bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Chemical Doping on the Lithiation Processes of the Crystalline Si Anode: A First-Principles Study
Authors: Kuo Chin-Lung , Chiang Han-Hsin
Published: February 2020

In this study, we have performed density functional theory calculations and ab initio molecular dynamic simulations to investigate the kinetics and dynamics of the lithiation processes of the doped and undoped c-Si anodes for their application in Li-ion batteries.  Our ab initio molecular dynamic simulations showed that the lithiation process of c-Si can be remarkably improved by phosphorus-doping while that for the boron-doped Si is simply comparable to the performance of the undoped Si electrode.  To explore the physical origins of the enhanced rate capability of the phosphorus-doped Si anode, we calculated the insertion and migration energy barriers of Li ions in c-Si, and then simulated the mechanical response of the Li-inserted Si matrix under different hydrostatic stresses.  Our calculated results showed that boron-doping can effectively lower down the insertion barrier of a Li atom into the Si-matrix but phosphorus-doping may lead to the increment of the Li insertion energy in c-Si.  Furthermore, although the diffusion energy barriers of Li may slightly decrease (increase) by ~0.2 eV in the phosphorus (boron)-doped Si matrix, these changes were found to be highly localized within the range of the nearest-neighbor distance.  Accordingly, the enhanced lithiation rate in the phosphorus-doped Si electrode cannot be attributed to the increased Li diffusion rate or the reduction of the insertion energy barriers of Li atom into the c-Si electrode.  On the other hand, our calculated mechanical response of the Li-inserted Si matrix showed that the phosphorus-doped Si matrix can become more ductile and more easily undergo plastic deformation upon hydrostatic stresses, but on the contrary, the Si matrix may become more brittle and stiffer as it was doped with boron atoms.  Our ab initio molecular dynamic simulations also showed that the phosphorus-doped Li-inserted Si matrix can easily undergo structure amorphorization within 10 ps, but the boron-doped and undoped Si matrices can still or mostly hold in the diamond structures within the same elapsed time of MD simulations.  These results clearly indicate that mechanical softening of the Si bond network can be one of the major reasons that leads to the enhanced lithiation rate of the phosphorus-doped Si electrode.
Numerical Analysis on Lithiation and Delithiation Kinetics of Composite Silicon-Graphite Electrodes
Authors: Cao Lei , Yang Chuanbo , Kim Gi-Heon
Published: February 2020

To study electrochemical lithiation and delithiation kinetics in silicon-graphite composite anode for lithium-ion batteries, a discrete diffusion particle model (DDPM) is developed and validated. Our recent study indicates conventional single-particle model shows limited representation of mixed chemistry. This model solves solid-phase lithium diffusion dynamics and transfer kinetics in a discrete diffusion particle system, which can be used to address the effects from composition of active particles of different chemistry, particulate morphology and size distribution. Half cells are built and tested for modeling parameter identification and validation. Tests include constant-current / dynamic charge and discharge at various temperatures. Results show well captured characteristics of inhomogeneous use of different materials, especially at state of charge region close to 0% and 100%. Comparison between modeling and testing suggests the model gives a reasonable accuracy and could be used to quantify the impacts of electrode design parameters, providing insights for improving the performance of the mixture negative electrodes.
The Interactions Between Chlorides and Zn(001) Surfaces in Zinc/Bromine Flow Battery Electrolytes
Authors: Rajarathnam Gobinath Pillai , Montoya Alejandro , Vassallo Anthony
Published: February 2020

Chloride-based supporting electrolytes are conventionally used in zinc/bromine (Zn/Br) and other flow batteries to ensure good conductivity during charge/discharge operation. This work presents preliminary results from experimental and periodic density functional studies of the interactions between chlorides and electrodeposited zinc generated during the charging phase of the Zn/Br system. Scanning electron microscopy and X-ray diffraction analysis show that even relatively low concentrations (0.5 M) of ZnCl2 supporting electrolyte influences zinc electrodeposition behaviour during the charging phase, with a strong preference for the (004) orientation. Molecular modelling carried out in this work provides a foundation for understanding how chlorides present in the supporting electrolyte interact with and alter the electrodeposited zinc surface in Zn/Br flow batteries. Chloride strongly binds above the Zn(001) surface with binding energies of 260–288 kJ mol-1 at 0.11–0.33 ML coverage. Chloride binding lowers the Zn(001) surface uniformity, with higher coverage resulting in lower binding energies. These findings warrant further investigation of the influence and behaviour of supporting electrolytes on the primary electrolyte and at the electrode-electrolyte interface. While this work focuses on Zn/Br systems, the findings are also potentially applicable to other types of RFBs which utilise chloride-containing electrolytes.
(Invited) Glimmers of New Point-of-Care Sensors through the Patent Thicket
Authors: Cunningham David Dean , Smith Connor T. , Miller Courtney N.
Published: February 2020

Commercially successful sensors used in the Point-of-Care market involve integration of sensitive sensor components into robust analytical systems.  Technologies incorporated into these systems generally converge upon a very small number of methodologies compared with the large variety reported in journals and patents.  Sorting through this literature to discern which innovations might appear in commercial products is a daunting task.  One useful tool is analysis of the intellectual landscape via free patent searches, but the product of these efforts can lack organization.  Relationships been technologies have often been depicted in patent maps which focus on technologies, products and ownership.  Newly emerging tools in this realm will be described to identify market leaders, innovators and explorers.

