bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysing Gas-Liquid Flow in PEM Electrolyser Micro-Channels Using a Micro-Porous Ceramic as Gas Permeable Wall
Authors: Sadeghi Lafmejani Saeed , Olesen Anders Christian , Al Shakhshir Saher , Kær Søren Knudsen
Published: February 2020

The modern civilization is working based on a secure, sustainable, and economic energy. With the increasing share of renewable energies like solar and wind power, the secure and sustainable energy production will go under threat due to highly fluctuating electricity generated from these energy sources. An opportunity is to store energy as a means of energy surplus absorption. Polymer Electrolyte Membrane Electrolysis Cell (PEMEC) as a method of long term (more than an hour) energy storage, converts the unstable generated electricity to hydrogen. It is a key technology for closing the renewable energy economical system loop. It converts water to oxygen and high pressure hydrogen using electricity with a fast response rate that suits to damp grid fluctuations. One of the issues within these electrolysers is their high cost. One means of the cost reduction is to increase production from the existing cell by increasing its current density from 1 (A/cm2) (at the existing conventional cells) to 5 (A/cm2). At high current densities, due to high rate of oxygen generation and concentrated heat generation in the cell, issues related to heat and gas management come up which must be managed. In this study, an experimental setup is made of plexiglass, Titanium-felt (Ti-felt) and nano-porous ceramic. The setup demonstrates a similar gas-liquid flow encounters in PEM water electrolysis micro-channels and anode porous media. The nano-porous ceramic plate simulates small bubbles generation on the real membrane electrode assembly (MEA) surface. The movement of gas-liquid flow upward in the micro-channel at several water stoichiometric numbers are analysed and compared with a transparent PEMEC.

Figure 1
Relating Temperature-Dependent Aging Rate to Cathode Materials in Commercial 18650 Li-Ion Battery
Authors: Wang Han , Whitacre Jay
Published: February 2020

Temperature plays an important role in battery aging rate. Previous reports1-3of commercial batteries with different cathode materials revealed the relationship between aging rate and cycling temperature ( between 25oC and 70oC ) can be described by Arrhenius plot. In other words, battery aging rate increases with increasing cycling temperature within range from 25oC to 70oC. While most Li-ion batteries suffer significant capacity loss when cycled at elevated temperatures, previous report4 has suggested that high temperature abuse testing had nearly no effect on aging rate of commercial 18650 NCA-based batteries, an effect not reported for batteries with LiCoO2or other common chemistries. We have investigated this effect further and reported that long-term constant current cycle testing of commercial 18650 NCA–based batteries at elevated temperature showed less capacity loss than control testing performed at room temperature, as shown in figure 1. Furthermore, the batteries cycled at room temperature exhibited excessive SEI formation on anode surface whereas there was much less SEI formation in the elevated temperature testing.

Mechanisms such as excessive lithium plating have been put forward as a possible cause4, though this would not explain why NCA-based batteries outperform batteries based on other similar cathode chemistries. We will present several possible hypotheses that describe this aging mechanism with a focus on understanding the relationship between SEI formation on the anode and cathode surface chemistry.

Reference:

1. Ramadass, P.; Haran, B.; White, R.; Popov, B. N., Capacity fade of Sony 18650 cells cycled at elevated temperatures Part I. Cycling performance. J Power Sources
2002,
112(2), 606-613.

2. Situ, W. F.; Yang, X. Q.; Li, X. X.; Zhang, G. Q.; Rao, M. M.; Wei, C.; Huang, Z., Effect of high temperature environment on the performance of LiNi0.5Co0.2Mn0.3O2 battery. Int J Heat Mass Tran
2017,
104, 743-748.

3. Waldmann, T.; Wilka, M.; Kasper, M.; Fleischhammer, M.; Wohlfahrt-Mehrens, M., Temperature dependent ageing mechanisms in Lithium-ion batteries - A Post-Mortem study. J Power Sources
2014,
262, 129-135.

4. Waldmann, T.; Kasper, M.; Wohlfahrt-Mehrens, M., Optimization of Charging Strategy by Prevention of Lithium Deposition on Anodes in high-energy Lithium-ion Batteries – Electrochemical Experiments. Electrochim Acta
2015,
178, 525-532.

Figure 1
Oxygen Redox in Li-Ion Battery Chemistries
Authors: Roberts Matthew , Bruce Peter G. , Luo Kun , Guerrini Niccolo
Published: February 2020

The energy density of lithium batteries is currently restricted by the cathode material, delivering ~ 160-190 mAh g-1.1 New high-energy-density cathode materials are much sought after to meet the increasing requirements of consumer electronics, electric vehicles and grid energy storage. The so called lithium-rich layered oxide materials (e.g. Li1-x[Li0.2Mn0.6Ni0.2]O2), exceed the conventional limit of charge storage as far more lithium (x ≈ 1, corresponding to 310 mAh g-1) can be extracted than can be accounted for through transition metal oxidation (x ≈ 0.4). The source of this “extra” capacity has been explained previously by a number of models including oxygen loss, electrolyte decomposition and anion redox.

