bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Electrically Switchable Surface Properties Using End-Charged Polymers and pH-Responsive Swelling of Polymer Brushes Via Self-Consistent Field Theory
Authors: Wu David , Hu Renfeng 
Published: February 2020

As electroactive or stimuli-responsive materials, polymers offer advantages related to the variety, complexity and control of the molecular structure possible with well-developed modern synthesis methods. Choice of monomer and sequence allows coupling of response to electric fields or pH to the molecular nanostructure of the polymer chains. We discuss two such representative materials as modeled using Self-Consistent Field Theory (SCFT). The first is an electroactive polymer brush layer composed of surface-grafted chains with a terminal charge that can fold back in response to an applied field. We show that by judicious design of the chain sequence as a diblock copolymer with unequal block lengths, the chain folding can create a change in the apparent surface properties due to switching of the exposed block. The second is a pH-responsive polymer brush that swells as the polymer is increasingly protonated with decreasing pH. We show that the maximum responsiveness in swelling occurs at a pH that is shifted from the intrinsic pKa of the constituent monomers.
Development of Screen Printed Electrodes Chemically Modified with Schiff Base Films for Application in Forensic Chemistry
Authors: de Oliveira Marcelo Firmino 
Published: February 2020

Electrochemical techniques have often been used to analyze a broad range of substances of forensic importance. These techniques can offer certain operational advantages such as ease of automation, potential for field use and the capability of in vivo analysis. They can also furnish information about reaction mechanisms. Additionally, chemical modification of conventional electrode surface is commonly employed for increasing specificity or selectivity in drug analysis. In the case of cocaine, for example, a variety of modifiers have been used, including polymers, Schiff bases, and biological materials.
In this work, chemically modified screen printed electrodes (CM-SPE) using different Schiff base films were employed in the voltammetric investigation of cocaine, 3,4 - methylenedioxymethanphetamine (MDMA), and morphine. Dip coating process was chosen for the surface chemical modification. Three different electrode plateforms were employed: carbon, gold, and platinum. with methanolic solution containing different Schiff base complexes with subsequent drying step at room temperature. The voltammetric measurements were carried out in 50:50 v/v methanol:water solution containing 0.05 mol L-1 KCl and 0.1 mol L-1 LiCl as a supporting electrolyte without oxygen elimination by inert gas flow. The best results were obtained with carbon electrodes. Cocaine exhibits a well defined irreversible anodic peak current (ipa) at a potential (Epa) of 0.85V vs Ag/AgCl.
Voltammetric parameters such as Eprec, v, and tprec were optimized in this study, being obtained the values of -0.80V (vs Ag/AgCl), 120 s, and 100 mV s-1, respectively. The optimized amount of the chemical modifier was found to be 30 mg per electrode. Detection and quantification limits were obtained in 110 and 390 mmol L-1, respectively. Additionally, intra and inter-day repeatability of 2.61% and 3.77%, were obtained for cocaine determination. It was possible to obtain a transductor for cocaine in presence of morphine and MDMA with high specificity in trace levels.
The author acknowledges FAPESP (2013/17630-7) and CAPES (25/2014 Pro-Forenses) for financial suport.
The Suppression Effect of 830nm Laser Irradiation on Porous Silicon Formation
Authors: Chiang C. -C. , Huang Y.-C , Juan P.- C. , Lo F. -S. , Lee T. -H. 
Published: February 2020

