bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Chemical and Electrochemical Stability of Fast Lithium Ion Conducting Garnet-Type Metal Oxides in H2o, Aqueous Solution, CO2, Li and S
Authors: Thangadurai Venkataraman
Published: February 2020

Fast lithium ion conducting garnet-type metal oxides are promising electrolytes for next-generation all-solid-state Li batteries and beyond Li-ion intercalation batteries, including Li-air and Li-S.1 Li-stuffed garnets show high total Li-ion conductivity (> 10-4 S/cm at room temperature) and good chemical stability against reaction with elemental Li.2,3 In the presence of moisture and aqueous environments, lithium-stuffed garnets are known to undergo fast H+/Li+ exchange, 3 while they are known to react with carbon dioxide, forming Li2CO3, under ambient atmosphere.4 Li-stuffed garnets exhibit wide electrochemical stability window of 9 V vs. Li+/Li at room temperature.4 Li dendrite formation and high area specific resistance for the reaction are being addressed by surface modification.5,6 In this talk, an overview of the chemical and electrochemical stability of various lithium-based garnets, developed in authors’ group and also elsewhere, against moisture/humidity, carbon dioxide, sulfur, and metallic lithium will be discussed.4

References

A. Manthiram, X. Yu and S. Wang, Nat. Rev. Mater., 2, 16103 (2017).

V. Thangadurai, S. Narayanan and D. Pinzaru, Chem. Soc. Rev., 43, 4714 (2014).

K. Hofsetetter, A.J. Samson and V. Thangadurai, Solid State Ionics, 318, 71 (2018).

V. Thangadurai, K. Hofstetter, A.J. Samson and S. Narayanan, J. Power Sources, Submitted.

X. G. Han, Y. H. Gong, K. Fu, X. F. He, G. T. Hitz, J. Q. Dai, A. Pearse, B. Y. Liu, H. Wang, G. Rublo, Y. F. Mo, V. Thangadurai, E. D. Wachsman and L. B. Hu, Nat. Mater., 16, 572 (2017).

K. K. Fu, Y. H. Gong, B. Y. Liu, Y. Z. Zhu, S. M. Xu, Y. G. Yao, W. Luo, C. W. Wang, S. D. Lacey, J. Q. Dai, Y. N. Chen, Y. F. Mo, E. Wachsman and L. B. Hu, Sci, Adv., 3, 11 (2017).
Influence of Growth Parameters on Optical and Electrical Properties of Nanostructured Ceria Thin Films Obtained By Spray Pyrolysis
Authors: García Sánchez Mario Fidel , Malagón García José Francisco , Romero Ibarra Issis Claudette , Santana Rodriguez Guillermo
Published: February 2020

Recently, it has been demonstrated that nanostructured materials increase the transport properties of oxides used as electrolytes in solid oxide fuel cells (SOFC) [1-2]. However, the physical basis of this phenomenon it is not fully understood yet [3,4]. In thin films, electrical properties depend on the technique used and the growth conditions. In this work, nanostructured ceria thin films have been prepared by ultrasonic spray pyrolysis using cerium acetylacetonate as metallo-organic precursor dissolved in anhydrous methanol. The influence of flow rate and substrate temperature in the structural, optical and electrical properties of films was studied. The morphology, structure, optical and electrical properties were studied using scanning electron microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and impedance spectroscopy (IS). The influence of thermal annealing at 900 ºC on the structural properties of films was studied. The substrate temperature were optimized for obtaining smooth, dense, uniform and homogeneous nanocrystalline films with grains sizes smaller than 20 nm. The flow rate modified the morphology and the grain size of prepared films. By XPS were demonstrated the presence of Ce3+, even in treated films. The Ce3+ concentration do not depend on the grown temperature. The different signals observed in PL after the thermal annealing are associated to the presence of defects induced by levels in the band gap created by the Ce3+ atoms. The low values of total conductivity and activation energy measured by IS are related to the nanometric grain size.

The authors acknowledge financial support for this work from IPN with projects 20181399 and 20181907; CONACyT under project PN 1373 and “Red Temática de Almacenamiento”; and SECITI 095-2017.

References

M. F. García-Sánchez, J. Peña, A. Ortiz, G. Santana, J. Fandiño, F. Cruz, Solid State Ionics, 179 (2008) 243.

M. F. García-Sánchez, A. Ortiz, G. Santana, M. Bizarro, F. Cruz Gandarilla, M. A. Aguilar-Frutis, J. C. Alonso, J. Am. Ceram. Soc. 93 (2010) 155.

J. L. M. Rupp Solid State Ionics 207 (2012) 1.

A. Benítez-Rico, M. F. García-Sánchez, M. Picquart, B.M. Monroy-Peláez, G. Santana-Rodríguez, J. Nanomaterials 2015 (2015) 692648.
Probing Colossal Ion Conductivity Hypotheses
Authors: Francis Michael F
Published: February 2020

Fuel cells have long promised to bring high efficiency to the production of energy. In practice, fuel cells have been limited to hydrogen systems, where the high diffusivity of hydrogen through membranes allows high current densities. Hydrogen based fuel cells pose three major limitations: the requirement of expensive catalysts, the expensive or dangerous shipping of hydrogen, and the limitation to the single fuel that is hydrogen. Alternatives are present in the form of solid oxide fuel cells (SOFCs), which are composed of earth abundant materials, and may utilize arbitrary fuels. Despite the prospects of SOFCs, their deployment has been limited by low current densities caused by the slow diffusion of oxygen through SOFC membranes. A scientific solution to the problem of low current density was found in the form of Colossal Ion Conductivity (CIC), where large changes in ion conductivity were observed in heterolayer environments. Both because of the complexity of this problem, and the importance of it as a technological solution, CIC immediately became hotly debated, with several researchers offered mechanistic hypotheses.
Advancements in Performance and Durability of Metal-Supported Solid Oxide Fuel Cells
Authors: Dogdibegovic Emir , Wang Ruofan , Lau Grace , Byrne Conor , Tucker Michael C
Published: February 2020

Metal-supported solid oxide fuel cells (MS-SOFC) display a number of advantages over conventional all-ceramic SOFCs, including low-cost structural materials (e.g. stainless steel), mechanical ruggedness, excellent tolerance to redox cycling, and extremely fast start-up capability. These properties make MS-SOFCs ideally suited for range extenders in vehicles due to tolerance to thermal fluctuations following load changes or intermittent fuel flow. Directly fueled with ethanol or ethanol-water mixture, MS-SOFCs provide promising alternative for mobile applications.

