Low Cathodic Potentials Research Articles

Increase in lactate yield by growing Corynebacterium glutamicum in a bioelectrochemical reactor

Under conditions conductive to growth, Corynebacterium glutamicum showed higher lactate yield from glucose (1.62 ± 0.04) in a bioelectrochemical reactor including 0.2 mM of anthraquinone 2,6-disulfonate with the electrode potential regulated at -0.6 V (vs. Ag/AgCl) than in a non-regulated environment (1.10 ± 0.03), clarifying that low cathodic potential is beneficial for lactate production.

Redox chemistry of trifluoromethyl sulfonium salts as CF3 radical sources

The electrochemical behaviour of Umemoto reagent 5 and the sulfonium-based Shibata reagents 7, 8, 12 and 13 was investigated in anhydrous acetonitrile, N,N-dimethylformamide and methanol using cyclic voltammetry. In MeCN, all reagents are reduced in two distinct steps with the first reduction occurring at low cathodic potentials between −0.49 and −0.72V on a glassy carbon electrode. This event probably corresponds to the cleavage of the SCF3 bond with formation of the trifluoromethyl radical. In contrast to the Umemoto reagent 5, the Shibata reagents 7, 8, 12 and 13 were found to be unstable in N,N-dimethylformamide (in the absence of electrochemical or photochemical activation), giving either the ring-opened alkyne 14 for Shibata reagent 7 or the corresponding 2-substituted benzothiophene derivatives 15–18 for reagents 8, 12 and 13. In MeOH, the Umemoto reagent 5 and Shibata reagent 7 underwent irreversible reductions at more cathodic potentials than observed in MeCN and DMF; the Shibata reagent 7 was unstable in this solvent. The electrochemical data obtained in this study should be of general interest for those interested in the development of trifluoromethylation processes carried out under photoredox and electrochemical conditions.

Electrochemical lithiation and passivation mechanisms of iron monosulfide thin film as negative electrode material for lithium-ion batteries studied by surface analytical techniques

The lithiation/delithiation reaction mechanism of iron monosulfide (troilite Fe(1−x)S, x=0.07) as negative electrode material for lithium-ion batteries and the electrode passivation induced by reductive decomposition of the electrolyte were studied by combining surface (X-ray photoelectron spectroscopy, XPS, and time-of-flight secondary ion mass spectrometry, ToF-SIMS) and electrochemical analysis (cyclic voltammetry, CV) of thin films grown by thermal sulfidation of metal iron substrate. XPS analysis performed at different stages of the first lithiation/delithiation cycle shows that the reversible formation of metallic iron and lithium sulfide is not solely limited to the principal cathodic/anodic peaks at 1.23/1.89V and that disulfide products, possibly Li2FeS2, are also formed at lower cathodic potentials. ToF-SIMS depth profiling of the thin film electrode confirms an incomplete process of conversion/deconversion and reveals an expansion/shrinkage of the material induced by electrochemical lithiation/delithiation. The solid electrolyte interphase (SEI) layer formed on the iron monosulfide thin film electrode is mostly composed of Li2CO3 with some presence of ROCO2Li. For the first time, it is shown that the SEI layer thickness varies upon conversion/deconversion, between 9 and 4.5nm in the lithiated and delithiated states, respectively, on a conversion-type electrode. Moreover, the electrolyte decomposition products penetrate the bulk electrode until the current collector owing to pulverization/cracking caused by expansion and shrinkage of the thin film material upon cycling.

