bluuebunny/crossref_metadata_2025 huggingface dataset:
In-Situ X-ray Absorption Spectroscopy Elucidating Mechanisms in HT-PEM Fuel Cells
Authors: Roth Christina , Kaserer Sebastian , Caldwell Keegan M. , Ramaker David E.
Published: February 2020

The development of phosphoric acid (H3PO4) imbibed polybenzimidazole (PBI) membranes used in so-called high temperature polymer electrolyte membrane fuel cells (HT-PEMFC) has attracted increasing interest lately. Working temperatures of up to 180 °C can be utilized in this approach, which offers several advantages. For instance, it allows the use of less pure and therefore less expensive anode feeds due to a higher tolerance towards impurities, such as CO and H2S, easier water management, simpler cooling systems and enhanced electrode kinetics. However, at these elevated temperatures degradation phenomena may play an important role and phosphate adsorption may poison electrode surfaces. These need to be understood in detail in order to develop both more active as well as more durable materials.

X-ray absorption spectroscopy (XAS) is a technique optimally suited to in-situ studies, as neither UHV conditions, nor long-range order in the sample are required. It can be applied to monitor the geometric structure of the catalytically active nanoparticles directly following particle oxidation and growth during operation. With the delta µ XANES method and complementary theoretical FEFF8 calculations [1] it is possible to identify different adsorbates on small Pt nanoparticles and follow their change in coverage. Phosphoric acid [2], which is used as electrolyte, or impurities in the fuel gases may strongly adsorb and alter the reaction mechanisms.

In this work the coverage of different adsorbates and possible poisons on the anode and cathode side in H3PO4 imbibed PBI HT PEM fuel cells was investigated. At the cathode side, the adsorption of phosphoric acid and OH on the Pt surface was followed at different temperatures and potentials. At the fuel cell anode, the effect of CO and water was analysed.

1 Teliska M., O’Grady W. E., Ramaker D. E., J. Phys. Chem. B,
108, 2333 (2004); 109, 8076 (2005).

2 Zelenay P., Scharifker B. R., Bockris J.O´M., J. Electrochem. Soc.,
133, 2262 (1986).
Universal Activity Volcano for 2e- and 4e- Reduction of Oxygen on Metal Surfaces
Authors: Viswanathan Venkatasubramanian , Hansen Heine , Nørskov Jens
Published: February 2020

Oxygen reduction reaction (ORR) has been a subject of major interest in electrochemistry owing to its technological and scientific importance. The fundamental understanding of this reaction has been largely based on the surface science approach to electrocatalysis.[1] The surface science approach has allowed the bridging of theory and experiment by enabling direct theoretical investigations of the reaction mechanism of oxygen reduction reaction on model systems.

In this talk, we will address the issue of 2e− versus 4e− reduction of oxygen on metal surfaces. Using a detailed thermodynamic analysis based on density functional theory calculations, we show that to a first approximation an activity descriptor, ΔGOH*, the free energy of adsorbed OH*, can be used to describe trends for the 2e− and 4e− reduction of oxygen. We demonstrate the existence of a universal activity volcano shown in the Figure and find quite a remarkable agreement between the predictions of the model and experimental results spanning nearly 30 years.[2-4]

References

[1] Fuel Cell Catalysis: A Surface Science Approach, Marc Koper and Andrzej Wieckowski, (2009)

[2] V. Viswanathan, H. A. Hansen, J. Rossmeisl, and J. K. Nørskov, ACS Cat., (2012) 2, 1654-1660.

[3] V. Viswanathan, H. A. Hansen, J. Rossmeisl, and J. K. Nørskov, J. Phys. Chem. Lett., (2012) 3, 2948-2951.

[4] H. A. Hansen, V. Viswanathan and J. K. Nørskov, (submitted).

Fig 1: Activity volcanoes for the 2e− and 4e− reduction of oxygen are shown in red and blue respectively. The source of the experimental data for the 2e− and 4e− reduction of oxygen are listed in ref. [3]. The experimental value of the limiting potential, UL, is determined by the half-wave potentials for the 4e− reduction and by the onset of ring current for the 2e− reduction. The activity of (111) and (100) surfaces has been plotted in circles and squares, respectively.
Understanding the Oxygen Reduction Reaction on a Y/Pt(111) Single Crystal
Authors: Ulrikkeholm Elisabeth Therese , Johansson Tobias Peter , Malacrida Paolo , Vej-Hansen Ulrik Grønbjerg , Hernandez-Fernandez Patricia , Friebel Daniel , Nilsson Anders , Rossmeisl Jan , Stephens Ifan Erfyl Lester , Chorkendorff Ib
Published: February 2020

Polymer electrolyte membrane fuel cells (PEMFC) hold promise as a zero-emission source of power, particularly suitable for automotive vehicles. However, the high loading of Pt required to catalyse the oxygen reduction reaction (ORR) at the PEMFC cathode, prevents the commercialisation of this technology. Improving the activity of Pt by alloying it with other metals could decrease the loading of Pt. An earlier theoretical study conducted at our laboratory identified PtxY as an active and stable catalyst for oxygen reduction. Experiments conducted on sputter-cleaned polycrystalline Pt3Y confirmed that it showed exceptional activity for the ORR [1]. Later studies also revealed that Pt5Y, prepared in the same manner also showed similar high activity, as shown in Figure (a) below. However, our X-ray photoelectron spectroscopy measurements revealed that the structure formed under reaction conditions was significantly different from our initial expectations.

