Electrocatalytic reduction of CO 2 on modified electrodes with alkylcyclam-metal complex Langmuir-Blodgett films

Abstract

Two amphiphilic nickel(II) complexes with the long-alkyl-substituted 1,4,8,11-tetraazacyclodecane cyclam were synthesized, i.e. nickel tetrakis( N-hexadecyl)cyclam and nickel N-hexadecyclam. Monolayers of these complexes were immobilized onto glassy carbon (GC) disc electrodes using the Langmuir-Blodgett (LB) technique, and the electrocatalytic activities of these electrodes were examined by cyclic voltammetry in aqueous solutions saturated with nitrogen or carbon dioxide. The redox waves of the LB films of the nickel alkylcyclams observed in nitrogen were shifted in the anodic direction relative to those of nickel cyclams in a homogeneous solution. In carbon dioxide, the increase in the reduction current on these electrodes compared with that in nitrogen was observed at more negative potentials than - 1.3 V vs. a saturated calomel electrode in a solution with a constant pH value. This result shows that the LB films of these complexes possess sufficient electrocatalytic activity to reduce carbon dioxide despite their small amounts when compared with the amounts of homogeneous catalyst.