bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrogen Production By Photocatalytic Water Splitting Using Mixed Oxide Solid Solutions Under UV-Vis Light Irradiation
Authors: Duconge José J , García Abraham , Cotto María , Ortiz Dayna , Márquez Francisco
Published: February 2020

Photocatalytic water splitting with generation of hydrogen is a green process that concerns activity of a semiconductor material under sunlight irradiation and ambient pressure and temperature. This process has been regarded as a promising solution to resolve the global energy and environmental problems. In this research, photocatalytic hydrogen generation by water splitting, H2O (l) → H2 (g) + 1/2 O2(g), has been studied on photocatalysts based on mixed oxide solid solutions (ZnCdFeCuS), synthesized by coprecipitation of different metal precursors.  Iron and copper nanoparticles were incorporated as cocatalysts to enhance the photocatalytic activity of the ZnCd solid solution. The effect of the different synthesis parameters, including temperature, elemental atomic ratios, amount of S, Cu and Fe incorporated in the catalyst, and calcination temperature, on the photocatalytic production of hydrogen has been studied in order to determine the best experimental synthesis conditions. The catalysts have been characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), and BET.

The experiments of photocatalytic water splitting were performed in aqueous solution of the photocatalysts. Before use, the catalysts were either activated under a nitrogen flow of 300 mL min-1 at different temperatures (400, 700 and 900°C) for 2 hours. In all cases, the photocatalytic activity was measured by dispersing 50 mg of the catalyst in deionized water in an ultrasound bath at room temperature and atmospheric pressure containing 0.5 M Na2S and 0.03 M Na2SO3 as sacrificial reagents. The catalytic peak for the overall water splitting reaction occurs in a short pH range, typically 4-5.2 and for this reason, solutions were pH-adjusted. The reaction mixture was purged with N2(g) for 30 min and after that evacuated several times to completely remove the air prior the irradiation process. The water splitting reaction was conducted in a quartz reactor equipped with a water-cooling jacket. The reaction mixtures were irradiated at different light wavelengths (from 220 to 700 nm) using a solar simulator and appropriate cutoff filters in a static air atmosphere. The evolved gases were analyzed by GC-TCD, using N2 as carrying gas.
Transport Phenomena in Electrical Double Layer Capacitors with Highly Ordered 3D Porous Carbon Electrodes
Authors: Mei Bing-Ang , Pilon Laurent
Published: February 2020

Electric double layer capacitors (EDLCs) store energy via ion adsorption in the electric double layer forming at the electrode/electrolyte interfaces in highly porous carbon electrodes. This charge storage mechanism is very fast and highly reversible resulting in large power density and long cycle life. Applications range from regenerative breaking for hybrid electric vehicles to the smart grid. The architecture of the carbon electrodes is known to have a significant effect on the performance of EDLCs. Unfortunately, experimental optimization can be time consuming and challenging due to the large number of design parameters. Numerical simulations could offer a faster and less costly alternative.

This study aims to demonstrate the use of numerical tools to simulate transient three-dimensional interfacial and transport phenomena in EDLCs with realistic electrode architecture. It also aims to derive design rules for EDLC porous electrodes. To do so, cyclic voltammograms were numerically generated for EDLCs consisting of electrodes with highly-ordered spherical carbon nanoparticles arranged in simple cubic (SC) or face-centered cubic (FCC) packing in LiClO4/propylene carbonate electrolyte. Simulations were performed for different carbon nanoparticles diameter, electrode thickness, and scan rate. The continuum model was based on the modified Poisson-Nernst-Planck model and accounted for (i) the Stern layer at the electrode/electrolyte interface, (ii) finite ion size, (iii) binary and symmetric electrolyte, and (iv) three-dimensional electrode morphologies. In all cases, the areal capacitance was independent of scan rate at low scan rate but decreased beyond a critical scan rate corresponding to the diffusion-limited regime when ion transport cannot follow the rapid changes in electric potential. The results indicate that the areal capacitance (in F/m2) increased with decreasing sphere diameter below 40 nm due to the increasing surface curvature resulting in larger surface electric field. In addition, FCC packing featured larger capacitance that SC packing thanks to larger surface electric field for given sphere diameter and low scan rate . However, the ion diffusion regime was reached at lower scan rates in FCC packing because of the higher turtuosity limiting the ion transport in the electrode.
(Invited) Interfacial and Transport Phenomena in Hybrid Pseudocapacitors
Authors: Pilon Laurent , Girard Henri-Louis , Mei Bing-Ang
Published: February 2020

Electrochemical capacitors have attracted significant attention in recent years due to their promise as electrical energy storage devices for high energy and power applications. They are typically classified as either electric double layer capacitors (EDLCs) or pseudocapacitors depending on the energy storage mechanism. EDLCs store energy physically in the electric double layers (EDLs) forming near the electrode/electrolyte interfaces. Thus, EDLCs feature highly reversible charge storage and long cycle life. However, their energy density remains low compared with that of batteries. On the other hand, pseudocapacitors store energy via the electric double layers as well as via reversible oxidation-reduction (redox) reactions with or without insertion or intercalation. Pseudocapacitors tend to feature larger capacitances and energy densities than EDLCs because the amount of charge they can store is not limited by the surface area of the electrode/electrolyte interface. Finally, hybrid pseudocapacitors are devices combining a pseudocapacitive electrode made of a porous transition metal oxide (e.g., RuO2, MnO2, Nb2O5, MoO3) and an EDLC-type electrode typically made of porous carbon.

