bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of the Surface on the Delithiation Mechanism of LiNi0.8Co0.15Al0.05O2 positive Electrodes for Li-Ion Batteries
Authors: Grenier Antonin , Liu Hao , Wiaderek Kamila M , Borkiewicz Olaf J , Chupas Peter J , Chapman Karena W
Published: February 2020

The occurrence of an apparent two-phase delithiation mechanism reported for LiNi0.8Co0.15Al0.05O2 (NCA)1 is not intrinsic to the material but is due to a surface layer.

Ni-rich layered oxides like NCA are the most important class of positive electrodes for high-energy-density Li-ion batteries. These materials react with H2O and CO2 from air to form surface layers mainly composed of Li2CO3
2–5. The presence of such a surface layer is deleterious to the electrochemical performance of this class of material. We show, using in-situ synchrotron X-ray diffraction measurements, that this surface layer also induces the presence of a second phase during the 1st electrochemical delithiation. Such a mechanism is however not intrinsic to NCA. Indeed, a sample stored and handled in an argon atmosphere presents a typical solid solution behavior, as expected for this class of material.

1. R. Robert, C. Bunzli, E. J. Berg and P. Novák, Chem. Mater., 2015, 27, 526–536.

2. H. Liu, Y. Yang and J. Zhang, J. Power Sources, 2006, 162, 644–650.

3. G. V. Zhuang, G. Chen, J. Shim, X. Song, P. N. Ross and T. J. Richardson, J. Power Sources, 2004, 134, 293–297.

4. H. S. Liu, Z. R. Zhang, Z. L. Gong and Y. Yang, Electrochem. Solid-State Lett., 2004, 7, A190–A193.

5. K. Matsumoto, R. Kuzuo, K. Takeya and A. Yamanaka, J. Power Sources, 1999, 81–82, 558–561.

Figure 1
Revisiting the Electrochemical Stability of Solid Electrolytes
Authors: Han Fudong , Yue Jie , Fan Xiulin , Gao Tao , Wang Chunsheng
Published: February 2020

The development of a high-performance bulk-type all-solid-state lithium battery requires a better understanding of the high interfacial resistance between the electrode and solid electrolyte. In this presentation, we propose that the electrochemical stability window of solid electrolyte was overestimated by the conventional experimental method, and the electrochemical decompositions of solid electrolyte could cause high interfacial resistance in the bulk-type solid-state battery depending on the conducting properties of the decomposition interphases. A novel experimental method using a Li/electrolyte/electrolyte-carbon cell was proposed to approach the intrinsic stability window of the most promising solid electrolytes, Li10GeP2S12 (LGPS) and garnet-type Li7La3Zr2O12 (LLZO). The results indicate that both of these solid electrolyte materials have much narrower electrochemical window than claimed. The decomposition products for both electrolytes were also characterized by XPS test. Suppressing the unwanted electrochemical decomposition of solid electrolyte at the interface is critical for achieving a high performance bulk-type solid-state battery. The idea is supported by our most recent experimental result. By introducing an (electro)chemically stable and ionically conductive interphase between LiCoO2 and garnet-type LLZO solid electrolyte, the electrochemical decomposition of LLZO at the LLZO/LiCoO2 interface could be suppressed, which enables a cycling-stable Li/LLZO/LiCoO2 cell with a full-ceramic cathode.
Virtual Design of Thick Electrodes for Li-Ion Batteries
Authors: Danner Timo , Hein Simon , Westhoff Daniel , Haselrieder Wolfgang , Schmidt Volker , Kwade Arno , Latz Arnulf
Published: February 2020

Li-Ion batteries are commonly used in portable electronic devices due to their outstanding energy and power density. A remaining issue which hinders the breakthrough e.g. in the automotive sector is the high production cost. Going ‘giga’ is one approach currently pursued but requires large investments. Recently, battery concepts with thick electrodes were presented as attractive alternative1. Batteries with thicker electrodes provide higher theoretical energy densities with only a few electrode layers which reduces production time and cost2.

In our contribution we present 3D micro-structure resolved simulations of thick (electrodes > 300µm) Graphite-NMC batteries based on our thermodynamically consistent simulation framework BEST3. The parametrization and validation of our model is presented in a recent publication4 and simulation results agree favourably with experimental data2. As a major problem we identified transport limitations in the electrolyte at comparatively small C-rates2,4. Novel design and operation strategies of the battery and its components are needed to mitigate this issue. In this presentation we will focus on our on-going electrode design studies. Two different design concepts using laser perforation and/or porosity gradients were evaluated regarding their performance at high C-rates. Therefore, multiple realizations of electrode structures were generated with a stochastic 3D geometry generator5. The structures and corresponding electrochemical simulations were validated against tomography and experimental data of model electrodes. The virtual screening of different configurations provides material-structure-function relationships which are a helpful tool for the processing of thick electrodes on larger scales.

1. Hopkins, B. J. et al, Component-cost and performance based comparison of flow and static batteries. J. Power Sources
293, 1032–1038 (2015).

2. Singh, M. et al, Thick Electrodes for High Energy Lithium Ion Batteries. J. Electrochem. Soc.
162, A1196–A1201 (2015).

3. Latz, A. et al, Multiscale modeling of lithium ion batteries: thermal aspects. Beilstein J. Nanotechnol.
6, 987–1007 (2015).

4. Danner, T. et al. Thick electrodes for Li-ion batteries: A model based analysis. J. Power Sources
334, 191–201 (2016).

5. Westhoff, D. et al. Parametric stochastic 3D model for the microstructure of anodes in lithium-ion power cells. Comput. Mater. Sci.
126, 453–467 (2017).

