Novel chemical pathways and charge-transport dynamics of electrodes modified with electropolymerized layers of [Co(v-terpy)2]2+ (original) (raw)
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Inorganic Chemistry, 1995
4-Vinyl-and 6-vinylterpyridine (4-v-tpy; 6-v-tpy) complexes of chromium, nickel, cobalt, iron, ruthenium and osmium have been prepared. These materials can be electropolymerized onto glassy carbon electrodes and the resulting films have been characterized, by cyclic voltammetry and rotated disk electrode voltammetry in aqueous media and under nitrogen and carbon dioxide atmospheres. The electropolymerized films exhibit electrocatalytic activity toward the reduction of C02 with formaldehyde as virtually the only product. The magnitude of the catalytic effect and the efficiency are a function of the metal center and the location of the vinyl group(s) within the ligand. The catalytic activity of complexes having metal-based redox processes at negative potentials was superior to that of complexes where the relevant redox processes were ligand based. Complexes of first row transition metals were more active than those of the second or third row owing to the lower stability of the complexes. The presence of coordinating anions suppressed the electrocatalytic activity with HP04-2 causing a complete inhibition. Electropolymerized films of [Cr(4-v-tpy)2I2+ exhibited a current efficiency of 87%. Turnovers in excess of 15 000 were achieved with electropolymerized films of [Fe(4-v-tpy)2I2+. The kinetics of the reaction were relatively slow, especially when compared to the analogous process in non-aqueous solvents such as DMF. This has been ascribed to differences in the overall reaction and products.
Inorganica Chimica Acta, 2006
As the greenhouse effect increases, the development of systems able to convert with high efficiency CO 2 to energetically rich molecules owns a crucial weight in the technological and environmental domain. As catalyst, rhenium complexes, of the type fac-[Re(L)(CO) 3 Cl] (i.e. L = 2,2 0 -bipyridyl or 4,4 0 -bipyridyl), have attracted a large interest demonstrating promising catalytic properties. fac-[Re(v-bpy)-(CO) 3 Cl]-based polymer deposited onto a solid support has been already investigated as heterogeneous catalyst in the reduction of CO 2 . Here, we deposited by electrochemical polymerization fac-[Re(v-bpy)(CO) 3 Cl] onto a nanocrystalline TiO 2 film on glass and we investigated by cyclic voltammetry the properties of such heterogeneous catalyst in the electrochemical reduction of CO 2 . We demonstrated that the nanoporous nature of the substrate allows to increase the two-dimensional number of redox sites per surface area and hence to get a significant enhancement of the catalytic yield.
Journal of Electroanalytical Chemistry, 1996
Electrocatalytic CO, reduction was carried out using a modified graphite electrode coated with a poly(4-vinylpyridine) (PVP) membrane containing cobalt phthalocyanine (CoPc). In a typical electrolysis in a 0.1 M NaH,PO, aqueous phase (pH 4.4), the catalyst membrane achieved a much more selective CO, reduction than that by a neat CoPc coating. The degree of the selectivity, defined as the ratio of CO to H, produced, was about 6 at -1.20 V vs. AglAgCl. The catalytic activity of CoPc was ascribed to the properties of PVP which is co-ordinative and weakly basic. Important factors affecting the CO, reduction were investigated, such as applied potential, pH and CoPc concentration in the membrane. An optimum applied potential of -1.20 V vs. AglAgCl was found for selective CO production. As for the pH, an optimum condition was obtained at pH = 5 where the PVP provides a partially protonated environment around the CoPc. The CO/H, selectivity was strongly dependent on the CoPc concentration in the membrane ([CoPc],,) especially at lower applied potentials; higher [CoPc],, brings about higher CO/H, selectivity. As for the effects of PVP, coordination of the pyridine group to CoPc as well as the microenvironment around CoPc provided by the polymer were concluded as dominant factors. A concerted protonation-deprotonation mechanism for the CO production process assisted by partially protonated PVP species was suggested. From the voltammetric and in situ potential-step chronoamperospectroscopy measurement, it was proposed that the CoPc/CO, intermediate accepts a third electron to produce CO.