In this talk, the recent progress on performance and durability of symmetric MS-SOFCs, pioneered at LBNL, will be addressed. The development of new electrolyte, new cathode and anode catalysts, optimized cell configuration, and processing techniques will be discussed. The catalyst infiltration technique allows for flexible and layered electrode composition, depending on the system applications and fuels. Our current state-of-the-art MS-SOFCs achieve power density of ≥1.5 W/cm2 at 700 °C and ≥2.85 W/cm2 at 800 °C when fueled with humidified hydrogen which is, to the best of our knowledge, the highest performance reported in the literature for stainless steel MS-SOFCs. However, catalyst coarsening and Cr deposition from the stainless steel metal support are known to occur1, and the primary degradation mechanisms are elucidated and tackled to improve the durability. The cell area specific resistance (ASR) of <0.144 W∙cm2 at 700 °C meets the projected requirements for commercialization in vehicles. Initial studies on button cells fueled with ethanol/water mixture are investigated and further efforts towards increasing power density and durability are addressed.

1M.C. Tucker, Journal of Power Sources, 369, 6-12, Nov. 2017.

Acknowledgments

The information, data, or work presented herein was funded in part by the Advanced Research Projects Agency – Energy (ARPA-E), U.S. Department of Energy under work authorization number 13/CJ000/04/03. This work was funded in part by the U.S. Department of Energy under contract no. DE-AC02-05CH11231.

Figure 1.
(a) Illustration of a symmetric MS-SOFC configuration developed at LBNL, and (b) the highest cell performance obtained so far on the stainless steel MS-SOFCs.

Figure 1
Luminescence of Mn4+ in Solids for LED Application
Authors: Srivastava Alok M
Published: February 2020

The development of narrow band red emitters, that are based on the luminescence of Mn4+, is an important goal of current LED phosphor research. It is of fundamental interest to understand the “Mn4+-host” interaction that can tailor the luminescence of Mn4+ ions to match the requirements of the LED device. This talk will discuss the approach to understanding this interaction by examining the luminescence of Mn4+ in a wide variety of host materials (fluorides and oxides). The influence of compositional variations on the strength of the crystal-field and covalence of Mn4+ -ligand bonding will be explored. These factors tune the optical properties of the Mn4+ ion and their understanding is important in designing phosphors that will fulfill the requirements of the modern-day LED devices.
Pr3+ Luminescence to Improve the Range, Accuracy and Sensitivity of Temperature Measurement
Authors: Brites Carlos Delgado Sousa , Fiaczyk Karolina , Ramalho Joao Filipe Candeias Baptista , Sójka Małgorzata , Carlos Luís D , Zych Eugeniusz
Published: February 2020

For years, various contact techniques were used to measure temperature. Development of novel and evolving technologies raised the interest in elaboration of non-contact thermometry. Nowadays, this is radiation pyrometry which is the method of choice for such purposes. Yet, it has important limitations – sensitivity to stray light or reflected radiation as well as sensitivity to flame interferences. Also accuracy of temperature measurement, which is not better than ~2 K, is not always satisfactory. Today technologies do not fulfill the needs of temperature sensing in microelectronics, microoptics, photonics, microfluidics, nanomedicine and they require alternative solutions.

Among promising approaches, overcoming the limitations of other techniques, luminescent methods are of great interest. While the idea is not new [1], a real breakthrough using this technique was not yet achieved. Combining a high sensitivity and accuracy as well as broad range of temperature usability within one temperature sensor appeared challenging [2,3].

In this presentation we shall prove that Pr3+ luminescence characteristics may offer a lot in this field. While in some compositions this ion generates only 4f®4f luminescence due to relaxation of the higher 3P0 and lower 1D2 levels, in some others also 5d®4f luminescence may take place. We explored the possibility to use all these three luminescent components to sense the temperature accurately and in a broad range. The main argument for that is that all the three emissions are characterized by different mechanisms of their thermal quenching. Furthermore, temperature strongly affects the non-radiative relaxation between the three levels. Our presentation will show first results of the approach presented above using data for Sr2GeO4:Pr and will prove a validity and potential of this new attitude. Figure 1 presents profound changes in emission spectra of Sr2GeO4:Pr in the range of 17-600 K.

[1] P. Neubert, US2085508 A, 1937.

[2] L. D. Carlos, F. Palacio, Thermometry at the Nanoscale: Techniques and Selected Applications, Royal Society of Chemistry, Oxfordshire 2016.

[3] C. D. S. Brites, P. P. Lima, N. J. O. Silva, A. Millán, V. S. Amaral, F. Palacio, L. D. Carlos, Nanoscale 2012, 4, 4799.

