bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Phosphor-in-Glass Luminescent Materials for Solid State Laser Lighting
Authors: Xie Rong-Jun , Zhu Qiang-Qiang , Takeda Takashi , Hirosaki Naoto
Published: February 2020

Laser-based solid state lighting is superior to the LED-based counterpart in terms of much high input power and lumens, which requires phosphors to be more thermally stable and less luminescence saturation under high-density laser irradiations. To minimize thermal quenching and luminescence saturation of phosphors, a revolutionary method is to apply phosphor-in-glass or ceramic phosphors rather than phosphor-in-silicone (polymer binder) in remote-phosphor technologies because bulk luminescent materials have higher thermal conductivity and less degradation than phosphor/silicone mixtures.

In this work, we will report the preparation and optical properties of nitride phosphor-in-glass luminescent materials. The nitride phosphor (β-sialon:Eu2+) was co-fired with the glass frit in the system of ZnO-B2O3-Ba2O3-Al2O3 at 630-650oC. No interfacial reaction occurred during the co-firing. The quantum efficiency and transmittance of the phosphor-in-glass luminescent materials were greatly affected by the phosphor concentration, firing temperature and holding time. Upon the blue laser irradiation, a linear relationship between the luminous flux and the incident laser power was observed when the flux density was below 0.7 W/mm2. A serious luminescence saturation was seen when a high flux density was applied. The saturation was perhaps due to the extremely low concentration and relatively longer decay time of Eu2+. This phosphor-in-glass luminescent materials could be used for low-power solid state laser lighting.
(Keynote) Advanced Platform Technologies for the Near Future Electrochemical Biosensing
Authors: Sode Koji
Published: February 2020

Glucose sensing is the most popular analytical method in the use of the electrochemical biosensing technology. Simultaneously, it is one of the most popular, commercial available, and commoditized biotechnology relating products, where the most advanced but economical materials and technologies are utilized. Current market products in the glucose sensors for the self-monitoring of blood glucose (SMBG) or in the continuous glucose sensing (CGM) systems, the electrochemical principle, either the “1st generation”, which utilizes oxygen as the electron acceptor, or the “2nd generation” principles, which utilizes artificial electron acceptors, has been employed. All other sensing targets by the biochemical analyses in the metabolic disorder syndromes, such as cholesterol, neutral lipid, uric acid, glycated proteins, amino acids, lactates, etc., are also being electrochemically measurable based on these principles, and some are already commercially available.

However, recent emergent requirement in the development of accurate and precise sensing systems, which meet the strict regulation with competitiveness in the harsh market of blood glucose monitoring, accelerate the demands in the development of novel platform technologies in the electrochemical biosensing system, which are ready to use in the market grade product.

In this presentation, I introduce three indispensable platform technologies which accelerate the development of the near future electrochemical biosensing, especially in the amperometric enzyme sensors; 1) engineered flavin dependent oxidoreductases, 2) disposable interdigitated electrode, and 3) a novel artificial electron acceptor (mediator).
Molecular Dynamics Simulation of Substrate Transport on Alpha-Helix Peptide for Multistep Catalysis
Authors: Liu Yuanchao , Calabrese Barton Scott
Published: February 2020

Multistep electrocatalysis has the potential to fully utilize the energy stored in high molecular weight fuels, enabling biofuel cells with high energy density.[1] In multistep cascades, however, the mass transport of intermediates between catalyst sites becomes a potential limitation. Substrate channeling, in which intermediate transport is achieved without diffusion into the bulk, has attracted significant attention recently and is utilized in numerous biological contexts.

Electrostatic interactions between a charged intermediate and an oppositely charged pathway represents on such channeling mechanism.[2] Molecular Dynamic (MD) simulation enables the study of electrostatic interactions that may be inaccessible to experiment, and provides a framework for molecular design of such systems. Here, we describe MD simulations of charged intermediate transport in the presence of alpha-helix peptides that act as catalyst site linkers.[3] In this project, we generated a set of polypeptides comprised of charged residues chains (e.g. Arg, Lys) and simulate the interaction between these peptides and oppositely charged intermediate molecules in explicit water. Figure 1a shows an example on how an oxalate molecule can be adsorbed on a peptide, featuring corresponding coulomb energy between the two species. Strong energy fluctuations usually indicate surface-bound transport. By tuning the side chain type and interspatial distance, as shown in Figure 1b, energy fluctuation can be controlled. Based on the results from different peptides coupled with various intermediate molecules, we are able to define the range of conditions over which electrostatic interactions are beneficial. More importantly, surface diffusion diffusion is quantified, giving detailed understanding of the range of transport rates available. Acknowledgement We gratefully acknowledge support from Army Research Office MURI (#W911NF1410263) via The University of Utah. References [1] M. J. Moehlenbrock, M. T. Meredith, and S. D. Minteer, ACS Catal., 2, 17–25 (2012) doi:10.1021/cs200482v. [2] I. Wheeldon et al., Nat. Chem., 8, 299–309 (2016) doi:10.1038/nchem.2459. [3] J.-L. L. Lin and I. Wheeldon, ACS Catal., 3, 560–564 (2013) doi:10.1021/cs300766d. Figure 1. MD simulation of oxalate molecule (-2 charged) on alpha-helix peptide with +1 charged side chains (e.g., Arg and Lys). a) Oxalate molecule (red) on peptide with Arg side chains marked in blue (Arg-6*Ala-Arg-6*Ala-Arg-3*Ala), clearly showing various adsorption configuration and corresponding calculated coulomb energy. b) Oxalate molecule on peptide with more dense Lys side chains (3*Ala-Lys-3*Ala-Lys-3*Ala-Lys-3*Ala), featuring an adsorption region with frequent coulomb energy fluctuation and showing substrate transport along the helical axis of peptide.

