William J. Pietro

Monomeric and Polymeric Tetra-aminophthalocyanatocobalt(II) Modified Electrodes: Electrocatalytic Reduction of Oxygen

The monomeric and polymeric tetra-aminophthalocyane to, cobalt(II) species adsorbed onto graphite electrodes are active in electrocatalytic oxygen reduction. While the monomeric species is unstable, the polymerized species is an effective and stable reduction catalyst over a wide pH range. Both the two-electron reduction of oxygen to hydrogen peroxide and the four-electron reduction of oxygen to water are characterized by cyclic voltammetry, rotating disc and rotating ring-disc studies with appropriate theoretical analysis. Some mechanistic information is obtained. This is the first cobalt phthalocyanine species to provide a four-electron reduction pathway which exists over a wide pH range and is stable. The stability is associated with the polymerization since the monomeric species is not stable.

Electrocatalytic activity of N,N′,N″,N‴-tetramethyl-tetra-3,4-pyridoporphyrazinocobalt(II) adsorbed on a graphite electrode towards the oxidation of hydrazine and hydroxylamine

The complex N,N′,N″,N‴-tetramethyl-tetra-3,4-pyridoporphyrazinocobalt(II) ([Co(II)Tmtppa]4+) irreversibly adsorbed on a graphite electrode displays electrocatalytic activity towards the oxidation of both hydrazine and hydroxylamine. The kinetics of the electrocatalytic four-electron oxidation of NH2NH2 and two-electron oxidation of NH2OH are examined using cyclic voltammetric and rotating disk electrode methods, and the corresponding kinetic parameters are obtained. The possible application of the [Co(II)Tmtppa]4+ modified electrode in sensing NH2NH2 and NH2OH is also discussed in this paper.

Surface copper immobilization by chelation of alizarin complexone and electrodeposition on graphite electrodes, and related hydrogen sulfide electrochemistry; matrix isolation of atomic copper and molecular copper sulfides on a graphite electrode

Abstract The irreversibly adsorbed alizarin complexone (AC) was employed to immobilize and maintain Cu II ions on the graphite electrode. The coordination chemistry between the adsorbed alizarin complexone ligand and the Cu II ion on the surface was examined by surface cyclic voltammetry. Upon reduction of the Cu II center to a Cu 0 atom, a submonolayer of individual atoms of Cu 0 rather than a continuous layer is formed on the electrode surface. The immobilized surface displays electrocatalytic activity towards the oxidation of sulfide ion from [S 2− ] ion to S 0 . The electrocatalytic activity for the sulfide oxidation on a [Cu II (AC)] − adsorbed electrode is shown to be essentially identical with that of a electrode that contains an electrodeposited submonolayer of Cu 0 . The active catalyst in both cases is identified to be a submonolayer of cupric sulfide. The electrochemistry of the Cu 0 submonolayer-coated electrode in aqueous solution containing hydrogen sulfide was also examined. When the modified electrode was polarized from −1.1 V to 0.2 V, three electrode processes were observed. The first, near −0.7 V, is a surface reaction between surface Cu 0 and adsorbed [S 2− ] ion to form a submonolayer of cuprous sulfide. The second appeared near −0.23 V and is another surface process between Cu 2 S and adsorbed sulfide ion to form a submonolayer of cupric sulfide. The third reaction is the electrochemical oxidation of sulfide ion catalyzed by CuS to form sulphur which deposits on the electrode surface when the potential is positive of −0.2 V.

Poisoning effect of SCN−, H2S and HCN on the reduction of O2 and H2O2 catalyzed by a 1:1 surface complex of Cu: 1,10-phenanthroline adsorbed on graphite electrodes, and its possible application in chemical analysis

Abstract The copper complex with a single 1,10-phenanthroline ligand can be irreversibly adsorbed on graphite electrodes, catalyzing the reduction of both O 2 and H 2 O 2 . The electrocatalytic kinetics of both substrate reductions were studied by cyclic voltammetric and rotating disk electrode methods. The addition of a very small quantity of a species such as SCN − , H 2 S or HCN in the test solution poisons the electrocatalytic activity for O 2 and H 2 O 2 reduction. A theoretical model is proposed to describe this poisoning effect based on the coordination equilibrium between poisoning species and surface adsorbed catalyst, the inner-sphere mechanism of substrate reduction, and Koutecky-Levich theory. The model is supported by experimental results. The surface behaviour of the adsorbed [Cu(phen)] 2+ ads in the presence of the poison species clearly shows the formation of a new surface complex with [Cu(phen)] 2+ ads . These new “poisoned” surface complexes are electrocatalytically inactive towards O 2 and H 2 O 2 reduction. The possible application of this poisoning effect for the analysis of trace SCN − , H 2 S and HCN was explored.