Figure 1
Fabrication and Phase Transition of La2-X
Lu
x
Zr2O7 Transparent Ceramics
Authors: Wang Shiwei , Wang Zhengjuan , Zhou Guohong
Published: February 2020

Materials with A2B2O7 formula have been drawing the attention of researchers for a diversity of applications, such as fast-ion conductors, photocatalysts, thermal barrier coatings, matrices for immobilization of highly active radionuclides from nuclear wastes and host materials for scintillators. A2B2O7 materials have three crystal phases decided by the ionic radius ratios (r
A/r
B). According to the rule of Subramanian et al
[1], pyrochlore phase was favored when r
A/r
B lay within the range of 1.46~1.78. Defective fluorite phase is stable for r
A/r
B < 1.46, whilst the monoclinic phase is stable for r
A/r
B > 1.78. In this study, a new series of La2-x
Lu
x
Zr2O7 (x = 0~2.0) transparent ceramics [2] with high density and average atomic number, which are hoped to be scintillator matrix, were fabricated by vacuum sintering and an interesting phenomenon was found. As Lu content increased, the crystal phase gradually transformed from pyrochlore to defective fluorite phase with the existence of a two-phase region (x = 0.6 ~ 1.2) (Figure 1). The appearance of a two-phase region illustrated that Subramanian’s theory is not available when there is large difference in ionic radii of the elements that occupy at Ln position (r
La
3+ = 1.160 Å, r
Lu
3+ = 0.977 Å). In addition, the grain growth of pyrochlore phase was inhibited due to the appearance of defective fluorite phase. Grain sizes of samples dominated by pyrochlore phase were 11~14 μm. Samples with two phases (x = 0.6~1.2) have much smaller grain sizes (< 3 μm), while samples dominated by defective fluorite phase have larger grain sizes (82~60 μm). All the samples (except for x = 0) are transparent and the highest in-line transmittance is reached to 72.4% (1100 nm) at x = 1.2 though two phases coexist. To verify that the two-phase region was not an accident, we fabricated LaLuZr2O7 powder by combustion method instead of solid state reaction and sintered in the same way. From XRD results, two phases are observed in both the synthesized powder and ceramic. Also, With 2 ~ 3 μm average grain size, the LaLuZr2O7 ceramic reaches high transparency with an in-line transmittance of 73.4% at 1100 nm, which is slightly higher than that made by solid state reaction method, showing the advantage of combustion method in synthesizing good powder. Rayleigh-Gans-Debye scattering theory was used to explain the high transmittance of the ceramics with two phases. When the refractive indices of the coexisting two phases are close to each other and the average grain size is smaller than 10 μm, the two phases have little influence on transparency of the ceramics.

[1] Subramanian MA, Aravamudan G, Subba Rao GV. Oxide pyrochlores-A review. Prog Solid State Chem 1983, 15: 55-143.

[2] Z.J. Wang, G.H. Zhou, X.P. Qin, F. Zhang, J.P. Ai, P. Liu, S.W. Wang. Fabrication and phase transition of La2-xLuxZr2O7 transparent ceramics. J Eur Ceram soc 2014, 34: 3951–3958.

Figure 1
Interfacial Stability of Argyrodite-Based Solid Electrolytes in All-Solid-State Batteries
Authors: Strauss Florian , Bartsch Timo , Kim A-Young , Janek Jürgen , Hartmann Pascal , Brezesinski Torsten
Published: February 2020

All-solid-state batteries (ASSBs) are currently attracting much attention as next generation energy storage systems, with potentially both higher energy and power densities than state-of-the-art lithium-ion batteries (LIBs). The latter may be realized by combining layered Ni-rich oxide cathode materials such as Li1+x
(Ni1
–

y

–

z
Co
y
Mn
z
)1
–

x
O2 (NCM) and thiophosphate-based solid electrolytes (SEs). As for SEs, in particular argyrodites, Li6PS5X (X = Cl, Br), show great promise since they exhibit sufficient Li-ion conductivity (~2 mS/cm) and because of the simplicity of preparation.1 However, their practical implementation is hindered by poor electrochemical stability at the interface, in particular with positive electrode materials.2,3 In order to pave the way for rational interface design, processes occurring between cathode and electrolyte need to be better understood. Following these guiding principles, we herein report our recent efforts in implementing various in situ and ex situ techniques (X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, differential electrochemical mass spectrometry etc.) to gain mechanistic insight into interfacial SE degradation when in direct contact with NCM622 (60% Ni). We reveal the potential resolved formation of degradation products, which are found to be responsible in part for irreversible capacities and performance decay of ASSB cells. However, we also demonstrate that by using protective oxide coatings such as LiNbO3, these detrimental side reactions can be suppressed to a large extent. In summary, we reveal the importance of developing in situ characterization techniques in the area of ASSBs and provide valuable insight into the cathode/SE interfacial chemistry.

References:

[1] Bachman, J. C.; Muy, S.; Grimaud, A.; Chang, H.-H.; Pour, N.; Lux, S. F.; Paschos, O.; Maglia, F.; Lupart, S.; Lamp, P.; et al. Inorganic Solid-State Electrolytes for Lithium Batteries: Mechanisms and Properties Governing Ion Conduction. Chem. Rev.
2016, 116 (1), 140–162.

[2] Richards, W. D.; Miara, L. J.; Wang, Y.; Kim, J. C.; Ceder, G. Interface Stability in Solid-State Batteries. Chem. Mater.
2016, 28 (1), 266–273.