 Recently, several groups have identified that this “extra” capacity is resulting from a reversible oxygen redox process2-7. In this work, we examine in detail the charging process in Li[Li0.2Ni0.2Mn0.6]O2 with direct experimental evidence of a dominant O redox process, accompanied by a minor contribution from oxygen loss, when the material is charged beyond 4.4 V. The formation of hole states around the oxygen during charging was probed using soft x-ray absorption spectroscopy (SAXS), as shown in Figure 1. Additionally, recent results that underpin the oxygen redox process in a number of closely related Li-rich compositions will be discussed, as well as the requirements necessary to form holes on the oxygen in these compounds. The conclusions of this work, and that of other researchers working to understand anion redox, provide us with a guidance which can be used to discover future high energy density cathode materials.

References

1. Goodenough, J. B.; Kim, Y. Chem Mater
2010, 22, (3), 587-603.

2. Luo, K.; Roberts, M. R.; Hao, R.; Guerrini, N.; Pickup, D. M.; Liu, Y. S.; Edstrom, K.; Guo, J. H.; Chadwick, A. V.; Duda, L. C.; Bruce, P. G. Nat Chem
2016, 8, (7), 684-691.

3. Luo, K.; Roberts, M. R.; Guerrini, N.; Tapia-Ruiz, N.; Hao, R.; Massel, F.; Pickup, D. M.; Ramos, S.; Liu, Y. S.; Guo, J.; Chadwick, A. V.; Duda, L. C.; Bruce, P. G. J Am Chem Soc
2016, 138, (35), 11211-8.

4. Koga, H.; Croguennec, L.; Menetrier, M.; Mannessiez, P.; Weill, F.; Delmas, C. J Power Sources
2013, 236, 250-258.

5. Koga, H.; Croguennec, L.; Menetrier, M.; Mannessiez, P.; Weill, F.; Delmas, C.; Belin, S. J Phys Chem C
2014, 118, (11), 5700-5709.

6. Sathiya, M.; Rousse, G.; Ramesha, K.; Laisa, C. P.; Vezin, H.; Sougrati, M. T.; Doublet, M. L.; Foix, D.; Gonbeau, D.; Walker, W.; Prakash, A. S.; Ben Hassine, M.; Dupont, L.; Tarascon, J. M. Nat Mater
2013, 12, (9), 827-835.

7. Seo, D. H.; Lee, J.; Urban, A.; Malik, R.; Kang, S.; Ceder, G. Nat Chem
2016, 8, (7), 692-7.

Figure 1
Development of Novel Electrolyte Additives for Designed Surface Modification
Authors: Lucht Brett L
Published: February 2020

An investigation of the effect of electrolyte on performance of in lithium ion batteries will be presented

The electrochemical performance of common electrolyte formulations will be discussed along with

detailed ex-situ surface analysis of the cycled electrodes. The ex-situ analysis allows the development of

an understanding of the role of the electrolyte and common additives in the structure of interfacial

electrode films on both the anode (solid electrolyte interphase, SEI) and on the cathode. Correlation of

the structure of the surface films with the performance limiting reactions in lithium ion batteries affords

insight into the mechanism of interfacial film formation and function. The mechanistic insight is used to

systematically develop novel additives designed for specific electrode surface modification to afford

optimized electrochemical performance. The electrochemical performance and ex-situ surface analysis of

electrodes cycled with novel Additives for Designed Surface Modification (ADSM) will be presented.
Sodium Titanate Nanowires As High Rate Anode Materials for Lithium-Ion Batteries
Authors: Liao Jinyun , Smith Taylor , Xing Yangchuan
Published: February 2020

Sodium titanate has been studied as an attractive anode candidate for Na-ion batteries due to its low cost, environmental friendliness, ease of synthesis, and structural stability during cycling. However, Na ions are about 25% larger than lithium, which leads to slower charge/discharge rates. In addition, the larger diameter of Na ions compared with lithium causes the volume changes that occur from intercalation to be even more severe. Few reports thus far have focused on sodium titanate as an anode material in Li-ion batteries (LIBs), where Li+ can also be inserted into sodium titanate at low voltage.

The main disadvantage for sodium titanate as an anode material for LIBs is its low electronic conductivity, resulting in poor rate capability. Several approaches have been taken in an attempt to improve the electronic conductivity of sodium/lithium titanate, such as electronic material coating/mixing, ionic doping, comminution, etc.; but as of yet there has been no uniform carbon coating reported on sodium titanate for LIBs. In this work, we detail a facile technique to create uniform thin carbon coating layers on Na2Ti6O13 nanowires (NTO-C). In addition, we also explored self-doped Ti3+ on carbon coated Na2Ti6O13 nanowires (NTO-Ch) in an effort to further improve its electronic conductivity. The detailed results of the synthesis, characterization, and electrochemical performance of the NTO-based materials (NTO, NTO-C and NTO-Ch) will be presented.

Fig. 1 (a, b) TEM and HRTEM images of NTO-Ch nanowire. (c) Rate capability comparison of NTO-based nanowire electrodes in Li-ion batteries.

