bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Elucidating Oxygen Evolution on Model Oxide Electrodes
Authors: Stephens Ifan Erfyl Lester
Published: February 2020

It is particularly challenging to catalyse oxygen evolution under the acidic conditions of polymer electrolyte membrane (PEM) electrolysers. All compounds, apart from IrO
x
and RuO
x
, are catalytically inactive or unstable. I will present a series of model studies where we aim to elucidate the factors that control oxygen evolution.

Using thin films of RuO2, we showed that continuous mass losses occur in parallel to oxygen evolution, even when the electrochemical response is stable.1 This finding demonstrates that short term electrochemical measurements are an insufficient measure of long term stability. Our experiments on mass-selected Ru and RuOx particles revealed the high sensitivity of the oxygen evolution performance of nanoparticulate catalysts to the exact oxidation treatment.2,3 X-ray absorption measurements, taken in-operando, provide spectroscopic evidence for the potential dependent coverage of the reaction intermediates. Moreover, tests on oriented thin films indicate that the “coordinatively unsaturated” surface site is responsible for the activity of RuO2.4 Our very recent studies suggest that the dissolution rate of RuO2 is also highly dependent on the orientation.

The scarcity of RuOx and IrOx could limit the scalability of PEM electrolysers. An alternative strategy could be utilise non-precious metal oxides to catalyse oxygen evolution in acid. However, most non-precious metal oxides exhibit poor stability. Theoretical calculations predicted that MnO
x
could be stabilised against corrosion by the presence of TiO
x
at its surface, without affecting the catalytic activity. Our experiments on sputter-deposited thin films verify this notion. 5

The catalysts under investigation include model-size selected nanoparticles, commercial high surface area catalysts, sputtered films and oriented thin films. We have probed these surfaces with electrochemical measurements, ultra-high vacuum based surface science methods, electron microscopy, synchrotron-based spectroscopy and density functional theory calculations.

1 Frydendal, R., Paoli, E. A., Knudsen, B. P., Wickman, B., Malacrida, P., Stephens, I. E. L. & Chorkendorff, I.
ChemElectroChem
1, 2075, (2014).

2 Paoli, E. A., Masini, F., Frydendal, R., Deiana, D., Malacrida, P., Hansen, T. W., Chorkendorff, I. & Stephens, I. E. L.
Catal.

Today
262, 57, (2016).

3 Paoli, E. A., Masini, F., Frydendal, R., Deiana, D., Schlaup, C., Malizia, M., Hansen, T. W., Horch, S., Stephens, I. E. L. & Chorkendorff, I.
Chemical Science
6, 190, (2015).

4 Stoerzinger, K. A., Diaz-Morales, O., Kolb, M., Rao, R. R., Frydendal, R., Qiao, L., Wang, X. R., Halck, N. B., Rossmeisl, J., Hansen, H. A., Vegge, T., Stephens, I. E. L., Koper, M. T. M. & Shao-Horn, Y.
ACS Energy Letters
, 876, (2017).

5 Frydendal, R., Paoli, E. A., Chorkendorff, I., Rossmeisl, J. & Stephens, I. E. L.
Adv. Energy Mater.
5, 1500991, (2015).
Stochastic Generation of Sintered Titanium Powder-Based Porous Transport Layers in Polymer Electrolyte Membrane Electrolyzers and Investigation of Structural Properties
Authors: Lee Jason Keonhag , Bazylak Aimy
Published: February 2020

One of the factors leading to a decrease in the efficiency of polymer electrolyte membrane (PEM) electrolyzers is the blockage of water transport pathways through the porous transport layer (PTL). The oxygen bubbles generated from the electrochemical reaction at the catalyst layer accumulate in the PTL, impeding the transport pathways and reaction sites for the reactant water (1). An improved understanding of oxygen bubble accumulation and water transport behaviour in porous transport layers is essential to reduce mass transport losses in PEM electrolyzers.

 

This study presents a method to stochastically generate a PTL composed of sintered titanium (Ti) powders and investigate the transport properties using pore network modeling. A microscale X-ray computed tomography (µ-CT) was performed for a sintered Ti powder PTL sample to obtain a 2D density map. The density map contains material content information, providing higher intensity at the positions with higher material content. With the density map as an input, a stochastic model of the PTL was generated by placing Ti powder particles at positions decided by the density map and a probability function until the model reached the target volume (2). Two critical parameters are considered in this model: the seeding parameter, α, and a filling radius, β. The seeding parameter controls the number of Ti powder “seeds” that act as nucleation sites. The second parameter, the filling radius, allows the model to mimic the morphology of the sintered regions. The structural properties of the stochastic model are investigated by comparing the pore size distribution, throat size distribution, and the porosity profile to the µ-CT reconstruction.

 

Pore network modeling is an alternative to continuum modeling for simulating transport in porous media. Pore network modeling simplifies the solution of differential equations for mass transport by treating the pore space as a network of pores and narrow throats (3). Using pore network modeling as the analysis tool, the in-plane permeabilities of the µ-CT reconstruction and the stochastic model were compared.

 

The stochastic modeling of PTLs will facilitate the detailed parametric studies of PTL structural property impacts on transport and provide novel insights into mass transport behavior in PEM electrolyzers.

References

H. Ito, T. Maeda, A. Nakano, Y. Hasegawa, N. Yokoi, C. M. Hwang, M. Ishida, A. Kato, and T. Yoshida, International journal of hydrogen energy
35(18), 9550-9560 (2010).

