bluuebunny/crossref_metadata_2025 huggingface dataset:
Neutron Radiographic Investigations on the Effect of Hydrophobicity Gradients within MPL and MEA on Liquid Water Distribution and Transport in PEMFCs
Authors: Mohseninia Arezou , Kartouzian Dena , Markötter Henning , Ince Utku U. , Scholta Joachim , Manke Ingo
Published: February 2020

Neutron radiography imaging is employed to investigate the effect of hydrophobicity gradients between the membrane electrode assembly (MEA) and microporous layer (MPL) of a low-temperature polymer electrolyte membrane fuel cell (PEMFC) on the water distribution and transport in operating cells. Single cells specially developed for neutron imaging experiments with an active area of 8 cm² are equipped with in-house made MEAs and MPLs featuring different degrees of wettability. Imaging is performed with a pixel size of 13 µm and the cells are operated at two different current densities of 1 and 0.75 A cm-2 and a relative humidity of RH=70% and RH=120% at a temperature of 55°C. A first quantitative analysis of the water thickness in electrodes and gas diffusion layers (GDLs) of 3 cells at RH=120% and i=1 A cm-2 as well as an exemplary radiogram for the water distribution inside one of the cells is shown in figure 1.

It is observed that the implementation of both a more hydrophobic MEA and MPL results in an increase of overall water content inside the cell. Nevertheless, the effect of a more hydrophobic MPL on the increase of the water content of the cell, under the operating conditions investigated here, is apparently more significant compared to the effect of a more hydrophobic MEA. As expected, the amount of water found on the cathode side is higher than on the anode side for all components of the cell. The sudden accumulation of water on anode side which is appearing in periodic peaks with equal time intervals is associated to an increased rate of back diffusion mechanisms. The cell with a more hydrophobic MEA has decreased the magnitude of these fluctuation peaks by 30%, whereas this reduction ratio is 60% for the cell with more hydrophobic MPL, resulting to a more balanced water profile across the membrane. In this presentation, we will show further morphological and wetting property characterization results of various MEAs and MPLs and analyze the effect of hydrophobicity on the dynamical changes of water distribution and transport at different operating conditions.

Figure 1
Ionic Liquid Functionalized Cathode Catalyst Support for Carbon Dioxide Conversion Using Proton Exchange Membrane Fuel Cell
Authors: Ramaprabhu Prof S , Sreetama Ghosh , Seshadhri Garapati Meenakshi
Published: February 2020

Carbon dioxide is a major anthropogenic greenhouse gas produced primarily from combustion of fossil fuels (coal, natural gas and oil), automobile emission and from industrial exhausts that has posed a huge danger for the environment in recent times. About 81 % of the overall greenhouse gases production is contributed by CO2. Electroreduction of CO2 into useful fuels has gained huge attention in the past few years. The advantage of polymer electrolyte membranes (PEM) is already well recognized in fuel cells. The reverse action of fuel cell can be employed for protonation of CO2 to fuels, which has an advantage in prevention of products from re-oxidation. Several studies on PEM cell based electrochemical conversion of CO2 into useful hydrocarbons have been reported. In this particular work, we aim to convert CO2 into some useful nontoxic hydrocarbon using proton exchange membrane fuel cell by selectively functionalizing the cathode catalyst support material. Room temperature ionic liquids exhibit some significant properties, which owe to their popularity such as low vapour pressure, high chemical and thermal stability, tunable properties, good ionic conductivity and high CO2 solubility. Due to their negligible vapour pressure and nonflamability, they are often called “green solvents”. The cathode catalyst support used in this present work is iron carbide encapsulated nitrogen doped carbon nanotubes, which is anticipated to increase both the CO2 reduction and catalytic activity of cathode electrode. Further, surface functionalization of the cathode catalyst support with ionic liquid moieties and dispersion of Pt catalytic nanoparticles were performed to use in a Proton Exchange Membrane (PEM) CO2 conversion cell. The ionic functionalized sample shows better CO2 reduction than the pure support material due to improved interaction of the ionic functionalized catalyst with CO2 molecules and also facilitates the reaction kinetics due to the presence of high electrical conductivity and preferable catalytic sites. Moreover, Fe containing precursors also participate in CO2 electroreduction. The present investigation describes the synergistic effect of Fe as well as nitrogen doped ionic functionalized CNT for electrochemical reduction of CO2.
(Invited) Understanding Charge Separation in Semiconductor for Efficient Photoelectrochemical Water Splitting
Authors: Hwang Yun Jeong , Chae Sang Youn , Min Byoung Koun
Published: February 2020

To mitigate the global warming issue caused by the current heavy dependence on fossil fuels, the researchers propose hydrogen as an alternative energy carrier, which can be produced from water splitting in a photoelectrochemical (PEC) cell. In the PEC cell, sunlight can be absorbed and stored in the form of chemical energy (i.e. hydrogen) by using a semiconductor photoelectrode. To achieve an efficient photocatalytic electrode, the semiconductor material has to satisfy several requirements such as high visible-light absorbing ability, effective charge separation, and fast catalytic reaction on its surface. However, a single semiconductor material often fails to have poor overall efficiency. Therefore, combination of two or more semiconductor junctions are suggested to compensate the other material’s drawbacks.