This invited talk will present recent advances in physical modeling of interfacial, transport, and electrochemical phenomena in pseudocapacitors. It aims to provide physical interpretation of cyclic voltammograms obtained experimentally either from hybrid pseudocapacitors or from pseudocapacitive electrodes using three-electrode systems. First, it will present a continuum model simultaneously accounting for (i) charge transport in electrodes and electrolyte, (ii) the dynamics of the electric double layer, (iii) steric repulsion due to finite ion sizes, (iv) redox reactions, and (v) intercalation. Second, it will report selected numerical simulations of CV curves for different electrode thickness and electron and ion transport properties in the electrodes and electrolyte, representative of actual situations. These results will be used to elucidate the respective contributions of faradaic reactions and electric double layer formation to charge storage in pseudocapacitors. Particular attention will be paid to the so-called b-value characterizing the power law evolution of the total current with respect to scan rate for a given potential. Special effort will be made to systematically compare model predictions with experimental data.
Stereoselective Nucleophilic Additions to the N-Acyliminium Ions: Elucidation of Stereoselectivity By Spectroscopic Conformational Analysis
Authors: Suga Seiji , Yamamoto Junya , Akagi Tomoya , Haisa Masahiro , Mitsudo Koichi
Published: February 2020

N-Acyliminium ions are versatile cationic intermediates for the synthesis of a variety of alkaloids having biological activities. Enormous numbers of stereoselective reactions and syntheses based on the nucleophilic additions to the N-acyliminium ions as key steps have been developed. Despite extensive efforts to understand these selectivities, however, a strong experimental elucidation has not been established, because it is rather difficult to obtain their conformational information by spectroscopic analysis. N-acyliminium ions are generally generated by an acid promoted reaction from their precursors, and the ions and the precursors are usually in equilibrium. Instability of N-acyliminium ions is also problematic, and makes a direct spectroscopic measurement very difficult.

Recently, we have developed the “cation pool method” and the “indirect cation pool method”, involving generation and accumulation of organic cations without nucleophiles. These methods are advantageous to detect organic cations such as N-acyliminium ions and alkoxycarbenium ions by NMR spectroscopy. For example, using the indirect cation pool method, alkoxycarbenium ions which could be identified by the NMR measurement are rapidly and irreversibly generated from thioacetals by the treatment of electrochemically generated ArS(ArSSAr)+  (Scheme 1).1)

Under the circumstances, we are highly motivated to investigate the conformation of N-acyliminium ions which are practically used for the stereoselective reactions (Scheme 2). N-Acyliminium ions having a piperidine skeleton were chosen because the functionalized piperidines frequently show interesting biologically properties. In addition, the conformations of the 6-membered rings should be relatively more rigid compared with 5-membered ring, and hence it is predicted that the conformational information could easily be obtained. Thus, we attempted to generate a variety of N-acyliminium ions having a substituent from the corresponding precursors by using the “indirect cation pool method”.

In this presentation, we will discuss about stereoselectivities of the nucleophilic additions to the N-acyliminium ions based on the conformational analysis of cationic intermediates.

1) Suga, S.; Matsumoto, K.; Ueoka, K.; Yoshida, J. J. Am. Chem. Soc.
2006, 128, 7710-7711.  Matsumoto, K.; Suga, S.; Yoshida, J. Org. Biomol. Chem.
2011, 9, 2586-2596.

Figure 1
Electrocatalytic Diels-Alder Reactions Assisted By Aromatic Redox Tag
Authors: Chiba Kazuhiro , Yamaguchi Yusuke , Ozaki Atsushi , Okada Yohei
Published: February 2020

Although the Diels-Alder reaction is one of the most classic organic transformations, it is still in the front line of carbon-carbon bond formation toolbox and has been producing modern research topics in synthetic chemistry. Especially, the reaction mechanism has been studied intensively and also expanding to a wide variety of the combination of diene and dienophile. The reaction partners must be electronically matched, namely, electron-rich and electron-deficient substrates are required. In order to overcome this limitation, electron transfer strategy can be used. Typically, the reaction between both an electron-rich diene and dienophile are electronically mismatched, however, one electron oxidation by chemical oxidants or photosensitizers can produce a radical cation of one component, which is then trapped by the other component.

We have been developing electrocatalytic intermolecular carbon-carbon bond formations in lithium perchlorate/nitromethane electrolyte solution. We have designed the reaction based on an aromatic “redox tag” concept, that is, the aromatic ring which provides both as an oxidant and a reductant in an overall electrochemical transformation. Since radicals, ions, and radical ions are all significantly stabilized by an aromatic ring and the redox potentials can be fine-tuned by the number and/or position of substituents, programmed electron transfer events could be achieved. These results in hand, we herein demonstrate electrocatalytic Diels-Alder reactions based on an aromatic redox tag strategy.

Initially, we tried to optimize the reaction conditions by using trans-anethole and isoprene as a model reaction partner. These substrates are both relatively electron-rich, therefore, no reaction occurred without an electron transfer. In this context, we found that only a catalytic amount of electrical input was able to complete the reaction, even in high concentration conditions. We also found that the reaction partners were able to be designed by an expected manner by using an aromatic redox tag concept. In the presentation, the synthesis and electrochemical details will be discussed.
Intramolecular Electron Interaction in Various Oligo-nitro-Thiacalix[4]Arenes and Their Electrochemical Reduction
Authors: Ludvík Jiří , Liška Alan
Published: February 2020

Calixarene skeleton is a stable supramolecular frame which is electrochemically inactive. Suitable substitution on the upper and lower rim, alternatively structure modification or introduction of heteroatoms lead to unusual and surprising properties of this system.

