bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Steam Electrolysis Using Proton-Conducting Perovskites: Prospects and Challenges
Authors: Matsumoto Hiroshige , Kwati Leonard , Fujisaki Takaya
Published: December 2020

This paper demonstrates and discusses steam electrolysis performance using proton-conducting solid oxide materials with respect to the benefit and prospects as well as challenges toward the technical application for hydrogen production.

Water electrolysis will take an important role as the energy storage for the vast use of renewable energy. Steam electrolysis is characterized by high energy conversion efficiency compared to low temperature water electrolysis. However, the conventional technique is accompanied by high operation temperature because the ionic conduction in solids needs high temperature. As a mean to reduce the operation temperature, the proton conducting perovskite is thus a choice for the electrolyte since it works in intermediate-temperature regime. We have reported so far SrZr0.5Ce0.4Y0.1O3-δ (SZCY541) [1] and BaZr0.44Ce0.36Y0.2O3-δ (BZCY(54)8/92) [2] to be highly proton conducting and sufficiently stable in steam at the inter mediate temperatures. The latter exhibits the conductivity of 10-2 S/cm in moist hydrogen at 500°C and has been demonstrated as the electrolyte for steam electrolysis [3].

The most remarkable difference of proton conductors from other solid electrolytes is the mechanism for the generation of proton conducting charge carriers. It takes place as a result of hydration of oxide ion vacancies. One of the challenges for the material is the volumetric deformation accompanied by hydration/dehydration that possibly leads fatigue of the cell structure. Another is originated from the defect chemistry, that is the hydration is competing with oxygen incorporation to the oxide ion vacancy that result in the electronic hole formation in oxidative atmosphere. Electronic leakage, reduction of Fardaic efficiency, is originated from this hole conductivity intrinsically being in the materials. Mixed-conducting electrode materials are still under investigation by many researchers. Another issue is the inter-diffusion of transition metal species from the electrodes to the electrolyte causing the reduction of the proton conductivity. These challenges will be discussed for improving the reliability of the proton conductor steam electrolysis.

Acknowledgement

This work was supported by the Council for Science, Technology and Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), "energy carrier" (Funding agency: JST), the JSPS-NSF Partnerships for International Research and Education (PIRE), the JSPS Core-to-Core Program of Advanced Research Networks (Solid Oxide Interfaces for Faster Ion Transport), METI International joint research and development of innovative energy technology, JST SICORP, and World Premium International Research Center Initiative (WPI), MEXT Japan.

References

[1] Matsumoto et al., Pure Appl. Chem., 85, 427–435, 2013

[2] Leonard et al., Inter. J. Hydrogen Energy, 42, 3926-3937, 2017

[3] Leonard et al., J. Mat. Chem A, 6, 19113-19124, 2018

[4] Fujisaki et al., Solid State Ionics, 333, 1-8，2019
Hybrid Electrochemical Deposition for the Nanofabrication of Cr-Poisoning-Tolerant La(Ni,Fe)O3-Δ Cathode for Solid Oxide Fuel Cells
Authors: Shaur Ahmad , Rehman Saeed Ur , Kim Hye-Sung , Joh Dong Woo , Song Rak-Hyun , Lim Tak-Hyoung , Hong Jong-Eun , Park Seok-Joo , Lee Seung-Bok
Published: December 2020

The Cr-poisoning of cathode materials is one of the main degradation issues hampering the operation of solid oxide fuel cells (SOFCs). To overcome this shortcoming, LaNi0.6Fe0.4O3-δ (LNF) has been developed as an alternative cathode material owing to its superior chemical stability in Cr-environments. In this study, we develop a hybrid electrochemical deposition technique to fabricate a nanostructured LNF-GDC (n-LNF-GDC) cathode with enhanced active reaction sites for the oxygen reduction reaction (ORR). For this purpose, Fe and Ni cations are co-deposited onto an electrically conductive carbon nanotubes (CNT)-modified GDC backbone by electroplating, whereas La cations are successively deposited through a chemically assisted electrodeposition method. The proposed method involves a low-temperature (900 °C) calcination step of electrodeposited cations which avoids the need of fabricating a GDC diffusion barrier layer which is otherwise needed to avoid the formation of insulating phases (e.g., La2Zr2O7) when fabricating by conventional high temperature (≥1000 °C) sintering. SEM images reveal a unique nanofibrous structure of the n-LNF-GDC, which is believed to play an instrumental role in enhancing the electrochemical characteristics by increasing the active triple-phase boundaries. An anode-supported SOFC with the n-LNF-GDC cathode showed the superior performance of 0.984 W cm-2 at an intermediate temperature of 750 °C as compared to the power densities of 0.495 and 0.874 W cm-2 produced by LNF-GDC and state of the art LSCF (La0.6Sr0.4Fe0.8Co0.2O3-δ)-GDC composite cathodes fabricated by conventional sintering. A short-term accelerated Cr-poisoning durability test indicated good electrochemical stability of the n-LNF-GDC, whereas LSCF exhibited severe degradation. The electrochemically engineered nanostructured n-LNF-GDC can serve as an effective cathode for SOFCs to achieve high performance and long-term durability.
Numerical Modeling for the Performance of Reversible Solid Oxide Fuel Cell
Authors: Yang Tao , Lee Shiwoo , Fan Yueying , Lei Yinkai , Liu Jian , Guan Bo , Wen You-Hai , Kalapos Thomas , Abernathy Harry , Hackett Gregory A
Published: December 2020

