Combination Of Cyclic Voltammetry Research Articles

The Influence of Pyridinium-Based Additives on Zinc Electrodeposition in Aqueous Solution

The suitability of N-ethylpyridinium bromide as a potential electrolyte additive for zinc electrodeposition in aqueous solution has been investigated by a combination of cyclic voltammetry, bulk electrolysis, scanning electron microscopy, synthesis and NMR spectroscopy. The current magnitudes of the Zn/Zn(II) redox reaction observed at the electrode decreased dramatically after a single deposition/stripping cycle in the presence of N-ethylpyridinium bromide at switching potentials more negative than −1.30 V vs Ag/AgCl. This is attributed to the reduction of the N-ethylpyridinium cation to form a pyridyl radical that subsequently and rapidly dimerizes. The proposed dimer was synthesized and shown to have a low solubility in aqueous solutions, consistent with a passivation of the electrode surface by precipitation and inhibition of redox behavior. Based on this understanding for the pyridinium cation reduction, alternative pyridinium-based additives have been examined in order to determine their influence on zinc electrodeposition.

Group 6 Metal Complexes as Electrocatalysts of CO2 Reduction: Strong Substituent Control of the Reduction Path of [Mo(η3-allyl)(CO)2(x,x′-dimethyl-2,2′-bipyridine)(NCS)] (x = 4–6)

A series of complexes [Mo(η3-allyl)(CO)2)(x,x′-dmbipy)(NCS)] (dmbipy = dimethyl-2,2′-bipyridine; x = 4–6) have been synthesized and their electrochemical reduction investigated using combined cyclic voltammetry (CV) and variable-temperature spectroelectrochemistry (IR/UV-vis SEC) in tetrahydrofuran (THF) and butyronitrile (PrCN), at gold and platinum electrodes. The experimental results, strongly supported by density functional theory (DFT) calculations, indicate that the general cathodic path of these Group 6 organometallic complexes is closely related to that of the intensively studied class of Mn tricarbonyl α-diimine complexes, which, themselves, have recently been identified as important smart materials for catalytic CO2 reduction. The dimethyl substitution on the 2,2′-bipyridine ligand backbone has presented new insights into this emerging class of catalysts. For the first time, the 2e– reduced 5-coordinate anions [Mo(η3-allyl)(CO)2)(x,x′-dmbipy)]− were directly observed with infrared spectroelectro...

Dynamic electrochemical impedance study of methanol oxidation at Pt at elevated temperatures

The methanol oxidation reaction (MOR) is studied at temperatures up to 140 °C by a combination of cyclic voltammetry, chronoamperometry, and dynamic electrochemical impedance spectroscopy (dEIS). A mechanistic analysis of the reaction is done based on the Tafel relation, the calculated activation energy, and the fitting of dEIS data. At the fuel cell relevant potentials, 0–0.80 V vs RHE, the MOR mechanism is similar at all temperatures. The rate-determining step is the adsorption of water at low overpotentials (< 0.50 V vs RHE), a combination of the methanol adsorption reaction and the surface reaction between adsorbed CO and OH at intermediate potentials (0.50–0.65 V vs RHE), and the methanol adsorption reaction at high potentials (> 0.65 V vs RHE). The shoulder on the oxidation peak at 0.60–0.65 V vs RHE corresponds well with where the CO coverage approaches zero.

Chemisorbed Oxygen-Species-Mediated Electrocatalytic Oxidation of Thiourea and Thiosulfate

The electrocatalytic oxidation of two sulfur(-II) species (thiourea and thiosulfate) on a polycrystalline platinum electrode was studied by combining cyclic voltammetry (CV) with high-performance liquid chromatography and capillary electrophoresis. The surface sulfur species distribution and the charge transfer peaks of the CV curves depend on the formation of chemisorbed oxygen (such as OHads and Oads), indicating that these electrocatalytic reactions are mediated via the chemisorbed oxygen species. The formation of chemisorbed oxygen species plays a dual role during the electrode processes as the poison for metal degradation and the bridge for the electrocatalytic reaction.

Manganese-Driven Carbon Oxidation at Oxic-Anoxic Interfaces.

