Controlled Potential Electrolysis Research Articles

Electrocatalytic Water Oxidation with Surface Anchored Mononuclear Manganese (II) ‐ Polypyridine Complexes

AbstractCatalytic oxidation of water by manganese complexes is of great interest because it can serve as a model for the natural oxygen evolving complex, Mn4CaO5. Complex compounds are highly active and tunable, but their limited stability and solubility restrict them for practical water oxidation applications. In the present article we have prepared surface anchored Mn(II)‐complexes, [MnII(H2O)2(X)2(dcbpy)] (where dcbpy= 4,4′‐dicarboxy‐2,2′‐bipyridine; X=acetate, sulphate, chloride ions) on gold electrode surface using self‐assembly process and applied for the electrocatalytic oxidation of water in neutral pH. The modified electrode was characterized by using different spectral, microscopic and electrochemical techniques. The Mn(II)‐acetate containing gold electrode (Mn(II)‐dcbpy‐Au) electrocatalytically oxidized water at a current density of 1.6 mA cm−2 with low overpotential ∼ 310 mV and a Tafel slope of 56 mV/decade. The modified electrode showed high electrochemical stability during controlled potential electrolysis. It was also observed that the Mn(II)‐acetate immobilized on dcbpy‐Au electrode showed higher electrocatalytic activity in oxidation of water than Mn(II)‐chloride or Mn(II)‐sulfate containing dcbpy‐Au electrode. The newly in‐situ generated Mn(II)‐complex modified electrode is inexpensive and highly efficient for the catalytic oxidation of water than the surface bound Mn‐based electrocatalysts reported previously.

One-Pot Anodic Conversion of Symmetrical Bisamides of Ethylene Diamine to Unsymmetrical gem-Bisamides of Methylene Diamine.

Symmetrical bisamides of ethylene diamine of type ArCONHCH2CH2NHCOAr undergo anodic C-C bond cleavage in acetonitrile-LiClO4 under controlled-potential electrolysis. The electrogenerated carbocation intermediates react with the solvent acetonitrile to afford unsymmetrical gem-bisamides of type ArCONHCH2NHCOMe in aone-potreaction. The yields of the latter products are moderate (up to 60%). Other minor products involve two symmetrical gem-bisamides of type ArCONHCH2NHCOAr and MeCONHCH2NHCOMe and fragmentation products (e.g., ArCONHCHO, ArCONH2, and ArCN).

Electrochemical Oxidation of Theophylline in Organic Solvents: HPLC‐PDA‐ESI‐MS/MS Analysis of the Oxidation Products

AbstractThe electrochemical oxidation of theophylline was investigated by controlled potential electrolysis in two different organic solvents and in water for comparison. The anodic oxidation was monitored by cyclic voltammetry in situ and UV‐Vis spectrophotometry ex situ and the final electrolyzed solutions were analyzed by tandem mass spectrometry after chromatographic separation with an HPLC‐PDA‐ESI‐MS/MS system. The main oxidation products evidenced as the main diode array chromatographic peaks were tentatively assigned to dimeric forms of theophylline, two of which have never been reported before, on the base of retention time, UV‐Vis spectrum, m/z ratio in both positive and negative ESI modes and fragmentation pattern. Two chemical paths following the primary mono‐electronic anodic oxidation of theophylline to the final evidenced oxidation products have been proposed.

Group IV transition metal based phospho-chalcogenides@MoTe2 for electrochemical hydrogen evolution reaction over wide range of pH

Electrochemical water splitting proved to be one of the most attractive sources of green fuel energy but the easy and time-consuming synthesis of highly active, low-priced, steady and earth-abundant metals electrocatalysts is still a challenge among the researcher. In this work, we have reported the fabrication of Group IV transition metal (M = Ti, Hf, and Zr) based phospho-chalcogenides and their composite with MoTe2 via simple hydrothermal synthesis process. The prepared nanocomposites (MP2S6@MoTe2) were compared with respect to their best performance towards HER over the entire pH range. Among the different kind of prepared nanocomposite, TiP2S6@MoTe2 exhibited special almond like shape with self-layered morphology and henceforth selected as best catalyst on the basis of their low Tafel slope, small onset potential, low charge transfer resistance and small overpotential value over the wide range of pH. It was also found that nanocomposites modified working electrode showed long cycle durability in the acidic pH in controlled potential electrolysis study.