Early identification of important new advances also depends on a firm understanding of the capabilities of sensors currently on the market.  Current products can be broadly divided into detection of ions, small molecules and proteins.  A review of products in these categories will be provided to allow assessment of the potential for new technologies that may impact or disrupt the field.  Several potentially disruptive electrochemical technologies including digital microfluidic immunoassays will be described.  Finally, relatively incremental, but effective, examples of advances in multi-enzymatic amperometric systems and their incorporation into robust polymer formulations will be presented.  Combining the analysis of emerging intellectual property and experimental studies is suggested as a powerful approach for identifying areas ripe for discovery, as well as predicting the future trajectory of new products.
Fe3O4 on Graphene Oxide Nanosheets for Electrochemiocal Detection of Cancer Biomarker Proteins
Authors: Sharafeldin Mohamed , Bishop Gregory William , Bhakta Snehasis , Rusling James F
Published: February 2020

An ultrasensitive mediator-free electrochemical detection method for proteins has been developed on an 8-sensors microfluidic platform. In this method, a sandwich immunoassay approach was used to detect prostate cancer biomarkers on screen-printed carbon electrodes. Fe3O4 nanoparticles with peroxidase like-activity were loaded onto graphene oxide nano-sheets resulting in a Fe3O4@GO composite with 1 µm average diameter as determined by dynamic light scattering and electron microscopy. Voltammetric studies and colorimetric assays confirmed the Fe3O4@GO composite material exhibited catalytic activity toward hydrogen peroxide reduction. Detection antibodies were covalently attached to Fe3O4@GO composite, the resulting biocomposite was used as a detection label in sandwich immunoassays for Prostate Specific Antigen (PSA) and Prostate Specific Membrane antigen (PSMA). The sensor surfaces of the array were coated with electrochemically reduced graphene oxide to improve conductivity and increase surface area, and then capture antibodies were attached through either adsorption or covalent binding to residual carboxylic groups on surface.  An optimized simple microfluidic system was used to deliver reagents to the electrode arrays and wash/remove unbound species. This sandwich assay based on catalytic reduction of hydrogen peroxide by Fe3O4@GO detection labels exhibited detection limits of 61 fg/mL for PSA and 9.8 fg /mL for PSMA.
Development of an Electronic Skin Wafer for the Minimization of Peristomal Irritant Dermatitis
Authors: McLister Anna , McCreadie Karl , Davis James
Published: February 2020

An ostomy is created in response to a gastrointestinal injury or disease, such as Ulcerative Colitis, Crohn’s disease and cancer. A stoma is created by a surgical opening in the lower abdomen, which allows for a section of the intestine to be brought to the surface to allow for the excretion of waste products. The resulting effluent is collected through an ostomy pouch that is attached to the abdomen via an adhesive skin wafer (baseplate) as indicated in Figure 1A. In recent years there has been a tremendous effort expended in the design and development of ostomy appliances, which has helped to revolutionize stoma care and management. However, despite the numerous advances, peristomal skin damage remains an issue and arises as a consequence of the gradual erosion of the protective skin wafer. This results in the underlying skin being exposed to the caustic ileostomy fluid (Figure 1B) which subsequently compromises the integrity of the skin barrier and inevitably leads to irritation and ulceration. In the USA alone, it is estimated that one million patients deal with the routine care of an ostomy, and at some stage they are likely to have experienced an incidence of peristomal skin complication (PSC). Although, there have been improvements in the development of materials used within ostomy appliances, there has been little technological innovation in regards to the active prevention of PSCs.

A novel skin wafer containing a printed electrode array has been designed which can permit the monitoring of the skin pH in situ and thereby alert the patient when the baseplate has been compromised (Figure 1B). The system is based on a conductive carbon layer which has been modified with a range of peptide agents to confer pH selectivity. This electrode layer is integrated within a hydrocolloid (carboxymethylcelluose based gel) which provides a protective layer from the effluent debris that would otherwise compromise the operation of the sensor. As the skin becomes compromised, the pH can be expected to increase and at this point the patient can be alerted to the situation and the pouch appliance replaced before the onset of a PSC. The design and construction of the skin wafer is described and its operation in ileostomy fluid is critically assessed. 

Figure 1
Temperature-Responsive PNIPAM-Grafted-Alginate Core Wrapped with LbL Assembled Chitosan/DNA Membranes for Development of Controlled Drug Release System
Authors: Zhang Yuanyuan , Arugula Mary A , Simonian Aleksandr
Published: February 2020