Figure 1
(Invited) Narrow Band Emission of Nitrides Phosphors and All Inorganic Perovskite Quantum Dots for the Application in Light Emitting Diodes
Authors: Liu Ru-Shi
Published: February 2020

A narrow band emission nitride SrLiAl3N4:Eu2+ (SLA) red phosphor prepared through a high-pressure solid state reaction was coated with organosilica layers in 400 ~ 600 nm thickness to improve its waterproof property. The coated samples showed excellent moisture resistance while retaining an external quantum efficiency (EQE) of 70% of its initial EQE after being aged for 5 days in harsh conditions. White light-emitting diodes (LEDs) of SLA red-phosphors and commercial Y3Al5O12:Ce3+ (YAG:Ce) yellow-phosphor on a blue-InGaN chip were shown high color rendition (CRI = 89, R9 = 69) and low correlated color temperature of 2406 K. All-inorganic CsPbX3 (X = Cl, Br, I) perovskite quantum dots (PQDs) with narrow emission bad were synthesized by hot injection methods. We propose an efficient and simple method to prevent the anion-exchange effect. We mixed green CsPbBr3 PQDs with purchased mesoporous silica. We applied the new PQD-based LEDs for backlight displays. Our white LED device for backlight display passed through a color filter with an NTSC value of 113% and Rec. 2020 of 85%. For lighting application, we used red perovskite quantum dots assisted by a yellow YAG:Ce phosphor were integrated on a blue chip. This warm white light with CCT (3328K), high color rendering index (CRI = 84.7) and a super high value of saturated red color component R9 as 96. Nitrides phosphors and all inorganic quantum dots were a good candidate for the application of white light LEDs with narrow emission band.
Enhanced Understanding of Persistent Luminescence in Submicron Particles of SrAl2O4:Eu2+,Dy3+
Authors: Finley Erin , Cobb Angelica , Danthanarayana Adheesha , Goux Heather , Willson Richard , Brgoch Jakoah
Published: February 2020

Bioanalytical applications such as in vivo imaging and point-of-care diagnostics have taken a special interest into the use of persistent luminescence phosphors. Their notable long luminescent decays and environmentally benign materials make them excellent candidates for testing platforms like lateral flow assays (LFAs). However, LFAs require particle sizes that range from 250 nm to 500 nm for adequate spontaneous flow without being subject to gravitational sedimentation or clogging of the assay due to large particle agglomerates. Synthesis methods to produce submicron particle sizes of these materials are widely studied and have shown successful reduction in size. Nevertheless, the shortfall of many of these methods is a lack of understanding on how reduction in particle size affects optical properties, namely a potential significant loss of the characteristic long lifetimes. Here, commercially purchased SrAl2O4:Eu2+,Dy3+ was wet milled followed by a series of centrifugal sedimentation steps to produce nearly monodispersed particles in the diameter (D) range of D ≤ 150 nm to 1000 nm. A detailed analysis of luminescent behavior as a function of particle size was studied on particles before milling, after milling and as a function of particle size. Furthermore, SrAl2O4:Eu2+,Dy3+ is widely known to decompose when exposed to an aqueous environment thus, making it necessary to encapsulate the particles in silica when being used in any bioanalytical testing format. Therefore, analysis of optical properties was also conducted on the varying particle sizes after being encapsulated in silica and compared to optically neutral 500 nm nanospheres exposed to the same optical characterization condition. This investigation gives valuable insight into the effects of post processing to achieve the necessary submicron particles required by bioanalytical applications, while also establishing a more robust understanding of how size impacts the unique characteristics of persistent luminescent phosphors.
Fabrication of Green Light-Emitting Diode Using N-in2O3 nanorods Formed on Surface Modified P-GaN Template
Authors: Shin Dong Su , Kim Taek Gon , Heo Dongwook , Yoon Hahnjoo , Park Jinsub
Published: February 2020

The metal-oxide (MO) nano-materials with wide energy band gap are promising candidates for versatile research fields such as transparent electrode, light emitters, full-color display, sensors, etc, due to their unique semiconducting properties. Especially, various nanostructures of MO have great advantages to realize the high efficiency optoelectronic devices by modification of surface and light guiding effects. Recently, more assertive efforts to use MO nanomaterials as for various nano-hybrid LEDs combined with MO nanostructures have been performed using p-GaN templates. In this study, we demonstrate the green light-emitting diodes (LEDs) using n-In2O3 nanorods(NRs)/p-GaN pn junction with an insertion of Ga2O3 interfacial layer formed on p-GaN surface by O2 plasma treatment. The X-ray photoelectron spectroscopy patterns clearly show the formation of thin Ga2O3 on p-GaN surface by O2 plasma treatment. The In(OH)3 NRs are uniformly grown on surface treated p-GaN by using hydrothermal method, which were finally converted to In2O3 NRs by calcination process. The electroluminescence of fabricated LEDs using n-In2O3/ Ga2O3/p-GaN heterojunction shows the green emission (λ ~ 554 nm) at forward bias condition. As a possible light emission mechanism from our suggested structures, the various defects energy states mediated green emissions were considered.
The Effect of Electron and Hole Transfer Layers on the Electro-Optical Properties of Solution-Processed QD-LED
Authors: Choi Woon-Seop
Published: February 2020