Figure 1
Develop a Facil Syntheis Process for Si-Alloy Anode Material for Li-Ion Batteries
Authors: Yang Johnny , Li Bin
Published: February 2020

Silicon is regarded as one of the most promising anode materials because of its theoretical specific capacity (4200mAh/g) compared to commercially available graphite anodes (370mAh/g). However, Si electrodes suffer considerable volume expansion of up to 300% during electrochemical lithiation, leading to electrode cracking and pulverization of the Si, causing rapid capacity degradation. Various approaches had been used for using nanostructured Si materials have been applied to solve this problem, since the interval distance between nano structures and internal spaces in them can act as structural buffer space to accommodate the volume expansion of Si. Although some of the nanostructured Si materials achived considerably high capacity and cyclability, they are usually prepared by complicate and high cost synthetic process which are difficult to extend to large scale. The other approach is using active/inactive alloys as an efficient way to reduce volume expansion and improve cycling performance. The volume expansion of Si can be suppressed by the presence of inactive components, resulting in the maximum energy density at a given volume expansion. Literature has also shown commercially available and low-cost Si alloys can serve as high capacity Li-storage anodic host materials with certain cyclability. If such Si alloy compounds can be made with required chemical stoichiometry and structural architecture though a simple mechanochemical process.

Wildcat Discovery Technologies is developing facile synthesis pathway to prepare Si-alloy active/inactive material. Our approach utilized high-throughput combinatorial research to optimize synthesis process, Si-alloy composition and electrode component to improve the cycling performance of the anode material. Here we demonstrate that with optimized synthesis process, varied active Si and inactive alloy composition reveal a strong correlation between capacity and cyclability.
Highly Efficient Gel Polymer Electrolyte Operating at Room Temperature for All Solid State Battery Applications
Authors: Piana Giulia , Armel Vanessa , Franger Sylvain , Duffault Jean-Marc , Porthault Hélène
Published: February 2020

Numerous incidents occurred in the past decades involving lithium batteries, from the explosion of car battery pack to the smartphones burning, highlighting the security issues of this kind of battery. The main danger comes from the liquid electrolyte which is thermally unstable and represents a weak barrier against lithium dendrite growth upon cycling. Polymer electrolytes are an interesting alternative to current liquid ones. Solid polymer electrolytes (SPE) are solvent free electrolyte and are composed of a salt and a polymer which gives mechanical properties. These SPE present an important safety increase but the electrochemical performance, especially at room temperature, remains very low. Another material family is under development: the Gel Polymer electrolyte (GPE). GPE are composed of a lithium salt, a polymer and a solvent which improves the electrochemical performance1,2.

In this work, we want to develop an original ‘’wet’’ chemical process to realize the electrolyte thin film. The chosen gel polymer electrolyte (GPE) is composed of an acrylate polymer matrix which gives the mechanical behavior and a liquid phase which gives the electrochemical properties. The liquid phase is a mixture of an ionic liquid and a lithium salt. The electrolyte is polymerized by UV-curing (Fig.1). In a first step, the GPE was characterized with an original in-situ impedance spectroscopy to monitor the polymerization reaction (Fig.2). Conductivity measurements reveal very high ionic conductivity (> 1 mS/cm), whatever the electrolyte composition, which was expected considering the high ionic content in the liquid phase. However, the lithium transference number is very low (< 0.1) leading to low lithium conductivity (~10-12S/cm). Raman spectroscopy was used to determine Li-TFSI coordination (Fig.3) which, could partially explain the low transference number. Electrolyte composition was improved to increase the transference number (up to 0.29). The as-obtained electrolyte was integrated in an all solid state battery with LiCoO2 cathode. Galvanostatic cycles of batteries integrating a GPE or a standard liquid electrolyte are presented in Fig.4. Cycling was done at ambient temperature with a high 1C C-rate and electrochemical results are very similar despite a slightly higher polarization with the GPE.

[1] M. Armand, Solid State lonics 69 (1994) 309-319.

[2] A. Arya, Ionics (2017).

Figure 1
Electrodeposition of Metal Oxide Nanoparticles for Li-Ion Battery Anodes
Authors: Ates Mehmet Nurullah , Busbee John
Published: February 2020

Electrodeposition technique is one of the unique ways to synthesize cathode and anode active materials for Li-ion batteries. At Xerion Advanced Battery, we couple this technique with a technology where we deposit active materials directly to the current collector. Thus, we eliminate the use of the binder, conductive carbon in addition to their complex preparation. In this work, we report a facile non-aqueous electrodeposition method to obtain anode active materials for Li-ion batteries. This single step synthesis method offers several benefits for the active material. Of particular significance are i-) it can be directly deposited on 3D substrate ii-) nano-sized active materials can be achieved due to low-temperature synthesis and iii-) high purity.

Although Li insertion into the metal oxide anodes has relatively higher voltages than that of commercial anodes (graphite), they still offer great benefits such as low output voltages of Li-ion cell which is necessary for devices requiring low voltages. This application is particularly received great attention from electronic (optics and chips) industry. We will specifically discuss the Co and Mn-based metal oxides and their electrochemical performances in conjunction with their structural and morphological data. Anode active materials on different 3D structures, including Ni scaffold and corrosion resistance fibers, will be evaluated and discussed. Figure 1 shows the FESEM image of a direct conformal deposition of Co3O4 nanoflakes on corrosion resistance fibers. Our preliminary data revealed that this anode material can deliver up to 2000mAh/g capacities at relatively low rates. Rate capabilities will be evaluated using different 3D substrates.