Telomere DNA Binding, Cleavage and Anticancer Activity of [Cu(phendione)(Hpyramol)Cl

Background:The ligand Hpyramol is a redox active, which on coordination with Cu(II) cleaves DNA without any added reductant. Another ligand phendione is known for its wide application towards anticancer activities. We combined the ligands with CuCl2 to have an intercalation moiety and a redox active ligand in participation towards telomere DNA cleavage and anticancer activity.Objective:In this study, our aim is to interact it with Human telomere DNA and to see their effects on cancer cells.Methods:The complex [Cu(L)(L’)Cl] has interacted with the human telomere DNA sequence (TTAGGG), HTelo20. The HTelo20 was stabilized under both parallel and antiparallel G-quadruplex conformations and the complex [Cu(L)(L’)Cl] has interacted followed by circular dichroism spectroscopy and gel electrophoresis.Results:The parallel G-quadruplex and randomly coiled conformations of HTelo20 were easily cleaved than the anti-parallel G-quadruplex conformation. The nature of DNA cleavage was found to be oxidative rather hydrolytic. The formation of phenoxyl radical species under electrochemical and controlled potential electrolysis conditions by the complex [Cu(L)(L’)Cl] proves the possibility of oxidative nature of DNA cleavage. The comet assay also proves the DNA cleavage induced by the complex [Cu(L)(L’)Cl] inside the nucleus of HeLa cancer cells.Conclusion:The complex [Cu(L)(L’)Cl] was tested for anticancer activity, induced by ROS and DNA cleavage. The IC50 values resulted in nanomolar concentrations with selected cancer cell lines. Relatively the Cu complex shows less toxicity with the normal cell line L132.

Enhanced hydrogen evolution reaction on highly stable titania‐supported PdO and Eu2O3nanocomposites in a strong alkaline solution

In this work, PdO/TiO2 and Eu2O3/TiO2 nanocomposites (NCs) were synthesized using a new facile, template-free, and one-step solvothermal approach and characterized by several instrumentation techniques. X-ray photoelectron spectroscopy studies revealed the presence of oxidized form of the Pd and Eu nanoparticles within the NC materials (PdO and Eu2O3). The two catalysts exhibited remarkable activity for the hydrogen evaluation reaction (HER) in a strong alkaline solution (4.0 M NaOH) with PdO/TiO2 catalyst being the best, which recorded an exchange current density (jo) of 0.26 mA cm−2 and a Tafel slope (βc) of 125 mV dec−1. Such parameters are not far from those recorded for a commercial Pt/C catalyst (0.71 mA cm−2 and 120 mV dec−1) performed here under the same operating conditions. Eu2O3/TiO2 catalyst recorded jo and βc values of 0.05 mA cm−2 and 135 mV dec−1. The Tafel slopes 125 and 135 mV dec−1 calculated on the PdO/TiO2 and Eu2O3/TiO2 catalysts suggest a HER kinetics controlled by the Volmer step. PdO/TiO2 catalyzed the HER with a high turnover frequency of 2.3 H2/s at 0.2 V versus the reversible hydrogen electrode, while Eu2O3/TiO2 catalyst only measured a turnover frequency value of 1.25 H2/s at the same overpotential. The two catalysts exhibited excellent stability and durability after 10 000 cycles and 72 hours of controlled potential electrolysis at a high cathodic overpotential, reflecting their practical applicability. Scanning electron microscope and X-ray photoelectron spectroscopy examinations revealed that the morphology and chemistry of both catalysts were not altered as a result of the performed long-term stability and durability tests.

Electrosynthesis of N-Methylisatin.

Isatin in a solution of dry N,N-dimethylformamide/NaClO4 is electroreduced in the presence of CH3I. N-methylisatin (NMI) is obtained in quantitative molar yield and high current efficiency by controlled potential electrolysis (CPE). NMI and N-methylisatoic anhydride are the reaction products when CPE is performed in the absence of CH3I, but adding it once the CPE was completed. The water effect on the identity and yield of the reaction product(s) is investigated. Reaction pathways are proposed.

