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In this work, a gold electrode modified with self-assembled layers (SAMs) composed of 3-mercaptopropionic acid, cysteamine and gold nanoparticles was prepared. The electrode with SAMs endowed with gold nanoparticles gave the high catalytic effect for monoethanolamine (MEA) electrooxidation in solution at pH 7. For this novel sensor, a linear relationship between the current response of MEA at the potential of peak maximum (j p) and the concentration of this compound in solution (c MEA) was found, over the range 0.1 μM to 0.8 M with the detection sensitivity equal to about 5 A cm−2 mol−1 dm3 (at v = 0.1 V s−1) and the detection limit of 0.046 μM.

Kinetics and mechanism of formic acid (FA) oxidation on platinum and upd-lead ad-atoms modifiedplatinum electrodes have been studied using unlabelled and deuterated compounds. Poisoning of theelectrode surface by CO-like species was prevented by suppression of dissociative chemisorption of FAdue to a fast competitive underpotential deposition of lead ad-atoms on the Pt surface from an acidicsolution containing Pb 2þ cations. Modification of the Pt electrode with upd lead induced a catalyticeffect in the direct electrooxidation of physisorbed FA to CO 2 . With increasing degree of H/D substi-tution, the rate of this reaction decreased in the order: HCOOH > DCOOH HCOOD > DCOOD. HCOOHwas oxidized 8.5-times faster on a Pt/Pb electrode than DCOOD. This primary kinetic isotope effectproves that the CeH- and OeH-bonds are simultaneously cleaved in the rate determining step. Asecondary kinetic isotope effect was found in the dissociative chemisorption of FA in the hydrogenadsorptionedesorption range on a bare Pt electrode after H/D exchange in the CeH bond, wherein theinfluence of deuterium substitution in the OeH group was negligibly small. Thus the CeH bondcleavage is accompanied by the CeOH and not the OeH bond split in the FA decomposition, producingCO-like species on the Pt surface sites. 2013 Elsevier B.V. All rights reserved.

Gold electrodes modified successively with gold nanoparticles (Au-NPs), meso-2,3-dimercaptosuccinic acid (DMSA) and cysteamine (CA)/Au-NPs layers were applied for quantitative determination of epinephrine (EP) in the absence or the presence of ascorbic acid (AA) and uric acid (UA) in aqueous electrolyte solutions. The cyclic voltammograms (CVs) and differential pulse voltammograms (DPVs) proved the highest catalytic activity of the Au/Au-NPs/DMSA/CA/Au-NPs electrode for the oxidation of EP as well as for AA and UA. The respective current peaks were clearly separated from each other enabling selective detection of all these compounds coexisting in a mixture, e.g. in physiological samples. For this novel sensor a linear relationship between the current response of EP at the potential of peak maximum ( j p ) and the concentration of this compound in solution ( c EP ) was found over the range 0.0001 mmol dm −3 to 0.8 mmol dm −3 with the detection sensitivity j p / c EP equal to about 7 A cm −2 mol −1 dm 3 (at v = 100 mV s −1 ) and the detection limit of 2.8 10 −5 mmol dm −3 .

Electrooxidation of epinephrine (EP) in the presence of secondary amine as a nucleophile was investigated on a bare polycrystalline gold electrode in a phosphate buffer solution of pH 7. The results have shown that electrochemically produced epinephrinequinone underwent an attack by morpholine (MO) via 1,4-Michael addition. The reaction products were identified by electrospray ionisation mass spectrometry (ESI-MS). A linear relationship between the current response and epinephrine concentration in the presence of morpholine was obtained in the range of 2 × 10 −5 mM to 0.7 mM with the detection limit 1.5 × 10 −5 mM. The procedure of using morpholine as an additive in analysed solutions was proven to be suitable for quantitative epinephrine determination in samples containing an excess of the ascorbic acid (AA) and uric acids (UA) without the necessity of any preceding modification of a gold electrode surface.