Figure 1
Chemiresistive and Switching Characteristic with Reduced Graphene Oxide Biosensor Fabricated Using Antibody-Antigen Binding System
Authors: Kim Yo-Han , Jung Hunsang , Lee Hyun Ho
Published: February 2020

Bistable resistive switching within graphene-oxide (GO)-based memory devices have been recently developed by many research groups. Its switching mechanism was frequently explained by the formation and rupture of conducting filaments induced by the diffusion of metal or oxygen ions.1 Meanwhile, significant applications in biosensors have been continuously reported with the graphene or GO devices. Very recently, a stress hormone, cortisol, is being increasingly focused on in psychobiological stress research. For this end, salivary cortisol is a major correlator of the neuroendocrine stress response and has been increasingly studied as a stress biomarker.

In this study, we demonstrated reduced graphene oxide (rGO) biosensor structure for cortisol sensing with chemiresistive and its switching system.2 The device structure was stepwise self-assembly monolayers (SAMs) stacked by reduced graphene oxide between indium tin oxide (ITO) two electrodes. The GO`s surface was anchored with cortisol monoclonal antibody (C-mab) as probe molecules.

For the cortisol detections, the device, the current versus voltage (I-V) curve was examined by chemiresistive current and switching characteristics, which demonstrated the possibility of sensing mechanism. For the cortisol detection purpose, a microfluidic system was constructed on the GO chemiresistive sensor. Therefore, this research establishes the feasibility of chemiresistive real-time detection device for biosensor applications.

References

S.K. Kim, J.Y. Kim, S.Y. Choi, J.Y. Lee and H. Y. Jeong, Advanced Functional Materials, 25, 6710-6715 (2015)

Yusuke Tahare, Zhe Huang, Tesuro Kritoshi, Takeshi Onodera and Kiyoshi Toko, Bioengineering and Biotechnology, 2, 15, 1-6 (2014)

Figure 1
Expanded Scope of Methodology and Polymer Functionality for Photoredox-Mediated Ring-Opening Metathesis Polymerization
Authors: Pascual Laura M M , Goetz Adam E , Dunford Damian G , Ogawa Kelli A , Ashikari Yosuke , Boydston Andrew J
Published: February 2020

Photoredox-mediated ring-opening metathesis polymerization (Photo-ROMP) is an emerging polymerization method. In contrast to traditional ROMP, which uses a well-defined metal initiator (typically Ru, W, or Mo) that covalently bonds in stoichiometric amounts with each polymer chain end, Photo-ROMP utilizes a photo-oxidant to oxidize an organic polymerization initiator. This obviates the need for purification processes to remove the metal initiator for use of the resulting polymer in biomedical, electronics, and optics applications. We have recently studied the efficacy of a variety of photo-oxidants and expanded the monomer scope to include polar functionality. In an evaluation of pyrylium and thiopyrylium photo-oxidants, more electron-rich photo-oxidants (weaker photo-oxidants) achieved higher conversion to polynorbornene. Additionally, thiopyrylium photo-oxidants displayed higher rates of conversion than similarly functionalized pyryliums. While our previous studies identified 2,4,6-tris(4-methoxyphenyl)pyrylium tetrafluoroborate as an effective photo-oxidant for Photo-ROMP, in our recent evaluation of additional pyryliums and thiopyryliums, the correspondingly functionalized thiopyrylium emerged as a successful alternative for achieving rapid polymerization. In addition to evaluating various pyrylium and thiopyrylium photo-oxidants, we recently identified a variety of monomers and co-monomers with polar functionality for Photo-ROMP. Our previous studies identified norbornene, dicyclopentadiene, and dihydrodicyclopentadiene as effective monomers for Photo-ROMP. Recently, we've identified several new monomers. Remarkably, a TBS-ether-funtioncalized norbornene was co-polymerized with norbornene and homopolymerized in good yields. The resulting polymer was successfully deprotected to give the corresponding alcohol-functionalized polynorbornene. Additionally, a Boc-functionalized copolymer with norbornene was successfully synthesized and the Boc groups subsequently thermally removed. Interestingly, while 2-chloro-2,3-dihydro-endo-dicylopentadiene was precluded from copolymerization with norbornene due to slow initiation kinetics, it did successfully homopolymerize via Photo-ROMP to give the resulting homopolymer in moderate yields. These functionalized monomers could facilitate post-polymerization modification. In addition to these recent developments in expanding the methods and scope of Photo-ROMP, ongoing work in evaluating alternative photo-oxidants and monomers will also be discussed in this presentation.
Electrooxidative Coupling of Functional Primary Alkylamines and Aromatics Via Heterocyclization
Authors: Yoshida Jun-ichi , Morofuji Tatsuya , Shimizu Akihiro
Published: February 2020

