Cyclic Voltammetry In Acidic Media Research Articles

Synthesis and Characterization of Platinum and Platinum based Alloy Nanoparticles Anchored on Various Carbon Materials for Methanol Oxidation in a DMFC – A Short Review

In the fabrication of direct methanol fuel cells (DMFCs) having high performance the essential conditions are (i) the design and construction of a suitable anode electrocatalyst comprising of Pt or a Pt based alloy nanoparticles methanol oxidation reaction (MOR) efficiently and effectively (ii) nature of support materials onto which these nanoparticles are anchored. In MOR one of the major problems is the adsorption of poisoneous carbonmoxide and other similar intermediates near the active surface of Pt active leading to its deactivation and also the crossover of methanol solution towards the cathodic side. All these factors, therefore, lower the overall electrochemical performance of the electro-catalysts. In the present review paper we report some of our important results of the synthesis of different Pt and Pt based anode electro-catalysts (Pt, PtCo alloys, PtCu alloys) anchored on different support materials such as reduced graphene oxide (rGO), Nitrogen doped rGO and a hybrid of rGO/CNTs for MOR and compared with few of those already reported recently. A detailed characterization of raw materials and the electro-catalysts synthesized in this work is also discussed using XRD, FT-IR, SEM, TEM etc. The electrochemical measurements were made using cyclic voltammetry in acidic medium at room temperature.

Electrochemical reduction on nanostructured TiO2 for enhanced photoelectrocatalytic oxidation

The influence of an electrochemical treatment method was investigated for two different TiO2 nanostructured materials, anatase nanotubes (TNT) and rutile nanorods (TNR). The treatment was done by performing cyclic voltammetry in acidic media. XPS measurements revealed a shift in Ti 2p peaks, suggesting the presence of Ti3+ after the partial reduction, as well as an increased peak associated to a higher hydroxylation degree of the surface. The treatment leads to an increase in the maximum photocurrent density, confirmed from linear sweep voltammograms and photon-to-electron conversion efficiencies (IPCE). The treatment is assumed to modify the charge carrier separation kinetics by inducing partial reduction of the TiO2. A markedly increased of two and three-fold in the IPCE was obtained for the reduced TNT and TNR, respectively, up to a maximum of 77% for TNR. This electrochemical treatment represents a facile and systematic approach to modify TiO2 nanostructured electrodes to achieve enhanced photoelectrocatalytic properties, as demonstrated by the current doubling experiments with MeOH.

Pd-Shaped Nanoparticles Modified by Gold ad-Atoms: Effects on Surface Structure and Activity Toward Glucose Electrooxidation.

Palladium nanoparticles (Pd-NPs) with controlled distributions of sizes and shapes (nanospheres–Pd-NS-, nanocubes -Pd-NC-, and nanooctahedrons -Pd-NO-) are synthesized by wet chemistry methods and characterized by TEM/HRTEM. The surfaces of Pd-NPs are modified by spontaneous adsorption of gold and characterized by cyclic voltammetry in acidic medium. It is shown that the modification of Pd-NPs by dipping in HAuCl4 solutions of different concentrations allows controlling the surface coverage by gold. It is also shown that the modification of Pd-NPs surfaces involves first the formation of PdAu surface alloys. For higher coverages, both PdAu surface alloys and pure Au structures are formed. The activity toward the glucose electrooxidation reaction is determined by linear scan voltammetry (LSV). Higher activity is observed on pure Pd-NC presenting extended (100) surfaces than on Pd-NO with mainly (111) surface orientation and on Pd-NS without preferential surface orientation, both these latter Pd-NPs displaying almost the same activity. The modification of the surface by spontaneous adsorption of gold greatly improves the activity of all Pd-NPs. However, Au-modified Pd-NC materials remain the most active catalysts. PdAu surface alloys seem to be involved in the improvement of the catalytic activity at low potentials, although the role of pure gold structures on Pd-NPs toward the enhancement of the catalytic activity cannot be excluded for high gold coverage. The study allows a better understanding of the material structure/electrocatalytic behavior relationship.