An appreciable enhancement of the rate of propene electroreduction was discovered under CV conditions on a polycrystalline Pt electrode in a strongly acidified solution containing cationic Mo(VI) oxo-species. Simultaneously, the electroreduction of these species was found to be remarkably more effective in the presence of propene in comparison with that obtained using a supporting electrolyte without the alkene. Evidence was provided that the catalytic effect results from the continuous regeneration of the electroactive molybdenum moieties via a non-faradaic reaction between propene and the reduced forms produced at the electrode/solution interface from the parent Mo(VI) cationic species in the preceding one and three electron-transfer reactions. Keywords: Electrocatalysis, Electroreduction, Pt/molybdenum(VI), Propene system

a b s t r a c t Kinetics of the electroreduction of molybdenum(VI) species and allyl alcohol (AA) alone as well as of AA after the addition of Na2MoO4 to perchloric acid solutions (HClO4) on a polycrystalline Pt electrode was characterized under the conditions of cyclic voltammetry (CV). Using the XPS technique evidence was provided that mixed valent Mo(V/VI) layer is formed upon reduction of Mo(VI) moieties present in 1 M HClO4 solution, while the cationic Mo(VI) species existing in strongly acidified solutions are reduced successively to relevant Mo(V) and Mo(III) species at E < 0.25 V. It was ascertained that a relatively fast adsorption of AA precedes its hydrogenation to propene and propane in the absence of Mo(VI) in the electrolyte solution. However, the Pt surface is partially poisoned with CO-like species due to a rupture of the C3-carbon backbone in the potential range of hydrogen adsorption-desorption. A considerable enhancement of the cathodic current corresponding to the AA electroreduction was discovered in the presence of cationic Mo(VI) species in 4 M HClO4 solutions. Simultaneously, the rate of electroreduction of this species was effectively increased on the addition of AA in comparison with that in the absence of AA. According to the proposed reaction pathways, AA is reduced via a catalytic chemical reaction with Mo(III) and/or Mo(V) cationic species. The cyclic regeneration of the electroactive Mo(VI) and/or Mo(V) species accounts for the observed catalytic phenomenon. Furthermore, the decomposition of the C3-carbon skeleton of AA molecules and formation of strongly adsorbed CO-like species is eliminated in the presence of Mo(VI). The optimal conditions for monitoring of AA and/or Mo(VI) in electrochemical

Gold electrodes were modified with self assembled layers (SAMs) composed of mercaptopropionic acid, thiodipropionic acid, dithiodipropionic acid, cysteamine and gold nanoparticles and used to study the electrooxidation of dopamine (DA) in solution at pH 7. SAMs endowed with gold nanoparticles gave the highest catalytic effect. The results showed that such electrodes are capable of resolving the oxidation peaks of DA, ascorbic acid, and uric acid which is most favourable with respect to the detection of DA in physiological matrices.

Novel self-assembled monolayers were obtained on silver using 4,7-diazaheptyl-trimethoxy-silane (SiN) and vinyl-trialkoxy-silane (SiVA, where the alkyl group is 3,6,9,12,15,18,21,24,27,30,33,36,39,42,45,48,51,54,57,60-eicozaoxa- hexaheptaconan). It was shown that thus modified metal surface was protected against electrooxidation. A densely packed monolayer remained stable and did not desorb from the Ag electrode on the potential cycling. The structure of SiN and SiVA as well as their complexes with Li + cations were calculated and visualised by the AM1d and PM5 semi-empirical methods.

A novel stable self-assembled chemisorbed layers, providing protection of metal surface against electrooxidation capable of blocking propylene carbonate (PC) electroreduction and Li electrodeposition, were produced from 3-[tris-(2-methoxyethoxy)silyl]-propanethiol (SIS2) on silver. Reflection-absorption infrared spectroscopy (RAIRS) indicated cleavage of the S-H bond upon adsorption of SIS1 [3-(trimethoxysilyl)-propanethiole] and SIS2 species with the formation of S-Ag bonds on the metal surface. By cyclic voltammetry it was found that the primary adsorbate formed on a Ag electrode at E ad (between -0.2 and - 1.2 V vs. SCE) underwent reductive desorption at E