The reactions of primary alkylamines bearing a functional group such as a hydroxyl group with nitriles or their equivalents gave the corresponding heterocycles. The electrochemical oxidation of aromatic substrates in the presence of the heterocycles afforded the coupled ionic species, which were successfully converted under non-oxidative conditions to the desired arylalkylamines bearing the functional group on the alkyl chain. The present method serves as a new approach for electrooxidative coupling of aromatic compounds and primary alkylamines bearing a functional group. The key to the success of the transformation is heterocyclization of functional primary alkylamines prior to the electrooxidative coupling.
(Invited) Electrolytic Macrocyclizations on Scale
Authors: Harran Patrick
Published: February 2020

Electrochemical oxidation at surfaces can elicit unique reactivity and facilitate transformations that would be difficult, if not impossible, otherwise. This lecture will describe an example wherein complex macrocycle formation was uniquely enabled by anodic oxidation. Adaptations of the method for use on manufacturing scales will be discussed, as will attempts to generalize the technique for constructing other highly functionalized, large ring structures.
Cyclic Voltammetry Studies of a Redox-Responsive 4 H-Bond Ureidopyrimidinone Alkyl-Pyridinium Capable of Self-Dimerization
Authors: Darzi Ghazwan M , Smith Diane K.
Published: February 2020

The design of stimuli-responsive systems in which supramolecular structure changes in response to external signals, such as the change in voltage of an electrode, is important for many applications, for example, self-healing polymers and gels, triggered release of entrapped molecules for drug delivery, and “smart” materials. In this study, a four H-bond ureidopyrimidinone (UPy) array with an alkyl-pyridinium, (RP), redox center has been synthesized, UPy(RP), shown below. This array prefers the tautomer that presents an ADAD H-bond motif in the starting oxidation state. Due to electrostatic repulsions and unfavorable secondary H-bond interactions, this motif would form a dimer with relatively weak H-bonding. Upon 2e- reduction, where 1e-is gained per R-pyridinium redox center, the H-bond strength should increase due to the loss of the repulsive charges, making the nitrogen a stronger hydrogen acceptor. Because the nitrogen is now a better hydrogen acceptor, there could be a possibility of an intermolecular proton transfer. This would encourage the tautomer to have an AADD motif that will make the H-bonding stronger by increasing the favorable secondary H-bond interactions.

UPy dimers can exist in two tautomeric forms called pyrimidinol and pyrimidinone. In order to more efficiently study the electrochemistry of the two forms, two compounds, 4-acetylpyridinium (AcP) and N-methyl-4,4’-bipyridinium (MeV+), were used as model compounds. AcP resembles the pyrimidinone tautomer and MeV+ resembles the pyrimidinol tautomer. The cyclic voltammetry (CV) scans for the two model compounds in CH2Cl2 and CH3CN show two widely spaced, reversible redox waves. UPy(RP) is insoluble in CH2Cl2, but soluble in CH3CN. The concentration dependent NMR spectra suggest that UPy(RP) is a monomer in acetonitrile. The CV’s of UPy(RP) in CH3CN show three reductions. The first occurs at a potential very similar to that seen with simple model compounds. The second is considerably positive of that observed for the model compounds and the third is very close to the second reduction peak of the model compounds. The first reduction is reversible if the scan direction is switched immediately after the peak, but irreversible if the scan direction is switched after the second reduction peak. As the scan rate increases, the second and the third reduction peaks disappear and a new peak emerges in between. Going through the second and third reductions also leads to the appearance of new oxidation waves at more positive potentials. DFT calculations suggest the preferred tautomer changes upon reduction, and this may explain the unexpected voltammetry observed in acetonitrile where the compound is not dimerized. Further studies to help elucidate what is actually happening in this system will include using a new counter anion in the electrolyte to help the solubility of the compound in CH2Cl2.

Figure 1
Electrocatalytic Generation of Amidyl Radicals for N-Heterocyle Synthesis
Authors: Xu Hai-Chao
Published: February 2020

Nitrogen-centered radicals are versatile intermediates for the construction of N-heterocycles. Unfortunately, their use in synthesis is limited due to the difficulty associated with their preparation. We have developed electrocatalytic methods for the generation of amidyl radicals from stable and easily available N-H amides1. Application of these reactive intermediates in synthesis leads to the efficient and chemoselective construction of several classes of N-heterocycles including cyclic carbamates and ureas, indoles, imidazopyridines, and benzothiazoles.

References:

1. Zhu, L.; Xiong, P.; Mao, Z. Y.; Wang, Y. H.; Yan, X.; Lu, X.; Xu, H.-C. Angew. Chem. Int. Ed. 2016, 55, 2226.

Figure 1
Electrochemiluminescence Microscopy Imaging Using Ru(bpy)3
2+ Doped in Silica Microspheres
Authors: Ma Cheng , Zhu Jun-Jie
Published: February 2020