A. Ebrahimi Khabbazi, J. Hinebaugh, A. Bazylak, Science Bulletin, 61(8), 601-611(2016).

A. Putz, J. Hinebaugh, M. Aghighi, H. Day, A. Bazylak, and J. T. Gostick, ECS Transactions, 58(1), 79-86 (2013).
(Invited Plenary) Fuel Cell Stack Development in Toyota
Authors: Amemiya Kazuki
Published: February 2020

After commercializing MIRAI in 2014, Toyota is focusing more on further cost reduction, and improvement in performance, durability and reliability, which are still challenging for wide-spreading commercialization enabling PEFC technology for next generation FCVs. To enhance PEFC performance directly impacts towards cost reduction due to reduce an amount of PEFC stack materials. Significant R&D efforts and advancements have been made towards filling the gap to the target on PEFC performance. For example, catalyst research aims not only to improve ORR activity itself but also to enhance mass transport performance in the high current region. The mass transport performance depends greatly on its microscopic structure of electrodes. Electrodes are fablicated from catalyst ink, which is a multi-component system, consisting of catalyst carbon, ionomer, and solvent. We employed several visualization techniques to unveil the structure of catalyst ink and electrodes respectively and discuss the relationship between the structure of catalyst ink and electrodes, and its performance. The technical prospects and R&D approaches for the remaining technical challenges on durability and reliability for the next generation FCVs will be also discussed.
Dendrite-Suppressed Lithium Plating from a Carbonate-Based Liquid Electrolyte
Authors: Park Kyusung , Goodenough John B.
Published: February 2020

Lithium metal is an ultimate anode material to achieve the highest energy density for a given cathode by providing a higher cell voltage and capacity. However, lithium is not used as the anode in commercial lithium-ion batteries because electrochemical dendrite formation and growth during charge can induce a cell short-circuit and the corresponding safety hazards. Plating of lithium through a bed of solid electrolyte particles is shown to transform dendrite growth into a three-dimensional lithium network formed by wetting the particle surfaces in the presence of a carbonate-based liquid electrolyte. It was also found that not every solid electrolyte could be wet by lithium in our systematic investigation.

Upon wetting by lithium metal, a higher overpotential during Li deposition than that with dendrite growth was observed in galvanostatic charge/discharge tests. The characteristic overpotential increase could be correlated with the morphological changes and a more isotropic growth behavior. The origin of the bonding responsible for wetting of the solid-electrolyte particles by lithium will be discussed.
Electrode Processing Towards Ultra-High-Energy-Density Electrode and Its Electrochemical Performance Research
Authors: Fu Yanbao , Song Xiangyun , Liu Gao , Battaglia Vince
Published: February 2020

Now worldwide effort is underway to develop electric vehicles (EVs) or hybrid electric vehicles (HEVs) to reduce fossil fuel consumption in the transportation area. Lithium ion batteries are considered as the first candidate to be used in EVs and HEVs due to their high energy and power density in the existing commercial battery system. The most essential parameters in batteries are energy density, cost and safety. The cell energy density depends on the cell chemistry and geometry. Even batteries are with the same active materials, but they can be engineered to meet specific power and energy demands. A laminate of a given thickness and porosity can be compressed to different thicknesses and associated porosities. This leads to electrodes of different energy and pulse power densities. In this research, we focused on material properties and the processing necessary for making ultra-thick electrodes with optimum energy and power density for EVs and HEVs. We determined the maximum energy density that can be achieved with a cathode of NCM that still meets the EV pulse power requirement. To achieve this goal variables are the molecular weight of the binder, viscosity of slurry and calendering. We also examined the role of processing conditions of battery slurries on binder distribution and in turn on the electrode’s mechanical and electrochemical performance properties.

Figure 1
First Principles Calculations of Interfacial Models for Nucleation Processes during NiO Conversion Reactions
Authors: Warburton Robert , Yildirim Handan , Fister Timothy T , Evmenenko Guennadi , Chan Maria K. Y. , Fenter Paul , Bedzyk Michael J. , Greeley Jeff
Published: February 2020

Oxide conversion reactions may yield Li-ion battery electrodes with exceptionally high capacities in comparison to intercalation materials, with Li2O-encompassed transition metal nanoparticles as the ideal discharge product. Nanoscale confinement has been demonstrated to facilitate the reversibility of these conversion reactions1–3. The NiO conversion reaction, in particular, has a high theoretical capacity (718 mAh g-1), but there is significant hysteresis between the experimental and theoretical voltage (0.6 V and 1.9 V, respectively), and the molecular origins of this hysteresis are poorly understood. In this work, we will present an integrated computational modeling approach, using classical molecular dynamics and first principles density functional theory calculations, with classical nucleation theory, to directly probe the role of interfaces during NiO conversion. These efforts are informed, in part, by recent work suggesting a strong role of interfaces during conversion, as lithiated domains propagate from the surface to the bulk of NiO nanomaterials4. Different nucleation schemes are evaluated, considering potential-dependent bulk and interfacial free energies to determine critical nucleation radii and energy barriers, as well as possible mechanisms for exceeding theoretical capacity limits. Theoretical predictions are directly compared to experimentally observed Ni/NiO multilayer electrode morphologies determined from in-situ X-ray reflectivity measurements.

