light harvesting assemblies. The crystal-, micro- and surface-interface structure could be tailored by utilizing various synthesis strategies, which would incur the nanomaterials with novel PEC/PC properties. Furthermore, combined in
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situ spectroscopic characterization could provide more detail structural information and redox process over micro-interface, which would be beneficial for design efficient solar and energy conversion based materials at molecular utilization and/or atomic level. The tailored hierarchical nanomaterials may find novel applications in multidisciplinary fields.
Recent Advances with Terpyridine-Based Monolayer Electrochromic Materials
Authors: Easton E. Bradley , Poisson Jade , Laschuk Nadio O , Geoffrey Heather L , Allan Jesse T.S. , Ebralidze Iraklii , Quaranta Simone , Zenkina Olena V , Gaspari Franco
Published: February 2020

Electrochromic (EC) materials are a class of “smart” materials that change their optical properties in response to an applied potential. This optical change can be the development, loss, or variation in the color of the material. EC materials have recently become a research focus because of their high commercial applicability in “smart” windows, antiglare mirrors, and low-power displays. Most current EC materials are based on thick layers of EC molecules or EC molecules/ conductive polymer blends on the electrodes. The device properties depends strongly on the overall composition and distribution of the EC species in the polymer structure.

We have developed an EC systems that contain as little as a monolayer of the EC molecules deposited onto a surface-enhanced conductive support [1]. The process involves the covalent attachment of various terpyridine-based ligand to the surface of a nanostructured conductive indium − tin oxide (ITO) screen-printed support by a simple submerging of the support into an aqueous solution of L. Subsequent reaction of with metal ions (e.g. Fe, Ru) leads to the formation the monolayer of the redox-active metal complex covalently bound to the ITO support. In addition, isolated and well-defined terpyridine- based metal complexes (Fe, Os,Co) were simply deposited on ITO screen-printed surface via conventional chlorobenzylsiloxane-based template.

Our fabrication approach utilizes the inter-particle porosity of the support and requires as low as a monolayer of EC active molecule, giving significant molecular economy when compared with traditional polymer-based EC devices.

This presentation will feature an overview of our synthetic methods, including how we can alter the color of the films by changing either the metal center of the ligand itself [2]. Spectro-electrochemical studies enabled us to correlation optical density with redox site density. Furthermore, detailed electrochemical studies enabled the determination of the kinetic rate constants for electron transfer for these films [3], which were considerably higher than other approaches in the literature. These novel light-reflective EC materials demonstrate a high color difference, significant durability, fast switching speed, excellent stability and high EC reversibility.

References

[1] J.T.S. Allan, S. Quaranta, Ebralidze, II, J.G. Egan, J. Poisson, N.O. Laschuk, F. Gaspari, E.B. Easton, O.V. Zenkina, ACS Appl Mater Interfaces, 9 (2017) 40438-40445.

[2] N.O. Laschuk, Ebralidze, II, J. Poisson, J.G. Egan, S. Quaranta, J.T.S. Allan, H. Cusden, F. Gaspari, F.Y. Naumkin, E.B. Easton, O.V. Zenkina, ACS Appl Mater Interfaces, 10 (2018) 35334-35343.

[3] J. Poisson, H.L. Geoffrey, I.I. Ebralidze, N.O. Laschuk, J.T.S. Allan, A. Deckert, E.B. Easton, O.V. Zenkina, The Journal of Physical Chemistry C, 122 (2018) 3419-3427.

Figure 1