For example, WO3/BiVO4 heterojunction is one of the successful combinations in which WO3 play a role in electron transfer and BiVO4 increases the visible light absorption to increase the photoanodic water splitting performance. The charge separation properties at the WO3 and BiVO4 interface are characterized by measuring the photocurrent in the absence/presence of hole scavengers, light absorption spectroscopy, and intensity-modulated photocurrent spectroscopy (IMPS). The morphology and the thickness of the mesoporous WO3 layer were controlled to monitor to understand the charge separation efficiency at the interface. Our study can provide insights to heterojunction design.

Meanwhile, a p-type chalcopyrite Cu(In,Ga)(Se,S)2 (CIGS) semiconductor was prepared by a solution precursor processed method and used as a photocathode for hydrogen evolution reaction, and charge separation properties on its surface was studied by electrochemical impedance spectroscopy measurement. By controlling the surface states and introducing the passivation layer of ZnS, the photocurrent with the CIGS thin film on the transparent FTO substrate was significantly improved. Also, CIGS on FTO substrates was useful to compare PEC performances under forward and backward illumination conditions. Since slow electron transfer in CIGS photocathode is believed to limit PEC performance, further decrease of the defect structure of CIGS film is desirable for efficient solar-to-hydrogen conversion.
Highly Aligned Oxide Nanotubes: Engineering Reactive Centers for Photocatalysis
Authors: Schmuki Patrik , Zhou Xuemei , Liu Ning , Altomare Marco
Published: February 2020

TiO2 nanomaterials have over the last 30 years attracted tremendous scientific and technological interest. Particularly various 1D and highly defined TiO2 morphologies were explored for the replacement of nanoparticle networks and were found in many cases far superior to nanoparticles or their assemblies. Nanotubes or wires can be grown by hydrothermal or template methods, or even more elegantly, by self-organizing anodic oxidation. The latter is not limited to TiO2 but to a full range of other functional oxide structures on various metals and alloys can be formed. These advanced and doped morphologies can be grown on conductive substrates as ordered layers and therefore can be directly used as functional electrodes (e.g. photo-anodes). The presentation will focus on these highly ordered nanotube arrays of TiO2 (and similar) and discuss most recent progress in synthesis, modification and applications towards photocatalytic and photoelectrochemical applications such as noble-metal-free H2 generation or the site-selective placement of active centers onto/into these tube layers.

Literature:

- P. Roy, S. Berger, P. Schmuki, Angew. Chem. Int. Ed. (2011), 2904

- K. Lee, A. Mazare, P. Schmuki, CHEMICAL REVIEWS, 114 (2014) 9385

- N. Liu, P. Schmuki et.al. Nano Letters, 14 (2014) 3309

- N. Liu, P. Schmuki et.al. Angew. Chem. Int. Ed. 53 (2014) 14201

- X. Zhou, N.Liu, P.Schmuki ACS Catal., ,7 (2017) 3210
In-Situ Growth of Polymeric Carbon Nitride Films for Efficient Photoelectrochemical Water Splitting
Authors: Xue Can
Published: February 2020

We present successful growth of high quality carbon nitride based copolymer (CNBC) films on various substrates (glass, FTO, TiO2) through solvothermal approaches with post-annealing. Structural characterizations of the films reveal the polymeric carbon nitride network consisting of tri-s-triazines and s-triazines bridged by different functional groups. The strong bonding between CNBC films and the substrates via covalent linkage ensures intimate contact and smooth interfacial charge transport. As such, the CNBC films exhibit excellent photoelectrochemical performance, which is attributed to strong visible light harvesting, excellent conductivity, and efficient charge separation and transport. Further, we demonstrate that similar solvothermal approach can be also used to create CNBC films on TiO2 surface, and the resulted CNBC/TiO2 junction allows for vectorial charge transfer, giving greatly enhanced photocurrent responses. Our studies provide a general solvothermal-based strategy for in-situ growing metal-free films on various substrates towards efficient photoelectrochemical water splitting.
Enhanced Electrochemical Ammonia Production Via Peptide-Bound Metals and Effects on the Hydrogen Evolution Reaction
Authors: Loney Charles , Suttmiller David , Acharya Prashant , Maheshwari Sharad , Wiles Luke , Ayers Katherine E , Gellett Wayne L. , Janik Michael John , Greenlee Lauren F , Renner Julie N.
Published: February 2020

Approximately half of the people on the planet are alive due to synthetically produced ammonia. However, due to the fossil fuels used in the current process, ammonia production contributes a significant amount to the world’s greenhouse gas emissions. By taking an electrochemically-based approach to this process, those emissions can be eliminated. However, current catalysts are not selective for the desired reaction. We hypothesize that 3D surface modifications can be utilized to overcome these limitations and create catalysts which mimic the selectivity of the nitrogenase enzyme, an enzyme that catalyzes the reduction of nitrogen to ammonia at mild temperatures and pressures. Therefore, in this study, peptide sequences have been designed to mimic the general function of the naturally-occurring nitrogenase enzyme. Recent results in an alkaline, solid-state electrochemical cell show promise using a synthetic peptide bound to iron(iii) oxide nanoparticles, which yield an electrochemical ammonia production rate that is 10x higher than the catalyst without bound peptide. Preliminary, repeated experiments in a liquid electrolyte cell at room temperature and atmospheric pressure illustrate similar promising results. Furthermore, gas adsorption isotherms suggest that this peptide does not significantly block nitrogen adsorption, and that the catalysts maintain the same surface area after binding to the peptides.