Colloidal quantum-dots-based light emitting diodes (QD-LEDs) have been considered attractive display devices because of the remarkable electrical/optical characteristics of colloidal quantum dots. QD-LEDs have attracted particular interest not only because of their wide-range color tunability, high brightness and good color purity by the narrow emission bandwidth, but also because of their printability with a large size under atmospheric pressure.Nevertheless, achieving optimal control of charge transport/light emission and forming the necessary multilayer device structures is still a major challenge. The hole transport layer (HTL) and electron transport layer (ETL) thickness should be optimized to confine the electron and holes to the recombination zone in an emitting material layer (EML), i.e., the QD layer. For all-solution-processed QD-LEDs, inorganic and organic layers as the ETL and HTL were employed and optimized to achieve improved electroluminescence performances. Red QDs in the core/shell/shell type multi-structure, ZnO nanoparticles, and TiO2 were synthesized using the procedures reported elsewhere. The QD-LEDs were fabricated on patterned ITO glass. As a hole transfer layer, a PEDOT:PSS solution was spin coated. The organic hole transport layer, PVK, was coated on the PEDOT:PSS layer at a different rates to obtain a range of thicknesses. The CdSe/CdS/ZnS QDs (20 mg/mL) were spin coated. On the QD layers, various concentrations of ZnO NPs or TiO2 layers were spin-coated. Finally, 100 nm aluminum, as a cathode layer, was deposited on the ZnO NPs layer by vacuum evaporation

As electron charge transport layers and hole charge transport layer, zinc oxide nanoparticles and polyvinyl carvazole (PVK) were applied to all solution-processed quantum dot light emitting diodes. The quantum dot as the emitting layer, and the zinc oxide nanoparticles and titanium oxide, as the carrier transporting layers were synthesized using a solution mediated process. The optimized device using 45 nm zinc oxide nanoparticles as the electron transport layer and 18 nm PVK as the hole transport layer showed a lower turn-on voltage and better luminescence, resulting in a luminance of 13,730 cd/m2, current efficiency of 3.27 cd/A, and EQE of 2.67%.
Synthesis, Structure and Luminescence of Dy Doped Na0.25K0.25Bi0.5TiO3
Authors: Medic Mina , Đačanin Far Ljubica , Papan Jelena , Đorđević Vesna , Dramicanin Miroslav
Published: February 2020

Bismuth sodium titanate (NBT) is one of the most promising lead-free piezoelectric material suitable to replace widely used lead-based piezoelectric materials. With general formula A+
0.5Bi3+
0.5Ti4+O3, where A = Na+ or K+, perovskite structure can crystallise in rhombohedral, cubic or tetragonal phase, depending on temperature and type (content) of monovalent cation. Doping this material with optically active ions, such as Dy3+, provides a new phosphor material with potentially interesting combination of piezoelectric and luminescence properties.

In this work we demonstrate the preparation of Na0.25K0.25Bi0.48Dy0.02TiO3 powder material. The material was synthesized via solid-state reaction by using TiO2, Bi2O3, Na2CO3, K2CO3 and Dy2O3 as precursor materials. These powders were ball milled in ethanol for 12 h, then dried and calcined at 850°C for 2 h. Subsequently, obtained powder was additionally milled in ethanol for additional 12 h, and finally sintered at 850°C for 4 h. Structural analysis was done by X-ray diffraction and showed tetragonal P4bm structure without impurities. Optical characterization including photoluminescence excitation and emission spectra and diffuse reflection measurements were performed. Emission spectra showed characteristic bands of Dy3+ ions with pronounced emissions originating from f–f electronic transitions. A dominant band in the blue region with maximum at around 477 nm originates from magnetic-dipole 4F9/2→6H15/2 transition, and another in the yellow region with maximum at around 574 nm originates from electric-dipole 4F9/2→6H13/2 transition. A small intensity higher energy band cantered at around 457 nm originates from 4I15/2→ 6H15/2 transition provides the possibility to use this type of emitting material as temperature sensor using the LIR method.
Lanthanide-Doped Luminescent Materials for Use As Temperature Sensors Under Extreme Conditions
Authors: Eilers Hergen , Anderson Benjamin Richard , Gunawidjaja Ray
Published: February 2020

We are continuing the development of ex-situ and in-situ temperature sensors for use under extreme conditions such as in explosions and under shock conditions. The sensors consist of trivalent lanthanide-doped luminescent materials. For the ex-situ measurements we have developed temperature and thermal impulse (temperature and time) sensors based on inorganic materials. We are using the fluorescence from the lanthanides to monitor temperature-induced irreversible phase transitions in these materials. Comparisons with thermocouple data and simulations show good agreement for explosion tests. For the in-situ temperature sensors we use two-color fluorescence thermometry of lanthanide doped inorganics as well as lanthanide-based organic complexes. Using these materials we are able to image sub-second laser-induced heating events.
Temperature Sensing Using Upconversion in Rare Earth Doped Thermographic Phosphors
Authors: Jakka Suresh Kumar , Krishnapuram Pavani , Soares Manuel Jorge , Graça Manuel Pedro Fernandes
Published: February 2020