This research was supported as part of the Center for Electrochemical Energy Science, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
Porosity Controlled TiNb2O7 Nanotubes As High Power Anode Materials for Li-Ion Batteries
Authors: Shin Donghyeok , Kwon Jiseok , Park Hyunjung , Song Taeseup , Paik Ungyu
Published: February 2020

Porosity of transition metal oxides makes their unique physicochemical properties for using energy storage. However, synthesizing active materials by a simple method is still hard to develop without sacrificial templates. In this regard, we report a synthesis of hollow TiNb2O7 nanotubes through dual nozzle electrospinning as a high power anode material for LIBs. The porosity of hollow TiNb2O7 nanotube was controlled by molar ratios of acetic acid to Ti/Nb alkoxide precursors and degree of Ti/Nb metal hydroxides formation in electrospun fibers. The TiNb2O7 nanotubes have the average diameter of 260 nm and a surface area in the range of 52–151 m2g-1. Moreover, the porous nanotubes consist of micropores below 2 nm and mesopores in the range of 5–60 nm in their walls that are connected to the inner hole with a diameter of 150 nm. Particularly, the unique structure of the nanotubes shows a high discharge capacity of 294 mAh g-1, stable cycle performance of 86% capacity retention over 700 cycles, and superior rate capability of 230 mAh g-1 at high 50C. Our strategy confirmed a facile synthesis of porous TiNb2O7 nanotubes without templates and the potential to use of high power anode material for LIBs.
Photoluminescence Properties of Red-Emitting Ca3ZrSi2O9:Eu2+ Phosphors
Authors: Sato Yasushi , Miyake Riho , Tomita Koji , Kakihana Masato
Published: February 2020

It has been well-known that silicon-based nitride phosphors such as CaAlSiN3:Eu2+ and Sr2Si5N8:Eu2+ possess excellent red-light emission when excited by blue-light region. However, preparation of such silicon-based nitride phosphors in pure form should be needed to sinter precursor powders under high pressure and temperature conditions. On the contrary, Eu2+-activated silicates with alkaline earth ions have been reported as high efficient phosphors. Such silicon-based oxide phosphors in pure form can be easily obtained by simple preparation techniques without any critical conditions mentioned above. Therefore, productivity and production cost for silicate phosphors are advantageous for the commercial production of red phosphors. We have reported red-emitting Ca1.2Eu0.8SiO4 phosphors excited by blue light region.1) The wavelength at the maximum emission of Ca1.2Eu0.8SiO4 phosphors was 650nm.1) We have recently discovered new red-emitting Ca3ZrSi2O9:Eu2+ phosphors with high Eu2+ concentration excited by near-UV and blue-light region. Ca3ZrSi2O9 activated by low Eu2+ concentrations (Eu2+: 1 mol%) exhibited a green emission at 530 nm. However, with increasing Eu2+ concentration to 10 mol%, Ca3ZrSi2O9:Eu2+ phosphors exhibited red emission peaking at 650 nm while the green emission disappeared. Based on the crystal structure data of Ca3ZrSi2O9, there were three Ca sites in Ca3ZrSi2O9, where Eu2+ ions were occupied.2) Two of the Ca sites were smaller than another Ca site. We presume that emission at 530 nm from Eu2+ occupying the large Ca site was not observed owing to Eu2+ concentration quenching, as well as reabsorption of the green emission light from Eu2+ at the large Ca site by Eu2+ at the two small Ca sites. Thus, the deep-red emission of Ca3ZrSi2O9:Eu2+ phosphors observed is considered to be emission from Eu2+occupying these small Ca sites.

1) Y. Sato, H. Kato M. Kobayashi, T Masaki, D. H. Yoon and M. Kakihana, Angew. Chem. Int. Ed.
53(2014) 7756.

2) J. R. Plaister, J. Jansen, R. G. de Graaff, D. J. W. IJdo, J. Solid State Chem.
115 (1995) 464.
Electrochemical Characterization of Chitosan Films As Proton-Conducting Layers for Bioprotonic Devices
Authors: Pietron Jeremy , Robinson Jeremy T. , Blue Brandon , Josberger Erik , Deng Yingxin , Rolandi Marco
Published: February 2020

We describe the lithographic fabrication, electrochemical characterization, and modeling of bioprotonic conduction channels, using a proof-of-concept material, chitosan, as a proton-conducting film deposited onto palladium electrodes. Linear sweep voltammetry (LSV) has been used to probe both the electrochemical generation of protons from H2 feed gas and the conduction of those protons through channels fabricated with different molecular weights of chitosan. Higher MW chitosan produces channels with significantly higher proton conductivity. Additionally, rigorous evaluation of the LSV data by both standard electroanalytical expressions and by digital simulation reveal that proton generation at the PdHx electrodes varies substantially between devices of different geometries. Multiple hydrogen oxidation reaction (HOR) pathways are operational at some devices, while at others a single pathway dominates. The analyses reveal the sensitivity of proton-generation kinetics on the chitosan/PdHxinterface, and furthermore, to the geometry of the device itself. Simulations of the proton conductivity in the chitosan membrane, however, yields excellent agreement between devices. Direct measurement of proton conductivity using electrochemical impedance spectroscopy further corroborates this agreement, yielding proton conductivity values nearly identical to those determined by analysis of the LSV results.