[3] Auvergniot, J.; Cassel, A.; Ledeuil, J.-B.; Viallet, V.; Seznec, V.; Dedryvère, R. Interface Stability of Argyrodite Li6PS5Cl toward LiCoO2, LiNi1/3Co1/3Mn1/3O2 , and LiMn2O4 in Bulk All-Solid-State Batteries. Chem. Mater.
2017, 29 (9), 3883–3890.
Impact of Cathode Material Particle Size and Applied Pressure on the Cycling Performance of All-Solid-State Batteries
Authors: Bartsch Timo , Strauss Florian , Kim A-Young , Janek Jürgen , Hartmann Pascal , Brezesinski Torsten
Published: February 2020

All-solid-state batteries (ASSBs) containing solid electrolytes (SEs) are considered promising for use as next-generation energy storage devices in electric vehicles and portable electronics. Apart from safety benefits, in principle, they offer both higher energy and power densities than conventional lithium-ion batteries (LIBs) using a liquid carbonate-based electrolyte. However, ASSBs will only become competitive in the near future if some major problems are solved. These concern mainly technical functionality aspects, SE conductivity, and the stability of the electrode-solid electrolyte interface. The latter is not only crucial in terms of enabling the use of a Li-metal anode, but also at the cathode side, where a stable and robust contact between the SE and the cathode active material (CAM) is vital for long-term cycling performance. For example, this is the case when using layered Ni-rich oxide CAMs such as Li1+x
(Ni1-y-z
Co
y
Mn
z
)1-x
O2 (NCM) with high specific capacity and thiophosphate-based solid electrolytes.

Here we report on the strong impact of both CAM particle size and external applied pressure on the capacity of bulk-type ASSBs. Our model cell system comprised compacted pellets of NCM622 (60% Ni) as CAM, ß-Li3PS4 or Li6PS5Cl as SE, and In-metal as anode. In particular, we demonstrate the benefit of using small-size cathode particles (≤ 5 μm) to achieve virtually full theoretical specific capacity at low external pressure. This finding is rationalized through complementary galvanostatic cycling and X-ray diffraction on operating cells (in situ) as well as on harvested CAM/SE composites (ex situ). Besides, we reveal the significance of considering electrochemically inactive CAM in ASSBs, the proportion of which is equally increased for large particles and low applied pressure. Using charge transport measurements, we provide evidence that the presence of inactive CAM is due to a lack of electronic contact; ionic percolation seems not to be an issue for the two-phase cathode composites employed here. Overall, the results emphasize the importance of using size-tailored CAM, allowing for good electronic percolation, and thus conductive additives, which may cause SE degradation upon cycling, can be avoided.

Figure 1
Enhancement of Bifunctional Effect of NO3
- Anion By Using Glyme-Based Dual Solvent Electrolytes for Li-Air Batteries
Authors: Ishii Shunya , Yamada Shinya , Ishikawa Taro , Fujinami Taichi , Hayashi Yoshiya , Otsuka Hiromi , Ito Kimihiko , Kubo Yoshimi , Saito Morihiro
Published: February 2020

In recent years, non-aqueous type rechargeable Li-air (O2) batteries (LABs) have attracted much attention as large-scale energy storage devices for electric vehicles because of the high energy density over 5 times larger than that of the conventional Li-ion batteries (LIBs) [1]. However, there are some problems to be solved for the practical use such as smooth deposition/decomposition reaction of Li2O2 at air electrode and suppression of Li dendrite growth at Li metal negative electrode (NE). To address these problems, we selected 1.0 M LiNO3/tetraglyme(G4) electrolyte and added acetonitrile (AN) or dimethyl sulfoxide (DMSO) with both high dielectric constant ε and low viscosity η to enhance the Li salt dissociation and lowering the electrolyte viscosity. Namely, the NO3
- anion was reported to work as a mediator to decompose the Li2O2 product at air electrode [2] and to form Li2O layer on the surface of Li metal NE to suppress the Li dendrite growth [3,4] and extra electrolyte decomposition. In this study, we investigated the bifunctional effects of NO3
- anion and its enhancement by using the dual solvent system for electrolyte. As a reference, 1.0 M LiOTf/G4 was also examined in the same way.

Figure 1 shows the η values for 1.0 M LiNO3/G4+X and 1.0 M LiOTf/G4+X (X= DMSO, AN) electrolytes. The both η values decreased with an increase in the content of mixed solvents especially for AN because of one tenth lower η (0.37 mPas) than G4. As a result, the σ value was drastically improved (Fig. 2). For the addition of DMSO, the decrease in the η was not so big. However, the σ value effectively increased as well as those for the AN. This indicates that the relative high ε (47) of DMSO enhanced to dissociate the Li salts and improved the σ value by increasing the number of carrier ions. In fact, the effect was confirmed by Raman spectra and Walden plots. Figure 3 shows the discharge/charge curves for the LAB cells using the dual solvent electrolytes at the applied current of 0.20 mA cm-2. By mixing DMSO, the overpotential was drastically reduced especially during discharge process. This effect was enhanced at a higher rate operation. In addition, Li deposition/dissolution tests using Li foil | Cu mesh cell also exhibited improved performances for the 1.0 M LiNO3/G4 electrolytes. The effects for the dual solvent system will be reported in more detail at the meeting.

This study was supported by JST Project “ALCA-SPRING”, Japan.

[1] P. G. Bruce et al., Nature materials, 11, 19 (2012).

[2] D. Sharon, et al., ACS App. Mater. & Int., 7, 16590 (2015).

[3] J. Uddin, et al., J. Phy. Chem. Lett., 4, 3760 (2013).

[4] M. Saito et al., J. Electrochem. Soc., 164(12), A2872 (2017).

