bluuebunny/crossref_metadata_2025_split huggingface dataset:
Insight into Oxygen Evolution Reaction Kinetics from Gas Fed Polymer Electrolyte Water Electrolysis
Authors: Schuler Tobias , Kimura Taro , Schmidt Thomas J. , Büchi Felix N 
Published: February 2020

In polymer electrolyte water electrolysis (PEWE) oxygen evolution reaction (OER) kinetics are a major efficiency limitation. At least with thin membranes, the anode kinetic overvoltage is the main voltage loss. The reaction mechanism for IrO2 in the most stable surface (110) configuration in acid environment was investigated by DFT calculation in literature and postulated according to reactions R1 to R4 [1]. The concept of gas feed electrolysis enables the identification of the rate determining step in the OER mechanism by using the additional freedom of water concentration variation. Therefore the activity of water was varied between 0.6 to 0.95 at 80°C. The determined reaction order is compared to proposed reaction mechanisms in literature.
The used materials were validated by determination of the IrO2 activity as function of the loading. CCMs were prepared by automated spray coating process using IrO2/TiO2 catalyst. The loadings were varied from 1mg/cm2 to 3mg/cm2. In analogy to liquid PEWE, the CCMs were tested in cell configuration by using commercial Ti sinter based porous transport layers. The loading trends of exchange current densities estimated from Tafel fitting were compared to specific capacity determined by cyclic voltammetry at 1.0V. The linear dependence of specific capacity with loading exemplifies a constant roughness factor as shown in Figure 1. The catalyst layer utilization doesn’t show any impact on loading/catalyst layer thickness.
Reference
[1] J. Rossmeisl, Z.W. Qu, H. Zhu, G.J. Kroes, J.K. Nørskov, Electrolysis of water on oxide surfaces, J. Electroanal. Chem., 607 (2007) 83-89.

Figure 1
Development and Evaluation of Ir Based Anode Electrocatalysts for Water Electrolysis
Authors: Muto Marika , Nagayama Mayumi , Sasaki Kazunari , Hayashi Akari 
Published: February 2020

Introduction

Hydrogen production through PEM type water electrolysis followed by hydrogen storage and use has been focused on as one of the efficient uses of renewable energy. Although PEM type water electrolyzer has an advantage on reduced ohmic resistance between two electrodes, it has also a disadvantage that common carbon supports cannot be used in order to disperse small catalyst particles under the high potential condition over 1.5 V at the anode. That leads to low active surface area of anode electrocatalysts, resulting in high cost. Therefore, the purpose of this study is to develop carbon-free porous anode electrocatalysts with high active surface area. So far, our group has been working on mesoporous carbon materials for PEFC studies1, and we have found that such a porous structure is kept even after being built into the device and can improve the mass transfer within catalyst layers. Then, basic concepts of mesoporous carbon are applied to this study. We propose development of carbon-free porous metal catalysts to enhance the performance of water electrolyzer.

Experimental method

Ir(acac)3 and Pluronic F127 were used as a metal precursor and a template to form a porous structure, respectively. A mixture of the metal precursor, solvent, and surfactant was heated up by step-by-step treatments in N2 or Air atmosphere to make the porous structure. After the fundamental material characterizations of the resulting Ir material, electrochemical measurements were performed using a common half-cell setup in the acidic solution. Oxygen evolution reaction (OER) activity was evaluated as anode electrocatalysts. Also, membrane electrode assembles (MEAs) were developed, and then a single cell performance was evaluated.

Results and discussion

Based on nitrogen sorption measurements and a SEM image as shown in Figure 1, the porous structure consisted by aggregation of particles was confirmed for the obtained Ir material. The resulting pore diameter was mostly smaller than 70 nm. When OER activity of porous Ir material was measured and compared with commercial IrO2 electrocatalyst (Figure 2), initial OER activity was lower than IrO2. This was due to fact that porous Ir material is mainly composed by Ir metal, which was confirmed by XRD. Then, the surface of porous Ir was activated via electrochemical oxidation. As a result, activated porous Ir/IrOx showed equivalent OER activity to commercial IrO2 as seen in Figure 2. Even though OER activity was just equivalent to commercial IrO2 as powder, the difference was seen when electrocatalysts were built into MEAs. The details of IV characteristics will be discussed. Furthermore, we have also worked on durability analyses against potential fluctuation derived by renewal energy, which will be also discussed.
Reference
(1) Hayashi, et al., Electrochim. Acta,
53, 6117-6125 (2008).

