Voltammetry In Alkaline Medium Research Articles

Highly effective bi‐functional electrochemical activity of Ag 2 O‐PrO 2 / γ‐Al 2 O 3 electrocatalysts towards OER and ORR

The oxygen reduction and evolution reaction (ORR/OER), are the keystones for many energy generating and storage devices, have influence with many electrocatalytic reactions. The sluggish kinetics of these reaction is a challenging situation on the surface of electrodes which imposes large over-potential and affects the energy output of fuel cells. Although the platinum-based electrode materials have excellent activity toward ORR/OER but their high cost limits commercialization of fuel cells. To deal with this problem, platinum-free electrode materials has aroused the considerations of scientists. The present work is proposed to study the oxygen reduction reaction and water oxidation on the surface of xAg2O-yPrO2/γ-Al2O3/Glassy-Carbon. The ORR was studied electrochemically via cyclic voltammetry on the surface of these nano-catalysts while the OER was investigated via cyclic voltammetry and linear sweep voltammetry in alkaline media. The mechanism of ORR on catalysts surface was enquired and the results indicate that ORR followed two electrons pathway in case of 10PrO2/γ-Al2O3/Glassy-Carbon while four electrons reduction pathway is identified on surface of others catalysts which divulged that addition of silver with praseodymium shifted the mechanism from 2e− to 4e− pathway. The electrocatalysts featured the stability during multiple scans and no corrosion of electrode in OER/ORR is observed. Different kinetic parameters for both reactions are determined which affirmed that both ORR and OER on the active surface of catalysts is irreversible and diffusion controlled. 4Ag2O-6PrO2/γ-Al2O3 is indicated to be proficient electro-catalyst among other members of the series, having greater value of mass transport and diffusion coefficients. The bi-functionality of all electrocatalysts are verified by their electrochemical responses in alkaline medium. The catalytic reduction of oxygen and oxidation of water by these electro-catalysts imitates their potential as electrode material in batteries and unitized regenerative fuel cells (URFC) technology for energy production as substitute of platinum electrode.

Electro-Oxidation of Metal Oxide-Fabricated Graphitic Carbon Nitride for Hydrogen Production via Water Splitting

Hydrogen is a great sourcez of energy due to having zero emission of carbon-based contents. It is found primarily in water, which is abundant and renewable. For electrochemical splitting of water molecules, it is necessary to use catalytic materials that minimize energy consumption. As a famous carbon material, graphitic carbon nitride, with its excellent physicochemical properties and diversified functionalities, presents great potential in electrocatalytic sensing. In the present work, graphitic carbon nitride-fabricated metal tungstate nanocomposites are synthesized by the hydrothermal method to study their applications in catalysis, electrochemical sensing, and water splitting for hydrogen production. Nanocomposites using different metals, such as cobalt, manganese, strontium, tin, and nickel, were used as a precursor are synthesized via the hydrothermal process. The synthesized materials (g-C3N4/NiWO4, g-C3N4/MnWO4, g-C3N4/CoWO4, g-C3N4/SnWO4, g-C3N4/SrWO4) were characterized using different techniques, such as FTIR and XRD. The presence of a functional groups between the metal and tungstate groups was confirmed by the FTIR spectra. All the nanocomposites show a tungstate peak at 600 cm−1, while the vibrational absorption bands for metals appear in the range of 400–600 cm−1. X-ray diffraction (XRD) shows that the characteristic peaks matched with the JCPDS in the literature, which confirmed the successful formation of all nanocomposites. The electrochemical active surface area is calculated by taking cyclic voltammograms of the potassium–ferrocyanide redox couple. Among the entire series of metal tungstate, the g-C3N4/NiWO4 has a large surface area owing to the high conductive properties towards water oxidation. In order to study the electrocatalytic activity of the as-synthesized materials, electrochemical water splitting is performed by cyclic voltammetry in alkaline medium. All the synthesized materials proved to be efficient catalysts with enhanced conductive properties towards water oxidation. Among the entire series, g-C3N4-NiWO4 is a very efficient electrocatalyst owing to its higher active surface area and conductive activity. The order of electrocatalytic sensing of the different composites is: g-C3N4-NiWO4 > g-C3N4-SrWO4 > g-C3N4-CoWO4 > g-C3N4-SnWO4 > g-C3N4-MnWO4. Studies on electrochemically synthesized electrocatalysts revealed their catalytic activity, indicating their potential as electrode materials for direct hydrogen evolution for power generation.

