bluuebunny/crossref_metadata_2025_split huggingface dataset:
Study of Magnetic Effects on Lanthanide Electrochemistry
Authors: Knoche Krysti L. , Leddy Johna 
Published: February 2020

Lanthanide isotopes are produced during fission of 235U, most of which decay to stable nonradioactive lanthanide elements in a relatively short amount of time1. The lanthanide elements can be difficult to separate from each other in solution because they have extremely similar properties, including masses, ionic radii, oxidation states, and standard potentials2. Present lanthanide detection and separation methods are tedious and time-consuming.
Lanthanides do have different numbers of unpaired 4f electrons, resulting in distinct magnetic properties. Here, Boron-doped diamond (BDD) electrodes are magnetically modified to exploit this difference. Recent data suggests that modification of electrodes with chemically inert magnetic particles enhances current for electrochemical reactions3. The effect scales with the magnetic moment of the redox species and the number of unpaired electrons.
Electrochemically, lanthanide analysis is limited by their standard potentials (in the range of -1.99 and -3.90 V vs NHE4). These potentials fall outside of the potential window of common electrolyte solutions. For example, in aqueous solutions at platinum, the potential window is limited between +1.3 and -0.7 V vs NHE by solvent electrolysis5. Previously, researchers have resorted to mercury drop electrodes or chemically modified carbon paste electrodes to look at lanthanide compounds2. BDD electrodes offer a safer, simpler alternative; the overpotentials for hydrogen and oxygen occur at very extreme potentials on BDD compared to other materials such as glassy carbon, platinum, and gold. This allows for a wider potential window for investigation of lanthanide compounds. Here, nonaqueous lanthanide solutions are investigated at a BDD electrode6.
1. Binnemans, K., Chem Rev
2007, 107 (6), 2592-2614.
2. Schumacher, P. D.; Doyle, J. L.; Schenk, J. O.; Clark, S. B., Rev Anal Chem
2013, 32 (2), 159-171.
3. Lee, G. G. W.; Leddy, J.; Minteer, S. D. Chem Commun
2012, 48 (98), 11972-11974.
4. Cotton, S., Lanthanide and actinide chemistry. Wiley: 2007; Vol. 27.
5. Bard, A. J.; Faulkner, L. R., Electrochemical Methods, Fundamentals, and Applications. 2 ed.; John Wiley & Sons, Inc: New York, 2001.
6. Martin, H. B.; Argoitia, A.; Landau, U.; Anderson, A. B.; Angus, J. C. J Electrochem Soc
1996, 143 (6), L133-L136.
Dissolved Hydrogen Voltammetric Probe and Its Application for Photosynthetic Bacterial Hydrogen Production Rate Evaluation
Authors: Zlatev Roumen , Stoytcheva Margarita , Medina Pablo Alberto Romero , Reyes Ana Luisa , Magnin Jean-Pierre 
Published: February 2020

As known, the dissolved hydrogen undergoes electrochemical oxidation, the mechanism of which depends on the electrolyte pH. In alkaline solutions the OH- participates in the hydrogen oxidation according to the reaction: H+ OH-= H2O+2e-, while in acid solutions the electrochemical oxidation is direct: H2=2H++2e-. In both cases electrolyte acidifying occurs because of the OH- consumption or H+generation, making suitable the application of very acid electrolytes to avoid the sensor characteristics changes caused by a great pH changes over time.
A 3-electrode probe similar to the Clark type oxygen probe construction was proposed, elaborated, and characterized as a dissolved hydrogen sensor. Its analytical characteristics such as LOD, sensitivity, response time, and linear response concentration range were determined as a function of the temperature, membranes materials, the electrolytes composition, and pH. Coulometric controlled electrochemical hydrogen generator was applied for standard solution preparation.
The sensor characterization results are presented and discussed together with the results obtained from its application for the real time determination of the rate of hydrogen production by the varieties B10 and IR3 of the photosynthetic strain Phodobacter Capsulatus.