While considerable consumers experience a more-than-recommended-dose usage of commercially available scar cream for scar therapy treatment, we report here a novel and smart thermally controlled drug delivery gel patch system for scar therapy purpose. The gel patch contains a core of amine-terminated-poly(N-isopropylacrylamide) (NH2-PNIPAM) grafted alginate wrapped with outer membranes consisting of layer-by-layer (LbL) assembled Chitosan and DNA thin films. NH2-PNIPAM cross-linked onto side chain of alginate exhibits contraction and expansion above and below its Lower Critical Solution Temperature (LCST: 32℃) and therefore serves as a switch turning “on and off” the release of drug entrapped in the core. The difference in the release of Texas-Red conjugated Epidermal Growth Factor (EGF-TR) at 33℃ and 22℃ were monitored with fluorescence microscopy and the system showed higher release of EGF-TR at 33℃ than at 22 ◦C. Below LCST (at 22℃), the expanded NH2-PNIPAM resembles stretched arms that close the release of EGF-TR, while above LCST (at 33℃), the NH2-PNIPAM arms coil and allow the release of EGF-TR. The outer membranes consisting of optimized seven oppositely charged Chitosan and DNA layers via LbL assembly controlled the rate and profile of EGF-TR release, as well as dramatically reduced the burst effect in the delivery process. A diffusion controlled behavior was observed for the proposed system and a mathematic model to predict the diffusion efficient of EGF from such gel patch system was further established.
Durability Study of Intermediate Temperature-Solid Oxide Fuel Cells with Excellent Cathode Materials
Authors: Yang Ja-Yoon , Park Jun-Young
Published: February 2020

Solid oxide fuel cells (SOFCs) which can directly covert the chemical energy of fuel to electric energy have received as one of alternative energy sources because of their high energy conversion efficiency, fuel flexibility and low emission of pollutant to the environments. However, there are still several technical issues for making commercialization of SOFCs such as limited durability and long start-up time. Hence, recent studies of the SOFCs have focused on improving performance of SOFCs in the intermediate temperature (IT) to achieve technical goals such as high stability, low-cost component materials, easier sealing and quicker start-up time.

In particular, stable long-term performances of SOFCs are one of the essential factors for commercialization of fuel cell systems. However, the sudden unstable situations such as frequent electrical load on-off and high load can often occur during the SOFCs operations, and thus, these unexpected situations can affect the durability of SOFCs systems. Therefore, we need to investigate performance change of SOFCs under various electrical load conditions including the constant current, current on-off cycles and irregular current change. In addition, post-mortem analysis of SOFCs are necessary to find the main degradation mechanisms after various durability tests.

In this work, Ni-cermet anode supported cells are fabricated by the tape-casting method with neodymium doped ceria and double-perovskite structure based cathode materials (NdBa0.5Sr0.5Co1.5Fe0.5O5+δ). The performance of the cells are investigated by I-V measurement and the durability test also conducted by using load trip (0~200 mAcm-2) and load cycle (120~200 mAcm-2) techniques with controlled current condition at 650 oC.

For electrochemical analysis, electrochemical polarization and characterizations are conducted using an electrochemical impedance spectroscopy (EIS) with a Potentiostat/Galvanostat instrument using a frequency range from 1 MHz to 1Hz. The several physicochemical analyses are also investigated using field emission-scanning electron microscopy (FE-SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD).

References

E. D. Wachsman and K. T. Lee, Science
334 (2011) 935-939.

S. B. Adler, Chem. Rev. 104 (2004) 4791-4843.

E. Park, S. Taniguchi, T. Daio, J. T. Chou and K. Sasaki, Solid State Ionics 262 (2014) 421-427.

B. C. H. Steele and A. Heinzel, Nature 414 (2001) 345-352.

S. Omar, E. D. Wachsman and J. C. Nino, Solid State Ionics 177 (2006) 3199-3203.

M. Kahlaoui, S. Chefi, A. Inoubli, A. Madani and C. Chefi, Ceram. Int. 39 (2013) 3873-3879.

Keywords : Solid oxide fuel cells; intermediate-temperature; durability; perovskite.
Predicting the Formation of Electrodeposition Patterns Caused By Interfacial Instabilities
Authors: Wang Chun-Chieh , Ziegler Kirk J , Narayanan Ranga
Published: February 2020

Electrodeposition is a common process via which metal ions are reduced at a cathode as a thin film. However, the deposited film on the cathode often exhibits a unique interfacial pattern that is dependent on the applied voltage, the concentration, and the distance between electrodes. Although these morphological instabilities have been observed in the past, it still remains difficult to predict the interfacial pattern formed during electrodeposition. These morphological patterns arise in an electrolytic cell because the reduction reaction runs faster than oxidation. Therefore small crests or troughs on the surface of the electrode act as a disturbance that alters the rate and uniformity of metal deposition at these sites, initiating the growth of an interfacial pattern.

We first develop a model that describes the electrodeposition instabilities that lead to these interfacial patterns. Transport and kinetic reactions described by Butler-Volmer equations are used to calculate and predict the growth characteristics of the film. It is found that the patterns of the film are periodic and harmonic waves composed of different wavelengths. While each wavelength corresponds to a specific growth rate, many wavelengths have similar growth rates. Changes to surface tension and ionic diffusion can yield narrower distributions of the wavelengths observed.

A simple Cu-Cu electrodeposition system is then investigated to observe the instabilities. The pattern on the cathode is observed as a function of deposition time in the presence of random disturbances. By image analysis, the wavelength distribution of the interfacial pattern is detected, which is consistent with the developed model. Due to its inherent instability, the harmonic waves of the pattern are not identical every time under the same experiment condition. Nevertheless, the wavelengths observed during deposition are still located within the predicted range.