Figure 1
(Invited) Additively Manufactured Gain Media for Lasers
Authors: Payne Stephen , Cherepy Nerine , Jones Ivy K , Seeley Zachary , Duoss Eric
Published: February 2020

We are developing an innovative approach for fabricating laser gain media, such as laser rods, based on utilizing the direct ink write (DIW) additive manufacturing methodology, together with ceramics processing. For DIW, the key is to formulate the ink so that has three main properties: (1) experiences shear-thinning so that it can pass through a nozzle of 250-500 mm; (2) encounters considerable “gelation” after exiting the nozzle so that the structure remains relatively firm; and (3) must include ~50% loading of the gain medium by volume, e.g. YAG. In Fig. 1, we see the DIW instrument, an example of a laser rod written with both doped and undoped regions, and the rheology curve for a typical ink. After writing the part, the next steps include heating near 1000C to remove the solvents, cold isostatic pressing to a green body, sintering (usually near 17000C) to about 95% density, and finally heating under pressure (HIP’ing) to generate a clear part. The main advantage of this optical design for a laser rod is that it will strongly induce the TEM00 mode of the laser and thereby increase the beam quality. In this talk we will discuss both the laser physics and the materials issues associated with the new pathways for fabricating laser elements.

This work was performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Figure 1
Systematic First-Principles Calculations of Charge Transfer Transitions of Rare Earth Ions in Oxides Using Simple Cubic Model Cluster
Authors: Takemura Shota , Ogasawara Kazuyoshi
Published: February 2020

[Introduction] It is important for trap levels to capture carriers for persistent phosphors, and the properties depend on the positions of the trap levels within the band gap [1]. It is necessary to estimate the positions of impurity levels which work as trap levels for material design of the persistent phosphors. As one of the ways, the position of the impurity level within the band gap can be estimated by calculating the charge transfer transition energy from the valence band (Ligand to Metal Charge Transfer: LMCT). However, calculation of the LMCT based on quantum theory is exceedingly difficult in d electron system like transition metal and f electron system like rare earth ion because the calculation requires to consider many-electron effect, symmetry and relativistic effect such as spin-orbit interaction. Recently, we successfully reproduced the LMCT energies and their experimental trend of transition metal ions in α-Al2O3 by performing configuration interaction (CI) calculation using the DVME method [2]. From these results, we expect that the relativistic DVME method can be also applied to rare earth ions. In this study, as a first approach, in order to obtain the LMCT energy for various trivalent RE ions in REO8
13- cubic model cluster, we performed first-principles calculations using the DVME method and constructed the theoretical energy diagram of the rare earth ions, and compared it with the reported LMCT energies in YPO4 [3] and YAG [4].

[Computational Method] We constructed a 9-atom cluster consisting of the central RE ion and the 8 oxygen ions with Oh symmetry (cubic) and 2.4 Å bond length. We considered the ground state configuration 4f
n
2p48 and one-electron excitation configuration 4f
n

+12p47, where n is the number of 4f electrons. In order to improve the computational accuracy, the configuration dependent correction (CDC) was considered. The LMCT energy was calculated as the transition energy from the top of the valence band corresponding to the highest one of the MOs mainly consisting of oxygen 2p orbital to the MO mainly consisting of RE 4f orbital based on the MO calculation using the DV-Xα method and the CI calculation using the DVME method.

[Result] The theoretical LMCT energies calculated with CDC are shown as the diagram in Fig. 1 together with the diagram for the reported values in YPO4 and YAG. The figure shows that the reported trend, especially around Eu to Gd, was successfully reproduced by first-principles calculations. The overestimation for Ho to Tm is probably due to the insufficient consideration of electron correlation.

[1] J. Ueda, et al,. Appl. Phys. Lett. 104, 101904, (2014).

[2] K. Ogasawara, et al., Phys. Rev. B, 64, 115413, (2001).

[3] E. Nakazawa, J. Lumin. 100, 89, (2002).

[4] P. Dorenbos, J. Lumin. 134, 310, (2013).

Figure 1
(Invited) Up-Conversion Luminescence of Lanthanide Activated Phosphors
Authors: Swart Hendrik C , Kroon RE , Terblans JJ , Pandey A , Kumar A , Holsa J
Published: February 2020

The major problem that limits solar cells’ efficiency is their insensitivity to the whole solar spectrum which is the so-called spectral mismatch. Therefore, several mechanisms have been explored based on photoluminescence (PL) to convert the solar cell spectrum where the spectral response of the solar cell is low to regions where the spectral response of the solar cell is high. Downconversion, up-conversion (UC) and downshifting are some of the mechanisms that may be applied to improve the spectral response. Upconversion nanoparticles (UCNPs) have shown some promising possibilities to be considered in this respect, however, low UC efficiency of UCNPs is still the most severe limitation of their applications. This study reports on the PL and cathodoluminescence (CL) behaviour of different phosphors. The vastly studied lanthanide pairs in UC are Er3+, Ho3+ and Tm3+ with Yb3+ as a sensitizer. Whereas, very few UC studies have been carried out for Yb3+/Tb3+ and Yb3+/Eu3+ pairs. The reason behind these two categories of lanthanides is the way they transfer their energies. Er3+, Ho3+ and Tm3+ co-doped with Yb3+ can be excited by ground state absorption (GSA), excited-state absorption (ESA) and energy transfer up-conversion (ETU) mechanisms whereas the energy transfer from Yb3+ to Tb3+/Eu3+ is due to co-operative energy transfer (CET). Since, Tb3+ and Eu3+ do not have energy levels which can absorb the near infra-red (NIR) light directly, Yb3+ is the best choice in order to obtain the UC luminescence in Tb3+/ Eu3+ doped system. Yb3+ has a single electronic transition within the 4f subshell. The transition from the lower level through ground state absorption can be easily achieved by using NIR radiation, and resulting energy from two or more excited Yb3+ ions can be utilized in the excitation of a single Tb3+ or Eu3+ ion, for gaining improved UC emission. Doping different host materials with these lanthanide pairs were investigated and tested for possible increase in solar cell efficiency. Power tuneable visible UC and infrared emissions were detected upon excitation with a 980 nm diode laser.
Changes in the Optical and Electronic Properties of CdTe Quantum Dots By the Effect of Interaction with Free Radicals in Aqueous Solution
Authors: Navarrete Emilio Alonso , Pérez-Prieto Julia , Rojas Víctor , Román Javier , Henríquez Rodrigo Gonzalo , Schrebler Ricardo Silvio , Muñoz Eduardo Carlo
Published: February 2020