In order to understand this phenomenon, we investigated a Y/Pt(111) single crystal, formed by depositing large amounts of Y om Pt(111) under ultra-high vacuum (UHV) conditions and annealing to high temperatures. We subsequently characterised the surface using electrochemical measurements, low energy electron diffraction, ion scattering spectroscopy, angle resolved X-ray photoelectron spectroscopy, temperature programmed desorption of CO, and synchrotron based X-ray absorption spectroscopy and surface sensitive X-ray diffraction. These measurements were supported by DFT calculations. From the experimental investigations of the crystal structure, it could be concluded that we have obtained a Pt5Y structure with a 5.5 % compressive strain compared to Pt. Electrochemical measurements show that the activity approximates that of sputter-cleaned Pt3Y, as shown in Figure A. Since there is no Y in the first few atomic layers, we attribute the high activity to the compressive strain exerted onto the surface by the alloy bulk.

[1] J. Greeley, I.E.L. Stephens, A.S. Bondarenko, T.P. Johansson, H.A. Hansen, T.F. Jaramillo, J. Rossmeisl, I. Chorkendorff, J.K. Nørskov, Nature Chemistry, 1 (2009) 552-556.
Electron Transfer in One- and Zero-Dimensional Nanooptofluidic Devices
Authors: Bohn Paul W. , Ma Chaoxiong , Zaino Lawrence P. , Wichert William , Contento Nicholas M.
Published: February 2020

Working in the same hallway as Prof. Wieckowski and his students for 22 years taught us to appreciate the beauty of heterogeneous electron transfer. We are now pursuing that appreciation through coupled electron transfer and spectroscopic probing of processes in zero- and one-dimensional nanostructures.

One-dimensional architectures are explored in two formats: (1) a horizontal geometry in which a small number of nanochannels are arrayed at the top surface of a fluidic device so that optical spectroscopy can be employed to augment studies of electrochemistry at embedded planar electrodes; and (2) vertically-oriented nanopores supporting embedded annular nanoband electrodes (EANEs) in massively parallel high-density arrays. Because transport and electron transfer are intimately coupled, high efficiency (unit efficiency in many cases) electrochemical conversions can be achieved in many structures, and the horizontal geometry allows detailed measurements of the spatiotemporal distributions of electrochemical products for comparison with finite-element modeling.

Zero-dimensional architectures are also being studied in two formats: (1) arrays of nanoconfined recessed ring-disk electrodes (RRDEs), in which redox cycling can be carried out at very high efficiency; and (2) electrochemically-active zero-mode waveguides (ZMWs), in which strongly confined optical fields can be coupled to single molecule electron transfer events in order to study the dynamics of single enzyme molecules and single redox-active organic chromophores. Nanoscale separation in RRDE arrays allows ultra-efficient coupling of counterpoised electron transfer processes at the bottom disk and upper ring electrodes in an attoliter-volume nanopore, processes that can be exploited for improving both sensitivity and selectivity in electroanalysis. In the other geometry, the Au optical cladding layer of a ZMW is used as the working electrode in order to couple the local potential to the fluorescence dynamics of molecules exhibiting large changes in emission quantum efficiency with redox state. These experiments allow the distributions of single molecule E
eq values and other details of electron transfer reactions to be measured on a single molecule basis.
Sonoelectrochemistry: Modeling Acoustic Energy in a Thin Layer System
Authors: Landgren Jeffrey K , Null Emily M , Duda Chester G , Strohmer Gerhard , Leddy Johna
Published: February 2020

Recent experiments in thin layer sonoelectrochemistry demonstrate that sonication increases the rates of electrocatalysis. Heterogeneous electron transfer rates increase substantially upon ultrasound irradiation1. A model is developed to understand catalytic effects observed when sound waves are applied in a thin layer electrochemical cell.

The cell consists of a hollow Teflon cylinder with a transducer as the base seen in Figure 1. A three electrode system is used with the electrodes spaced equally apart and parallel to the cylinder base. The cylinder is filled with a redox probe and electrolyte solution such that a meniscus forms at the top. The transducer propagates sound waves through the solution (i.e., sonication). A comparison of cyclic voltammograms before, during, and after sonication reveals enhancement effects from the sound waves. For redox probes with slow kinetics, sonication simultaneously increases currents and appears to shift the reaction to more reversible. Data indicate that a combination of the height and shape of the meniscus play a vital role in this enhancement effect.

Numerical analysis is used in conjunction with partial differential equations to develop the model. It takes into account the shape and height of the meniscus as well as the pressure, density, elasticity, mass, and surface tension of the fluid near the meniscus. The model then reveals the standing waves of the system. Standing waves occur in a stationary medium when waves are traveling in opposite directions and cause interference with one another. In general, if this scenario occurs with waves of approximately the same amplitude there is no net change in energy, another indication that the height of the meniscus is relevant.

This model is important for prediction of behavior of the sound waves before and after they contact the top boundary and the role of the meniscus convexity. This will lead to advances in understanding the experimental system for applications in electrocatalysis.

Duda, C. G. Thin Layer Sonoelectrochemistry. Ph.D. thesis, University of Iowa. 2012.