Figure 1
Composite of Vn/Carbon Nanofibers As a Protective Layer on Cathode for High Performance Li-S Batteries
Authors: Kim Han-Byeol , Ngo Duc Tung , Park Chan-Jin
Published: February 2020

With increasing demand for large scale energy storage systems (ESS), Li-S battery is regarded as a potential candidate for ESS, due to its high theoretical energy density and natural abundance of the cathode material. However, for conventional Li-S batteries, sulfur cathode has suffered from many issues such as low intrinsic electrical conductivity and instability leading to the insufficient utilization of sulfur. In particular, the dissolution of polysulfide intermediates into electrolyte results in the rapid capacity fading of the batteries. Therefore, for the development of the highly efficient Li-S battery, it is essential to improve the conductivity of the sulfur based cathode and maintain/reuse the soluble polysulfide within the cathode structure. To address these issues, some researchers used protective layer composed of carbon, metal oxides or polymers on the sulfur cathode. According to previous studies, carbon based materials as a protective layer on cathode reduced the charge transfer resistance of the sulfur cathodes by acting as an upper conducting network and localized the soluble polysulfides during cycling. This strategy is regarded as a simple and effective solution to make high capacity rechargeable Li-S batteries. In addition, other group demonstrated that Pt as an electrocatalyst could help to convert polysulfide deposits back into soluble long-chain polysulfide, and hence enhanced reaction kinetics and retained high Coulombic efficiency. Catalytic role of vanadium nitride, VN resembles that of more precious Pt. VN has desirable advantages for a sulfur cathode: (1) strong chemical adsorption of polysulfides on it, leading to suppressing the shuttle effect, (2) its high electrical conductivity, and (3) good catalytic activity for enhancing red-ox reaction kinetics.

In the present work, we fabricated a composite of VN/carbon nanofibers (VN/CNFs), as a protective sulfur electrode on cathode for Li-S cell, using electrospinning method. The morphology and chemical composition of electrospun VN/CNFs were characterized by SEM, TEM, and XPS, respectively. The Li-S cell with VN/CNFs protective layer exhibited excellent electrochemical performance in terms of specific capacity, cyclability, and rate capability. Owing to the strong and synergic polysulfides anchoring effect of the VN/CNFs, a high initial discharge capacity of 1,480 mAh g-1 and a Coulombic efficiency of ~98% were measured at a rate of C/2, when used in Li-S cell. Further, the Li-S cell exhibited a long-term cyclability: 82% capacity retention even after 200 cycles.

Figure 1
P,O,N-Co Doped Carbon Scaffolds from LiFePO4 Nanoparticles As Sulfur Hosts for Lithium-Sulfur Batteries
Authors: Lee Jeongyeon , Piao Yuanzhe
Published: February 2020

Lithium-sulfur (Li-S) batteries are well knowned as one of the promising energy applications with high specific capacity, such as electric vehicles and energy storage system, owing to their high theoretical capacity of 1672 mA h g−1, eco friendliness, and the abundance all over the world. However, Li-S batteries have some challenge, such as the poor Coulombic efficiency, fast capacity fading, and unstable cycle performance by the dissolution of lithium polysulfides (LiPSs) in the electrolyte by shuttle mechanism during long cycling. To challenge these problems, we suggest that P, O, and N co-doped hollow carbons with graphene from LiFePO4 nanoparticles are very efficient as sulfur hosts for Li-S batteries. This sample from LiFePO4 nanoparticles provides sufficient spaces with the variety of pore sizes for storage of sulfur and various heteroatoms doping to minimize the dissolution of the LiPSs. This sample can block the dissolution of LiPSs due to the efficient hosts and the excellent chemical affinity with LiPSs. Its electrode indicates the very stable cycle performance and high rate capability, as proved by LiPSs adsorption test. We suggest that this sample has high potential as a sulfur host for real application in Li-S batteries with more optimization.
Highly Stable Sodium Metal Anodes for Sodium Batteries By Tactically Regulating the Solid Electrolyte Interphase
Authors: Li Weiyang , Wang Huan , Wang Chuanlong
Published: February 2020

Sodium (Na) metal holds great promise as an attractive anode material for grid-scale energy storage systems owing to its high theoretical specific capacity, low electrochemical potential, low cost and high natural abundance. However, its highly reactive nature with organic electrolyte leads to the formation of unstable solid electrolyte interphase (SEI) and dendritic/mossy Na growth. To overcome these issues, we present highly stable and dendrite-free Na metal anodes over a wide current range and long-term cycling via versatile tactical tunings of the SEI. Stable Na metal cycling in carbonate electrolyte without any additives over 100 cycles can be achieved at a current density up to 2 mA/cm2 with a high capacity of 3 mAh/cm2. In ether-based electrolyte, a superior cycling performance of Na anode can be achieved at a high current density up to 10 mA/cm2 and a capacity up to 5 mAh/cm2 over 100 cycles. Moreover, we found that despite the many similarities in the chemical and physical properties of lithium (Li) and Na, the strategy that was able to stabilize Li metal could not be directly applied to Na metal, but requires more meticulous investigations, thus providing new insights into understanding the differences between Li and Na systems.
Correlating Molecular-Level Environments of Chloroaluminate Species with Electrochemical Behavior in Rechargeable Aluminum-Graphite Batteries
Authors: Xu Jeffrey , Turney Damon , Messinger Robert J.
Published: February 2020

Aluminum metal has long been envisioned as an electrode for high-performance rechargeable batteries due to its high global abundance, low cost, non-flammability, and high volumetric capacity. Graphite has recently been shown to pair as a cathode with aluminum anodes when using chloroaluminate-containing ionic liquid electrolytes, exhibiting capacities that are stable at high charge/discharge rates and over long cycle lifetimes. However, there are presently unanswered questions related to the intercalation of sterically bulky chloroaluminate anions (e.g. AlCl4
-), structural changes of the cathode after prolonged cycling, and more generally, the relationship between the local structures of different graphitic materials and their electrochemical properties.