The formation of reactive manganese (Mn) species is emerging as a key regulator of carbon oxidation rates, and thus CO2 emissions, in soils and sediments. Many subsurface environments are characterized by steep oxygen gradients, forming oxic-anoxic interfaces that enable rapid redox cycling of Mn. Here, we examined the impact of Mn(II)aq oxidation along oxic-anoxic interfaces on carbon oxidation in soils using laboratory-based diffusion reactors. A combination of cyclic voltammetry, X-ray absorption spectroscopy, and X-ray microprobe imaging revealed a tight coupling between Mn(II)aq oxidation and carbon oxidation at the oxic-anoxic interface. Specifically, zones of Mn(II)aq oxidation across the oxic-anoxic transition also exhibited the greatest lignin oxidation potential, carbon solubilization, and oxidation. Microprobe imaging further revealed that the generation of Mn(III)-dominated precipitates coincided with carbon oxidation. Combined, our findings demonstrate that biotic Mn(II)aq oxidation, specifically the formation of Mn(III) species, contributes to carbon oxidation along oxic-anoxic interfaces in soils and sediments. Our results suggest that we should regard carbon oxidation not merely as a function of molecular composition, which insufficiently predicts rates, but in relation to microenvironments favoring the formation of critically important oxidants such as Mn(III).

Implications of Pyran Cyclization and Pterin Conformation on Oxidized Forms of the Molybdenum Cofactor.

The large family of mononuclear molybdenum and tungsten enzymes all possess the special ligand molybdopterin (MPT), which consists of a metal-binding dithiolene chelate covalently bound to a pyranopterin group. MPT pyran cyclization/scission processes have been proposed to modulate the reactivity of the metal center during catalysis. We have designed several small-molecule models for the Mo-MPT cofactor that allow detailed investigation into how pyran cyclization modulates electronic communication between the dithiolene and pterin moieties and how this cyclization alters the electronic environment of the molybdenum catalytic site. Using a combination of cyclic voltammetry, vibrational spectroscopy (FT-IR and rR), electronic absorption spectroscopy, and X-ray absorption spectroscopy, distinct changes in the Mo≡O stretching frequency, Mo(V/IV) reduction potential, and electronic structure across the pterin-dithiolene ligand are observed as a function of pyran ring closure. The results are significant, for they reveal that a dihydropyranopterin is electronically coupled into the Mo-dithiolene group due to a coplanar conformation of the pterin and dithiolene units, providing a mechanism for the electron-deficient pterin to modulate the Mo environment. A spectroscopic signature identified for the dihydropyranopterin-dithiolene ligand on Mo is a strong dithiolene → pterin charge transfer transition. In the absence of a pyran group bridge between pterin and dithiolene, the pterin rotates out of plane, largely decoupling the system. The results support a hypothesis that pyran cyclization/scission processes in MPT may function as a molecular switch to electronically couple and decouple the pterin and dithiolene to adjust the redox properties in certain pyranopterin molybdenum enzymes.

Poly(3,4‐Propylenedioxythiophene) Capsulated Yolk–Shell Carbon Spheres for High‐Performance Electrochemical Capacitors

In this article, the yolk–shell structure of resin‐based carbon spheres (YRFC) and the solid structure of resin‐based carbon spheres (SRFC) were prepared by condensation polymerization, and then novel spherical composites of poly(3,4‐propylenedioxythiophene)/YRFC (PProDOT/YRFC) and PProDOT/SRFC were obtained by in situ chemical oxidative polymerization. The prepared composites were characterized by Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible absorption spectra (UV–vis), Raman, X‐ray diffraction (XRD), Brunauer–Emmett–Teller (BET), X‐ray photoelectron spectrometer (XPS), scanning electron microscope (SEM), and transmission electron microscopy (TEM). Electrochemical behavior of the composites were investigated with reference to their suitability as electrode materials in electrochemical capacitors (ECs), which were accomplished by a combination of cyclic voltammetry and galvanostatic charge/discharge cycles. The resultant PProDOT/YRFC composite showed ideal charge storage capacity with a specific capacitance of 327.5 F g−1 at the current density of 1 A g−1, which is much higher than that of the materials of PProDOT/SRFC (298.1 F g−1) and PProDOT (180.9 F g−1). Furthermore, long cycle life was achieved with the optimized PProDOT/YRFC and the capacitance retention is 87.3% after 10,000 charge/discharge processes, which was attributed to its uniformly dispersible fluffy structure. POLYM. COMPOS., 40:1989–1999, 2019. © 2018 Society of Plastics Engineers