Acknowledgement. This work was supported by CONACyT Mexico: Research grant No. 152961, CONACYT-SENER “Sustentabilidad Energética” 2010-01.
Enhanced Transport and Electrocatalysis in External Magnetic Field
Authors: Nowicka Anna Maria , Kowalczyk Agata , Donten Mikolaj , Stojek Zbigniew Jan 
Published: February 2020

Recently we have turned to a new material for modification of glassy carbon electrodes: carbon nanocapsules with iron core (C-Fe). The carbon coating plays an important role; it separates the magnetic nanoparticle from the medium, protects it against oxidation and dissolution and adsorbs strongly on GC surface. C-Fe nanocapsules appeared to be a useful surface modifier. We have found that the adsorption of the nanocapsules on the GC electrode surface led to a shift of the reduction voltammetric peak/wave of oxygen by more than 200 mV toward less negative potentials. After applying an external magnetic field in the cell a substantial increase in the reduction current was observed. Similar increase of current was noted for ferroceneacetate anion, a paramagnetic molecule.
The C-Fe nanocapsule layer appeared also to be a good matrix for immobilization of laccase. The presence of laccase on the electrode surface modified with carbon nanocapsules caused an additional significant shift, compared to the C-Fe layer, of the position of the oxygen reduction signal toward positive potentials. The application of an external magnetic field led again to a strong increase in the reduction current. We have characterized the effect in function of the magnetic field intensity, the angle between the electrode surface and the magnetic field direction and the concentration of the substrate.
The application of magnetic field apparently helped to get appropriate orientation of the immobilized laccase at the surface. The high efficiency of electroreduction of oxygen was maintained after removal of the magnets.
The significant enhancement of dioxygen reduction current was compared with the simulations. For this purpose the profile of the magnetic field in the neighborhood of the electrode surface was constructed and the force of interactions of paramagnetic oxygen molecules with magnetic nanoparticles was calculated.
Electrochemical Characterization Reveals Multiple Distinct Electron Transport Pathways in Anode Biofilms of Geobacter Sulfurreducens
Authors: Popat Sudeep , Yoho Rachel , Ajulo Oluyomi , Torres César 
Published: February 2020

Geobacter sulfurreducens has become a model microorganism for anode respiration in the field of microbial electrochemistry. Our group has studied the sigmoidal behavior of the current/potential response of G. sulfurreducens, modeled through the Nernst-Monod relationship. In its current form (Fig. 1), the Nernst-Monod relationship assumes that there is a single limiting redox process, which governs the energy that is gained by G. sulfurreducens from anode respiration.
Fig. 1 shows the Nernst-Monod equation. Here, j is the current produced at the anode potential E, jmax
is the maximum current, n is the number of electrons transferred, F is the Faraday constant, R is the gas constant, T is the temperature, and EKA
is the anode potential that results in j as half of jmax
.
Our previous studies have used the Nernst-Monod relationship to model slow-scan cyclic voltammograms (CV) of G. sulfurreducens grown at -0.4 V vs. Ag/AgCl with n=1, and an EKA
= -0.42 V vs. Ag/AgCl. Our ability to fit the data further corroborated the assumption of a single redox processes controlling the metabolic response of G. sulfurreducens. However, several published studies and our own recent work also suggested that the Nernst-Monod relationship did not always fit the CV data. Thus, we used electrochemical impedance spectroscopy (EIS) as a function of anode potential in a G. sulfurreducens biofilm, with the aim of getting further insight on the electron transport processes for anode respiration. EIS can theoretically allow separating the contribution of various processes governing electron transfer rates, as long as they are separated in their characteristic frequency (i.e. have different time constants).
We have performed EIS analyses, at various anode potentials, on G. sulfurreducens biofilms grown at -0.3 V vs. Ag/AgCl. These have shown the existence of more than one charge transfer process governing its electron transport, each with a different EKA
. This suggests that there are multiple governing redox cofactors in G. sulfurreducens that are used in combination to perform anode respiration. Through chronoamperometry experiments we have also further shown that G. sulfurreducens has the ability to change which cofactors are used depending on the poised anode potential.
We hypothesize that the distinct redox cofactors possibly help G. sulfurreducens respire different forms of iron, whose oxide forms present in nature have different redox potentials. Our results also suggests that the Nernst-Monod relationship needs to be expanded to include the presence of multiple redox cofactors with different EKA
, and these may differ for different anode-respiring bacteria.
Oxygen Reducing Enzymes Encapsulated in Silica Matrix By Chemical Vapor Deposition
Authors: Perry Albert Thomas , Babanova Sofia , Atanassov Plamen 
Published: February 2020