Electrochemiluminescence (ECL) is a controllable form of chemiluminescence where emission intensity is affected by a voltage imposed at an electrode surface. ECL microscopy imaging is a imaging technique aimed at light-emitting close to electrode surface with highly temporal and spatial resolution. Because ECL emitters are generated in situ at electrode surfaces, ECL imaging reflects the local surface reactivity and has a near-zero background. These features make ECL very useful in imaging applications, such as multiplexed ECL sandwich immunoassays, parallel single-cell analysis and latent fingerprints ECL imaging. Here we synthesized Ru(2,2’-bipyridine)3Cl2-doped silica (RuDS) microspheres via Stober method for single microsphere ECL imaging. The RuDS microsphere consisted of a silica core and a Ru(2,2’-bipyridine)3Cl2-doped silica shell via sol−gel process to immobilize Ru(bpy)3Cl2 into silica shell. Rougher sufaces and some defects indicated imperfect growth of Ru(2,2’-bipyridine)3Cl2-doped silica shell. We also noticed that RuDS microspheres tended to aggregate in the growth of Ru(2,2’-bipyridine)3Cl2-doped silica shell, since electrostatic interaction between Ru(bpy)3Cl2 and silica matrices decreased negatice charges on the surfaces of silica microspheres. Then an electrode modified with RuDS microspheres was placed in a cell under the microscope. The bright field image showed the positions of the RuDS microspheres. The bright ECL image of RuDS microspheres suggested that intermediates generated by electrooxidation of tripropylamine (TPA) can move up to several micron to cause the excitation of Ru(bpy)3Cl2. Interestingly, the ECL intensity from different single microspheres exhibited obvious distinctions, which may derive from local heterogeneity of electrode surface and RuDS microspheres. Moreover, the image sequences showed the areas without any microspheres also produced a weak ECL background signal, as a result of the electrooxidation of TPA itself. Simultaneously, the oxidation current of TPA in cyclic voltammetry and the ECL emission intensity of RuDS microspheres dramatically decreased along with increase of scan times, indicating the passivating of the surface of electrode was occured when the potential was applied. These results demonstrated that ECL microscopy imaging of single RuDS microsphere appearing high temporal and spatial resolution, is a powerful tool in terms of further understanding of detailed ECL mechanisms, both emiters and coreactants, and potential application in single molecule detection, etc.
New Family of High-Efficieincy Oxygen Evolution Electrocatalyst Based on Ni-Fe Mixed Chalcogenides
Authors: Swesi Abdurazag T , Masud Jahangir , Nath Manashi
Published: February 2020

Over the last several decades water oxidation has been investigated in pursuit of clean, sustainable and efficient energy conversion and a substitute for fossil fuels. During water oxidation, oxygen evolution reaction (OER) plays a critical role in the advancement of renewable energy technologies like metal-air batteries or solar-to-fuel energy production. However, OER involving a complex 4 electron process, has several steps that have large reaction barriers, which lead to large required overpotentials.1 Recently we have observed that the family of Ni-chalcogenides can function as more-efficient, stable, earth-abundant electrocatalysts for the OER reaction in alkaline medium with low overpotential thus enhancing the energy conversion efficiency.1 Interestingly, Ni is always found in combination with iron (Fe) on earth and Fe impurities in the nickel hydroxide (Ni(OH)2) electrodes can cause destructive effects on Ni-based alkaline batteries by greatly lowering the OER overpotential.3 This phenomenon inspired us to investigate the influence of Fe content and synthesizing a NiFe-composite compounds in order to obtain better OER electrocatalysts. Here we report, for the first time, a nickel−iron selenide (Ni1-xFexSey) thin film with high OER catalytic activity and stability.

The electrocatalysts NixFe1-xSey were grown by electrodeposition on conducting substrates and detailed electrochemical studies with stationary as well as rotating disc electrodes were performed to investigate the catalytic efficiencies. The deposition parameters including pH of the electrolytic bath, deposition potential were seen to have some influence on the catalytic activity. In some compositions these transition metal mixed chalcogenides even outperform the noble metal and oxide based catalysts like IrO2, RuOx and NiOx. Our studies indicate that the overpotential for producing 10 mA/cm2 current density under oxygen evolution conditions can be achieved to be as low as 210 mV by optimizing the ternary composition of the selenide films and tuning the structural details. In addition to low overpotentials, these NixFe1-xSey electrodeposited films were seen to be exceptionally stable under conditions of continuous O2 evolution for extended period (>24 h). We will present a systematic study of investigating the OER catalytic efficiencies of the ternary chalcogenides, Ni­1-xFexSey and their detailed characterization with powder X-ray diffraction, scanning and transmission electron microscopy, Raman, and X-ray photoelectron spectroscopy.

References:

1. E. Mirzakulova, R. Khatmullin, J. Walpita, T. Corrigan, N. M. Vargas-Barbosa, S. Vyas, S. Oottikkal, S. F. Manzer, C. M. Hadad, and K. D. Glusac, Nature Chem. 2012, 4, 794.

2 McCrory, C. C. L.; Jung, S. H.; Peters, J. C.; Jaramillo, T. F. J. Am. Chem. Soc. 2013, 135, 16977.

3. Munshi, M. Z. A.; Tseung, A. C. C.; Parker, J. J. Appl. Electrochem
. 1985, 15, 711.
Rational Band Structure Engineering of TiO2 for Photoelectrochemical Water Splitting
Authors: Yin Wan-Jian
Published: February 2020