2. Leddy, J.; Duda, C.G.; and Leddy, W.J. provisional patent application, 2013.
New Insights into the Formic Acid Oxidation Mechanism on Platinum Electrodes
Authors: Herrero Enrique , Perales Juan V. , Feliu Juan
Published: February 2020

In the formic acid oxidation reaction only two electrons are exchanged. Despite the apparent simplicity of this reaction, the oxidation mechanism is still a subject of debate. The major issue is the role of formic acid, solution formate and adsorbed formate in the oxidation mechanism. In order to shed light into this issue, formic acid oxidation on platinum single crystal electrodes has been studied to determine the effects of pH and specific anion adsorption in the oxidation mechanism. It has been found that the solution pH has an important effect in the oxidation currents. As has been already observed for polycrystalline electrodes [1], currents are proportional to the solution pH. Thus, it can be proposed that the active species in the oxidation mechanism is formate. On the other hand, the specific adsorption of sulfate on the Pt(111) electrode has a catalytic effect on the oxidation since the onset potential is displaced towards more negative values. This unexpected result indicates that the adsorbed anions have an important role in the oxidation mechanism as DFT calculations suggest [2]. In order to get further insight into the oxidation mechanism, activation energies have been calculated, both for the route through the active intermediate and for the route through CO. The activation energy of the process diminishes in the presence of adsorbed sulfate, which confirms the active participation of the adsorbed anion in the oxidation mechanism. Using previous data obtained with fast voltammetry [3], an oxidation mechanism is proposed for the direct route. In this mechanism, the oxidation through the active intermediate route requires an adsorbed anion (formate or sulfate) and a free platinum site where a solution formate species can bond. The currents calculated with this mechanism are compared with the experimental currents. An excellent agreement is found between both results, which supports the validity of the proposed oxidation mechanism.

References

1. Joo J, Uchida T, Cuesta A, Koper MTM, Osawa M (2013) J Am Chem Soc 135:9991-9994

2. Wang H-F, Liu Z-P (2009) J Phys Chem C 113:17502-17508

3. Grozovski V, Vidal-Iglesias FJ, Herrero E, Feliu JM (2011) ChemPhysChem 12:1641-1644
Facet-Controlled Metal Alloy Electrocatalysts for Oxygen Reduction Reaction
Authors: Yang Hong
Published: February 2020

Recent advancement of low-temperature proton-exchange membrane (PEM) fuel cell technology can be attributed in part to the rapid development of electrocatalysts for reduction of oxygen. Such electrocatalysts can now be prepared with very high level of precision in size, shape and composition to meet the increasingly stringent performance targets in activity and durability [1]. The new synthetic methods are based predominately on the solution phase approach where the control of reaction kinetics can be more precise than that for the impregnation method [2].

In this talk, I will present the recent progress on the design and synthesis of metal alloy nanostructures. I will discuss the approach to the preparation of facet-controlled Pt alloy nanoparticles based on the gas reducing agent in liquid solution (GRAILS) method [3-4] and how this method is used in the development of structurally tuneable electrocatalysts for reduction of oxygen. A range of plutonic shapes including {111} faceted octahedron, icosahedron and twin defect-regulated morphologies can now be made (see the TEM images). I will illustrate the relationship between size, composition, structure (including surface strain) and catalytic property (activity and stability) of these bimetallic and multimetallic nanostructured catalysts for oxygen reduction reaction (ORR) and present the likely venues for the scaled-up production.

References:

(1) Peng, Z. M.; Yang, H. Nano Today, 2009, 4, 143-164; Wu, J. B.; Yang, H. Acc. Chem. Res., 2013, 46, 1848-1857.

(2) You, H. J.; Yang, S. C.; Ding, B. J.; Yang, H. Chem. Soc. Rev., 2013, 42, 2880-2904.

(3) Wu, J. B.; Qi, L.; You, H. J.; Gross, A. Li, J. Yang, H. J. Am. Chem. Soc., 2012, 134, 11880-11883.

(4) Wu, J. B.; Gross, A.; Yang, H. Nano Lett.,
2011, 11, 798-802.
Probing the Active Site Chemistry of Supported Gold Catalysts with Charged Au25

q
Nanoclusters (q = -1, 0, +1)
Authors: Kauffman Douglas R. , Alfonso Dominic , Matranga Christopher , Deng Xingyi , Ohodnicki Paul , Siva Rajan , Jin Rongchao
Published: February 2020

Charged Aun+/− sites are hypothesized as key reaction centers in gold catalysis, but their charge state and mechanistic roles remain controversial. Two examples include CO2 reduction and CO oxidation. Converting CO2 into value-added products is critical for green-house gas mitigation and renewable fuels discovery, and oxidizing CO in the presence of water is central to the industrially important water gas shift reaction (WGS: CO + H2O → CO2 + H2). Debate surrounds the charge state of Au active sites, and variously charged Aun+/0/− species and/or the catalyst-support have all been proposed as reaction centers for CO oxidation and CO2 reduction. We used differently charged Au25

q
clusters (q = −1, 0, +1) to precisely identify the role of active site charges in heterogeneous gold catalysis. Au25

q
are unique because they have three stable charge states, their crystal structure has been solved, and their small size (~1nm) allows computational modeling of realistic cluster-adsorbate systems. In this regard, Au25

q
can serve as well-defined active sites for probing the chemistry of charged catalyst species. Experimental studies and density functional theory identified a relationship between the active site charge, the stability of adsorbed reactants or products and the reaction rate. We found charge-dependent electrocatalytic activity for CO2 reduction, CO oxidation and O2 reduction reactions in aqueous media. Anionic Au25‾ promoted CO2 reduction by stabilizing CO2 + H+ coadsorption. Cationic Au25
+ promoted CO oxidation by stabilizing CO + OH− coadsorption. Finally, stronger product adsorption at Au25
+ inhibited O2 reduction. These results provide insight into the role of charged active sites and should help guide future catalyst design.
A Temperature-Controlled Microwell Platform for Electrochemical Melting Analyses
Authors: Shen Zuliang , Sintim Herman O. , Semancik Steve
Published: February 2020