This work is supported by the Office of Naval Research.
Molybdenum Borides for Hydrogen Evolution Reaction: Theoretical Study and Experimental Proof
Authors: Fokwa Boniface P.T.
Published: February 2020

In recent years’ molybdenum-based materials have been considered as alternative catalysts to noble metals, such as platinum, for the hydrogen evolution reaction (HER) [1, 2]. We have synthesized bulk binary metal borides (Mo2B, MoB and MoB2) by arc-melting as well as MoB and MoB2 at the nanoscale by solid-state reaction and study their electrocatalytic activity towards HER in acid conditions for the first time. Among all the binary molybdenum borides, MoB2 shows excellent HER activity in both micro- and nanoscale. However, the nanoscale MoB2 shows a lower onset overpotential of about 150 mV compared to microscale MoB2 under same conditions. The electrochemical studies clearly indicating that the HER activity was greatly dependent on their crystallographic structures (boron-dependency) as well as particle size [2]. Also, our recent density functional theory (DFT) calculations on MoB2 suggest that boron is playing a prominent role in the catalytic activity of this compound. Detailed synthetic procedures, electrochemical properties and DFT calculations for these binary molybdenum borides will be discussed.

References:

J. Guo, J. Wang, Z. Wu, W. Lei, J. Zhu, K. Xia and D. Wang, J. Mater.
Chem. A
5 (2017) 4879-4885.

Seh et al., Science
355 (2017) https://doi.org/10.1126/science.aad4998.

H. Park, A. Encinas, J. P. Scheifers, Y. Zhang and B. P. T. Fokwa, Angew. Chem. Int. Ed.
56 (2017), https://doi.org/10.1002/anie.201611756.
In Situ and Operando Observation of Oxide Layer on Electrodes during the Oxygen Evolution Reaction
Authors: Toparli Cigdem , Rabe Martin , Erbe Andreas
Published: February 2020

Water electrolysis is a promising approach of electrochemical energy storage.[1] The generation of molecular oxygen at the anode limits the efficiency of the water electrolysis by creating a large anodic overpotential during the overall water splitting process. In particular, the bottleneck is the high dissolution rate and instability of the metal/metal oxides under conditions of the oxygen reduction reaction (OER).[2] In this context, manganese oxides are candidates as earth abundant and low cost water oxidation electrocatalysts.[3]

This study compares the state of oxides during electrode polarisation up to potentials with OER and transpassive dissolution on two metals, manganese and copper.[4,5] For this purpose, metallic manganese and copper electrodes were prepared by physical vapor deposition. In situ spectroscopic ellipsometry was used to investigate the oxide growth and stability. From an analysis of ellipsometric spectra, based on a previous analysis procedure,[4,5] the oxide thickness was determined as a function of electrode potential, using chronoamperometry. The nature of oxides was studied through in situ Raman spectroscopy. Information on electronic structure was derived from analysis of spectroscopic data from ellipsometry, and by UV/VIS reflection measurements. In addition, the photoluminescence background in the Raman spectra contains valuable information. The spectroscopic data was complemented with ex situ analyses, including X-ray photoelectron spectroscopy (XPS). The current results suggest that the defect formation is critical for the oxide stability and that the oxides are highly dynamic under OER condition.

[1] M. G.Walter, E. L.Warren, J. R. McKone, S. W. Boettcher, Q. Mi, E. A. Santori and N. S. Lewis, Chem. Rev., 2010, 110, 6446-6473.

[2] I. Katsounaros, S. Cherevko, A. R. Zeradjanin, and K. J. J. Mayrhofer, Angew. Chem., Int. Ed., 2014, 53, 102-121.

[3] A. Ramírez, P. Hillebrand, D. Stellmach, M. M. May, P. Bogdanoff, and Sebastian Fiechter, J. Phys. Chem. C, 2014, 118 (26), 14073–14081.

[4] C. Toparli, A. Sarfraz, A. Erbe, Phys. Chem. Chem. Phys. 2015, 17, 31670-31679.

[5] C. Toparli, A. Sarfraz, A. D. Wieck, M. Rohwerder and A. Erbe, Electrochim. Acta, 2017, 236, 104–115.
(Invited) Hydrogen and Methylcyclohexane Production By Solar Water Splitting Using Photoelectrochemical Cells
Authors: Minegishi Tsutomu , Domen Kazunari
Published: February 2020

Production of energy carriers through the solar water splitting have been attracted huge attentions as the key technology to construct a sustainable energy society. Hydrogen is the promising candidate for energy carrier because of its simple production through water splitting and utilization in many devices including fuel cells. On the other hand, Methylcyclohexane (MCH) is the promising hydrogen carrier because of its high hydrogen content per volume and usability of existing infrastructures. Herein, we investigated photoelectrochemical (PEC) hydrogen production from water and PEC MCH production through hydrogenation of toluen in existence of water as a hydrogen source.

For efficient PEC solar hydrogen and MCH production, utilization of photocatalytic materials with narrow bandgap energy is indispensable. The combination of a photoanode and a photocathode can relax the requirements for the photoelectrodes through the accumulation of driving forces.

The solid solution of ZnSe and Cu(In, Ga)Se2, ZnSex:CIGS1-x, shows relatively large cathodic photocurrent with high onset potential under simulated sunlight.1,2) The PEC cell composed of surface modified ZnSe-CIGS photocathode and BiVO4 photoanode could drive water splitting reaction with a solar-to-hydrogen conversion efficiency of hither than 1%. The PEC cell consisting of ZnSe-CIGS based membrane-photoelectrode assembly (MPA) and a BiVO4 photoanode also showed spontaneous conversion of toluene to MCH with water as a hydrogen source. In the presentation, the effects of surface modifications on durability and performance of the PEC cell for direct production of hydrogen and MCH will be discussed. 

1) H. Kaneko, T. Minegishi, M. Nakabayashi, N. Shibata, Y. Kuang, T. Yamada, K. Domen, Adv. Func. Mater., 2016, 26, 4570-4577.