The search for new semiconducting materials or the engineering of existing semiconductors for commercially viable photoelectrochemical (PEC) water splitting has been extremely challenging. Meeting that challenge requires the discovery of a semiconductor with several tightly coupled material property criteria such as appropriate band gap (1.6 – 2.2 eV), efficient visible light absorption, high carrier mobility, and correct band edge positions that straddle the water redox potentials. However, previous searches/modifications of semiconducting materials for PEC water splitting application have often focused on a particular individual criterion such as band gap, neglecting the possible detrimental consequence to other important criteria. In this talk, general strategies for the rational design of semiconductors such as TiO2 to simultaneously meet all of the requirements for a high efficiency solar-driven PEC water splitting device are discussed. Density-functional theory calculations reveal that with appropriate donor-acceptor co-incorporation, heavily doped anatase TiO2 hold great potential to satisfy all of the criteria for a viable PEC device. Other approaches to modify the band structure of TiO2, such as the application of strain, will also be discussed.
(Invited) Photoelectrochemical Water Splitting and CO2 Fixation Using Powdered Photocatalyst Materials
Authors: Kudo Akihiko
Published: February 2020

Water splitting and CO2fixation of uphill reactions can be regarded as artificial photosynthesis, because light energy is converted to chemical energy. In the present paper, we introduce various metal oxide and sulfide photocatalysts and photoelectrochemical cells aiming at artificial photosynthesis. Rh and Sb-codoped SrTiO3 photocatalyst loaded with IrO2 is active for water splitting into H2 and O2 under visible light and simulated sunlight irradiations as a single particle type photocatalyst. This photocatalyst responds to 500 nm. SrTiO3:Rh of a H2-evolving photocatalyst and BiVO4 of an O2-evolving photocatalyst construct various type of Z-schematic photocatalyst systems with Fe3+/Fe2+, [Co(bpy)3]3+/2+, [Co(phen)3]3+/2+, and a conductive reduced graphene oxide (RGO) as an electron mediator and even without an electron mediator. It is noteworthy that a sheet photocatalyst consisting of SrTiO3:Rh,La and BiVO4powders with a Au contacting layer shows a quite high activity. Metal sulfide photocatalysts that are normally unstable for water splitting into H2 and O2 in the absence of an electron donor can be employed for Z-schematic photocatalyst systems for water splitting. Z-schematic photocatalyst systems combining metal sulfide photocatalysts as a H2-evolving photocatalyst with TiO2 (RGO/TiO2) and BiVO4+Co complex (an electron mediator) as an O2-evolving photocatalyst show activity for water splitting into H2 and O2. These photocatalyst materials can also be employed for a photoelectrochemical system for solar water splitting. Ag/BaLa4Ti4O15 and Ag/KCaSrTa5O15 photocatalysts with wide bandgaps show activities for CO2 reduction to form CO and HCOOH in an aqueous medium without any sacrificial reagents. O2 evolved with a stoichiometric amount indicating that water reacts as an electron donor indicating that an uphill reaction of CO2 reduction accompanied with water oxidation was achieved.
Lipophilic Redox Buffers for Polymeric Solid-Contact Electrodes
Authors: Buhlmann Philippe , Zou Xu U. , Zhen Xue V , Hu Jinbo , Stein Andreas
Published: February 2020

A calibration-free measurement with an ion-selective membrane requires that only the phase boundary potential at the sample/sensing membrane interface is variable, i.e., either dependent on the activity of the target ion in the sample, as in a potentiometric experiment, or determined by an applied potential, as in a voltammetric experiment. All the other phase boundary potentials in the electrochemical cell are constant. Unfortunately, one of the biggest challenges in the fabrication of devices comprising solid-contact membranes has been to establish a reproducible phase boundary potential at the interface of the hydrophobic ion-selective membrane and the underlying electron conductor. This talk will address our use of ion-selective membranes doped with lipophilic redox buffers, both in view of potentiometry and voltammetry.

Solid contact ion-selective electrodes (ISEs) typically have an intermediate layer between the ion-selective membrane and the underlying solid electron conductor that reduces the irreproducibility and instability of the measured electromotive force (emf). Nevertheless, the electrode-to-electrode reproducibility of the emf of current solid-contact electrodes in a zero-current measurement is widely considered to be unsatisfactory. To address this problem, we reported on lipophilic redox buffers consisting of the Co(III) and Co(II) complexes with hydrophobic ligands such as 1,10-phenanthroline (e.g., [Co(phen)3]3+/2+) paired with tetrakis(pentafluorophenyl)borate as counterion [1,2]. The resulting electrodes exhibit zero-current emf values with an electrode-to-electrode standard deviation as low as 1.7 mV after conditioning of freshly prepared electrodes for 1 h. While many prior examples of solid contact ISEs also used intermediate layers that contained redox-active species, the importance of selecting a balanced ratio of the reduced and oxidized species has typically been difficult and was often ignored, contributing to emf irreproducibility. The ease of the control of the [Co(phen)3]3+ / [Co(phen)3]2+ ratio explains the high emf reproducibility, as confirmed by the emf decrease of 58 mV per tenfold increase in the ratio of the reduced and oxidized redox buffer species. The result is an electrode-to-electrode standard deviation of Eº of 0.7 mV after 1 week of exposure to KCl solution. The use of this redox buffer in combination with colloid-imprinted mesoporous carbon [3,4] will also be discussed.

[1] Zou, X. U.; Cheong, J. H.; Taitt, B. J.; Bühlmann, P., Anal. Chem.
2013, 85, 9350–9355.

[2] Zou, X. U.; Zhen, X. V.; Cheong, J. H.; Bühlmann, P. Anal. Chem.,
2014, 86, 8687–8692.