We have designed and fabricated a miniature device for proof-of-concept studies on biomolecular interactions using electrochemical melting analysis. A collection of temperature controlled three-electrode platforms was built on a 100-mm glass wafer, and it includes a total of eight separate probe sites. Each site consists of one 200 nm thick platinum (Pt) heater, one 200 nm gold (Au) electrode and two 200 nm Pt electrodes, as well as a 10 µL polydimethylsiloxane (PDMS) well, all used for probing electrochemical signals as a function of sample temperature. Our Pt heaters have the ability to control sample solution temperatures in the microwell from 4 °C to 120 °C. Heaters were fabricated with different geometries (width and shape) in order to select the best candidate for future device fabrication. Electrochemical melting analysis has been performed by detecting signals derived from changes in methylene blue (MB)-labeled DNA that occur during the heating process. The MB-labeled single strand(ss) DNA was added to hybridize with its matched thiolated ssDNA on Au electrode surface to form duplexes. Electron-transfer(eT) was monitored using square wave voltammetry (SWV) from the beginning of a thermal cycling process. During the heating process the eT was limited significantly when the heater temperature reached the duplex melting temperature. The dehybridized MB-labeled ssDNA left the Au electrode surface causing a current decrease. As a result, a current vs. temperature melting curve was obtained that allowed us to determine the sample DNA melting temperature. The rapid heating capability provided by the Pt heater allows the electrochemical melting measurements to be completed in 20-30 minutes, and that is significantly faster than the typical time for optical melting methods. Figure 1 illustrates the wired microsystem used in the DNA experiment, and includes an enlargement showing the configuration of the miniature electrodes and heater. We plan to build the described probes into a 3x3 array-based microchip for demonstrating the potential for high throughput DNA melting analyses to study biomolecular binding stability.
The Expression and Electroochemical Characterization of Fructose Dehydrogenase
Authors: Kawai Shota , Kitazumi Yuki , Shirai Osamu , Kano Kenji
Published: February 2020

Redox enzymes and proteins are related to the many vital processes, such as tricarboxylic cycle and respiratory chain. There are only a limited number of redox enzymes and proteins that enable to couple enzyme reaction and electrode reaction without any mediators. In other words, they can transfer the electron to (or from) electrodes directly. This reaction is called direct electron transfer (DET)-type bioelectrocatalysis reaction. DET reaction has received considerable attention for construction of electrochemical applications, such as biosensors and biofuel cells. There must be several factors governing the DET reaction, but the details have not yet clearly elucidated.

D-Fructose dehydrogenase (FDH; EC 1.1.99.11) from Gluconobacter japonicus NCBR 3260 is a heterotrimeric membrane-bound enzyme. Subunits I and II have covalently bound flavin adenine dinucleotide (FAD) and three heme C moieties, respectively. FDH shows strict substrate specificity to D-fructose and is used in diagnosis and food analysis. FDH is one of the DET-type enzymes. FDH has high DET activity. DET reaction of FDH occurs at a large variety of electrodes. The FAD in subunit I is the catalytic site to accept electrons form the substrate, and the electrons are transferred to the electrode through the heme C in subunit II.

For the first step to explore the mechanisms of the DET reaction of FDH, we sequenced the genes encoding each subunit of the FDH complex from G. japonicus NBRC3260 and constructed an expression system to highly produce FDH in a G. oxydans strain. We also constructed derivatives modified in subunit I/III subcomplex (ΔcFDH) lacking of the heme C subunit. The recombinant FDH reacts with electrode directly. However, ΔcFDH catalyzes the oxidation of D-fructose with several artificial electron acceptors, but loses the DET ability. The formal potentials (E˚') of the three heme C moieties of FDH have been determined to be –10 ± 4, 60 ± 8 and 150 ± 4 mV (vs. Ag|AgCl|sat. KCl) at pH 5.0, while the onset potential of FDH-catalyzed DET-type bioelectrocatalytic wave is –100 mV. Judging from these results, we conclude that FDH communicates electrochemically with electrodes via the heme C.
Enzyme Cascade for Catalyzing Sucrose Oxidation in a Biofuel Cell
Authors: Hickey David P , Giroud Fabien , Schmidtke David W. , Glatzhofer Daniel T. , Minteer Shelley D.
Published: February 2020

Biofuel cells provide a safe and renewable means of powering small electronic devices. We have recently demonstrated a bioanode that is capable of extracting four electrons from a single molecule of sucrose by way of a three-enzyme cascade. Invertase, fructose dehydrogenase and glucose oxidase are immobilized in a ferrocene-modified linear poly(ethylenimine) (LPEI) hydrogel onto the surface of a carbon electrode. Fuel sources are generated in the polymer film by (1) hydrolyzing sucrose into fructose and glucose, and then (2) electroenzymatically oxidizing fructose and glucose to produce a current response. A previously unreported synergistic effect is observed between glucose oxidase and fructose dehydrogenase that results in a current response that is considerably higher than expected. The newly described enzyme cascade generated 302 ± 57 μA/cm2 at 25 oC and 602 ± 62 μA/cm2 at 37 oC and when poised against an air breathing platinum cathode in a biofuel cell, the multienzyme-containing film generated 42 ± 15 μW/cm2 at 172 mV with a maximum current density of 344 ± 25 μA/cm2 in 100 mmol/L sucrose at 25 oC.
Investigating the Role of Orientation of PQQ-Dependent Dehydrogenases on Electrochemical Performance of a Bioanode
Authors: Minteer Shelley D. , Xu Shuai
Published: February 2020