Iridium Core/Shell Catalysts for PEM Water Electrolyzer Anodes Synthesized Via Galvanic Exchange

The transfer to renewable energy requires stable long-term storage of any surplus energy created by e.g. solar power. Water electrolysis is a simple method for conserving energy in the form of hydrogen gas. Offering several advantages compared to alkaline water electrolysis, the polymer electrolyte membrane water electrolyzers (PEMWEs) can respond more rapidly to fluctuations in the power grid and enables a more compact cell design[1]. However, the components used in PEM cells are more costly. As different cost-reduction measures are being implemented, the anode catalysts fraction of the total cost is increasing. This calls for reducing the amount of scarce and precious iridium catalyst for the oxygen evolution reaction (OER). Galvanic exchange is a well-known way of producing metal thin-films on different metal substrates, where the substrate acts as both a reducing agent and template for a more noble metal. Applying iridium as a thin film on to a suitable substrate using galvanic exchange is a promising way of drastically reducing the iridium loading in PEMWE units. Although a substantial amount of effort has been made in producing core/shell electrocatalysts by galvanic exchange, not so much has been done on iridium structures[2]. A few groups have used nickel as a template for exchange in aqueous solution, either in the form of a thin metal foil[3, 4] or as nickel electrodeposited on to a glassy carbon electrode[5] or a nickel electrode[6]. Copper has also been used as a template in organic solvents [7, 8]. Although yielding promising results, the use of small-scale synthesis methods using expensive and toxic organic components is not feasible for industrial upscaling. Thus, we aim to use simple, scalable water-based methods for the synthesis of iridium electrocatalysts via galvanic exchange. In this work, we have exchanged nickel and copper nanoparticles supported on metal oxides (MOx) for iridium by galvanic exchange in an aqueous iridium solution. The Ir:M’@MOx electrocatalysts (M’=Ni,Cu) have been evaluated for stability and activity towards the OER in acidic media. For comparison, Ir:M’ catalysts were also made from a simple organic phase synthesis of M’ nanoparticles[9], which were subjected to galvanic exchange by iridium using different methods. Figure 1 illustrates the first cycle during cyclic voltammetry in acidic media of Ir:Ni electrocatalysts synthesized from galvanic exchange between iridium and nickel in aqueous iridium solutions at different temperatures. As is clearly shown in the figure, the sample synthesized at 95⁰C displays voltammetric signatures consistent with the formation of iridium oxide at the substrate. In addition to outlining the conditions for the formation of iridium oxide, polarization data and other characteristics of iridium oxide made by galvanic displacement will be described. The discussion will emphasize the feasibility of manufacturing core/shell or other overlayer structures of iridium for application in PEM water electrolysis. Carmo, M., et al., A comprehensive review on PEM water electrolysis. International Journal of Hydrogen Energy, 2013. 38(12): p. 4901-4934.Papaderakis, A., et al., Electrocatalysts Prepared by Galvanic Replacement. Catalysts, 2017. 7(3): p. 80.Duca, M., et al., Activation of Nickel for Hydrogen Evolution by Spontaneous Deposition of Iridium. Electrocatalysis, 2013. 4(4): p. 338-345.Mellsop, S.R., A. Gardiner, and A.T. Marshall, Spontaneous Deposition of Iridium onto Nickel Substrates for the Oxygen Evolution Reaction. Electrocatalysis, 2016. 7(3): p. 226-234.Papaderakis, A., et al., Oxygen Evolution at IrO2 Shell–Ir−Ni Core Electrodes Prepared by Galvanic Replacement. The Journal of Physical Chemistry C, 2016. 120(36): p. 19995-20005.Vázquez-Gómez, L., et al., Hydrogen evolution on porous Ni cathodes modified by spontaneous deposition of Ru or Ir. Electrochimica Acta, 2008. 53(28): p. 8310-8318.Park, J., et al., Iridium-Based Multimetallic Nanoframe@Nanoframe Structure: An Efficient and Robust Electrocatalyst toward Oxygen Evolution Reaction. ACS Nano, 2017. 11(6): p. 5500-5509.Pei, J., et al., Ir–Cu nanoframes: one-pot synthesis and efficient electrocatalysts for oxygen evolution reaction. Chemical Communications, 2016. 52(19): p. 3793-3796.Manikandan, M., et al., In nascendi. 2017. Captions Figure 1: Cyclic voltammogram (1st cycle) of Ir:Ni electrocatalysts in acidic media. The Ir:Ni catalysts were synthesized by galvanic exchange between iridium and nickel in aqueous iridium solutions at different temperatures. As clearly shown, the temperature of the aqueous iridium solution strongly affects the oxidation state of the iridium in the resulting Ir:Ni catalyst. Figure 1