[3] Hu, J.; Ho, K. T.; Zou, X. U.; Smyrl, W. H.; Stein, A.; Bühlmann, P. Anal. Chem.,
2015, 87, 2981–2987

[4] Hu, J.; Stein, A.; Bühlmann, P. Angew. Chem. Int. Ed., in press (DOI: 10.1002/anie.201603017).
Integrating Two CdS-Based Z-Scheme Heterostructures for Realizing Overall Photoelectrochemical Water Splitting
Authors: Chang Yung-Shan
Published: February 2020

As inspired by the natural photosynthesis, semiconductor nanostructures with Z-scheme charge transfer mechanism have been regarded as the ideal photocatalyst platform for realizing overall water splitting. The Z-scheme charge transfer mechanism involves a two-step photoexcitation process, in which a vectorial charge transfer pathway can be attained to evince strong redox powers for driving efficient photochemical reactions. In this work, two different configurations of CdS-based Z-scheme heterostructures were proposed and integrated to demonstrate photoelectrochemical overall water splitting. The samples were prepared by depositing Au particles on the CdS nanowires arrays, followed by the selective growth of ZnO or Cu2O on the Au surface. For CdS-Au-ZnO, the embedded Au may mediate interfacial charge transfer to effectuate electron concentration on CdS and hole accumulation on ZnO. As to the CdS-Au-Cu2O, an analogous vectorial charge transfer results in electron concentration on Cu2O and hole accumulation on CdS. The two composite structures of CdS-Au-ZnO and CdS-Au-Cu2O can respectively work as photoanode and photocathode in a single photoelectrochemical cell for achieving overall water splitting. The demonstration from this work delivers a novel structural engineering strategy for designing unique yet practical photoelectrochemical systems capable of performing artificial photosynthesis as well as solar fuel generation.As inspired by the natural photosynthesis, semiconductor nanostructures with Z-scheme charge transfer mechanism have been regarded as the ideal photocatalyst platform for realizing overall water splitting. The Z-scheme charge transfer mechanism involves a two-step photoexcitation process, in which a vectorial charge transfer pathway can be attained to evince strong redox powers for driving efficient photochemical reactions. In this work, two different configurations of CdS-based Z-scheme heterostructures were proposed and integrated to demonstrate photoelectrochemical overall water splitting. The samples were prepared by depositing Au particles on the CdS nanowires arrays, followed by the selective growth of ZnO or Cu2O on the Au surface. For CdS-Au-ZnO, the embedded Au may mediate interfacial charge transfer to effectuate electron concentration on CdS and hole accumulation on ZnO. As to the CdS-Au-Cu2O, an analogous vectorial charge transfer results in electron concentration on Cu2O and hole accumulation on CdS. The two composite structures of CdS-Au-ZnO and CdS-Au-Cu2O can respectively work as photoanode and photocathode in a single photoelectrochemical cell for achieving overall water splitting. The demonstration from this work delivers a novel structural engineering strategy for designing unique yet practical photoelectrochemical systems capable of performing artificial photosynthesis as well as solar fuel generation.
Photoelectrochemical Evaluation of Single Nanoparticles
Authors: Tkacz Kevin , Sanborn Christopher D. , Ardo Shane
Published: February 2020

Mechanisms of nanoparticle photocatalysis are not well understood. Like state-of-the-art photovoltaics, photocatalysis particles absorb light, separate charge, and generate photovoltages and photocurrents. However, unlike state-of-the-art photovoltaics, these photovoltaic parameters have never before been measured on single (to few) nanoparticles wetted by electrolyte. Prior work using scanning Kelvin probe force microscopy on dry mesoporous films has shown that photovoltages result from optical excitation but less is known about the behavior of particles wetted by liquid electrolyte on both sides.

Herein, using bipolar electrochemistry we report photovoltage responses from single (to few) photocatalyst nanoparticles jammed in a conical nanopore. The nanopore was etched in poly(ethylene terephthalate) or Kapton polyimide. Electrophoretic (or chemical) deposition jammed (or covalently linked) TiO2 nanoparticles into the nanopore therefore occluding ionic migration between the anolyte and catholyte. The circuit was completed when two redox reactions were driven on opposite poles of the nanoparticle to facilitate charge migration across the cell. Solar photocurrent was too small to be measured precisely using electrochemistry. However, motivated by work from the single molecule fluorescence community, single-particle open-circuit photovoltage measurements were taken every 200 ns. This timescale is important because it is on the order of the RC time constant to charge all interfaces yet slower than charge recombination.

Generally, less than 1 mV photovoltage responses were observed under illumination. This value was consistent with a hypothesis of double-layer charging or charging of a parallel plate capacitor with a TiO2 dielectric. The magnitude of this value also suggested that the full potential of the energized electron was not being sensed. We learned that using bipolar electrochemistry we cannot measure the majority of the photon energy transiently stored as the electron–hole pair. This is because the chemical potential change in electrons and holes is not sensed by the reference electrodes used in the studies.