2) H. Kaneko, T. Minegishi, M. Nakabayashi, N. Shibata, K. Domen, Angew. Chem. Int. Ed., 2016, 55, 15329-15333.
(Invited) Semiconductor Photocathode Materials for Direct Solar Fuel Production
Authors: Sivula Kevin
Published: February 2020

The development of robust and inexpensive semiconducting materials that operate at high efficiency are needed to make the direct solar-to-fuel energy conversion by photoelectrochemical cells economically viable. In this presentation our laboratory’s progress in the development new light absorbing materials as photocathodes will be discussed along with the application toward overall solar water splitting tandem cells for H2 production. Specifically, this talk will highlight recent results with the ternary oxide CuFeO2, 2D transition metal dichalcogenides, and organic (π-conjugated) semiconductors as solution-processed photoelectrodes.

With respect to CuFeO2, in our recent work [1] we demonstrate state-of-the-art sacrificial p-type photocurrent with optimized nanostructuring. Recent results addressing interfacial recombination by the electrochemical characterization of the surface states and attached co-catalysts will be presented along with approaches to overcome the limitations of this material.

In addition, two-dimensional (2-D) transition metal dichalcogenides (TMDs) generally have intriguing electronic properties making them promising candidates for high-efficiency solar energy conversion. However, it is notoriously difficult to fabricate thin films of 2-D TMDs over the large areas required to convert solar energy on a practical scale. We recently developed a simple method to fabricate high-quality thin films of 2-D layered TMDs at low cost and with good efficiency towards solar-to-fuel energy conversion [2]. The challenges with charge transport, separation [3] and water redox catalysis in these systems will also be discussed with respect to the 2D flake size.

Finally, with respect to π-conjugated organic semiconductors, in our recent work [4] we demonstrate a π-conjugated organic semiconductor for the sustained direct solar water oxidation reaction. Aspects of catalysis and charge-carrier separation/transport are discussed.

[1] Prevot, M. S.; Li, Y.; Guijarro, N.; Sivula, K. J. Mater. Chem. A
2016, 4, 3018-3026.

[2] Yu, X.; Prevot, M. S.; Guijarro, N.; Sivula, K., Nat. Commun. 2015, 6, 7596.

[3] Yu, X.; Rahmanudin, A.; Jeanbourquin, X. A.; Tsokkou, D.; Guijarro, N.; Banerji, N.; Sivula, K. ACS Energy Lett. 2017, 2, 524.

[4] Bornoz, P.; Prévot, M. S.; Yu, X.; Guijarro, N.; Sivula, K. J. Am. Chem. Soc. 2015, 137, 15338.
(Invited) Design of Plasmonic Catalysts Efficient H2 Production from Hydrogen Storage Molecules
Authors: Yamashita Hiromi , Mori Kohsuke , Kuwahara Yasutaka , Cheng Hefeng , Wen Meicheng , Verma Priyanka , Yin Haibo
Published: February 2020

Nanostructured plasmonic noble metals such as Au and Ag are attractive materials that strongly absorb visible light owing to their localized surface plasmon resonance (LSPR). [1-6] Up to now, the search for efficient and safe hydrogen storage materials is of crucial significance. Ammonia borane (AB: NH3BH3) and formic acid (FA) with high hydrogen content are attractive chemical hydrogen storage candidates. In this study, we demonstrated that the plasmonic nanostructures, including color-controlled Ag nanoparticles (NPs), novel MoO3-x nanosheets, and core-shell Au@Pd NPs on Metal organic frameworks (MOFs) was used as efficient catalysts under visible light for H2production from these hydrogen storage molecules.

The Ag NPs were prepared on SBA-15 mesoporous silica by microwave-assisted alcohol reduction in the presence or absence of sodium laurate. MoO3-x nanosheets were prepared by oxidizing metal molybdenum powders with H2O2 followed by the solvothermal treatments in ethanol. The catalytic performances were investigated for dehydrogenation of AB in aqueous suspensions with plasmonic catalysts. The activity for H2 production was greatly enhanced by the visible light irradiation induced by LSPR specially on the rod type Ag NPs with lager aspect ratio. Plasmonic semiconductors is another novel category with low resistive loss and earth abundance. By a facile nonaqueous access, MoO3-x nanosheets with tunable LSPR from visible light to near infrared were prepared. Under visible light irradiation, such plasmonic MoO3-x nanosheets displayed dramatically enhanced H2 production rate from AB. Furthermore, a synergistic catalysis of plasmonic Au@Pd NPs supported on titanium doped zirconium based amine-functionalized MOF(UiO-66(Zr100-xTix)) was observed for boosting H2 production from FA. The electronically promoted Pd by the charge transfer arising from the difference in work function of Pd and Au metals and the LSPR effect of Au play a crucial role in achieving high catalytic activity for H2production from FA.

1) P. Verma, Y. Kuwahara, K. Mori, H. Yamashita, Chem. Eur. J., 23, 3616 (2017). [Front Cover]

2) M. Wen, K. Mori, Y. Kuwahara, H. Yamashita, ACS Energy Lett.
2, 1 (2017.)

3) H. Cheng, M. Wen, Y. Kuwahara, K. Mori, Y. Dai, B. Huang, H. Yamashita, J. Am. Chem. Soc., 138, 9316 (2016). [Featured in JACS Spotlights]

4) P. Verma, Y. Kuwahara, K. Mori, H. Yamashita, J. Mater. Chem. A, 4, 10142 (2016). [Front cover]

5) H. Cheng, T. Kamegawa, K. Mori, H. Yamashita, Angew. Chem. Int. Ed., 53, 2910 (2014).