Sigma and Chi Phases Analysis in UNS S32750 Superduplex Stainless Steel by Optimized Linear Sweep Voltammetry in Alkaline Medium

Linear sweep voltammetry (LSV) test parameters in alkaline medium were optimized by Doehlert matrix design in order to quantify the deleterious phases in a superduplex stainless steel UNS S32750. The microstructural analysis was performed, in several heat treated specimens, by Light Optical (LOM) and Scanning Electron (SEM) Microscopies and correlated with the electrochemical tests. In these tests, optimized parameters were obtained for tests in aqueous solutions of KOH. The concentration of 3.55 mol l−1, scan rate of 3.42 mV s−1 and initial potential of −0.818 V, showed a good correlation between the deleterious phases precipitated and charge density values. Differently from LOM characterization, chi and sigma deleterious phases can be distinguished by LSV optimized test. Finally, this test can be a non-destructive powerful tool of quality control to detect embrittlement and corrosion resistance decay that commonly affected this stainless steel as consequence of inadequate fabrication processes.

Electro Oxidation of Methanol on Ni/Ni-Co Coated SS Mesh Electrode

In this work, the oxidation of methanol was carried out using Ni and Ni-Co alloy electrodeposited on stainless steel mesh substrate with a view to replace expensive and sensitive platinum and platinum alloy catalysts. The performance of electrode was assessed through cyclic voltammetry in alkaline media. The operating conditions of the electrode were optimized.

Electrochemical properties of Ce-doped SrFeO3 perovskites-modified electrodes towards hydrogen peroxide oxidation

Ce-doped SrFeO3 perovskites with different cerium content have been prepared by solution combustion synthesis and investigated as electrocatalytic materials for H2O2 oxidation. Cyclic voltammetry in alkaline medium have been used to evaluate the electrochemical behaviors towards H2O2 of perovskite-modified screen printed carbon electrodes (SPCE). The structural, surface and morphological properties of the investigated samples along with their reduction behavior and interaction with oxygen have been correlated with their electrochemical sensing characteristics. Results demonstrated that the contemporary presence of Ce and Fe in the perovskite structure enhances the electrocatalytical activity towards the oxidation of H2O2. An amperometric sensor based on the Sr0.85Ce0.15FeO3 perovskite has been also developed for hydrogen peroxide determination in aqueous solution showing a sensitivity of about 60μAmM−1cm−2 and a lower detection limit of 10μM (S/N=3).

Molecular imprinting method for fabricating novel glucose sensor: Polyvinyl acetate electrode reinforced by MnO2/CuO loaded on graphene oxide nanoparticles

An enzyme free glucose sensor was prepared by a molecular imprinting method (MIP). The procedure was developed by in situ preparation of a new polyvinyl acetate (PVA) electrode reinforced by MnO2/CuO loaded on graphene oxide (GO) nanoparticles (PVA/MnO2@GO/CuO). The nanocomposite was modified in the presence of glucose and then imprinted. A carbone paste method with voltammetry was used in the fabrication of the sensor from prepared MIP nanocomposite. PVA/MnO2@GO/CuO electrode was characterized by X-ray diffraction, FT-IR spectroscopy and scanning electron microscopy. Electrocatalytic activity of the electrode toward glucose oxidation was then investigated by cyclic voltammetry in alkaline medium. The results show that the response of PVA/MnO2@GO/CuO MIP is much higher than PVA/MnO2@GO/CuO non-imprinted electrode toward glucose oxidation. The detection limit was 53μM, and the sensor responses are linear for concentrations from 0.5 to 4.4mM. Relative standard deviations for intra- and inter-day determination were less than 6.0%. The relative recoveries for different samples were 96%.

Highly dispersed Pd nanoparticles on 9-amino-1-azabenzanthrone functionalized graphene-like carbon surface for methanol electro-oxidation in alkaline medium

A simple and convenient procedure has been reported for the preparation of high dispersion Pd nanoparticles on a graphene-like carbon (GLC) surface functionalized by 9-amino-1-azabenzanthrone (AABZ). Catalyst activity for methanol electro-oxidation in fuel cells was investigated by cyclic voltammetry in alkaline medium. It was observed that the forward peak current density of Pd–AABZ/GLC catalyst is 770 A g−1Pd, which is 1.9 and 1.2 times higher than that of the Pd on commercial carbon black and reduced graphene oxide. The current at 3600 s of the chronoamperometric experiments for the Pd–AABZ/GLC catalysts is 230 A g−1Pd, which is 2.54 times higher than that of Pd/XC-72 (Pd/commercial Vulcan XC-72 carbon black). Pd–AABZ/GLC composite exhibits superior electro-catalytic activity toward methanol oxidation and is a promising candidate for application in direct methanol fuel cells. Besides, these findings will be propitious to the use of GLC as catalyst carrier for direct methanol fuel cells.