Figure 1
Surfactant-Free Preparation of Ir Based Oer Catalysts in Low Boiling Point Solvents and Their Catalytic Evaluation
Authors: Bizzotto Francesco , Quinson Jonathan , Bucher Jan , Zana Alessandro , Kunz Sebastian , Arenz Matthias 
Published: February 2020

We introduce a simple and scalable preparation method for colloidal precious metal nanoparticles (NPs) that overcomes the typical restrictions in catalyst synthesis, i.e. the independent control of individual parameters such as size, size-distribution, and particle density (metal loading). Our Co4Cat (Colloids for Catalysts) synthesis concept uses alkaline low-boiling point solvents without the use of additional surfactants. It can be applied to different mono- and multimetallic precious metal NPs as well as different support types. In the presented work, the Co4Cat concept is used to prepare Ir based NPs that are tested as oxygen evolution reaction (OER) catalysts for water electrolysis under acidic conditions. In electrochemical half-cell tests, it is shown that due to the very high surface area, exceptional mass activities can be achieved.
The Co4Cat concept is an advancement of our “toolbox” synthesis approach that was previously applied to Pt based PEM fuel cell catalysts. In the presentation, the general idea as well as the individual synthesis steps are discussed in detail and the electrochemical testing is benchmarked against literature values as well as commercially available OER catalysts.
Frequency-Resolved Evaluation of Electrode Oxidation State in La0.6Sr0.4CoO3 Thin Films with Operando XAS
Authors: Gerwe Brian S , Mizuno Keita , Sekizawa Oki , Nitta Kiyofumi , Amezawa Koji , Adler Stuart B. 
Published: February 2020

Commercial adoption and implementation of renewable, but intermittent, energy sources relies on a new generation of high-performance energy conversion and storage devices, such as solid oxide fuel cells (SOFC) and solid oxide electrolysis cells (SOEC). Performance of the oxygen electrode in SOFC is a limiting factor; however, improvements are hindered by inadequate understanding of electrochemical reaction and ionic diffusion processes. AC impedance and DC polarization techniques are typically used to infer relationships between driving energy and reaction rate, but uniquely understanding reaction mechanisms without direct chemical state measurements of the electrode is challenging.
In recent years, workers have developed in operando X-ray absorption spectroscopy (XAS) to study oxygen chemical potentials in SOFC cathodes under operating temperatures and Po2. Determining the oxygen chemical potential is based on shifts in the X-ray absorption edge of 3d transition metals due to valence changes to compensate for oxygen vacancies. So far, operando XAS has only been measured under DC polarization, and thus lacked the ability to probe processes of different timescales [1]. In this work, we extend operando XAS to AC impedance measurements, allowing direct frequency-resolved measurement of electrode oxidation state. This approach can potentially be applied to nonlinear harmonic responses, and the first step in the spatially-resolved mapping of the local steady-periodic electrode response.
A dense film of La0.6Sr0.4CoO3 (LSC) was deposited on a mirror polished Gd-doped ceria pellet by pulsed laser deposition as the working electrode with porous Pt counter and reference electrodes. Absorption spectra of the Co K-­edge were collected from fluorescent X-rays to determine the detection energy most sensitive to changes in Co valence state. Operando XAS measurements were conducted at 973 K in 10% O2 at the predetermined X-ray energy, typically around 7.718 keV, under electrical perturbations large enough to excite moderate nonlinearity.
The frequency resolved oxidation state response of the electrode is obtained by converting X-ray absorption data to oxygen chemical potentials via sets of calibration XAS spectra at various effective Po2. As a result, the data can be treated by the same analysis methods developed for the voltage response in AC impedance measurements.

References

[1] Y. Orikasa, T. Ina, K. Yamamoto, T. Nakao, et al., Electrochemistry
82(10), 897-900 (2014)
(Invited) Expansion in proton-Conducting Ceramic Based Devices
Authors: Ricote Sandrine , Dubois Alexis , Taghikhani Kasra , Braun Robert J. , Berger John , Kee Robert J. 
Published: February 2020