Electrochemical Reduction of Acetochlor at Carbon and Silver Cathodes in Dimethylformamide

Chloroacetamides are a popular class of herbicides often used against weeds in a variety of major crops, such as corn, cotton, rice, and soybeans.1 One such herbicide is acetochlor or 2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)acetamide that, since its registration in 1994, has become commonly used in the United States.2 Although acute and chronic toxicological effects in humans of acetochlor at low environmental exposures are still unknown, animal tests have shown in some species the development of lung tumors, nasal epithelia, and thyroid cancer; for that reason, the U.S. EPA classifies acetochlor as likely to be carcinogenic in humans.3,4 This project’s primary objective is to investigate the electrochemical behavior of acetochlor and to develop a possible degradation method for acetochlor as well as other chloroacetamide-type herbicides. To the best of our knowledge, previous electrochemical studies of acetochlor have been performed only via anodic Fenton treatment;5 electrochemical reduction has not yet been pursued. In the present study, we have conducted cyclic voltammetry to evaluate the electrochemical behavior of acetochlor at carbon and silver cathodes in dimethylformamide (DMF) containing 0.05 M tetramethylammonium tetrafluoroborate (TMABF4). Glassy carbon is a traditional electrode material and silver has been shown to be catalytic for the cleavage of carbon–halogen bonds. Reduction of acetochlor at silver (–0.95 V vs. Cd/Hg) occurs at more positive potentials than at carbon (–1.4 V vs. Cd/Hg) and affords primarily the dechlorinated parent compound, N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)acetamide. In addition, reduction of acetochlor in the presence of electrogenerated nickel(I) salen (–0.95 V vs. Cd/Hg) indicates that nickel salen complexes can be an alternative to silver in order to achieve catalytic reduction. Controlled-potential (bulk) electrolysis coupled with traditional analytical methods such as gas chromatography–mass spectrometry (GC–MS) led to the identification and quantitation of reduction products. References Lamberth, C. Chloroacetamide Herbicides. In Bioactive Carboxylic Compound Classes, Pharmaceuticals and Agrochemicals, Lamberth, C., Dinges, J., Eds.; Wiley: Germany, 2016; pp 293–302.Lerro, C. C.; Koutros, S.; Andreotti, G.; Hines, C. J.; Blair, A; Lubin, J.; Ma, X.; Zhang, Y.; Beane Freeman, L. E. Int. J. Cancer. 2015, 137, 1167–1175.U.S. Environmental Protection Agency. Acetochlor (Harness) Pesticide Petition Filing 1/00. Fed Regist. 2000, 65, 3682–3690. Report of the Food Quality Protection Act (FQPA) Tolerance Reassessment Progress and Risk Management Decision (TRED) for Acetochlor. EPA 738-R-00-009; U.S. Environmental Protection Agency (U.S. EPA): 2006, 1–9.Friedman, C. L.; Lemley, A. T.; Hay, A. J. Agric. Food Chem. 2006, 54, 2640–2651.

Metal–Organic Frameworks as Porous Templates for Enhanced Cobalt Oxide Electrocatalyst Performance

Water oxidation to dioxygen is an essential energy capture process in biological systems mediated by the oxygen-evolving complex. It continues to attract interest as a half-reaction in electrochemical water-splitting to hydrogen and dioxygen in abiotic systems. There is a corresponding interest in improving the activity of nonprecious metal electrocatalysts for this reaction. One of the most well-known water oxidation catalysts is amorphous cobalt oxide. This catalyst can operate in water at neutral pH with low overpotentials and is known to continually reform under catalytic conditions, a type of self-healing. The active sites for the electrocatalytic reaction are thought to be adjacent octahedral cobalt sites in the bulk material, meaning that only the surface of the material is active. Thus, catalytic activity could be improved by increasing the surface area to volume ratio of the active material. To this effect, codeposited microporous materials such as metal organic frameworks (MOFs) can be used to control the morphology of cobalt oxide thin films. This study employs a highly stable MOF, UiO-66, to act as a templating agent for an electrodeposited cobalt oxide film. By depositing this porous crystalline MOF on the electrode surface prior to the electrochemical growth of the catalyst, we show the catalytic current density of the cobalt oxide material can be increased relative to the unmodified material. Through cyclic voltammetry (CV), controlled potential electrolysis (CPE), and electron microscopy studies, we show that the increase in current density is likely due to an increase in the effective surface area of the catalyst resulting from catalyst deposition around the MOF particles.