PQQ-dependent multi-heme containing aldehyde dehydrogenase (PQQ-AlDH) has been previously demonstrated to be capable of performing direct electron transfer (DET). However, theory predicts that the rate of direct bioelectrocatalysis for complex multi-subunit proteins such as PQQ-AlDH is closely related to the proximity and orientation of the enzymes toward the electrode surface, which determines the electron tunneling distances and the current density. In order to investigate the impact of enzyme orientation on the catalysis rate, we immobilized PQQ-AlDH via a site specific immobilization technique to form a monolayer of biocatalysts with a uniform orientation on a gold electrode. Six recombinant PQQ-AlDHs were employed, where the enzymes had been labeled with six-histidine tags (His-tag) at the N- or C-terminus of each of the three subunits. These His-tags were utilized as linking sites to perform site specific isotropic immobilization of PQQ-AlDHs. Results show that the orientation of PQQ-AlDHs can affect direct biocatalysis rate greatly by varying the electron tunneling distances. The favorable orientation with a minimal heme c electron transfer distance showed a current density that is 6.6-fold higher than the electrode with the orientation closest to the active site of the enzyme, while the unfavorable attachment to a non-electroactive subunit showed no bioelectrocatalytic current.
Enzyme-Metal Oxide Composite As Catalysts for Enzymatic Oxygen Reduction
Authors: Zhou Yan , Umasankar Yogeswaran , Ramasamy Ramaraja P
Published: February 2020

Laccase is widely used in enzymatic fuel cell as cathode catalyst. There has been a lot of work using carbon nanostructures as immobilization support for laccase to demonstrate bio-electrocatalytic activity towards oxygen reduction reaction.1,2,3 The metal oxide nanoparticles studied were TiO2, ZnO and SnO2. The immobilization of laccase on these metal oxide nanoparticles were achieved. The coupling agent was silane and the crosslinking agents were dithiobis[succinimidyl propionate] (DSP), 1,5-Difluoro-2,4-dinitrobenzene (DFDNB) and succinimidyl iodoacetate (SIA). Attenuated total resonance fourier transform infrared spectroscopy (ATR-FTIR) was performed on the nanocomposites and the results confirmed that laccase was attached on to the metal oxide nanoparticles through the molecular crosslinkers. The resulting laccase-metal oxide nanocomposites were deposited onto screen printed carbon electrode and tested for oxygen reduction electro-catalysis in an electrochemical cell using 0.2 M sodium acetate buffer as the electrolyte. The composite modified electrode showed an open circuit potential of 0.61V vs Ag/AgCl. Cyclic voltammograms showed a clear difference between unmodified and laccase modified TiO2 in the oxygen reduction region with an onset potential of 0.57 V. In comparison the laccase physisorbed onto TiO2without the molecular crosslinkers showed no obvious electrocatalytic activity. The work adds significant value to the biofuel cell community as it introduces a new class of material as enzymatic support for bio-electrochemical reactions.

Fig. 1: Schematic representation of Laccase immobilized onto metal oxide nanoparticles through molecular crosslinkers.

Fig. 2
: Cyclic voltammetry of crosslinked and physisorbed laccase on TiO2 nanoparticle electrodes in O2 saturated sodium acetate buffer electrolyte.

Acknowledgements:

The authors would like to thank University of Georgia for providing seed funds to carry out this research.

References:

1. Ramasamy, R. P.; Luckarift, H. R.; ivnitski, D. M.; Atanassov, P. B.; Johnson, G. R., High electrocatalytic activity of tethered multicopper oxidase- carbon nanotube conjugates. Chemical Communications
2010, 46 (33), 5977-6188.

2. Naga S. Parimi; Yogeswaran Umasankar; Plamen Atanassov; Ramasamy, R. P., Kinetic and Mechanistic Parameters of Laccase Catalyzed Direct Electrochemical Oxygen Reduction Reaction. ACS Catalysis
2012, 2, 38-44.

3. Umasankar, Y.; Brooks, D. B.; B., B.; Zhou, Z.; Ramasamy, R. P., Three dimensional carbon nanosheets as novel catalyst support for enzymatic bioelectrodes. Advanced Energy Materials
2013 (accepted paper).
From Twitching to Nanowires Toward a Holistic Understanding of Motility Structures and Extracellular Electron Transfer in Shewanella Oneidensis
Authors: Ista Linnea K , Cornejo Jose A , Babanova Sofia , Schuler Andrew J , Atanassov Plamen
Published: February 2020

Extracellular electron transfer (EET) in dissimilatory metal reducing bacteria, such as Shewanella oneidensis and Geobacter spp., is thought to be mediated by nanowires composed of type IV pili encased in membrane-bound cytochromes. 1,2 Type IV pili are also required for EET competent biofilm formation in these organisms. 3 Although the necessity for the involvement of T4P in biofilm formation has been established, surface motility has not been observed in these organisms, 3,4 whereas it is required in other g-proteobacteria. 5

Using self-assembled monolayers (SAMs) of ω-substituted alkanethiolates on gold, we have recently demonstrated that twitching motility occurs in Shewanella oneidensis MR1 and that it is responsive to the chemistry of the substratum. In addition, using deletion mutants, we are eludicating the roles of the two classes of T4P present (PilA and Msh) in S. oneidensis in surface motility and their significance in biofilm formation. (Figure 1) We have found that while both types of pili are required for wild-type early biofilm formation, either pilus on its own is sufficient for twitching surface motility. We are also exploring the formation of nanowires and subsequent EET for this set of mutants.

In this presentation, we discuss the known and possible interrelationships between surface motility, nanowire production, biofilm formation and EET, including mechanisms for their molecular coordination. We predict that manipulation of engineerable parameters can modulate these cellular activities for better design of microbial biofuel cells.