The suppression effect of 830nm laser irradiation is fuond on the formation of fine porous silicon, which used hydrofluoric acid (HF) containing electrolyte for electrochemical etching. The photoluminescence (PL) profile shows a single peak at 1.94 eV corresponding to red emission at room temperature. On the laser-irradiated surface, the suppression/etching rate was changed by the laser power. Our study shows that the suppression effect of laser irradiation on the porous silicon layer be considered to a feasible technology for fabricating a uniform sub-5 nm thick porous layer.The thickness of porous layer can be precisely controled by the intensity of laser power and etching time with a tolerance in minutes.
In the study, we used 5×5 cm2, boron-doped, 1 to10 Ωcm, (100) Si specimens and the laser with wavelength of 830nm at maximum power of 5.0mW with beam size of 1.0mm. The laser institutional platform was added the polarizer to control the power of the laser beam.
The power of laser was adjusted to1.0mW, 2.0mW, 3.0mW, 4.0mW, and 5.0mW in air at room temperature. In Fig. a and b, the pictures show the suppression of formation of porous silicon by the 830nm laser at 3.0mW after electrochemical etching in HF solution with current of 100mA for 10 minutes. The thickness of porous silicon varies of the outer region of laser-irradiated area could be observed by Field Emission Scanning Electron Microscope (FE-SEM). A straight-line slope of a porous silicon layer between the laser irradiation and non-laser irradiation that confirms the size of Gaussian beam with the suppression phenomenon of porous silicon. We called the propagating out profie of a Gaussian beam in the laser irradiation is the transition zone of porous silicon formation (TZPS).

Figure 1
Chemical Deposition of Vanadium Oxide Electrode for Electrochemical Capacitors
Authors: Wu Haoran , Lian Keryn 
Published: February 2020

INTRODUCTION

Vanadium oxides have been investigated as pseudocapacitive electrode material because of their low cost, abundance in nature and high energy capacity [1-2]. The performance of the electrodes strongly depends on the fabrication methods. However, a technique that can produce vanadium oxide with high performance, low cost and ready to scale up is yet to be developed. In this work, we demonstrate a novel and simple chemical method to deposit vanadium oxides with potential applications in electrochemical capacitors.

EXPERIMENTAL

A thin Titanium foil was ultrasonically cleaned by acetone and immersed in a 20ml 0.5M VOSO4solution. 0.3ml 1M NaOH was added to initiate a chemical precipitation process. The titanium substrate was left un-stirred in the solution for 5 days until the surface was covered by a greenish film.
Scanning electron microscopy (SEM) images were taken to examine the surface morphology. Cyclic voltammetry (CV) was used to characterize the electrochemical performance of the samples in 1 M LiCl solution.

RESULTS AND DISCUSSION

The SEM image of the surface, illustrated in Fig. 1, showed the chemical deposited vanadium oxide had layered structure with a denser layer at the bottom and a sparser and island-like layer on the top. Yet two layers are highly porous with meso- and macro- porosity, suggesting the chemical deposition enabled a large surface area that might contribute to a high capacitance. It was found the entire surface was covered by the porous vanadium oxide, showing the chemical deposition is evenly distributed on the substrate.
The cycle life of vanadium oxide electrode was shown in Fig.2, where the CV of the 1st cycle, 1000th cycle, 2000th cycle and 3000th cycle were compared. The result depicted a very rectangular and ideal capacitive behavior, suggesting the deposited vanadium oxide is suitable in electrochemical capacitors application. As a comparison, the CV of the Ti substrate showed very little capacitance. Moreover, it showed little change in CV profile from 1st to 3000thcycle, indicating that the electrode was stable for long time cycling in 1 M LiCl. There was a slight decrease in capacitance after 3000 cycle (ca. 10%), likely due to the some degradation on the surface. However, since vanadium oxide was usually reported to have poor stability due to pulverization and dissolution [1], the results in Fig. 2 is still very promising.
In addition to the morphology and electrochemical characterizations, the composition and crystal structures of the produced vanadium oxide were also investigated. These results will be presented as well.

REFERENCES

[1] G. Wang, X. Lu, Y. Ling, T. Zhai, H. Wang, Y. Tong, Y. Li, ACS Nano, 6, 10296 (2012)
[2] I.-H. Kim, J.-H. Kim, B.-W. Cho, K.-B. Kim, Journal of The Electrochemical Society, 153, A1451 (2006)

Figure 1
Studies of Mass Transport in Semiconducting Thin Film Electrodes
Authors: Parr Daniel , Meunier Carl , Roberts Ethan , Remsen Edward E. , Haverhals Luke M. 
Published: February 2020