Electrochemical reduction of 2-halo-N-phenylacetamides at glassy carbon cathodes in dimethylformamide

Cyclic voltammetry and controlled-potential (bulk) electrolysis have been employed to investigate the direct electrochemical reductions of 2-bromo-N-phenylacetamide (1a) and 2-iodo-N-phenylacetamide (1b) at glassy carbon cathodes in dimethylformamide containing tetramethylammonium tetrafluoroborate (TMABF4) as supporting electrolyte. Cyclic voltammograms for reduction of 1a and 1b each exhibit a pair of irreversible cathodic peaks; the first peak arises from a combination of one-electron and two-electron reductive cleavage of the respective carbon–halogen bond and the second peak is due to overall two-electron reductive cleavage of the carbon–halogen bond to produce a free halide ion together with 2-oxo-2-(phenylamino)ethan-1-ide. Controlled-potential (bulk) electrolysis of a 5mM solution of 1a or 1b at a potential corresponding to either the first or second cathodic peak affords only phenylacetamide. However, bulk electrolysis of a 10mM solution of 1a or 1b at a potential corresponding to either cathodic peak leads to a mixture of phenylacetamide and 1,4-diphenylpiperazine-2,5-dione. In the presence of a large excess of 1,1,1,3,3,3-hexafluoro-2-propanol (a proton donor), bulk electrolyses of 1a or 1b at a potential on the first peak give phenylacetamide exclusively. When either 1a or 1b is electrolyzed in the presence of 1M D2O, the resulting phenylacetamide is deuterated to a very significant extent (evidence for a carbanion intermediate), and a small quantity of 2-(dimethylamino)-N-phenylacetamide is seen as a side-product. Mechanisms to account for the behavior of 1a and 1b are proposed.

A tunable pair electrochemical strategy for the synthesis of new benzenesulfonamide derivatives

A green, facile and tunable pair electrochemical process was developed for the synthesis of new benzenesulfonamide derivatives by using reductive controlled potential electrolysis of dinitrobenzene (DNB) in the presence of arylsulfinic acids (ASAs). In addition to the usual features associated with paired electrochemical methods, eg high energy efficient, this method has a tunable characteristic, so that, by adjusting the potential, different products can be synthesized. By applying the potential of −0.4 V vs. Ag/AgCl, N-hydroxy-N-(4-nitrophenyl)benzenesulfonamide derivatives are selectively formed, while, by applying the potential of −1.1 V vs. Ag/AgCl, the final products are N-(4-amino-3-(phenylsulfonyl)phenyl) benzenesulfonamide derivatives. This work beautifully shows the potential applications of the electrochemistry as a powerful tool for the synthesis of organic compounds.

A trinuclear cobalt-based coordination polymer as an efficient oxygen evolution electrocatalyst at neutral pH

The dearth of an efficient, robust, abundant and cost-effective water oxidation catalyst is debatably the major hurdle for the technological advancement of artificial photosynthesis devices. Herein, a three dimensional (3D) cobalt-based coordination polymer {[Co3(pyz)(fa)3(dmso)2]·2H2O}n, (1) (pyz = pyrazine, fa = fumarate, dmso = dimethyl sulfoxide) has been synthesized and demonstrated to act as an efficient electrocatalyst towards water oxidation at neutral pH. Compound 1 displays a stair-like arrangement parallel to the b-axis, with the cobalt clusters arranged in a zigzag fashion, and contains small, honeycomb-like channels parallel to the c-axis. Compound 1 shows a remarkable activity for water oxidation and attains a current density of 1 mA.cm−2 at low overpotential (η = 257 mV) with a Tafel slope value of 80.5 mV.dec−1. This high performance of 1 in catalysing the water oxidation reaction is attributed to its unique 3-D architecture. The results of electrochemical investigations, including long-term and controlled potential electrolysis, are anticipated to guide the forthcoming advancement in creating efficient, cheap and noble metal (Pt/Ru/Ir) free catalysts for the water oxidation reaction.