Thermometry based on the use of thermographic phosphors utilises the physical properties of the phosphor particles for assessing temperature. The phosphor particles used in thermometry are usually inorganic materials having a powder form. Fluorescence intensity ratio (FIR) technique is widely used for the temperature sensors based on phosphors doped with RE3+, providing high detection spatial resolution, precision and excellent sensitivity. Such a phosphor consists of a host material and a doping agent from which the light is emitted. Low temperature sensing using and NIR to visible upconversion (UC) emission could be very useful for biological applications. One of the important conditions an upconversion material should satisfy in order to be used as temperature sensor is that the radiative transitions from a fluorescent level should dominate its non-radiative transitions. This could be achieved only when the host has considerably low maximum phonon energy. This condition is also relevant to achieve UC, since a material which has low maximum phonon energy can be effectively used for RE3+ UC. These thermographic phosphors cover a wide range of temperatures, from cryogenic temperatures up to 1700 ºC or higher, making them suitable for many different applications. Each phosphor that is selected is highly sensitive within a specific range of temperatures, exhibiting accuracies in the order of 1-5 ºC. After excitation of the thermographic phosphor, the subsequent emission is imaged onto a detector. The temperature can then be deduced from the spectral or temporal properties of the recorded signal. This technique provides a two dimensional measurements and remote thermometry, as well as a high degree of accuracy. These advantages have allowed thermographic phosphors to be used in a wide variety of applications and in harsh environments. Many of the trivalent lanthanides such as Er3+, Tm3+, Ho3+, Nd3+, Dy3+ and Eu3+ have been used as PL centers of optical thermometry. But the Er3+ ion has proved itself to be an efficient UC centre among RE3+ ions and tremendous increase in its efficiency when combined with Yb3+ ions, acting as sensitizer, makes it the ultimate choice among UC ions. Apart of Er3+, Yb3+ combination, Tm3+ ions can also find their way for a better sensitivity depending on the host characteristics. In view of the above advantages of thermographic phosphors, structural, physical, morphological and temperature sensing characteristics of visible upconversion emission of different hosts namely SrLaAlO3, BiNbO4, LaNbO4 and YNbO4 doped with rare earth ions at low temperatures and excited by NIR excitation using FIR technique would be presented in detail.
Impact of Processing on Photoluminescence Properties of 4H-SiC for Potential Qubit Applications
Authors: Pavunny Shojan Pullockaran , Banks Hunter , Klein Paul , Daniels Kevin , DeJarld Matthew T , Glaser Evan , Carter Sam G , Myers-Ward Rachael L. , Gaskill Kurt
Published: February 2020

Single silicon vacancies VSi 
in silicon carbide nanostructures hold great promise for future technological applications in scalable quantum computing and information processing for simulation, sensing, and communication. These defects are typically created by ion implantation or neutron/electron irradiation. Identification of these defects, knowledge of their characteristics, control of their concentrations, isolation of single spin defects and understanding the effects of semiconductor processing on their properties are crucial to the applications of SiC in quantum electronic and integrated photonic devices. These vacancies embedded in photonic crystal cavities (PCC) have the capability of high efficiency emission of single photons which can significantly improve the performance of on-chip photonic networks and long-distance quantum communication systems, as compared to conventional solid-state emitters. Here we investigate the impact of processing on the photoluminescence properties of PCCs fabricated using three approaches: hydrogen implantation to form thin SiC layers on an oxide layer that can be easily etched away to form an air gap under the PCC, wafer bonding and mechanical thinning of the SiC, also on an oxide layer, and selective photo-electrochemical etching of an n-p epitaxial SiC structure to form an air gap. We also assess the impact of electron irradiation for these three fabrication approaches.
Biosensor Experiments in Undergraduate Laboratories
Authors: Suroviec Alice H
Published: February 2020

This talk will describe a junior/senior level undergraduate laboratory for analytical or physical chemistry that can be used to demonstrate the use of self-assembled monolayers (SAM) to produce biosensors. The laboratory has the students form SAMs on the surface of the electrode and then examine how they pack onto a surface. The laboratory experiment will also introduce students to electrochemical techniques, instrumentation and surface analysis techniques. This experiment uses both chronocoulometry to determine the surface area of an electrode as well as using reductive desorption to determine the surface coverage and packing of the SAM. Use of these SAM modified electrodes as biosenors is also discussed.
Heat-Treated Transition Metal Hexacyanometallates with Trace Amount of Pt As Electrocatalysts for the Oxygen Reduction Reaction Based on Nitrogen Doped Graphene: Catalysts Development and Electrode Structure Design
Authors: Miecznikowski Krzysztof , Dembinska Beata , Zoladek Sylwia , Rutkowska Iwona Agnieszka , Negro Enrico , Kulesza Pawel J , Di Noto Vito
Published: February 2020

In the recent research years is observed huge interest in design of new functional nanomaterials for developing new electrocatalysts for oxygen reduction reaction (ORR) in acid and alkaline media. The research has been focused on developing carbon nanostructures especially graphene/graphene oxide materials with the different transition metals (e.g. Co, Ni, Ag, Au, Cu, Mn) analogue of polynuclear Prussian Blue, namely with ultra-thin Co, and Ni hexacyanoferrate layers and trace amount of platinum for fuel cell applications. Electrocatalysts based on graphene and graphene-oxide (GO) are more homogeneous and possess properties such as excellent conductivity, good chemical stability and can be functionalized in a controlled manner. Following the heat-treatment step at higher temperatures, some thermal decomposition of the cyanometallate network occurs and, consequently, metallic sites are generated. Their formation and distribution are facilitated by the voltammetric potential cycling in acid and alkaline electrolytes. The most promising electrocatalytic results with respect to the reduction of oxygen (the highest currents and the most positive electroreduction potentials) have been obtained when graphene nanostructures are combined with analogue of polynuclear Prussian Blue and trace amount of Pt nanoparticles. What is even more important that, due to the presence of the polynuclear cyanoferrate modifier or linker, the amounts of the undesirable hydrogen peroxide intermediate are significantly decreased. An electrocatalytic system, that utilizes metal hexacyanometallates nanoparticles with trace amount of Pt modified graphene and graphene related materials, is developed and characterized here using transmission electron microscopy and such electrochemical diagnostic techniques as cyclic volammetry and rotating ring-disk voltammetry in a 0.5 M H2SO4 electrolyte and in a 0.1 M KOH electrolyte and upon introduction (as cathode) to the low-temperature hydrogen-oxygen fuel cell. Comparative measurements have been performed against the model noble metal (Vulcan-supported platinum nanoparticles) catalyst.
New Insights into Organic Dye Regeneration Mechanism in Dye-Sensitized Solar Cells: A Theoretical Study
Authors: Hailu Yohannes Mulugeta , Shie Wan-Ru , Nachimuthu Santhanamoorthi , Jiang Jyh-Chiang
Published: February 2020

