bluuebunny/crossref_metadata_2025 huggingface dataset:
Activation of Platinum-Based Centers through Modification with Metal Oxo Species toward Electrocatalytic Oxidation of Dimethyl Ether and Methanol
Authors: Rutkowska Iwona Agnieszka , Sek Jakub P. , Marks Ewelina , Zelenay Piotr , Kulesza Pawel J
Published: February 2020

We have considered nanonstructured metal oxides as promoters for platinum, palladium or bimetallic platinum-ruthenium nanoparticles to fabricate electrocatalytic systems capable of efficient oxidation of dimethyl ether, a potentially new fuel of importance to low temperature fuel cells. The research has been performed in comparison to methanol. We explore the fact that certain inorganic oxides (e.g. WO3, TiO2, ZrO2 and CeO2) and polyoxometallates of molybdenum or tungsten tend to influence supported metal centers in ways other than simple dispersion over electrode area. Among useful characteristics of metal oxides and related systems are the following: they can generate –OH groups at low potentials that induce oxidation of passivating CO adsorbates (e.g. on Pt); they can potentially break C-H bonds (e.g. by hydrogen tungsten oxide bronzes); and they can possibly weaken C-O bonds during dimethyl ether oxidation (e.g. through changes of the electronic properties of Pt or Pd as additional component). Also nanostructured gold in combination with platinum has been demonstrated to enhance the overall electrocatalytic performance during oxidation of such small organic molecules as methanol and dimethyl ether.

We pursue a concept of utilization of functionalized titanium dioxide, tungsten oxide and/or zirconium oxide matrices (by admixing them with polyoxometallate-modified gold nanoparticles) for supporting and activating noble metal nanoparticles (Pt, Pt-Ru, Pd, Pt-Pd) toward electrooxidation of dimethyl ether in comaprison to methanol. Remarkable increases of the respective electrocatalytic currents measured under voltammetric and chronoamperometric conditions have been observed. The most likely explanation takes into account improvement of overall conductivity (due to the presence of nanostructured gold) at the electrocatalytic interface (formed by metal oxide support), as well as and possibility of specific Pt-metal oxide or Pt-Au electronic interactions and existence of active hydroxyl groups on transition metal oxo species.in the vicinity of catalytic Pt sites. Further, the capping layers of Keggin-type phosphomolybdates, which are known to undergo fast stepwise multi-electron redox processes as well as to activate Pt-based electrocatalysts, may also contribute to the overall enhancement effect.
Sustainable Electrochemistry: From Lignin Processing to Paired Electrolysis Reactions
Authors: Nguyen Bichlien H. , Perkins Robert J , Smith Jake A. , Moeller Kevin D
Published: February 2020

When evaluating the sustainability of an electrochemical synthesis, the source and efficient use of electricity, the generation of waste byproducts, and the source of chemicals used should be considered in the development of a greener process.

     Constant current electrochemical oxidation reactions increase functionality of a molecule but are limited in scope based on oxidation potential. This shortcoming disappears when using a chemical oxidant, which can select based on steric hindrance, chirality, chelation control, and other factors. However, a major pitfall of any stoichiometric chemical oxidation reaction is the generation of a stoichiometric reduction byproduct, oftentimes a metal waste product. To circumvent this problem, chemical oxidants can be recycled directly at the anode while generating only H­2 gas at the cathode and can be powered by a simple photovoltaic power supply.1,2

     From a green chemistry standpoint, the substrates used in anodic oxidations should have their origins from renewable feedstocks. Lignin, a biopolymer found in wood, has been disassembled into small monomers and converted into substrates for synthesis of heterocyles and quinones.3 Ideally, to maximize efficiency of these and other electrochemical processes, one wants to perform a useful oxidation at the anode simultaneously with a useful reduction at the cathode.  Using this idea of a paired electrolysis, electrochemical oxidation of lignin-derived substrates has been coupled with CO2 reduction.

     In this presentation, the recycling of a variety of chemical oxidants at an electrode using simple photovoltaics as the source of electricity will be discussed.  Furthermore, breakdown of lignocellulosic biomass into chemical building blocks for use in paired electrolyses will be explored (Figure 1).

References:

Nguyen, B. H.; Redden, A.; Moeller, K. D. “Sunlight, Electrochemistry, and Sustainable Oxidation Reactions.” Green Chem.
2014, 16, 69-72.

Anderson, L. A.; Redden, A.; Moeller, K. D. “Connecting the Dots: Using Sunlight to Drive Electrochemical Oxidations.” Green Chem.
2011, 13, 1652-1654.

Unpublished results with Robert Perkins, Jake Smith and Kevin Moeller.

Figure 1
Electrochemical Cyclization of Brominated Allyl Ethers with the Aid of a Chiral Catalyst
Authors: Pasciak Erick , Rittichier Jonathan , Medeiros M. J. , VanNieuwenzhe Michael , Peters Dennis G
Published: February 2020

Control over the stereochemistry of a desired product in chemical synthesis is an ongoing problem.  Specifically, the selectivity of chiral molecules has been the most challenging problem in organic synthesis.  Often, to overcome this problem, chiral catalysts are employed to induce preference for one chiral product over another.  One catalyst, known as the Jacobsen catalyst, has been utilized for the enantioselective oxidative conversion of alkenes to epoxides in the presence of a large amount of an oxidizer.1

In the field of electrochemistry, Duñach and co-workers utilized nickel(II) and cobalt(II) complexes with a Jacobsen ligand (a chiral, substituted salen) in constant-current experiments for the electrochemical reductive cyclization of brominated allyl ethers at room temperature, for which they achieved an enantiomeric excess as high as 16%.2  In the present work, we have explored the use of the same cobalt(II) catalyst as Duñach and co-workers, but conducted the experiments under controlled-potential conditions in order to increase the enantiomeric excess.  We expanded the study to more substrates to observe how ther products change as a function of structure.  A generalized reaction is shown in Scheme 1 for the one-electron reductive cyclization of brominated allyl ethers to form the chiral product of interest.   Experiments have been conducted to optimize reaction conditions such as temperature, concentration, and solvent.  Finally, we changed the stereochemistry of the catalyst from the R species to the S species for the purpose of controlling the identity of our products.