6) K. Fuku, T. Kamegawa, K. Mori, H. Yamashita, Angew. Chem. Int. Ed., 52, 7446 (2013).

Figure 1
Combustion Synthesis and Photoelectrochemical Characterization of Metal Oxynitrides Using GaxZn1-XOyN1-Y as a Model Candidate
Authors: Meekins Benjamin Highsmith
Published: February 2020

Utilization of solar energy is a necessary path forward to deal with the looming energy crisis and worldwide effects of fossil fuel usage. A key component of this utilization is how to store excess solar energy for use on demand. One such method is splitting water into hydrogen and oxygen, both of which can be stored and either burned as fuel or used as feedstock components in industrial processes to synthesize high-value materials. Metal oxynitrides have shown great potential as photocatalysts for overall water splitting applications. Incorporation of nitrogen into metal oxides narrows the band gap to enable absorption of light in the visible spectrum. The typical synthesis of a metal oxynitride, however, requires annealing temperatures at or above 1000 oC and nitridation by flowing pure ammonia gas for anywhere from 1 to 48 hours. Such harsh synthesis conditions can limit the discovery of new candidate materials.

In our work, we have prepared an array of gallium zinc oxynitrides (GaxZn1-xOyN1-y) as a model system using a combustion synthesis method and demonstrate that gallium zinc oxynitrides can be synthesized in 30 minutes at 500 oC using this method. X-ray diffraction (XRD), UV-visible spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) are used to characterize the physical properties of the as-synthesized materials. XPS analysis reveals that as much as 50% nitrogen substitution in the metal oxide lattice can be achieved, dependent on the ratio of gallium and zinc nitrates used as precursors. XPS also reveals that the nitrogen valency is that of a nitride material, as would be expected for a substitution into the crystal lattice. Relative atomic concentrations from XPS also reveals that the complex formed is essentially GaN:ZnO. UV-visible spectroscopy reveals that the band gap of the GaxZn1-xOyN1-ymaterials can be controlled simply by altering the precursor ratio. X-ray diffraction measurements reveal shifts in the crystalline peaks from ZnO toward GaN, confirming the incorporation of nitrogen into the lattice. The as-synthesized products are capable of generating photocurrent from visible light irradiation and are able to carry out water splitting in pure water without any co-catalysts, such as Pt, IrO2, or Rh/Cr2O3.

Finally, we discuss how to take the results gained from this work and expound upon it to begin the search for new candidate oxynitride materials, including potential high-throughput methods for rapid screening of such candidates. We also discuss the apparent conditions necessary for successful formation of an oxynitride material based on initial experiments with new candidates.

Figure caption: Picture of as-synthesized powders from an initial Ga:Zn:urea molar ratio of (A) 1:1:0 and (B) 1:1:10.

Figure 1
(Keynote) Ionic Liquid-Based Electrolytes for Alkali Metal Batteries
Authors: Moretti Arianna , Passerini Stefano
Published: February 2020

Li-metal batteries have known a continuous development since the introduction of PEO based electrolytes [1]. The coming on the market in 2012 of a Li-metal polymer powered car with 250 km driving range (BlueCar) has confirmed the possibility to implement lithium metal batteries in the market. Moreover, most of the ‘next generation’ batteries such as Li-S or Li-air are based on Li-metal negative electrodes. If the present Li-metal electrolytes are based on polymer electrolytes, ionic liquids (ILs) based electrolytes such as LiFSI-PYR14FSI [2] or crosslinked PEO-PYR14TFSI-LiTFSI [3] have demonstrated very reversible lithium plating/stripping.

IL-based electrolytes are also showing promising performance in novel energy storage systems such as Na/seawater batteries [4].

A review of our results on the use of ionic liquid-based electrolytes for lithium, sodium, and multivalent cations will be presented.

Acknowledgement:

This work is supported by the European Commission within the projects LABOHR and INFLUENCE and the Helmholtz Gemeinschaft within the project “Helmholtz-Energie-Allianz - Stationaere elektrochemische Feststoff -Speicher und –Wandler” (HA-E-0002).

References :

1. M. Armand, M. Duclot, J. M. Chabagno, EU 00013199

2. E. Paillard, Q. Zhou, W. A. Henderson, G. B. Appetecchi, M. Montanino and S.Passerini,

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Enhanced Intermediate-Temperature CO2 Splitting Using Non-Stoichiometric Ceria and Ceria-Zirconia
Authors: Zhao Zhenlong , Uddi Mruthunjaya , Tsvetkov Nikolai , Yildiz Bilge , Ghoniem Ahmed F.
Published: February 2020