The electrolytic conductivity and viscosity of lithium perchlorate in bis-1,4-dioxapentyl sulfate (IV) [OS22] and 1,4,7-trioxaoctyl sulfate (IV) [OS32] were determined as a function of salt concentration (0.00005–2 M) and temperature (286–318 K). At 298 K, the highest conductivity (κ=2.77×10−3 Ω−1 cm−1) was achieved for OS22 based solutions containing 1–2 M LiClO4. Formation of electrically neutral ion pairs appeared to be the main reason for a continuous decline in the molar conductivity (Λ) observed in dilute solutions with increasing salt concentration. Additionally, an increase in the dynamic viscosity (η) accounted for a decrease in the mobility of charge carriers with increasing length of the oxaalkyl chain in the podand molecules. The temperature dependence of the conductivity and viscosity was found to be of the Arrhenius type for both systems investigated, while the activation energies, Eκ# and Eη#, varied in parallel with the degree of interionic aggregation. CVs obtained on a polycrystalline Pt electrode indicated the electrochemical stability of OS22 in the potential range between −0.8 V and 4.7 V versus Li+/Li. A linear current density–potential dependence, with the same slope for the anodic and cathodic branches proved the reversibility of lithium electrodeposition and re-dissolution at the Pt/1 M LiClO4+OS22 interface.

The electrochemical reactivity of propene at the polycrystalline Pt/acidic solution interface was studied by on line differential electrochemical mass spectrometry (DEMS). It was shown that a relatively fast adsorption of hydrocarbon molecules on the electrode surface preceded their electroreduction and electrooxidation at E 0.6 V, respectively. The adsorbate consisted of associatively bonded propene, partially dehydrogenated C3-hydrocarbon residues, as well as C3-, C2-, and/or C1-oxygen-containing species in relative amounts dependent on the adsorption potential and the subsequent potential sequence. The maximum electrode coverage of 0.58 nmol cm-2 was achieved in the potential range 0.3−0.5 V, where the major part of the surface species was propene itself, oriented with the carbon chain almost parallel relative to the electrode/solution interface. The oxygenated C3-species were formed favorably in the presence of coadsorbed water and/or OH species, at 0.5 V < E < 0.8 V. Propane was ident...

The complex formation of lithium and sodium ions with silicon podand solvents: phenyl-tris(1,4-dioxapentyl) silane (PhSi23) and ethyl-tris(1,4-dioxapentyl) silane (EtSi23) has been studied by FTIR, 1 H-, 13 C-, 7 Li- and 23 Na NMR. The far FTIR spectra show that the Li + cations fluctuate very fast whereas Na + cations are still localised between the oxygen atoms of the oxaalkyl chains. The 7 Li NMR spectra prove that one Li + cation can be coordinated not only by one but also two silicon podand molecules. The concentration dependence of the molar conductivity of LiClO 4 in the podand solvents indicates charge transfer between ion clusters.

Electrocatalytic ethyne oxidation and reduction on Pt was studied by on-line mass spectrometry (DEMS). It was shown that the initial step in both processes involves a rapid reactant adsorption on the metal surface. The adsorbate consists of molecular ethyne, partially dehydrogenated hydrocarbon residues C 2 H x and C 2 -oxygen-containing species in a ratio dependent on the electrode potential. The maximum electrode coverage is achieved in the potential range 0.2–0.4 V, whereas the major part of the adsorbate is ethyne itself. Ethane was identified as the main volatile product of the cathodic hydrogenation of the surface species. A trace amount of 1-butene was formed in a slow side reaction. Evolution of a mixture of ethane and ethene was observed in the presence of bulk reactant. Measurements at various sweep rates revealed that electrooxidation of the preadsorbed ethyne to CO 2 at E >0.8 V is much faster than its electroreduction in the hydrogen potential region. The optimal conditions for monitoring and/or utilization of ethyne in an electrochemical cell working in a programmed step potential mode are specified.