Abstract

Understanding the regeneration mechanism of an oxidized dye with redox couples is significant in improving the efficiency of dye-sensitized solar cells (DSSCs). However, all the previously considered regeneration mechanisms are failed to match the incident photon-to-current efficiency (IPCE) and the UV-vis absorption spectra. Herein, we propose a new regeneration mechanism for organic dyes by assuming the probability of two electron injection from the stable dye-iodide intermediate complex. Thus, the stability and optoelectronic properties of the dye-iodide intermediate complexes of our elementary steps for the regeneration mechanism have been systematically investigated using density functional theory (DFT) and time-dependent (TD)-DFT calculations. Our results highlight the possibility of two electron injection into the semiconductor surface during dye regeneration mechanism, rather than the conventional one electron injection. In addition, the calculated UV-vis absorption spectra for the considered intermediate complexes clearly indicate blue/redshift (see Fig. 1) compared to that of isolated dye, which reflects the IPCE spectra.

Keywords: Dye regeneration mechanism; Organic dye; Electron injection; Dye-sensitized solar cells; Density Functional Theory; UV-vis spectra

Figure 1
Comparative Electrochemical, Photoelectrochemcal and Photocatalytic Abatement of Emerging Pollutant
Authors: Hussain Sajjad
Published: February 2020

Drug residues are unregulated emerging pollutants and are frequently found in the aquatic environment. Due to their extensive use, presence in the aquatic environment and their potential for impacts on wildlife and humans, it is becoming an important environmental issue. The present study evaluates the photo-assisted electrochemical treatment of sulfamethoxazole (SMX), an antibiotic used in the prevention and treatment of human and animal diseases. The experiments were carried out in a photo illuminated flow cell reactor and the effects of current density (10-60 mA cm-1) and concentration of sodium chloride in the supporting electrolyte were determined. The Drug could be removed completely at all current densities while TOC abatement was appreciable during the process. The process followed pseudo-first order kinetics and values of electrical energy-per-order were dependent on current density and sodium chloride concentration. Different reaction intermediates were separated and identified by liquid chromatography coupled with mass spectrometry (LC-MS), thereby providing an insight into the mechanistic details of the degradation pathway. The photo-assisted electrochemical degradation proceeded through competitive reactions such as chlorination, hydroxylation and substitution on the aromatic ring, while further ring opening gave rise to more simple organic compounds and, ultimately, the mineralization of SMX. The possible degradation route were also proposed and discussed. . The efficiency of photoelectrochemical process was compared with photo-catalytic and electrochemical separately, and showed a synergism for TOC removal.
Investigation on Sulfide-Enhanced Oxygen Reduction Reaction Activity By in-Situ Electrochemical Infrared Spectroscopy
Authors: Chen Dejun , Wang Yanyan , Allison Thomas C , Tong YuYe
Published: February 2020

Oxygen reduction reaction (ORR) has been intensively investigated due to its relevance to fuel cell applications. It was discovered recently that sulfide (S2-), a potent poison of Pt, could be a promotor for both ORR activity and stability of Pt. However, the underlying chemistry of working mechanism is still unclear. Understanding the mechanistic effect of non-metallic promotor(s) should help broaden the prospect of developing better ORR catalysts. In this presentation we will discuss the insights we have gained in this respect by in-situ electrochemical infrared spectroscopy and theoretical simulations. Figure 1a and b show the δ(HOO) infrared vibration bands of ORR intermediates HOOad and HOOHad and v(O-O) vibration of O2−
ad under the kinetic potential control regime (at ~0.9 V vs. RHE) on PtSad with different sulfur coverage. The IR bands of intermediates HOOad and HOOHad are larger at lower Sad coverages at which the enhanced ORR activity was observed. The observation of the O2−
ad band at higher Sad coverage is consistent with the increase in H2O2 production during ORR. Interestingly, even a small fraction of Sad, say a coverage of 0.1, can play a significant role in modifying the ORR reaction pathway by preventing the cleavage of O-O bonding of O2 molecule. The theoretical simulations in Figure 1c~d confirmed that the turnover frequency (TOF) of H2O produced at 0.9 V by ORR on PtSlow is much bigger than that on PtShigh. As a conclusion, our finding suggests that the catalyst design by shifting the pathway of ORR from cleavage of O-O bonding on pure Pt to HOOad or HOOHad pathway would accelerate water production on the fuel cell cathode.
Probing Self-Organization of Molecular Ions at the Interface between Graphene and Ionic Liquids
Authors: Wu Judy
Published: February 2020