Quantum Dots (QDs) are semiconductor nanomaterials with interesting optical properties, which are dependent on the nanoparticle size, i.e., the quantization of the energy levels that lead to a confinement of the loaders. These nanoparticles exhibited a wide excitation spectrum along with a narrow emission (size-adjustable), high photostability and photobleaching resistance [1]. Generally, QDs consist of group II atoms (alkyls, metallic oxides or organic salts) and group VI (Se, S and Te). The luminescent properties present in this type of nanomaterials, in addition to an elevated area-volume relation, allow their application in the field of biological species sensors [2,3]. The physicochemical interaction QDs-molecule causes changes in the fluorescence emission intensity of the nanoparticle (quenching of the fluorescence), where such change is measurable. In the present work we studied the interaction of different sizes of CdTe QDs with 3 free radicals: 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), 4-Amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO), and hydroxyl radical (●OH). Emission intensity spectra and lifetime decay curve were obtained by UV-Vis spectroscopy and fluorescence spectroscopy. On the other hand, transmission electron microscopy (TEM), dynamic light scattering (DLS) and X-ray diffraction (XRD), are used for the morphological and structural characterization of the CdTe nanoparticle. Finally, voltammetric profiles and impedance plots of QDs supported on electrodes were obtained before and after exposure to free radicals. The previous results have obtained important information about the interaction between QDs and free radicals, for which they constitute the fundamental bases for an eventual development of the sensors for these reactive species.

Figure 1
Analysis of Cerium Oxide Doped Anti-Corrosion Coatings By Scanning Electrochemical Microscopy and Electrochemical Impedance Spectroscopy
Authors: Murphy Jules , Lancaster Fred , Calhoun R. L.
Published: February 2020

Previously, a protocol was developed to use SECM (scanning electrochemical microscopy) to screen for the effectiveness of new anti-corrosion coatings produced by the Navy.[i]Briefly, increasingly positive potentials at the Al substrate are applied while the tip is in the substrate generation tip collection (SGTC) mode. Poor coatings show significant tip currents while good ones do not.

The current work used this protocol on coatings provided by engineers from Naval Air Systems Command that had been doped with varying amounts of CeO. Initial voltage applications showed coating breakdown with increasing current at ever more positive potentials. However, a maximum was seen and at potentials above 2V, the coatings appear to have improved.

In an effort to elucidate what caused this effect, Electrochemical Impedance Spectroscopy (EIS), laser profiling, and x-ray fluorescence studies were performed to look for changes in the coating. Preliminary EIS results (Figure 1) indicate the resistance due to pores increased after higher potential application hinting the pores may be becoming smaller.[ii]The value of the real component of the complex impedance, where the left side of the semicircle begins, is the sum of the uncompensated resistance and pore resistance. Spectra were taken after the Al substrate was exposed to the indicated DC potential. While not large, it can be seen the resistance increased as the applied potential increased. X-ray results as well as laser profiling (not shown) indicate the coating at and near the surface is changing. The X-ray data show other components of the coating (Ti, Fe, etc) are migrating to/from the surface. The laser generated topographical data also shows morphological changes on the surface all of which may be the cause of the pore size reduction.

All data were taken at the U.S. Naval Academy, an undergraduate only institution, by one student. Projects such as this where the midshipmen conduct two semesters of research under the supervision of a professor, became part of USNA’s chemistry major over a decade ago. While not compulsory, some 70% of the majors elect this option and most result in at least a published conference proceeding. This is even more remarkable in that the students do not have the flexibility to conduct experiments outside the normal school day.

[i] Lee, C., Calhoun, M., Dorriety, W., Hanrahan, R., Lancaster, F., Calhoun, R., ECST, 66 (30) 65-71 (2015).

[ii] Loveday, D., Peterson, P., Rodgers, B., JCT Coatings Tech, Oct, 88-93 (2004).

Figure 1
Elucidating Electro-Hydrodynamics at a Liquid Metal Oxide-Electrolyte Interface Via Electrochemical Impedance Spectroscopy
Authors: Joshipura Ishan D , Dickey Michael D.
Published: February 2020

This work characterizes the behavior of a eutectic alloy of gallium and indium (75% Ga, 25% In, by weight, ‘EGaIn’) in response to electric fields. The metal is a liquid at room temperature (M.P., 15.5 °C) and exhibits low toxicity. These fluidic metals may be injected into microfluidic systems, fibers, and capillary networks to form soft electronic devices that are soft and compliant. Once injected, the metal remains in its place because of the adhesive nature of its thin native oxide. Preventing the oxide adhesion within microchannels enables reversible actuation of EGaIn. Actuating liquid metals may be useful for soft actuators, reconfigurable optical displays, frequency tunable antennas, and other opto-fluidic technologies.