Metal hydride electrodes are of particular interest owing to their potential and practical application in batteries. A large number of hydrogen storage materials has been characterized so far. This paper deals with the effect of the chemical nature and stoichiometry of specific alloy families (AB5, A2B, AB/AB2 and AB2) on the hydride stability, hydrogen storage capacity and kinetics of hydrogen sorption-desorption in the solid phase/gas and solid phase/electrolyte solution systems. Special attention has been paid towards the electrochemical properties of metal hydrides in terms of their performance in Ni-MH rechargeable alkaline cells.

A survey of studies on adsorption behaviour of monohydric alcohols and diols at the sp and sd metal electrode/aqueous solution interface is given. Particular attention is paid to the effect of the molecular structure of the surfactants (carbon chain length, number and arrangement of functional groups as well as multiple carbon–carbon bonds) on their interfacial arrangement and interactions.

The adsorption of benzylamine on a polycrystalline gold electrode from aqueous solutions of KClO 4 and HClO 4 has been studied using differential capacitance measurements (tensammetry) and in situ surface enhanced Raman scattering (SERS). Differences in adsorption parameters of benzylamine adsorbed from neutral solutions at θ θ > 0.7 can be explained on the basis of the reorientation of adsorbate molecules. Values of the free enthalpy of adsorption ΔG ad 0 = −40.0 kJ · mol −1 and the interaction coefficient a = −1 at θ ΔG ad 0 = −24.3 kJ · mol −1 with a = 0.55 at θ > 0.7 were obtained. SERS results indicate an edge-on adsorption of benzylamine from KClO 4 solution, with a small contribution from molecules adsorbed flat on the gold surface. For benzylamine adsorbed on gold from acidic solution an end-on orientation of molecules with an interaction via the amino group is concluded.

The electrosorption of 2-propen-1-ol, 2-propin-1-ol, 2-butene-1, 4-diol, and 2-butyne-l,4-diol from an aqueous solution of NaClO4 at a gold(100) single crystal electrode has been studied by tensammetry. The results are discussed with respect to the surface properties of the single crystal electrode, the different structures of the adsorbed molecules, and possible contributions from the multiple bonds and functional groups therein.

The electro-oxidation of formaldehyde at platinum—silver and platinum−gold alloys in alkaline solution was studied with cyclic voltammetry and a rotating-disc electrode at various temperatures. Influences of the alloy composition, the pH and the temperature were identified. In the framework of the proposed reaction sequence the change in the apparent energy of activation is related to the electronic and adsorption properties of the alloys.

The electrooxidation of the three isomeric 1,2-, 1,3-, and 1,4-cyclohexanediols at a gold electrode in contact win an alkaline electrolyte solutior has been studied with cyclic voltammetry. Signficant differences in the electrochemical activity of the isomers were found. The 1,2-diol is by far the most active one. Its trans-isomer is more reactive than the cis-isomer. These differences are rationalized based on the molecular structure and the different elearosorption properties.

The electro-oxidation of 2-propen-1-ol, 2-propyn-1-ol, 2-butene-1,4-diol and 2-butyne-1,4-diol at a polycrystalline gold electrode in alkaline aqueous solutions has been studied with cyclic voltammetry. Additional information about the absorption of the alcohols preceding their oxidation was obtained with tensammetry. Results are discussed with respect to the different structures of the molecules and possible contributions of the multiple bonds therein. The influence of different adsorptivities of the investigated alcohols and the dominating contribution of resonant stabilisation of the radical intermediates being more effective with compounds containing a double bond as compared to a triple or a single bond are discussed.

The electro-oxidation of a series of selectively deuterated alcohols (2-propanol, 1,2-butanediol, 1,4-butanediol and 2,3-butanediol) at a polycrystalline gold electrode in alkaline solutions was studied with cyclic voltammetry. Results were evaluated with respect to the mechanism of the electro-oxidation and the conceivable mode of adsorptive interaction between the alcohol and the surface. Differences in electrochemical reactivity are explained in terms of the molecular structure of the transition state and the participation of adsorbed OH-species.