Chemical Communications, 2013
Irreversibly adsorbed cyanide adlayers formed on single-crystal platinum electrodes were studied by cyclic voltammetry and in-situ FTIR spectroscopy in a perchloric medium. A vibrational band around 2100 cm 1 was assigned to the C-N stretching vibration of adsorbed cyanide on the three electrode surfaces. Cyanide adlayers seem to be stable on Pt(lll) in a wide range of potentials. Tuning rates of 100 and 30 cm -1 V -i were measured for the band at 2100 cm -~ below and above 0.5 V, respectively. Adsorbed cyanide has a complex behavior on Pt (100). The polarization of the cyanide-covered Pt(100) electrode in the potential region below 0.4V (RHE) leads to the formation of a CO adlayer (band at 1820cm-1). The oxidation of adsorbed cyanide on the Pt(100) electrode produces CO 2 (band at 2344 cm -i) and adsorbed NO (band at 1624 cm-1), which shows a characteristic voltarnmetric behavior. Adsorbed cyanate (band at 2175 cm-1) was also identified as an intermediate product during adsorbed cyanide oxidation on Pt(100). Finally, for Pt(110), adsorbed cyanide is slowly desorbed below 0.1 V (RHE).
Electrochimica Acta, 2006
The electrochemical behaviour of [Ni(bpy) 3 (BF 4) 2 ], [Co(bpy) 3 (BF 4) 2 ], and Co(salen) (where bpy = 2,2-bipyridine, and salen = N,Nbis(salicylidene)ethylenediamine) is studied at a glassy carbon electrode modified with the poly(estersulfonate) ionomer Eastman AQ 55 in acetonitrile (MeCN). It is shown that the nickel complex is strongly incorporated into the polymer. The reduction of the divalent nickel compound features a two-electron process leading to a nickel(0) species which is released from the coating because of the lack of electrostatic attraction with the ionomer. Yet, the neutral zerovalent nickel-bipyridine complex is reactive towards ethyl 4-iodobenzoate and di-bromocyclohexane despite the presence of the polymer. The activation of the aryl halide occurs through an oxidative addition, whereas, an electron transfer is involved in the presence of the alkyl halide making the catalyst regeneration much faster in the latter case. The electrochemical study of [Co(bpy) 3 (BF 4) 2 ] shows that incorporation of the cobalt complex into the polymer is efficient, provided excess bpy is used. This excess bpy does not interfere with the electrocatalytic activity of the cobalt complex incorporated in the AQ coating and efficient electrocatalysis is observed towards di-bromocyclohexane and benzyl-bromide as substrates. Finally, replacement of the bpy ligand with the macrocycle N,N-bis(salicylidene)ethylenediamine, salen, leads to the incorporation of the non-charged Co II (salen) complex into the AQ 55 polymer showing the relevancy of hydrophobic interactions. The reaction between the electrogenerated [Co I (salen)] − with 1,2-dibromocyclohexane exhibits a fast inner sphere electron transfer.
Growth and Electrochemical Behaviour of a Poly [tricarbonyl(viny(bipyridy))rhenium chloride] Film
The chemical transformations of this film on reduction to -1.9V have been studied by in situ FTIR spectroscopy in the presence and absence of CO,, and the spectra assigned using Timney's ligand effect parameters. This analysis shows that the reduction chemistry is somewhat simplified as compared to the homogeneous case studied earlier, with dimerisation of the reduction products much less prevalent. The films are highly active for C02 reduction but show long-term degradation, and one possible mechanism for this is explored with a combination of ellipsometry and FTIR.
Revista de la Sociedad Química de Mexico, 2015
In this work the electrochemical behavior of Co(II) com-plexes with substituted bidentate and tridentate polypyridine ligands [CoL3](BF4)2 and [CoL´2](NO3)2 in 0.1M phosphate buffer pH 7.2 was studied. A reversible electrochemical process Co(II)Ln → Co(III) Ln +1eˉ was observed. A linear relationship between the redox poten-tial (E°) and the pKa of the non-coordinated ligand was found. It was demonstrated by DFT calculations the use of pKa value as a descriptor of the π acceptor character of a ligand. The electrochemical response in the presence of glucose oxidase (GOx) was also studied. It was pos-sible to establish a tendency between the homogeneous electron trans-fer rate constant (ks) and the redox potential (E°) for the compounds studied in this work and other examples taken from the literature.