Electrochemical effect manifests itself as an unfavorable nonlinear response to an applied electric field in electrochemical devices and links intimately to the configuration of the molecular ions in the electric double layer (EDL) formed at the electrolyte/electrode interface. In this work, we probe the origin of the electrochemical effect using a double-gate graphene field effect transistor (GFET) of ionic liquid DEME-TFSI (or BMP-TFSI) top-gate, paired with ferroelectric Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) back-gate of compatible gating efficiency. By measuing the GFET Dirac point shift in response to the bi-polar charge doping of the EDL molecular ions, the configurations of the interface molecular ions can be extracted and their dynamic response to visible light and gate electric field, quantified. We have observed that a strong electrochemical effect sets in as a consequence of the TFSI molecular anions self-organizing on a treated GFET surface, resulting in the Dirac point shift to a large positive voltage. Moreover, a reversible order-disorder transition of this molecular ion monolayer can be triggered using light illumination, revealing the critical role of the surface ion configuration on the overall performance of electrochemical devices.
A Simple Flow Cell for the Measurement of Groundwater Arsenic(3+/5+) in the Field
Authors: Mays Douglas , Hussam Abul
Published: February 2020

The focus of this methodology is to use high performance automated square-wave anodic stripping voltammetry (HPSWASV - A technique where the background is subtracted dynamically in a square wave format while anodic stripping voltammetry is being recorded with two current sampling on the pulse. We have built the potentiostat and wrote the code to perform this technique specifically suitable for arsenic measurement on a gold microwire electrode.) as the technique in a system that is field deployable with a 2-electrode cell (a working and a reference electrode). The counter electrode, often made of platinum and can be one of the most expensive components is not needed in this system given the small current generated during the electroanalytical process. This methodology is perfectly suitable with microelectrodes with low current demand. It is inexpensive, simple and easy to fabricate anywhere or produced commercially. The cells can last for hundreds of measurements with novel in-situ pulsed cleaning. The estimated total cost with dedicated potentiostat, cell, and laptop computer is approximately 1000 USD. This a one-time cost.

The specifics of the electrochemistry are as follows: using anodic stripping voltammetry with reagent grade hydrochloric Acid (HCl) and 100 s deposition time. This deposition time shows the best results without any data exclusion. The preconditioning procedure employed was cyclic voltammetric (CV) from 0.0 to 1.5 V at a scan rate of 100 mV/sec in 0.5 M H2SO4. Oxidation and reduction peak potentials were examined closely. In the analysis of 200+ CV runs, the average oxidation and reduction peak potentials were 1.284 ± 0.01 V and 0.849 ± 0.005 V respectively. These values are within 10 – 15% of those potentials cited in the literature. The calculated surface areas were 0.0607 ± 0.0054 cm2 and 0.0095 ± 0.0030 cm2 for oxidation and reduction respectively. The average oxidation surface area was larger than the reduction and might be explained by differing oxidation states of clusters of Au atoms on the surface not being reduced or not in close enough proximity to the surface for reduction. A solid gold wire electrode, which requires no separate gold deposition, is much more acceptable when in the field.

Results from my prototype systems measure between 10 -100 ppb As(III) with good repeatability. As(V) is measured by first scanning for As(V) which comes off at a higher potential than As(III) and then determining the concentration using the method of standard addition. The As(V) in the sample solution is then reduced to As(III) and the sample solution is scanned again for As(III) and a standard addition conducted. The difference between the two (2) unknown sample concentrations is the quantitation of As(V).

Figure 1
Special Active Pt(100) Site for Room Temperature Electrochemical Activation of Methane
Authors: Ma Hai-bin , Sheng Tian , Zhou Zhi-You , Sun Shi-Gang
Published: February 2020

Methane is the main component of natural gas and a byproduct of oil refining and chemical processing. Due to its inertness, high temperature and high pressure are required for the most popular way of converting methane. Electrochemical conversion of methane has been put a lot of interests due to its facile control of selectivity by monitor electrode potential and its relatively mild working conditions. Although many studies have been conducted to improve methane conversion rate and selectivity based on solid oxide fuel cells, the basic methane electrooxidation mechanism remians poorly understood. Single crystal electrode with defined atomic arrangement proves to be a good model for the study of surface reaction mechanism.

In this study, the interaction between methane and well-defined Pt single crystal surfaces at room temperature was studied by electrochemical method and in situ FTIR spectroscopy. The results demonstrated that, amongst the three basal planes of Pt single crystal (Pt(111), Pt(110), Pt(100)), only Pt(100) can activate methane, in which the dissociation of methane could be detected at potentials above 0.0 V (vs.SCE) (Fig.1). At potential range between 0.0 V and 0.15 V, methane may be mainly dehydrogenated to produce spices like CO/COH, resulting in the decrease of Hudp on Pt(100). At potentials above 0.15 V, such spices can be further oxidized to form CO2. In situ FTIR spectroscopy studies indicated that methane can be oxidized to CO on Pt(100) surface and the CO mainly bound to hollow sites, moreover no oxidation product was detected on Pt(111) and Pt(110). DFT calculations show that on Pt(111) and Pt(100), the most stable surface species both are CH*, while on Pt(100) the most stable one is CH2*. On Pt(100), CH* prefers to be oxidized by O* with the lowest barrier being 0.4 eV. However, on Pt(110) and Pt(111), CHx* oxidation is much more difficult since the coupling between the carbon species and OH* is as high as 1.03 eV and 0.85 eV, respectively.

This study revealed the surface structure-reactivity in methane activation on platinum catalyst, and will give more insight into the design and synthesis of electrocatalyst for methane conversion.