Controlling Selectivity in the Electrochemical Reduction of Acrylonitrile: Towards a Solar-Driven Nylon 6,6 Production Process

Fossil fuel derived carbon dioxide (CO2) emissions have continuously increased over the past century and their impact in climate change is self-evident. The chemical industry is a large contributor to this increase, accounting for more than 5.5% of the global CO2 emissions. Implementing electrochemical routes for the production of large volume chemicals can allow for the direct integration of renewable energy sources into chemical manufacturing. In this way, solar- or wind-powered electrochemical processes could greatly contribute to the reduction of the carbon footprint of the chemical industry. Although inorganic electrosynthetic processes have been successfully implemented in industry at scale (i.e. chloro-alkali and Aluminum production), the implementation of electrochemical methods for the production of organic chemicals has been limited. Adiponitrile (ADN) is the largest-volume organic chemical product currently produced electrochemically (>1.5 million tons/year). ADN is a precursor used in Nylon 6,6 manufacturing and it can be obtained via the electrohydrodimerization of acrylonitrile (AN). Although the electrosynthesis of ADN is considered the most successful organic electrochemical process in industry, it still faces many challenges owing to its energy conversion efficiency and selectivity. Optimizing the composition of the electrolyte can result in significant performance improvements. The implementation of tetraalkylammonium (TAA) ions has been shown to increase the reaction selectivity towards adiponitrile, but there is limited understanding on their role in the mass transport and kinetic aspects of the transformation. In this study, we provide experimental insights into the effects of TAA ions in the selectivity and efficiency of the AN electrohydrodimerization reaction. TAA ions can limit the hydrogen evolution reaction by sterically hindering water molecules from approaching the electrode surface and locally increasing the concentration of organic reactants. These effects are believed to be responsible for the increase in selectivity towards the reduction of AN. In our study, we explored electrolytes containing TAA ions with varying lengths of the alkyl substituents (i.e., methyl, ethyl, butyl and hexyl) and assessed the effects of their molecular size, affinity towards AN, and concentration on the electrolyte conductivity and selectivity. Using a combination of cyclic voltammetry, electrochemical impedance spectroscopy, and chronoamperometry at a cadmium electrode, we showed that optimal performance is achieved for electrolytes containing tetrabutylammonium (TBA) ions. A maximum selectivity towards ADN of 80% was demonstrated for TBA concentrations ranging between 0.04 to 0.5 mM. Furthermore, we studied the effects of TAA ions on the ohmic and mass transport limitations under varying current densities. Our results suggest that (i) the local concentration of AN in the electrical double layer strongly depends on the nature of the TAA and the applied current density and (ii) that this concentration is important in determining the predominant reaction pathways and thus the product distribution between ADN and other electrochemical side products (e.g., propionitrile and 1,3,6 tricyanohexane). The results obtained in this study can be used to derive electrolyte design guidelines which will improve the efficiency of the electrochemical adiponitrile production process. Furthermore, understanding the effects of current density in the selectivity of the reaction allows for the design of operating protocols to directly drive electrochemical transformations with intermittent sources of energy such as solar power. These design guidelines can lead to highly efficient solar-ADN reactors and enable the clean manufacture of precursors for the polymer industry. The performance of proof-of-concept prototypes solar-AND devices will be discussed. Figure 1

Radical formation in polymeric nickel complexes with N2O2 Schiff base ligands: An in situ ESR and UV–vis–NIR spectroelectrochemical study

A series of electrochemically generated polymeric nickel (II) Schiff base complexes was investigated by in situ electron spin resonance (ESR)/ultraviolet–visible–near infrared (UV–vis–NIR) spectroelectrochemistry and the combination of cyclic voltammetry and quartz crystal microbalance (QCM) techniques. The comparative analysis of the in situ ESR and UV–vis–NIR (including low-energy NIR range) spectra of poly-[Ni(Schiff)] films recorded during their oxidation at ambient temperature was performed, which allowed us to monitor the formation of different charge carriers in the polymer at different doping levels and elucidate their structure as well as the extent of their delocalization. The polymer doping level achieved by its oxidation within selected range of potentials was determined by combining the results of cyclic voltammetry and QCM measurements. The influence of the substituents in the diamine backbone and phenolate moieties of the ligand on the spectroscopic properties of the oxidized polymers and number of electrons per monomer unit exchanged in the redox processes was studied in detail. Integration of data from all techniques allowed us to propose the existence of both inter- and intrachain delocalization of radical cations generated in the doped polymers and show that the highest doping levels (up to two positive charges per a monomer unit) are attained in the poly-[Ni(Schiff)] films with highly localized biphenoxyl radical cations.

