Application of a polymer solid electrolyte for the vapor-phase electrocatalysis of dioxygen reduction by some cobalt porphyrins

An electrochemical cell suitable for the study of dioxygen reduction electrocatalysis by films of cobalt metalloporphyrins on electrodes in the absence of liquid electrolytes is described. The glassy carbon disk of a (stationary) ring-disk electrode is coated with either an electropolymerized film of cobalt tetra(o-aminophenyl)porphyrin or an adsorbed multimolecular layer of a dicobalt cofacial porphyrin, Co₂ FTF4. Then the disk, the ring (serving as an auxiliary electrode), and a peripheral silver wire (serving as a pseudo-reference electrode) are coated with a thin film of an ionically conducting polymer: poly(ethyleneoxide) containing a 16:1 ether oxygen/Li⁺ concentration of lithium triflate. Bathing this solid state cell in moist, acidic or neutral bathing gases containing dioxygen produces electrocatalytic currents for dioxygen reduction. The fraction of the reduction leading to H₂O₂ was determined with a twin electrode sandwich modification of the above cell in which a Au film electrode atop a Nucleopore membrane is contacted to the top surface of the PEO₁₆·Li(CF₃SO₃) film. No H₂O₂ was produced in the case of the Co₂FTF4 catalyst in a neutral bathing gas; this electrocatalysis was also quite stable.