The results demonstrate that the wavelengths of the pattern are predictable but difficult to control because of inherent disturbances on the surface. Further, the growth of the patterns creates localized flow convection that leads to the formation of dendritic patterns. Now that the model can predict these patterns, the goal will be to find experimental conditions that can either minimize pattern formation or generate a single wavelength.
Reverse Microemulsion Vs Ultrasound-Assisted Synthesis of PtCu/MWCNT Towards Oxygen Reduction Reaction with Possible Application in Fuel Cells
Authors: Rivera-Lugo Yazmin Yorely , Félix-Navarro Rosa María , Reynoso-Soto Edgar Alonso
Published: February 2020

Over the years, production of energy has been based on fossil fuels, which naturally arose millions of years ago and include carbon, natural gas and oil. During power generation, these materials generate high concentrations of CO2 in the atmosphere that are harmful to the environment. In addition, it is expected that by 2050 the oil and natural gas will be exhausted.1

A good alternative for power generation are fuel cells, which are devices that convert chemical energy into electrical energy, but for continuous production must implement a continuous supply of reagents. These cells have the advantage of generating energy through chemical processes rather than combustion, thus generating clean processes.

In some fuel cells, such as hydrogen/oxygen cell, the limiting reaction is oxygen reduction, so some studies have focused on optimizing this process. In these cells, the following reactions are performed:2

Anodic reaction (oxidation)         H2 → 2 H+ + 2 e-                                E°=0.000 V

Cathodic reaction (reduction)     O2 + 4 H+ + 4e- → 4 H2O                   E°=+1.229 V

                                              ____________________________________________

Overall reaction                          2 H+  + O2 → 2 H2O                          E°=+1.229 V

A primary component of fuel cells is the catalyst which is responsible for accelerating the reaction and it’s regenerated at the end. Platinum is the most used noble metal as electrocatalyst in fuel cells because of its high activity and stability, however one of the major challenges is inactivity of platinum caused by carbon monoxide. To overcome this challenge has been proposed Pt alloy with Cu, since it has been reported that Pt alloy to non-noble metals generates higher catalytic activity in the reduction reaction of oxygen compared with platinum alone.3

In this work we compares the catalytic activity in the reduction reaction of oxygen of PtCu/MWCNT synthesized by inverse microemulsion against ultrasound assisted synthesis, which has the advantage of being a green synthesis to be free of solvents and organic surfactants.

References

Cyber quote on: Proyecto de educación ambiental. Virtual page Cambio climático, http://unidades.climantica.org/es/unidades/02/crise-enerxetica-e-cambio-climatico/o-esgotamento-dos-combustibles-fosiles-e-o-cambio-climatico/1, february 3rd of 2015.

Ojani, R; Valiollahi, R.; Raoof, J.B. Energy 2014, 74, 871 – 876.

Maillard, F.; Martin, M.; Gloaguen, F.; Leger, J. M. Electrochim. Acta 2002, 47, 3431 – 3440.

Figure 1
Synthesis and Characterization of Functionalized CdS-QD Polymeric Nanocomposite Film to Mitigate Laser Attacks on Commercial Aircrafts
Authors: Brain Samantha J. , Zaleski Michelle , Hofmann James , Santefort David , Kozminski Joesph , Crowder Charles , Keleher Jason J
Published: February 2020

In 2015, the Federal Aviation Administration (FAA) has reported over 3,700 cases of lasers penetrating aircraft windshields. These laser attacks typically involve the use of commercially available laser pointers and pose a number of threats to pilots ranging anywhere from visual distraction to flash blindness. They typically occur at aircraft altitudes less than 4,000 feet when the pilots’ visibility is especially critical to successful takeoffs and landings. The laser pointers used in these attacks are manufactured in a variety of different colors including purple (405nm), blue (445nm), green (532nm), and red (650nm), and are available to the public. This work proposed a donor/acceptor functionalized quantum dot (QD) incorporated polymeric nanocomposite film to mitigate the laser intensity via fluorescence resonance energy transfer (FRET).  More specifically, CdS core-shell quantum dots (QDs) functionalized with photoactive organic ligands were immobilized on the CdS nanocrystals via a non-covalent self-assembly scheme.  This configuration allowed accurate control of the donor-acceptor separation distance and provided a good model system to explore FRET phenomena in polymeric films.  Under aqueous conditions, heat was used to control the diameter of the CdS quantum dots. Current results show that in liquid phase, the addition of an organic dye non-covalently linked to the CdS surface showed sufficient fluorescence quenching.  Initial results of simulated aircraft green laser testing revealed that there is significant energy dissipation and a noticeable (20 -50 nm) wave-shift upon exposure to nanocomposite films.
Refining the Structure of Graphite Oxide through Selective Labeling of Functional Groups
Authors: Eng Alex Yong Sheng , Chua Chun Kiang , Pumera Martin
Published: February 2020