Thiacalix[4]arenes contain four aromatic units connected by sulphur atoms. This contribution will be focused especially on two series of 1,3-alt-conformers bearing one or more nitro groups as electrochemical probes.

The first series consists of eight para-tetranitro derivatives which resemble each other in their electrochemical response: first two two-electron reversible waves are followed by final step during which a tetrakis(hydroxylamino) derivative is formed. This reduction pattern is analogous to the “standard” methylene-bridged para-tetranitrocalix[4]arenes, where no mutual electron interaction takes place, all nitrogroups are totally indepencent and finally tetraanion tetraradical is formed  [1,2].

The second series includes four meta-nitro derivatives. Generally, the electroreductive behaviour of them is more complicated (except the first member which bears only one nitrogroup). Presence of two and three nitro groups in the same molecule in position meta to lower rim (that means in position ortho- and para- towards the thia bridges), exhibit clear intramolecular communication in contrary to the methylene-bridged calixarenes [3]. This phenomenon was confirmed by quantum chemical calculations. 

Acknowledgement:  This work was supported by the GACR grant No. 13-21704S, by institutional support RVO: 61388955 and by the  GAUK project No. 798214. The authors thank prof. Pavel Lhoták for granting the compounds.

References:

[1]   Alan Liška, Pavel Vojtíšek, Albert J. Fry, Jiří Ludvík: J.Org.Chem 78 (2013) 10651 – 10656.

[2]   Alan Liška, Marco Rosenkranz, Jiří Klíma, Lothar Dunsch, Pavel Lhoták, Jiří Ludvík:  Electrochimica Acta 140 (2014) 572 – 578.

[3]   Alan Liška, Karolína Flídrová, Pavel Lhoták, Jiří Ludvík: Monatsh. Chem 146 (2015) 857–862.
Short-Step Anodic Synthesis of Color-Tunable Emissive Nucleoside Analogues
Authors: Okada Yohei , Shimada Kouhei , Kitano Yoshikazu , Chiba Kazuhiro
Published: February 2020

Since natural nucleobases are not emissive, emissive nucleoside analogues have been widely used to monitor fundamental biochemical transformations directly. Nowadays, useful libraries of synthetic emissive nucleoside analogues have been constructed and researchers have a wide variety of choices. A typical approach to prepare these synthetic probes is “pre-formed” manner, namely, a glycosylation is carried out using emissive nucleobases under carefully selected conditions to control both stereoselectivity at the anomeric position and regioselectivity of the aglycon attack. Such a glycosylation usually requires a time-consuming trial-and-error procedure, because the reaction selectivities are affected by the interaction of the protected groups of both the sugar and aglycon. On the other hand, the preparation approach based on “post-forming” manner would be effective since a cumbersome glycosylation could be done in an early synthesis stage.

We have been developing anodic intermolecular cycloadditions in lithium perchlorate/nitromethane electrolyte solution. In this electrolyte solution, unactivated alkenes can function as effective carbon nucleophiles to trap anodically generated cations or radical cations, leading to the formation of corresponding ring systems. Especially, we previously reported that the anodic oxidation of methoxyphenols in the presence of alkene nucleophiles was able to give highly emissive dihydrobenzofuran derivatives through formal [3 + 2] cycloadditions. These results in hand, we herein demonstrate a short-step “post-forming” synthesis of novel emissive nucleoside analogues based on the anodic cycloadditions.

Initially, we tried to attach a methallyl moiety to a ribose scaffold as an alkene nucleophile. After the numerous optimizations, we finally accomplished the stereoselective allylation at the anomeric position to obtain both a- and b-methallyl ribose and we were able to use each corresponding pure form for further transformations. The anomeric stereochemistry was successfully fixed at the first synthesis stage. Methoxyphenols were then anodically oxidized in the presence of the methallyl ribose and we found that emissive dihydrobenzofuran structures were able to be constructed on the sugar moiety in one step. The emission color was significantly affected by the carbonyl substituent, ranging roughly from 400 nm to 500 nm with long stokes shift values. In the presentation, the synthesis details and photophysical properties will be discussed.
Electrochemical Study of Reactivity of Orthophthalaldehyde with Primary Amines
Authors: Donkeng Dazie Joel , Ludvík Jiří
Published: February 2020

Orthophthalaldehyde (OPA) is an aromatic dialdehyde with aldehydic groups in positions 1 and 2. The two formyl groups exhibit inductive, resonance and steric effects. Due to the inductive and resonance effects, one aldehydic group is activated by the other one and, as a result, the molecule is strongly reactive towards nucleophiles. In addition to this, the mutual ortho-position of the carbonyls  enables intramolecular ring formation.  