Single-crystalline nanotubes of spinel lithium nickel manganese oxide with lithium titanate anode for high-rate lithium ion batteries

Single-crystalline nanotubes of LiNi0.473Mn1.473Al0.054O4 (LNMAO-NT) have been synthesized and evaluated as cathode using LNMAO-NT/Li half cell and LNMAO-NT/Li4Ti5O12 (LTO) full cell, respectively. Galvanostatic charge/discharge tests show that the LNMAO-NT half cell exhibits discharge capacity of 118 mAh g−1 and specific energy (calculated only based on the cathode material) of 508 Wh kg−1 at 5 C. Two types of full cells (LTO-limited and LNMAO-NT-limited cell) are constructed using three-electrode configuration. Measurement results reveal that LTO-limited full cell has a lower cathode potential vs. Li metal than LNMAO-NT-limited one at the end of cutoff voltage. The LNMAO-NT/LTO full cell exhibits discharge capacity of 158 mAh g−1 at 0.5 C and 120 mAh g−1 at 10 C, respectively, showing superior high-rate capability of LNMAO-NT. In addition, 87% of capacity retention of the LNMAO-NT/LTO full cell can be achieved after 200 cycles at 5 C, indicating good structural stability of one dimensional LNMAO-NT. Moreover, study of in situ Raman spectra at different potentials reveals good structural reversibility during charging and discharging process, indicating that LNMAO-NT would be one of the most promising high-voltage cathodes for high power lithium ion batteries.

New insight into the mechanism of cathodic electrodeposition of zinc oxide thin films onto vitreous carbon

In this study, the mechanism of zinc oxide (ZnO) electrodeposition from aqueous zinc nitrate solution at 70°C was investigated on vitreous carbon and bulk zinc electrodes using cyclic voltammetry experiments. The first widely accepted route corresponds to ZnO precipitation from Zn2+ and OH− produced by NO3− reduction; the second route, which is discussed in this article, is due to Zn2+ reduction into metallic Zn followed by its oxidation by nitrate ions. For this case, we demonstrate why Zn formation cannot be observed while Zn2+ reduction was detected. Structure and morphology of bulk deposits were investigated using X-ray diffraction and scanning electron microscopy. Thin films of well-oriented ZnO nanorods were grown on vitreous carbon from Zn(NO3)2 solution at low cathodic potential corresponding to that of zinc metal deposition. X-ray diffraction (XRD) measurements showed that the nanorods are crystalline and preferably grow along the (002) direction.

A highly-ordered porous carbon material based cathode for energy-efficient electro-Fenton process

Electro-Fenton process for water purification utilizes electrical energy for chemical transformation. However, its key step, oxygen reduction reaction (ORR) to generate H2O2, suffers from added energy consumption due to a side reaction of H2 evolution. This study attempted to make this process energy effective by using an innovative gas diffusion electrode (GDE) fabricated from a carbon material with highly-ordered pores and large surface area (CMK-3). It was found that the employment of this cathode enabled a low cathodic potential of −0.5V (vs. SCE), at which H2 evolution could be greatly eliminated. Meanwhile, the H2O2 built-up at CMK-3 GDE was 3.1 and 4.4 times higher than those at the other two carbon electrodes (graphite GDE and carbon paper). Moreover, dimethyl phthalate (DMP) degradation in the electro-Fenton process using CMK-3 GDE occurred much more rapidly with a reaction apparent rate constant about 8.8 and 11.5 times higher than those using the other two types of electrodes, respectively, whereas the corresponding energy consumption on CMK-3 GDE at the degradation half-life time was only 50% and 27%, respectively.

Electrochemical analysis of separators used in single-chamber, air-cathode microbial fuel cells

Polarization, solution-separator, charge transfer, and diffusion resistances of clean and used separator electrode assemblies were examined in microbial fuel cells using current–voltage curves and electrochemical impedance spectroscopy (EIS). Current–voltage curves showed the total resistance was reduced at low cathode potentials. EIS results revealed that at a set cathode potential of 0.3V diffusion resistance was predominant, and it substantially increased when adding separators. However, at a lower cathode potential of 0.1V all resistances showed only slight differences with and without separators. Used separator electrode assemblies with biofilms had increased charge transfer and diffusion resistances (0.1V) when one separator was used; however, charge transfer resistance increased, and diffusion resistance did not appreciably change with four separators. Adding a plastic mesh to compress the separators improved maximum power densities. These results show the importance of pressing separators against the cathode, and the adverse impacts of biofilm formation on electrochemical performance.