The various inherent functional groups within graphite oxide (GO) are of significant interest for numerous research applications exploiting their reactivity. While there has been much advance in the research of graphenes and GO over the years, our current understanding of GO structure is primarily derived using spectroscopic techniques such as XPS, NMR, FTIR and Raman spectroscopies. In contrast, we report an alternative electrochemical approach to investigate the composition of GO, previously developed to study surface functionalities within other carbon-based materials. In separate reactions, four electroactive labels were first employed to selectively label the various functional groups in GO, followed by their subsequent quantification using cyclic voltammetry. Distinct functional group compositions were consequently found depending on the choice of GO oxidation method, either via chlorate or permanganate oxidations. An additional advantage of the method is the ability to distinguishing the types of carbonyl groups such as quinonyl species over isolated ketones. Thus, we noted that permanganate oxidation produced GO with its carbonyls mainly existing as 1,2-quinones, while chlorate oxidation resulted primarily in aliphatic ketones. Furthermore, carboxylic groups that were erstwhile thought to be responsible for the acidic nature of GO were observed to be low in permanganate-GO and non-existent in chlorate-GO. We also deduced that epoxides likely exist as the main functionality within permanganate-GO, and discuss that the relatively low labelled-hydroxyl content may be due to previously proposed disproportionation reactions which result in formation of other groups. Overall, this selective labelling and electrochemical detection method has provided an improved and refined understanding of GO structures.
(Invited) Silicon Quantum Dots: From Single-Dot Studies to Highly Luminescent Ensembles
Authors: Linnros Jan
Published: February 2020

The luminescent properties of nanoscale silicon were demonstrated in 1990 triggering the interest in Si nanostructures for optical emission. While the luminescence was quite strong even at room temperature, the micro-second long PL lifetimes revealed an inherited indirect bandgap from bulk Si. The luminescence mechanism was heavily debated whether quantum confinement really played a role or the emission would be due entirely from surface states. Many studies have confirmed the quantum confinement model but it has also been shown that the emission can be widely tuned by changing the surface passivation or by adding different ligands to the shell. The physics of the emission was however obscured by inhomogeneous line broadening due to the large size dispersion of the emitting entities in porous silicon or in matrices containing silicon nanocrystals. This called for single-dot spectroscopy studies as demonstrated for single molecules and later for nanocrystals of direct bandgap semiconductors.

In this talk I will start by reviewing our work on PL emission and spectroscopy of individual Si quantum dots. These were initially fabricated using electron-beam lithography, plasma etching and oxidation resulting in micron spaced Si quantum dots that could be individually distinguished in an optical microscope. More recently we have also looked at more “randomly” spaced Si nanocrystals as well as colloidal nanocrystals dispersed on a wafer. These single-dot studies have revealed many of the phenomena observed for the II-VI nanocrystals such as on/off intermittency (blinking), spectral diffusion and narrow linewidth. Indeed, the linewidth at low temperatures was found to be ~250 µeV, limited by system resolution while the room temperature homogenous linewidth was shown to depend on the surface passivation and ligand shell. Recently, we have also performed absorption measurements of single nanocrystals revealing several distinct absorption levels above the fundamental bandgap that can be compared to theoretical calculations.

Finally, in a collaboration with the group of Prof Veinot at the Univ. of Alberta, we have examined colloidal dispersions of Si nanocrystals fabricated from HSQ (hydrogen silsesquioxane). Recent data show very high quantum yields approaching 70 % for these nanocrystals. Lifetime measurements  suggest that near 100 % internal quantum efficiency can be reached paving the way for many applications.
(Invited) Nanophotonic Designs for Luminescent Quantum Dots and Application to Photovoltaics
Authors: Ferry Vivian E.
Published: February 2020

The combination of photonics with light-emitting materials offers the ability to enhance luminescence efficiency through manipulation of the radiative rates in addition to the transformation of devices utilizing luminescent materials.

The initial portion of this talk will discuss the combination of quantum dots with plasmonic nanostructures for enhanced luminescence efficiency, comparing the effects of controlling the radiative rates with designs to enhance and direct luminescence over large area films.

We will then discuss the design and considerations behind photonic luminescent solar concentrators. Luminescent solar concentrators offer many advantages over traditional concentrator geometries, including the ability to capture diffuse illumination, and the potential for integration with architectural materials. In a standard LSC design, incident sunlight is absorbed by a luminophore embedded within a plastic sheet, re-emitted at longer wavelengths that are trapped by total internal reflection, and eventually concentrated to an edge-mounted solar cell. Although promising, such devices suffer from losses including reabsorption of the emitted light by the luminophore, non-unity quantum yields, and incomplete light guiding to the solar cell.

Recent work has focused on the development of luminescent materials based on colloidal nanocrystals with large Stokes shifts to overcome the reabsorption losses. These colloidal nanocrystals hold other advantages as luminescent materials, as their narrow emission bandwidth enables the use of photonic structures that address other light guiding losses. Such photonic designs must operate over a broad spectral range and range of incident angles. By combining luminescent materials with photonic structures, longer propagation lengths and higher concentration factors can be reached.