Figure 1
Effect of Anion Choice on Conducting Polymer Crystallinity
Authors: Rubinson Judith F
Published: February 2020

It is widely accepted that the identity of the anion dopant in electrodeposited conducting polymer films impacts the electrical properties of the resulting polymer. We focus here on the effect of size, charge, and pi-pi interactions on films based on 3-methylthiophene and 3,4-ethylenedioxythiophene. Results of characterization of the films based on cyclic voltammetry, electrochemical impedance spectroscopy, Raman spectroscopy, scanning electron microscopy, and grazing angle x-ray powder diffraction will be used to provide insight into trends in conjugation length of the polymer and its crystallinity as well as charge transport through the film.
Polymer-Coated Boron Doped Diamond Optically Transparent Electrodes for Spectroelectrochemistry
Authors: Rechenberg Robert , Rusinek Cory Allen , Becker Michael , Heineman William R.
Published: February 2020

Spectroelectrochemistry is a well-known technique used to achieve multimode selectivity in one sensor. The sensor usually consists of an optically transparent electrode (OTE) coated with a charge selective polymer film. These polymer films are employed to pre-concentrate analyte at the OTE surface so that it can be sufficiently detected optically through electrochemical modulation. OTEs such as Indium Tin Oxide (ITO) have been used extensively in this method but little is known about the applicability of such sensors using other OTE materials, such as Boron Doped Diamond (BDD). One distinct advantage of BDD OTEs over ITO OTEs is their significant increase in sensitivity for organic compounds, such as para-aminophenol and hydroquinone. With this, we have developed absorption and fluorescence-based sensing methods with a BDD OTE coated with a sulfonated ionomer film, Nafion. This is demonstrated with tris(2,2’-bipyridyl)ruthenium(II) ion [Ru(bpy)32+] using an attenuated total reflectance (ATR) flow cell setup for both absorbance and fluorescence. With a Nafion coated BDD optically transparent thin layer electrode (OTTLE), we developed a fluorescence based sensor for a common polyaromatic hydrocarbon (PAH), 1-hydroxypyrene (1-pyOH), achieving a detection limit of 80 nM (17 ppb). Using these techniques, we were able to manifest new sensing applications while broadening the use of spectroelectrochemistry, OTEs, and BDD as an electrode material.

Figure 1
Hydrogen and Nitrogen Modification of Anodized TiO2 Nanotube Arrays for Photoelectrochemical Oxidation of Water
Authors: Xu Yin , Zangari Giovanni
Published: February 2020

TiO2 nanotube arrays (NTs) made by electrochemical anodization exhibit significant potential as a photoanode in low cost, sustainable photoelectrochemical cells for solar water oxidation.1 The wide bandgap (3.2eV, λ < 387 nm) of these materials, however, limits the photocurrent, and the low mean free path of charge carriers further limits performance. Formation of substoichiometric phases or generation of suitable defects have been proven to enhance photoresponse.2 Thermal treatment of TiO2 under reducing atmosphere, for example, generates high-conductivity, oxygen deficient TiO2-xmaterials, including the Magneli phases. Similarly, nitrogen doping may decreases the band gap, enabling increased light absorption.

In this work, anodized TiO2 nanotubes were modified via hydrogen or ammonia gas treatments to generate various substoichiometric phases, characterized by reduced bandgap and higher conductivity. In particular, annealing in partial hydrogen pressure (5 at%) leads to a gradual phase transformation of anatase to rutile and various Magneli phases, yielding an enhanced photoelectrochemical response up to 2.2-fold at 1.23VRHE. Annealing in ammonia and argon flow on the other hand results in oxygen loss with barely detectable N incorporation, resulting in a 4-5 fold photocurrent enhancement at 1.23VRHE with a significant cathodic shift (~100 mV) of the onset potential. The fraction of the photogenerated charges utilized for water splitting was estimated by comparing photoelectrochemical performance with or without hole scavenger species.3 All modified samples displayed higher water oxidation efficiency (above 80%) compared with unmodified TiO2(~65%). In order to evaluate the surface disorder introduced by the modification, electrochemical impedance spectroscopy (EIS) was carried out, showing higher charge carrier density. Overall, this work demonstrates that hydrogen or ammonia annealing treatments enhance significantly photoelectrochemical performance.

References:

1. L. Tsui and G. Zangari, J. Electrochem. Soc. , 161, D3066–D3077 (2014)

2. X. Chen, L. Liu, and F. Huang, Chem. Soc. Rev., 44, 1861–1885 (2015)

3. L. Tsui, Y. Xu, D. Dawidowski, D. Cafiso, and G. Zangari, J. Mater. Chem. A, 4, 19070–19077 (2016).

Figure 1. Photochemical response of hydrogen reduced TiO2 (a) and nitrogen modified TiO2 (b). 

Figure 1
Solar Photoelectrochemical Water Purification
Authors: Cruse Ryan , Sullivan Michael John , Smotkin Eugene S.
Published: February 2020

Bipolar electrodes based on titanium dioxide are configured for water purification. The TiO­2 photo-anode oxidizes organic pollutants. Concomitant with photooxidation, oxygen is reduced at the dark cathode to yield hydrogen peroxide which serves as a bio-disinfectant. The device uses a very low cost semiconductor material (titanium dioxide with no sensitizer) and requires only low technology fabrication methods. The photoanode is prepared by arc-anodization of titanium foil. The dark cathode is prepared from hydrophilic carbon gas diffusion material typically used in fuel cells. The cell design and bio-disinfectant efficiency will be discussed.
Effects of Nanoscale Interfacial Design on Photocatalytic Hydrogen Generation Activity at Plasmonic Au–TiO2 and Au–TiO2/Pt Aerogels
Authors: Pietron Jeremy , DeSario Paul A. , Brintlinger Todd , Baturina Olga A , Stroud Rhonda , Rolison Debra R.
Published: February 2020

We demonstrate that composite catalytic aerogels represent a superior materials design motif for the creation of solar fuels photocatalysts. We couple surface plasmon resonant (SPR) guests to the inherent compositional and interfacial design flexibility of catalytic aerogels to photogenerate molecular hydrogen (H2). We investigate the effects of synthetically modifying the TiO2 aerogel network and the nanoparticulate Au||TiO2 interfaces in plasmonic Au–TiO2 aerogels on H2 evolution under both broadband (i.e., UV + visible light) and visible excitation. We also introduce non-plasmonic Pt co-catalyst nanoparticles into our composite aerogels, creating Au–TiO2/Pt aerogels that perform visible light SPR-driven photocatalytic reduction of water to generate H2.