Electrochemical properties of NASICON-structured glass-ceramics of the Li1+xCrx(GeyTi1-y)2-x(PO4)3 system

The electrochemical stability window of NASICON-structured glass-ceramics of the Li1+xCrx(GeyTi1-y)2-x(PO4)3 system is investigated by a combination of cyclic voltammetry, electrochemical impedance, and X-ray photoelectron spectroscopy techniques. Cyclic voltammetry analyses are performed using a three-electrode setup cell where Ag3SI/Ag is applied as a reference electrode. Cyclic voltammetry measurements are followed by in situ electrochemical impedance spectroscopy, enabling the effect of oxidation and reduction reactions on the electrical properties of the glass-ceramics in question to be determined. X-ray photoelectron spectroscopy, in turn, is applied to determine which chemical species undergo reduction/oxidation. Our findings reveal that the electrochemical stability of this material is limited by the reduction of Ti+4 cations in low potentials (around 2.1 V vs. Li+/Li) and by the oxidation of O−2 anions in high potentials (about 4.8 V vs. Li+/Li). After the first cycle, the electrolytes seem to be stable within a much broader electrochemical window than in the first cycle. However, the results indicate not only that the reduction at low potential is not deleterious to the electrical properties of the electrolytes but also that the oxidation reaction at high potentials is highly detrimental. These findings contradict the common perception about the outstanding stability of NASICON-structured electrolytes in oxidation potentials.

Combination of cyclic voltammetry and single-particle Brownian dynamics methodology to evaluate the fluidity of phospholipid monolayers at polarized liquid/liquid interfaces

The present work shows, for the first time, the use of single-particle Brownian dynamics methodology, followed by optical microscopy, coupled with electrochemistry techniques to evaluate the fluidity of phospholipid films adsorbed at liquid/liquid interfaces. The combination of the two methods allows observing the movement of latex beads at the liquid/liquid interface modified by a phospholipid monolayer, with and without polarization by linear potential scans or potential steps. In this way, the effect of polarization on distearoylphosphatidylglycerol (DSPG), dimyristoylphosphatidylcholine (DMPC), and distearoylphosphatidylcholine (DSPC) monolayers, adsorbed at the water/1,2-dichloroethane interface, could be directly observed and diffusion coefficient values were derived. Lateral motilities of these particles can be correlated with the monolayer fluidity and solid character. A comparison with the behavior of the lipids at air/water interfaces is also included.

Nanoscale Engineering of Efficient Oxygen Reduction Electrocatalysts By Tailoring the Local Chemical Environment of Pt Surface Sites

The oxygen reduction reaction (ORR) is the major source of overpotential loss in low-temperature fuel cells. Expensive, Pt-based materials have been found to be the most effective catalysts, but exploration of alternatives has been hampered by stability constraints at the typical operating conditions of low pH and high potential. I will discuss our studies of elementary mechanism of ORR on various metal electrodes using kinetic and micro-kinetic analysis of reaction pathways and quantum chemical calculations. These studies allowed us to identify the elementary steps and molecular descriptors that govern the rate of ORR. Using these performance descriptors we have been able to identify families of Pt and Ag-based alloys that exhibit superior ORR performance is acid and base respectively. We have synthesized these alloys to demonstrate the superior ORR activity with rotating disk electrode experiments. We have also performed thorough structural characterization of the bulk and surface properties with a combination of cyclic voltammetry, x-ray diffraction, and electron microscopy with spatially resolved energy-dispersive x-ray spectroscopy and electron energy loss spectroscopy. Xin, H.; Linic, S., J. Chem. Phys. 2016 144 (23), 234704Van Cleve T, Moniri, S, Linic, S, 2016, ACS Catalysis 7 (1), 17-24Moniri S., Van Cleve T., Linic S., Journal of Catalysis 345, 1-10Holewinski and Linic. J. Electrochem. Soc. 159, (2012).Adam Holewinski, Juan-Carlos Idrobo, Suljo Linic. Nature Chemistry , 6, 828-834, 2014.

