Carbon dioxide electrochemical sensor based on lipid cubic phase containing tetraazamacrocyclic complexes of Ni(II)

Liquid-crystalline cubic phases formed by polar lipids in an aqueous medium were used as hosting layers for catalytic tetraazamacrocyclic Ni(II) complexes. The role of the cubic phase is to hold the catalyst close to the electrode surface, to retain its catalytic activity and to provide suitable environment for the catalytic reaction. The properties of the cubic phase Q224 (monoolein:water:catalyst) were investigated by microscopy with polarized light and electrochemical techniques. Nickel (II) complexes with derivatives of 1,4,8,11-tetraazacyclotetradecane were incorporated into bicontinuous cubic liquid-crystalline layer modifying the thin mercury film or glassy carbon electrode and used for the study of catalytic reduction of carbon dioxide. The reproducibility of the catalytic current of CO2 reduction was found better than obtained using other methods based on modified electrodes. The linear dependence of catalytic reduction current on the concentration of CO2 allowed the use of the system for carbon dioxide sensing in the solution. The sensor described in the present report was found useful also in case of CO2 determination in the gas phase. In such environmentally interesting measurements, CO2 was absorbed directly by the cubic phase in which the three electrodes: working, counter and reference were placed.