 

1.  Jacobsen, in: I. Ojima (Ed.), Catalytic Asymmetric Synthesis, VCH, New York, 1993 (Chapter 4.2).

2.  Duñach, E.; Esteves, A. P.; Medeiros, M. J.; Pletcher, D.; Olivero, S. J. Electroanal. Chem.
2004, 566, 39–45.

Figure 1
Electrochemical Character and Application of Halide Mediators Using CF3CH2oh As Solvent
Authors: Lam Chiu Marco , Zeng Chengchu , Little R. Daniel
Published: February 2020

The electrochemical characteristics of bromide and iodide in 2,2,2-trifluoroethanol (TFE) has been investigated and studied by cyclic voltammetry.

TFE is a protic solvent that has different nucleophilicity compared to other common alcohol solvents. Based on the experimental results, iodide and bromide lose two electrons and form a triiodie/tribromide system in one oxidation wave in TFE. The processes were found to be diffusion-controlled.

Different types of electrochemical reactions were attempted and studied in TFE. TFE found to be useful for the synthesis and benzylic C-H bond activation.
Electrochemical Reduction of Flavones
Authors: Medeiros M. J. , Pasciak Erick , Mubarak Muhammad , Peters Dennis G
Published: February 2020

Flavone and its derivatives comprise an important class of compounds due to their diverse biological properties and therapeutic applications.  They are commonly used as precursors in the preparation of various biologically active compounds, such as anticancer pharmaceuticals [1].  Dimerization of flavone may lead to new and alternative drug candidates with improved pharmacological profile.

In this work, we report electrochemical results obtained by means of cyclic voltammetry and controlled-potential electrolysis for the reduction of flavones in both aprotic and protic media containing tetraalkylammonium salts, under various experimental conditions, including an aprotic solvent (DMF) with an added proton donor.  We have identified and quantitated the various electrolysis products with the aid of GC–MS and GC.  A mechanistic pathway is proposed to account for the formation of products.

 

ACKNOWLEDGMENT

 We are grateful to the Fundação para a Ciência e Tecnologia (PestC/QUI/UI0686/2013 and FCOMP-01-0124-FEDER-037302) for financial support of this work.

 

REFERENCE

 [1] R. H. Greg, R. H. James, J. Biol. Chem. 1997, 272, 5396.
Electronic Structure Effects on Electron Transfer Controlled Hydrogen Bonding in Substituted Dinitrobenzene Electrogenerated Anions As Receptors for 1,3-Diethylurea
Authors: Martinez-Gonzalez Eduardo , Frontana Carlos
Published: February 2020

In Electron Transfer Controlled Hydrogen Bonding (ETCHB), switching molecules experiment changes in their reduction potential values as hydrogen bond donor species (DH) are added to the solution. ETCHB is the basis of operation of many molecular switches [1-3]; therefore a comprehensive understanding of the mechanistic routes that govern electron transfer in these systems would allow the design of devices with more specific applications. These processes have been extensively studied employing model molecules, such as nitrocompounds as receptor species [1-3]. In the case of complexes formed via ETCHB with electrogenerated anions from dinitrobenzene isomers [3-7], proton transfer reactions were also observed, thus diminishing the stability of these intermediates. Therefore, in this work, a similar electrochemical analysis was performed using 1,3-diethylurea to avoid protonation. The results showed two sequential reversible voltammetric signals, from which Kb (binding constant) values were calculated. The experimental behavior suggest that the mechanistic routes for ETCHB depend on the relative position of the nitro groups within the molecule: For o- and p-dinitrobenzenes radicals, a reduction involving an Erev Erev C mechanism occurs while for with m-dinitrobenzene radicals, the reaction evolves by an Erev C Erev route. By employing m-dinitrobenzenes substituted in 5 position as receptors, results revealed an inductive effect on Kb values in the formation of the anion radical binding complex.

Acknowledgments

E. M.-G. thanks CONACYT for support his M. Sc. Studies (scholarship no. 270926). C. F.  thanks CONACYT for support through project 107037.

References

[1]. E. Martínez-González, C. Frontana. J. Org. Chem. 2014. 79, 1131-1137.

[2]. J. Bu, N. D. Lilienthal, J. E. Woods, C. E. Nohrden, K. T. Hoang, D. Truong, D. K. Smith. J. Am. Chem. Soc. 2005, 127, 6423-6429.

[3]. C. Chan-Leonor, S. L. Martin, D. K. Smith. J. Org. Chem. 2005, 70, 10817-10822.

[4]. M. A. Syroeshkin, A. S. Mendkovick, L. V. Mikhal chenco, A. Rusakov, V. P. Gultyai. Russian Chemical Bulletin, International Edition. 2009, 58, 468-472.   

[5]. A. S. Mendkovich, M. A. Syroeshkin, L. V. Mikhalchenko, A, I. Rusakov, V. P. ultyai. Russian Chemical Bulletin, International Edition. 2008, 57, 1492-1495.

[6]. M. Mohammad, A. Rauf, S. Rauf, M. Tariq. J. Phys. Org. Chem. 2012, 25, 1269-1274.