In this study, the performance of solid oxide cells (SOCs) under both electrolysis mode and fuel cell mode is investigated via in-house developed high fidelity multiphysics simulations. The full parameter space with various fuel/steam supply conditions is explored to investigate the trends of button cell performance under different working loads. For each specific working loads, a global minimum resistance is found, but the conditions for the global minimum resistance shift for different working loads under different working modes. The trends are also verified by the good agreements between simulations and experiments. Furthermore, the performance degradation due to Ni redistribution in the active layer of hydrogen/steam electrode is also investigated by implementing the microstructural properties change into the developed model. The results show that main performance degradation occurs on the high frequency range (> 1000 Hz), indicating that the Ni redistribution inside the active layer mainly affects the charge transfer processes in the hydrogen/steam electrode. This study can provide guidance for the design of reversible solid oxide fuel cell (r-SOFC) system as well as performance stability improvements.
Effect of Elemental Substitution in (Ba,Sr)6RE2Co4O15−BaCe0.5Pr0.3Y0.2O3-δ for Cathodes of Proton-Conducting Ceramic Fuel Cells
Authors: Kunimoto Naoki , Muroyama Hiroki , Matsui Toshiaki , Eguchi Koichi
Published: December 2020

Solid oxide fuel cells are promising energy conversion devices because of high efficiency and high fuel flexibility, but their high-operating temperature (700-900 ºC) causes problems such as fast degradation of components and long start-up/shut-down time. To overcome these problems, low- temperature operation is preferable. Proton-conducting ceramic fuel cells (PCFCs) are promising energy conversion devices for intermediate-temperature operation, especially below 600 ºC. This is because the activation energy of proton migration in proton-conducting oxides, such as rare earth-doped barium cerate, is lower than that of the oxide ion. At the current state, however, the performance of PCFCs is mainly limited by the cathode materials.

Recently, we have reported that the composite of Ba4Sr2Sm2Co4O15 (BSSC4224)–BaCe0.5Pr0.3Y0.2O3 (BCPY) showed higher activity below 600 ºC in 3% humidified synthetic air, as compared with high-performance cathodes reported1). In this composite, BSSC4224 mainly served as an active site for the dissociative absorption of oxygen.

In this study, then, the effect of the elemental substitution, especially the Ba/Sr ratio and rare-earth elements, in (Ba,Sr)6
RE
2Co4O15, on the ASR was studied. Symmetric cells consisting of the BaCe0.8Y0.2O3 (BCY) disk electrolyte and Ba5SrRE
2Co4O15 (RE =Nd, La, Eu, Sm, Pr, and Gd), Ba4Sr2Gd2Co4O15 or Ba5SrGd2Co4O15 (BSGC5124)–BCPY electrodes were fabricated. The electrode performance was measured in 3% humidified synthetic air (21% O2–79% N2) at 450–700 ºC by impedance spectroscopy.

In impedance analysis, BSGC5124 had the lowest ASR below 550 ºC among Ba5SrRE
2Co4O15 electrodes. Then, the composite of BSGC5124–BCPY was prepared and its performance was compared with that of BSSC4224–BCPY composite. We found that BSGC5124–BCPY has comparable area-specific resistance and activation energy to BSSC4224–BCPY although BSGC5124 itself had much lower area-specific resistance and activation energy than BSSC4224. Therefore, we concluded that the dissociative adsorption of oxygen on the BSGC5124 phase is not the rate limiting step for the oxygen reduction reaction in this composite system.

[1] T. Matsui, K. Manriki, K. Miyazaki, H. Muroyama, K. Eguchi, J. Mat
er. Chem. A, 6, 14188 (2018).
Electrode Degradation in Proton-Conducting Ceramic Electrochemical Devices
Authors: Hernandez Rodriguez Marcos , Hernandez Carolina Herradon , Le Long Quoc , Sullivan Neal P
Published: December 2020

We present our efforts to identify, quantify, and mitigate sources of degradation in proton-conducting ceramic electrochemical devices. As described in another presentation, researchers at the Colorado School of Mines are currently scaling up proton-conducting ceramics into multi-cell stacks for both fuel-cell and electrolyzer applications. This integration of novel protonic-ceramic materials with stack packaging materials brings questions regarding materials compatibility and stack-level degradation. The lower operating temperature (500 – 600 ºC) of protonic-ceramic devices presents promise for reducing the driving forces behind several well-established degradation mechanisms found in more-prevalent oxygen-ion conducting ceramics. Nickel sintering in the anode support should decrease, as should chromia-scale growth and electrode poisoning from metallic interconnects. That said, other aspects of protonic ceramics could enhance degradation. For example, under fuel-cell operation, water vapor is formed at the cathode, increasing oxygen partial pressure and promoting chromia poisoning. Further, these degradation mechanisms are presented over thousands of hours of stack operation, often happening simultaneously, clouding our understanding.

In this presentation, we describe our efforts to identify and mitigate the key degradation mechanisms found in proton-conducting ceramic electrochemical devices and stacks. Through collaboration with the University of Bordeaux, we have developed unique device packaging and experimentation to enable careful measurement of electrochemical performance at electrode-electrolyte interfaces over thousands of hours of operation. As shown in the figure, a ~ 2-mm-thick BaCe0.4Zr0.4Y0.1Yb0.1O3-δ (BCZYYb4411) electrolyte is sandwiched between two identical BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY) air electrodes to form an electrolyte-supported symmetric cell. Fuel electrodes can also be studied. The cell is packaged, perhaps with metallic interconnects, within carefully designed alumina fixturing that maintains consistent electrical connections throughout the long testing periods. The assembly is sealed within a quartz reactor and placed within a furnace, and enables exploration of a wide range of operating conditions, gas compositions, and temperatures.

