Studies in Modified Electrodes

In the case of metallophthalocyanines and metalloporphyrins different ways to modified electrodes have been reported deposited onto electrodic surfaces complexes immobilized or incorporated in polymeric membranes as electropolymerized complexes , gas 

The intermittent plasma-assisted vacuum deposition technique has been found to introduce the effective electrocatalytic activity and stability for CO2 reduction into metal phthalocyanine thin films formed on a glassy carbon. The films properties are significantly influenced by the chemical state of the Aim. It has been suggested that the electrode process is determined by the surface chemical reaction involving adsorbed H and/or H+ and a carbon containing intermediate .  

Kapusta and Hackerman in 1984, reported that working at pH (3-7) the main reaction product was formic acid when the catalysts were CoPc and NiPc. Formate ion was also produced at pH 5. Methanol is also produced at lower pH values. And the phthalocyanines become inactive when the medium is less acid. The order in activity was found to be Co Ni Fe + = Cu + Cr3+, Snii3. 

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. 

In 1995 Zhang and coworkers studied the electrochemical detection of CO2 in rotating ring (Pt)-disk graphite electrode coated with the macrocyle Co N, N, N , N -tetramethyl-3,4-pyridoporphyrazine and protected by a Naflon film. In this work it was informed that the CO detection on the Pt ring is proportional to the CO2 concentration. CO2 reduction was analyzed in the concentration 

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Clearly ellipsometry has much to reconunend it for studies in modified electrodes however until recently its application to electrochemical problems was restricted by several severe problems. Firstly it is not mathematically straightforward to extract optical data from parameters measured by ellipsometers. Secondly collecting each data point used to involve tedious and slow manual determination. In the last 15 years however, two developments have overcome these problems the development of inexpensive microcomputers and automation of the data collection process. The only drawback now remaining is the capital cost of suitable equipment, and even this is declining rapidly as new and simpler types of ellipsometer become available. 

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