Phthalocyanines electrode modification

Erdogmus A, Booysen I, Nyokong T (2011) Synthesis and electrochemical properties of new tetra substituted cobalt phthalocyanine complexes, and their application in electrode modification for the electrocatalysis of 1-cysteine. Synth Met 161 241-250... 

Metallophthalocyanines (MPcs) are well known as electrode modifiers for elec-trocatalytic applications. MPcs whose metal J-orbitals lie between the highest occupied molecular orbital (HOMO) and lowest imoccupied molecular orbital (LUMO) levels of the Pc ligand, such as Mn, Fe, and Co, are known to be good electrocatalysts [1]. A good electrocatalyst must lower the redox potential, increase sensitivity and selectivity, and should show stability. In our previous book chapter [1], electrode modification using mononuclear phthalocyanines (Pcs) was extensively reviewed. The current chapter will review electrocatalytic behavior of mononuclear MPc complexes when combined with various nanomaterials. In addition, the chapter presents electrode modification using the least studied, binu-clear phthalocyanines alone or in the presence of nanomaterials. 

The chapter summarizes the dilFerent types of electrode modifications using ph-thalocyanines alone or in the presence of nanomaterials. Simple adsorption is a prominent method employed in the presence of nanomaterials. The review includes electrode modification using binuclear phthalocyanines which are less studied compared to mononuclear phthalocyanines. The nanomaterials most studies in the presence of bis phthalocyanines and mononuclear phthalocyanines are carbon nanombes. Some studies on quantum dots and metal nanoparticles are also presented. Electrode characterizalion methods using different techniques are included. X-ray photoelectron spectroscopy, in particular, has been shown to be very effective on the characterization of modified electrodes. 

As shown in this symposium, interest in chemical modification of electrode surfaces has been extended in many directions, including the study of light-assisted redox reactions, and the use of modified electrodes in electrochromic devices (1,2). Our own studies have centered on the study of metal and metal oxide electrodes modified with very thin films of phthalocyanines (PC) and on the electrochromic reaction of n-heptyl viologen on metal oxide electrodes, and on the effect on these reactions of changing substrate chemical and physical composition (A,5). 

In the cases described the order of activity was similar and also a very important dependence with negative limit of the potential and the stability of the macrocycles was found. Indeed, if the modified electrode is swept at more negative potentials, they become less active with the time. This fact is probably associated with the deactivation of the macrocycle. Also the poor selectivity of these modified electrodes has been noted. -. With these factors in mind another kind of modification has been developed, the incorporation of the macrocycles either phthalocyanines or porphyrins in polymeric membranes. 

Another method for the modification of carbon electrodes with macrocycles towards the electroreduction of CO2 is to form chemical bonds between the electrode and the macrocycle. Several studies have shown that it is possible to attach small organic molecules, to the polished gassy carbon surface and then this attached molecule could be an anchor for another molecule, in this case Coporphyrins or Co-phthalocyanine ... 

Modification of the electrode started with academic studies on physical and chemical adsorption, i.e., with the appearance of fundamental researches on adsorption of different species on electrode surfaces, both under polarization and at open circuit potential [3]. The properties of similar chemically modified electrodes , in which the modifier consists of a monolayer of a variety of chemical species with different characteristics, possessing (or not) particular properties, were initially studied in a purely electrochemical context, aimed at the collection of fundamental physico-chemical data. A small group of electrochemists were among those involved in these basic studies, envisioning the perspectives opened by the novel systems. In the first, really fascinating, work with similar monomolecular layers, cobalt porphyrin and phthalocyanine, as well as deliberately synthesized dicobalt face-to-face porphyrins were adsorbed on Pt or C surfaces to catalyze molecular oxygen reduction [4]. However, similar systems were not always used or adequately tested in proper amperometric sensing by researchers more interested in electroanalysis dicobalt face-to-face porphirins still constitute a rare example of tailored materials for selective amperometric detection. 

UVERS study of the formation of electron conducting polymer films at a gold electrode, and of their modification by intercalation of metal aggregates or of iron phthalocyanine ... 

Modification of PANI-coated electrodes with metal tetrasul-fonated phthalocyanines (MeTSPc), where the metal is cobalt or iron, resulted in significant changes in the electrocatalysis of the reduction of diojygen [504]. Obviously, insertion of the MeTsPc into the polymer occurs [505]. This was supported in an investigation by Coutanceau et al. by the results of in situ UV-vis spectroscopy. The role of the polymer in the mechanism and the kinetics of dioxygen electroreduction seemed to be somewhat difficult to elucidate. Insertion of CoTsPc resulted in a positive shift of the onset of dioxygen reduction. The two-electron pathway that results in hydrogen peroxide as a reduction product remains. 

Modification of Electrode Surfaces with Metallo Phthalocyanine Nanomaterial Hybrids... 

Modification of Glassy Carbon Electrode with Binuclear Cobalt Phthalocyanine/Surfactant/Ordered Mesoporous Carbon... 

Modification of SPEs with different mediators including TCNQ mediator [7,7,8,8-tetracyanoquinonedimethane] in the graphite electrode, " " cobalt(II) phthalocyanine (CoPC), " and o-phenylenediamine onto carbon/CoPC " can be found in the literature. In 1994 Hart and Hartley studied the electrochemical mechanism of a CoPC-modified screen-printed device using cychc voltammetry. " The voltammograms... 

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