In this work, we utilize low voltages (<2 V) to reversibly move droplets of EGaIn through microchannels. Pre-wetting the channels with an aqueous solution prior to injecting the metal prevents oxide adhesion; the water forms an interfacial ‘slip-layer’ the metal and channel wall. Thereafter, an applied electric field (~10-20 V/m) actuates the liquid metal by establishing a gradient of surface tension; this effect is known as continuous electrowetting (CEW). Although CEW has been utilized before with mercury, which is toxic, the adhesive nature of the Ga oxide complicates CEW behavior. This work utilizes optical microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS) to characterize electro-hydrodynamics of CEW with EGaIn under a variety of conditions. Specifically, we compare electro-hydrodynamic behavior of EGaIn with and without the presence of an oxide ‘skin’. In addition, we elucidate the influence of material properties of the electrolyte on the metal-electrolyte interface. An equivalent circuit model from EIS experiments is proposed to understand the metal-electrolyte interface and to control the movement of the liquid metal within microfluidic systems.
Influence of Morphology Controlled Gold Underlayer on Photoelectrochemical Water Splitting of Copper (I) Oxide As a Photocathode
Authors: Lan Tian , Mundt Colton , Padalkar Sonal
Published: February 2020

Copper (I) oxide (Cu2O) is a very favorable p-type semiconductor. It is an appealing candidate for photoelectrochemical water splitting. Here the fabrication and performance of gold (Au) underlayer - Cu2O composite photocathode for photoelectrochemical water splitting will be presented. The composite photocathode was fabricated by the electrodeposition technique. The different morphologies of the Au underlayer were achieved via variation in the process parameters including applied potential, electrolyte pH and the presence of L-cysteine in the electrolyte. The Cu2O overlayer was also deposited using electrodeposition. Additionally, the influence of morphology variation, of the Au underlayer, on the performance of the composite photocathode was evaluated. It was observed that the performance of the composite photocathode increased by 81% when compared to a control sample of Cu2O. The composite photocathodes were characterized by scanning electron microscopy, X-ray diffraction and electrochemical impedance spectroscopy.
Current-Voltage Relationship Considering the Direction of the Electrical Field in Mixed Ionic-Electronic Solid Conductors
Authors: Miyashita Tomofumi
Published: February 2020

Numerous approaches have been used to solve the transport equation describing a solid-oxide fuel cell with mixed ionic and electronic conductors, such as Sm-doped ceria. Typically, the open circuit voltage is calculated using Wagner’s equation. The current-voltage relation can also be calculated using conventional models. According to the conventional models, ionic current flows from the anode to the cathode. Electronic current flows from the cathode to the anode. Ionic current is purely drift current. Electronic current consists of drift current and diffusion current. However, the separation of electron drift current and electron diffusion current has never been calculated. Considering the direction of the electrical field, we can separate the electron drift current and electron diffusion current in a current-voltage relationship using Sm-doped ceria electrolytes.
(Invited) Reflections on Rust: Iron Oxide Photoelectrodes for Solar Energy Conversion and Storage
Authors: Rothschild Avner
Published: February 2020

Solar water splitting is a promising route for sustainable and scalable hydrogen production from renewable sources: water and sunlight. The hydrogen can be used as a clean fuel for refueling fuel cell electric vehicles with zero emissions. Hydrogen can also serve as a feedstock for the production of drop-in liquid fuels by CO2 hydrogenation, and ammonia via the Haber–Bosch process. The greatest challenges towards viable solar water splitting technology lay in the selection and design of photocatalytic materials and devices that harvest sunlight and split water efficiently and produce hydrogen at a competitive cost. To this end photocatalytic materials that are stable in alkaline or acidic aqueous solutions, absorb visible light, promote water oxidation or reduction reactions and comprise of abundant materials must be employed.

Iron oxide (α-Fe2O3, hematite), aka rust, is one of few materials meeting these criteria, but its poor transport properties and fast charge recombination present challenges for efficient charge carrier generation, separation and collection. We explore innovative solutions to these challenges using ultrathin (20-30 nm) films on specular back reflectors. This simple optical cavity design effectively traps the light in otherwise nearly translucent ultrathin films, amplifying the intensity close to the surface wherein photogenerated charge carriers can reach the surface and split water before recombination takes place. This is the enabling key towards the development of high-efficiency iron oxide photoelectrodes whose structure and properties can be tailored by design. However, the design rules for these devices remain elusive because iron oxide behaves differently than conventional semiconductors such as silicon, probably due to the strong correlation between the electrons that give rise to the current and the ions that form the crystalline lattice.

Our first goal is to discover the physico-chemical processes that limit the performance of iron oxide photoelectrode and devise design principles that enable overcoming these limitations through material design at the nanoscale that combines iron oxide together with selective underlayers and overlayers that separate positive and negative charge carriers, thereby reducing recombination losses and increasing efficiency. The second goal is to apply these design principles to construct high-efficiency solar water splitting devices. The third and final goal is to invent new device architectures and operation schemes that enable affordable solar hydrogen production in large-scale applications, closing the gap between basic research on lab-scale devices and a new solar energy technology that provides stable power on demand.