Investigation in Mediated Heterogeneous Oxygen Reduction of Immobilized Laccase

Dynamics of heterogeneous catalysis on oxygen reduction for Lac based electrode capped with a layer of Chitosan-multi-wall carbon nano-tubes complex in the presence of dissolved mediator, was investigated on the basis of precondition that the detainment of substrate and mediator could be neglected. Rates of steps involved in the whole catalytic cycle were determined by the means of UV–Vis spectroscopy, atomic adsorption spectroscopy, linear sweeping voltammetry and cyclic voltammetry in combination with rotating disk electrode technique. These kinetic parameters were normalized under the same dimension. Thus rate determining step was verified to be the diffusion of external mediator. Results also revealed the fact from analysis in changes of morphology and electric conductivity after protein incorporation into nano-composite that random adsorption of enzyme molecules on the conductive support resulted in the decrease in conductive area of nano-composite and hindered the direct electron transfer between active sites in enzyme molecules and conductive matrix. Non-oriented arrangement of protein molecules on the matrix also crippled the mechanical stability of nano-complex with enzyme resulting from weak interaction between incorporated protein molecules and carrier. Catalytic effect on dissolved oxygen reduction reaction for electrode which was over-coated by a layer of nano-complex with immobilized Laccase consisting of Chitosan and multi wall carbon nano-tubes, were found to be restrained by diffusion of electron relay.

Investigating the Electrode-Electrolyte Behaviour of Carbon Materials in Various Non-Aqueous Electrolytes

Charge storage in electrochemical capacitors has been shown to be via charge separation at the electrode-electrolyte interface (so called electrical double layer charge storage) and via pseudo-capacitance, which is often described as fast redox reactions through the same interface. Charge storage via both of these mechanisms depends heavily on the interaction between the electrode morphology (electrochemically active surface area, pore size distribution, etc.) and the solvated ion in the electrolyte. In this work the interaction between a series of carbon-based substrates and various electrolyte species has been investigated. Electrolytes examined include tetraethylammonium bis(trifluoromethane)sulfonimide (Et4NTFSI), 1-butyl-1-methylpyrrolidinium tetrafluoroborate (PYR14BF4), 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI), and tetraethylammonium tetrafluoroborate (Et4NBF4) in acetonitrile. The interaction between these electrolytes and various carbon-based substrates was examined using a combination of cyclic voltammetry (CV) and step potential electrochemical spectroscopy (SPECS). These techniques have enabled differentiation of the charge storage mechanisms based on ion size, solvated ion size and charge density, as well as substrate surface area and porosity.

Deconvoluting Capacitive and Pseudo-Capacitive Contributions to Electrochemical Capacitor Electrode Behaviour

Generally the capacitive behaviour of the electrochemical capacitors are associated with electrical double layer at the surface of the electrode, and in some materials pseudo-capacitance, which results from faradaic processes. Several electrochemical methods have been developed for determining the contribution of different charge storage mechanisms such as via the electrical double layer and diffusion-limited processes. This includes using a cyclic voltammetry (CV) data at different scan rates to obtain the relationship between a voltammetric current and scan rate (v). In this method, it can be assumed that the total current response for a particular potential is a summation of the current associated with a capacitive processes and a current associated with a diffusion-limited process. While, the capacitive current is proportional to v, and the diffusion limited current is relative to v1/2 (Conway, et al. 1998). The cyclic voltammetry data also can be applied to determine the relationship between a voltammetric charge and scan rate. The charge attributed to the surface capacitive processes is assumed to be constant with scan rate while, the charge attributed to diffusion-limited processes varies with v-1/2 (Trasatti, et al. 1990). Both approaches have been used widely for characterization of the performance of electrochemical systems. However, these methods have some limitations as the relationship between current and v1/2 and also, between charge and v-1/2 is not always linear in a different range of scan rates. Step potential electrochemical spectroscopy (SPECS) also, has been used to effectively differentiate between different charge storage mechanisms. The SPECS method is based on applying a series of equal magnitude potential steps on a working electrode, with sufficient rest time to allow for equilibrium to be established for each step throughout an applied potential window. This slow scan rate enables an electrode to approach its maximum charge storage capabilities. More importantly, it allows separation of the charge storage mechanisms, such as electrical double layer charge storage and diffusion-limited processes. The aim of this study is to compare these three methods experimentally and also to discuss about their limitations and advantages for interpreting the current data and their ability to distinguish between different charge storage mechanisms. Moreover, the relationship between voltammetric current and scan rate has been modified by introducing the constant parameter of residual current. The modified relationship then, can be used over the entire range of potential scan rate. In this work, the combined CV and SPECS methods have been applied to electrolytic manganese dioxide (EMD) in 0.5 M K2SO4 between 0.0 – 0.8 V (vs SCE). Firstly, EMD electrode was cycled for 250 cycles at different scan rates ranged from 1 to 100 mV/s. Subsequently, the SPECS method was applied using 25 mV potential steps and 300 s equilibration time. Eventually, the contribution of capacitive and diffusion-limited processes were obtained using three techniques which were discussed here. The linear dependence of current to v1/2 and the linear dependence of capacity to v-1/2 have not been observed. However, it can be seen that there is a good agreement between the modified model of the scan rate dependence of current and experimental data. Liu, T. C., Pell, W. G., Conway, B. E., & Roberson, S. L. (1998). Behavior of molybdenum nitrides as materials for electrochemical capacitors comparison with ruthenium oxide. Journal of the Electrochemical Society, 145(6), 1882-1888. Ardizzone, S., Fregonara, G., & Trasatti, S. (1990). “Inner” and “outer” active surface of RuO2 electrodes. Electrochimica Acta, 35(1), 263-267.