Electroreductive dechlorination of γ-Hexachlorocyclohexane catalyzed by Rh2(dpf)4 in nonaqueous media, where dpf = N,N′-Diphenylformamidinate (1-) ion

The electroreductive dechlorination of γ-hexachlorocyclohexane (lindane) was investigated in non-aqueous media using as a catalyst the dirhodium complex Rh2(dpf)4, where dpf=the anion of N, N′-diphenylformamidinate. Rh2(dpf)4 undergoes two reversible one-electron redox processes in pyridine and/or N,N′-dimethylformamide (DMF), corresponding respectively to Rh24+/Rh25+ and Rh24+/Rh23+. Electrochemical and spectroelectrochemical measurements indicate that lindane reacts with the Rh23+ center in singly reduced [Rh2(dpf)4]−, giving a transient carbon-bonded dirhodium complex along with Cl−. Further catalytic dechlorination of lindane subsequently occurs with the activity of Rh2(dpf)4 as a catalyst depending upon the solvent conditions. Rh2(dpf)4 shows a higher catalytic reduction current in pyridine than in DMF for the degradation of lindane. This catalytic current can be further enhanced if 6% water (v/v) is added to the pyridine solution. Bulk controlled-potential electrolysis combined with GC–MS verified that although the addition of water to the neat pyridine increased the catalytic activity of Rh2(dpf)4, neat pyridine is still a better solvent for the formation of more extensively dechlorinated products of lindane. In neat pyridine, lindane can be converted stepwise to tetrachlorocyclohexene, dichlorobenzene isomers, chlorobenzene and the fully dechlorinated product benzene, the last of which becomes predominant at the end of the electrolysis. In pyridine having 6% added water, other than those dechlorinated products seen above, trichlorobenzene isomers are formed upon lindane degradation. Meanwhile, the relative concentrations of dichlorobenzene isomers and chlorobenzene become higher, while the yield of benzene becomes lower than the corresponding results obtained in neat pyridine. Based on the measured distribution of the products under the different solvent conditions, an overall pathway for the degradation of lindane is proposed.

Comparative Study between Pristine Ag and Ag Foam for Electrochemical Synthesis of Syngas with Carbon Dioxide and Water

The electrosynthesis of syngas (H2 + CO) from CO2 and H2O can reduce greenhouse gas emissions and address the energy crisis. In the present work, silver (Ag) foam was employed as a catalytic electrode for the electrochemical reduction of CO2 in aqueous solution to design different syngas ratios (H2:CO). In addition to H2 and CO, a small amount of formic acid was found in the liquid phase. By contrast, the planar polycrystalline Ag yields CO, formic acid, methane and methanol as the carbon-containing products. During the potential-controlled electrolysis, the Ag foam displayed a relatively higher activity and selectivity in the electroreduction of aqueous CO2 to CO compared with its smooth surface counterpart, as evidenced by the lower onset potential, higher partial current density and Faradic efficiency at the same bias voltage. Moreover, the electrode remained stable after three successive cycles. Based on the characterization using X-ray diffraction, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, potential step determination and density functional theory calculations, superior performance was credited to the three-dimensional structure of Ag foam constructed with coral-like Ag particles, in which the numerous edge sites are beneficial for the stabilization of the surface adsorbed COOH species and the exposed {111} facets favor the desorption of adsorbed CO species.

Phase I and phase II metabolism simulation of antitumor-active 2-hydroxyacridinone with electrochemistry coupled on-line with mass spectrometry