Here, we report on the investigation of charge storage and ion transport mechanisms in graphitic cathodes and their implications on bulk electrochemical behavior. Three types of graphites (pyrolytic, natural and synthetic) were studied. Solid-state 27Al magic-angle-spinning (MAS) NMR measurements on intercalated graphitic cathodes reveal the presence of chloroaluminate anions in different local environments and with different mobilities that evolve as a function of state-of-charge. Cyclic voltammetry experiments at varying scan rates were conducted to yield insights into ion transport phenomena and to disentangle the Faradaic and capacitive contributions to the total discharge capacity. Additionally, the surface area and porosity of the cathode materials, which affect the number of accessible sites for ion electrosorption, were quantified and correlated to the observed capacitance and overall energy density. Our findings reveal molecular-level insights into the intercalation processes and redox mechanisms of graphitic cathodes that can be collectively used to better understand and optimize aluminum-graphite battery performance.

Figure 1
(Invited) Theory of Radiative Lifetime of an Activator Ion Due to Surface Plasmons
Authors: Mishra Kailash C. , Piquette Alan , Collins John
Published: February 2020

One means of controlling the color, brightness, and directional profile of light emitted from LEDs or luminescent materials, in general, is through the use of nanostructures. Metallic films and structures are a particular class of material that have been of considerable interest for this purpose in recent times. In this talk, we consider the lifetime and efficiency of a phosphor layer situated near a metallic film.

We will first make general observations of the effects of the plasmons on the lifetime and quantum efficiency of the activator ions in the phosphor and on the role of the plasmons in the emission process. The effect of the plasmons in the excitation process and on the total luminescence from the system will also be discussed.

Finally, an expression for the lifetime of the optical ions interacting with the surface plasmon modes will be derived using the relevant Einstein A and B coefficient. This requires a determination of the mode density of the surface plasmons. Since the surface plasmons represent a 2-dimensional system, a length parameter must be introduced in order to calculate the mode density. We derive this parameter using a semi-classical approach, and show its dependence on the dielectric constants of the system and on the distance from the metallic layer.
(Invited) Eu2+-Doped KxNa1-XLuS2 Ternary Sulfides: Application and Perspectives in White LEDs
Authors: Jary Vitezslav , Havlak Lubomir , Barta Jan , Bystricky Ales , Rejman Martin , Nikl Martin , Martin Lisa I D J , Joos Jonas J , Smet Philippe F
Published: February 2020

The presented work gives an overview of recent advances in research and development of novel phosphors based on Eu2+-doped KxNa1-xLuS2 ternary sulfides which may be used as phosphors in white LED sources with tunable color correlated temperature. Tunability is achieved by using two different kinds of excitation diodes (nearUV and blue) in combination with the proper K/Na ratio in KxNa1-xLuS2:Eu2+ structure. Intense photoluminescence due to the Eu2+ 5d – 4f allowed transition covers a broad emission region in visible range under both nearUV (~390 nm) and blue (~450 nm) excitations. The possibility to change the intensity ratio of the excitation diodes yields the changes of the output color correlated temperature. These changes are clearly demonstrated by shifts in the CIE color space; light quality is also quantified and discussed using CRI (color rendering index) and CQS (color quality scale) metrics [1].

However, to fully understand the Eu2+ emission mechanisms in these sulfidic hosts and to be able to optimize phosphor preparation and its performance, additional experimental techniques are applied to characterize these KxNa1-xLuS2:Eu2+ phosphors. When a focused electron beam impinges on a cathodoluminescent (CL) material in a scanning electron microscope (SEM), secondary electrons, characteristic x-rays and visible photons are emitted. These signals can be used to construct a two-dimensional topographical, chemical and luminescence map, respectively [2]. Furthermore, thermal quenching and quantum efficiency measurements of KxNa1-xLuS2:Eu2+ phosphors will be discussed for the first time.

V. Jarý, L. Havlák, J. Bárta, M. Rejman, A. Bystřický, Ch. Dujardin, G. Ledoux, M. Nikl. Circadian Light Source Based on KxNa1-xLuS2:Eu2+ Phosphor. ECS Journal of Solid State Science and Technology, 7 (1), R3182-R3188, (2018). doi: 10.1149/2.0231801jss.

L.I.D.J. Martin, D. Poelman, P.F. Smet, J.J. Joos, Microscopic Study of Dopant Distribution in Europium Doped SrGa2S4: Impact on Thermal Quenching and Phosphor Performance. ECS Journal of Solid State Science and Technology, 7 (1) R3052-R3056 (2018). doi: 10.1149/2.0341709jss.
(Invited) Concentration Quenching in LED Phosphors
Authors: Setlur Anant A
Published: February 2020

One aspect in the practical application of LED phosphors is the appropriate optimization of activator concentrations since this balances phosphor absorption and emission with potential efficiency losses at high concentrations. In this presentation, we discuss this balance with respect to Ce3+-doped LED phosphors as well as Mn4+-doped complex fluorides, specifically the TriGain K2SiF6:Mn4+ phosphor made by GE. These examples point out two separate cases where aspects for concentration quenching can be related to inherent properties versus those that can be addressed by improved phosphor synthesis and processing. Finally, we discuss how concentration quenching can be described using existing literature models along with practical implications.
Use of a Redox-Responsive 4 H-Bond Ureidopyrimidone (UPy) Array to Control Polymerization in a Upy-Based Supramolecular Polymer
Authors: Vuong Katrina , Clare Laurie A. , Smith Diane K.
Published: February 2020