In this talk, we will present results focusing on degradation at the cathode-electrolyte interface. The effect of H2O concentration, and the role of metallic interconnects in cathode degradation will be presented.

Figure 1
The Equilibrium Shapes of Exsolved Ni Nano-Catalyst on a-Deficient and High Ni Doping Perovskite for Diverse Energy Applications
Authors: Kim Yo Han , Myung Jae-Ha
Published: December 2020

Controlling the geometric shape of catalyst plays a key role in obtaining unique properties including activity, selectivity and stability. However, the shapes of exsolved nanoparticles on oxide surface have been less addressed contrary to colloidal particles. Here we investigated the equilibrium shape of exsolved nanoparticle during a wide range of growth by controlling reduction (growth) time and temperature. The quasi-spherical shape of initial nanoparticles has changed into the polyhedral shape during particle growth. The surface of exsolved Ni particle finally bounded by most stable {111} facet, while the particle mainly bounded by unstable {110} facet is not observed. In terms of thermodynamics, we described that the shape of exsolved Ni could become various shape without spherical shape at large-scale growth due to difference between surface energy and interface energy. The shapes of exsolved Ni particle on oxide surface are determined by the orientation of exposed surface. Our findings suggest that the shape of nanoparticle on oxide could be controlled due to epitaxial growth and size of exsolved particle. These shape-controlled nanoparticles on oxide have potential for application of high temperature catalyst and energy conversion application such as solid oxide cells, metal-air battery.
Electrochemical Characterization of Pr(A)MnO3 Perovskites As Oxygen Electrodes for Solid Oxide Fuel-Assisted Electrolysis Cells
Authors: Yaremchenko Aleksey , Boiba Dziyana , Patrakeev Mikhail , Arias-Serrano Blanca I.
Published: December 2020

Long-term degradation remains the main issue for the viability of solid oxide electrolysis cell (SOEC) technology as a practical hydrogen production system. The major specific degradation mechanism in SOECs relates to delamination phenomena at or near electrolyte/anode interface. The principle of so-called fuel-assisted electrolysis is to supply the carbon-containing species which can react with oxygen at the anode side thus bringing down the oxygen chemical potential at the electrolyte/anode interface and improving its stability. The present work is aimed at the characterization of PrMnO3-based perovskites for potential application as anodes in solid oxide fuel-assisted electrolysis cells.

Pr0.6-x
A0.4MnO3
±δ (A = Sr, Ca; x = 0 and 0.05) powders were synthesized by glycine-nitrate combustion technique. The characterization included XRD, SEM/EDS, XPS, dilatometry and thermogravimetry, measurements of electrical properties, and determination of oxygen nonstoichiometry by coulometric titration. XRD analysis confirmed the formation of solid solutions with orthorhombic perovskite-like structure. Pr0.6-x
A0.4MnO3
±δ exhibit negligible variations of oxygen content with temperature and oxygen partial pressure under oxidizing conditions, while reducing p(O2) below 10-4 atm results in a progressive oxygen losses from the lattice and reduction of variable-valence cations. The low-p(O2) stability boundary of the perovskite phase at 800°C corresponds to ~10-17-3×10-16 atm; the stability domain is wider for Ca-substituted compositions and narrows with introduction of A-site vacancies. Dilatometric studies confirmed a good thermomechanical compatibility with common solid electrolytes. The electrical conductivity of Pr0.6-x
A0.4MnO3
±δ ceramics is p-type electronic and decreases with reducing p(O2), but still exceeds 40-50 S/cm under oxygen chemical potentials anticipated for the oxygen electrode operation conditions at 800°C. The electrochemical performance of Pr0.6-x
A0.4MnO3
±δ porous electrode layers was evaluated in contact with yttria-stabilized zirconia solid electrolyte using symmetrical cell configuration as function of relevant parameters (electrode fabrication conditions, with and without ceria-based interface layers, modifications via impregnations by praseodymia or gadolinia-doped ceria).
Enhanced Long Term Durability of Metal-Supported Solid Oxide Electrolysis Cells By Advanced Coatings
Authors: Shen Fengyu , Hu Boxun , Tucker Mike C
Published: December 2020

Metal-supported solid oxide electrolysis cells (MS-SOECs) with symmetric cell architecture were developed for high temperature electrolysis at Lawrence Berkeley National Laboratory (LBNL). The cell is comprised of a thin ceramic electrolyte and porous electrode backbones sandwiched between stainless steel metal supports. MS-SOECs offer a number of advantages over conventional all-ceramic SOECs due to their low-cost structural materials (e.g. stainless steel), mechanical ruggedness, excellent tolerance to redox cycling, and extremely fast start-up capability. The current density of MS-SOEC at 1.3 V and 50 vol% steam content is improved by optimizing microstructure of electrode backbone and procedure of catalyst infiltration. MS-SOEC with composite LSCF-SDC air electrode catalyst displays a degradation rate of 1.6%/100 h with current density of 0.33 A cm-2 at 700 °C in 1000 h test (Figure 1). Post-mortem analysis reveals that the degradation is caused by the primary modes of fuel electrode catalyst coarsening and Cr poisoning on air electrode catalyst, and secondary modes of metal support oxidation and local elemental accumulation of Ni. In an effort to suppress Cr migration thereby improving long term durability, advanced coatings, such as CoOx, NiFe2O4, (Co,Mn)3O4, etc., are applied to the cathode-side support by atomic layer deposition or electrodeposition. The impact of coating composition and deposition method will be reported.

