The electrocatalytic reduction of oxygen on pristine and on electro-oxidized carbon fibre electrodes modified by hemine is investigated in aqueous, methanolic and acetonitrile solutions. The attached iron porphyrin on the modified electrodes exists in two forms, monomeric and dimeric, the latter consisting of two Fe(III)-protoporphyrin molecules held together with an oxygen atom. The catalytic activity of the electrodes is attributed to the hemine monomers, which have the ability to bond the O2molecule at the axial position of the metal ion of the porphyrin. The catalytic reduction of O2in acidic aqueous and methanolic solutions produces H2O, whereas in acetonitrile H2O2is formed. The electro-oxidized modified electrodes show a catalytic efficiency four-times greater than the pristine electrodes, which is consistent with the analogous increase of the effective electrode area after the electro-oxidation procedure. © 1989.
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