Aerial Oxidation of Protonated Aromatic Amines. Isolation, X-ray Structure, and Redox and Spectral Characteristics of N- Containing Dyes

This work reports the results of our investigation on the aerial oxidation of aromatic amines that are promoted by protic acid. While primary aromatic amines produce substituted phenazines as major products, N-phenyl-o-phenylenediamine produces polycyclic aromatic heterocycles like azaacene and secondary and tertiary amines give exclusively the dyes containing a triphenylmethane moiety. Isolation of the compounds and the effects of substitutions on the aromatic rings have been investigated. In this context, plausible reaction steps that are involved have been discussed. Single-crystal X-ray structure analyses of the representative compounds are solved to authenticate their formation. In almost every case, a high degree of delocalization of electron was noted. The compounds have been characterized thoroughly and show rich spectral properties. For example, the phenazine molecules exhibited absorption peaks between 475 and 605 nm because of the charge-transfer transition from the amine and tricyclopyrazine moiety. Their acidochromic and solvatochromic behaviors, which are supported by theoretical calculations, are investigated. The polycyclic azacene molecule exhibits strong absorption in the visible region and fluoresces with high quantum yield. The phenazine dyes undergo a quasi-reversible reduction at a low cathodic potential that varies linearly as a function of Hammett's constant.

A study on the electrochemical deposition behavior of uranium ion in a LiCl–KCl molten salt on solid and liquid electrode

Electrochemical behaviors of uranium ion (U3+) from a molten salt electrolyte to metal solid and liquid cathodes were studied for an electrorefinning recovery in pyrochemical separation. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were carried out to investigate the interfacial processes related with cathodic reduction of uranium ion. Electrodeposition at solid Mo and liquid Cd electrodes are discussed as well as mass transfer in liquid Cd metal and LiCl–KCl molten salt phases. The reduction of U3+/U at both of the electrodes preceded a (quasi-)reversible reaction with exchange of three electrons. The difference of the standard formal potential at both solid and liquid electrodes was found which may be attributable to lowering activity of U in liquid Cd phase. The impedance data measured at different potentials were fitted to the equivalent circuits for each electrode. In case of solid electrode, the impedance spectrum was related with surface diffusion followed by lattice formation as well as charge transfer at low cathodic potential. At high cathodic potential, the effect of surface relaxation induced by U deposition on the surface of Mo electrode was found. In case of liquid electrode, the atomic diffusion of reduced U metal in liquid Cd phase appeared before the saturation of Cd by U. Over the solubility limit, the formation of U dendrite on the Cd surface made the impedance magnitude decreased by increasing the electrode surface area.

Electrodeposition of bismuth telluride nanowires with controlled composition in polycarbonate membranes

Bismuth telluride nanowires were potentiostatically deposited from a water/DMSO 50%, v/v electrolyte within polycarbonate etched ion-track membranes covered by a platinum substrate. The presence of DMSO shifts the potentials to more negative values and slows down the cation diffusion. Cyclic voltammetries on recessed Pt nanoelectrodes using polycarbonate membranes highlight a complex electrochemical behavior through several cathodic and anodic peaks which are not observed onto platinum discs macroelectrodes. Analytical investigations enabled the determination of appropriate deposition conditions to finely tune the average composition of the nanowires. Calibrated TEM-EDX analyses evidence high aspect ratio nanowires, whose composition is strongly dependent on the deposition potential. In the same manner as for bismuth telluride film electroplating, bismuth enrichment occurs at more cathodic deposition potential whereas tellurium enrichment is observed at low cathodic potentials. Stoichiometric nanowires of 60nm diameter were obtained at −100mV vs Ag/AgCl from an electrolyte which contains [Bi3+]=1.5[HTeO2+]=15mM. The composition is homogeneous along the nanowire except at both edges: the cap is rich in bismuth whereas the base is rich in tellurium. The composition at the nanowire base is adjusted by setting a short initial voltage step (Ui=−300mV vs Ag/AgCl, ti=2s). In the case of stoichiometric compounds, the resulting nanostructures were found to be polycrystalline with a preferential orientation along the direction perpendicular to the planes (015).