In addition, a simple and tunable peptide system has been designed to better understand how peptides influence electrochemical reactions. Emphasis is placed on understanding the hydrogen evolution reaction (HER) on Au, Fe2O3, and Pt metal surfaces, as HER is the main competing reaction for ammonia production. One of our main tools used to understand these peptide effects is a quartz crystal microbalance with dissipation (QCM-D), which is utilized in combination with an electrochemistry module (QEM) and humidity module to give real-time electrochemical and surface information. Importantly, the QCM-D is sensitive enough to measure the mass loading of the peptide on metal surfaces. Furthermore, the humidity module allows us to study the peptides’ effects on water uptake, which will also be useful for understanding HER in a basic environment, as water is the proton source. For instance, preliminary results show that at least one tripeptide species has a significant hydrophilic effect on water uptake when used on an Au sensor. Overall, these data are anticipated to influence general guidelines when designing selective catalysts for electrochemical reactions.
(Invited) Exceptional Electrocatalytic Oxidations of Small Molecules on Perovskites and Perovskite Derivatives for Advanced Energy Generation and Storage
Authors: Forslund Robin , Stevenson Keith J
Published: February 2020

As the need for clean energy generation and storage grows, the efficiency for low cost hydrogen generation needs to be addressed to further the pragmatic development of this key technology. Given that the efficiency of electrochemical hydrogen generation is limited primarily by the sluggish kinetics of the anodic reaction used, such as the oxygen evolution reaction, extensive efforts have been made to reduce the overpotentials for the anodic reaction in alkaline media with advanced catalysts. The electrooxidation of urea, hydrazine, and other small molecules has attracted considerable attention for the electrochemical generation of hydrogen due to the lower electrochemical potential required to drive these reactions. By tuning the electronic structure of nickel-containing perovskites as well as derivatives of the perovskite structure, higher oxidation states of nickel active sites can be achieved, leading to increased catalytic activities at a fraction of the cost of other nickel-rich materials.
Design and Synthesis of Photo-Clickable Au Nanoparticles and Polymers and Their Redox-Active Conjugate Materials
Authors: Workentin Mark , Luo Wilson , Gobbo Pierangelo , Vasdev Rajeshwar , Gilroy Joseph
Published: February 2020

Functional materials are predicted to have an enormous impact on the field of nanotechnology and these can be expanded by further derivatization of their surfaces on a molecular level to allow for the control of the interactions between material surfaces and their environment. To this end, the cycloaddition chemistry between strained-cyclooctynes and 1,3-dipolar molecules offers a simple, clean, and highly reliable protocol for the modification of material surface functionalities. However, the high reactivity of the strained C-C triple bond of these systems renders the incorporation of these cyclooctyne moieties into materials synthetically challenging or, in some cases, inaccessible. To circumvent this challenge, we seek to employ cyclopropenones as 1) a photo-cage for strained-cyclooctynes to allow for facile incorporation onto material surfaces and 2) a photochemical precursor that, upon decarbonylation, affords the parent strained-alkyne that can be employed in subsequent cycloaddition chemistry. This two-step methodology was applied to the synthesis of photo-clickable Au nanoparticles and norbornene-based polymers. The design, fabrication, and characterization of these materials — Au nanoparticles and polynorbornenes — and their redox-active conjugates will be discussed. Our ability to quantitate surface functionalities and monitor the interfacial chemistry via various spectroscopies (NMR, IR, and UV-Vis) and TGA and TEM will be highlighted. The photoactivated nature of this cycloaddition chemistry will allow for spatial control that will be amenable to the fabrication of nanoelectronic devices. I will also present reflections of my 25+ year relationship with on our Baizer Award winner Professor Flavio Maran.
Post-Functionalization of P3HT Via Anodic Oxidation with High Current Efficiency
Authors: Kurioka Tomoyuki , Nishiyama Hiroki , Tomita Ikuyoshi , Inagi Shinsuke
Published: February 2020

Recently, post-functionalization has attracted attention as a useful strategy to obtain functional polymers. We have already reported the anodic chlorination of poly(3-hexylthiophene) (P3HT) in the presence of chloride ions under a constant potential condition, and found that introduction of a chlorine atom to the 4-position of the thiophene rings could tune the optoelectronic properties of P3HT. However, the current efficiency of this reaction was low because of the competitive oxidation between P3HT and the chloride ions used as a chlorine source.1

In this study, we improved the current efficiency of the anodic chlorination of P3HT by using boron trifluoride-diethyl ether complex (BFEE). BFEE is well-known to decrease oxidation potentials of aromatic compounds due to the π-complex formation between BF3 and aromatic rings.2 BFEE used as a solvent and an electrolyte in voltammetric studies successfully decreased the oxidation potential of P3HT, and increased the oxidation potential of chloride ions. These interesting effects of BFEE also worked in the macroscale electrolysis of P3HT, giving higher current efficiency compared to the conventional methods.

