Modified electrode surfaces for catalytic reduction of carbon dioxide

Ni(II) complexes with substituted tetraazacyclotetradecanes were incorporated into Nafion films or assembled in monolayers on electrodes in order to obtain electrocatalytic systems for the reduction of carbon dioxide. Reproducible and stable loading of the Nafion films with the complexes has been observed. Systematic increase of N-methyl substitution of the catalytic [Ni(cyclam)](2+) complex leads to a shift of the Ni(II)L/Ni(I)L formal potential to more positive values, however, at the same time to a decrease of the catalytic current of CO2 reduction. Monolayer techniques - the Langmuir-Blodgett and self-assembly methods - were found advantageous for the preparation of electrode surfaces active in the catalytic reduction of CO2 compared to Nafion coatings containing the catalyst. Glassy carbon electrode was suitable for the transfer of Langmuir-Blodgett monolayers. Catalysis was observed only when the electrode was touching the monolayer at the air-water interface or was covered in the dipping mode, hence when the catalyst molecules were oriented with their alkyl chains towards the substrate and macrocyclic head-group towards the solution. Most efficient catalysis was found using electrodes coated by the self-assembly procedure with monolayers of the cyclam complex modified with a pyridine side group. The role of the pyridine moieties was to anchor the catalytic monolayer to the electrode surface. (C) 1999 Elsevier Science B.V. All rights reserved.