One of the key advantages of these luminescent nanocrystals is their tunability. Here we focus particularly on core-shell quantum dot heterostructures. We will show the effects of tuning the luminophore shape on the conversion efficiency, with respect to both the changing optical properties due to quantum confinement effects and the scattering due to the volume of the nanocrystal. Using a wavelength-selective photonic mirror, which is designed to accept blue light and trap the luminescent light, we then explore how the combination of a tunable luminophore and tunable photonic structure can be implemented to improve light guiding efficiency. Finally, we will compare different photonic designs for implementation with these nanocrystals.
In Situ Liquid-Cell Transmission Electron Microscopy Investigation of Nickel Electrodeposition
Authors: Wang Yuxuan , Li Zhe-Fei , Wang Dan , Botte Gerardine G
Published: February 2020

Nickel electrodes prepared through electrodeposition processes have been demonstrated as promising catalysts for urea electrolysis, towards the applications of urea removal from urea-rich wastewater and hydrogen production.[1-5] The urea electrochemical oxidation process in alkaline media can be described as the equations below:

CO(NH2)2(aq) + 6OH− → N2(g) +5H2O(l) +CO2(g) +6e−      (1)

6H2O(l) + 6e−→3H2(g) +6OH−
(aq)                                       (2)

Reaction (1) and (2) happen at the anode and cathode of the urea electrolyzer respectively.[5] The overall reaction is shown below:

CO(NH2)2(aq) +H2O(l)→N2(g) +3H2(g) +CO2(g)                   (3)

However, there is still lack of knowledge on how the nickel catalysts behave during the electrodeposition and urea electrolysis process.

Recent development of in-situ transmission electron microscopy (TEM) with liquid cell has provided an excellent tool to direct observe material evolution at nanoscale in a liquid environment.[6] With this technique, sample behavior under dynamic operating conditions, such as various electrochemical reactions with the help of incorporated three-electrodes setup, can be imaged in the real time, which could further assist the understanding of the reaction process along with the mechanism behind it.

Within this study, the nickel electrodeposition process has been investigated using in-situ liquid-cell TEM. The experiments were carried out with a state-of-the-art flow cell TEM holder equipped of three electrodes system. The nickel particles were electrodeposited on a thin glassy carbon working electrode during the cyclic voltammetry (CV) scans, as shown in Figure 1.  The TEM images were recorded using JEM 2100F field emission TEM. This work revealed the formation process of the nickel particles and made it possible to achieve the precise control of electrode synthesis. It also opened a window for understanding other electrodeposition processes and urea electrolysis with nickel based catalysts.

Figure 1 shows the TEM image of electrodeposited nickel particles on the platinum working electrode of the in situ TEM cell along with the cyclic voltammgraphs (inserted) to obtain these nickel particles.

References

[1]   B. K. Boggs, R. L. King, G. G. Botte, Chem. Commun. 2009, 32, 4859-4861

[2]   A. N. Rollinson, J. Jones, V. Dupont, M. V. Twigg, Energy Environ. Sci. 2011, 4(4), 1216-1224

[3]   D. Wang, W. Yan, S. H. Vijapur, G. G. Botte, J. Power Sources 2012, 217, 498-502

[4]   W. Yan, D. Wang, G. G. Botte, Electrochim. Acta 2012, 61, 25-30.

[5]   D. Wang, G. G. Botte, ECS Electrochem. Lett. 2014, 3(9), H29-H32

[6]   H. Liao, K. Niu, H. Zheng, Chem. Commun., 2013, 49, 11720-11727

Figure 1 TEM image of nickel particles with inserted CV curves for electrodeposition.

Figure 1
Self-Terminated Electrodeposition Reactions for Electrocatalysis
Authors: Moffat Thomas P. , Liu Yihua , Ahn Sang Hyun , Wang Rongyue , Ritzert Nicole L. , Schwarz Kathleen , Gokcen Dincer , Hangarter Carlos , Bertocci Ugo
Published: February 2020

Development of a sustainable hydrogen economy based on water electrolysis and fuel cells is constrained by the performance, longevity and high cost of Pt group electrocatalysts. Important strategies for improving catalytic reactivity include alloying, forming bimetallic or alloyed surfaces, and engineering substrate–catalyst interactions. At the same time, significant effort is underway to minimize the loading of Pt group metals by examining new synthesis methods and electrode geometries. Of particular interest is atomic layer deposition (ALD) for growing ultrathin films that maximize utilization of rare, expensive metals and facilitate the exploration of bimetallic effects in electrocatalysis.

Recently, an inexpensive “wet form” of ALD based on self-terminated electrodeposition reactions was uncovered that enables controlled formation of ultrathin films of Pt, Ir and iron group metals and alloys thereof. The mechanism of self-terminated deposition reactions will be discussed and the utility of these films as bimetallic electrocatalysts will be demonstrated. For example, monolayer equivalent Pt and Ir films were found to match or exceed the best known specific HER/HOR activity for bulk polycrystalline Pt or Ir electrodes and thereby offer the promise of increasing the scalability of these important precious metals in energy conversion devices.
Gas-Transport Resistances in Fuel-Cell Catalyst Layers
Authors: Schuler Tobias , Tucker Michael C , Weber Adam Z
Published: February 2020

The commercialization of PEFCs depends significantly on reduction of the costly precious metal content in fuel-cell electrodes. To achieve this goal, a high-performance low-loaded electrode must be utilized; and there is a need to understand the key transport resistances and processes within such a structure. The catalyst layer represents the most complex system in a PEFC due to the existence of multiple phases and a heterogeneous structure. Within catalyst layers, gas transport dominates the performance at high current densities, resulting in mass-transport limitations. To quantify these resistances, limiting-current measurements can be used. In this talk, we report on such mass-transport resistances utilizing a hydrogen-pump limiting current under various operating conditions including gas pressure and gas chemical identity for various low-loaded catalyst structures. In this fashion, one can separate the various resistances into molecular versus Knudsen diffusion and bulk versus non-bulk resistances.