References

S. Hayashi, S. Inagi, K. Hosaka, T. Fuchigami, Synth. Met., 2009, 159, 1792.

S. Jin, G. Xue, Macromolecules, 1997, 30, 5753.

Figure 1
Anodic Thiocyanation of Alkenes in Formic Acid
Authors: Becker James Y. , Gitkis Anna
Published: February 2020

Previously we studied the anodic thiocyanation of aromatic compounds [1, 2] followed by a one-pot anodic thiocyanation and isothiocyanation of alkenes in both acidic two-phase (water-dichloromethane) and homogeneous one-phase (water-acetonitrile) media [3]. The present talk will describe a two-step thiocyanation of alkenes in formic acid [4] and a plausible mechanism for this reaction.

At the bottom there is a typical example showing the type of a major product obtained in this process.

References

[1] A. Gitkis, J.Y. Becker, J. Electroanal. Chem., 593 (2006) 29-33.

[2] A. Gitkis, J.Y. Becker, Electrochim. Acta, 55 (2010) 5854-5859.

[3] A. Levy, J.Y. Becker, Electrochim. Acta, 178 (2015) 294–302.

[4] A. Gitkis, J.Y. Becker, Electroanalysis, 28 (2016) 2802-2807.

Figure 1
Mechanistic Studies of Protein-Based, Metal Nanoparticle Biosynthesis
Authors: Macazo Florika C. , Minteer Shelley D.
Published: February 2020

The synthesis of metal and semiconductor nanoparticles and nanostructures has seen a tremendous advancement in the field of nanomaterials research owing to their high optical, electrical, catalytic and photocatalytic properties. To date, a number of methods have been reported for the synthesis of nanoparticles, however, they typically require costly and hazardous chemicals and do not usually produce particles of high yields and uniform sizes and monodispersity. Hence, there still remains a need to develop cost-efficient and greener means of synthesizing nanostructures at an industrial scale. As such, we aim to utilize the machinery of biological organisms in biologically synthesizing nanoscale materials with great control over their size and shape to design innovative bionanomanufacturing platforms that will enable reproducible and large-scale synthesis of metal nanostructures with uniform size, shape and high purity. Herein, we demonstrate the in situ microbial synthesis of silver (Ag) and gold (Au) nanoparticles using the cell filtrates of Rhodobacter sphaeroides, Rhodobacter capsulatus, and Bacillus subtilis, which resulted in spherical nanoparticles with uniform sizes (5 ~ 20 nm) and monodispersity. We studied the effect of incubation time and metal ion concentration on the growth and size of the particles, and our data indicate that there is a linear relationship between the particle size, incubation time and metal ion concentration. We also performed preliminary screening of the proteins responsible for the nanoparticle biosynthesis by carrying out enzyme inhibition studies and proteomics analysis of the cell filtrates. Our initial results provide insights into the mechanism of biological nanoparticle synthesis, and thus, lay the groundwork for the isolation of the active proteins and translation into in vitro and cell-free, protein-based nanofabrication techniques, which offer great avenues for both fundamental and applied nanomaterials research.
Controlled Interactions between Engineered Proteins and Acidic Polymer Electrolytes
Authors: Su Zihang , Waston Skylar T. , Renner Julie N.
Published: February 2020

Bio-electrochemical technologies have an important and growing role in healthcare, with applications in sensing and diagnostics, as well as the potential to be used as implantable power sources and be integrated with automated drug delivery systems. Enzymatic bio-electrodes are especially attractive because they are biocompatible, highly selective, and efficient catalysts at physiological conditions. Challenges associated with enzyme-based electrodes include low current density and short functional lifetimes. An important aspect in creating efficient electrochemical devices is facilitating proton transfer in electrode layers. Often solid polymer electrolytes (ionomers) are utilized in industrial devices such as fuel cells and electrolyzers, but these polymers need to be carefully controlled in bio-electrochemical environments, such that they do not denature enzymes.

Protein engineering is emerging as a powerful tool to overcome the challenges in manufacturing enzyme-based electrodes. By taking advantage of the ability to precisely define protein sequences, electrodes can be organized into high performing structures. While many protein engineering tools have been developed for bio-electrodes, no proteins have been specifically designed to help organize ionomer on conductive surfaces. We propose to utilize highly tunable and easily manufactured structural protein sequences found in nature to control the placement of these ionomers, thus potentially enable their use in a multitude of devices.

In this talk, we will discuss the protein design, binding and aggregation behavior with ionomer, the effect of ionomer on protein secondary structure, and surface analysis of samples. Specifically, mass change data from a quartz crystal microbalance with dissipation (QCM-D) and hydrodynamic radii data gathered using dynamic light scattering (DLS) show proteins can be modified to bind with ionomer (Nafion®), and this interaction happens in solution as well as when the proteins are immobilized on metal surfaces. Circular dichroism (CD) data shows the secondary structures of the proteins in the presence on ionomer remain unchanged. Surface analysis is performed using x-ray photoelectron spectroscopy (XPS) and an atomic force microscope (AFM) and corroborate the binding analysis results. Since the purpose of these composite materials is to facilitate proton transfer, conductivity through thin films is also characterized. Overall, this work shows for the first time that protein sequences could serve as a promising tool in controlling ionomer architecture. This discovery has broad applications in bio-electrodes, but can also be used to understand the impact of ionomer organization on fuel cell and electrolysis membrane electrode assemblies as well.
Optically Guided Directional Electrodeposition of Semiconductors Mimicking Natural Phototropism
Authors: Meier Madeline Claire , Carim Azhar I , Hamann Kathryn R , Thompson Jonathan R , Atwater Harry A , Lewis Nathan S
Published: February 2020