Figure 1. Durability of the cell with LSCF-SDC air electrode catalysts at constant current of 0.33 A cm-2 and 700 °C, with 50 vol% H2-50 vol% H2O.

Figure 1
Ammonia As an Energy Vector
Authors: Soloveichik Grigorii L.
Published: December 2020

The Advanced Research Projects Agency (ARPA-E) funds high risk, high reward transformational research to reduce energy related emissions, reduce imports of energy from foreign sources, improve energy efficiency across all economic sectors, and ensure US technological lead in advanced energy technologies, including electrochemical technologies for energy transformation and storage for distributed, grid scale and automotive applications.

Ammonia is produced at a scale of about 180 million tons per year and is easily stored and transported. Currently it is mostly used as a fertilizer and a feedstock for production of various chemicals. However, its physical properties, high energy density, the absence of carbon emissions, availability of feedstock (air and water), and well developed synthesis and infrastructure make ammonia almost ideal energy vector. Produced using renewable energy, it can be used for long duration energy storage and as a zero-emission transportation fuel as well as a hydrogen carrier. To address these technological challenges, ARPA-E launched the Renewable Electricity to Fuels through Utilization of Energy-dense Liquids (REFUEL) program. This program and, in part, OPEN program fund the development of transformational technologies for the conversion of intermittent renewable energy, water and air to energy-dense carbon neutral liquid fuels including ammonia and their conversion to hydrogen or back to electricity using fuel cells. All these directions will be covered in the presentation with emphasis on ammonia fuel cells.

Fuel cells provide the most efficient conversion of ammonia to electricity. Indirect fueling includes the intermediate ammonia cracking to hydrogen (Industrial process runs at 850oC but temperature could be substantially lower with advanced catalysts), which can be purified to PEM fuel cell grade. Direct fueling requires less capital expenses, and can be used with different types of fuel cells (SOFC, PCFC, AEMFC and molten carbonate fuel cells). Performance of direct ammonia fuel cells (DAFC) was demonstrated to be very close to the performance of the same cells fueled by hydrogen (with correction for the dilution). Issues of crossover (for polymer membranes), electrocatalyst stability (nitridation), cell architecture, and operation parameters will be discussed.

Recent advances in the development of novel DAFCs that is being funded by ARPA-E via REFUEL and OPEN 2018 programs will be presented. Comparison of DAFCs with combustion engines fueled by ammonia for energy applications will be given.
Unbiased Identification of Optimal Chemical Pathways in Electrochemical Reaction Cascades
Authors: Blau Samuel M , Dwaraknath Shyam , Spotte-Smith Evan Walter Clark , Persson Kristin A.
Published: December 2020

Electrochemically-driven reaction cascades are responsible for solid-electrolyte-interphase (SEI) formation in metal-ion batteries and anolyte/catholyte degradation in flow batteries, critically controlling stability and lifetimes of energy storage systems. However, the reactive complexity and long timescales involved in such processes limit the insight that can be obtained experimentally or from atomistic simulations like classical or ab initio molecular dynamics. To avoid the limitations of atomistic dynamics, we aim to construct a chemical reaction network (CRN) which includes all possible species and reactions that may participate in SEI formation. Such a CRN could identify the collection of reaction pathways that control the growth of the SEI, a key step towards engineering functional electrochemical reactivity.

Utilizing our novel computational infrastructure that enables accurate and high-throughput simulations of electrochemically-relevant species, we performed over 20,000 density functional theory calculations in order to construct a CRN characterizing SEI formation, which includes more than 8,000 species and 100,000 reactions. To our knowledge, the resulting reaction network is over five times larger and includes substantially more complex chemistry than any previously reported CRN.

However, the size and complexity of our network necessitates a novel approach to identify optimal reaction paths. We therefore developed an improved graph representation of multi-reactant reactions such that optimized pathfinding algorithms can be applied to general reaction networks for the first time. This allowed us to identify the optimal chemical pathways involved in the formation of a key Li-ion SEI product in an automated and unbiased fashion. Our approach can be readily applied to modeling other critical reaction pathways in any electrochemical system, from redox flow batteries and fuel cells to electrocatalytic processes.
Multielectron Bifunctional Systems for Symmetric Nonaqueous Redox Flow Batteries
Authors: Porath Anthony , Cook Korey , Duda Addison , Dan Adina , Guarr Thomas F. , Hoekstra Elizabeth
Published: December 2020

The introduction of renewable energy generation sources onto the electrical grid is critically dependent on the development of reliable, inexpensive energy storage technology. Redox flow batteries (RFBs) may offer a solution, but many issues remain. For example, aqueous systems are limited in cell voltage owing to the accessible potential window of water. While other electrochemically useful solvents could provide a larger window, their cost and durability have been problematic. Moreover, the need for an ion-exchange membrane to prevent crossover further increases cost and adds significant cell resistance, especially in nonaqueous systems.

We have previously reported the use of linked electron donor/acceptor D-L-A or D-L-A-L-D compounds (where L represents a simple alkyl or aryl linker) to allow the replacement of the expensive ion-exchange membrane with a simple porous separator. Such systems have at least three accessible stable redox states: the “parent” D-L-A state, an oxidized form D+-L-A (catholyte), and a reduced form D-L-A-
(anolyte).