The adsorption of a series of terminal and vicinal aliphatic diols at a polycrystalline gold electrode from a solution of 0.02 M NaClO4 has been studied. Significant trends and differences in the electrosorption behavior clearly related to the molecular structure of the alcohols were found.

The electrochemical adsorption of 1,1,1, tichloroethane on Pt in sulphuric acid was studied by on-line mass spectrometry. The adsorption is highest in the hydrogen region suggesting a reductive adsorption process. About 75% of the adsorbate can be desorbed cathodically; the products being ethane, butane and, to minor degree, hexane and possible higher alkanes. The ratio of these products depends on the adsorption potential. The only oxidation products is CO 2 . H/D-exchange experiments suggest that the adsorbate is an ethylidyne species.

Metal hydride electrodes are of particular interest owing to their potential and practical application in batteries. A large number of hydrogen storage materials has been characterized so far. This paper deals with the effect of the chemical nature and stoichiometry of specific alloy families (AB5, A2B, AB/AB2 and AB2) on the hydride stability, hydrogen storage capacity and kinetics of hydrogen sorption-desorption in the solid phase/gas and solid phase/electrolyte solution systems. Special attention has been paid towards the electrochemical properties of metal hydrides in terms of their performance in Ni-MH rechargeable alkaline cells.

Using differential electrochemical mass spectrometry, we determined the amount of H2-evolution occuring during formaldehyde oxidation as a function in the potential region of the first oxidation wave. In the second wave, the oxidation product is CO2 in pH 8 solution, as opposed to more alcaline solutions where only formiate is formed. Formaldehyde is reduced to methanol at potentials negative of the RHE.—An electrochemical formaldehyde sensor was built with a sensitivity below 1 ppm. Cross sensitivities towards alcohols can be lowered by UPD of Ag or Hg.

The adsorption of three isomer butanediols on a polycrystalline gold electrode from a 0.02 M NaClO 4 electrolyte solution has been studied with tensammetry. The free enthalpy of adsorption for 2,3-butanediol is higher than the enthalpy of 1,3- and 1,4-butanediol; this is rationalized in terms of a molecular structure dependent surface-adsorbate interaction. The electrooxidation of 2,3-butanediol at the gold electrode in a solution of pH 13 is much faster than the oxidation of the two other isomers; this is explained with the stronger adsorption of this isomer and the resonance effect, especially of the vicinal OH-group, which results in an easier C-H-bond rupture and increased stability of the radical reaction intermediate.

The process of adsoprtion of butan-1-ol on a polycrystalline gold electrode from an aqueous solution of 0.02 M NaF has been studies. The results proved that this process could be described bya Frumkin isothern of adsoprtion. Basic parameters of this isothern were determined.

Using fast linear sweep voltammetry, the adsorption behaviour of formaldehyde, formic acid and methanol was studied on an electrochemically modified (100)-like Pt electrode without or covered with UPD-lead. It was found that both the lead inhibits the formation of strongly bound intermediates and the intermediates inhibit the deposition of lead. This is explained by a mutual hindrance after the “third body” concept. This cannot explain, however, the electrocatalytic effect of UPD-lead on the oxidation of the above fuels since this effect has its maximum at θPb > 0.5. Therefore, we postulate that UPD-lead catalyzes the direct oxidation of formic acid and formaldehyde at potentials between 0.2 and 0.7 V. On the other hand, the direct oxidation of methanol on smooth Pt occurs at potentials more positive than 0.6 V where UPD-lead is already anodically dissolved. Therefore, only a small catalytic effect of UPD-lead on methanol oxidation is observed.

Zusammenfassung Die elektrokatalytische Aktivitat von Gold im Prozess der anodischen Oxidation von Alkoholen in alkalischer Losung wird mit Hilfe zyklischer Voltammetrie untersucht. Der Einfluss der Struktur der Alkohole auf die Geschwindigkeit ihrer Oxidation wird diskutiert.