Template-free photoelectrochemical deposition of semiconducting Se-Te films spontaneously produces highly ordered subwavelength scale 3D nanostructures with significant anisotropy and periodicity. The degree and direction of anisotropy can be tuned by the input polarization and feature size and pitch by the wavelength. The optical control of the resultant physical morphology is a consequence of the material self-optimizing to maximize light collection. Here we investigated the capability of the material to mimic natural phototropism exhibited by sunflowers and palm trees wherein the angle of the illumination incidence controls the direction of the structure growth out of the substrate plane. Additionally, morphological complexity could be generated by varying the polarization vector while utilizing non-normal incidence. The phototropic growth response can be dynamically directed using temporal changes in illumination; for example, zig-zag structures were produced by oscillating the illumination incidence about the surface normal while maintaining a constant polarization. The deposition was simulated using a finite-difference time domain method to model light absorption and a Monte Carlo method for mass addition and the results of the simulation successfully reproduced the experimentally observed morphologies, affirming that the phototropic response was a fully optically-induced phenomenon. The generation of these highly anisotropic light-tracking features demonstrates the ability of this technique to mimic naturally occurring phototropism to optimize the light absorption of the material.
Electron Transfer Processes Enabling Genotoxicity Sensor Arrays
Authors: Rusling James F
Published: February 2020

Design of biosensor arrays for drug development and diagnostic applications has become a major activity in bioelectrochemistry. Achieving efficient electron transfer processes to produce reliable, reproducible, and sensitive output signals is a critical goal for such devices. This paper describes key electron transfer processes in our development of sensors for the chemistry of genotoxicity, defined here as resulting from the damage and oxidation of DNA by chemicals and their metabolites. This research is driven mainly by the need to screen for the potential genotoxicity of new drug and environmental chemical candidates, about 30% of which have toxicity issues that do not manifest until human clinical trials. A major issue is metabolic chemistry driven mainly by cytochrome (cyt) P450s and other enzymes, and we needed to produce metabolites in our arrays. Metabolic chemistry involves electron-transfer catalysis of organic reactions, usually involving oxygen transfer in the case of cyt P450s. We have found ways to efficiently transfer electrons into cyt P450s in thin films via their natural reductase electron-transfer partners to catalyze metabolic reactions electrochemically via mechanisms that are the same as in our livers and other organs. Optimizing the electrode-driven electron transfer chain from electrode to reductase to cyt P450 has allowed us to replace expensive NADPH as reducing agent and simplify our genotoxicity arrays.

We also needed a way to detect the resulting metabolite-related DNA damage in sensors combining thin LbL films of metabolic enzymes and DNA in which the metabolites are generated and react with DNA. We found that guanines in DNA chains can react in an electrocatalytic process involving electron transfer to a Ru or Os metallopolymer (RuPVP) to output visible light via electrochemiluminescence (ECL). A complex electron transfer sequence drives an electrocatalytic process that oxidizes RuII to RuIII to oxidize guanine moieties in the DNA and produces visible light. The OsII/OsIII redox couple can be used in a similar ways to design sensor arrays selective for DNA oxidation.

Electrocatalytic Cyt P450 oxidations, ECL generation and microfluidics are combined in our most sophisticated genotoxicity sensor arrays. When DNA is adducted by metabolites, its double-stranded structure is disrupted and RuIII sites in the film gain better access to guanine moieties to produce more ECL light. The primary oxidation product in DNA oxidation is 8-oxo-guanine, which in a second step is selectively oxidized by OsIII complexes to give ECL at a lower applied potential that for RuIII/RuII. Examples of metabolite-related DNA damage and oxidation, including the genotoxic potential of e-cigarettes, will be discussed.
TEMPO-Based Organocatalyst Design
Authors: Hickey David P , Sigman Matthew S , Minteer Shelley D.
Published: February 2020

Recently there has been an increased interest in the development of small molecule electrooxidation catalysts such as (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), for multistep electrochemical alcohol oxidation. Several TEMPO derivatives have long been used to electrochemically oxidize short chain alcohols and various sugars to the corresponding aldehydes and carboxylic acids under physiological aqueous conditions. However, many nitroxyl radical-containing species decompose rapidly in an oxidized state and are therefore ineffective as alcohol oxidation catalysts. Furthermore, building libraries of such a catalyst is difficult due to the limited number of commercially available TEMPO derivatives and the lack of modular synthetic pathways for more complicated TEMPO structures. A promising alternative to the physical preparation of such libraries is the use of computational modeling to allow for in silico catalytic screening of a much wider range of TEMPO compounds. We have recently developed a descriptive model that correlates the electrocatalytic activity of nitroxyl radical catalysts to their redox potentials under aqueous conditions. Based on fundamental insights derived from this model, we have designed several highly active and promiscuous catalytic materials in the form of redox polymers capable of oxidizing a wide range of primary and secondary alcohols as well as several amines. In addition, we have recently aimed at enhancing the selectivity of nitroxyl radical catalysts by incorporating highly active TEMPO derivatives into the active site of an artificial thermostable protein.
Speciation and Electronic Structure of La1
-XSrxCoO3
-Δ during Oxygen Evolution
Authors: Stoerzinger Kelsey A. , Wang Xiao Renshaw , Hwang Jonathan , Rao Reshma R , Hong Wesley T , Shao-Horn Yang
Published: February 2020