Numerous systems of this type have now been prepared and characterized, yielding nominal cell potentials over 2 V, with promising stability. Several of these systems have the capability of undergoing a net 2e- oxidation as well as a net 2e- reduction, allowing for increased energy density. One such compound is shown below.

The electrochemical properties of several representative linked electron donor/acceptor materials will be described, including progress toward the development of a 4e- system having 9 (nine!) accessible stable redox states. Preliminary data from a prototype RFB device employing such compounds as active materials will also be presented.

Figure 1
Full Spectrum Phosphors for White LEDs and Virtual Windows for Light and Health Applications
Authors: Dutta Partha S.
Published: December 2020

Light and health is a topic of significant importance and requires fundamental studies of human interactions with light. This talk will present a review of some of the on-going studies on light and health by holistically exposing the humans to the outdoor conditions, while they are confined in indoor spaces. The designs of a new lighting-display fusion system along with examples of emerging commercial products will be discussed. Full spectrum lighting is a critical component of such systems. Results of phosphor blends based on well known thiogallates and sulfide phosphors for designing full spectrum lighting that could replicate sunlight quality will be presented. The synchronous modulation of phosphor based full spectrum light sources with electronic display playing real time outdoor videos creates a new tool for systematically studying the cognitive psycho-physiological health of human beings under different environmental conditions.
A Comparatitive Study on Photoluminescence and Color Propertites between Amorphous and Crystalline Organic-Inorganic Hybrids As Single-Phased and Single-Phased Phosphor for White-Light Emission
Authors: Guo Gong-Yi , Chen Yu-Li
Published: December 2020

We have examined some zirconium organic complexes via an array of characterization techniques, showing that they are amorphous single-phased and single-doped phosphors for white-light emission. Combined with thermogravimetric measurement coupled with a quadrupole mass spectrometer, and inductively coupled plasma-atomic emission spectroscopy and/or mass spectrometry measurements, the detailed infrared spectroscopy analyses indicate that the amorphous phosphor is a sulphur species-doped zirconium oxy-hydroxyl acetate complex.The phosphors exhibit the photoluminescence and color properties comparable to or better than those of the crystalline metal-organic frameworks (MOFs). or organic-inorganic hybrid semiconductors for white-light emission.
Revisiting the Theory of Vibronic Transitions of Optical Ions in Solids
Authors: Mishra Kailash C , Collins John
Published: December 2020

In order to improve the performance of phosphors in lighting and display devices, one needs to understand the temperature dependence of the radiative and nonradiative processes of optical ions in solids. In this presentation, we have revisited the theory of radiative transitions from an excited state of a polyatomic system within the framework of the proper adiabatic theory. First the transition rate for spontaneous emission from an excited state to the ground state has been derived rigorously using the methods of molecular quantum electrodynamics. It is assumed that this transition is associated with a loss of energy through the creation of p phonons in the system. It will be shown for the first time in a rigorous manner that only limited number of vibrational modes for which the Huang-Rhys parameter, s, is nonzero will participate. These modes will be identified as the active modes. Other modes will be completely passive during the relaxation process. It is speculated that these active modes are the local vibrational modes, and can be identified from the vibronic spectra of rare earth ions, particularly at low temperature. Based on the present formulation of the problem, the band shape function, W(p,T), will be derived. This band shape function will be used to interpret available vibronic spectra for some optical ions at low temperature.
First-Principles Study of the Crystal-Field and Racah Parameters of Cr3+ in Alumina
Authors: Ogasawara Kazuyoshi , Mishra Kailash C , Collins John
Published: December 2020

The development of blue LEDs [1] enabled one to construct white LEDs by combining them with appropriate phosphors. Recently Mn4+-doped fluorides have been put into commercial use as the red phosphors for high color-rendering white LEDs [2]. However, in order to suppress the degradation due to high humidity and high temperature, a special surface treatment is required for these phosphors. Therefore, the search of other red phosphors activated by Mn4+ is still desired. For theoretical design of novel phosphors, non-empirical prediction of optical parameters such as the crystal-field and Racah parameters is quite important. The purpose of this study is to establish a first-principles approach to predict these parameters of transition metal ions in crystals.

In this work, the crystal-field and Racah parameters of ruby (Cr3+ doped α-Al2O3) were evaluated based on the first-principles calculations using the relationship between the ligand-field theory and the molecular orbital (MO) theory derived by Sambe and Felton [3]. Two types of first-principles methods were adopted. One is the discrete-variational (DV)-Xα method [4], which is an MO calculation method based on the one-electron approximation. The other is the discrete variational multi-electron (DVME) method [5], which is a configuration-interaction (CI) calculation method based on the explicit many-electron wave functions. The estimation of the crystal-field and Racah parameters were performed in the following three approaches.

(1) Estimation based only on the DV-Xα method

(2) Estimation based only on the DVME method

(3) Estimation based on the combination of the DVME method and the DV-Xα method

The results show that the values of the crystal-field and Racah parameters obtained by the approach (3) are in the best agreement with the values obtained by fitting to the experimental data [6], indicating that CI calculations using some corrections based on the one-electron MO calculations are effective for the non-empirical estimation of the crystal-field and Racah parameters [7]. These results also provide theoretical basis for the configuration-dependent correction and the correlation correction introduced in our previous CI calculations of ruby [5]. This approach could be applied to prediction of d-d transitions of Mn4+ in crystals to find a suitable host for novel Mn4+-activated red phosphors for white LEDs.