Figure 1
(Invited) NSF's Energy for Sustainability Program: Research Supporting Solar Fuels
Authors: Read Carole J , McCabe Robert
Published: February 2020

This talk will discuss programs in NSF ENG's Division of Chemical, Bioengineering, Environmental, and Transport Systems (CBET) that support fundamental engineering science in the area of solar fuels. Programs in the CBET Division's Process Systems Cluster include the Catalysis and Energy for Sustainability programs. The cluster's programs stress fundamental hypothesis-driven research for novel materials, processes, and/or tools that seek to improve the throughput, resource efficiency or process intensification of chemical conversion processes. Focus in on fundamental understanding emphasizing molecular-level engineering to link to understanding of performance at the process/system level. The talk will include examples of recent grants that support solar fuels that have been awarded by these CBET programs.
Oxidation−Stable Plasmonic Copper Nanoparticles in Photocatalytic TiO2 Nanoarchitectures
Authors: DeSario Paul A. , Pietron Jeremy , Brintlinger Todd , Parker Joseph F. , Baturina Olga A , Stroud Rhonda , Rolison Debra R.
Published: February 2020

We describe the incorporation of plasmonic copper (Cu) nanoparticles into titania (TiO2) aerogels and demonstrate surface plasmon resonance (SPR)–driven photoelectrochemical oxidation of methanol under visible light. Copper could provide a more abundant, less expensive alternative to gold and silver as a visible light–active plasmonic metal, however, the propensity of Cu to oxidize at the expense of its plasmonic character greatly limits its potential applications. Most reports of supported, plasmonic Cu nanoparticles describe the necessity of preventing Cu oxidation by maintaining strictly anoxic environments or relying on surface-obscuring chemical stabilizers. We stabilize plasmonic Cu nanoparticles by establishing extensive interfacial contact between Cu nanoparticles and a TiO2 aerogel support. The multiple points of contact between 2–3 nm Cu nanoparticles photodeposited at the networked ~10 nm TiO2 particulates of the aerogel stabilizes Cu against oxidation to an extent that preserves the plasmonic behavior of the nanoparticles, even after long-term exposure to ambient air. The wavelength dependence of photoelectrochemical methanol oxidation at Cu/TiO2 aerogel photoanodes verifies the plasmonic origin of the photoelectrochemistry. Plasmonic behavior is not seen for Cu photodeposited at a commercially available, non-networked TiO2 nanopowder in which the primary particle size is ~10× greater than the size of the supported Cu particle. The divergent behavior of Cu when a 3D Cu||oxide interface is formed on aerogel supports compared to the 1D junction between Cu on commercial TiO2 nanopowder supports highlights the importance of the interfacial design motif on preserving plasmonic Cu.
Improved Stability and Photoelectrochemical Performance of Al2O3 Passivated CdS/1D Zr:Fe2O3 Heterojunctions for Solar Hydrogen Generation
Authors: Mahadik Mahadeo A , Subramanian Arunprabaharan , Chung Hee-Suk , Cho Min , Jang Jum Suk
Published: February 2020

Al2O3 passivated CdS sensitized 1D Zr:Fe2O3 nanorod arrays have been synthesized on fluorine-doped tin oxide (FTO) by hydrothermal method and dip coating methods. The photoelectrochemical study of CdS/1D Zr:Fe2O3 photoelectrode exhibits the current density of 4.2 mA.cm-2 at 0 V (vs. Ag/AgCl) which is 2.8 time higher than the bare 1D Zr:Fe2O3. The reduced recombination and the effective transport of photogenerated holes in CdS facilitates the enhancement in photoelectrochemical performance. Furthermore, the photocurrent and stability of the CdS/Zr:Fe2O3 nanorods was significantly enhanced by Al2O3 compared to bare CdS/Zr:Fe2O3 heterojunction due to its ability to act as an effective hole transport as well as photocorrosion protecting layer. The chemical analyses and nanostructural study of the Al2O3 coated CdS/1D Zr:Fe2O3 photoelectrodes confirms the presence of Al2O3 on surface of CdS and 1D Zr:Fe2O3 nanorods embedded in the CdS flakes. These remarkable enhancements in light energy harvesting, improvement in charge transport and stability directly suggest the usefulness of photoelectrodes for solar hydrogen generation.

KEYWORDS: Al2O3 passivation; Zr:Fe2O3 nanorod arrays; CdS Sensitizer; Hydrogen generation

ACKNOWLEDGMENT

This research was supported by the BK21 plus program, the Korean National Research Foundation (Nano-Material Fundamental Technology Development, 2016M3A7B4909370).
All Electrodeposited Nanowire Array Based Multi-Junction Photovoltaic Devices
Authors: Cheng Wei , Lee Joun , Young Graham , Mubeen Syed
Published: February 2020