High temperature proton conductors such as barium zirconate/cerate (BaCexZr0.9-xY0.1O3- δ referred to as BCZY) have become increasingly more popular, with a large number of potential applications including protonic ceramic fuel/electrolysis cells (PCFC/PCEC) and membrane reactors for steam methane reforming, methane dehydroaromatization or ammonia synthesis. It was also demonstrated that PCFCs can operate with high efficiency while remaining cost competitive in the temperature range 500-600 °C compared to traditional solid oxide fuel cells at 800 °C [1].
Contrary to traditional oxygen ion conductors (such as yttria stabilized zirconia) that display only thermal expansion, chemical expansion is also present in high temperature proton conductors upon hydration (equation 1) where protonic defects are incorporated into the oxygen sublattice [2-4].
(1) H2O (g) + OO
x + VO°° ↔ 2 OHO°
First, techniques for thermal and chemical expansion measurements will be presented together with the analysis/interpretation challenges. Then, an overview of the literature data on the expansion in high temperature proton conductors will be provided. While all these measurements are performed in a single atmosphere, it is important to be able to predict the expansion with different gas compositions on both sides of the membrane to mimic a real device application. To do so, we developed a computational model based on a Nernst-Planck-Poisson formulation and included a chemo-thermo-mechanical component. Defect concentrations and mobilities were taken from previous conductivity measurement modelling [5], whereas mechanical properties (Young modulus, Poisson ratios) were determined experimentally.
References:
[1] Dubois A., Ricote S., Braun R.J., Benchmarking the expected stack manufacturing cost of next generation, intermediate-temperature protonic ceramic fuel cells with solid oxide fuel cell technology. J. Power Sources 369 (2017) 65-77.
[2] Andersson A.K.E., Selbach S.M., Knee C.S., Grande T., Chemical expansion due to hydration of proton-conducting perovskite oxide ceramics. J. Am. Cream. Soc. 97 (2014) 2654-2661.
[3] Hiraiwa C., Han D., Kuramitsu A., Kuwabara A., Takeuchi H., Majima M., Uda T., Chemical expansion and change in lattice constant of Y-Doped BaZrO3 by hydration/dehydration reaction and final heat-treating temperature. J. Am. Cream. Soc. 96 (2013) 879-884.
[4] Hudish G., Manerbino A., Coors W.G., Ricote S., Chemical expansion in BaZr0.9− xCexY0.1O3−δ ( x = 0 and 0.2) upon hydration determined by high-temperature X-ray diffraction. J. Am. Ceram. Soc. 101 (2018) 1298-1309.
[5] Zhu H., Ricote S., Coors W.G., Kee R.J., Interpreting equilibrium-conductivity and conductivity-relaxation measurements to establish thermodynamic and transport properties for multiple charged defect conducting ceramics. Farad. Discuss. 182 (2015) 49-74.
Modeling of Temperature Distribution in a Proton-Conductive Ceramic Fuel Cell
Authors: Araki Takuto , Okuyama Yuji , Li Kunpeng , Toshiki Kawamura , Yamaguchi Toshiaki , Shimada Hiroyuki 
Published: February 2020

Proton-conductive Ceramic Fuel Cells (PCFCs) have potential to achieve higher energy efficiency compared with conventional SOFCs, since protons react with oxygen to generate water at cathode side and the fuel at anode side does not diluted. However, some part of generated electrons reacts with transferred electron holes, and the total numbers of electrons in external circuit decrease. The generation and extinction of holes result in loss of energy and excessive heat generation. Then, the hole current should be carefully examined and controlled.
The conductivity of holes strongly depending on local temperature, thickness of electrolyte, partial pressure of oxygen etc.. Therefore, for optimizing the performances of a given PCFCs, coupled analysis considering local temperature, partial pressures, ionic current density is mandatory. Especially, the temperature is one of the strongest factors of the conductivity. Then, the temperature distribution was discussed with results from coupled numerical model considering local temperature distributions, partial pressures, geometries of a cell, and overpotentials.

Figure 1
First-Principles Modelling of the Local Atomic and Electronic Structures of Luminescent Centers in Complicated Materials
Authors: Ma Chong-Geng 
Published: February 2020