[7]. M. F. Nielsen, V. D. Parker. Acta Chemica Scandinavica B. 1988, 42, 93-100.
Correlating Nafion Membrane Microstructure with Vanadium Redox Flow Battery Performance
Authors: Wang Wei , Vijayakumar Murugesan , Luo Qingtao , Lloyd Ralph , Nie Zimin , Wei Xiaoliang , Li Bin , Sprenkle Vincent , Londono J-David , Unlu Murat
Published: February 2020

This presentation describes the correlation established between the Nafion membrane microstructure and the vanadium redox flow battery performance. The impact of the equivalent weight on the microstructure of the membrane and thus the performance of VRBs is systematically studied. By tailoring the equivalent weight and membrane thickness, the new membrane contains optimal pore geometry with extremely low vanadium-ion permeability was developed. In addition, its area resistance is comparable to, and its cost is significantly less than, the widely used Nafion 115 membrane. Excellent VRB single-cell performance (89.3% energy efficiency at 50mA∙cm-2) was achieved along with a stable cyclical capacity over prolonged cycling (>200 cycles). The chemical composition, pore geometry, transport properties and flow cell performance will be reported.
Simulation and Mechanism Analysis of Electrochemistry of the Vanadium Redox Couples By a Rotating Disk Electrode
Authors: Pan Jianxin , Li Xue , Zhao Yubin , Xie Xiaofeng , Ramani Vijay K
Published: February 2020

A redox flow battery is the one of most potential and commercial electrochemical energy storage technologies. During all types of redox couples, the vanadium couples received the remarkable attention and wildly investigated in the past two decades. Usually, the electrochemistry of vanadium redox couple is experimentally studied by electrochemical methods such as cyclic volt-ampere measurement, linear voltage scanning, electrochemical impedance spectroscopy, and rotating disk electrode. Beside those methods, rotating disk electrode is the most complicated and contains a large amount of electrochemical information.

A mathematical mechanism model has been developed based on the physical phenomenon and equations of diffusion, convection, electro-migration, and electrochemical reaction dynamic.  The effect of rotating rate on the performance of vanadium couples is simulated, analyzed and comprised with the experimental data. The distributions of velocity, concentration, potential, and current have been provided while the traditional experimental methods could not been done. The simulation technique not only can provides more electrochemical information, but also gives a better understanding of the electrochemical process for the teaching and research. 

Key words: redox couples, flow battery, simulation, mechanism model

Acknowledgment: This work was supported by the National High Technology R&D Program of China (2012AA053401)
One Dimensional Mathematical Modelling of the All-Vanadium and Vanadium/Oxygen Redox Flow Batteries
Authors: Chakrabarti Barun Kumar , Chen Ching Liang , Yeoh Hak Koon , Brandon Nigel P.
Published: February 2020

A simple stationary, isothermal one-dimensional (1-D) volumetric model for the all-vanadium redox flow battery (VRFB) and the vanadium/oxygen system (VORFB) is presented in this work. The model incorporates species conservation equations along with an advection term to describe the concentration changes in the porous electrodes. In addition, a complete Nernst equation, which accounts for proton concentrations in the VRFB is also included to improve the cell voltage prediction without using any arbitrary fitting contact voltage. In addition, the model is coupled with the electrochemical reaction kinetics of the vanadium species and the gaseous oxygen. The 1-D model is validated against experimental data from the literature and the ability of the model to predict the cell performance is investigated. The cell voltage prediction compares surprisingly well with higher-dimensional models. This enhanced 1-D model is also capable of capturing the cell performance at different electrolyte flow rates, especially evidenced by the polarization curves. The effect of the electrolyte flow rate and the carbon porous electrode design employed for the vanadium half-cells on the overall cell performance are also detailed for the VORFB. The results form an important basis to determine the optimum electrolyte flow rate range and the design modifications for carbon porous electrode as to further improve the performance. Some possible improvements for both of the systems and future works are suggested.

Figure 1
Modeling and Analysis of All-Vanadium Redox Static Cells
Authors: Lee Seong Beom , Soundappan Thiagarajan , Suthar Bharatkumar , Sonawane Dayaram , Subramanian Venkat R.
Published: February 2020

Progress made in renewable energy technologies (e.g. solar, wind and tidal energy) has fueled the research in energy storage technologies which are indispensible for the success of these intermittent sources of energy. Electro-chemical energy storage systems specially redox flow batteries (RFB) offer modular and scalable energy storage systems for large scale energy storage1.

Research in different RFBs has been pursued to improve the efficiency, cost and safety aspects of these systems. While research on most aspects requires small scale (lab-scale) redox flow battery, research on some aspects can be performed and analyzed using a static cell set up (e.g. cross contamination, characterization of membrane and electrolyte etc.).

These static cells (H cell) can be used to quickly estimate the performance of redox flow batteries (at least at the lab scale) including capacity loss due to cross contaminations2. Use of static cell with simplified modeling approach (including capacity loss) to validate experimental data is demonstrated by Tang et. al.2 on vanadium redox flow battery. This approach can be made more robust and general to be useful for any redox couple by combining electrochemical models and robust optimization framework (parameter and state estimation techniques) to increase the confidence in predictions made by static cell.

This presentation will focus on electrochemical models for static cell with parameters and state estimation framework to increase the fidelity of results obtained by experiments performed.

Acknowledgements

The authors acknowledge financial support from the U.S. Department of Energy’s Advanced Research Projects Agency- Energy (ARPA-E), and the Solar Energy Research Institute in India and the United States (SERIIUS), as well as, Washington University in St. Louis’ McDonnell Academy Global Energy and Environmental Partnership (MAGEEP) and SunEdison Grant.