[1] I. Akasaki and H. Amano, Jpn. J. Appl. Phys. 45, 9001 (2006).

[2] J. E. Murphy, F. Garcia-Santamaria, A. A. Setlur, and S. Sista, SID 2015 DIGEST, 927 (2015).

[3] H. Sambe and R. Felton, Int. J. Quant. Chem., 10, 155 (1976).

[4] H. Adachi, M. Tsukada, and C. Satoko, J. Phys. Soc. Jpn. 45, 875 (1978).

[5] K. Ogasawara T. Ishii, I. Tanaka, and H. Adachi, Phys. Rev. B 61, 143 (2000).

[6] W. M. Fairbank, Jr., G. K. Klauminzer, and A. L. Schawlow, Phys. Rev. B 11, 60 (1975).

[7] K. Ogasawara, K.C. Mishra, and J. Collins, ECS J. Solid State Sci. Technol. 9, 016011 (2020).
Passivation to Improve the Efficiency and Reliability of III-Nitride Micro-Light-Emitting Diode
Authors: Lee Da , Seong Tae-Yeon , Amano Hiroshi
Published: December 2020

Because group III-V and nitride-based micro light-emitting diodes (micro-LEDs) exhibit excellent performance, such as fast response, low power consumption, and thermal stability, they have been widely applied for display and biomedical applications, including optogenetics and multi-site neuron. However, unlike conventional LEDs (> 300 × 300 µm2), micro-LEDs (> 100 × 100 µm2) suffer from severe Shockley Read-Hall (SRH) non-radiative recombination, which is related to sidewall damage introduced by ICP-RIE dry-etching process for LED isolation. As the size of LEDs decreases, such non-radiative recombination phenomenon increases due to the increase in the sidewall surface ratio. Many attempts have been made to improve such defect-related recombination in micro-LEDs. In other words, sidewall passivation using dielectric materials was reported to be effective in alleviation sidewall-related leakage characteristics.

In this study, we investigated the electrical and optical properties of GaN-based micro-LEDs (blue) as a function of the number of passivation layers. The passivation layers were deposited using plasma enhanced chemical vapor deposition (PECVD) or/and atomic layer deposition (ALD). It is shown that by employing combined deposition techniques of ALD and PECVD, the optical and electric performance of 10 µm-size micro-LEDs are significantly improved. Compared with the conventional PECVD passivation method, the combined ALD/PECVD passivation showed the smaller ideality factor. For the 10 µm-size micro-LEDs, maximum external quantum efficiency (EQE) was obtained at 35 A/cm2 when the stacked ALD/PECVD passivation layer was used, whereas it was attained at 79 A/cm2 when the PECVD passivation was used. Based on the emission microscopy results, leakage paths were observed. The results show that the use of stacked ALD/PECVD passivation layer could serve as a potentially important process for the fabrication of high-performance micro-LEDs (< 10 × 10 µm2).
Electro-Oxidation of Oligosaccharides
Authors: Neha Neha , Coutanceau Christophe , Baranton Stève
Published: December 2020

Keywords: electrocatalytic oxidation, glucose, methylglucoside, cellobiose, trehalose, electrolysis, platinum, bismuth, selectivity

Different catalysts (Pt/C, Pt9Bi1/C, Pt9Sn1/C, Pt7Ni3/C, Pt7Sn3/C and Pd3Au7/C) have been synthesized by a “water in oil” micro-emulsion method with nominal metal loading of 40 wt% and further characterised by physicochemical methods: thermogravimetric analysis, transmission electron microscopy, X-Ray diffraction, etc., to assess the metal loading, composition and size of nanoparticles. Linear scan voltammograms (Fig.1) have been performed to study the electrocatalytic behaviour of the catalysts towards electro-oxidation of glucose, methylglucoside, cellobiose and trehalose in 0.1 M NaOH as background electrolyte at 0.05 V s-1 scan rate. Pt9Bi1/C, most active one, leads to the lowest onset potentials of ca. 0.050 V, 0.100 V, 0.050 V and 0.200 V vs RHE for glucose, methylglucoside, cellobiose and trehalose oxidation respectively. To further gain an insight about the mechanism and species formed, in situ Fourier transform infrared spectroscopy has been used which demonstrated that in the case of glucose and methylglucoside oxidation, different reaction products were formed, i.e. gluconate and methyglucuronate, respectively1. In the case of cellobiose, a reducing disaccharide, transformation of C1 anomeric function to carboxylic acid occurred, while in the case of trehalose, a non-reducing disaccharide, mono and dicarboxylic acids were formed from C6 oxidation.

Chronoamperometry measurements were carried out for 6 hours in a 25 cm2 electrolysis cell with Pt9Bi1/C as anode catalyst for the electro-oxidation of 0.1 M glucose, methylglucoside, cellobiose and trehalose and Pt/C as cathode catalyst with simultaneous production of hydrogen at different potentials. The reaction products formed every hour for 6 hours were neutralized, identified and quantified by HPLC, MS and 1H and 13C NMR. At low cell voltages, high selectivity and significant conversion yields to monocarboxylic acids of these saccharides were obtained.

Acknowledgements: the authors gratefully acknowledge the INCREASE Federation (FR CNRS 3707), the technogreen chair, the European communities (FEDER) through the ECONAT project, the “Région Nouvelle Aquitaine” and the PEPS CNRS Energie for financial supports.