The electrochemical reduction of di-(2-ethylhexyl) phthalate (DEHP) in acetonitrile

The redox behavior of the extensively utilized plasticizer and toxicant, di-(2-ethylhexyl) phthalate (DEHP), was studied in acetonitrile solutions using a combination of cyclic voltammetry (at varied scan rates, temperatures, and concentrations) and controlled potential electrolysis techniques. Overall, DEHP was found to be reducible by two one-electron steps at moderately large negative potentials to form a radical anion (Epred≈−2.47 vs. (Fc/Fc+)/V, where Epred=cathodic peak potential and Fc/Fc+=ferrocene/ferrocenium) and dianion (Epred≈−2.65 vs. (Fc/Fc+)/V), respectively. The results revealed that the cathodic reactions were only moderately chemically reversible, even when measured at high scan rates or lowered temperatures, as the reduced forms of DEHP were involved in several chemical transformations (dimerization and decomposition) following their generation. Based on the voltammetric and electrolytic responses gathered, a mechanism was proposed for the electrochemical reduction of DEHP, and the heterogeneous electron transfer and homogeneous reaction steps were modeled by digital simulations to determine the associated thermodynamic and kinetic parameters.

Functional Circuitry Effect of Ventral Tegmental Area Deep Brain Stimulation: Imaging and Neurochemical Evidence of Mesocortical and Mesolimbic Pathway Modulation.

Background: The ventral tegmental area (VTA), containing mesolimbic and mesocortical dopaminergic neurons, is implicated in processes involving reward, addiction, reinforcement, and learning, which are associated with a variety of neuropsychiatric disorders. Electrical stimulation of the VTA or the medial forebrain bundle and its projection target the nucleus accumbens (NAc) is reported to improve depressive symptoms in patients affected by severe, treatment-resistant major depressive disorder (MDD) and depressive-like symptoms in animal models of depression. Here we sought to determine the neuromodulatory effects of VTA deep brain stimulation (DBS) in a normal large animal model (swine) by combining neurochemical measurements with functional magnetic resonance imaging (fMRI).Methods: Animals (n = 8 swine) were implanted with a unilateral DBS electrode targeting the VTA. During stimulation (130 Hz frequency, 0.25 ms pulse width, and 3 V amplitude), fMRI was performed. Following fMRI, fast-scan cyclic voltammetry in combination with carbon fiber microelectrodes was performed to quantify VTA-DBS-evoked dopamine release in the ipsilateral NAc. In a subset of swine, the blood oxygen level-dependent (BOLD) percent change evoked by stimulation was performed at increasing voltages (1, 2, and 3 V).Results: A significant increase in VTA-DBS-evoked BOLD signal was found in the following regions: the ipsilateral dorsolateral prefrontal cortex, anterior and posterior cingulate, insula, premotor cortex, primary somatosensory cortex, and striatum. A decrease in the BOLD signal was also observed in the contralateral parahippocampal cortex, dorsolateral and anterior prefrontal cortex, insula, inferior temporal gyrus, and primary somatosensory cortex (Bonferroni-corrected < 0.001). During neurochemical measurements, stimulation time-locked changes in dopamine release were recorded in the NAc, confirming that mesolimbic dopaminergic neurons were stimulated by DBS. In the parametric study, BOLD signal changes were positively correlated with stimulation amplitude.Conclusions: In this study, the modulation of the neural circuitry associated with VTA-DBS was characterized in a large animal. Our findings suggest that VTA-DBS could affect the activity of neural systems and brain regions implicated in reward, mood regulation, and in the pathophysiology of MDD. In addition, we showed that a combination of fMRI and electrochemically-based neurochemical detection platform is an effective investigative tool for elucidating the circuitry involved in VTA-DBS.