Applications of novel thin film electrodes are enabling the development of new commercial products ranging from in vivo biosensors, solar cells, and lithium-ion energy storage. A critical consideration that enables informed engineering of working devices is mass transport of electro-active species (EAS) and electrolytes within porous thin film electrodes. Initially we focus on the fabrication and characterization of transport within thin film electrodes fabricated from titanium dioxide, hydrogen titantate nanotubes, and zinc oxide via a sol-gel method. Characterization data for films deposited on indium tin oxide coated glass slides by doctor blade techniques are also discussed and include bright field microscopy, powder x-ray diffraction and, mass transport properties as investigated by cyclic voltammetry. Additionally we will discuss the creation and characterization of graphene nanosheets via the reduction of graphite oxide.
Electrochemical Synthezis of Co-Rh Alloys
Authors: Mech Krzysztof , Zabinski Piotr , Kowalik Remigiusz , Wojnicki Marek 
Published: February 2020

Rhodium is a very important element due to a wide range of its applications in electronic devices, jewellery and catalysis. Rhodium like other platinum group metals (PGMs) presents a high catalytic activity for many chemical and electrochemical reactions. The position of rhodium on –logi0 - DGM-H plot shows its high catalytic activity for hydrogen evolution reaction (HER) [1]. The mentioned dependency may result in a conclusion that also alloys obtained through combination of elements from the transition group can demonstrate properties interesting from the point of view of catalytic activity for HER.
The present work shows results of tests over electrochemical synthesis of Co-Rh alloys from acid chloride electrolytes. Particular attention was devoted to the influence of electrolysis parameters on properties of the deposited alloys, such as the composition, structure and their morphology. The work elaborates also the mechanism responsible for formation of Co-Rh alloys through electroreduction of aquachloro- complexes of Co(II) and Rh(III) in acid environment. The identification of electrode reactions was performed based on voltammetric and electrogravimetric tests. Also, current efficiency of electrolysis was assessed. The electrolyte stability was tested with the use of UV-Vis spectrometry. The potentials range enabling the alloys synthesis was selected based on electrochemical tests. The tests included influence of concentration of Σ[CoClx(H2O)6-x]2-x (x = 0, 1, 2) and Σ[RhCly(H2O)6-y]3-y (y = 4, 5, 6), working electrode potential, electrolyte pH and temperature on the composition, structure and morphology of Co-Rh alloys deposited at potentiostatic conditions. The conducted tests indicate a possibility of alloys synthesis of a wide range of elemental composition and diversified morphology. The performed structural analysis showed a high influence of the synthesis conditions on the structure of the synthesized alloys.
[1] N. Pentland, J.O. Bockris, E. Sheldon, Hydrogen Evolution Reaction on Copper, Gold, Molybdenum, Palladium, Rhodium, and Iron - Mechanism and Measurement Technique under High Purity Conditions, J Electrochem Soc 104 (1957) 182-94.
Electrochemical Characterization of Li4Ti5O12 By Single Particle Measurements Using a Particle - Current Collector Integrated Microelectrode
Authors: Sakurai Yoji , Kawashiri Shuhei , Utagawa Masahiro , Tsuda Takao , Tojo Tomohiro , Inada Ryoji 
Published: February 2020