In the last decades, the local coordination environments and valence states of luminescent centers in optical materials have been investigated mainly by using the combination of the spectroscopy techniques, such as the EPR or optical spectra, and the simple and qualitative theoretical models, such as the crystal-field theory (CFT) [1]. However, the reliability of the obtained local structures and oxidation numbers of doped optical centers is still questionable due to the empirical character of those models. Nowadays, the quick development of quantum chemistry theory for strongly-correlated d- and f-elements [2], together with an increase of the computational resources, has made it possible to quantitatively predict the structural and electronic properties of lanthanide- and transition metal(TM)- doped materials and further provide a deeper insight into the measured spectroscopic data.
In this talk, we will employ three typical examples to demonstrate how the first-principles calculations model the local structures and valence states of impurities in optical materials. First, the loss of the local inversion symmetry of Eu3+ ions doped in disordered compound Ca2La3Sb3O14 will be theoretically confirmed and the loss mechanism obtained here may be used for other systems as well to enhance spectral intensity for an improvement of characteristics of phosphor materials [3]. Second, the first-principles calculations of Cr-doped ZrSiO4 will show us the conversion mechanism from a pair of Cr4+ ions formally appearing in the chemistry concept to the combination of both Cr3+ and Cr5+ centers [4], which indicates the treatment of the valence states of TM ions should be so delicate as to need to be paid more attention. Third, a simple calculation scheme for the structural determination of the 5d lowest excited state of lanthanide ion is proposed and successfully applied to the case of Tb3+-doped Cs2NaYF6
[5]. In addition, a CFT-based methodology for solving the multiple minima problem in the HSE06 calculations of lanthanide-doped materials is suggested and applied to cubic elpasolites doped with Ln
3+ ions (Ln=Ce-Tm), and the calculation results present a good agreement with empirical “zigzag” model of Dorenbos [6].
References:
[1] N.M. Avram, and M.G. Brik, Optical Properties of 3d-Ions in Crystals: Spectroscopy and Crystal Field Analysis, Springer and Tsinghua University Press, 2013.
[2] R. Gillen, S.J. Clark, and J. Robertson, Phys. Rev. B
87 (2013) 125116.
[3] D.X. Liu, C.-G. Ma, P.W. Hu, Z. Li, Y. Tian, P. Su, M.G. Brik, A.M. Srivastava, and S. Tanabe, J. Am. Ceram. Soc. DOI: 10.1111/jace.15406, 2018.
[4] M. Gaft, G. Boulon, G. Panczer, Y. Guyot, R. Reisfeld, S. Votyakov, and G. Bulka, J. Lumin.
87-89 (2000) 1118.
[5] C.K. Duan, P.A. Tanner, A. Meijerink, and V. Makhov, J. Phys. Chem. A
115 (2011) 9188.
[6] P. Dorenbos, Phy
. Rev. B
85 (2012) 165107.
First-Principles Calculations of 4f-5d Transition Energy of Ce3+ in Y(Al1-xGax)5O12
Authors: Ogasawara Kazuyoshi 
Published: February 2020

The crystals doped with Ce3+ are utilized as various optical materials such as solid-state lasers, scintillators, and phosphors. Since the 4f-5d transition energy of Ce3+ in crystals strongly depends on the coordination environment, it is important to understand the relationship between the energy levels and the coordination environment for theoretical design of novel optical materials. For this purpose, garnet solid solutions are useful as host crystals since the physical properties can be modified by forming variety of solid-solutions through cation substitution. For example it is known that the 4f-5d transition energy of Ce3+ in Y(Al1-xGax)5O12 increases monotonically as x increases [1].
In this work, in order to investigate the relationship between the 4f-5d transition energy and the coordination environment of Ce3+ in Y(Al1-xGax)5O12, first-principles calculations were performed using the relativistic DV-Xα molecular orbital method [2]. At first YO8 clusters with D2 symmetry were constructed based on the crystal structure of Y(Al1-xGax)5O12 [3,4]. Then Ce was substituted for Y and the Ce-O bond lengths were adjusted based on the Shannon’s crystal radii [5] so as to consider the lattice relaxation effect [6]. In order to produce the effective Madelung potential, point charges were located at the atomic sites outside the cluster. As the exchange-correlation potential, the VWN potential [7] with the relativistic correction [8] was adopted. The 4f-5d transition energy was calculated using the Slater’s transition state method [9].
The calculated results showed that the variations of the average energy and the crystal field splitting of 5d levels of Ce3+ depending on x can be understood by the variations of the bond lengths, they are not monotonic. Although the 4f-5d transition energy is basically determined by these factors, interestingly the resultant theoretical 4f-5d transition energy showed monotonic variation. As a result the experimentally observed increasing tendency of the 4f-5d transition energy for increasing x was well reproduced.
[1] P. Dorenbos, J. Lumin., 134, 310 (2013).
[2] A. Rosén, D.E. Ellis, H. Adachi, and F.W. Averill, J. Chem. Phys., 65, 3629 (1976).
[3] A. Nakatsuka, A. Yoshiasa, and S. Takeno, Acta Crystallogr., B51, 737 (1995).
[4] A. Nakatsuka, A. Yoshiasa, and T. Yamanaka, Acta Crystallogr., B55, 266 (1999).
[5] R.D. Shannon, Acta Crystallogr.,
A32, 751 (1976).
[6] S. Watanabe, T. Ishii, K. Fujimura, and K. Ogasawara, J. Solid State Chem., 179, 2438 (2006).
[7] S. H. Vosko, L. Wilk, and M. Nusair, Can. J. Phys. 58, 1200 (1980).
[8] A. H. MacDonald and S. H. Vosko, J. Phys.
C12, 2977 (1979).
[9] J. C. Slater, Quantum Theory of Molecules and Solids (McGraw-Hill, New York, 1974), Vol. 4.
Luminescent Thermometry Using Mn4+ Doped Li2TiO3 Probe
Authors: Kuzman Sanja , Ristic Zoran , Milićević Bojana , Medic Mina , Djordjevic Vesna , Lukic Petrovic Svetlana R. , Dramicanin Miroslav 
Published: February 2020