The in-situ method based on H2limiting current measurements was used for the characterization of catalyst-layer resistances in porous Pt/C based electrodes. The parameters studied were the ionomer to carbon ratio, the platinum loading, and the influence of different carbon supports. The effect of platinum loading on hydrogen transport resistance shows that the catalyst-layer resistance is inversely proportional to the roughness factor of the electrode as shown in the figure. The dominant transport mechanism is estimated to be Knudsen diffusion for vulcan-based catalyst layers. An increase of molecular diffusion can be observed by diluting Vulcan black by Ketjen black. Overall, the technique allows for quantification of the local transport resistances within the catalyst layer using a simplified experiment, thereby suggesting that the ionomer film is key in controlling the resistance. Furthermore, the observed trends can be used to guide optimization of novel low-loaded fuel-cell electrodes.

Acknowledgements

This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Fuel Cell Technologies Program of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 and by CRADA agreement LB08003874 between Lawrence Berkeley National Laboratory and Toyota Motor Company.

Figure 1. Total cell resistance as a function of inverse roughness factor at 40°C, 0.5psi. The catalyst layer resistance is inversely proportional to the roughness factor of the electrode, as represented by the linear regression function.

Figure 1
Electrochemical Impedance Spectroscopy Study of Alkali-Metal Insertion Processes on Hard Carbon Electrodes
Authors: Väli Ronald , Jänes Alar , Kanarbik Rait , Lust Enn
Published: February 2020

Sodium-ion batteries have attracted great deal of attention due to sodium’s abundance and lower price compared to lithium and cobalt. A major obstacle that prevents sodium-ion batteries from going into mass-scale production is the negative electrode (anode during discharge). Graphite is currently the safest negative electrode material for lithium-ion batteries, but does not intercalate sodium reversibly, because sodium ions prefer prismatic or octahedral coordination sites [1].

Our previous work [2] focused on the synthesis and electrochemical characterization of glucose-derived hard carbon negative electrodes for sodium-ion batteries. The results inspired us to conduct a more detailed impedance study of the electrode processes.

Hard carbons have shown to absorb/insert and desorb/de-insert sodium reversibly [2,3]. However, the exact mechanism is difficult to understand without detailed studies which apply different physical and electrochemical methods. Therefore, electrochemical impedance analysis with equivalent circuit fitting (Figure 1a, b) was conducted to analyse surface processes at various potentials. ICP-MS, SEM-EDS (Figure 1c) and TOF-SIMS confirmed alkali-metal absorption in the carbon structure.

Acknowledgements

This research was supported by the EU through the European Regional Development Fund TK141 “Advanced materials and high-technology devices for energy recuperation systems”, Estonian target research project IUT20–13 and personal research grant PUT55. The authors thank Dr. Kalle Kirsimäe for ICP-MS analysis.

References

1. J. Qian, X. Wu, Y. Cao, X. Ai, and H. Yang, Angew. Chem. Int. Ed., 52, 4633 (2013).

2. R. Väli, A. Jänes, T. Thomberg, and E. Lust, J. Electrochem. Soc.(2016), under review.

3. S. Prabakar, J. Jeong, and M. Pyo, Electrochim. Acta, 161, 23 (2015).

Figure 1
Path Dependence in Lithium-Ion Batteries Degradation - a Comparison of Cycle and Calendar Aging
Authors: Dubarry Matthieu , Devie Arnaud
Published: February 2020

The Hawai‘i Natural Energy Institute (HNEI) is leading research efforts to understand the degradation of lithium-ion batteries under two distinct projects. The first research project is focused on grid-scale battery energy storage systems (BESS) while the second project is targeting electric vehicles (EVs) and their synergy with the grid.

Both applications require a combination of long cycle-life (1000 cycles or more) and long shelf-life (10 to 20 years in operation) to meet the expectations of the customers. To determine whether these durability goals are realistic or not, we performed accelerated testing of different lithium-ion battery technologies in the laboratory. For each technology, we conducted a series of cycle and calendar aging experiments. The results of these studies will be used to develop predictive performance models.

The concept of accelerated aging is only valid if the degradation the cell underwent is the same than of the one it experienced in real life. In this presentation, we want to share our preliminary observations regarding the differences between cycle aging and calendar aging across the different chemistries and across the industries (EVs, BESS). Our primary objective is to showcase the different degradation pathways, whether calendar-driven or cycle-driven, which can lead to identical capacity losses. This concept is better known as path dependence and this talk will highlight its implications for the design of long-life battery systems, the laboratory testing it requires and the validity of accelerated testing strategies.

[1] M. Dubarry, N. Vuillaume and B. Y. Liaw, J. Power Sources 186(2), (2009) 500-507.

[2] M. Dubarry, C. Truchot and B.Y. Liaw, J. Power Sources 219 (2012) 204-216.