Novel organic–inorganic hybrid material based on tris(2,2′-bipyridyl)dichlororuthenium(II) hexahydrate and Dawson-type tungstophosphate K 7[H 4PW 18O 62]·18H 2O as a bifuctional hydrogen peroxide electrocatalyst for biosensors

In this study, we synthesized a new hybrid material using Wells–Dawson K 7[H 4PW 18O 62]·18H 2O (PW 18) and tris(2,2′-bipyridyl)dichlororuthenium(II) hexahydrate ([Ru(bpy) 3]Cl 2·6H 2O). CHN elemental analyses depicted that 1 mol of [H 4PW 18O 62] 7− reacts with 3 mol of [Ru(bpy) 3] 2+ to form K[Ru(bpy) 3] 3H 4PW 18O 62. By adding the mild reducing agent (KI), CHN analyses illustrated that 1 mol of [H 4PW 18O 62] 7− reacts with only 1 mol of [Ru(bpy) 3] 2+ to yield K 5[Ru(bpy) 3]H 4PW 18O 62 hybrid material. FT-IR spectra showed the presence of both [Ru(bpy) 3] 2+ cation and the Dawson anion. K 5[Ru(bpy) 3]H 4PW 18O 62 was immobilized on glassy carbon (GC) electrode and the modified electrode was subjected to cyclic voltammetry and amperometry in presence of hydrogen peroxide (H 2O 2) and found to exhibit a notable bifunctional catalytic activity towards the oxidation and the reduction of H 2O 2 at neutral pH and at reasonably low cathodic and anodic potentials. Reductive determination was found to be more efficient than the oxidative detection. The resulting H 2O 2 sensor K 5[Ru(bpy) 3]H 4PW 18O 62/GC based reductive detection at −0.4 V vs. Ag/AgCl has a sensitivity of ∼0.78 μA/mM mm 2, fast response time (<5 s), low detection limit (<0.5 μM), high selectivity towards endogenous interferences such as uric acid, acetaminophen and ascorbic acid, a linear range from 0.5 μM to at least 90 mM H 2O 2 and was stable for at least 5 weeks. This type of hybrid catalysts could be of great relevance for applications in oxidase based biosensors.

High Electron Transfer Efficiency of Titania Dioxide Nanotube for Low Potential Electrochemiluminescent Biosensing

AbstractStrong electrochemiluminescence (ECL) of titania dioxide nanotubes at physiological condition was observed, with relatively low cathodic potential due to its large surface area and high electron transfer efficiency. The coreactant of the ECL emission was proved to be H2O2, produced from the reduction of dissolved oxygen, leading to a mild ECL system for biosensing. Based on “coreactant inhibition” mechanism, the ECL quenchers could be measured by inhibiting the transformation of O2 to H2O2. Using hemoglobin as a model, the quenched ECL emission followed SternVolmer equation in a wide linear range. Thus a novel methodology for detection of “coreactant inhibition”‐related quencher could be developed with acceptable sensitivity.

Characterization of nanocrystalline Co–W coatings on Cu substrate, electrodeposited from a citrate-ammonia bath

Cobalt–tungsten nanocrystalline coatings were electrodeposited on copper substrate using different current densities. The deposited coatings were single phase solid solution with an average grain size of about 18nm, showing a nodular type of surface morphology. By increasing the deposition current density, the density of nodules was increased, with no obvious variation in grain size. Electrochemical impedance spectroscopy (EIS) confirmed the codeposition of tungsten through reduction of tungsten oxide film formed during the electrodeposition process. However, the role of ternary complexes in the bath cannot be ruled out, especially at lower cathodic potentials. The Co–W coating deposited at lower current densities showed higher tungsten content, microhardness, wear resistance and friction coefficient. However, this coating showed an inferior corrosion resistance. By increasing the deposition current density, a low tungsten coating with high corrosion resistant was obtained. This is attributed to the lower value of exchange current density of water reduction in the present of oxygen (i0H2O) achieved on the coating with lower tungsten content.