References

1.              B. R. Chalamala, T. Soundappan, G. R. Fisher, M. R. Anstey, V. V. Viswanathan and M. L. Perry, Proceedings of the IEEE, 102, 976 (2014).

2.              A. Tang, J. Bao and M. Skyllas-Kazacos, J. Power Sources, 196, 10737 (2011).
Investigation on the Microfluidics in PEM Water Electrolyzers
Authors: Mo Jingke , Steen Stuart M. , Barnhill William , Zhang Feng-Yuan
Published: February 2020

A sustainable and robust electrochemical energy storage and/or a hybrid system to accommodate daily, even hourly changes of renewable resources becomes more critical. An advanced polymer electrolyte membrane water electrolyzer (PEMWE) has been shown to be effective energy storage medium by producing hydrogen/oxygen from water with electricity from renewable sources. When the renewable resources are available, hydrogen will be produced and stored, such that it can later provide a constant power supply with a PEM fuel cell, which is a reverse device of the electrolyzer. This entire portfolio will make renewable and hybrid energy systems effective to provide reliable and multiscale energy whenever needed.

In proton exchange membrane water electrolyzers (PEMWEs), water is electrochemically splitting into oxygen and hydrogen. The oxygen generated at the anode side and the circled water flowing over the liquid/gas diffusion layer yield two-phase transport conditions in micro-channels and pores of LGDL, which significantly impact the performance. Due to limitations of the design of conventional PEMWEs and LGDLs,  the in-situ phenomena of two-phase flow has few been explored in operating PEMWEs. In this research, an innovative design of a transparent PEMWE is developed coupled with the thin and well-tuned titanium LGDLs with straight pores. The high-speed and micro-scale visualization system (HMVS), and electrochemical impedance spectroscopy will be used for in-situ characterizations. Visualization results are used for better understanding the behavior of two-phase flow and its effects on the PEMWE performance. Patterns of gas-bubble formation, evolution, departure and transport are identified. The effects of property of materials, including LGDL pore sizes, channel dimensions, are also investigated.
Development of High Surface Area Carbon Electrodes for the Bromine Reactions in H2-Br2 fuel Cells
Authors: Yarlagadda Venkata , Nguyen Trung Van , Lin Guangyu , Chong Pau Ying
Published: February 2020

The H2-Br2 system is considered as one of the viable options for  large scale electrical energy storage due to faster H2 and Br2 reaction kinetics, low cost, and high round-trip efficiency. Since the bromine reactions in this fuel cell system do not need any precious metal catalysts, plain porous carbon paper can be used as an electrode material. However, these porous carbon electrodes have low surface area and hence multiple electrode layers are employed to improve the active surface area. While the active surface area is enhanced by using multiple electrode layers, it could lead to mass transport limited performance at higher current densities. To overcome this problem, porous carbon electrodes with multi-wall carbon nanotubes grown directly on their surface were developed. The cross section of a carbon nanotube based electrode is shown in Figure 1. In this presentation, we will discuss the synthesis and characterization of carbon nanotube based electrodes as well as their durability and actual performance in a H2-Br2  fuel cell. Also, the advantages of these carbon nanotube based electrodes over conventional porous carbon electrodes will be highlighted.

Acknowledgements

This work was funded by NSF through grant number EFRI-1038234 and DOE/ARPA-E under award number DE-AR0000262.

References

Haley Kreutzer, Venkata Yarlagadda, and Trung Van Nguyen, J. Electrochem Soc., 159(7), F331 (2012).

Venkata Yarlagadda and Trung Van Nguyen, J. Electrochem. Soc., 160(6), F535 (2013).

Cheng Wang, Mahesh Waje, Xin Wang, Jason M. Tang, Robert C. Haddon, and Yushan Yan, Nano Letters, 4(2), 345 (2004).

Chunyu Du, Baorong Wang, and Xinqun Cheng, J. Power Sources, 187, 505 (2009).

Venkata Yarlagadda and Trung Nguyen, ECS Transactions, 58(36), 25 (2014).

Figure 1
Dissecting the Quinone-Bromide Flow Battery
Authors: Chen Qing , Gerhardt Michael R. , Eisenach Louise , Marshak Michael P. , Gordon Roy G. , Aziz Michael J.
Published: February 2020

The excitement brought by the quinone-bromide flow battery resides not only in the low cost of materials, but also in the high performance, reaching 1.0 V open circuit voltage and 1.0 W/cm2 peak galvanic power density to date. Further performance improvements require better understanding of the loss mechanisms. Here, we present a detailed examination of the losses in the system, via installation of a reference electrode, electrochemical impedance spectroscopy, and ex-situ measurements of ohmic resistance. Cell overvoltage is then dissected into contributions from charge transfer kinetics, mass transport, membrane resistance, etc. and interpreted. We address current efficiency through measurements of active species cross-over rates and molecular stability.
On the Capacity and Cycle Stability of Na3MnCO3PO4 - a High Capacity, Multi-Electron Transfer Redox Cathode Material for Sodium Ion Batteries
Authors: Wang Chuanlong , Sawicki Monica , Emani Satya , Liu Caihong , Shaw Leon
Published: February 2020