Surface electrochemistry of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide ([MTT]Br) adsorbed on a graphite electrode

Abstract 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide ([MTT]Br), which is of importance as a biological redox indicator, irreversibly adsorbs on a graphite electrode and exhibits two surface electrochemical redox processes. The mechanism of reduction and re-oxidation of this species on the surface is discussed as a function of pH. AM1 calculations and redox data are interpreted to show that protonation of the first reduced product leads to a ring-opening pathway, eventually generating the two-electron reduced formazan species. Cyclic voltammetry, rotating-disk voltammetry, pH dependence studies and electronic spectroscopy are used to characterize the system.

REDOX ACTIVE, MULTI-CHROMOPHORE RU(II) POLYPYRIDYL-CARBAZOLE COPOLYMERS: SYNTHESIS AND CHARACTERIZATION

A novel diimine ligand, 2-(2-pyridyl) 4-carboxyquinoline (pcq) and its corresponding polypyridyl Ru(II) complex were synthesized, characterized, and covalently attached to a carbazole based copolymer via post polymer modification. The resulting modified electroactive and multi-chromophoric polymer was readily characterized by UV-visible, FT-IR, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and elemental and electrochemical analysis. Results from cyclic voltammetry and FT-IR analysis both confirmed the covalent attachment of redox active Ru(II) center into the polymer. The emission spectrum of the copolymer, in comparison to that of Ru(II) complex, demonstrated that the excited-state properties of the metal complex is maintained, in contrast to the electronic absorption spectrum, which is sensitive to the hydrophobic polymeric chain surrounding the redox sites. The thermal analysis suggested that this metallopolymer also possesses high thermal stability. The ruthenium content was also found to be 7%, which corresponds to 80% of the maximum loading, by elemental analysis.

A high‐stability quartz crystal microbalance electrode for simultaneous solution‐phase electrochemistry/microgravitometry

A quartz crystal microbalance (QCM) oscillator circuit is described which incorporates a high‐gain feedback amplifier controlled by an automatic gain network. Signal level in the oscillator feedback loop is automatically optimized to provide sufficient gain necessary to sustain stable oscillation, but not so much gain as to induce waveform clipping, which would detriment frequency stability. The crystal is driven and loaded by a low‐impedance network, and one side of the crystal is held at low impedance to ground. In this way, the microbalance crystal may be used in place of a working electrode in an electrochemical apparatus. Gravitometric studies at the surface of the electrode may be combined simultaneously with cyclic voltammetry, chronocoulometry, chronoamperometry, or any other electrochemical experiment in aqueous and nonaqueous solutions. The QCM signal is heterodyned with a reference signal to produce a difference frequency on the order of a few hundred Hertz. An optional frequency‐to‐voltage con...

Linkage isomers of alizarin-bis(bipyridine)ruthenium(II)

Abstract Alizarin-bis(bipyridine)ruthenium(II) complexes exhibit a unique interconversion and coordination not reported in other metal-alizarin complexes. Previously communicated linkage isomers of alizarin-bis(bipyridine)ruthenium(II) ((1,2) and (1,9) coordinated complexes) are characterised here by FT-IR and NMR (1D and 2D) spectroscopic techniques, giving definitive results on the previously proposed mode of coordination. This work also includes the FT-IR of the (1,2) coordinated one-electron oxidation product, as well as that of the similarly coordinated complex, 1-hydroxyanthraquinone-bis(bipyridine)ruthenium(II).

Surface functionalization of cadmium sulfide quantum confined nanoclusters6: Evidence of facile electronic communication between remote surface sites

Abstract The preparation and derivatization of a series of surface functionalized ∼30 A cadmium sulfide nanoclusters possessing surfaces of varied electron demand, tethered covalently to an electroactive fluorescent ruthenium polypyridyl complex, are described. Electrochemical analyses of these nanoclusters bearing ruthenium moieties yield a monotonic relationship between the Ru(II/III) oxidation potential and the electron withdrawing nature of the cluster surface, indicating that the electron density at the electroactive ruthenium center is indeed influenced by remote electropositive and electronegative substituents attached to the nanocluster. Further evidence of cluster mediated electronic interactions between remote surface moieties presents itself in the form of a dependence of the integrated ruthenium based MLCT emission intensity on the mole per cent of attached thiolate capping agent possessing an electron withdrawing substituent in the position para to the point of cluster attachment.

Electrochemical Reduction of Nitrous Oxide (N2O) Catalysed by Tetraaminophthalocyanatocobalt(II) Adsorbed on a Graphite Electrode in Aqueous Solution

The surface electrochemical response of the CoII/CoI redox process of tetraaminophthalocyaninatocobalt(II) (CoIITAPc) adsorbed on a graphite electrode, was studied in the pH range of 2–13. In aqueous solution, the CoIITAPc adsorbed graphite electrode displays very strong electrocatalytic activity toward N2O reduction to N2, a process which was examined by cyclic and rotating disk electrode voltammetries. The possible application of this CoIITAPc modified electrode in N2O analysis was explored.