Transition metal oxides present a promising alternative to noble metals for oxygen electrocatalysis, including cobalt-containing perovskite oxides for the oxygen evolution reaction (OER) in alkaline electrolyzers. However, a lack of fundamental understanding of oxide surfaces impedes rational catalyst design for improved activity and stability. Investigation of epitaxial oxide thin films allows quantification of the intrinsic activity, as well as examination of their chemical speciation in an aqueous environment using ambient pressure X-ray photoelectron spectroscopy (AP-XPS). We couple electrochemical studies of epitaxial La1-xSrxCoO3
-δ films with in situ and operando AP-XPS to investigate the surface chemistry and electronic structure. By quantifying the formation of hydroxyl (OH) groups in situ, we compare the relative affinity of different surfaces for this key reaction intermediate in oxygen electrocatalysis. Operando measurements of La0.8Sr0.2CoO3
-δ in alkaline electrolyte indicate that the surface is stable during OER and behaves as a metal, with the voltage drop confined to the electrolyte. Furthermore, OH and carbonate species persist on the electrode surface even under oxidizing conditions, and may impact the availability of active sites or the binding strength of adsorbed intermediates via adsorbate-adsorbate interactions. The accumulation of OH species with oxidative potentials suggests that, for covalent oxides with facile charge transfer kinetics, the rate of reaction could be limited by proton transfer kinetics. This operando insight highlights the potential importance of carbonates in oxygen electrocatalysis and will help guide modeling of self-consistent oxide electrocatalysts.
THz SERS Observation of Benzenethiol Monolayers on Electrode Surfaces
Authors: Ikeda Katsuyoshi
Published: February 2020

Surface-selective vibrational spectroscopy is a powerful tool to study various interfacial phenomena such as electrochemical reactions at electrode/electrolyte interfaces. Among various spectroscopic methods, surface enhanced Raman scattering (SERS) is a promising method to conduct in-situ observation in IR- and THz-opaque media. According to recent technological advancements in fabrication of optical filters, elimination of Rayleigh scattering has become highly efficient. Thus, it is now expected that very low-frequency vibrations such as THz vibrations can be observed even in aqueous solutions [1]. Figure shows that an extramolecular vibration of benzenethiol monolayers with ultra-low frequency is indeed observable using this method. We will discuss charge transfer resonances at metal/molecule interfaces based on this low frequency vibration.

Figure caption

THz-SERS spectra of monolayers of benzenethiol derivatives on a roughened Au substrate

Reference

[1] M Inagaki, K. Motobayashi, K. Ikeda, J. Phys. Chem. Lett., 8, 2017, pp. 4236-4240.

Figure 1
Dark Field Scattering Spectroelectrochemistry of Single Au Nanoparticles at Transparent Planar and Micro-Sized Electrodes
Authors: Pan Shanlin , Ma YanXiao , Highsmith Alton L.
Published: February 2020

Boron dipyrromethene (BODIPY) molecules with donor-acceptor configurations are of great interests for harvesting and converting solar energy in a solar cell. Au nanoparticles have been applied to enhance solar energy harvesting and conversion efficiency of organic solar cells because of their surface plasmon properties for increasing light absorption cross-section of an organic dye. Electrochemical properties of single BODIPY dyes and plasmonic Au nanoparticles (NPs) are studied using combined optical and electrochemical methods to reveal their structure-function relationship at the nanometer scale. Our study shows a heterogeneous half redox potential distribution for the BODIPY molecules embedded in polystyrene film because of the heterogeneity in their charge transfer rates. Single molecules adsorbed onto a TiO2 surface with ordered nanostructures show surprising fluorescence blinking activity with the shortest ON duration time in comparison to bare glass and indium-doped tin oxide (ITO) surfaces. Dark field scattering (DFS), photoluminescence (PL), and electrogenerated chemiluminescence (ECL) are used to probe local redox reactions of single Au nanoparticles at transparent planar and micro-sized electrode. Our study shows that these optical responses at individual plasmonic NPs are strongly dependent on particle size, and are affected by the local chemical and charge transfer environment of the NPs.
Detection of Reactive Oxygen Species in AEM Fuel Cells Using in Situ Fluorescence Spectroscopy
Authors: Zhang Yunzhu , Parrondo Javier , Sankarasubramanian Shrihari , Ramani Vijay
Published: February 2020

Anion exchange membrane (AEM) stability is a long-standing challenge that has limited the widespread development and adoption of AEM fuel cells. It is essential to understand the mechanism of AEM degradation during fuel cell operation. There are multiple modes of AEM degradation, broadly classified as chemical, mechanical and thermal degradation. Chemical degradation is among the most destructive modes, and can be further sub-divided into nucleophilic degradation (induced by the hydroxide ion), and oxidative degradation (induced by reactive oxygen species). While the former has been extensively studied, there has been minimal work on oxidative AEM degradation.

The reactive oxygen species produced during the operation of an AEM fuel cell have hitherto not been detected during operation. Given the high pH, it is postulated that superoxide anion radicals (O2
⋅-), as opposed to hydroxyl radicals, are primarily involved in the degradation progress. The objective of this study was to confirm O2
⋅- formation during AEM fuel cell operation and to monitor in real-time the rate of O2
⋅- generation in an operating fuel cell using in situ fluorescence spectroscopy.

