Electroreduction of oxygen enriched in a [poly(ethyleneiminato)]cobalt(ii) layer

Abstract

An aqueous solution of a [poly(ethyleneiminato)]cobalt(II) complex that reversibly binds and releases O₂ functions as an O₂-enriching medium for an O₂ electrode to enhance the current for the uncatalyzed reduction of O₂. The effect of the electrochemically inactive cobalt complex is to supply reducible O₂ to the solution within the diffusion layer near the electrode by releasing the bound O₂ from the O₂ adduct, which contributes to a decrease in the diffusion layer thickness of O₂. Based on the rapid release of O₂ from the O₂ adduct, a diffusion-limited current is obtained for the reduction of O₂. The hypothetical concentration of the enriched O₂ supplied under pure diffusion control (i.e. unperturbed by the kinetics of the O₂ binding) is several times larger than that of the actual concentration of O₂ due to the higher solubility of the O₂ adduct than the physical solubility of O₂ in H₂O at room temperature under an atmosphere of air. An insoluble membrane of a cobalt(II) complex with a cross-linked poly(ethyleneimine) ligand that has the ability to swell serves as an O₂-enriching material to concentrate O₂ from aqueous electrolyte solutions. A new type of O₂-diffusion electrodes for metal/air batteries and fuel cells is proposed using the O₂-enriching material immobilized at the electrode surface.