The reactivity of OPA with amines is widely used since many years in the determination of amino acids [1] and in application of OPA as a biocide [2]. In the literature related to these applications the mechanism of reaction of OPA with amines is not completely understood. The present study was made in order to describe the detailed mechanism of OPA with primary amines using DC- and DP-polarography and UV/Vis spectrophotometry. The experiments were performed in aqueous buffered solutions of different pH, in non-aqueous acetonitrile and in mixed acetonitrile/H2O media with aqueous or non-aqueous stock solution of OPA. It has been observed that at pH between 7.5 and 10.5, OPA is reduced in three waves of reduction instead of two as mostly mentioned in the literature [3,4]. Its reduction is strongly influenced by pH-dependent hydration. It was found that there is a significant difference in reaction pattern, when using hydrated or non-hydrated form of OPA, respectively. Although the dialdehydic form was always considered as the species reacting with amines [5,6], the experiments showed that the reactivity of OPA with amines is directly related to the hydrated form of OPA, while the non-hydrated OPA undergoes hydration reaction prior the reaction with amines. It was also found that the reaction rate of OPA with primary amines is strongly influenced by the number of H-atoms at the α–carbon atom which may reflect the steric hindrance.

Acknowledgement: The material support from the grant GACR No. 13-21704S and the institutional support RVO 61388955 are acknowledged.

References

(1) Norton, D. R.; Howell, N. Analytical Chemistry
1954, 26, 1116-1119.

(2) Simoes, M.; Simoes, L. Journal of Basic Microbiology
2007, 47, 230-242.

(3) Norton, D. R.; Mann, C. K. Analytical Chemistry
1954, 26, 1111-1115.

(4) Zuman, P.; Salem, N.; Kulla, E. Electroanalysis
2009, 21, 645-649.

(5) Kulla, E.; Zuman, P. Organic & Biomolecular Chemistry
2008, 6, 3771-3780.
Redox-Responsive 4 H-Bond Arrays for Supramolecular Applications
Authors: Smith Diane K. , Cedano Mario , Clare Laurie A. , Darzi Ghazwan M
Published: February 2020

Due to the ease of synthesis and strong H-bonding, Meijer’s ureidopyrimidone (UPy) 4 H-bonding array has been extensively investigated for use in a variety of functional supramolecular assemblies and polymers.  However, somewhat surprisingly, there are relatively few examples of electroactive UPy’s, particularly ones in which electron transfer has a significant effect on the dimerization of the self-complementary AADD or ADAD arrays.  Recently we have described an electroactive UPy that contains a phenylenediamine redox couple formed by attachment of a p-dimethylaminophenyl group to R1. In this system the AADD tautomer is favored.  Two electron oxidation of the phenylenediamine leads to a sufficient increase in the acidity of one of the urea H donor sites such that proton transfer occurs, resulting in breakup of the dimer. In more recent work we have been investigating the effect of redox couples attached at the R2 position. In one example, based on initial studies by Alexander et al. (Chem Comm 2007, 22, 2246), a ferrocene is attached to this position.  CV studies indicate that like the phenylenediamine system, oxidation of the ferrocene leads to break up of the dimer.  In another example, an alkyl pyridinium group is attached to the R2 position to create a “monoquat” (N-alkyl-4,4'-bipyridinium) type redox couple.  In this case, the weaker binding DADA array is favored in the starting oxidation state.  Reduction of the pyridinium should increase the negative charge on the pyrimidinol leading to stronger rather than weaker H-bonding as observed in the other cases.  Initial CV studies suggest that this is happening, although the voltammetry is much more complicated than that observed in the other examples. More detailed investigations, currently in progress, will help to ascertain whether the binding strength is indeed increasing upon reduction.

Figure 1
Limits of Acetonitrile Dryness Via Molecular Sieve Method
Authors: Staley Patrick Andrew , Lopez Eric M , Metzger Joy , Smith Diane K.
Published: February 2020

Acetonitrile (MeCN) is a common solvent in synthetic chemistry and electrochemistry where it is often used when a polar, aprotic solvent is needed.1,2 In the past few years, the importance of controlling water content of aprotic solvents has been pointed out several times2,3 and the suggestion of allowing the solution to sit for a time over 3A molecular sieves has been proposed.4 There should be no surprise that there is a definite limit to the utility of this method, as complexes with closely spaced Lewis acids and bases have been shown to have catalytic effects in the past5 and molecular sieves often consist of main group metal oxides and halides.

We report here a definite limit to solvent dryness where MeCN left over 3A molecular sieves for more than a few days will decay into one or more products that include acidic goups, aromatic groups, and one or more functional groups that will adhere to an electrode surface after a reduction/oxidation cycle. We present CV experiments involving duroquinone (DQ) as a probe molecule to show how surface coverage of the electrode differs between three common electrode materials—Pt, Au, and glassy carbon—changes over time, and also how CV characteristics typical of protonation show up after just allowing the MeCN to sit over the molecular sieves for a little while. Finally, we use NMR spectroscopy, Raman spectroscopy, and mass spectrometry to gain some understanding of the identity of the one or more decay products.

1. D. Bradley, G. Williams, and Michelle Lawton. “Drying fo Organic Solvents: Quantitative Evaluation of the Efficiency of Several Desiccants”. J. Org. Chem. (2010) Vol. 75, iss. 24, pp. 8351-8354.

2.Yanlan Hui, Elaine Lay Khim Chng, Cheryl Yi Lin Chng, Hwee Ling Poh, and Richard D. Webster. “Hydrogen-Bonding Interactions between Water and the One- and Two- Electron-Reduced Forms of Vitamin K1: Applying Quinone Electrochemistry To Determine the Moisture Content of Non-Aqueous Solvents”. J. Am. Chem. Soc. (2009) Vol. 131, iss. 4, pp. 1523-1534.