Journal of Solid State Electrochemistry, 2004
We have studied for the first time the ability of a conducting polymer film, p(Tc3Py), representing a polypyrrole matrix with covalently attached titanocene dichloride (TcCl 2 ) centers, to serve as an intermediator for the electron charge transport between the electrode and the reaction sites of solute reactants. The standard potential of the first of these electroactive species, ferrocene (Fc), is in the range where the polymer matrix is in its slightly oxidized state so that solute Fc species give a reversible response at the surface of this modified electrode. Another solute reactant, TcCl 2 , was studied in solutions in which it demonstrates a (quasi)reversible behavior at bare electrode surfaces, THF+TBAPF 6 and AN+TEACl. The standard redox potential of this species belongs to the range of the electroactivity of immobilized TcCl 2 centers (where the matrix is in its non-conducting state) so that the electron charge has to be transported via stepwise redox reactions between neighboring centers inside the film. The combination, solute reactant+film, results in a greater CV current compared to the response of the film in background solution or of the solute species at the bare electrode surface. This current for THF solution even exceeds the sum of separate currents for the film and the reactant. This finding is attributed to a catalytic effect of solute species as redox intermediators for the transformation of immobilized electroactive centers leading to a greater degree of the film reduction. The presence of solute TcCl 2 species results in a much greater stability of immobilized centers (compared to the corresponding reactant-free solution), both in the course of CV with the passage of the range of their response and in experiments with the film holding at the potential within this range. This holding leads to an almost constant current related to the reaction of solute species at the film/ solution interface. Our estimate shows that immobilized centers undergo above 10,000 reversible transformations (without an observed tendency to the degradation) to ensure the passage of this current. The conclusion has been drawn that immobilized TcCl 2 centers are able to serve as sufficiently stable redox intermediators for the electron charge transport across the film, a prerequisite for the catalytic applications of such films.
Analytical Chemistry, 1997
An electrochemical time-of-flight technique is employed in the investigation of charge transport dynamics in a cobalt bipyridine redox polyether hybrid. Measurements of the apparent diffusion coefficient, D APP , provide insight into electron self-exchange reactions in the undiluted molten metal complex. Results from time-of-flight measurements are compared to those from potential step chronoamperometry and cyclic voltammetry; good agreement is observed. Peak shapes are compared with simulations from a previous report; disparities noted are ascribed to differences in the potential pulse profile employed. Electroactive polymer films 1 have experienced intensive research owing to their potential applications in chemical sensors, electrocatalysis, electrochromic devices, and energy storage. These materials include films of redox polymers, 2 where an electroactive probe is covalently attached to a polymeric lattice, and polyelectrolyte membranes, 3 such as Nafion, into which charged probes have been incorporated. The rate of electron hopping 1,4 or electron self-exchange transport through the films is a property both of fundamental significance in electron-transfer dynamics and of practical importance since this process transports oxidizing or reducing equivalents through films in their applications. Electrochemical methods used to measure diffusion rates within these polymers have included transient ones like potentialstep chronoamperometry and chronocoulometry 5 and cyclic voltammetry, 6 and a variety of steady-state methods. 7
Journal of Electroanalytical Chemistry, 2006
The binuclear ½RuðbpyÞðCOÞ 2 ðCH 3 CNÞ 2þ 2 (bpy = 2,2 0 -bipyridine) complex is an excellent precursor for the formation of redox polymeric Ru-Ru bonded films [Ru(bpy)(CO) 2 ] n on electroactive surfaces by a two-electron reduction process. The resulting molecular cathodes are highly efficient electrocatalysts for the selective reduction of CO 2 in pure aqueous media. In this paper, the simple in situ synthesis and the electrochemical behavior of a series of binuclear complexes ½RuðLÞðCOÞ 2 ðCH 3 CNÞ 2þ 2 (L = bipyridyl ligands substituted by one or more pyrrole groups) are reported. In addition, to generating [Ru(L)(CO) 2 ] n electropolymerization, anodic oxidation of the complexes allow the formation of functionalized polypyrrole films. The electrochemical properties of these films towards CO 2 reduction have been also investigated.