Electrocatalysis chelates

Electrocatalysis in fuel cells requires as well substances capable of catalyzing the anodic oxidation of fuels as catalysts for the cathodic reduction of oxygen. Several dyestuffs that catalyze oxygen reduction are known, but up to now only one has been described as active in anodic reactions. All these dyestuffs are N4-chelates. 

There are many organic dyestuffs but only one class, that of the metal chelates, has been found to be active in electrocatalysis. The first compounds described were the phthalocyanines 1-4), which are similar in structure to the heme in the blood pigment, hemoglobin in both, the metal atom is surrounded by four nitrogen ligands. 

The first chelate found to be electrocatalytic was cobalt phthalocyanine x>, which functions as an oxygen catalyst in alkaline electrolytes. Soon afterwards we were able to show 3,4,10,11) -that several phthalocyanines are also active in commercially important, sulfuric acid containing media. A comparison of various central atoms showed that activity increased in the order Cu Ni iron phthalocyanine, the nature of the carbon substrate plays a very important part FePc is more active on a carbon substrate with basic surface groups than on one with acid surface groups3). This property is however specific to phthalocyanines (Pc). 

Table 5. Activities of some metal chelates in the catalytic decomposition of hydrogen peroxide and in electrocatalysis with an oxygen cathode 38>...

Bagotzky, V.S. et al., Electrocatalysis of the oxygen reduction process on metal chelates in acid electrolyte, J. Power Sources, 2, 233, 1977. 

The following properties of the polymer chelates in each specific chapter are described binding of small molecules like oxygen catalytic properties electrocatalysis like fuel cell light energy conversion like photoredoxreaction electrical conductivity thermal stability... 

Fig. 21. Tentative chemical structures of polymeric transition metal complexes (chelates, 29-33) of potential interest for electrocatalysis...

Zhang JJ, Anson FC (1993) Complexes of Cu(II) with electroactive chelating ligands adsorbed on graphite-electrodes - Surface coordination chemistry and electrocatalysis. J Electroanal Chem 348(l-2) 81-97... 

Bagotskii VS, Tatasevich MR, Levina OA, Radyushkina KA, Andraseva SI (1977) Electrocatalysis of the reductimi of oxygcui on metal chelates in an acid electrolyte. Dokl Akad Nauk SSSR 233 889-891... 

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