Towards Practical Applications of EQCN Experiments to Study Pt Anchor Sites on Carbon Surfaces

This work investigates the viability and outlines the current challenges in electrochemical quartz crystal nanobalance (EQCN) experiments on supported Pt catalysts. EQCN experiments involving Pt supported on 2-D “surface-treated graphite sputtered onto quartz crystal” (Pt/MFG-H) catalysts were compared to standard polycrystalline Pt (Ptpoly), which showed similarities in frequency versus potential trends; however, the Pt/MFG-H catalysts obtained higher frequencies due to the support capacitance. The physical characterizations (XRD and XPS) and electrochemical responses, mainly cyclic voltammetry in acidic media and the ferri/ferrocyanide couple, of the 2-D Pt/MFG-H were compared to the representative 2-D Pt supported on treated highly orientated pyrolytic graphite (Pt/HOPG-H), in order to make assertions on the similarities between the two catalysts. The XRD diffraction patterns and the XPS valence band structure for the treated and untreated MFG (-H and -P, respectively) and HOPG (-H and -P, respectively) demonstrated similarities. Nevertheless, the cyclic voltammograms and peak positions of the ferri/ferrocyanide couple between the treated and untreated MFG and HOPG catalysts were dissimilar. However, EQCN may be used qualitatively between the two different 2-D catalysts since the same trends in electrochemical responses before and after treatment of the MFG and HOPG catalysts were seen. Hence, the EQCN technique can be used in future studies as an alternative method to study degradation mechanisms of Pt and carbon for PEFCs.Graphical ᅟ

Photoelectrochemical deposition of ZnO films via nitrate ions reduction in the presence of thiourea on p-type Cu(In,Ga)Se2 semiconducting electrodes for photovoltaic applications

This work describes the electrodeposition of ZnO layers on p-type copper indium gallium diselenide [Cu(InGa)Se2] substrates via nitrate ions reduction in the presence of thiourea. The substrate stability domain has been determined by means of cyclic voltammetry in acidic medium. The optimal deposition range has been studied in zinc nitrate electrolyte containing concentrations of thiourea between 0 and 1.0 M. Zinc oxide films have been photoelectrodeposited in a potential range between − 0.95 and − 1.1 V/MSE depending on thiourea concentration. The morphology and composition analyses by scanning electron microscopy, X-ray diffraction spectroscopy, and energy dispersive X-ray spectroscopy have highlighted that the deposited films are composed of well-crystallized ZnO presenting wurtzite-type structure with no significant sulfur incorporation.

Electrochemical Study of Dopamine at Electrode Fabricated by Cellulose-Assisted Aqueous Dispersion of Long-Length Carbon Nanotube

A long-length (hundred micrometers) carbon nanotube is successfully dispersed in aqueous solution with surfactant cellulose while maintaining its length. An electrochemical study of the synthetic pathway of dopamine (DA), dopamine-o-quinone (DAQ), leucodopaminechrome (LDAC), and dopaminechrome (DAC) at the electrode fabricated by the long-length carbon nanotube dispersed solution is presented. The sequence DA ⇌ DAQ ⇀ LDAC ⇌ DAC for the reaction is electron transfer-chemical reaction-electron transfer (ECE)-type, which is a chemical reaction (DAQ ⇀ LDAC, C) interposed between two electron transfer reactions (DA ⇌ DAQ and LDAC ⇌ DAC, E). The salient electrochemical signals due to both DA ⇌ DAQ and LDAC ⇌ DAC can be obtained at the long-length carbon nanotube electrode, unlike other carbon electrodes such as carbon paste, graphene, fullerene, nanofiber, and graphite. The overall reaction is dominated by step DAQ ⇀ LDAC and is sensitive to pH. With cyclic voltammetry in acidic media, the peak current due to L...