References

(1) El-Naggar, M. Y.; Finkel, S. E. Scientist
2013, 27, 38.

(2) Lovley, D. R. Energy & Environmental Science
2011, 4, 4896.

(3) Saville, R. M.; Dieckmann, N.; Spormann, A. M. FEMS Microbiol Lett
2010, 308, 76.

(4)Thormann, K. M.; Saville, R. M.; Shukla, S.; Pelletier, D. A.; Spormann, A. M. J Bacteriol
2004, 186, 8096.

(5)O'Toole, G. A.; Kolter, R. Mol Microbiol
1998, 30, 295.

Acknowledgements

This work was supported through ARO grant W911NF-12-1-0208.
Sub-1 V Electrolyte-Gated Polymer Transistors with Ionic Liquid Electrolyte and High-Surface Area Carbon Gate Electrode
Authors: Soavi Francesca , Sayago Jonathan , Cicoira Fabio , Santato Clara
Published: February 2020

Electrolyte-gated (EG) transistors permit to achieve current modulations of several orders of magnitude at relatively modest gate voltages, by exploiting the exceptionally high capacitance of electrical double layer forming at the electrolyte/transistor channel interface. Different doping mechanisms have been proposed to explain the gating process in EG transistors. For organic polymers, the common doping mechanism is faradic, depends on the channel electrical potential and the doping charge is about two orders of magnitude larger than for electrostatically doped non-porous materials. Moreover, organic channel and electrolyte have to be selected taking into account that channel modulation has to be performed by applying gate-source voltages (Vgs) which are compatible with the electrochemical stability window of the electrolyte. Ionic liquid electrolytes, for their exceptionally high chemical and electrochemical stability and good conductivity at room temperature are of interest as electrolyte gating media in EG transistor. The faradic nature of the polymer channel doping also requires the use of gate electrode materials that are non-limiting in terms of their capability to supply the charge required for channel modulation within the electrochemical stability window of the electrolyte.

We targeted the use of high surface area carbons as gate electrode materials because of their capability to electrostatically supply the charge required to dope organic polymer transistor channels, within narrow electrode potential excursion.

Here, we report on a new generation of low voltage EG transistors making use of a low-cost, high surface area gate electrode, an organic electronic polymer, like MEH-PPV (poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene), as the channel material and ionic liquid, like [EMIM][TFSI] (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide), as the electrolyte gating medium. Using such configuration, is it possible to apply Vgs biases lower than 1.0 V to achieve effective channel modulations (ON/OFF ratio larger than 103) and hole mobility of about 10-3 cm2V-1s-1.

Acknowledgement

This work was financially supported by NSERC (Discovery grants, CS and FC) and FQRNT (Nouveau Chercheur, CS). JS acknowledges financial support by CONACYT.

References

[1] J. Sayago, F. Soavi, F. Cicoira, C. Santato, Adv. Mater., submitted.
Nature of Proton Transport in Membranes for Fuel Cell Applications
Authors: Choe Yoong-Kee
Published: February 2020

Development of polymer electrolyte fuel cells (PEFCs) is actively ongoing nowadays because of their potential applications in portable and stationary systems. Polymer electrolyte membranes (PEMs) are important component of PEFC, whose role is to facilitate proton conduction and to separate the anode and the cathode. In the present contribution, we report results of first-principles molecular dynamics (FPMD) simulations carried out for various types of hydrocarbon membranes for fuel cell applications with an emphasis on how molecular structure of membranes affect the transport property of proton. Especially, we applied FPMD to sulfonated poly phenoxy benzoyl phenylene (SPPBP) and sulfonated (arylene ether ether nitrile) (m-SPAEEN). The results of FPMD show that various hydrophilic functional groups, such as the carbonyl group, affect the nature of proton transport in the hydrocarbon membranes. Details on the proton transport mechanism are discussed.
Photoluminescence Investigation of Fundamental Charge Transfer Processes in Stable Nitroxyl Radical-Containing Polymers
Authors: Hughes Barbara Katherine , Ferguson Andrew , Braunecker Wade A. , Gennett Thomas
Published: February 2020

The electrochemical redox reactions of stable organic polymer materials with unpaired electrons is a relatively new and exciting area of battery research. Specifically, stable nitroxyl radical-containing polymers have displayed excellent characteristics as the cathode-active material and have presented themselves as low-cost and environmentally friendly alternative to the current Li-ion battery technologies. However, with the advancement of organic-radical battery technology there is a lack of fundamental understanding of the dynamics of charge transfer processes, electronic and ionic, within organic radical-containing polymers. In order to elucidate the mechanisms further, we have conducted an extensive photoluminescence investigation of the polymers in various oxidation states

Since nitroxyl radicals are known fluorescence quenchers, we probed the charge transport in this system by the incorporation of fluorescent perylene markers into the radical-containing polymer matrix. We have investigated the interplay between collisional and static quenching processes using steady-state and time-resolved photoluminescence quenching studies of perylene by TEMPO (2,2,6,6-tetramethylpiperidinyloxyl), radical-containing species. Quenching studies for these model systems, including both free TEMPO monomers and non cross-linked, solution-phase PTMA-nitroxy polymers, (poly(4-methacryloyloxy-2,2,6,6-tetramethylpiperidine-N-oxyl) have allowed us to calculate optimal synthetic parameters for construction of polymer cathode systems. We have determined how such polymer properties as average chain length, spacing between pendant groups, proclivity for polymer folding, and solvent swelling affect both the mechanism of quenching as well as the efficiency of charge transfer. As a function of polymer length, we observe a change in quenching mechanism, while the density of radical moieties has significant affects on quenching/charge transfer efficiency. The quenching sphere of action and thus the optimal distance between radical moieties and fluorophores for the most efficient charge transfer has also been determined and will be discussed at length.
Polyoxometalates As Versatile Components for Hybrid Electrode and Electrolyte Materials
Authors: Gómez-Romero Pedro
Published: February 2020