Ureidopyrimidinone (UPy) derivatives, introduced by Meijer and co-workers, are capable of forming dimers linked by four strong H-bonds. They have been widely used as reversible crosslinkers in self-healing supramolecular polymers and gels. The goal of the project to be presented is to create a redox-controllable UPy supramolecular polymer system by adding a redox-responsive UPy monomer as a capping agent to a solution of a non-redox-active UPy supramolecular polymer. Specifically, a UPy containing a phenylenediamine redox couple, UPyH, that we have previously studied,1 will be used as the capping agent. In previous work we have shown that UPyH dimerizes in methylene chloride with Kdim > 105 as expected. Oxidation of the phenylenediamine to the radical cation does not break apart the dimer at mM concentrations. However, further oxidation to the quinoidal dication weakens the binding enough to allow an external base to remove the most acidic protons and thereby create a non-self-complementary H-bonding motif that cannot dimerize. As long as the base is not too strong the process is reversible on the cyclic voltammetric time scale, leading to re-formation of the UPyH dimer upon reduction. Previous studies show that 1 equivalent of 4-trifluoromethylpyridine is a good choice for the base. To create the redox-responsive supramolecular polymer system, a known UPy oligomer will be used to prepare a supramolecular polymer solution in methylene chloride electrolyte solution. The degree of polymerization will be assessed by measuring the viscosity of the solution. UPyH plus an equal amount of 4-trifluoromethylpyridine will be then added until there is a significant decrease in viscosity indicating that the UPyH is H-bonding to the UPy’s in the non-redox active UPy oligomer and thereby decreasing the length of the supramolecular chains. The solution will then be oxidized either chemically or electrochemically to convert the UPyH to its fully oxidized, de-protonated form. Since this form is incapable of dimerizing with itself or another UPy, the UPyH will lose its viability as a chain terminator, thus allowing the non-redox active Upy oligomers to reform supramolecular chains. This will be signaled by an increase in the viscosity of the solution.

1L. A. Clare and D. K. Smith, Chemical Communications
2016, 52, 7253-7256.
Nitrogen-Doped Highly Disordered Carbon for Nitrogen Reduction Reaction during Electrochemical Ammonia Synthesis
Authors: Wu Gang
Published: February 2020

Ammonia (NH3) is considered an important chemical for both agriculture fertilizer and renewable energy. The conventional Haber-Bosh process to produce NH3 is energy intensive and leads to significant CO2 emission. Alternatively, electrochemical synthesis of ammonia (ESA) through the nitrogen reduction reaction (NRR) by using renewable electricity has recently attracted significant attention. Herein, we report a metal-organic framework-derived nitrogen-doped nanoporous carbon as electrocatalysts for the NRR. It exhibits a remarkable production rate of NH3 up to 3.4×10−6 mol cm−2 h−1 with a Faradaic efficiency (FE) of 10.2% at −0.3 V vs RHE under room temperature and ambient pressure using aqueous 0.1 M KOH electrolyte. Increasing the temperature to 60 °C was found to further improve production rates to 7.3×10−6 mol cm−2 h−1. The stability of the nitrogen-doped electrocatalyst was demonstrated during an 18-hour continuous test with constant production rates. First principles calculations were used to elucidate the possible active sites and reaction pathway. The moiety, which consists of three pyridinic N atoms adjacent with one carbon vacancy embedded in a carbon layer, is able to strongly adsorb N2 and further realize N≡N triple bond dissociation for the subsequent protonation process. The rate-determining step of the NRR is predicted to be the adsorption and bond activation of the N2 molecule. Increasing overpotentials are favorable for the protonation process during NH3 generation. Further doping Fe into the nitrogen-doped carbon likely blocks the N3 active sites and facilitates the hydrogen evolution reaction, a strong competitor to the NRR, thus yielding negative effect on ammonia production. This work provides a new insight into the rational design and synthesis of nitrogen-doped and defect-rich carbon as efficient NRR catalysts for NH3 synthesis at ambient conditions.
Photoelectrochemical Properties of p- and n- Type 4H-SiC Epilayers: Doping Concentration Dependence and Dopant Selectivity
Authors: Pavunny Shojan Pullockaran , Myers-Ward Rachael L. , Daniels Kevin , Sridhara Karthik , Boyd Anthony K , DeJarld Matthew T , Gaskill D Kurt
Published: February 2020

Exceptional chemical stability resulting from a large bandgap and low-lying valence band edge narrows the wet-etching based micromachining choices of the covalently bonded electronic and photonic device material, SiC, to mainly photoelectrochemical (PEC) dissolution. The PEC etching process has an anisotropic nature with the accompanying advantages of dopant, bandgap, and spatial selectivity, light intensity dependence, reduced ion damage, and the ability to undercut heterostructures. For the first time, a comprehensive photogenerated minority carrier assisted etching investigation was carried out on Si polar surface of high-quality (micropipe density <1 cm-2) p- and n- type (0001) 4H-SiC epilayers having intentional or unintentional doping densities in the 1014–1018 cm-3 range. Cyclic voltametry and chronoamperometry studies under a parallel supra-bandgap (~320 nm) light illumination with varying intensities (≤0.85 Wcm-2) in a highly basic etching medium (1 wt% KOH solution, pH ~12) revealed the dependence of etch voltage and etch rate (~30–90 nm/min) on type and concentration of doping. In addition, a mutually exclusive etch voltage window (~±0.3–0.5 V versus saturated calomel electrode) was established for both types of conductivities in the diffusion-limited regime. Results to be presented can provide key insight in design and fabrication for higher performance three dimensional SiC homojunctions for various applications including photonic crystal cavities.
In Search of the Active Chlorine Species on Ti/ZrO2-RuO2-Sb2O3 Anodes Using Dems and XPS
Authors: Palma Goyes Ricardo Enrique , Vazquez-Arenas J. , Ostos Carlos , Manzo-Robledo Arturo , Romero-Ibarra Issis , Calderón Jorge , González I
Published: February 2020