Future efforts aimed at measuring the photoelectrochemical properties of single (to few) particles will be important. With this information, we hope to clarify the fundamental cause of photovoltaic action so that future nanoparticle materials properties can be rationally designed.
Profiling Carrier Generation in Semiconductor Microwire Arrays Via Photoelectrochemical Metal Deposition
Authors: Dasog Mita , Carim Azhar I , Yalamanchili Sisir , Atwater Harry A , Lewis Nathan S
Published: February 2020

Semiconductor microwire arrays are promising next-generation solar absorption materials as their geometry enables decoupling of the direction of the light absorption and charge-carrier collection. The high aspect ratio of microwire arrays provides high surface area for catalyst placement to perform photo-electrochemical reactions. Since the light scattering and absorption dynamics of semiconductor microwire arrays are complex, it is important to place the catalyst in optimal place to enhance the device efficiency. Furthermore, precise catalyst placement allows for reduced wastage of the catalyst material. In order to understand the absorption of light in such semiconductor architectures, gold was photoelectrochemically deposited onto p-Si microwires on Si substrates to profile the photoinduced charge-carrier generation in individual wires in a photoactive semiconductor wire array. Along with the charge-carrier generation as a function of the incident light wavelength, influence of other factors such as microwire pitch, shape of the wires, and wire diameter was also investigated.
Study of the Ammonia Oxidation Mechanism By a Normal Pusle Voltammetry
Authors: Shirasaka Ryo , Shiroishi Hidenobu , Harada Yuya , Nishitani-Gamo Mikka , Nagai Keiji
Published: February 2020

Although ammonia is expected as the next generation of energy medium, even platinum, which is a relatively active ammonia oxidation (AO) catalyst, have an insufficient performance for direct ammonia fuel cells (DAmFCs) operating below 100°C. Highly active AO catalysts at low temperatures needs to be developed in order to use ammonia as a fuel for DAmFCs. AO mechanism on platinum is reported as follows: After NH3 is adsorbed on the platinum surface, the AO proceeds via two competitive paths. One is the formation of hydrazine analogues, followed by the oxidation of the analogues to release N2 molecules. The other is the oxidation of an ammonia molecule to form nitrogen atoms adsorbed onto the surface of platinum (Nads) known as poisoning species. However, after the surface of the platinum is covered with Nads, the elimination process of Nads is not known. In this study, the elimination process was studied by a normal pulse voltammetry.

33.6 wt% Pt/MWCNT (average particle size: 5.57 ± 0.11 nm) catalyst was synthesized by a microwave polyol method. A 2 mg of Pt/MWCNT was suspended in 1 mL of Pt/MWCNT-0.1 wt% Nafion-MeOH by ultrasonication for 10 min. 10 μL of the suspension was cast onto a glassy carbon (GC) disk electrode (6 mm φ), followed by drying for 1 h in air. Electrochemical measurements were performed with a conventional three electrode system equipped with the modified GC electrode, an Au wire counter electrode and a reversible hydrogen electrode (RHE) in 0.1 M KOH or 0.1 M NH3-0.1 M KOH. The normal pulse voltammetry was performed as follows: After the Nads was formed by applying 0.6 V for 180 s, E
recover (V) was applied for various times (1 s，5 s，10 s，20 s，60 s, and 180 s) to eliminate Nads. Then, the AO current at 0.6 V after 1 s was used as an indicator for the amount of Nads poisoning.

Fig. 1 shows the dependence of AO current at 0.6 V after 1 s on recovery potential. The AO current gradually recovered by maintaining the potential below 0.4 V vs. RHE, indicating that the adsorbed N atoms were eliminated from the catalyst surface. It took a few minutes to recover the AO current. In addition, the decrease in potential accelerated the recovery of the AO current, especially below 0.3 V vs. RHE. The final percentage of the recovery increased with a decrease in the potential. The recovery rates below 0.25 V called hydrogen adsorption/desorption region increased with decreasing potential, probably due to the reduction of Nads. The time dependence of the recovery rate was analyzed by the sum of two exponentials, suggesting that the fast and slow reactions exists in the recovery process.

Figure 1
Developing Molecular Imprinted Layers As Electro-Analytical Probes for Dydrogesterone Determination
Authors: Mujahid Adnan , Hussain Tajamal , Ashraf Sobia , Raza Hamid
Published: February 2020

Dydrogesterone is a synthetic derivative of female sex hormone whose structure and pharmacological action is similar to progesterone. This drug is used in various conditions including lack of endogenous, hormone replacement therapy and others. The increasing use of dydrogesterone as synthetic hormone also demands its rapid and accurate analysis in biological as well as environmental bodies. In this perspective, we developed molecular imprinted polymer (MIPs) coatings as recognition element for electro-analytical determination of dydrogesterone. Imprinted polymers are synthesized by self-organization of monomer chains around template structure keeping high percentage of cross-linker. Dydrogesterone-imprinted polymer gel is synthesized by free radical polymerization taking methacrylic acid and methyl methacrylate (functional co-monomers), ethyleneglycol dimethacrylate (cross-linker) and dydrogesterone (template). The non-imprinted polymer layer was taken as control material i.e. synthesized using the same polymer composition without introducing template. Following spin coating method, the developed polymeric gel was integrated with interdigital electrodes (IDEs) i.e. patterned on printed circuit board. IDEs fabricated with imprinted as well as non-imprinted polymer layer, respectively were connected to impedance analyzer. The subsequent shift in capacitive values of imprinted and non-imprinted layers was determined respectively as function of dydrogesterone concentration. The shift in capacitive values for imprinted layer was higher than the non-imprinted one. As the imprinted layer offers geometrical as well as chemical adaptation sites and upon fitting in these cavities the charge transfer between two electrode fingers is reduced which results in higher capacitance shift. On the other hand, the non-imprinted layer lack such functionality and offer only non-specific binding thus, leads to lower capacitive shifts. These results suggest that imprinted layers integrated with IDEs can be suitably used for dydrogesterone determination in complex matrices.
Mediated and Direct Electrocatalytic Oxidation of Glucose and Cellulose: Towards Glucose and Cellulosic Air Batteries
Authors: Aldous Leigh , Abdulkhaliq Habib
Published: February 2020