 The fuels production achieved with this multicomponent photocatalytic nanoreactor demonstrates that the nanostructured high-surface-area network in the aerogel can spatially and effectively separate charge while electrochemically connecting plasmonic nanoparticle sensitizers and metal nanoparticle. In doing so, we prove several crucial concepts: (1) integration of a plasmonic sensitizer with a separate water reduction co-catalyst within the ultraporous aerogel nanoarchitecture; (2) wiring the electron–hole pairs generated under visible light at the plasmonic Au||TiO2 interface to the co-catalyst via the nanoscale TiO2 network; and (3) combining both the photocatalytic oxidation and reduction reactions critical to solar fuels photocatalysis into one composite material at length scales compatible with the reaction kinetics.

This work is supported by the Office of Naval Research.
(Invited) Photoelectrochemical Hydrogen Evolution Based on Plasmon-Induced Charge Separation
Authors: Tatsuma Tetsu , Kao Kun-Che , Wu Ling , Kuroiwa Yoshinori , Nishi Hiroyasu
Published: February 2020

Plasmon-induced charge separation (PICS) occurs at the interface between plasmonic nanostructures of gold, silver, or copper and a semiconductor such as titanium oxide.1-3 PICS involves energetically uphill transfer of electrons (or holes) from the plasmonic nanostructure to the semiconductor, so that the active carriers are retained in the semiconductor for a certain period of time and used for electrochemical reduction (or oxidation). We reported PICS for the first time more than 10 years ago1-3 and studied its mechanisms1-6 and applications2,3 including photocatalysis. We have reported oxidation of alcohols and aldehydes by PICS,1 and recently worked on photocatalytic reduction of water to hydrogen based on PICS at gold nanoparticle/titanium oxide systems.

We coated an indium-tin oxide transparent electrode with a titanium oxide thin film. We deposited a hexagonal array of small plasmonic gold nanoparticles on the titanium oxide film, followed by deposition of cocatalysts such as platinum nanoparticles. This working electrode was connected with a counter electrode such as a platinum wire and those electrodes were immersed in an electrolyte solution containing an electron donor such as methanol. The working electrode was irradiated with visible light, and hydrogen was evolved at the counter electrode even without bias voltage application, although the hydrogen evolution rate was enhanced when a bias voltage was applied. We will report optimization of the cocatalyst systems.

1. Y. Tian and T. Tatsuma, J. Am. Chem. Soc., 127, 7632 (2005).

2 . T. Tatsuma, Bull. Chem. Soc. Jpn., 86, 1 (2013) [account].

3. T. Tatsuma, H. Nishi, and T. Ishida, Chem. Sci., in press (doi: 10.1039/C7SC00031F) [review].

4. E. Kazuma and T. Tatsuma, Adv. Mater. Interfaces, 1, 1400066 (2014).

5. H. Nishi and T. Tatsuma, Angew. Chem. Int. Ed., 55, 10771 (2016).

6. K. Saito, I. Tanabe, and T. Tatsuma, J. Phys. Chem. Lett., 7, 4363 (2016).
(Invited) Plasmonic Driving of Chemical Reactions
Authors: Wang Jianfang
Published: February 2020

Noble metal nanocrystals, possessing localized surface plasmon resonance, can interact strongly with light, efficiently converting light into heat and generating hot electrons and hot holes. Both plasmonic photothermal conversion and generation of hot charge carriers can accelerate chemical reactions. While the acceleration of chemical reactions by photothermal conversion is straightforward, the driving and acceleration of chemical reactions by plasmonic hot charge carriers represents a new research field. Plasmonic hot charge carriers can not only enhance the reaction yield and selectivity, but also introduce new reaction pathways. A full understanding of the latter process requires the knowledge of localized plasmon, electron/hole dynamics, charge transfer, and electron/hole-induced reactions. The study of plasmonic driving of chemical reactions will be rewarding in both fundamental and technological aspects.

The lifetime of plasmonic hot charge carriers is on the femtosecond scale. Without utilization, they will rapidly relax, converting their energy into heat. Two approaches have mainly been developed to facilitate the utilization of plasmonic hot charge carriers. The first is the integration of Au or Ag nanocrystals with Pd or Pt nanoparticles. Au and Ag nanocrystals possess strong localized plasmon resonance, while Pd and Pt nanoparticles are excellent catalysts for a variety of chemical reactions. A combination of the two types of metal nanocrystals can lead to efficient light absorption and generation of plasmonic hot charge carriers, which can subsequently inject into molecules that are adsorbed on the Pd or Pt component. The second is the integration of plasmonic metals with semiconductors. A barrier is formed at the interface. The generated hot electrons and holes can quickly inject into the conduction or valence band and therefore get separated. The injected charge carriers can then drive chemical reactions. We have synthesized bimetallic nanocrystals as well as metal/semiconductor hybrid nanostructures to demonstrate plasmonic driving of chemical reactions by both approaches.