Influence of Ethanol Catalyzed Oxidation on the Activity of Pd/C with Different Ratio of Pd and Carbon

To investigate the influence of ethanol catalyzed oxidation on activity of Pd/C with different ratio of Pd and C. Pd/C catalyst samples with Pd loads of 20, 30, 40 and 50 wt% were obtained by chemical reduction reaction of PdCl2 and NaBH4. The samples morphology and structure were characterized by XRD and SEM. The electrocatalytic oxidation activities of ethanol were examined by cyclic voltammetry in alkaline media. The results show that a face centered cubic (FCC) Pd phase can be identified in the sample powders. The average particle size of the Pd/C powder is about 10 nm. The performance of ethanol oxidation on 40 % Pd/C electro-catalyst is better than that of the other Pd/C samples.

The electrochemical characterization of copper single-crystal electrodes in alkaline media

The use of single-crystals in electrochemistry requires careful characterization of the surface structure. This paper addresses the characterization of Cu single-crystals using blank cyclic voltammetry in alkaline media. The adsorption and desorption of OH species in the underpotential region of Cu2O formation in alkaline media occur at different potentials on Cu(111) and Cu(100), whereas OH adsorption on Cu(110) is not observed in this potential region. This allows for a direct distinction of the Cu(hkl) basal planes. The adsorption of OH on Cu(111) induces a reconstructed adlayer on the surface. On Cu(322), a stepped surface with 5 atom wide (111) terraces, OH adsorption is observed in the same potential range as on Cu(111), but on Cu(322) reconstruction does not seem to take place. This is explained by the fact that the unit cell of the reconstructed layer is much larger than the (111) terrace width of Cu(322) and, therefore, reconstruction cannot take place. Cu(911), having 5 atom wide (100) terraces, exhibits the same voltammetric features as Cu(100), but with a lower intensity. This is explained by the lower amount of (100) terraces present on this surface.

Preparation and characterization of the electroactive composites containing nickel nanoparticles and carbon nanotubes

The composites containing Ni nanoparticles and N-doped carbon nanotubes were prepared using Ni–Al layered double hydroxides (LDHs) with various Ni/Al atomic ratios (2 and 3) and acetonitrile via catalytic chemical vapor deposition at 600, 700 and 800°C. Powder X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, thermogravimetric analysis and nitrogen sorption were employed to characterize their physicochemical properties. The electrochemical properties of the composites were evaluated by means of cyclic voltammetry in alkaline medium with the addition of methanol as a probe molecule.Application of different synthesis temperatures and Ni–Al LDHs with various Ni concentrations influenced the electrocatalytic performance of the composites for the methanol oxidation reaction as it affected the dispersion of Ni nanoparticles and electrode/electrolyte interfacial active area. The hybrid material prepared at the lowest temperature (600°C) and derived from LDHs with a lower Ni/Al=2 appeared to have the best electrochemical properties among the studied composites.

Passive Thin Film Coating through Electrodeposition of Salicylideneaniline

Basic salicylideneaniline compound was electro-oxidized using mild steel electrode through cyclic voltammetry in alkaline medium. Scanning Electron Microscopy analysis indicates the formation of thin organic film that high in ionic impedance. Current suppression detected in the cyclic voltammogram during the five CV cycles indicates an irreversible reaction with the mild steel surface becoming more passive with increase in number of cycles increased. This is due to the formation of organic layer on the mild steel surface that acts as a barrier for the electron transfer and making it difficult to further oxidize salicylideneaniline. Surface morphology of salicylideneaniline deposited on mild steel surface was studied by scanning electron microscopy (SEM). The effect of scan rate potential on the deposition of salicylideneaniline was also studied. The current peak increases with increase in scan rate and the peak also shifted to the more positive potentials due to the diffusion-controlled process. Slow scan rate was favored for optimum electrodeposition of salicylideneaniline.

Enhanced electrocatalytic activity of nickel particles electrodeposited onto poly ( m-toluidine) film prepared in presence of CTAB surfactant on carbon paste electrode for formaldehyde oxidation in alkaline medium

In this work, carbon paste electrode is coated with poly ( m-toluidine) film by potentiodynamic electropolymerization of m-toluidine monomer in the presence of cetyltrimethyl ammonium bromide (CTAB-PMT/MCPE). Then electrolysis at fixed potential (−1.0 V versus reference electrode for 15 min) is employed for electrodepositing of Ni from 1.5 M NiSO 4 acidic solution at the surface of polymer-modified electrode for preparation of Ni/CTAB-PMT/MCPE. The general electrochemical behaviors of these modified electrodes are characterized by cyclic voltammetry in alkaline media. In alkaline medium (i.e. NaOH 0.1 M) a good redox behavior of Ni(III)/Ni(II) couple at the surface of these electrodes can be observed. The nickel particles electrodeposited at the surface of Ni/CTAB-PMT/MCPE exhibits a significant electrocatalytic activity towards oxidation of formaldehyde. Moreover, the effects of various parameters such as concentration of CTAB, concentration of formaldehyde, film thickness and monomer concentration on the electrooxidation of formaldehyde as well as long-term stability of the Ni/CTAB-PMT/MCPE have also been investigated.