Silica encapsulation is becoming a promising technique used to preserve the activity and prolong the stability of different bacteria, enzymes, and organelles. This allows continued functionality, while ceasing colonial growth in bacteria, and decreasing the catalytic decay in enymes1. This approach was extensively studied and explored in the development of enzymatic and bacterial electrodes for biofuel cell application2,3.
University of New Mexico developed a technique for silica encapsulation - chemical vapor deposition (CVD). This technique relies on the extremely high volatility of the silica precursor (tetramethyl orthosilicate or TMOS), which interacts with water containing solution, carries out a hydrolysis and condensation creating silica gel (Fig. 1). This silica gel matrix is permeable to the electrolyte keeping the biological species hydrated.
In this study, the influence of silica encapsulation on the performance, activity, and stability of three different oxygen reducing enzymes (bilirubin oxidase, laccase and ascorbate oxidase) were evaluated. Ink composites consisting of carbon nanotubes, tetrabutylammonium bromide (TBAB) modified Nafion, 1-pyrenebutanoic acid succinimidyl ester (PBSE) and the enzymes were prepared. The inks were deposited on Rotating Disk Electrode (RDE)4. These electrodes were exposed to TMOS vapors to perform the encapsulation. The time of exposure was varied as a way to control the thickness of the created silica layer. Increased time of exposure leads to increased silica gel thickness and density. This was confirmed by the decrease of the generated current with the increased encapsulation time (Fig. 2). A thicker silicon layer introduces diffusional barrier that causes diffusional losses leading to decreased current production. Therefore the time of TMOS exposure is an important parameter that has to be carefully controlled.

Although a linear dependence of the current recorded during the RDE measurements and the square root of the rotation rate (Fig. 3) was observed we cannot use the Koutecky-Levich equation to determine the number of electrons exchanged during the oxygen reduction reaction. An alternative approach was applied.

References:

1. Bergogne, L., S. Fennouh, S. Guyon, J. Livage, C. Roux, Mol. Cryst. Liq. Cryst. Sci. Technol. Sect. A. Mol. Cryst. Liq. Cryst.
2000, 354, 79–89.
2. Luckarift, H. R., S. R. Sizemore, J. Roy, C. Lau, G. Gupta, P. Atanassov, G. R. Johnson Chem. Commun., 2010, 46, 6048–6050
3. Ivnitski, D., K. Artyuskova, R. A. Rincón, P. Atanassov, H. R. Luckarift, G. R. Johnson .Small
2008, 4 (3), 357–364.
4. Brocato, S., Lau, C., and Atanassov, P. (2012) Mechanistic study of direct electron transfer in bilirubin oxidase, Electrochim. Acta, Elsevier Ltd 61, 44–49.
Rational Design of Redox Mediators for Application to Enzymatic Fuel Cells
Authors: Kavanagh Paul 
Published: February 2020

Enzymatic fuel cells (EFCs) based on mediated electron transfer involve the ‘wiring’ of enzymes at the anode and cathode using redox mediators. The potential difference between the redox mediators used at the anode and cathode can influence the cell voltage and, consequently, the power output of the EFC.1,2
In addition, the potential difference between the redox mediator and the enzyme binding site can influence the rate of electron transfer (as predicted by Marcus theory) and hence, the catalytic turnover at each electrode. Ideally, for maximum power output, the catalytic reactions at each electrode should occur at low overpotentials (to ensure a large cell voltage) with a high catalytic turnover of substrates. Therefore, judicious choice of enzyme and redox mediator combination at the anode and cathode is essential. For example, it has been proposed that, at the anode, the redox potential of an electron mediator should have a value of about 50 mV downhill of the enzyme active site to generate current with minimal loss in cell voltage.3Although, under physiological conditions, the redox potential of the binding site of a wild type enzyme is, for the most part, fixed there is scope to manipulate the electronic character of the redox mediator. Here, we present an approach for the rational design of metal complexes which possess desirable electrochemical characteristics to act as redox mediators for specific enzymes, such as glucose oxidase, in an effort to maximise EFC power output.
1. S. C. Barton, J. Gallaway and P. Atanassov, Chem. Rev., 2004, 104, 4867–4886.
2. P. Kavanagh, D. Leech, Phys.Chem. Chem. Phys., 2013, 15, 4859-4869
2. A. Heller, AIChE J., 2005, 51, 1054–1066.
Photo-Induced Charge Transfer and Spectroscopy Across a Series of Pbttt Model Compounds
Authors: Callahan Rebecca , Springer Michael , Walba David , Rumbles Garry 
Published: February 2020