The electrochemical behaviour of β-MnO2 in 1 M LiClO4, 50% propylene carbonate (PC) + 50% 1,2-dimethoxyethane (DME) solution was investig

Zusammenfassung Die anodische Oxidation von Alkoholen an Gold wurde mit Hilfe zyklischer Voltammetrie und Chronopotentiometrie untersucht. Dabei ergaben sich folgende Messergebnisse: 1. Dem Elektronendurchtritt vom Alkoholmolekul ist die geschwindigkeitsbestimmende Spaltung der CH Bindung am α-Kohlenstoffatom vorgelagert. 2. Die Reaktion ist erster Ordnung bezuglich der Alkohole; die OH − -Ionen wirken sich im Prozess katalytisch aus. 3. In der Bruttoreaktion werden vier Elektronen pro ein Molekul der primaren Alkohole und zwei Elektronen pro ein Molekul der sekundaren Alkohole umgesetzt. Unter Berucksichtigung der experimentellen Ergebnisse wird eine Reaktionsfolge fur die Oxidation von Alkoholen aufgestellt.

The kinetic parameters of the anodic oxidation of formaldehyde in alkaline solution were measured using Pt, Au and a Pt/Au-alloy as electrode materials. Adsorption was studied on all three materials. The results are explained assunting a detailed mechanism and taking into account the formation of strongly bound intermediates via side reactions. The electrocatalytic effect of the alloy as well as the influence of OH − -ions can be understood on the basis of the mechanism proposed.

Zusammenfassung Mit Hilfe der potentiodynamischen Dreieckspannungsmethode wird gezeigt, das Golt-Platin-Legierunge im Prozess der anodischen Oxidation von aliphatischen Alkoholen in alkalischer Losung wesentlich bessere katalytische Eigenschaften aufweisen, als das reine Platin. An 60:40 Gold-Platin-Legierungselektrode wird die grosste Erhohung der Reaktionsgeschwindigkeit beobachtet. Diese Erscheinung lasst sich mit einer geringeren Adsorptionsenergie von dehydrierten Resten und Sauerstoffbelegung an Legierungen erklaren.

The electrochemical oxidation of formaldehyde has been studied by cyclic voltammetry on gold and silver rotating disc electrodes varying the sweep rate, the angular velocity, formaldehyde concentration and pH of the supporting electrolyte. The Tafel parameters and reaction orders as well as the rate constants have been determined. A reaction path is proposed which involves the release and oxidation of the first hydrogen atom under an interaction of formaldehyde molecule with the metal surface and with the OH − -ion, followed by a non-electrochemical reaction or a second charge transfer reaction, depending upon the electrode potential.

The catalytic reduction of ethene, propene and 1- butene on a polycrystalline Pt electrode in strongly acidic medium containing Mo(VI) oxo-species has been examined by cyclic voltammetry taking into account the influence of perchloric acid and molybdate concentration as well as that of the scan rate on the cathodic current response. About tenfold increase in the reaction rate of each alkene investi- gated has been achieved at the optimum molybdate concen- tration of 1-2.5 mM in 4-M HClO4 solution as a supporting electrolyte in comparison with that obtained in the absence of Mo(VI) oxo-species. It was ascertained that the catalytic reduction current strongly depends on the amount of cation- ic Mo(VI) oxo-species at the Pt electrode/solution interface. Simultaneously, the electroreduction of cationic Mo(VI) oxo-species was found to be effectively enhanced in the presence of alkene. According to the proposed reaction pathways, alkenes are reduced to alkanes via a non- faradaic reaction with Mo(V) and/or Mo(III) cationic moie- ties formed in the preceding reductive electron-transfer steps from the parent cationic Mo(VI) oxo-species. Continuous regeneration of the electroactive Mo(VI) and/or Mo(V) cat- ionic oxo-species accounts for the observed catalytic phenomenon.

Zusammenfassung Mit Hilfe des kinetischen Isotopieeffektes laβt sich zeigen, daβ geschwindigkeitsbestimmende Schritt bei der Oxidation von Alkoholen in alkalischer Losung an Goldelektroden in der Abspaltung des am α-Kohlenstoff gebundenen Wasserstoffs besteht.