A study on direct glucose and fructose alkaline fuel cell

Direct glucose fuel cell (DGFC) has huge potential as a power source in low power long term portable devices. Electro-oxidation of glucose and fructose on PtRu/C catalyst are studied using cyclic voltammetry in alkaline medium to study the reason for deactivation of glucose fuel cell. A simple direct glucose fuel cell with PtRu/C as anode and activated charcoal as cathode was constructed and operated to study the effect of different temperature and concentration of glucose and KOH. An open-circuit voltage (OCV) of 0.91 V is obtained using 0.3 M glucose in 1 M KOH solution. OCV increased with the increase in glucose concentration. The maximum peak power density of 1.38 mW cm −2 is obtained using 0.2 M glucose in 1 M KOH at 30 °C and it decreases with further increase in glucose concentration and temperature. In order to determine the reason for decrease in performance of glucose fuel cell due to conversion of glucose to fructose, the fuel cell was operated using 0.2 M fructose in 1 M KOH. The peak power density delivered is 0.57 mW cm −2. The DGFC is continuously operated for 260 h at constant load of 500 Ω produces final constant voltage of 0.21 V.

Electrochemical and Morphological Characterization of New Architectures Containing Self-Assembled Monolayers and Au-NPs

Pure 1,10-decanedithiol (C10-SH) and mixed (1-decanethiol:1,10-decanedithiol) self-assembled monolayers (SAMs) prepared from ethanolic solution on Au(111) surfaces have been used in order to investigate the effect of the SAM organization and the availability of free −SH groups at the SAM/solution interface on the development of layer-by-layer architectures containing SAMs and gold nanoparticles (Au-NPs). The SAM modified electrodes have been electrochemically characterized by cyclic voltammetry in alkaline medium (reductive desorption) and in the presence of an electroactive species, Fe(CN)63−, in KNO3 solution, enabling the evaluation of the stability and organization of the SAMs. Enhanced stability, organization, and hindrance to the electron transfer were found for the mixed SAMs with increasing thiol content, when compared with the pure dithiol SAM. The mixed SAM prepared from solution containing the thiol to dithiol proportion of (50:1) and pure C10-SH SAMs have been selected for further modification; the electrochemical quartz crystal microbalance (EQCM) enables the detection of different amount of citrate stabilized Au-NPs attachment to the selected SAMs modified electrodes due to distinct availability of free −SH groups at the SAM/solution interface and the electrochemical characterization of the layer-by-layer assemblies (based on pure C10-SH and mixed SAMs) showed that the electron transfer (ET) properties of the such architectures strongly depend on the nature of the base SAM and amount of immobilized Au-NPs. Atomic force microscopy (AFM) morphological characterization of the C10-SH SAM upon layer-by-layer modification was performed ex situ in air.

Electro-oxidation of Cyclohexanol on a Copper Electrode Modified by Copper-dimethylglyoxime Complex Formed by Electrochemical Synthesis

Copper-dimethylglyoxime complex (CuDMG) modified Copper electrode (Cu/CuDMG) showed a catalytic activity towards cyclohexanol oxidation in NaOH solution. The modified electrode prepared by the dimethylglyoxime anodic deposition on Cu electrode in the solution contained 0.20 M NH 4 Cl + NH 4 0H (pH 9.50) and 1 x 10 -4 M dimethylglyoxime. The modified electrode conditioned by potential recycling in a potential range of-900 ∼ 900 mV vs. Ag/AgC1 by cyclic voltammetry in alkaline medium (1 M NaOH). The results show that the CuDMG film on the electrode behaves as an efficient catalyst for the electro-oxidation of cyclohexanol in alkaline medium via Cu (III) species formed on the electrode.