Na3MnCO3PO4 has been predicted via ab initio calculations (Hautier, et al. 2011) to have a high specific capacity of 191 mAh/g, owing to its potential to deliver two-electron transfer reactions per formula via Mn2+/Mn3+ and Mn3+/Mn4+ redox reactions. This study demonstrates, for the first time, that Na3MnCO3PO4 can indeed display a specific capacity of 176.7 mAh/g experimentally, reaching 92.5% of its theoretical. The low electronic conductivity is found to be the limiting factor for the previously observed low specific capacities for Na3MnCO3PO4. Furthermore, the charge/discharge cycle life of the cathode is found to depend on the carbon concentration. The capacity retention improves with increasing the carbon concentration. This finding has been attributed to the improved uniformity in the participation of most of Na3MnCO3PO4 particles in redox reactions. With a specific capacity as high as 176.7 mAh/g, a clearly identified direction to enhance the capacity retention, and low cost of Na sources, Na3MnCO3PO4 has a great potential to be a viable cathode material for Na-ion batteries for large-scale energy storage.
High Ionic Conductivity of Flexible Polymer-Based Electrolyte with Low Porosity
Authors: Zhao Weiyun , Srinivasan Madhavi
Published: February 2020

Solid or polymer based electrolytes have attracted many interests with growing need for high-density power sources due to safety concerns. Among these ‘dry’ electrolytes, polymer-based electrolytes can be used widely in portable electronics or large scale industry energy storage thanks to its flexibility. However, low ionic conductivity of polymer is a drawback of these polymer-based electrolytes, especially for poreless membranes. In this work, various polymer-based membranes, e.g. polyvinylidene fluoride (PVdF) membranes, sulfonated poly(ether ether ketone) (SPEEK) membrane, were fabricated via various methods. We explored various methods to reduce porosity of membranes without decreasing their ionic conductivity. For example, hot pressing with poly 2-acrylamido-2-methyl-1-propanesulfonic acid (PAMPS) can significantly decrease the porosity of membranes while ionic conductivity of membranes remained the same. Filling pores with succinonitrile (SN) was even able to increase ionic conductivity as well as decreasing porosity. High ionic conductivity of ~10-4 S/cm was obtained on PVdF/SN membranes. SPEEK membranes without pores were also fabricated, achieving a high ionic conductivity of ~10-4 S/cm, which is suitable for applications such as flow battery electrolyte.
(Invted) Catalytically Accelerated Hydrogen Gas Detection at Electrodeposited Pd@Pt Nanowires
Authors: Penner R.
Published: February 2020

Platinum (Pt)-modified palladium (Pd) nanowires (or Pd@Pt nanowires) are prepared with control of the Pt coverage. These Pd@Pt nanowires are used as resistive gas sensors for the detection of hydrogen gas in air, and the influence of the Pt surface layer is assessed. Pd nanowires with dimensions of 60 nm(h) × 200 nm(w) × 20 μm(l) are first prepared using lithographically-patterned nanowire electrodeposition (LPNE). A thin Pt surface layer is elec- trodeposited conformally onto a Pd nanowire at coverages, θPt , of 0.10 monolayer (ML), 1.0 ML, and 10 ML. X-ray photoelectron spectroscopy coupled with scanning electron microscopy and electrochemical measurements are consistent with a layer-by-layer deposition mode for Pt on the Pd nanowire surface. The resistance of a single Pd@Pt nanowire is measured during the exposure of these nanowires to pulses of hydrogen gas in air at concentrations ranging from 0.04 to 5.0 vol%. Both Pd nanowires and Pd@Pt nanowires show a prompt increase in resistance upon exposure to H2 in air, caused by the conversion of Pd to more resistive PdHx. The Pt surface layer present at Pd@Pt nanowires modifies the response to H2 in two ways: First, the amplitude of the resistance change is reduced as θPt is increased, and second, the rate at which the nanowire resistance attains a new steady-state value upon a change in the H2 concentration - characterized by the response time and the recovery time - is accelerated. An optimum Pt coverage of θPt = 1.0 ML is seen for which nanowire response is accelerated by a factor of 2-3 while the recovery from H2 exposure is faster by an order of magnitude as compared to a pure Pd nanowire operating at the same elevated temperature.
(Invited) Fluorescence-Enabled Electrochemistry of Single Molecules and Nanoparticles
Authors: Zhang Bo , Oja Stephen , Lu Jin
Published: February 2020

We are developing a new electrochemical detection method to study redox properties of single molecules. This method relies on the use of fluorescence to amply the signal of single electron-transfer events at the electrode/solution interface. A bipolar electrode mechanism is used to couple a redox reaction of interest to a fluorogenic reaction.  The oxidation or reduction of the redox species at the bipolar electrode results in the generation of a highly fluorescence product at the opposite pole of the same bipolar electrode, which is optically monitored with total-internal reflection fluorescence microscopy (TIRFM). The use of this method allows one to resolve single redox events in an electrolyte solution at room temperature.  In this talk, I will first discussion some of our recent results on the detection of single redox molecules, including ferrocene and ferricyanide, and single nanoparticles. I will then discussion some of our new experiments on electrochemical coupling at single nanoparticles. I will also discuss a couple of experiments focusing on imaging and resolving single redox events with very large electrochemical arrays.
(Invited) Dendrite-Free Rechargeable Zinc-Based Batteries: Solving a Chronic Impediment through Architectural Design in 3D
Authors: Rolison Debra R. , Parker Joseph F. , Pala Irina R. , Chervin Christopher N. , Nelson Eric S. , Long Jeffrey W.
Published: February 2020

