Jiujun Zhang

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.

Rotating ring-disk electrode analysis of CO2 reduction electrocatalyzed by a cobalt tetramethylpyridoporphyrazine on the disk and detected as CO on a platinum ring

Abstract A rotating ring (platinum)-disk (graphite) electrode is employed to analyze CO2 in aqueous solutions. A graphite disk, coated with the complex N,N′,N′,N′-tetramethyltetra-3,4-pyridoporphyrazinocobalt(II) and protected by a Nafion® film, displays electrocatalytic activity toward CO2 reduction. The carbon monoxide generated can be thrown on to the platinum ring electrode where it is adsorbed and can be detected by its electrochemical oxidation. The CO oxidation current at the ring electrode is dependent on the CO2 concentration and the disk electrode potential. Although, as with most other catalysts, proton reduction also occurs, this does not interfere with the analysis procedure.

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.

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.

Surface electrochemistry of N,N',N″,N‴-tetramethyl-tetra-3,4-pyridinoporphyrazinocobalt(II)

The complex N,N,N″,N‴-tetramethyl-tetra-3,4-pyridinoporphyrazinocobalt(II) ([CoIITMPz[4+])4+ adsorbed on a graphite electrode undergoes spontaneous reduction, forming a surface containing CoI. Five reversible surface peaks are observed at low pH, two of which are two-electron concerted processes. At high pH, one of these two-electron processes splits into two one-electron waves. Both oxidation and reduction of the central metal can be observed, along with successive reduction steps involving the porphyrazine ligand. Notable is the marked shift to positive potentials of these processes, relative to unsubstituted cobalt phthalocyanine, due to the positive charge localized on the porphyrazine. The electrocatalytic activity of this complex modified electrode toward the reduction of hydrogen peroxide is also reported. We demonstrate that a series of different surfaces exist which are obtained by variation of pH and polarization potential and that these surfaces possess differing electrocatalytic activity. Surfaces inactive to hydrogen peroxide can exist at potentials more negative than active surfaces even though the driving force for peroxide reduction will be greater for the former.

Surface ion association of thehexacyanoferrate(III)/(II) ion bound by5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23H-porphine or5,10,15,20-tetrakis[4-(trimethylammonio)phenyl]-21H,23H-porphine adsorbed on a graphiteelectrode

A monolayer or submonolayer of the positively charged nmolecule of n5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23 nH-porphine (H n 2 nTMPyP) or n5,10,15,20-tetrakis[4-(trimethylammonio)phenyl]-21H n,23H-porphine (H n 2 nTAPP) irreversibly nadsorbed on a graphite electrode can associate with a nhexacyanoferrate(III) or nhexacyanoferrate(II) ion in solution to form nsurface ion pairs which have been examined by surface cyclic nvoltammetry. The electrochemical responses of adsorbed nH n 2 nTMPyP, H n 2 nTAPP, and associated n[Fe(CN) n 6 n] n 3-/4- n were employed to nestimate the surface coverage which was then used to nevaluate quantitatively the ion association equilibria nbetween adsorbed porphine and solution nhexacyanoferrate(III) or nhexacyanoferrate(II) ions. The competing nassociation of other common anions such as Cl n - n nand [SO n 4 n] n 2- n with n[Fe(CN) n 6 n] n 3-/4- n was also examined.