The electrochemical oxidation of glucose has been widely explored, primarily for analytical purposes. The combustion of glucose is also well established to occur. By combining an electrocatalyst for glucose oxidation, as well as an oxygen reduction electrocatalyst, it is possible to assemble air-batteries or fuel cells that can (non-enzymatically) harvest useful electrical energy from glucose. Cellulose is the most abundant biopolymer in the world, is a non-food crop waste material, and is made up on glucose sub-units. By studying the electrocatalytic oxidation of glucose, it is possible to develop electrochemical devices that could use cellulose (and by extension, waste lignocellulosic biomass) as a fuel. All that is required is a suitable electrolyte that can dissolve cellulose (and lignocellulosic biomass). Ionic liquids and certain aqueous hydroxides fulfil these criteria.

We have been investigating the oxidation of glucose and cellulose, and developing genuine air-batteries that can exploit these materials. Focus has been upon (i) the electrolyte, which is critical in both solubilising the fuel, and in impacting electrocatalytic trends, (ii) dissolved molecules which can act as facile solution-phase electrocatalytic mediators for the oxidation processes, and (iii) nanostructured electrodes such as nanoporous gold, which can act as electrocatalytic electrodes for the direct oxidation of glucose and cellulose. In particular, it has been ensured that the electrolyte assists in the electrocatalytic processes and encourages depolymerisation of cellulose into glucose, ensuring high power electrochemical devices can be developed. Our progress in this area will be summarised.
(Invited) Quantifying the Impact of Ionic Liquid Cations on the Properties of Cellulose Nanocrystals
Authors: Gilman Jeffrey W. , Woodcock Jeremiah , Fox Douglas M
Published: February 2020

Ionic liquids have you been used to modify the properties of many classes of materials. This includes their use as solvents and catalysts in simple chemical reactions. However, they have also been used to improve the synthesis and processing of materials as well.  This presentation will review our efforts to utilize ionic liquids to enable the processing and enhance the properties of polymer composites. Specifically, we will cover composites based on multiwalled-carbon-nanotube (MWCNT), Montmorillonite (MMT) and cellulose nanocrystals (CNC). Novel measurement methods, used to characterize the impact of ionic liquids on the material properties of polymers, nanoparticles and polymer nanocomposites, such as fluorescence life-time imaging and inverse gas chromatography (iGC) will also be presented.

Figure 1
Elecrochemistry of Uranium and Plutonium in Ionic Liquids
Authors: Chlistunoff Jerzy , Boland Kevin Sean , Gaunt Andrew , Goff George Scott , Runde Wolfgang
Published: February 2020

Actinides can exist in many oxidation states. The redox potentials for various oxidation states of actinides strongly depend on their electronic structures, but are also affected by the medium properties. The differences between the redox potentials of actinides, most notably uranium and plutonium, have been utilized in the traditional PUREX process (Plutonium Uranium Reduction EXtraction) developed during the 1947. PUREX is based on a nitric acid dissolution of used nuclear fuel followed by liquid-liquid extraction and utilizes hazardous chemicals such as concentrated nitric acid and volatile and hazardous organics like tributyl phosphate and dodecane or kerosene. In spite of the differences in redox chemistries of the actinides, electrochemical methods have never been applied for large scale used nuclear fuel processing. Molten salts (in particular halides) have been demonstrated to be better suited for actinide electrochemistry; however, the practical application of pyroprocessing is limited by the high temperatures and strongly corroding properties of molten salts. Ionic Liquids (ILs) are relatively new media that offer the benefits of molten salts, e.g., high ionic conductivity required for practical operations and wide electrochemical windows, but are also free of the molten salt shortcomings such as the high temperature and corroding properties. Their high ionic conductivity and low reactivity make them especially well-suited for electrochemical applications. While the high conductivity enables for electrochemical reactions at the high current densities required for practical operations, the low reactivity typically translates into a wide potential window, which allows access to electrochemical processes that cannot be accomplished in conventional media. Moreover, ILs offer a wide range of tunable physical properties, which could potentially be utilized not only in the electrochemical but also in numerous other separation techniques relevant to the nuclear industry, including solvent extraction, ion exchange, dissolution, crystallization, etc. The development of separation technologies for spent nuclear fuel in ILs could complement or replace current PUREX and/or high-temperature pyrochemical processing technologies.

The current state of understanding of the electrochemical behavior of actinides in ILs is far from satisfactory. As part of our multi-faceted approach to study the structural, thermodynamic, and kinetic behavior of actinides, we undertook electrochemical studies of uranium and plutonium in selected chloride and bistrifluorosulfonamide based-ILs in order to demonstrate the feasibility of using ILs for electrochemical actinide separations. In this presentation we will summarize our most recent results of those studies.