Large-scale solar fuel production using semiconductor based photoelectrochemical system requires inexpensive, efficient and stable devices that can provide photovoltages sufficient to overcome both the thermodynamic and overpotential losses of the redox reaction. Here we report all electrodeposited multi-junction photovoltaic (PV) devices for solar fuel production using serially connected multiple Cd/CdSe/Au Schottky barrier junctions with photovoltages exceeding 1.0 V. These PV devices are synthesized inside nanoporous alumina membranes with each nanoscale solar conversion units physically and electronically isolated from each other, making the entire device fault tolerant. The alumina membranes also serves to protect the semiconductor from chemical and photoelectrochemical corrosion. Ensemble and individual nanowire measurements were performed to understand charge carrier energetics and transport pathways across multiple interfaces.
Self-Formed Catalysts Using Electrochemical (de)Lithiation for Oxygen Evolution Reaction
Authors: Sumaria Vaidish Pravin , Krishnamurthy Dilip , Viswanathan Venkatasubramanian
Published: February 2020

Oxygen evolution reaction is a key process for enabling solar or electricity-driven water splitting. IrO2 and RuO2 are among the most active catalysts for OER, but material scarcity and high cost limits their usage in large-scale applications.[1] Here, we propose a new strategy for self-forming a range of electrocatalysts through electrochemical lithiation of functional metal oxides by potential control. The lithiated phases provide a strategy to tune the strain and electronic structure and thereby leading to efficient electrocatalysts. The most suitable reaction to demonstrate this strategy is the oxygen evolution reaction, which occurs in highly oxidizing environments.

In this work, we perform a thermodynamic analysis involving density functional theory (DFT) calculations to identify the effect of lithium intercalation into functional metal oxides. The intercalation of lithium ions induces both strain and compositional change. Small strains have been induced through core-shell catalysts and interlayers to significantly enhance the activity of Pt for Oxygen Reduction Reaction (ORR).[2],[3]
We will report on the possibility of using various functional layered metal oxides such as MnO2, CoO2, etc.

It has been shown that extraction of intercalated Li+ ions from LiCoO2 (during charging) causes expansion. When the Li+ ions intercalate, the lattice reversibly returns to its original spacing.[4]  Even small change in lattice volume is sufficient to produce enough strain in the lattice to alter its activity for a reaction. We illustrate the concept through the intercalation on CoO2 layer, as shown in the Figure. Upon lithiation, the binding strength of intermediates is affected by the compressive strain induced. We will report on calculations employing the Bayesian Error Estimation function with van der Waals exchange correlation to determine the O*, OOH* and OH* adsorption energies. This is used to determine the theoretical limiting potential, which is determined by UL= max [(ΔGO* - ΔGHO*), 3.2-(ΔGO* - ΔGHO*)]. Promising metal oxide catalysts with corresponding optimal degrees of lithiation will be identified using this framework to maximize activity. We will also use ensemble error estimation capability within BEEF to report on uncertainties associated with these calculations.[5] 

References:

1 Lee, Y. et.al. J. Phys. Chem. Lett., 3(3):399–404, 2012.

2 Friebel, D. et. al. J. Am. Chem. Soc., 134 (23), 9664–9671, 2012.

3 Strickler, A.L. ACS Energy Lett., 2 (1), 244-249, 2017

4 Wang, H. et. al. Science, 354(6315):1031–1036, 2016.

5 Wellendorff J. et. al. Phys. Rev. B, 85, 235149, 2012.

Figure 1
Catalyzed Oxidation of Chlorine and Bromine in Room Temperature Chloroaluminate and Bromoaluminate Melts
Authors: Krivan Emese , Foister Shane , Tian Mengkun , Elgammal Ramez Ahmed , Counce Robert , Zawodzinski Thomas A.
Published: February 2020

The use of haloaluminate room temperature molten salts has potential for interesting battery chemistries. This is particularly true for acidic (excess Lewis acid, e.g. AlCl3, over the organic chloride salts) compositions. In that case, Al is readily plated and stripped, as we discussed some time ago.1

A particularly interesting battery combination arises when the aluminum negative electrode is paired with the evolution of the halogen from the acidic melt. In that case, maximum redox active species concentration is achieved and maximum voltage can be obtained since the entire electrochemical window is utilized. However, several issues with chlorine evolution are known. First, in an acidic melt chlorination of imidazolium cations occurs. This can be partly mitigated by appropriate modification of the cation. A second problem is the somewhat sluggish catalysis of chlorine evolution observed on carbon surfaces.

In this work, we report results of efforts to improve on the latter aspect. Specifically, we describe the catalysis of chlorine evolution by catalytically active surfaces. In particular, we show significant enhancements in onset potential for chlorine evolution using supported Ru catalysts. In Figure 1, we compare the chlorine evolution voltammetry in 1.5:1.0 AlCl3:EMIC on bare glassy carbon to that observed on the same electrode coated with a sample of 60 wt% Ru on multiwalled nanotubes (prepared in-house). The onset of chlorine evolution occurs on the order of 300 mV less positive with the supported Ru catalysts. We have deposited the Ru on various carbon structures to explore the applicability of this catalyst system for batteries and flow batteries. Studies of the same reaction on Pt electrodes show that the supported Ru nanoparticles have similar activity to that of Pt for this reaction.

In addition, similar results were also obtained for bromine evolution. In that case, the lower volatility of the product allowed us to readily observe the bromine oxidation on the reverse scan. This reaction is substantially more reversible on these catalyzed surfaces.

Figure 1: Voltammetry of 60%Ru on MWNT on glassy carbon compared to that of the bare glassy carbon electrode.

Figure 1