3. Patrick A. Staley, Eric M. Lopez, Laurie A. Clare, and Diane K. Smith. “Kinetic Stabilization of Quinone Dianions via Hydrogen Bonding by Water in Aprotic Solvents”. J. Phys. Chem. C. (2015) Vol. 119, iss. 35, pp. 20319-20327.

4. Malcolm E. Tessensohn, Hajime Hirao, and Richard D. Webster. “Electrochemical Properties of Phenols and Quinones in Organic Solvents are Strongly Influenced by Hydrogen-Bonding with Water”. J. Phys. Chem. C. (2013) Vol. 117, iss. 2, pp. 1081-1090.

5. Deng Zhaoxiang, Qui Wenfeng, Li Weijia, and Li Yadong. “Cyclotrimerization of nitriles catalyzed by Li3N”. Chinese Science Bulletin. (2004) Vol. 49, No. 2, pp. 127-130.
Kinetics of Fast Electrochemical Processes Studied By Impedance Spectroscopy. Frequency Dispersion at High Frequency Range
Authors: Kulboka Pawel , Polczynski Piotr , Jurczakowski Rafal Robert
Published: February 2020

The difficulty of the kinetics determination for very fast electrochemical reaction by using impedance spectroscopy (EIS) is related to the fact that the charge transfer resistance for this process is much smaller than the solution resistance. Moreover, for very fast reactions only a low frequency part of the spectra can be observed when potentiostat is coupled with frequency response analyzer in a classical three electrode arrangement. In such case, the high frequency part of the spectra is very often entirely covered by artifacts related to a relatively low time constant of the potentiostat. A special experimental setup is needed for such experiments, in which impedance is measured in stand-alone mode of the frequency response analyzer. The solution resistance can be minimized by using twin electrode arrangement, in which two identical electrodes are facing each other [1]. However, at high frequency part of the impedance spectra a distinct frequency dispersion occurs due to an unequal and frequency dependent current distribution. Therefore a special attention has to be devoted to control the geometry of the electrode arrangement. Unequal current distribution can be eliminated by using recessed electrodes [2]. However, even for recessed electrodes, a distinct frequency dispersion can be observed at kHz region. This effect is more pronounced in the presence of specific adsorption [3]. To date its origin has not been fully understood.  

In this study high frequency impedance measurements (up to 1 MHz) have been carried out in a twin electrode and hanging meniscus configurations. Recessed electrodes have been used for the first time to study the kinetics of hydrogen electrosorption at Pt(111) at high frequency range. Hydrogen absorption in palladium thin layers (50 nm) covered by platinum monolayers (1ML/Pd) have also been investigated as model systems involving diffusion processes related to hydrogen absorption. In the 1ML/Pd system, the hydrogen insertion is particularly fast [4], the resistance of the charge transfer, related to this process, is in the order of 0.02 Ωcm2. For these model electrochemical processes the frequency dispersion at high frequency rage will be discussed.

Literature:

[1] B. Losiewicz, R. Jurczakowski, A. Lasia, Electrochim. Acta, 80 (2012) 292-301

[2] Frateur, I.; Huang, V. M. W.; Orazem, M. E.; Pebere, N.; Tribolletd, B.; Vivier, V., Electrochim. Acta 53 (2008) 7386-7395.

[3] T. Pajkossy, Z. Phys. Chem.,226 (2012) 935-943

[3] P. Połczyński, R. Jurczakowski, J. Power Sources, 2016 in press
Investigation of a Redox-Responsive 4 H-Bond Array Capable of Strong Self-Dimerization
Authors: Darzi Ghazwan M , Smith Diane K.
Published: February 2020

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

UPy dimers can exist in two tautomeric forms called pyrimidinol and pyrimidinone. In order to more efficiently study the electrochemistry of the two forms, two compounds, 4-acetylpyridinium (AcP) and N-methyl-4,4’-bipyridinium (MeV+), were used as model compounds. AcP resembles the pyrimidinone tautomer and MeV+ resembles the pyrimidinol tautomer. The cyclic voltammetry (CV) scans for the two model compounds in CH2Cl2 and CH3CN show two widely spaced, reversible redox waves. In contrast, CV’s of UPy(RP) in these solvents show two closely spaced reductions.  The first occurs at a potential very similar to that seen with simple model compounds.  The second is considerably positive of that observed for the model compounds, consistent with strong stabilization of the doubly reduced form by H-bonding.  However, the voltammetry is complex. The first reduction is partially reversible if the scan direction is switched immediately after the peak, but irreversible if the scan direction is switched after the second reduction peak.  Going through the second reduction also leads to the appearance of new oxidation waves at more positive potentials.  This behavior suggests, not surprisingly, that the second reduction induces proton transfer and tautomerization.  It is possible that the new oxidation peaks are due to oxidation of a more strongly H-bonded dimer. Further studies to help elucidate what is actually happening in this system will include concentration dependent CV’s and analysis of binding strength using NMR.