Evidence to what it is identified in the literature as “active chlorine” in indirect oxidation processes occurring on Ti/ZrO2-RuO2-Sb2O3 anodes is provided in this study. To discriminate such behavior, different catalysts are prepared using the Pechini method varying ZrO2 content, at different Zr/Ru molar ratios: 1, 0.5 and 0.3. The characterization of the materials using X-ray photoelectron spectroscopy (XPS) reveals that no solid solution (Ru-Zr) or any doping that affects the crystalline phase of Zr are obtained, while Sb2O3 was surface-segregated from the bulk to the anode surface affecting the outmost 3-5 nm surface layers. There are enormous impacts on the catalytic activity and adsorption properties of the structures as ZrO2 content is increased. The presence of ZrO2 and Sb2O3 shrink the number of favorable oxygen adsorption sites in Ti/ZrO2-RuO2-Sb2O3 catalysts, whence the adsorption energies for oxygen-metal interactions became lower than for Ti/RuO2. Differential electrochemical mass spectroscopy (DEMS) and electrochemical experiments qualitatively indicate that a lower amount of ZrO2 in the ternary electrode induce a better catalysis towards the oxygen evolution reaction (OER, O2 production), while the ionic currents for and species drop. This behavior suggests that chloride oxidation needs to encompass the mitigation of the OER as the percentage of ZrO2 is increased in the anode. Active chlorine could stem from species since it was produced in larger amounts than according to the pH of the electrolyte, and in adequate levels to generate the degradation of organic compounds.
Surface and Subsurface Effects in Electrochemical Water Splitting
Authors: Tavassol Hadi , Bloed Charles , Vuong Jiam , Siwabessy Andrew , Shelden Calum , Enriquez Alexis
Published: February 2020

We will report on the surface and subsurface electrode processes in aqueous solutions. We are particularly focused on anode and cathode processes in electrochemical water splitting. Well-defined model electrode materials of oxides and noble metal alloys are prepared to investigate structural and mechanistic details of water splitting.

Gas phase synthesis and controlled atmosphere electrochemical analysis of oxygen evolution electrocatalysis of CaxSr1-xFe2O6-δ perovskites where δ = 0-1, will be discussed. This system exhibits a wide range of activity depending on the A site composition. Our results suggest that surface and subsurface oxygen content controls the oxygen evolution catalysis. Although, current understanding from the d-orbital electron count (eg occupancy) predicts low OER activities for such a system, under specific solution conditions, some of the compounds in the Sr2-xCaxFe2O6-δ series exhibit higher activity than LaCoO3. We particularly use results of in-situ vibrational spectroscopy and electrochemical analysis to elucidate vacancy content and ordering effects on catalysis.

We will also discuss the influence of surface and subsurface structures of model Pt-M (M = Cu and Ni) surface alloys and bilayers during hydrogen adsorption relevant to hydrogen evolution reaction (HER). We use electrochemical measurements and in-situ surface stress analysis of these systems to elucidate activity trends from hydrogen adsorption affinities. Our results exhibit a correlation between the energetics of hydrogen underpotential deposition and HER catalytic activity.
Catalytic Activity Enhancement in Oxygen Evolution Reaction on LDH Nanosheets By Metal-Cluster Loading
Authors: Kitano Sho , Yamauchi Miho
Published: February 2020

Electrochemical water splitting enables to store electricity produced from intermittent renewable solar and wind energy resources in the form of H2. Development of highly active electrocatalysts for kinetically sluggish anode reaction, i.e., oxygen evolution reaction (OER) remains a major challenge for several decades. Recently, metal hydroxide nanosheets exfoliated from layered double hydroxide composed of Ni2+ and Fe3+ (NiFe-LDH) were found to show excellent catalytic activities for OER. However, a high overpotential on LDH was still required to accelerate OER. Considering that Fe sites are regarded as a catalytic site and the overpotential for OER on the LDH nanosheet catalysts depends on a binding energy between intermediate molecules and Fe sites, modification of electronic structure of LDH probably controls the binding states and enhances catalytic activities on LDH. In this study, we prepare NiFe-LDH nanosheets (NiFe-NS) decorated with Au clusters and examine influence of the Au loading both on electronic states of Fe sites and catalytic activities of the NS.

NiFe-LDH was synthesized by hydrothermal method and colloidal Au clusters were prepared in DMF as reported previously. Carbonate ions in NiFe-LDH were exchanged to perchlorate ions, and the perchlorate ion–intercalated sample was dispersed in formamide, resulting in formation of colloidal NiFe-NS solution. Au-cluster-loaded NiFe-NS (Au/NiFe-NS) was prepared by mixing colloidal solutions of the NiFe-NS and Au clusters. Scanning TEM measurements revealed that small Au clusters around 1.2 nm in diameter are homogeneously dispersed on LDH.

Fig. 1 shows iR-corrected polarization curves of pristine NiFe-NS, Au clusters and Au/NiFe-NS electrocatalysts in 1 M KOH aqueous solution. The Au/NiFe-NS exhibited much larger oxidation current at a lower potential than the pristine NiFe-NS whereas Au clusters showed negligible activity, indicating that catalytic activity of NiFe-NS was significantly enhanced through the Au-cluster loading. XPS and XAFS measurements elucidated that Fe sites of Au/NiFe-NS are in more reduced states compared to those in the pristine NiFe-NS, resulting from charge transfer from Au clusters to Fe sites. Since bond breaking between the Fe site and intermediates is a rate determining step, we then conclude that reduction of Fe ions contributes to weaken binding energy and enhance catalytic activities. We achieved enhancement of catalytic activities of NiFe-NS via modification of electronic states of Fe sites using charge transfer interaction induced by Au cluster loading.

Fig. 1 IR-corrected polarization curves for OER on pristine NiFe-NS, Au clusters and Au/NiFe-NS in 1 M KOH aqueous solution.

Figure 1