Luminescent thermometry is extensively investigated because it provides sensitive contactless temperature measurments. This method is proposed for measurements at place which are difficult to access and in a nanoscale environments. Two types of self-referenced luminescent thermometry methods were commonly used: fluorescence intensity ratio method, and thermometry based on an emission decay times.
Titanates activated with transition metals have wide applications. In this paper we show that Mn4+ doped Li2TiO3 powder can be used for the luminescence thermometry. Here, we investigated possibility of using this material for the temperature determination from emission decays over the room temperature to 100 deg temperature range. Emission decay curves were measured at the strongest emission peak (680 nm). Data analysis showed that thermometry with this probe shows 3.8%/K relative sensitivity and superiour temperature resolution of 0.03 K over the complete temperature range.

Figure 1
Discovery of New Solid State Materials for Phosphors and Their Photoluminescence Tuning
Authors: Xia Zhiguo 
Published: February 2020

Understanding and exploring the structural design principles of the inorganic hosts are necessary for the discovery of novel phosphors for white LEDs. Our recent work focuses on the discovery of new phosphor materials based on the structural evolution and the crystallographci sites engineering. Firstly, photoluminescence tuning can be realized via the cation substitution on one site, and hereby we have discovered several types of M2SiO4-based and M3(PO4)2-based phosphors with tunable emission for white LEDs.1-2 Secondly, we have recently proposed the concept of “chemical unit cosubstitution” as one potential design scheme, and the chemical unit cosubstitution strategy is applied to the melilite structure class designing the Ca2(Al1−x
Mg
x
)(Al1−x
Si1+x
)O7:Eu2+ solid solution phosphor via the [Mg2+−Si4+] for [Al3+−Al3+] cosubstitution.3 We also design the La5Si3O12N phase from La5Si2BO13 via the [B3+−O2−] by the [Si4+−N3−] cosubstitution.4 Thirdly, we have proposed a new insight into the design of the isostructural phases via the filling of M+ in the void channels of the Mg2Al4Si5O18 phase, so that the charge balance can be kept while the chemical composition varied, and this strategy will be also efficient in other porous inorganic hosts.5 Finally, we have recently studied the NaScSi2O6-based phosphor from CaMgSi2O6-based phosphor via the chemical unit cosubstitution of [Na+–Sc3+] for [Ca2+-Mg2+] unit.6 Further studies show that the isostructural solid-solution of (CaMg)
x
(NaSc)1-x
Si2O6 (0 < x < 1) can be formed, in which cation nanosegregation enables the presence of dilute Eu2+ at two centers and their intensities are linearly proportional to x, so that it represents a new cation nanosegregation tuning of photoluminescence for the exploration of color-tunable phosphor for white LEDs.7-10

References:

[1] H. Ji, Z. Huang*, Z. Xia*, et. al., J. Phys. Chem. C, 2015, 119 2038.
[2] M. Chen, Z. Xia* M. Molokeev, Q. Liu, Inorg. Chem., 2015, 54, 11369.
[3] Z. Xia*, C. Ma*, M. Molokeev, K. R. Poeppelmeier*, et. al. J. Am. Chem. Soc., 2015, 137, 12494.
[4] Z. Xia*, M. Molokeev, W. B. Im*, S. Unithrattil, Q. Liu,
J. Phys. Chem. C, 2015, 119, 9488.
[5] J. Zhou, Z. Xia*, M. Chen, M. Molokeev, Q. Liu, Sci. Rep., 2015, 5, 12149.
[6] Z. Xia*, Y. Zhang, M. Molokeev, V. Atuchin, Y. Luo, Sci. Rep., 2013, 3, 3310.
[7] Z. Xia*, K. R. Poeppelmeier*, Acc. Chem. Res., 2017, 50, 1222.
[8] Z. Xia*, G. Liu*, K. R. Poeppelmeier*, et. al., J. Am. Chem. Soc., 2016, 138, 1158.
[9] Z. Xia*, and Q. L. Liu, Prog. Mater. Sci., 2016, 84, 59-118.
[10] Z. Xia*, and A. Meijerink*, Chem. Soc. Rev., 2017, 46, 275-299.