The international effort to move beyond lithium-ion batteries—present-day’s ubiquitous electrochemical energy storage (EES) device—arises from the unending safety threat posed courtesy of flammable electrolytes and oxygen-releasing cathodes. The oft-posited “Beyond Lithium” as an R&D rationale for next-generation batteries needs to bypass not just lithium-ion, but Li-based batteries. Zinc-based batteries offer a compelling alternative thanks to nonflammable aqueous electrolytes augmented by the high domestic abundance of Zn and the high energy density of Zn-based batteries (comparable to or greater than Li-ion). The present performance, however, of traditional Zn-based batteries is hindered by suboptimal Zn utilization (typically <60% of theoretical capacity) and poor rechargeability—thanks to the complex dissolution/precipitation processes that accompany Zn/Zn2+cycling in alkaline electrolytes. We adapt the promise of three-dimensional (3D) battery architectures [1–3] to address these limitations by redesigning the zinc anode as a porous, highly conductive, and 3D-wired “sponge” architecture. These aperiodic electrode architectures achieve >90% Zn utilization when discharged in primary Zn–air cells, while retaining the 3D monolithic framework and exhibiting an impedance characteristic of the metal with uniform deposition of charge/discharge products at the external and internal surfaces [4]. We further show that the structural characteristics of the Zn sponge promote greater rechargeability when cycled in prototype Ag–Zn and Ni–Zn cells, even thwarting dendrite formation when cycled in a symmetric Zn–Zn cell at an applied current density twice that of the critical current density necessary to form dendrites [5]. Our results show that all Zn-based chemistries can now be reformulated for next-generation rechargeable, Li-free batteries.

The information, data, or work presented herein was funded in part by the Office of Naval Research and by the Advanced Research Projects Agency–Energy (ARPA–E), U.S. Department of Energy, under Award Number DE-AR-0000391; the work has been Approved for Public Release, Distribution Unlimited.

[1]   R.W. Hart, H.S White, B. Dunn, D.R. Rolison, Electrochem. Commun.
5(2003) 120–123.

[2]   J.W. Long, B. Dunn, D.R. Rolison, H.S. White, Chem. Rev. 104(2004) 4463–4492.

[3]   D.R. Rolison, J.W. Long, J.C. Lytle, A.E. Fischer, C.P. Rhodes, T.M. McEvoy, M.E. Bourg, A.M. Lubers, Chem. Soc. Rev.
38(2009) 226–252.

[4]  J.F. Parker, E.S. Nelson, M.D. Wattendorf, C.N. Chervin, J.W. Long, D.R. Rolison, ACS Appl. Mater. Interfac., in the press.

[5]   J.F. Parker, C.N. Chervin, E.S. Nelson, J.W. Long, D.R. Rolison, Energy Environ. Sci.
7 (2014) 1117–1124.
Electrochemical Kinetic Study on Various Immobilized Yeasts for Glucose Biofuel Cell Applications
Authors: Jeon Yang Bae , Tang Fusheng , Lee Jin Wook
Published: February 2020

Microbial fuel cells produce electricity directly from organic fuels such as glucose, sucrose, acetates and ethanol. In the present work, the electrochemical characteristics of immobilized yeasts against carbon electrode with various glucose concentrations are investigated experimentally. Three types of yeasts as anode catalyst are employed: (1) commercially available baker's yeast (S. cerevisiae); (2) wild type yeast cultured in our lab; and (3) respiration-free mutant yeast. As a baseline, non-immobilized baker's yeast is examined for comparision with the others. Kinetic parameters for the three types of yeasts are obtained by Tafel analysis. Cyclic voltammetry (CV) techniques are applied to investigate the reversibility of the redox reactions. Open current potentials (OCP) of each yeast are measured against a reference electrode to estimage the anodic potential with various glucose concentrations. Electrochemical impedance spectroscopy (EIS) of the half-cell is conducted to estimate the resistivity of the electrode and the overall ohmic resistance. With an intention to develop an in vivo glucose monitoring system, the experimental results from this fundamental kinetic study will be used as a guideline, and a novel biological glucose fuel cell is being designed.
Electrolytic and Electroless Fabrication of Al-Sc Alloys in KF-Naf-AlF3 Electrolytes
Authors: Tkacheva Olga , Suzdaltsev Andrey , Nikolaev Andrey , Zaikov Yurii , Shtefanyuk Yuriy , Pingin Vitaliy , Vinogradov Dmitriy
Published: February 2020

The Al-Sc alloys were obtained in the KF-NaF-AlF3 electrolyte containing Sc2O3  and  Al2O3  at 800 oC by chemical and electrochemical techniques. Electrolysis was performed in a 20 A lab-scale cell with graphite anode and aluminum cathode. An impact of the cathode current density (0-1 A∙cm-2), the Sc2O3 content (1, 2, 4, and 8 wt%) in the KF-NaF-AlF3 electrolyte, the rate of the molten aluminum agitation (0, 100 rotates/min), and the synthesis duration (30-210 min) on the Sc content in the Al-Sc alloy was studied. The Al-Sc alloys with the Sc content of 0.30-1.80 wt%, depending on the synthesis conditions, and with the uniform Sc distribution throughout the aluminum matrix were produced. The peculiarities of the electrolytic and electroless fabrication of the Al-Sc alloys in the KF-NaF-AlF3-Al2O3-Sc2O3 electrolytes at 800 oC in comparison with the processes occurred in the NaF-AlF3-Al2O3-Sc2O3 melts at 980 oC are discussed.
Monitoring Mechanical Modulation of Reactivity in Electrocatalysis
Authors: Deng Qibo , Weissmueller Joerg
Published: February 2020

Many modern catalyst materials exploit a strained surface layer as the active component, exploiting that reaction rates in heterogeneous catalysis vary when the substrate is elastically strained in the tangent plane. Here we report a direct and quantitative experimental monitoring of the modulation of the electrocatalytic reaction current while the electrode is strained. The hydrogen evolution reaction (HER) on Au and Pt electrodes in H2SO4 is studied as a model process.