Here, we report the metabolic profile and the results of associated metabolic studies of 2-hydroxy-acridinone (2-OH-AC), the reference compound for antitumor-active imidazo- and triazoloacridinones.Electrochemistry coupled with mass spectrometry was applied to simulate the general oxidative metabolism of 2-OH-AC for the first time. The reactivity of 2-OH-AC products to biomolecules was also examined. The usefulness of the electrochemistry for studying the reactive drug metabolite trapping (conjugation reactions) was evaluated by the comparison with conventional electrochemical (controlled-potential electrolysis) and enzymatic (microsomal incubation) approaches.2-OH-AC oxidation products were generated in an electrochemical thin-layer cell. Their tentative structures were assigned based on tandem mass spectrometry in combination with accurate mass measurements. Moreover, the electrochemical conversion of 2-OH-AC in the presence of reduced glutathione and/or N-acetylcysteine unveiled the formation of reactive metabolite-nucleophilic trapping agent conjugates (m/z 517 and m/z 373, respectively) through the thiol group. This glutathione S-conjugate was also identified after electrolysis experiment as well as was detected in liver microsomes.Summing up, the present work illustrates that the electrochemical simulation of metabolic reactions successfully supports the results of classical electrochemical and enzymatic studies. Therefore, it can be a useful tool for synthesis of drug metabolites, including reactive metabolites.

Catalytic Cyclization of Propargyl Bromoethers via Electrogenerated Nickel(I) Tetramethylcyclam in Ionic Liquids: Water Effects

Cyclic voltammetry and controlled-potential electrolysis have been employed to investigate the reductive intramolecular cyclization of propargyl bromoethers derivatives, catalyzed by electrogenerated (1,4,8,11-tetramethyl-1,4,8,11-tetraaza-cyclotetradecane)nickel(I), [Ni(tmc)]+, as the catalyst, in N,N,N-trimethyl-N-(2-hydroxyethyl)ammonium bis(trifluoromethylsulfonyl)imide, [N1 1 1 2(OH)][NTf2] and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C2mim][NTf2] in the absence and in the presence of water. The results show that the reaction leads to the formation of the expected heterocyclic compounds, in moderate to good yields. These compounds are important intermediates in the synthesis of natural products with possible biological activities.

Rapid and High‐Yield Electrosynthesis of Benzisoxazole and Some Derivatives

AbstractCyclic voltammetry and controlled‐potential (bulk) electrolysis have been used to explore the electrochemical reduction of o‐nitrobenzaldehyde (o‐NBA) and 8 other aldehydes and ketones at glassy carbon cathodes in dimethylformamide containing various tetraalkylammonium tetrafluoroborate salts along with a proton donor (4‐chlorophenol). Cyclic voltammograms for reduction of o‐NBA exhibit three cathodic peaks attributable in succession to (a) one‐electron generation of the nitro radical‐anion, (b) three‐electron formation of the hydroxylamine, and (c) two‐electron production of benzisoxazole (anthranil). These findings have been employed to develop efficient controlled‐potential (bulk) electrosyntheses of the following compounds: benzisoxazole, methylbenzo[c]isoxazole, [1,3]dioxolo[4′,5′,4,5]benzo[1,2‐c]isoxazole, naphtho[2,3‐c]isoxazole, 6‐chlorobenzo[c]isoxazole, 6‐methoxybenzo[c]isoxazole, 3‐methyl‐benzo[c]isoxazole, 3‐isopropylbenzo[c]isoxazole, and 3‐phenylbenzo[c]isoxazole. In addition, we have examined the use of a variety of proton donors to optimize the production of the desired product, and we have been able to recover the proton donor at the conclusion of the electrosynthesis. In each case, the synthesized product was separated by means of normal phase chromatography and identified with the aid of NMR spectros‐copy, gas chromatography (GC), and gas chromatography‐mass spectrometry (GC‐MS). Isolated yields of the desired products range from 63 to 92 %. Moreover, our electrosyntheses are catalyst‐free, environmentally green, and rapid (∼30 min).

Electrochemical Oxidation of the Phenolic Benzotriazoles UV‐234 and UV‐327 in Organic Solvents