Figure 1
Orientational Control of Electroactive Photosystem I on Chemically Modified Electrodes
Authors: Cliffel David , Gizzie Evan Alexander
Published: February 2020

The ability to control the orientation of proteins on chemically modified electrodes and within films of conducting or redox polymers would allow for the efficient electron transfer.  Unfortunately, extraction of proteins and protein complexes like photosystem I from biological membranes often scrambles the precise orientational control found in native plants.  In this talk, we will present alternative methods and chemical reactions that can help maintain the memory of the  correct protein orientation as originally in the membrane after the protein complex of photosystem I is extracted from spinach.  The resulting voltammetry and photochronoamperometry of these modified electrodes will be compared to non-modified protein extractions.
An Electroenzymatic CO2 Conversion to Formate on Cu Electrode Using NADH Co-Enzyme
Authors: Jung Kwang-Deog , Kim Seung-Han , Yoon Sungho
Published: February 2020

Mimicking photosynthesis using has been attempted to convet CO2. The reaction scheme consists of electrochemical NADH regeneration and enzymatic CO2 reduction. Carbon and metal electrodes were not suitable for electrochemical NADH regenreation because the inactive NADH formation by dimerization of NADH was not avoidable. Electron mediators were required to get nearly 100% active NADH by the electrochemical method. Rh carbene
Electrochemical Investigation of Titanium Electrode in Aqueous Tetrafluoroborate Solution and in Aqueous Formate Solution
Authors: May Michael , Paul Elizabeth , Katovic Vladimir
Published: February 2020

Titanium alloy electrodes are widely employed as both cathodes and anodic substrates.  The superior corrosion resistance and low density of titanium makes it a useful material for industrial applications. In oxygen containing environments such as air or water, a thin titania layer spontaneously forms on bare titanium surfaces. Historically, the operative surface states of titanium have been termed: active [essentially metallic], transitional, and passive [comprising a titania over-layer]. In this project, the electrochemical response of a titanium electrode in contact with aqueous tetrafluoroborate solution [or in contact with aqueous formate solution] was monitored to tentatively identify the surface states.

Tetrafluoroboric acid is strongly ionizable in water and resultant HBF4 solutions are able to oxidize various metals. Starting with either HBF4 or KBF4, the electrochemical response of a titanium disk electrode in contact with aqueous tetrafluoroborate solutions [sparged with argon gas] was recorded. Cyclic voltammograms of 0.1 molar HBF4 on titanium, without additional electrolyte, showed two cathodic features near -0.51 V and -0.95 V versus Ag-AgCl electrode [see figure below]. The more negative feature is posited to correspond to active state titanium with H2 evolution. Scan reversal near -0.95 V to the positive direction promptly generates a prominent anodic peak near -0.65 V though the post-peak current remains anodic and rather steady out to +2.0 V. The prominent anodic peak may correspond to dissolution of titanium metal. Interestingly, the shapes of the cyclic voltammograms of aqueous KBF4  solutions were experimentally determined to be pH dependent.

By contrast, formic acid is weakly ionizable in aqueous solutions. Cyclic voltammograms of 3.5 molar HCO2H solutions on titanium showed a cathodic feature near -0.87 V that may correspond to active state titanium and, upon positive direction scanning, an anodic feature that starts near -0.25 V and plateaus after +0.2 V. The anodic plateau is posited to correspond to passive state titanium. Cycling between about +0.55 V and -1.0 V led to a detectable negative potential shift in the H2 evolution reaction [possibly due to titania formation during positive scanning]. At the similar hydrogen ion condition of pH 1, cyclic voltammograms of aqueous HCO2H and HBF4 were different:  the prominent anodic peak was not observed for formic acid.

Figure 1
Polarization Controlled Electrocatalytic and Photoelectrocatalytic Activity of Ferroelectric Catalyst
Authors: Kushwahab Himmat Singh
Published: February 2020

The coupling effect between ferroelectric polarization and electrochemical processes makes possible the engineering of charge-carrier conduction characteristics at the heterojunction between a polarized ferroelectric catalyst and a chemical solution. It is well known that ferroelectricity can affect a material's surface physics which result into enhance catalytic properties. Ferroelectric materials have spontaneous polarization, which can be reoriented between equivalent domain states by an applied electric field. Therefore, ferroelectrics are potential material to achieve switchable surface chemistry for electrochemical applications.

In this work we are going to present polarization controlled electrocatalytic and photoelectrocatalytic activity of ferroelectric catalyst. The increase in remnant polarization shows appreciable enhancement in the electrochemical and photoelectrochemical activity towards OER in alkaline medium and waste water treatment. The photoelectrocatalytic acitivity was investigated for hazardous pharmaceutical pollutants.
Microstructure Analysis of Polymer Electrolyte Membrane Fuel Cell Catalyst-Ionomer Inks and Cathode Catalyst Layers By Ultra Small Angle X-Ray Scattering
Authors: Kariuki Nancy , Myers Deborah J , Fongalland Dash , Bonastre Alex M. , Sharman Jonathan
Published: February 2020

The successful development of novel materials for polymer electrolyte membrane fuel cell (PEMFC) electrodes is hindered by the lack of a fundamental understanding of the complex, multicomponent nature of the catalyst layer (CL), the interplay of its components, and their independent and cooperative effects on the effective properties. One of the most prevalent methods for preparing PEMFC membrane-electrode assemblies is the  thin film decal transfer (DT) method, which involves dispersing the catalyst powder and perfluorosulfonic acid ionomer in a solvent media to form a catalyst ink, and then forming a porous thin film CL which is then transferred to the membrane via hot-pressing. To achieve maximum performance, the CL needs to have (i) the maximum interface of ionomer and catalyst for the anode and cathode reactions, (ii) the appropriate pore structure to allow gas and water diffusion, and (iii) ionomer  networks that bind the carbon aggregates together, providing structural integrity for the catalyst layer and a proton conduction path. For optimization, the type of solvent, solvent-to-solids ratio, and ionomer-to-carbon ratio are variables which affect the resulting CL structure and performance. Characterization of both catalyst inks and catalyst layers is necessary to understand how processing, structure, properties, and performance are all related.