A single particle measurement is known as a characterization method of electrode material [1]. In a conventional single particle measurement, electrical contact between a microelectrode and an electrode particle is made while observing with an optical microscope.
Although the conventional single particle measurement can be electrochemically performed under an optical microscope by contacting the single active material particle with a Pt microfilament, the applicability of this technique is limited with respect to the size and shape of particles. Recently, we overcame the problem by using “a particle - current collector integrated microelectrode” , in which the single active material particle was directly-bonded on the tip of the microelectrode [2]. In this study, new measurement systems were constructed using the integrated microelectrode embedded in a three-electrode flange cell and a constant temperature bath in order to evaluate the electrochemical properties of Li4Ti5O12 (LTO) single particle, which includes the temperature dependency of the electrode kinetics.
Particle - current collector integrated microelectrodes were prepared as follows using a focused ion beam process unit (FIB): After attaching a tungsten probe coated with fluorinated resin to a manipulator in the FIB, the tip of the probe was cut off to expose the inner conductive probe. An ionic beam of platinum was positioned and deposited on contact between the top of the cut probe and a single LTO particle. The particle - current collector integrated microelectrode as the working electrode was assembled in a three-electrode flange cell with Li metals as the counter and reference electrodes. The electrolyte employed was 1mol/L Li(TFSI)/EC+PC(1:1 v/v%). Electrochemical measurements of the LTO single particle were carried out at 10 oC -40 oC.
Cyclic voltammograms of LTO single particle exhibited the well-defined reversible redox peaks at around 1.55V vs. Li/Li+ when the scan was initiated from reduction direction. The obtained phenomenon, higher anodic peak current than cathodic peak current, is indicative of faster reaction during Li+ extraction (i.e. discharge) than Li+ insertion (i.e. charge). At 40 oC, single LTO particle was found to deliver its 95% capacity upon discharge at 1000C. On the contrary, the capacity retention upon charge at 1000C retained only 37%. These tendencies in charge/discharge were also confirmed at all temperatures tested.
In this presentation, the peculiar reaction behavior mentioned above will be discussed in terms of reaction kinetics of LTO with lithium, through electrochemical impedance spectroscopies at various temperatures.
References
[1] I. Uchida et al., J. Power Sources, 68, 139 (1997) .
[2] Y. Sakurai et al., 65th Annual ISE Meeting, Mon S05, Lausanne, Switzerland (2014).
Nanoporous Structure Formatioon in Dealloying of Li Alloys
Authors: Chen Qing , Geng Ke , Sieradzki Karl 
Published: February 2020

Structural instability during cycling has long been a roadblock to the path of fulfilling Li alloys’ promise as high energy-density anodes for Li-ion batteries. While most investigations into this issue deal with mechanical fracturing, we focus our discussion on morphology evolution during the discharge process1. Bi-continuous porous structures that are often associated with noble metal alloy dealloying also evolve during de-lithiation. An important issue in dealloying of Li that is inconsequential for noble metal dealloying is that of bulk diffusion of the electroactive component, which adds new complexity to this problem. The interplay of bulk solid-state diffusion with percolation dissolution results in a variety of alternative morphologies including nonporous and core-shell particles. We use Li-Sn alloys as an exemplary system to illustrate how these factors impact the resulting dealloyed structures by investigating effects of alloy composition, dealloying rate and particle size. Our results have important implications for designing nanoporous materials from a variety of different parent-phase materials2,3.
References:
1. Chen, Q. & Sieradzki, K. Spontaneous evolution of bicontinuous nanostructures in dealloyed Li-based systems. Nat. Mater.
12, 1102–1106 (2013).
2. Chen, Q. Bi-Continuous Nanoporous Structure Formation via Compound Decomposition. J. Electrochem. Soc.
161, H643–H646 (2014).
3. Lin, F. et al. Phase evolution for conversion reaction electrodes in lithium-ion batteries. Nat. Commun.
5, 3358 (2014).

Figure 1
Impedance Study of Anodic Properties of Ni-Fe Impregnated SDC
Authors: Itagaki Yoshiteru , Takemasa Tomohisa , Yamaguchi Syuhei , Yahiro Hidenori 
Published: February 2020