1,3-diphenlisobenzofuran (DPBF) was chosen as the fluorescence probe, the sensitivity of which towards O2
⋅- was evaluated by performing ex situ experiments in a semi-batch reactor. We demonstrate that the fluorescence intensity of this dye selectively decreased upon exposure O2
⋅-. DPBF was then incorporated into an AEM (membrane was solution cast after mixing the dye with the casting solution), which was assembled into a fuel cell. O2
⋅-
generation in an operating AEM fuel cell was then monitored via in situ fluorescence spectroscopy using a bifurcated optical fiber probe, when the cell was operated in H2/O2 mode. To confirm the impact of O2
⋅- on AEM degradation, independent experiments (without dye) were performed under identical conditions, under both H2/O2 and N2/N2 modes, and the ionic conductivity and ion exchange capacity were monitored to estimate degradation extent based purely on nucleophilic degradation. From our in situ fluorescence studies, we were able to independently estimate the rate constants and activation energy for oxidative AEM degradation in an operating AEM fuel cell.
Understanding the Surface Corrosion Chemistry Towards Sustainable Semiconductor Photoelectrochemistry
Authors: Yu Weilai , Moreno-Hernandez Ivan , Papadantonakis Kimberly , Brunschwig Bruce S , Lewis Nathan S
Published: February 2020

Semiconductor photoelectrochemistry (PEC) has great potentials in addressing the issue of worldwide energy shortage by converting solar energy into chemical fuels. However, semiconductor materials immersed in strong aqueous acidic and alkaline electrolytes are prone to (photo)corrosion reactions and display limited stability either at applied bias or under light illumination. Among them, technologically-important III-V semiconductors (InP, GaAs, GaP etc.) with superior photovoltaic performances suffer from such surface corrosion processes. Herein, we systematically investigate the surface corrosion chemistry of these materials directly at the semiconductor/electrolyte interfaces in both strong acid and base. Various dark/light and open-circuit/applied-bias conditions are studied and compared in order to fully reveal the chemical, electrochemical and photoelectrochemical stability of these III-V semiconductors. Techniques including inductively coupled plasma mass spectroscopy (ICP-MS), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and atomic-force microscopy (AFM) are all employed to probe both the physical and chemical changes after their surface corrosion transformations. Combined with considerations of thermodynamic pourbaix diagrams, comprehensive understandings are gained over their diverse (photo)corrosion behaviors at different potentials. Eventually, rational strategies are devised to effectively protect these semiconductors from rapid corrosion while maintaining sustainable PEC performances for solar fuel production.
Characterization of the Electrochemical Detection of NG-Hydroxy-L-Arginine
Authors: Arral Mariah Lynn , Halpern Jeffrey Mark
Published: February 2020

NG-Hydroxy-L-arginine (NOHA) is a suspected biomarker in breast cancer due to its involvement in the L-arginine metabolism [1]. Previous research in human breast cancer cells has shown that NOHA, a potent arginase inhibitor, has an antiproliferative and apoptotic actions on the arginase-expressing cells [1]. NOHA is a stable intermediate product in the production of NO from the consumption of L-arginine [1]. L-ornithine and L-citrulline are also involved in the metabolism of L-arginine through the urea cycle; the urea cycle has been known to be disrupted in cancer patients [1]. Early detection of cancer is important for rapid treatment options to be available [2]. Electrochemical detection is an established, cost-effective method that has potential to detect the onset of cancer because of its ability to successfully detect low levels of analyte concentrations. Before a robust biosensor sensor can be made the characterization of the electrochemical detection of NOHA needs to be done.

Electrochemical activity of NOHA was investigated with cyclic voltammetry and differential pulse voltammetry. NOHA was found to have an oxidation and reduction peak at 355 mV and 188 mV vs. Ag/AgCl respectively. In cyclic voltammetric measurements a scan rate of 50 mVs-1 was used over the applied potential of -0.2 to 0.6 V vs Ag/AgCl. Triplicate data was obtained for serial dilutions of NOHA in two different buffers; Phosphate Buffer Saline solution pH 7.3 (PBS) and 100uM L-Ornithine, 10uM L-Citrulline, and 100uM L-Arginine in PBS (LOCA). The electrochemical detection of NOHA in a LOCA solution was done to understand the effect of a urea cycle metabolite mixture on electrode fowling and sensitivity. A shift in oxidation peak voltage was found for the LOCA solution by 5 mV to 360 mV. The sensitivity of the NOHA in PBS and LOCA solutions were found to be 5.4 nA/uM and 4.8 nA/uM respectively. In addition to our multiple data points to discuss sensitivity and reproducibility in the detection of NOHA, we will report kinetic information including the number of electrons transferred and diffusivity. We will also discuss our progress to decrease the limit-of-detection of NOHA in an effort to make a more sensitive bioanalyte sensor.