AbstractThe electrochemical behavior of selected phenolic benzotriazoles (BZTs), namely 2‐(2H‐benzotriazol‐2‐yl)‐4,6‐bis(1‐methyl‐1‐phenylethyl)phenol and 2,4‐di‐tert‐butyl‐6‐(5‐chlorobenzotriazol‐2‐yl)phenol (commercial names UV234 and UV327, respectively) were examined with cyclic voltammetry (CV) and controlled potential electrolysis (CPE) in acetonitrile and dichloromethane solutions. CV indicated that both phenolic BZTs undergo a chemically irreversible oxidation process at approximately Ep°x=+1.0 V vs. Fc/Fc+ (where Ep°x is the anodic peak potential and Fc=ferrocene) to form compounds that cannot be electrochemically converted back to the starting material on the voltammetric timescale. In basic conditions, cyclic voltammetry experiments indicated that the corresponding phenolates (prepared by reacting the phenols with equiv. mols of n‐Bu4NOH) were oxidized at Ep°x∼−0.2 V vs. Fc/Fc+ via a one‐electron diffusion controlled process with anodic (ip°x) to cathodic (ipred) peak current ratios (ip°x/ipred)≫1, suggesting that the produced phenoxyl radicals decomposed rapidly via a chemical step. However, electron paramagnetic resonance (EPR) experiments performed on the bulk electrolyzed solutions of the phenolates after one‐electron bulk oxidation indicated long lifetimes of the UV234. and UV327. phenoxyl radicals. Therefore, the long timescale CPE and spectroscopic (UV‐vis and EPR) studies provided good evidence of a reversible dimerization mechanism between the phenoxyl radicals, which explained the apparent discrepancy with the short timescale CV experiments.

Synthesis and Characterization of meso-Substituted Cobalt Tetradehydrocorrin and Evaluation of Its Electrocatalytic Behavior Toward CO2 Reduction and H2 Evolution.

A meso-aryl substituted cobalt(II) tetradehydrocorrin complex (Co(II)TDHC) has been synthesized and investigated. The corrin framework, determined by X-ray crystallographic analysis, is found to be relatively planar except at the C1 and C19 positions. Cyclic voltammetry (CV) measurements indicate two positively shifted reversible redox couples at -0.53 and -1.70 V vs Fc/Fc+ for [CoII]+/[CoI] and [CoI]/([CoI]•- and/or [CoII]-) ([CoII] = Co(II)TDHC), respectively, compared with the previously reported cobalt porphyrin complex, because the tetradehydrocorrin ligand efficiently promotes the formation of low-valent metal species due to its monoanionic character. Furthermore, it is found that the current in the CV measurement is significantly enhanced upon addition of H2O under a CO2 atmosphere, indicating the progression of electroreductive catalysis by Co(II)TDHC. However, controlled-potential electrolysis (CPE) using Co(II)TDHC under the same conditions shows generation of H2 as a major product and only a small amount of CO as a CO2 reduction product; Faradaic efficiencies are calculated to be 66.8 and 4.5%, respectively. The CPE with a buffer solution under an N2 atmosphere reveals that the selective H2 generation is promoted by the moderate acidification of the solution under CO2 saturation conditions. The present study demonstrates that the significantly stabilized Co(I) species with the monoanionic ligand framework preferentially catalyzes the thermodynamically favored H2 evolution rather than CO2 reduction.

NTBC and MTT Reduction Electrochemistry: Impact on Cu Superconformal Plating for Fabrication of Glass Interposers

Nitro blue tetrazolium chloride (NTBC) and thiazolyl blue tetrazolium bromide (MTT) are the organic additives applied successfully in Cu superconformal filling of through glass vias (TGVs) with aspect ratios 6:1 and 10:1. However, traces of purple inclusion were observed through the cross-sectioning of electroplated samples indicating that a reduction could likely be occurring during the plating process. In this work, the reduction propensity of NTBC and MTT in the course of Cu superconformal plating was assessed in the absence of Cu(II) ions by cyclic voltammetry, controlled-potential electrolysis (CPE), and UV-Vis spectroscopy. A CPE potential of −0.25 V vs Ag/AgCl reference electrode was selected aiming at studying the reduction process as close as possible to the actual potential range of Cu deposition. The CPE and UV-Vis results suggest that both additives reduce steadily with time generating different (by)products. Also, it is shown that the MTT reduces itself at a rate that is substantial at lower pH, producing both surface precipitates and soluble reduction products. Unlike that, the NTBC reduction exhibits weaker pH dependence and generates lower quantity of surface precipitates only. Thus, the reduction of MTT is expected to impact considerably stronger than NTBC the Cu superconformal plating process in TGVs.