Samaria-doped ceria (SDC) possesses a higher oxide ionic conductivity compared to YSZ, furthermore it exhibits a high electronic conductivity under a reducing condition. Therefore SDC can form electron conduction paths instead of Ni particles, which means Ni concentration can be suppressed to avoid their aggregation. As a result of suppressing Ni aggregation, the 20wt% Ni/SDC anode exhibited the higher performance compared to that containing lower or higher concentration of Ni. This is due to the increase in the number of reaction site, i.e., interfaces between Ni particles and SDC. Ni-Fe anodes with the high Ni-Fe concentrations have been already reported. Lu et al. evaluated the 50wt% Ni1-xFex/SDC anode in hydrogen fuel and reported their best performance at x=0.25. They assigned the modified performance to the electronic interaction between Ni and Fe. In the present study, we newly prepared Ni-Fe/SDC anode containing 20wt% Ni-Fe alloy, and their anodic properties were investigated by the impedance analyses. The Ni1-xFex/SDC particles were prepared by the impregnation method using the nitrates of the corresponding metals. The precursors were calcinated at 700oC for 10h. The obtained powers were deposited on the dense 10Sc1CeSZ disk and sintered at 900oC. The cathode was formed with Pt paste on the opposite surface of the 10Sc1CeSZ disk. 100%H2 and air were supplied on the anode and cathode, respectively. All the impedance spectra of the Ni1-xFex/SDC anodes were measured at 800oC with the three-terminal configuration under the OCV condition. The impedance spectra of the anodes exhibited an ohmic component and two depressed arcs. Therefore, the spectra were fitted by assuming the equivalent circuit of R
ohm(RHFQHF)(R
LH
Q
LF), where Q is a phase constant element. The R
HF component hardly influenced by P
H2, and on the other hand, the R
LF component was proportional to P
H2
0.5. From these results, we assigned the R
HF and R
LF to charge transfer process of hydrogen and surface diffusion of the hydrogen atoms, respectively. Furthermore, the R
LF component sensitively decreased by the humidification of hydrogen. Therefore it was found that the adsorbed water molecule or associated species helped hydrogen atom diffuse on the anode. The i-v characteristics of the cells with the Ni1-xFex/SDC anodes were resulted in order of 0.5 ≥ 0.2 > 0.8 ≥ 0. The crystallite sizes of the Ni1-xFex/SDC were dependent on x, and minimum at x=0.5. The i-v characteristics correlated with the crystallite size. The impedance spectra of the Ni1-xFex/SDC anodes were also fitted by assuming the equivalent circuit of R
ohm(RHFQHF)(R
LH
Q
LF). The R
LF, which can be assigned to the dissociative adsorption and surface diffusion of hydrogen, was most variable among the resistance components. The x=0.5 anode exhibited the R
LF minimum value. Therefore we tentatively conclude that Fe addition to Ni reduces the potential for the hydrogen dissociation and the surface diffusion processes.
An Accurate and Reliable Computational Approach for the Mechanical Stress Analysis of Planar SOFC Stack
Authors: Fang Xiurong , Li Ang , Lin Zijing 
Published: February 2020

Mechanical damage induced by operation under high stress conditions is one of the major factors limiting the long-term stability of SOFCs. Stress analysis is therefore important for the development the SOFC technology. To date, it is a common practice to focus the stress analysis at some interested component of an SOFC stack, e.g., PEN, glass-ceramic sealant, interconnector plate, etc. This approach is questionable as it is very difficult or even impossible to properly define the boundary conditions for the isolated component. To conduct a reliable stress analysis, it is desirable to carry out the stress computation on the entire stack. For that purpose, it is important to devise algorithm that confines the computational resource requirement at an affordable level. Here we report a grid matching method that enables the stress evaluation of the whole multi-cell SOFC stack. The basic idea of the grid matching scheme is to assign adequately fine grids for the interested stack components and their neighboring materials, while distant material components are assigned with coarse grids to reduce the computational burden. With appropriate free stress temperatures of materials, initial state of stress, material properties, boundary conditions and temperature profile of the SOFC stack, stress distributions inside the interested stack components can be calculated by solving the elastic matrix.
The method is tested with a 5-cell planar stack. The 5-cell stack is chosen so that the stress analysis with fine grids for all stack components is also affordable. The stack is of practical dimensions and material components such as the cells, frame, interconnects and glass-ceramic sealants, etc. For typical material combinations of SOFC stack and operation conditions, the stack temperature profiles were generated by a high resolution multi-physics numerical model. The test shows that the error for the maximal stress using coarse grids is limited to the order of 10% in comparison with that with fine grids for all stack components. In other words, the grid matching scheme is confirmed to be a computationally efficient and satisfactorily accurate method for the stress analysis. However, the maximal stress of a stack component evaluated with the commonly adopted method using a free boundary condition for the interested component is one order of magnitude smaller than the correct result. On the other hand, the stress of a stack component evaluated with a stiff boundary condition can be a few orders of magnitude higher than the true result. Clearly, the conventional stress analyzing approach with isolated stack components is prone to produce misleading results.
The proposed stress analysis method is valuable for reliably identifying stack components susceptible to mechanical damage. It can be used to improve the design of SOFC stack and to make informed selections of operating conditions.