[3] https://www.soest.hawaii.edu/HNEI/alawa/

[4] M. Dubarry, C. Truchot, A. Devie and B. Y. Liaw, J. Electrochem. Soc 162(6), (2015) A877-A884.
Modeling Volume Change and Battery Performance Due to Intercalation in Porous Electrodes
Authors: Garrick Taylor Reed , Dai Yiling , Higa Kenneth , Huang Xinyu , Srinivasan Venkat , Weidner John W.
Published: February 2020

In order to accurately predict the behavior or electrochemical devices, it is necessary to develop sophisticated models that take into consideration transport processes, electrochemical phenomena, mechanical stresses, and structural deformations on the operation of an electrochemical system. Many different models exist that can predict the electrochemical performance of these devices under a variety of operating and design conditions.[1-7] However, many of these models assume constant porosity and do not take into consideration the effects of a variable porosity on the porous electrode during cycling and what effects that may have on performance. In recent years, electrodes have been developed that show a significant volume change during intercalation and deintercalation, which are unable to be accurately predicted using these constant porosity models.

Porosity and dimensional changes in an electrode can significantly affect the resistance of the battery during cycling and cause premature failure of the battery due to generated stresses. Previously, we have shown the ability to incorporate dimensional and porosity changes in a porous electrode into a model to predict volume changes in the active material during intercalation through the coupling of porous rock mechanics and porous electrode theory.[6] However, that model incorporated many assumptions in order to obtain an analytical solution, including the assumption of bulk stress, strain, and porosity. Here, we present a model that removes those assumptions and illustrates the coupling of porous electrode theory and rock mechanics in order to predict stress, strain, and porosity gradients across a porous electrode during cycling.

1. M. Jain and J. W. Weidner, J Electrochem Soc, 146, 1370 (1999).

2. M. Jain, G. Nagasubramanian, R. G. Jungst and J. W. Weidner, J Electrochem Soc, 146, 4023 (1999).

3. P. M. Gomadam and J. W. Weidner, J Electrochem Soc, 153, A179 (2006).

4. X. C. Zhang, A. M. Sastry and W. Shyy, J Electrochem Soc, 155, A542 (2008).

5. J. Christensen and J. Newman, J Solid State Electr, 10, 293 (2006).

6. T. R. Garrick, K. Kanneganti, X. Y. Huang and J. W. Weidner, J Electrochem Soc, 161, E3297 (2014).

7. K. Higa and V. Srinivasan, J Electrochem Soc, 162, A1111 (2015).
Disulfonated Copolymer Membranes with Improved Selectivity and Lifetime for Vanadium Redox Flow Batteries
Authors: Kara Kenan , Sankir Mehmet , Demirci Sankir Nurdan , Agar Ertan
Published: February 2020

One of the critical needs to increase the widespread implementation of vanadium redox flow batteries (VRFBs) is identifying reliable and cost-effective membranes with improved lifetime. Among ion exchange membranes, Nafion® has been the most thoroughly studied and widely used material in VRFB applications due to its good proton conductivity, chemical stability and durability. However, the low vanadium selectivity of Nafion®, which leads to significant crossover and related capacity fade with cycling, hinders the use of this type of membrane for commercial VRFB applications [1].

In order to solve this problem, several post-sulfonated hydrocarbon polymers such as poly(sulfone) [2] and poly(benzimidazole) [3] have been studied to explore their effectiveness for use in VRFBs. Although these post-sulfonated membranes have been shown to provide improved proton conductivity and vanadium selectivity, one major limitation of the post-sulfonation method is that the amount of sulfonation and related ion exchange capacity (IEC) cannot be controlled precisely [4]. Especially, the sulfonation of polysulfone with strong acids (e.g. sulfuric and chlorosulfuric) often leads to undesirable side reactions (e.g. cross-linking) and chain cleavage, making the control of sulfonation even more difficult, thereby degrading the mechanical integrity of the final membrane [4]. One potential approach to precisely control the degree of sulfonation of an ion exchange membrane is using direct sulfonation by copolymerization [5]. With this technique, the sulfonic acid groups can be positioned on the more stable and more acidic deactivated sulfone unit, which results in more precise control of ionic group concentration in the final product.

In this talk, we will discuss the performance evaluation of disulfonated copolymer membranes for use in a VRFB application. Basic membrane properties and the results of charge/discharge cycling analysis with respect to various degrees of sulfonation and fluorination will be reported and then compared with Nafion® 212. The study will be presented with emphasis on tailoring the membrane properties of directly disulfonated copolymers and establishing the structure-property-performance relation for these membranes.

References:

[1] E. Agar, K.W. Knehr, D. Chen, M.A. Hickner, E.C. Kumbur, Electrochim. Acta,98, 66-74 (2013).

[2] D. Chen, S. Kim, L. Liyu, G. Yang, M.A. Hickner, RSC Adv., 2, 8087-8094 (2012).

[3] T. Luo, O. David, Y. Gendel, M. Wessling, J. Power Sources, 312, 45-54 (2016).

[4] F. Wang, M.A. Hickner, Y.S. Kim, T.A. Zawodzinski, J.E. McGrath, J. Membr. Sci., 197, 231-242 (2002).

[5] L. Semiz, N.D. Sankir, M. Sankir, J. Membr. Sci., 468, 209-215 (2014).