Organic-based excitonic photovoltaics are a promising low-cost renewable energy source. New solution-processable polymer and small molecule electron donor materials often utilize solubilizing alkyl tails. Herein we study the effects of alkyl tails on charge transfer between a fullerene and a model compound of the highly-conducting PBTTT polymer with varied alkyl tail lengths, ranging from one to thirteen carbons.
First, we photophysically characterize the model compounds. Solution-phase spectroscopy and electrochemistry demonstrate similar energetics across the compounds series. Intermolecular aggregation in films leads to two distinct film absorption and photoluminescence features, which interestingly does not appear to follow tail length or odd-even trends. Second, we utilize the electrodeless time-resolved microwave conductivity technique to study photo-induced charge transfer and carrier dynamics. Specifically we create a donor-acceptor heterojunction with the soluble fullerene PCBM. Last, we create an electron acceptor “dilute regime” to study the tail-length effects on charge transfer. Our transient microwave absorption experiments show that the charge generation yield is intimately tied to tail length across the model compound series. Alkyl tails, which are often incorporated to enable solubility, can in fact act as a charge transfer barrier in bulk heterojunctions.
Triplet Exciton Production and Lifetimes in Single-Wall Carbon Nanotubes
Authors: Hertel Tobias , Spaeth Florian , Kraus Hannes , Sperlich Andreas , Dyakonov Vladimir 
Published: February 2020

Despite a broad body of spectroscopic work on the photophysics of singlet excitons in SWNTs, triplet states and triplet–triplet interactions have mostly remained elusive. Here we report on the first spin sensitive study of triplet excitons in (6,5) SWNTs giving triplet lifetimes and the quantum yield of triplet exciton production using optically detected magnetic resonance (ODMR) [1]. SWNT samples were fabricated from aqueous suspensions and PFO-BPy dispersed CoMoCAT SWNTs. Triplet lifetimes of (30±10) µs were obtained from the modulation frequency dependence of ODMR signals at small excitation intensities. The yield of triplet exciton production of (5±2)% is determined using the intensity dependence of triplet-triplet annihilation, a process that competes with triplet decay as well as with non-radiative singlet decay. The results imply that steady state triplet concentrations in SWNTs are about 5 orders of magnitude higher than those of singlet excitons.
[1] D. Stich, F. Späth, H. Kraus, A. Sperlich, V. Dyakonov and T. Hertel, Nature Photonics, in press (DOI: 10.1038/NPHOTON.2013.316)
Improved CNT-Si Heterojunction Solar Cell with Structured Single-Walled Carbon Nanotubes
Authors: Maruyama Shigeo , Cui Kehang , Chiba Takaaki , Reynaud Olivier , Fujii Shunjiro , Nasibulin Albert , Chiashi Shohei , Kataura Hiromichi , Kauppinen Esko 
Published: February 2020

Single-walled carbon nanotubes (SWNTs) with outstanding electronic, optical, mechanical, and thermal properties are expected to be the most promising materials for next-generation energy devices as well as optical and electronic devices. However, the structure controlled assembly of SWNTs for various devices is still challenging. In this study, we discuss two different SWNT assemblies for SWNT-Si heterojuction solar cells.
We proposed a water vapor treatment to build up SWNTs to a self-assembled micro-honeycomb network for the application of solar cells [1]. The micro-honeycomb network consists of vertical aggregated SWNT walls and a buckypaper bottom (quasi 2 dimentional random network). This hierarchical structure exhibits lower sheet resistance and higher optical transmittance compared with the buckypaper. The heterojunction solar cell was fabricated by dry depositing the SWNT film to the 3 mm by 3 mm n-type silicon substrate. The pristine SWNT-Si heterojunction solar cell shows a record-high fill factor of 72 % as well as a power conversion efficiency (PCE) of 6 % without tuning the diameter or height of original vertically aligned SWNTs [2]. The PCE remains stable for months in ambient condition. A PCE exceeding 10 % is achieved in the dry state after dilute nitric acid treatment.
On the other hand, heterojucntion solar cells using highly transparent-conductive SWNT films from controlled bundle-diameter and long bundle length [3] are also promising. Here, SWNTs were synthesized by the thermal decomposition of ferrocene vapor in a carbon monoxide atmosphere, with the average diameter of approx. 2 nm. The SWNT films showed a sheet resistance of 117 Ω/sq. at the transmittance of 91 % over the AM1.5G spectrum. Our preliminary test result shows the PCE of 10.12 %, with short-circuit current, open-circuit voltage and fill factor of 30.9 mA/cm2, 540 mV and 60 %, respectively.
Both types of solar cells are stable after months, which is attributed to the high-purity pristine SWNTs. The updated performance of these solar cells and the detailed mechanism will be discussed.
References:
[1] K. Cui, T. Chiba, S. Omiya, T. Thurakitseree, P. Zhao, S. Fujii, H. Kataura, E. Einarsson, S. Chiashi, S. Maruyama, J. Phys. Chem. Lett., (2013), 4, 2571.
[2] Y. Murakami, S. Chiashi, Y. Miyauchi, M. Hu, M. Ogura, T. Okubo, S. Maruyama, Chem. Phys. Lett., (2004), 385, 298.
[3] A. G. Nasibulin, A. Kaskela, K. Mustonen, A. S. Anisimov, V. Ruiz, S. Kivistö, S. Rackauskas, M. Y. Timmermans, M. Pudas, B. Aitchison, M. Kauppinen, D. P. Brown, O. G. Okhotnikov, E. I. Kauppinen, ACS Nano, (2011), 5, 3214.
Carbon Single Wall Nanotubes As a Low-Barrier, Copper-Free Back Contact to CdTe Solar Cells
Authors: Phillips Adam B. , Khanal Rajendra R. , Song Zhaoning , Zartman Rosa M. , DeWitt Jonathan L. , Stone Jon M. , Roland Paul J. , Plotnikov Victor V. , Carter Chad W. , Stayancho John M. , Ellingson Randall J. , Compaan Alvin D. , Heben Michael J. 
Published: February 2020