Study on single step solid state synthesis of WC@C nanocomposite and electrochemical stability of synthesized WC@C & Pt/WC@C for alcohol oxidation (methanol/ethanol)

WC@C nano composite was prepared by a single step solid–state reaction through in situ reduction and carburization of WO3 in the presence of Mg and activated charcoal. The XRD results and thermodynamics analysis showed that the optimization of reaction temperature facilitates the reduction as well as carburization of tungsten oxide(s) at different reaction temperature. Thermogravimetric analysis of the product was done to assess the thermal stability in air. The Raman spectroscopy was used to find out the nature (amorphous/graphitic) of carbon in the obtained phase. The N2 adsorption–desorption measurement showed a narrow pore size distribution from 3 to 4 nm with BET surface area of up to 522.5 m2/g. TEM/HRTEM images confirmed formation of the WC nano particles with spherical morphology. Electrochemical stability of pure and platinized carbide sample (Pt/WC) has been investigated using cyclic voltammetry in acidic media for alcohol (methanol and ethanol) oxidation.

Antibacterial activity of nano fabricated polypyrrole by cyclic voltammetry

The oxidative chemical polymerization of pyrrole was synthesized by cyclic voltammetry in acidic medium using sulfuric acid as an electrolyte at 30 o C. The synthesized polymer was characterized by SEM, and XRD. The activity of the fabricated polymer was evaluated by agar well cut diffusion method against three bacteria: Streptococcus pneumonia (RCMB 010010), Enterococcus faecali (RCMB 010068), and Staphylococcus aureus (RCMB 010028). The polymer exhibited moderate antibacterial activity and significantly not active of antifungal. Keywords: polypyrrole; electropolymerization; characterization; antibacterial activity

Catalytic oxidation of methanol on Pt/X (X = CaTP, NaTP) electrodes in sulfuric acid solution

In this paper, we report the synthesis and characterization of electrodes based on NASICON type phosphates. The study of the electrochemical oxidation of methanol at ambient temperature on electrodes based on NASICON type Ca0,5Ti2(PO4)3 (CaTP) and Na5Ti(PO4)3 (NaTP) compared to that of the platinum electrode model has been conducted by cyclic voltammetry in acidic medium. The results showed a significant increase of current density on the electro oxidation of methanol on the material developed based NASICON structure CaTP, cons deactivation of the electro oxidation is observed the closed structure type NaTP.

Electrochemical behaviour of gamma hydroxybutyric acid at a platinum electrode in acidic medium

The electrooxidation of gamma hydroxybutyric acid (GHB) on a polycrystalline platinum electrode is studied by cyclic voltammetry in acidic medium. Two oxidation peaks, A and B, are obtained in the positive scan within the potential range of the double layer region and of the platinum oxide region, respectively. In the negative going potential sweep an inverted oxidation peak with an onset partially overlapping with the tail of the cathodic peak for the reduction of the platinum oxide formed during the anodic scan is obtained (peak C). This inverted peak can be observed at a potential close to +0.2V (vs Ag/AgCl at pH 2) and separated 0.4 and 0.8V from the two other oxidation peaks obtained during the anodic scan and in such conditions that the surface is particularly activated to favour this electrochemical process. The response obtained in the electronic current for the different peaks when GHB concentration and scan rate were changed to allows inferring that these are the result of a potential dependent mechanism. The behaviour observed is according with the oxidation of the alcohol group to the corresponding aldehyde and carboxylic acid (succinic acid) as main products.

Hydrogenotitanates nanotubes supported platinum anode for direct methanol fuel cell

Hydrogenotitanates nanotubes (HTNs) are prepared from TiO2 powder via hydrothermal processing in 11.25 M NaOH aq. The reaction temperature is 130 °C for 20 h. Afterward a heat treatment is done during 2 h at 500 °C in air, to obtain calcined HTNs (HTNs-cal). The structural change on the molecular TiO2 during the hydrothermal treatment is investigated in detail by various analytic techniques such as XRD and TEM, which reveal that the crystal structure of the HTNs materials is similar to that of H2Ti2O5·H2O nanotubes with 160 nm in length and 10 nm in diameter. Nitrogen adsorption–desorption isotherms indicate that synthesized solids are mesoporous materials with a multiwalled nanotubular structure and high specific surface area. Platinum nanoparticles are deposited on the HTNs by the impregnation method for a total noble metal loading of 10 wt%. The electrocatalytic activity of these electrocatalysts is evaluated by cyclic voltammetry in acid medium. Typical CO stripping voltammetry in acidic solutions is investigated. The results demonstrate that the HTNs can greatly enhance the catalytic activity of Pt for methanol oxidation. The CO stripping test shows that the Pt/HTNs can shift the CO oxidation potential to lower direction than Pt/C (XC72) and Pt/HTNs-cal catalysts.