Highly luminescent columnar ZnO films grown directly on n-Si and p-Si substrates by low-temperature electrochemical deposition

In this study, nanocolumnar zinc oxide thin films were catalyst-free electrodeposited directly on n-Si and p-Si substrates, what makes an important junction for optoelectronic devices. We demonstrate that ZnO thin films can be grown on Si at low cathodic potential by electrochemical synthesis. The scanning electron microscopy SEM showed that the ZnO thin films consist of nanocolumns with radius of about 150 nm on n-Si and 200 nm on p-Si substrates, possess uniform size distribution and fully covers surfaces. X-ray diffraction (XRD) measurements show that the films are crystalline material and are preferably grown along (0 0 2) direction. The impact of thermal annealing in the temperature range of 150–800 °C on ZnO film properties has been carried out. Low-temperature photoluminescence (PL) spectra of the as-prepared ZnO/Si samples show the extremely high intensity of the near bandgap luminescence along with the absence of visible emission. The optical quality of ZnO thin films was improved after post-deposition thermal treatment at 150 °C and 400 °C in our experiments, however, the luminescence intensity was found to decrease at higher annealing temperatures (800 °C). The obtained results indicate that electrodeposition is an efficient low-temperature technique for the growth of high-quality and crystallographically oriented ZnO thin films on n-Si and p-Si substrates for device applications.

Seedless Copper Electrodeposition onto Tungsten Diffusion Barrier

Copper was electrodeposited directly onto a sputter-deposited tungsten diffusion barrier layer in an acidic copper–ammonium–citrate bath. The nucleation characteristic of copper deposits according to applied cathodic potential was investigated. The nucleation mode, nuclei density, and dominant copper species to be preferentially reduced were critically dependent on the applied cathodic potential. Pure instantaneous or progressive nucleation of copper was not observed, but instead, mixed nucleation mechanisms appeared. For low cathodic potentials, the copper deposits, which were reduced mainly from cupric ions, showed consequently a progressive nucleation characteristic despite initial instantaneous nucleation. For large cathodic potentials, the instantaneous nucleation of copper was achieved from the reduction of copper complexes following the early stage of progressive nucleation. The copper nuclei density of calculated for filling the sub-70 nm damascene structures was approached by applying large cathodic potentials.

Single cell study of electrodeposited cathodic electrodes based on Pt–WO 3 for polymer electrolyte fuel cells

Cathodic electrodes based on electrodeposited Pt–WO 3 material for proton exchange membrane fuel cells (PEMFC) were studied in single cell configuration. Preparation of the electrodes was carried out by electrodeposition of Pt and WO 3 on commercial gas diffusion layer substrates (microporous carbon black layer on carbon cloth, ELAT E-TEK). The process of simultaneous electrodeposition of Pt and WO 3 is first analyzed from voltammetric curves. It is observed that the deposition of Pt is enhanced when WO 3 is present. Compositional analysis of the electrodes shows metallic platinum and WO 3 in variable proportions. The electrodeposited electrodes were characterized in single PEMFC. Membrane–electrode assemblies were prepared with Nafion ® 117 electrolyte membrane and a standard Pt/C anode. Pt–WO 3 electrodes showed enhanced stability and good response in single cell up to 1500 h. Performance degradation is attributed to a decrease in Pt electroactive area and increase of the internal resistance of the cell. These effects are possibly a consequence of the production of mobile tungsten species, like soluble WO 2 at high current demands and low cathode potentials.

