Insight into CO Activation over Cu(100) under Electrochemical Conditions

The reduction of CO₂ on copper electrodes has attracted great attentions in the last decades, since it provides a sustainable approach for energy restore. During the CO₂ reduction process, the electron transfer to CO_ads is experimentally suggested to be the crucial step. In this work, we examine two possible pathways in CO activation, i.e. to generate COH_ads and CHO_ads, respectively, by performing the state-of-the-art constrained ab initio molecular dynamics simulations on the charged Cu(100) electrode under aqueous conditions, which is close to the realistic electrochemical condition. The free energy profile in the formation of COH_ads via the coupled proton and electron transfer is plotted. Furthermore, by Bader charge analyses, a linear relationship between C-O bond distance and the negative charge in CO fragment is unveiled. The formation of CHO_ads is identified to be a surface catalytic reaction, which requires the adsorption of H atom on the surface first. By comparing these two pathways, we demonstrate that kinetically the formation of COH_ads is more favored than that of CHO_ads, while CHO_ads is thermodynamically more stable. This work reveals that CO activation via COH_ads intermediate is an important pathway in electrocatalysis, which could provide some insights into CO₂ electroreduction over Cu electrodes.

The electrochemical oxidation of hydrogen at activated platinum electrodes in room temperature ionic liquids as solvents

The oxidation of hydrogen was studied at an activated platinum micro-electrode by cyclic voltammetry in the following ionic liquids: [C(2)mim][NTf2], [C(4)mim][NTf2], [N-6.2.2.2][NTf2], [P-14.6.6.6][NTf2], [C(4)mim][OTf], [C(4)mim][BF4] [C(4)mim][PF6], [C(4)mim][NO3], [C(6)mim]Cl and [C(6)mim][FAP] (where [C(n)mim](+) = 1-alkyl-3-methylimidazolium, [N-6,N-2,N-2,N-2](+) = n-hexyltriethylammonium, [P-14,P-6,P-6,P-6](+) = tris(n-hexyltetradecyl) phosphonium, [NTf2](-) = bis(trifluoromethylsulfonyl)amide, [OTf] = trifluoromethlysulfonate and [FAP](-) = tris(perfluoroethyl)trifluorophosphate). Activation of the Pt electrode was necessary to obtain reliable and reproducible voltammetry. After activation of the electrode, the H-2 oxidation waves were nearly electrochemically and chemically reversible in [C(n)mim][NTf2] ionic liquids, chemically irreversible in [C(6)mim]Cl and [C(4)mim][NO3], and showed intermediate characteristics in OTf-, [BF4](-), [PF6](-), [FAP](-) and other [NTf2](-)-based ionic liquids. These differences reflect the contrasting interactions of protons with the respective RTIL anions. The oxidation peaks are reported relative to the half-wave potential of the cobaltocenium/cobaltocene redox couple in all ionic liquids studied, giving an indication of the relative proton interactions of each ionic liquid. A preliminary temperature study (ca. 298-333 K) has also been carried out in some of the ionic liquids. Diffusion coefficients and solubilities of hydrogen at 298 K were obtained from potential-step chronoamperometry, and there was no relationship found between the diffusion coefficients and solvent viscosity. RTILs possessing [NTf2](-) and [FAP](-) anions showed the highest micro-electrode peak currents for the oxidation in H-2 saturated solutions, with[C(4)mim][NTf2] toeing the most sensitive. The large number of available RTIL anion/cation pairs allows scope for the possible electrochemical detection of hydrogen gas for use in gas sensor technology. (c) 2008 Elsevier B.V. All rights reserved.

An electrochemical study of the oxidation of hydrogen at platinum electrodes in several room temperature ionic liquids

The electrochemical oxidation of dissolved hydrogen gas has been studied in a range of room-temperature ionic liquids (RTILs), namely [C(2)mim][NTf2], [C(4)mim][NTf2], [N-6,N-2,N-2,N-2][NTf2], [P-14,P-6,P-6,P-6][NTf2], [C(4)mpyrr][NTf2], [C(4)mim][BF4], [C(4)mim][PF6], [C(4)mim][OTf], and [C(6)mim]Cl on a platinum microdisk electrode of diameter 10 mu m. In all cases, except [C(6)mim]Cl, a broad quasi-electrochemically reversible oxidation peak between 0.3 to 1.3 V vs Ag was seen prior to electrode activation ([C(6)mim]Cl showed an almost irreversible wave). When the electrode was pre-anodized (

A comparative electrochemical study of diffusion in room temperature ionic liquid solvents versus acetonitrile

Measurements on the diffusion coefficient of the neutral molecule N,N,N',N'-tetramethyl-para-phenylenediamine and the radical cation and dication generated by its one- and two-electron oxidation, respectively, are reported over the range 298-348 K in both acetonitrile and four room temperature ionic liquids (RTILs). Data were collected using single and double potential step chronamperometry at a gold disk electrode of micrometer dimension, and analysed via fitting to the appropriate analytical expression or, where necessary, to simulation. The variation of diffusion coefficient with temperature was found to occur in an Arrhenius-type manner for all combinations of solute and solvent. For a given ionic liquid, the diffusional activation energies of each species were not only closely equivalent to each other, but also to the RTIL's activation energy of viscous flow. In acetonitrile supported with 0.1 M tetrabutylammonium perchlorate, the ratio in diffusion coefficients of the radial cation and dication tot he neutral molecule were calculated as 0.89 +/- 0.05 and 0.51 +/- 0.03, respectively. In contrast, amongst the ionic liquids the same ratios were determined to be on average 0.53 +/- 0.04 and 0.33 +/- 0.03. The consequences of this dissimilarity are considered in terms of the modelling of voltammetric data gathered within ionic liquid solvents.