CO2 splitting via thermo-chemical or reactive redox has emerged as a novel and promising carbon-neutral energy solution. Its performance depends critically on the properties of the oxygen carriers (OC). Ceria is recognized as one of the most promising OC candidates, because of its fast chemistry, high ionic diffusivity, and large oxygen storage capacity. The fundamental surface ion-incorporation pathways, along with the role of surface defects and the adsorbates remains largely unknown. This study presents a detailed kinetics study of CO2 splitting using CeO2 and Ce0.5Zr0.5O2 (CZO) in the temperature range 600-900℃. Compared to what has been reported previously, we observed higher splitting kinetics, resulting from the utilization of fine particles and well-controlled experiments which ensure a surface-limited-process. The peak rates with CZO are 85.9 μmole g–1s–1 at 900℃ and 61.2 μmole g–1s–1 at 700℃, and those of CeO2 are 70.6 μmole g–1s–1 and 28.9 μmole g–1s–1. Kinetics models are developed to describe the ion incorporation dynamics, with consideration of CO2 activation and the charge transfer reactions. CO2 activation energy is found to be – 120 kJ mole-1 for CZO, half of that for CeO2, while CO desorption energetics is analogous among the two samples with the value of ~160 kJ mole-1. The charge-transfer process is found to be the rate-limiting step for CO2 splitting. The evolution of CO3
2- with surface Ce3+ is examined based on the modeled kinetics. We show that the concentration of CO3
2- varies with Ce3+ in a linear-flattened-decay pattern, resulting from a mismatch between the kinetics of the two reactions. Our study provides new insights into the significant role of the surface defects and adsorbates in determining the splitting kinetics.
Synthesis of Nanoscale Li7La3Zr2O12 Solid State Electrolyte By Spray Drying
Authors: Uddin Md-Jamal , Letfullina Alla R , Alaboina Pankaj Kumar , Cho Jong-Soo , Cho Sung-Jin
Published: February 2020

To enable the futuristic applications of Li-ion batteries, significant boost in energy density and tremendous improvement in safety is required. Ceramic solid state electrolytes (SSE) with fast Li-ion diffusion are a promising class of materials that can potentially change the scenario because of their superior thermal and chemical stabilities and a wider operational temperature window. Among the numerous different solid-state oxide materials, Li7La3Zr2O12(LLZO) has gained significant interest due to its high ionic conductivity, good compatibility with lithium metal and stability in air. The preparation of LLZO is mostly based on the conventional solid state syntheses or sol-gel method, in which powders are calcined usually at temperatures above 850 °C. These current synthesis routes generally require higher calcination temperatures and longer heating duration.

In this work, we have reported spray-dried LLZO particles for the first time via a low-temperature calcination. Spray drying has allowed us to achieve a nanoporous LLZO precursor which was later calcined only at 450 °C for 4 hours to obtain the LLZO particles. The nanoporous spray-dried particles have aided in the sintering process because of higher surface energy, and thus has significantly reduced the calcination time and temperature. LLZO Pellets were prepared for further physical-chemical characterization. Electrochemical performance evaluation is also in order.
Structure-Property-Process Relationships of Melt-Blown PVDF: A Potential Li-Ion Battery Separator
Authors: Luiso Salvatore , Fedkiw Peter S , Spontak Richard J , Pourdeyhimi Behnam
Published: February 2020

While significant research efforts have focused on the negative and positive electrode materials in rechargeable Lithium-ion (Li-ion) batteries, battery separators have only recently received more consideration from the scientific community. The separator plays a critical role in Li-ion batteries by preventing physical contact between the positive and negative electrodes while permitting efficient ionic transport across the separator. There are four major types of separators: microporous polymeric membranes, nonwoven polymeric mats, gel-polymer electrolytes and composite membranes. Relative to the more conventional microporous membrane separators, nonwovens have the advantage of low cost, low mass and high porosity; in addition, the fibrous mat provides good structural cohesion due to its intertwined fibers. Although most polymers used to make nonwoven battery separators have resulted in lower cell performance (lower ionic conductivity and higher resistance) than conventional microporous separators, polyvinylidene difluoride (PVDF) shows promising results because of its stability and affinity for electrolytes commonly employed in Li-ion cells. The best manner to produce nonwoven PVDF would employ a melt-blowing process, which is a well-developed, high-volume production technology. To be melt-blowable, polymer resins must have high melt-flow rates but commercial PVDF resins did not possess this property until recently. Nevertheless, researchers have successfully electrospun PVDF from a solution with the goal of exploring this promising polymer as a nonwoven battery separator.

We are investigating the fundamental properties and characteristics of two novel melt-blowable PVDF grades (Kynar® 705 and Kynar® ADS II from Arkema) with the objective of elucidating their structure-property-process relationships and studying their performance as separators in Li-ion batteries. In this work, we will report on the physical, chemical, and electrochemical properties of nonwoven PVDF relevant to their use as battery separators.
Determining "Apparent" Diffusion of Electrons through a Nafion Membrane Using Hydrodynamic Voltammetry
Authors: Reynolds Marissa Kayle , Paul David W
Published: February 2020

Nafion is used extensively as a proton exchange membrane in PEM fuel cells. The membrane must be hydrated in order to function properly as an electrolyte and as a physical separation barrier between the anode and the cathode. In this project, potassium ferricyanide is added to the hydrating electrolyte solution and is shown to incorporate into the Nafion membrane. By using hydrodynamic voltammetry, the ferricyanide redox signals can be used as a diagnostic and an investigative tool to study the integrity and swelling properties of the Nafion membrane. When ferricyanide is absent from the hydrating solution, but present in the bulk electrolyte solution during the hydrodynamic voltammetry experiments, the signals produced (or lack thereof) can be used as a diagnostic tool for the physical integrity of the membrane. When ferricyanide is allowed to incorporate into the membrane, the properties of the hydrated membrane can be investigated. An new equation, known as the Tedford equation, was derived to determine the diffusion coefficient of the analyte in the bulk solution and an apparent diffusion of electrons within the membrane itself. The Tedford equation accounts for the dependence on the rotation rate as well as known membrane properties such as thickness and the concentration of the analyte incorporated into the membrane from the bulk solution during hydration.