Our experiment uses a lock-in technique for following the modulation of the electrocatalytic reaction current in situ while a small cyclic elastic strain (~ 10-4) is imposed on the electrode material. The approach yields well-defined and precisely quantifiable coupling coefficients linking the reactivity to strain. The coefficients are measured as the function of the overpotential. We advertise the fact, ignored in previous work on strained-layer catalysis, that the coupling strength depends on the overpotential by magnitude and, as we show, even by sign. Specifically, tensile strain enhances the reactivity at low overpotential, whereas the trend is inverted and the reactivity diminished at higher overpotential. Furthermore, we show that the data affords a quantification of strain-dependence of the adsorption and barrier energies. This quantification is another distinguishing feature of our approach.

The overpotential-dependent coupling is readily modeled by kinetic rate theory. To this end, we take the impact of strain for, e.g., Heyrowsky kinetics to be mediated by (i) a strain dependence of the activation enthalpy for the ion + atom reaction step, and (ii) an independent strain dependence of the hydrogen adsorption enthalpy. In agreement with experiment, the rate equation predicts the reaction current-strain coupling coefficient to invert its sign upon transition from dilute to concentrated hydrogen adsorbate layer.

Our method appears applicable quite generally to electrocatalytic reactions. Therefore it promises a new tool for studying strain-dependent catalysis and for identifying the underlying microscopic processes.
Determining Microwire Morphology and Current Transient Trends from Single Microwire Electrodeposition
Authors: Zhang Tim , Fahrenkrug Eli , Maldonado Stephen
Published: February 2020

This presentation describes work on understanding and controlling the electrochemical liquid-liquid-solid (ec-LLS) process for the preparation of crystalline semiconductor materials. In this work, data are presented to test the hypothesis that the current-time transient collected during a potentiostatic ec-LLS deposition of Ge microwires contains useful details about the crystal growth. A photoresist pattern with a single hole was fabricated on top of a conductive support to make an ultramicroelectrode (UME) with a defined diameter ranging between 10 and 35 microns. These single-hole UMEs were filled with a liquid metal which acted as the electrode and crystal solvent in ec-LLS. Individual germanium microwires were then electrodeposited onto the liquid metal by chronoamperometry from an aqueous solution using a variety of different potential, temperature, and liquid metal conditions. Current transients will be discussed in relation to their correlation with morphological and crystallographic features of as-prepared Ge microwires. The prospects for real-time adjustment of microwire growth during an ec-LLS process will be presented.
Plamonic-Based Electrochemical Imaging of the Crystal Facets of Single Metallic Nanoparticles
Authors: Wang Yixian , Shan Xiaonan , Tao Nongjian
Published: February 2020

Metallic nanoparticles (MNPs) have been widely used in catalytic electrochemistry. It is essential to investigate the surface structure, i.e., the facets of MNPs since they strongly affect the catalytic properties. Conventional electrochemistry can only provide averaged information of the facets of all MNPs in the sample, while through plamonic-based electrochemical imaging technique, we are able to image the crystal facets of single MNPs by tracking the redox reaction of single MNPs. Different MNPs (nanospheres, nanorods and nanocubes) were tested and cyclic voltammetry of different single MNPs will be shown.
Understanding of Rate-Limiting Behavior and of Diffusion in Commercial LiCoO2 Electrodes Via Electrochemical Impedance Spectroscopy
Authors: Ahmed Kazi Rakib , Ozkan Mihri , Ozkan Cengiz
Published: February 2020

Electrochemical impedance spectroscopy has been used to investigate rate-limiting conditions in commercial LiCoO2 cathodes. The insights gained may be extended to most lithium-ion battery systems. In general, two possible rate-limiting conditions may exist in a lithium-ion battery - i) diffusion limited, and ii) electron exchange-rate limited. In the former case, rate of diffusion (of ions) is slower than that of redox reactions occurring at active material surface - leading to a negative concentration gradient (of ions) toward the electrode surface for cathodic reactions. In the latter case, a positive concentration gradient persists toward the electrode surface for cathodic reactions.  Insights into electrical equivalent circuits derived via electrochemical impedance spectroscopy have led to novel ways of recognizing the rate-limiting behavior in LiCoO2 half-cell.
Rotational Waves in an Oscillatory Electrochemical System
Authors: Sebek Michael L , Kiss Istvan Z
Published: February 2020

The existence of waves in distributed systems has been observed in chemical systems mainly through reaction-diffusion methods and such waves can be rotational when performed on a ring-shaped surface. In such ring systems, phase model analysis predicts several waves may co-rotate in an even distribution over the ring.

In this contribution, an experimental setup composed of twenty nickel electrodes undergoing electrodissolution is constructed to investigate rotational waves. The electrodes are positioned into the ring topology by coupling. Only complete synchrony is attained when coupled. In order to arrive at a rotational state, the temporary application of topology alterations and global feedback is required.

Four rotational solutions are found, distinguished by the rotational velocity and the number of waves in each rotation. The rotational velocity is defined as ν0/m where ν0 is a base velocity of all rotations and m is the integer winding number which is equal to the number of waves in the rotation.  The non-rotational solution, m=0, is characterized by complete synchronization while the rotational solutions are winding numbers m=1,2,3,4 where a specific winding number is achieved by the application of appropriate topological tuning. Any further increase in winding number is shown to not be stable without external assistance. The results indicate rotational waves, predicted by phase model approximations, can be realized by the application of the experimental method.
In-Situ x-Ray Diffraction Study of Pt(111) Oxidation during Oxygen Reduction Reaction (ORR)
Authors: Drnec Jakub , Ruge Martin , Reikowski Finn , Rahn Bjorn , Carlà Francesco , Felici Roberto , Stettner Jochim , Magnussen Olaf M. , Harrington David A.
Published: February 2020

ORR is one of the most studied electrochemical reactions due to it’s tremendous fundamental and practical importance. Oxygen is common, readily accessible oxidizing agent and therefore Pt ORR cathode is part of many energy conversion devices, e.g., fuel cells. Unfortunately, slow kinetics of ORR negatively affects the performance and it is currently one of the main bottleneck in large scale fuel cells commercialization. It is partly caused by the presence of surface Pt oxides, which slow the reaction rate and trap reaction intermediates on the surface. The oxide formation and dissolution is also known to cause dissolution of Pt catalyst, which further degrades the performance.