In this study, a systematic approach was taken to study the microstructure of the catalyst ink formulations and the prepared CLs using ultra-small-angle X-ray scattering (USAXS). By combining USAXS with small angle X-ray scattering (USAXS-pinSAXS), it is possible to obtain scattered intensity spanning over several decades in scattering vector, q (q = 4πsinθ/l), which can provide size and structural information from 1 nm to 6 mm. USAXS-pinSAXS measurements were performed at the Advanced Photon Source (APS) at Argonne National Laboratory. Multiple-level curve fitting, using a suite of macros written for Igor Pro-based software, was used to extract from the scattering data the particle size, size distribution, and geometry of the carbon-supported Pt and Pt-alloy aggregates in catalyst-ionomer-solvent inks and catalyst layers. The USAXS-pinSAXS study showed formation of aggregated microstructures, which are different for the Pt and Pt-alloy catalyst inks and catalyst layers.
A Comprehensive DFT Guide for Highly Efficient Electrochemical Ammonia Synthesis on New Class of Electrocatalysts
Authors: Abghoui Younes , Skulason Egill
Published: February 2020

The results of a comprehensive computational screening for new electrocatalysts that are stable, active and selective towards electrochemical reduction of nitrogen to ammonia at room temperature and ambient pressure is presented on a range of transition metal nitride surfaces. Density functional theory (DFT) calculations are used to study the thermochemistry of cathode reaction so as to construct the free energy profile and to predict the required onset potential for activation of nitrogen to ammonia via a Mars-­van Krevelen mechanism. Five crucial criteria are investigated in this work to identify promising electrocatalysts for electrochemical ammonia formation in aqueous media; (1) identification of the reaction mechanism and calculation of the nitrogen splitting barrier, (2) investigation of the catalytic activity and quantification of the potential-determining/rate-determining steps, (3) determination of kinetic or thermodynamic barriers for vacancy diffusion into the bulk, (4) investigation of the stability of the surfaces against poisoning in an electrochemical environment, and (5) estimation of the potential required for removal of any oxygen atoms that may adsorb onto the surface upon exposure to electrochemical environment. With this approach, the (100) and (111) facets of the rocksalt as well as the (100) and (110) facets of the zincblende structures of all the naturally occuring d-block elements in the priodic table are scrutinized. The most promising candidates turned out to be the (100) facets of the rocksalt structure of VN, CrN, NbN and ZrN that should be able to form ammonia at ­-0.51 V, ­-0.76 V, -­0.65 V and -­0.76 V vs. SHE, respectively. All are found to be much more active towards nitrogen reduction than towards the competing hydrogen evolution reaction, in contrast to pure metals, which largely evolve hydrogen. Therefore, higher current efficiencies towards ammonia is expected at low onset potentials. An additional benefit to the present analysis is that the method presented in this work may be applicable to other aqueous phase heterogeneous catalytic reactions, where a Mars-van Krevelen mechanism is operative with both selectivity and activity being key catalytic criteria.

Figure caption: Free energy diagram for NH3 formation via a Mars–van Krevelen mechanism on the (100) facet of RS VN where all the possible adsorption sites for H are investigated and the most energetically favourable site and therefore the most stable intermediates are depicted.

Figure 1
One-Step Synthesis of Hydrangea-like Cu2O@N-Doped Activated Carbon As Air Cathode Catalyst in Microbial Fuel Cell
Authors: Li Kexun , Liu Ziqi
Published: February 2020

In present study electrochemical deposition technology was used to modify the activated carbon (AC) cathode with hydrangea-like Cu2O and notrogen simultaneously, and the performance was improved greatly. The maximum power density was 1613±25 mW m-2, 84% and 62% more than controls repsectively. The electrochemical performances of cathodes were evaluated by Linear sweep voltammetry, exchange current density (i0) and Electrochemical impedance spectroscopy. Hydrangea-like mophology provided more active sites and channels for electrons of oxygen reduction reaction. X-ray XRD, FTIR and XPS results the existence of oxygen vacancy, crystal defects, acidic functional groups and hydrophilic functional groups, and C-N bond, especially pyridine, pyrrole and quaternary N, played a significant catalytic role in oxygen reduction reaction. Electrodeposition is a promising way to modifi AC cathode with metal and nitrogen at the same time.
The Addition of Ortho-Hexagon Nano Spinel Co3O4 to Improve the Performance of Activated Carbon Air Cathode Microbial Fuel Cell
Authors: Ge Baochao , Li Kexun
Published: February 2020