Polyoxometalates are inorganic clusters with a unique combination of physical-chemical properties, including a rich redox chemistry, electron and proton-transfer. Their zero-dimensional nature and small size set them apart from conventional electrode materials. Yet, some of their characteristic properties have made them useful components in electrode materials (i.e. electroactivity), whereas others represent opportunities for their application as electrolytes (i.e. solid acids, proton conduction). In this conference we will present examples of both types of applications for a variety of devices, from fuel cells to supercapacitors and discuss further potential uses of these clusters.
Improving Electrolyte Characterization Methods/Tools: What the Data Really Means
Authors: Henderson Wesley A. , Seo Daniel M. , Han Sang-Don , Allen Joshua L , Yun Sung-Hyun , Daubert James S. , Borodin Oleg
Published: February 2020

Electrolyte formulations are frequently perceived to be a linchpin for enabling the use of new battery electrode chemistries. The electrolyte serves as the medium for the transport of active ions to and from the electrodes as the electrodes undergo redox reactions, but the molecular-level interactions which govern solvent-ion (solvation) and ion-ion (ionic association) interactions remain poorly understood. New electrolyte characterization methods/tools, or improvements for existing evaluation methods, are needed to obtain detailed information about such interactions...and how they, in turn, are determinants for bulk electrolyte properties. The interpretation of the data from many electrolyte characterization methods, however, is often flawed due to incorrect assumption and/or limitations of the techniques. This can result in a gross misunderstanding of the actually solution structure which exists for electrolyte formulations of interest thus leading researcher astray. This talk will thus explore the challenges associated with the use of solvent polarization parameters (e.g., dielectric constant (ε), Gutmann donor number (DN), etc.) and Raman spectroscopy for obtaining solvation numbers and ionic association interactions. New electrolyte characterization tools will be demonstrated and examples will be provided which explore how the conventional wisdom regarding electrolyte properties and behavior is often inaccurate.

ACKNOWLEDGEMENT

The authors wish to express their gratitude to the U.S. Department of Energy (DOE) Office of Basic Energy Science-Division of Materials Sciences and Engineering which fully supported the experimental research under Award DE-SC0002169.
Standard Potential of Ion-Sensors
Authors: Lewenstam Andrzej
Published: February 2020

The potentiometric measurement of ions belongs to the most frequently applied electroanalytical methods. It is owing to the need of routine determinations of the main blood electrolytes (Na+, K+, Cl-, and HCO3
-), pH and PCO2. Growing demand for improved reliability of the sensors response and manageable response time is associated with their fundamental properties characterized by sensitivity, selectivity, detection limit and standard potential [1]. The latter should be preferably stable over certain time, and in this way not to be a source of analytical error.

The interpretation of the standard (resp. formal) potential is often ignored owing to the application of internal electrode solution, i.e. symmetric ion-sensor systems. However, the present wave in ion-sensor technology typically utilizes all-solid-state sensor architecture, in which the internal liquid contact is substituted by a solid contact, with resulting assymetricion-sensors. This type of contact was first used for ion-selective electrodes with a solid-state (crystalline) membrane, and made by platinum, silver, carbon. More recently, conducting polymer as a solid-contact material for the ion-selective electrodes with plastic membranes was proposed [2]. Very recently the application of nanostructured materials was offered [3]. Beyond any doubt, the understanding of the reason(s) of standard potential stability of the asymmetric solid-contact ion-sensors is of a primary importance, but rarely undertaken.

Thermodynamic interpretation the standard potential of the asymmetric all-solid-state ion-selective sensors will be presented. This interpretation is related to the fundamental concepts metallic electrodes and all-solid-state electrodes presented by Trasatti [4] and Buck & Koebel [5], and extended by Lewenstam [6] for the solid contacts made of conducting polymers. The applicability of the interpretation for the whole family of all-solid-state ion-selective sensors will be discussed.

References

[1] A. Lewenstam, Clinical analysis of blood gases and electrolytes by ion-sensitive sensors, in: S. Alegret, A. Merkoci (eds.), Electrochemical Sensor Analysis (Comprehensive Analytical Chemistry vol. 49), Chapter 1, Elsevier, Amsterdam 2007.

[2] A.Cadogan, Z.Gao, A.Lewenstam, A.Ivaska and D.Diamond; Analytical Chemistry, 64 (1992) 2496; A. Lewenstam, in: G. Inzelt, A. Lewenstam, F. Scholz (Eds.), Handbook of Reference Electrodes, Springer, Heidelberg New York Dordrecht London, 2013, pp. 279-288.

[3] G.A. Crespo, S. Macho, F.X Ruis, Anal. Chem. 50 (2008) 1316-1322.

[4] R.P. Buck, V.R. Shepard, Anal. Chem. 46 (1974) 2097-2109; M. Koebel, Anal. Chem.,46 (1974) 1559–1563.

[5] A. De Battisi, S. Trasatti, 79 (1977) 251-258.