Even though the electrochemical formation of surface oxides on platinum surface has been extensively studied in the past, there are still many questions unanswered. Mainly about the detailed structure of the oxide and its growth mechanism [1 and references there-in]. Most of the studies were performed in the absence of O2, the fuel cell oxidant, and therefore they are less relevant to the fuel cell operation as gaseous O2 can modify the oxidation potentials and mechanism. Given the above, further fundamental understanding of Pt oxidation mechanism measured in-situ is clearly needed in order to determine the role of surface oxides in ORR and its effect on the fuel cell performance. Here we show the results of in-situ study of electrochemical oxide formation on Pt(111) and how it is influenced by presence of O2 during ORR.

We find that oxide growth, and Pt-O site switching, is present as soon as 700 mV vs. Ag|AgCl reference electrode in 0.1M HClO4 and causes slow, irreversible roughening of the surface. When the potential is increased, the roughening is more severe and after several tens of cycles from -125 mV to 900 mV, the surface loses it’s order. This is seemingly in contradiction with widely accepted notion that cycling the Pt(111) up to 900 mV does not affect significantly surface structure. We show that the roughening is dependent on the initial state of the sample and it is an autocatalytic process.

Adding oxygen into the electrolyte does not have any notable effect on the oxidation potentials or kinetics and it is in disagreement with previous results where negative shift of the oxidation onset was observed in O2 containing electrolyte [2]. This results points to the fact that OH- is dominated species during Pt electrooxidation and oxygen has only a side role.  However, depending on the history of the sample, it is likely that PtO species are present on the surface and should be taken into the account in theoretical investigations.

[1] Kongkanand and Ziegelbauer, Journal of Physical Chemistry C, 116 (2012) 3684-3693; [2] Matsumoto, Miyazaki, Imai, Phys. Chem. C, 115 (2011) 11163−11169.
Cobalt Phosphate Group Modified Hematite Nanorod Array As Photoanode for Efficient Solar Water Splitting
Authors: Fu Li , Yu Hongmei , Zhang Changkun , Shao Zhigang , Yi Baolian
Published: February 2020

Hydrogen production by photoelectrochemical water splitting based on modified nanostructure hematite is investigated for transformation and store of solar energy. Herein, nanorod hematite arrays were prepared by adjusted-hydrothermal method with a diameter of 30 nm. Phosphate group and cobalt ions were deposited of the surface of hematite by chemical immersion process to improve its photoelectrochemical performance and speed up the oxygen revolution reaction in water splitting. The CoPi-modified α-Fe2O3 nanorod arrays (NAs) showed a greatly enhanced electrochemical and photoelectrochemical property with a photocurrent density 270 μA/cm2 at 1.23V (vs. RHE) for FeCoPi-4 compared with 20 μA/cm2 for untreated α-Fe2O3 NAs. The effect of phosphate groups and cobalt ions on the α-Fe2O3 NAs were both investigated. The Co(Ⅱ) ion is connected closely with the α-Fe2O3 surface through phosphate groups by XPS detection. The phosphate enhances the transport of electron from the α-Fe2O3 to Co ion. The high performance domanstrated in photoelectrochemical test indicates that CoPi-modified α-Fe2O3 NAs is a potential photoelectrocatalyst for water splitting.

Figure 1
Exceptionally Fast Hydrogen Absorption and Desorption through Platinum Overlayers
Authors: Polczynski Piotr , Jurczakowski Rafal Robert
Published: February 2020

Palladium alloys are widely used in heterogeneous catalysis, in this group Pd–Pt systems are of particular catalytic interest. They are active components for anodes in low temperature fuel cells and hydrogenation of aromatic compounds in fuels. Platinum monolayers deposited on palladium have been recognized for their unique catalytic properties towards oxygen reduction reaction. However, the hydrogen absorption has never been studied on platinized palladium. In this work we have demonstrated for the first time that platinum overlayers deposited on palladium surface are not only permeable to hydrogen but also enhance the kinetics of the hydrogen absorption/desorption by several orders of magnitude. In this study palladium-hydrogen was chosen as a model system forming nonstoichiometric hydrides.

The hydrogen electrosorption in thin palladium films (50-1000nm) has been investigated at electrodes covered with platinum overlayers. The highest absorption kinetics have been observed for Pd electrodes fully covered with 1 – 3 platinum monolayers. By means of electrochemical impedance spectroscopy (EIS) we have shown that the process is diffusion limited at platinized samples. Diffusion coefficient, D
H, determined in EIS, is two orders of magnitude higher than that previously reported for thin palladium films and approaches D
Hfor bulk palladium. The approach provides insight into the mechanism of hydrogen absorption and the process of hydrogen transport in metals-hydrogen systems.

Surprisingly high stability of the platinized palladium enable its use in heterogeneous catalysis, hydrogenation reactions, or hydrogen purification. It should be stressed that palladium has already been proven to serve as an efficient catalyst to facilitate hydrogen insertion into other metal hydrides. Therefore, another set of potential applications is related to hydrogen storage or sensing systems, where fast and selective reaction in the presence of hydrogen is required.