N. Neha, S. R. B. Kouamé, T. Rafaïdeen, S. Baranton, C. Coutanceau. Remarkably Efficient Carbon-Supported Nanostructured Platinum-Bismuth Catalysts for the Selective Electrooxidation of Glucose and Methyl-glucoside, Electrocatalysis (2020) DOI : 10.1007/s12678-020-00586-y.

Figure 1
Use of TiO2-WO3 architecture for Photoelectrochemical Alcohol Oxidation
Authors: Hosseini Seyyedamirhossein , Peters Dennis G
Published: December 2020

Ethanol, the major component of biofuel mixture, has significantly lower heat capacity compared to that of longer-chain alcohols such as butanol. As a result, oligomerization of ethanol has gained much attention. A three-step process that includes transition metal catalyzed C-alkylation was proposed for alcohol oligomerization. This cycle includes: (I) alcohol oxidation to the corresponding carboxylic acid, (II) dimerization via carboxylic acid terminals, and (III) further reduction of the oligomer to form the saturated alcohol. In this context, TEMPO has been vastly utilized for the electrochemical oxidation of alcohols. This process suffers from shortcomings such as limited turnover frequency of the reagent and small conversion yield of the synthesis. There have been some reports on the application of semiconductor electrodes for oxidizing certain types of alcohols. This approach, however, has shown some pitfalls such as high oxidation overpotential, low reaction yield, and low stability of the working electrode.

The goal of this research is to fabricate a novel photoanode for oxidizing alcohols to their corresponding carboxylic acids. In this work, we aimed at fabricating an architecture shown in Fig. 1. To prepare such an electrode, a 10 nm layer of Ti was first deposited over fused silica substrate via thermal deposition method. Then, TiO2 with thickness of 500-µm was deposited with application of sol-gel technique, and finally WO3 was loaded onto the TiO2 with application of controlled-potential pulse deposition. Our experimental results have shown that this electrode have great stability toward photoelectron corrosion and the yield of conversion is the function of the deposited tungsten oxide.

Figure 1
(Invited) Toward Automated Electrochemical Assembly of Oligosaccharides
Authors: Nokami Toshiki
Published: December 2020

In April 1999 I joined the Yoshida group as a graduate student. I was deeply impressed that a variety of projects including flow and automated electrochemistry were in progress at the same time. I learned so many things during my master and PhD program in his group. After one year postdoc in Switzerland I came back to his group as an Assistant Professor and started to involve in organic electrochemistry. Electrochemical methods have been powerful tools for making oligosaccharides in efficient and automated manner. Not only linear oligosaccharides but also cyclic oligosaccharides have been synthesized by electrochemical methods. Oxidation potentials have been quite useful parameters to evaluate reactivity of carbohydrate building blocks. I would like to introduce some recent examples of electrochemical synthesis of oligosaccharides. This paper is dedicated to late Professor Jun-ichi Yoshida.
Chemical Hydrogenations Using an Electro-Generated Mediator
Authors: Symes Mark
Published: December 2020

The Electron-Coupled-Proton Buffer (see: Nature Chem.
2013, 5, 403-409; Nature Chem.
2018, 10, 1042-1047; Joule, 2018, 2, 1390-1395) permits the electrochemical oxygen evolution reaction from water to be coupled to the reversible reduction and protonation of a redox mediator (rather than the coupling of the oxygen evolution reaction directly with hydrogen production). Careful selection of this redox mediator, along with judicious choice of the electrode material for the cathode reaction, can allow reduced species to be generated that are thermodynamically unstable with respect to hydrogen generation (Science,
2014, 345, 1326-1330). These reduced mediators can either be used for spontaneous hydrogen generation (decoupled from the oxygen evolution step), or they can be used as soluble sources of hydrogen for performing the hydrogenation of organic molecules (Chem. Commun.
2018, 54, 1093-1096). In this talk, we such discuss current progress and potential future avenues for the use of Electron-Coupled-Proton Buffers as reducing equivalents in organic synthesis.
Exploring the Synergistic Relationship between Organic Synthesis and Electrochemistry
Authors: Jing Qiwei , Moeller Kevin D
Published: December 2020

Electrochemistry has long held potential as a tool for constructing organic molecules, and the organic chemistry community is both recognizing and impressively exploiting that potential with increasing regularity. Those efforts have taught us a great deal about how to think about electrochemical reactions, how to use the technique to accomplish new transformations that enrich the synthetic enterprise, and when to employ those methods.

Interestingly, the relationship between organic synthesis and electrochemistry can also be viewed in the opposite direction with the new synthetic chemistry being developed serving as a tool to facilitate and dramatically expand the scope of electrochemical methods. For example, new synthetic chemistry that allows for the site-selective generation of chemical reagents on an array have enabled the construction of complex, addressable molecular surfaces that can in turn be used to probe small molecule interactions with a variety of biological targets. The efforts set the stage for using microelectrode arrays as analytical devices for rapidly screening small molecule libraries in "real-time". The methods allow for the construction of libraries with tunable surfaces, careful control of surface concentrations, and previously unknown levels of quality control over the molecular library. The development of an even greater arsenal of synthetic tools for use on the arrays is underway, an effort that aims to expand the nature and size of the addressable libraries that can be used to probe the world around us.