Formation of Surface Traps on Quantum Dots by Bidentate Chelation and Their Application in Low‐Potential Electrochemiluminescent Biosensing

Bidentate chelation, meso-2,3-dimercaptosuccinic acid (DMSA), was used as a stabilizer for the synthesis of CdTe quantum dots (QDs). The bidentate chelate QDs, characterized with FT-IR, PL, and UV/Vis spectroscopy; element analysis; and high-resolution transmission electron microscope, exhibited surface traps due to the large surface/volume ratio of QD particle and the steric hindrance of the DMSA molecule. The unpassivated surface of the QDs produced a narrower band gap than the core and electrochemiluminescent (ECL) emission at relatively low cathodic potential. In air-saturated pH 7.0 buffer, the QDs immobilized on electrode surface showed an intense ECL emission peak at -0.85 V (vs. Ag/AgCl). H(2)O(2) produced from electrochemical reduction of dissolved oxygen was demonstrated to be the co-reactant, which avoided the need of strong oxidant as the co-reactant and produced a sensitive analytical method for peroxidase-related analytes. Using hydroquinone/horseradish peroxidase/H(2)O(2) as a model system, a new, reagentless, phenolic, ECL biosensor for hydroquinone was constructed, based on the quenching effect of ECL emission of QDs by consumption of co-reactant H(2)O(2). The biosensor showed a linear range of 0.2-10 μM with acceptable stability and reproducibility. This work opens new avenues in the search for new ECL emitters with excellent analytical performance and makes QDs a more attractive alternative in biosensing.

The effect of Tl(I) on the hard gold alloy electrodeposition of Au–Co from acid baths

The mechanism of gold alloy electrodeposition from acid baths in the presence of a trace amount of Tl + was investigated using cyclic voltammetry, chronoamperometry and chronopotentiometry. Analysis of chronoamperometric measurements showed a progressive and instantaneous nucleation and growth mechanism at low and high cathodic potentials, respectively. The current time transients of hard gold baths containing Tl + showed underpotential deposition (UPD) features. The surface morphology of the resultant deposits was studied by scanning electron microscopy (SEM). The SEM studies showed that addition of cobalt leads to the formation of fine sized grains. Also with addition of thallium to the solution, enhancement and inhibition of the gold deposition were observed at low and high cathodic potentials, respectively. A bright, grain refined, coherent deposit with high hardness resulted from hard gold plating bath by addition of Tl +.

Behavior of Al-Ga Alloy on the Negative Side of the Open - circuit Potential in Sodium Chloride Solution

The influence of the addition of small quantities gallium to high-purity aluminium on its electrochemical behaviour at high cathodic potentials (up to -2.0 V vs. SCE) was investigated using the potentiostatic pulse method. After cathodic polarization, anodic current was traced vs. time in order to determine the quantity of charge necessary for oxidation of substances formed. Anodic current responses to the return to the EOCP were also recorded in the period of 1 s. Time responses of the cathodic and anodic current were analyzed. The range of low and high cathodic potentials (LCP, HCP) was defined for all the samples. It has been established that the oxide film retains its properties in the LCP range, while in the HCP range cathodic breakdown and hydration of the oxide take place. Electrochemical methods complemented by SEM and EDAX analysis before and after the cathode pulse of -1.9 V vs. SCE.

Effect of anodic prepolarization on hydrogen entry into iron at cathodic potentials in 0.1 M NaOH without and with EDTA or sodium molybdate

Efficiency of cathodes for water electrolysis decreases after shut-downs due to corrosion at open-circuit potential. In the present work the effect of prepolarization at various potentials on hydrogen entry into iron during cathodic potential sweeps was studied by the measurement of the hydrogen permeation rate (HPR) through a 35-μm thick iron membrane in 0.1 M NaOH without and with EDTA or Na 2MoO 4 at 25 °C. Two types of the enhanced hydrogen entry at low cathodic polarizations were distinguished: one after prepolarization at low cathodic or low anodic potentials, and another after prepolarization at high anodic potentials. It is suggested that both types can be explained by acidification at the metal surface, the former due to anodic oxidation of iron, and the latter due to cathodic reduction of oxide layer (mainly of Fe 3O 4). XPS analysis revealed the presence of hydrated Fe–O species of unidentified valence. EDTA and Na 2MoO 4 increased the efficiency of hydrogen entry ( j H/ j c ratio), and molybdates also strongly increased cathodic currents of HER. Some of the effects of these additives can be explained in terms of their effect on surface layers.