Commercial Co3O4 and ortho-hexagon spinel nano-Co3O4 (OHSNC) were doped in the AC at a different percentage (5%, 10% and 15%) respectively to enhance the performance of microbial fuel cell (MFC). The maximum power density of MFC with 10% OHSNC doped cathode was 1500 ± 14 mW m-2, which was 97.36% and 41.24% higher than the bare AC air cathode and commercial Co3O4 respectively. The electrocatalytic behavior for their better performance was discussed in detail with the help of various structural and electrochemical techniques. The OHSNC was characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM). The results showed that the improved performance owed to both the enhancement of kinetics activity and the number of electron transfer in the ORR, and the internal resistance was largely reduced. Therefore, OHSNC was proved to be an excellent cathodic catalyst in AC air cathode MFC.
(Invited) Ion Diffusion in Ionic Liquids: Single Molecule Fluorescence Spectroscopy
Authors: Welton Tom , Edel Joshua B , McIntosh Alastair J.S. , Ivanov Aleksander , Nawawi Mohd A. B.
Published: February 2020

An ionic liquid is an ionic substance in which its constituent ions are in motion. Consequently, it is not possible to understand the nature of an ionic liquid without understanding how its constituent ions move. However, gaining a thorough understanding the nature of ion motion in ionic liquids remains a fundamental challenge.

 Single molecule fluorescence (SMF) confocal spectroscopy offers a powerful, but as yet largely underutilized tool to measure the diffusion of probe ions in an ionic liquid under a variety of conditions.

 To enable SMF measurements, it was necessary to develop the synthesis of ionic liquids with very low background fluorescence. The SMF derived diffusivity of the cationic probe Rhodamine 123 in dilute (ca. 100 pM) solutions in [C4C1im][NTf2] solutions was compared to diffusivity of the ionic liquid cations derived from Pulse Gradient Stimulated Echo NMR measurements. The SMF derived diffusivity of the cationic probe Rhodamine 123 was measured under various applied potentials and throughout the system’s relaxation back to its unperturbed state. This relaxation was found to be markedly slower than in salt solutions in molecular solvents.
The Effect of Pressure on the Role of Tfsa Conformational Exchange in Ionic Liquids
Authors: Suarez Sophia , Rua Armando , Cuffari David , Pilar Kartik , Hatcher Jasmine , Ramati Sharon , Wishart James
Published: February 2020

A comprehensive study of multi-nuclear (1H, 2H, and 19F) magnetic resonance self-diffusion coefficients (D) and spin-lattice relaxation times (T1) was done as functions of both temperature and pressure on selectively deuterated 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (EMIM TFSA) ionic liquid isotopologues and related ionic liquids. While variable temperature studies provided useful insight, pressure dependent studies were more elucidating as discussed below.  First, stronger electric field gradients were indicated in the alkyl chain region compared to the imidazolium ring of EMIM TFSA as determined from variable temperature 2H T1. Second and most significantly, variable pressure measurements of the EMIM and TFSA diffusion revealed independent motions for the cations and anions, with that of the TFSA anions being slowed much more by increasing pressure than for the EMIM cations.  Activation volumes were determined from the pressure dependent D data and values of 28.8 ± 2.5 cm3/mol and 14.6 ± 1.3 cm3/mol were obtained for TFSA and EMIM respectively.  Typically, smaller activation volumes support less restriction in motion. One possible explanation for this difference in behavior between EMIM and TFSA is that increasing pressure limits the conformational mobility of the TFSA. Third, variable pressure 2H T1 data shows two T1 regimes, for the MD3 and D2 isotopologues between 0.1-100 and 100-250 MPa respectively. These two regimes could represent dissimilar arrangements for the EMIM cation.  Activation volumes determined from the pressure dependent 2H T1 data were 21 and 25 (0-100 MPa) and 11 and 12 (100-250 MPa) cm3/mol for the MD3 and D2 isotopologues, respectively. These and other details will be discussed.
(Invited) High Pressure Investigation of Charge Transport in Ionic Liquids
Authors: Paluch Marian , Wojnarowska Zaneta
Published: February 2020

The purpose of this presentation is to present recent results obtained from the high pressure studies of the charge transport in ionic liquids. The experimental data from high pressure dielectric measurements will be analyzed in term of the density scaling concept [1,2].  As a result we will show that there is a relationship between intermolecular potential, thermodynamics and  electrical transport  properties of investigated ionic liquids.  In the second part of the presentation we will focus on the decoupling phenomenon between viscosity and dc-conductivity in protic ionic liquids at various temperature and pressure conditions [3-5]. Finally, the general rules governing the charge transport in this class of ionic liquids will be formulated.

References:

1. M. Paluch, S. Haracz, A. Grzybowski, M. Mierzwa, J. Pionteck, A. Rivera-Calzada and C. Leon, J. Phys. Chem. Lett. 1 987 (2010)

2. M. Paluch, Z. Wojnarowska, P. Goodrich, J. Jacquemin, J. Pionteck and S. Hensel-Bielowka, Soft- Matter  11, 6520-6526 (2015)

3. Wojnarowska, Z.; Roland, C. M.; Swiety-Pospiech, A.; Grzybowska, K.; Paluch, M. Phys. Rev. Lett. 108015701 (2012)

4. Wojnarowska, Z.; Wang, Y.; Pionteck, J.; Grzybowska, K.; Sokolov, A.P.; Paluch, M. Phys. Rev. Lett.
111225703 (2013)

5. Z. Wojnarowska, K. J. Paluch, E. Shoifet, C. Schick, L. Tajber, J. Knapik, P. Wlodarczyk, K. Grzybowska, S. Hensel-Bielowka, S. P. Verevkin, and M. Paluch,  J. Am. Chem. Soc.,  137 1157 (2015)