For a bare rotating disk electrode, the Levich equation can be used to determine the bulk diffusion coefficient (D) by plotting the diffusion limiting current (iL) against the square root of the rotation rate (ω).

iL=0.62nFAD2/3 ν-1/6 C* ω1/2 (1)

The slope is made up of the known variables where n is the number of electrons in the redox reaction, F is Faraday’s constant, A is the electroactive area of the electrode, ν is the kinematic viscosity of the solution, and C* is the concentration of the analyte in the bulk.

The Dahms-Ruff equation can be used to determine the apparent diffusion coefficient of electrons (DE) and the current due to this apparent diffusion (iE).

DE=D+kφ2 Cp* (π/4) (2)

iE=(FADE Cp*)/δm (3)

where k is the rate constant of the redox reaction, φ is the average distance between the redox centers in the membrane, Cp* is the total amount of analyte in the membrane, and δm is the membrane thickness.

Equations 1 and 3 were combined to derive the Tedford equation in relation to the peak current (ip).

ip=0.62nFAD2/3 v-1/6 ω1/2 (C*-Cm )+(nFADE Cm)/δ
m
(4)

This equation can be used to determine the apparent diffusion coefficient of the electrons with the ferricyanide redox centers in the membrane. It can also be used to compare membranes with differing hydration times and possibly to study hydrating properties.
Optical Cooling of CdSe/ZnS Quantum Dots Embedded in PMMA
Authors: Fontenot Ross , Mathur Veerendra , Barkyoumb John
Published: February 2020

In 1929, the German physicist Peter Pringsheim proposed that anti-Stokes emission can lead to the cooling of bulk matter. Anti-Stokes emission results in photons of shorter wavelength (higher photon energy) than that of the exciting light due to thermal absorption. In solids, the thermal energy is mostly due to the vibrational modes (phonons) of the lattice. Thus, using lasers to cool a solid, one has to irradiate a sample with laser light in the red tail of the absorption spectrum. The material to be cooled would then absorb a photon and absorb extra energy from a phonon to emit a blue-shifted photon of higher energy. By removing these phonons, the material is cooled.

Today, this technique is known as laser cooling of solids or optical refrigeration. It can be used to achieve an all-solid-state cryocooler that is compact, contains no moving parts, has a high reliability, and does not require the use of cryogenic fluids. Laser cooling also allows for the possibility of portable lasers that require no or smaller external cooling systems because the pump wavelength can be adjusted such that spontaneous anti-Stokes luminescence cooling compensates for the stimulated quantum defect heating. A thermally balanced laser such as this would not suffer from thermal defocusing or heat damage; therefore, such solid-state-lasers could achieve higher output powers. Unfortunately, for cooling to occur in solids, the quantum efficiency of the material must be high and nearly all the anti-Stokes luminescence must leave the material without being reabsorbed.

Recently, much research has been performed on rare-earth ions for laser cooling. However, the cooling efficiency of rare-earth ions approaches zero as the temperature decreases. As a result, they have a theoretical cooling limit about 90 K. On the other hand, semiconductors provide more efficient pump light absorption, the potential for lower temperatures of 10 K, and the ability to directly integrate the material into electronic and photonic devices. This coupled with the strong electron-phonon coupling of Group II-VI semiconductors and core-shell quantum dot structure minimizing the reabsorption of the anti-Stokes luminescence, makes direct bandgap semiconductors viable laser cooling candidate materials.

Owing to the possibility for near-unity quantum efficiency of CdSe/ZnS, we have chosen to investigate CdSe/ZnS quantum dots for laser cooling applications. Recently, we have utilized photothermal deflection techniques to show that CdSe/ZnS can be cooled at a microscopic level. Moreover, we developed a new photothermal technique that is capable of discerning heating or cooling inside a material using nothing but the probe deflection thereby eliminating the need for a Stokes and anti-Stokes laser. Using the information gained from the photothermal results, we have begun to cool CdSe/ZnS polymers. This talk will go over the cooling results as well as our new photothermal technique.
Study about an Experimental Design for CdTe Quantum Dots Synthesis. Analysis of the Optical Changes after Their Interaction with Hydroxyl Radicals
Authors: Muñoz Eduardo Carlo , Navarrete Emilio Alonso , Rojas Víctor , Román Javier , Henríquez Rodrigo Gonzalo , Schrebler Ricardo Silvio
Published: February 2020

Quantum dots (QDs) are semiconductor nanocrystals with diameters in the range of 2-10 nm and which exhibit electronic properties between bulk materials and molecules. Considering their optical properties, fluorescence processes exhibit real applications in sensor and biosensors fields. In fact, the fluorescent properties of these materials can be tuned depending on the particle size. Generally, a decrease of the QDs size produces an increase in the energy gap between the valence and the conduction band, which induces to a shifted of the emission wavelength toward shorter values. In this work we examined an optimization of the synthesis parameters of CdTe QDs using a Doehlert design of experiments. The synthesis employed Na2TeO3 and CdCl2 as precursors, mercaptosuccinic acid (MSA) as capping agent, NaBH4 as reducing agent and Borax/Citrate as buffer in a reflux system. The synthesis parameters optimized were: temperature, pH, molar ratio of precursors and reaction time. After, an analysis of the optical and electrochemical changes after the interaction with hydroxyl radicals was carried out. The optical changes were studied by fluorescence spectroscopy measurements evaluating the fluorescence lifetime. The changes in these properties were studied in absence and presence of hydroxyl radicals produced by a Fenton reaction (unstable radical), and presence of 2,2,6,6-tetramethylpiperidine-1-oxyl radical(TEMPO) (stable radical).