Electrochemically Identified Ultrathin Water-Oxidation Catalyst in Neutral pH Solution Containing Ni2+ and Its Combination with Photoelectrode.

Water oxidation electrocatalyzed by Ni2+ under neutral conditions was investigated using various electrochemical analyses. The addition of Ni2+ in a phosphate-buffered solution catalyzed the oxidation of water, as confirmed by the detection of oxygen generation via scanning electrochemical microscopy. A combination of cyclic voltammetry, coulometric titration, and electrochemical quartz microbalance measurements identified the catalysis as heterogeneous and the catalyst as a Ni-based ultrathin (<4 nm) layer (“Ni-Pi”). Analysis of the potential- and pH-dependency of the titrated amount of charge revealed that the catalyst was deposited only under anodic polarization conditions and was removed under unpolarized conditions; the catalyst may be Ni(III) oxide, and its formation and oxidation appeared to be chemically irreversible. The diffusion-limited nature of water oxidation catalyzed by Ni2+ was closely related to the phosphate ions involved in the catalyst formation and the accompanying catalysis. Although the catalytic performance of Ni2+ alone was not remarkable, it exhibited a synergetic effect with BiVO4 for photoelectrochemical water oxidation, which can compete with Co-Pi-decorated BiVO4.

Electrochemical oxidation of C3 saturated alcohols on Co3O4 in alkaline

In this work, we present a systematic study on the electrochemical oxidation of C3 saturated alcohols (propanetriol, 1,2-propanediol, 1,3-propanediol, 1-propanol, and 2-propanol) on Co3O4 in alkaline. Co3O4 electrode was prepared by electrodeposition of Co(OH)2 on graphite paper followed with a calcination step. The electro-oxidation of C3 saturated alcohols were investigated by a combination of cyclic voltammetry, multi-step chronoamperometry, and electrochemical impedance spectroscopy techniques in KOH solution. The electro-oxidation studies at Co3O4 electrode followed an activity trend in the following order: propanetriol (GLY)>1,2-propanediol (1,2-P)>1,3-propanediol (1,3-P)>1-propanol (1-P)>2-propanol (2-P). The NMR analysis of the oxidized products showed that C-C bond cleavage occurred faster in alcohols having adjacent hydroxyl groups. X-ray absorption near-edge structure (XANES) spectroscopy study showed that there was no significant difference in Co oxidation state in the absence and the presence of glycerol. It was also found that the KOH concentration influenced electro-oxidation of those alcohols bearing secondary hydroxyl group (GLY, 1,2-P, and 2-P) more dramatically than that of those primary alcohols (1.3-P and 1-P).

Study of Catalytic Reaction at Electrode–Electrolyte Interfaces by a CV-XAFS Method

A method combining cyclic voltammetry (CV) with x-ray absorption fine structure (XAFS) spectroscopy, viz. CV-XAFS, has been developed to enable in situ real-time investigation of atomic and electronic structures related to electrochemical reactions. We use this method to study the reaction of a Pt/C cathode catalyst in the oxygen reduction reaction (ORR) in an alkaline electrolyte, using x-ray energies near the Pt LIII edge for XAFS measurements. It was found that the current induced by the ORR was first observed at approximately 0.08 V versus Hg/HgO, although the Pt valence, which is reflected in the oxidation states, remained almost unchanged. The electronic structure of the catalytic surface in the ORR was observed to be different in the negative and positive scan directions of CV measurements. Hydrogen adsorption is also discussed on the basis of the observation of this spectral change. We have demonstrated that CV-XAFS provides dynamical structural and electronic information related to electrochemical reactions and can be used for in situ real-time measurements of a catalyst.