With a 1.45 eV band gap, a high absorption coefficient, and proven low-cost, high-volume manufacturing, CdTe-based photovoltaic (PV) technology accounted for more than 7% of the 100 GW of solar power generating capacity that was installed worldwide by the end of 2012. Copper doping of CdTe assists in forming back contacts to CdTe, but Cu is known to diffuse through the device and produce junction-shunting pathways. Because of the detrimental effects of Cu, several material systems have been investigated for use as the back contact for Cu-free CdTe devices. If long-term degradation of the photovoltaic performance could be eliminated, the levelized cost of electricity would be subtantially reduced without, in this case, significant changes in the device architecture or manufacturing process flow.
Here, we discuss results1 that demonstrate that carbon single-wall nanotube (SWNTs) films can make a high-performance electrical back contact to CdTe solar cells without the use of Cu. Back contacts formed with SWNT films showed improved open circuit voltage in comparison to cells fabricated with standard Au/Cu back contacts and, once overcoated with a thin metal layer, the solar-to-electric conversion efficiency was higher as well. The results are understood by considering that individual SWNTs within the film extend through the film’s thickness and make barrier-less contacts to individual CdTe grains in the active layer of the device.
This work was supported by the U.S. Department of Energy under Award Number DE-SC0006349 and by faculty start-up funds from the University of Toledo, and was conducted in collaboration with the Wright Center for Photovoltaics Innovations and Commercialization (http://www.utoledo.edu/research/pvic/)
(1) Phillips, et al., Nano Lett., 2013, 13 (11), pp 5224–5232
High Surface Area Graphene-Based Materials for Electrochemical Energy Storage
Authors: Kim TaeYoung , Ruoff Rodney S. 
Published: February 2020

We present an overview of work in the Ruoff group on graphene-based and graphene-derived materials in energy storage systems (EES).
With high electrical conductivity and surface area, graphene-based materials are being intensively studied as electrode material or support material in ultracapacitors and batteries. Graphene-based materials with different physicochemical properties have been studied including chemically reduced graphene oxide,[1] thermally reduced graphene oxide,[2] microwave exfoliated graphite oxide (MEGO),[3] and activated microwave-expanded graphite oxide (‘a-MEGO’).[4]
Our recent work based on a highly porous graphene-derived carbon material showed that extremely high specific surface area can be obtained by an activation process, which allows for extensive formation of an electrochemical double layer (EDL) and a high gravimetric capacitance in a symmetric ultracapacitor. In addition, activated graphene-based materials showed significantly improved performance in terms of energy density approaching that of conventional lead-acid batteries.[4, 5]
Other studies of highly porous graphene-derived materials in EES including Li-ion capacitors and Li-S batteries will also be presented, along with current efforts in our group on graphene-based and graphene–derived materials for electrical energy storage.

REFERENCES

1. Stoller, M.D., et al., Graphene-Based Ultracapacitors. Nano Letters, 2008. 8(10): p. 3498-3502.
2. Zhu, Y.W., et al., Exfoliation of Graphite Oxide in Propylene Carbonate and Thermal Reduction of the Resulting Graphene Oxide Platelets. ACS Nano, 2010. 4(2): p. 1227-1233.
3. Zhu, Y.W., et al., Microwave assisted exfoliation and reduction of graphite oxide for ultracapacitors. Carbon, 2010. 48(7): p. 2118-2122.
4. Zhu, Y.W., et al., Carbon-Based Supercapacitors Produced by Activation of Graphene. Science, 2011. 332(6037): p. 1537-1541.
5. Kim, T., et al., Activated graphene-based carbons as supercapacitor electrodes with macro- and mesopores. ACS Nano, 2013. 7(8): p. 6899-905.