[1] R. Singh, S. Pervin, A. Karimi, S. Cederbaum, and G. Chaudhuri, “Arginase activity in human breast cancer cell lines: Nω-hydroxy-L-arginine selectively inhibits cell proliferation and induces apoptosis in MDA-MB-468 cells,” Cancer Res., vol. 60, pp. 3305–3312, (2000)

[2] Zhen Zhang, Robert C. Bast, Jr., Yinhua Yu, Jinong Li, Lori J. Sokoll, Alex J. Rai, Jason M. Rosenzweig, Bonnie Cameron, Young Y. Wang, Xiao-Ying Meng, Andrew Berchuck, Carolien van Haaften-Day, and Neville F. Hacker, Henk W. A. de Bruijn, Ate G. J. van der Zee, Ian J. Jacobs, Eric T. Fung, and D. W. Chan, “Three Biomarkers Identified from Serum Proteomic Analysis for the Detection of Early Stage Ovarian Cancer,” Cancer Res., vol. 64, pp. 5882–5890, (2004)
Photorechargeable Lithium-Ion Battery Electrode Based on Nanocrystals of Anatase TiO2 Combining Energy Conversion and Storage
Authors: Bouteau Gaspard , Sagaidak Iryna , Andriamiadamanana Christian , Nguyen Van Nhien Albert , Sauvage Frédéric
Published: February 2020

The intermittent nature of renewable energies, in particular solar, limits its utilization at demand. Its hybridization with an energy storage reservoir is required, such as an electrochemical battery, to accommodate the balance between grid delivery and consumer demand. Although photovoltaic and batteries are two mature technologies widespread, their combination require electronics management, good assessment on both power dimensioning and ageing of each component, and still require a substantial cost reduction to become competitive with fossil fuels and nuclear.

With long term view, the approach of bridging together the functions of solar conversion and its storage at the molecular level is worth attention for both scientific and technological point of view to pave the way towards photo-rechargeable ion batteries or non-intermittent photovoltaic displays.

Tributsch in the early 80’s demonstrated the possibility to trigger light-induced interfacial ion transfer in mixed electronic/ionic semi-conductors as a result from the charge separation process within the depletion region (1). Up to now, the charges stored in such materials are only confined to the extreme surface (energy density less than 1 Wh/Kg), limited by the Debye length of the space charge layer (2). In this presentation, we will expose our strategy based on anatase TiO2 nanocrystals of 4 nm size assembled in carbon-free electrode to overcome this limitation. Anatase TiO2 with its n-type semi-conducting properties affords the de-insertion of lithium ions under illumination to counterbalance the hole transfer to Ti3+ induced by light. As a result from downsizing to such a nanoscale, surface reactions are promoted with respect to the total volume of particles. Consequently, our results, which will be discussed in-depth, show the possibility to quantitatively photorecharge an electrode of ca. 700 µAh/cm2 capacity in about one hour light exposure (Fig. 1). Both the mechanism and electrode performances will be discussed during this communication.

Figure 1
Design of Combined Scanning Ion Conductance and Atomic Force Microscope for Investigation of Lithium Iron Phosphate
Authors: Enright Tyler , Miyahara Yoichi , Mascaro Aaron , Aiken Connor , Grutter Peter
Published: February 2020

In this study we aim to create a scanning probe measurement device capable of studying the charging characteristics of battery materials. While Scanning Ion Conductance Microscopy (SICM) allows for local probing of conductance characteristics of materials, the poor spatial resolution of this technique limits its use to flat samples. By combining SICM with Atomic Force Microscopy we may overcome these issues and produce spatially resolved ionic conductance measurements in real time. This can be used to coordinate the charging characteristics of lithium iron phosphate battery materials with conformational changes which occur through charging events.
(Invited) Use of ALD by SLRR for the Growth of Layered Bi-Metallic Structures and Alloy Thin Films with Specific Functionality
Authors: Dimitrov Nikolay
Published: February 2020

The ingenious idea of surface limited deposition is among the brightest achievements of Radoslav Adzic. The proposed by his group in the beginning of this century approach of surface limited redox replacement (SLRR) for realization of monolayer thick coatings with catalytically active metals and alloys was used as foundation from others for the development of epitaxial thin film growth methods. Central stage in this direction takes the use of SLRR approach for coating nanoparticles and continuous nanoporous metal layers with ultrathin films of metal, layered bi-metallic structures, and/or alloys with specific functionality. Successful outcome of this coating renders the final product remarkably active and durable catalyst.

In this talk, the direct use of SLRR based protocols for the growth of layered bi-metallic films and alloys with targeted functionality. Specific consideration will be given to co- deposition modes in the systems Ag-Cu and Au-Cu. Factors controlling the quality of the deposited films in terms of morphology, orientation and composition will be comparatively considered. Emphasis will be placed on the thermodynamic miscibility of the metals participating in the deposition process as a factor controlling the final growth outcome in both cases; layered structures with sharp interface boundary in the Ag-Cu system and a single phase alloy in the Au-Cu system upon application of identical growth protocols. Results of electrochemical and SEM / STM characterization of the morphology, structure and/or orientation of the deposited films will be presented and critically discussed. Also, the parting behavior of both components upon anodic polarization scans will be considered in detail and studied with emphasis of post-anodization morphological characteristics of the remaining structures.

The discussion on the catalyst processing component based on coating of above described bi-metallic structures with ultra thin Pt and/or Pd layers will be the conclusion of this talk. It will be garnered by the demonstration of results of activity and durability testing of accordingly developed catalysts for organic fuel oxidation and/or nitrogen electrochemistry. Finally, a glimpse into the future of this rapidly developing field catalyst design at the atomic scale will be also provided.