[6] A. Lewenstam, J. Bobacka, A. Ivaska, J. Electroanal. Chem., 368 (1994) 23-31.
Traceability of pH Measurements
Authors: Camoes Maria Filomena , Spitzer Petra
Published: February 2020

The free acidity of an aqueous solution is usually expressed in terms of its pH, a measure of the hydrogen ions activity. Being the most often measured chemical parameter, pH values are meant to be used either in the assessment of other chemical species or in comparison exercises. The validity of conclusions requires that the values of pH measurements are linked through common references. Measurements are performed in pH meters submitted to prior calibration with reference pH buffers whose pH values have been established against conventionally assigned pH values of primary pH buffer standards. This chain of operations is supported on the quality associated with, namely, buffers, electrodes, procedures, calculations and model assumptions.

An overview will be given on recent fundamental and applied studies addressing these various issues, for the particular case of highly saline waters approaching the complex composition of seawater.
Electrochemical Sensors for Measurement of Glucose in Tiny Volumes of Tear Fluid
Authors: Meyerhoff Mark E. , Cha Kyoung-Ha , Qin Yu , Cohan Bruce C. , Balijepalli Anant , Jensen Gary C.
Published: February 2020

Tear glucose measurements have been suggested as a potential non-invasive alternative to blood glucose monitoring for diabetic patients [1,2]. While previous work has demonstrated a correlation between blood and tear glucose values in humans using complex LC-MS and capillary electrophoresis methods, this correlation has not been thoroughly established and additional clinical studies with a much larger patient population are sorely needed. This requires the availability of a very simple device that can quantitate the levels of glucose in tiny volumes (1 uL or less) of human tear fluid at the point of testing. Further, given the low levels of glucose found in tear fluid (10-300 µM), compared to blood plasma (3-15 mM), this creates a challenge for the conventional electrochemical measurement technologies typically employed for blood glucose measurements.

In preliminary efforts toward achieving this goal, we utilized miniaturized needle type amperometric glucose enzyme electrodes that can be inserted into a microliter glass capillary tube to measure the levels of glucose in tear fluid obtained from anesthetized rabbits and proved that there was a reasonable correlation between blood and tear glucose levels [3,4]. However, the sensors employed in these first studies required 3 µL or more of tear fluid and the capillary tube was used to conveniently sample such volumes.

A more attractive approach for determining glucose in < 1 µL tear volumes from human subjects is to use commercial electrochemical blood glucometer test strips in association with a laboratory quality, high current sensitivity potentiostat. Of many commercial blood glucose test strips evaluated, only one device has been found to be capable of achieving the low detection limits (< 10 µM) required for human tear glucose measurements. Using such strips, calibration data in the range of 0-300 μM glucose yield excellent precision and good selectivity over potential redox species found in tears (e.g., ascorbic and uric acids). Multiple measurements of glucose in tear fluid obtained from normal (non-diabetic) human subjects using commercial strips in conjunction with a laboratory potentiostat yield fasting tear glucose concentrations for non-diabetics within the range of 20-160 µM, similar to the values found by others using more complex LC-MS methods [1]. This glucometer strip based method could greatly facilitate more in depth clinical studies with a large number of patients (both normal and diabetic), to determine definitively whether tear glucose and blood glucose levels correlate well enough to enable routine measurements in tear fluid to supplement blood glucose testing.

References

[1] Lane JD, et al. Curr. Eye Research 31 (2006), 895–901.

[2] Baca JT, et al. Clin. Chem. 53 (2007), 1370-1372.

[3] Yan Q, et al. Anal. Chem. 83 (2011), 8341-8346.

[4] Peng B, et al. Biosens. Bioelectron. (2013) 49, 204-209.
Metal Deposition on Graphene Layers and Electrochemical Measurements at Liquid/Liquid Interface: Preparation of Graphene-Based Metal Nanostructures
Authors: Toth Peter S , Dryfe Robert AW
Published: February 2020

Polarisable liquid/liquid interfaces have been investigated for over 30 years, mainly in the context of ion and electron transfer reactions. Electrical polarisation of the interface between two immiscible electrolyte solutions (ITIES) generates electrochemical potential gradients capable of promoting ion and electron transfer across the molecular boundary. The potential drop across the liquid/liquid boundary is developed over a region of 1 to 10 nm. The nucleation of metallic structures, catalytic activity e.g. hydrogen and oxygen evolution, the assembly of nanoparticles or catalytic nanoparticles have received a great interest in the last years.1-2

Graphene nanomaterials were prepared in two ways: gravity exfoliation from natural graphite in 1,2-dichloroethane (DCE) dispersion and chemical vapor deposition (CVD) on copper foil. Both types of material were assembled at the interface between two immiscible electrolyte solutions. The graphene materials before and after assembly were characterized by Atomic Force Microscopy (AFM) and Raman spectroscopy. The electrochemical reactivity of assembled graphene materials was probed by model redox species at the ITIES.

In situ electrochemical and spontaneous metal deposition of palladium, gold and silver at the interface assembled carbon nanomaterials were studied. The identification and morphology of the deposited metal was determined using electron microscopy. The 2D graphene-based metal nanostructures effects were studied for the model redox species process at the ITIES.

The graphene-metal composites preparation procedure at the ITIES opens an alternative way to prepare catalyst materials. Deeper understanding of the behavior of model redox couples on graphene is of primary importance in the exploitation of this material in catalytic processes, such as of the oxidation of low molecular weight alkanes to liquid fuels.

1. Fermin, D. J.; Ding, Z.; Duong, H. D.; Brevet, P. F.; Girault, H. H., Journal of Physical Chemistry B, 1998, 102, 10334-10341.

2. Dryfe, R. A. W., Physical Chemistry Chemical Physics,
2006, 8, 1869-1883.