Electrochemical synthesis of flower-like Pd nanoparticles with high tolerance toward formic acid electrooxidation

Flower-like nanoparticles exhibit unique properties due to the presence of edge and corner atoms, ad-atoms, pits and other collection of defects. In this work, flower-like Pd nanoparticles were obtained by surfactantless and additiveless square wave voltammetry as an electrochemical method of synthesis. Furthermore, other well-defined Pd shapes with dendritic growth such as spinous flower-like, cone and coral reef-like shapes were obtained by electrochemical methods using cyclic voltammetry, differential pulse amperometry and second harmonic AC voltammetry. Crystal sizes were calculated through the X-ray diffraction patterns for the spinous flower-like, cone, flower and coral reef-like palladium architectures resulting in sizes of 33, 56, 44 and 47 nm, respectively. SEM and cross-section TEM images confirmed that the architectures were composed of micro and nanostructures with dendritic growths. Cyclic voltammetry in acidic medium confirmed the presence of certain facets and terraces in both, flower-like Pd and the dendritic growths. The electrocatalytic properties of the palladium architectures were evaluated to the formic acid electrooxidation at 0.1, 0.5 and 1 M. The flower-like Pd architectures exhibited the highest tolerance to CO poisoning due to the process being carried out by a direct pathway and can be related to the effect of the unique flower-like shape which due to its nature exhibits a high presence of terraces and defects.

Green Chemistry Route to the Synthesis of Palladium Nanoparticles on Reduced Graphene Oxide for Ethanol Fuel Cells Applications

In this article, we have demonstrated the synthesis of palladium nanoparticles decorated on reduced graphene oxide (RGO-Pd NPs) film via green chemistry route, one pot electrochemical reduction of graphene oxide and palladium ions without using any chemical reducing agents. Cyclic voltammetry in acid medium shows the characteristic nanosized palladium nanoparticles. The RGO-Pd NPs poses very high electrochemically active surface area and shows good catalytic properties for the elctrooxidation of ethanol in alkaline medium.

Voltammetric Study of the Molybdate Reduction and Subsequent Oxidation on Glassy Carbon Electrode in Acid Media

The electroreduction of molybdate and subsequent electro-oxidation on glassy carbon electrodes was studied by cyclic voltammetry in acid medium. The results show that the reduction of molybdate depends on applied potential and molybdate concentration in solution. The molybdate reduction process is characterized by cathodic peaks Ic (-0.143 mV), IIc (-0.270 mV) and the cathodic band (Bc) around -400 mV. Cathodic peaks Ic and IIc correspond to the early stages of reduction of molybdate. Both peaks show some degree of reversibility with respect to the anodic peaks Ia and IIa. As the cathode switching potential is more negative than -400 mV and the concentration of molybdate increases, the band Bc is the dominant factor in the reduction process, resulting in the formation of the anodic peaks IIIa (-217 mV) and IVa (477 mV) on voltammogram. This behaviour can be justified through the formation and oxidation of hydrogen molybdenum bronzes on the surface of glassy carbon.