Not surprisingly, the exploration of these new electrochemical tools is beginning to “give back” to the synthetic arena. A number of preparative scale synthetic applications have now arisen based on the concept of site-selective reagent generation. Chief among these is the use of paired electrochemical reactions for more sustainable reagent generation and the recent discovery that chemical reagents can be confined to specific regions within a preparative reaction; a development that potentially offers a new strategy for controlling the selectivity of a chemical reaction.

In the talk to be given, the interplay between organic synthesis and electrochemistry will be highlighted with a particular emphasis on how the interplay is shaping new avenues of research moving forward.

References:

For reviews see Moeller, K. D. Chem. Rev.
2018, 118, 4817-4833 and Jing, Q; Moeller, K. D. Accounts of Chem. Res.
2020,
53, 135-143.
(Invited) Electrochemical Dehydrogenative Cyclization Using a Halogen Mediator for the Synthesis of Thienoacene Derivatives
Authors: Suga Seiji , Mitsudo Koichi , Yonezawa Toki , Matsuo Ren
Published: December 2020

The formation of carbon–sulfur bond is one of the fundamental and important transformations in organic synthesis because C–S bonds are abundant and important skeleton in the field of pharmaceuticals and material science. For example, the antidepressant vortioxetine, and an antifungal medication sertaconazole are useful medicines. π-Expanded benzo[b]thiophene derivatives, such as [1]benzothieno[3,2-b][1]benzothiophene (BTBT) and dinaphtho[2,3-b:2’,3’-d]thiophene (DNT), have received considerable attention as key building blocks for use in organic field effect transistors.

The electrochemical carbon–heteroatom bond formation is known to be as an environmentally benign strategy that proceeds under mild conditions. Recently, several novel electrochemical carbon–heteroatom coupling reactions, such as those for C–N and C–O, have been reported. For instance, Lin and co-workers reported the 1,2-diazidation of alkenes, and Baran reported electrochemical allylic oxidations. Lei reported electro-oxidative intermolecular C–S bond formation via C–H/S–H bond cleavage. Intramolecular dehydrogenative coupling between an arene and a thiocarbonyl group was also effective for constructing C–S bonds. While electrochemical transformations have been studied intensively, to the best of our knowledge, there has been no report on electrochemical carbon–heteroatom bond formation for the construction of π-expanded thienoacene derivatives, which are potent candidates for useful organic materials.

From this perspective, we are focusing on an electrochemical C–S bonds formation for the synthesis of thienoacene derivatives, such as [1]benzothieno[3,2-b]benzo[2,3-d]furan (BTBF) and [1]benzothieno[3,2-b]benzo[2,3-d]thiophene (BTBT). We first assumed that intramolecular dehydrogenative C–H/S–H coupling of 2-arylbenzene-1-thiol would form π-expanded thiophenes, but the desired product was not obtained. During the course of further study, we found that the desired dehydrogenative C–S bond formation proceeded smoothly in the presence of electrogenerated [Br+] as a promoter. This strategy was effective for the synthesis of π-expanded thienoacenes such as BTBF and BTBT. We report here the first electro-oxidative dehydrogenative C–S bond formation promoted by electrogenerated [Br+] for the synthesis of BTBFs and BTBTs.

[1] Koichi Mitsudo, Ren Matsuo, Toki Yonezawa, Haruka Inoue, Hiroki Mandai, Seiji Suga, Angew. Chem., Int. Ed.
2020, 59, 7803–7807.

Figure 1
Realtime Transepithelial/Endothelial Electrical Resistance Measurements in Multiple Transwell Culture Inserts
Authors: Kaji Hirokazu , Raut Bibek , Hori Takeshi
Published: December 2020

Epithelial and endothelial cells line the surface of the body. Adjacent cells of both epithelial and endothelial cells are connected to each other via intercellular junction called tight junction that regulates the diffusion of molecules and ions between the apical and basolateral side of the body. Quantification of this barrier is important to evaluate the suitability of in vitro cellular barrier models for drug toxicity or transport studies. Transepithelial/endothelial electrical resistance (TEER), a quantitative technique to access electrical resistance of the cellular monolayer during culture has become one of the most popular quantitative techniques to evaluate the integrity of tight junction. The major advantage of the TEER technique over traditional permeability measurements is that it is quick, label-free, and non-invasive. As such, the TEER technique has been widely used to evaluate in vitro models such as the blood-brain barrier, the intestine epithelial barrier, the alveolar epithelial barrier, and the blood-retina barrier.

However, the reported normalized TEER values of a specific cell type in transwell inserts are inconsistent between different research groups. A major cause of data variation is the manual technique that is used for measuring TEER. Typically, a “chopstick” like electrode pair is immersed inside a cell cultured semi-porous transwell insert membrane to measure TEER. Due to the variation in the alignment of the electrodes every time a TEER value is measured, the actual values vary significantly between measurements. A second problem with the conventional manual measurement process is time gap between each measurement (typically 12h or 24h) since a more frequent measurement requires frequent opening and closing of cell culture incubator door that can disturb the cells and introduce potential contamination.

Thus, to enable consistency in TEER measurement, and allow automated real-time data acquisition in multiple samples, we built an add-on device (used atop EVOM®, a commercially available TEER instrument) consisting of a 3D printed electrode holder, a temperature sensor, and a custom designed data logger. The 3D printed electrode holder allowed data variation to be minimized by allowing perfect alignment of electrodes during measurement. The real-time data acquisition and in-situ temperature measurement allowed detection and correction of data offset during medium replacement process. The concept and device demonstration presented here should enable research labs to minimize data variations allowing them to produce consistent TEER results without having to spend extra time manually measuring multiple samples.