SO2 Saturation of the Room Temperature Ionic Liquid [C(2)mim][NTf2] Much Reduces the Activation Energy for Diffusion

The physical effect of high concentrations of reversibly dissolved SO2 on [C(2)mim][NTf2] was examined using cyclic voltammetry, chronoamperometry, and ESR spectroscopy. Cyclic voltammetry of the oxidation of solutions of ferrocene, N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD), and chloride in the room temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium bis(trifluoromethanesufonyl)imide ([C(2)mim][NTf2]) reveals an increase in limiting current of each species corresponding to the addition of increasing concentrations of sulfur dioxide. Quantitative chronoamperometry reveals an increase in each species' diffusion coefficient with SO2 concentration. When chronoamperometric data were obtained for ferrocene in [C(2)mim][NTf2] at a range of temperatures, the translational diffusion activation energy (29.0 +/- 0.5 kJ mol(-1)) was found to be in good agreement with previous studies. Adding SO2 results in apparent near-activationless translational diffusion. A significant decrease in the activation energy of rotational diffusion with the SO2 saturation of a 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) solution in [C(2)mim][NTf2] (29.9 +/- 2.0 to 7.7 +/- 5.3 kJ mol(-1)) was observed using electron spin resonance (ESR) spectroscopy. The reversible physical absorption Of SO2 by [C(2)mim][NTf2] should have no adverse effect on the ability of that ionic liquid to be employed as a solvent in an electrochemical gas sensor, and it is possible that the SO2-mediated reduction of RTIL viscosity could have intrinsic utility.

Electrochemical sensor for catechol and dopamine based on a catalytic molecularly imprinted polymer-conducting polymer hybrid recognition element

One of the difficulties with using molecularly imprinted polymers (MIPs) and other electrically insulating materials as the recognition element in electrochemical sensors is the lack of a direct path for the conduction of electrons from the active sites to the electrode. We have sought to address this problem through the preparation and characterization of novel hybrid materials combining a catalytic MIP, capable of oxidizing the template, catechol, with an electrically conducting polymer. In this way a network of "molecular wires" assists in the conduction of electrons from the active sites within the MIP to the electrode surface. This was made possible by the design of a new monomer that combines orthogonal polymerizable functionality; comprising an aniline group and a methacrylamide. Conducting films were prepared on the surface of electrodes (Au on glass) by electropolymerization of the aniline moiety. A layer of MIP was photochemically grafted over the polyaniline, via N,N'-diethyldithiocarbamic acid benzyl ester (iniferter) activation of the methacrylamide groups. Detection of catechol by the hybrid-MIP sensor was found to be specific, and catechol oxidation was detected by cyclic voltammetry at the optimized operating conditions: potential range -0.6 V to +0.8 V (vs Ag/AgCl), scan rate 50 mV/s, PBS pH 7.4. The calibration curve for catechol was found to be linear to 144 µM, with a limit of detection of 228 nM. Catechol and dopamine were detected by the sensor, whereas analogues and potentially interfering compounds, including phenol, resorcinol, hydroquinone, serotonin, and ascorbic acid, had minimal effect (=3%) on the detection of either analyte. Nonimprinted hybrid electrodes and bare gold electrodes failed to give any response to catechol at concentrations below 0.5 mM. Finally, the catalytic properties of the sensor were characterized by chronoamperometry and were found to be consistent with Michaelis-Menten kinetics. © 2009 American Chemical Society.

In situ catalyst activity control in a novel membrane reactor-Reaction driven wireless electrochemical promotion of catalysis

A dual chamber membrane reactor was used in order to study the effect of macroscopically applied oxygen chemical potential differences to a platinum catalyst supported on a mixed oxygen ion and electronic conducting membrane. It is believed that the oxygen chemical potential difference imposed by the use of an oxygen sweep in one of the reactor chambers causes the back-spillover of oxygen species from the support onto the catalyst surface, resulting in the modification of the catalytic activity. The use of different sweep gases, such as ethylene and hydrogen was investigated as the means to reverse the rate modification by removing the spilt over species from the catalyst surface and returning the system to its initial state. Oxygen sweep in general had a positive effect on the reaction rate with rate increases up to 20% measured. Experimental results showed that hydrogen is a more potent sweep gas than ethylene in terms of the ability to reverse rate modification. A 10% rate loss was observed when using an ethylene sweep as compared with an almost 60% rate decrease when hydrogen was used as the sweep gas. © 2009 Elsevier Ltd. All rights reserved.