Electrocatalytic oxidation of formaldehyde on palladium nanoparticles electrodeposited on carbon ionic liquid composite electrode

The electrocatalytic oxidation of formaldehyde on palladium nanoparticles electrodeposited on carbon ionic liquid electrode (Pd–CILE) has been investigated. The ionic liquid, octylpyridinum hexafluorophosphate ( [ C 8 Py + ] PF 6 - ) was incorporated in the electrode as the binder. The general electrochemical behavior was characterized by cyclic voltammetry in alkaline media. The results show that the Pd–CILE system exhibits a significant electrocatalytic activity towards oxidation of formaldehyde. An oxidation peak was obtained at a potential of ∼0.03 V vs. Ag/AgCl for 0.010 M formaldehyde. The interesting feature of this electrode is that its catalytic efficiency as well as its anti poisoning property are far superior compared to many of the previously reported formaldehyde sensors.

The influence of experimental parameters on the structure, morphology and electrochemical behavior of Pd–P thin films prepared by electroless deposition

Pd–P thin films over carbon steel were prepared by electroless deposition, using sodium hypophosphite as reducing agent. The influence of the plating conditions, on the properties of the coatings is investigated in detail. The deposits morphology was assessed by Scanning Electron Microscope and Atomic Force Microscopy imaging, their compositions and respective elements distribution determined by Energy Dispersive X-ray Spectrometry and structural information obtained by X-ray diffraction. It has been observed that the amount of co-deposited P depends on both the deposition time and the employed NaH 2PO 2 concentration, which in turn dictates the degree of amorphicity of the so-prepared Pd–P layers. The modified electrodes electrochemical behaviour, evaluated by cyclic voltammetry in alkaline media, revealed that the hydrogen adsorption/absorption process and the hydrogen evolution reaction are enhanced on alloys with phosphorus content below 10 at.%.

Methanol oxidation on gold nanoparticles in alkaline media: Unusual electrocatalytic activity

Methanol oxidation on gold nanoparticles has been studied using cyclic voltammetry in alkaline media. The onset for methanol oxidation in 0.1 M NaOH solutions is at ca. 0.3 V (RHE) and the currents reach a maximum value at 0.8 V. In 1 M NaOH solutions, oxidation currents are measured at potentials as low as 0.1 V. Although the currents are significantly smaller than the expected limiting diffusion current for methanol oxidation, oxidation currents are partially controlled by diffusion, as revealed by rotating disk experiments. This suggests that only a small fraction of the nanoparticles is active for the oxidation. It is proposed that formate is the final product of the oxidation and formaldehyde is an active intermediate in the process.

Electrocatalytic oxidation of methanol on a Nickel(II)-1-(2-pyridylazo)-2-naphthol complex modified glassy-carbon electrode in alkaline medium

Electrocatalytic oxidation of methanol on a glassy carbon disc electrode modified with Ni(II)-1-(2-pyridylazo)-2-naphthol (Ni-PAN) complex and conditioned by potential recycling in a limited range (between 100–600 mV) in 0.1 M NaOH solution, abbreviated as NiPANME, is studied by cyclic voltammetry in alkaline medium. The results are compared with those obtained for a NiO modified glassy-carbon electrode, NiOME, prepared in similar conditions. The findings show that the NiPAN film behaves as an efficient electrocatalyst for the oxidation of methanol in alkaline medium via Ni(III) species with the cross-exchange reaction occurring throughout the layer at a low concentration of methanol and for a thin film of modifier. Effects of the scan rate and methanol concentration on the methanol oxidation are investigated. The cyclic voltammetry and amperometry methods are used to investigate the methanol electrooxidation at the modified electrode.

Methanol electrooxidation on a nickel electrode modified by nickel–dimethylglyoxime complex formed by electrochemical synthesis

Abstract Nickel–dimethylglyoxime complex (NiDMG) modified nickel electrode (Ni/NiDMG) showed a catalytic activity towards methanol oxidation in NaOH solution. The modified electrode prepared by the dimethylglyoxime anodic deposition on Ni electrode in the solution containing 0.20 mol L−1 NH4Cl + NH4OH (pH 9.50) and 1.0 × 10−4 mol L−1 dimethylglyoxime. The modified electrode conditioned by potential recycling in a potential range of 100–700 mV (vs. SCE) by cyclic voltammetry in alkaline medium (0.10 M NaOH). The results show that the NiODMG film on the electrode behaves as an efficient catalyst for the electrooxidation of methanol in alkaline medium via Ni(III) species formed on the electrode with the cross exchange reaction occurring throughout the film at a low concentration of methanol. A plausible mechanism was proposed for catalytic oxidation of methanol at NiODMG-modified Ni electrode. Moreover, the effects of various parameters such as anodic deposition time, anodic deposition potential (both in modification step), potential scan rates, methanol concentration and media temperature on the electrooxidation of methanol were investigated.