Studies on degradation of reactive textile dyes solution by electrochemical method

The indirect electrochemical degradation of industrial effluents has become an attractive method in recent years. This paper deals with the electrochemical degradation of Novacron Deep Red C-D (NDRCD) and Novacron Orange C-RN (NOCRN) reactive azo dyes from aqueous solution using graphite carbon electrodes. The results indicated that initial pH, current density and supporting electrolytes were played an important role in the degradation of dyes. Electrochemical behavior of reactive azo dyes has been studied with cyclic voltammetry in acidic medium using pencil graphite as working electrode. The potentials selected for the two dyes were in the range +1.0 to −0.4 V and +0.5 to −0.2 V, respectively. The CV, UV–Vis and chemical oxygen demand (COD) studies were selected to evaluate the degradation efficiency. The maximum colour removal efficiency of 99% and 97% and chemical oxygen demand (COD) removal efficiency of 88% and 82% could be achieved for CDRCD and COCRN, respectively at 7 g L −1 of NaCl concentration. The LC–MS study revealed the degradation of both the dyes and confirmed that the azo groups and aromatic rings were destroyed. The results revealed the suitability of the present process for the effective degradation of dye effluents.

STM, SECPM, AFM and Electrochemistry on Single Crystalline Surfaces.

Scanning probe microscopy (SPM) techniques have had a great impact on research fields of surface science and nanotechnology during the last decades. They are used to investigate surfaces with scanning ranges between several 100 μm down to atomic resolution. Depending on experimental conditions, and the interaction forces between probe and sample, different SPM techniques allow mapping of different surface properties. In this work, scanning tunneling microscopy (STM) in air and under electrochemical conditions (EC-STM), atomic force microscopy (AFM) in air and scanning electrochemical potential microscopy (SECPM) under electrochemical conditions, were used to study different single crystalline surfaces in electrochemistry. Especially SECPM offers potentially new insights into the solid-liquid interface by providing the possibility to image the potential distribution of the surface, with a resolution that is comparable to STM. In electrocatalysis, nanostructured catalysts supported on different electrode materials often show behavior different from their bulk electrodes. This was experimentally and theoretically shown for several combinations and recently on Pt on Au(111) towards fuel cell relevant reactions. For these investigations single crystals often provide accurate and well defined reference and support systems. We will show heteroepitaxially grown Ru, Ir and Rh single crystalline surface films and bulk Au single crystals with different orientations under electrochemical conditions. Image studies from all three different SPM methods will be presented and compared to electrochemical data obtained by cyclic voltammetry in acidic media. The quality of the single crystalline supports will be verified by the SPM images and the cyclic voltammograms. Furthermore, an outlook will be presented on how such supports can be used in electrocatalytic studies.

Improved stability of PtOx sol-gel-modified diamond electrodes covered with a Nafion® film

The modification of boron-doped diamond (BDD) electrodes with platinum oxide particles deposited by the Sol-gel method and using several pre- and post-treatments of the surface is described. The electrochemical stability of the resulting catalytic coatings was evaluated by cyclic voltammetry in acid medium and was much greater than those previously reported in the literature for others deposition methods. A thermal pre-treatment of the BDD surface yielded electrodes that retained 91.6% of the coated material after 1000 voltammetric cycles carried out between the water decomposition reactions. The application of a Nafion® film on top of the coating preserved integrally the deposited platinum oxide. The use of such modified electrodes for practical applications is now feasible under the present experimental conditions.

Electrochemical Behavior of Fluorinated Boron-Doped Diamond

The surface properties and the electrochem. behavior of a fluorinated B-doped diamond (F-BDD) electrode prepd. by plasma treatment in CF4-He mixt. was studied by XPS and cyclic voltammetry in acidic media. The results showed C-F bonding (C-CF and C-F) on the surface of F-BDD, which made the surface more hydrophobic. Also hydrogen evolution was shifted to more cathodic potentials for fluorinated diamond, as compared with untreated BDD. Finally, the higher cathodic overpotential for hydrogen evolution permitted Ni deposition and nitrate redn. [on SciFinder (R)]

Application of an electrochemical quartz crystal microbalance to a study of water adsorption at gold surfaces in acidic media

Changes in surface mass at a Au electrode during cyclic voltammetry in acidic media were monitored with an electrochemical quartz-crystal microbalance. An unexpectedly large increase in surface mass was observed during the positive potential scan in the pre-oxide region beginning ca. 0.5 V negative of the potential for onset of formation of surface oxide (AuO). This mass increase is virtually independent of the acid and is interpreted on the basis of adsorption of H 2O via hydrogen bonding to the submonolayer of hydrous oxide (AuOH) generated in the pre-oxide region. The mass increase is consistent with an increase in surface hydration by about 32 H 2 O molecules per AuOH site.