Electrocatalytic reduction of carbon dioxide by nickel cyclam2+ in water: study of the factors affecting the efficiency and the selectivity of the process

Abstract

The electrocatalytic properties of Ni cyclam/sup 2 +/ in CO/sub 2/ reduction have been studies. The influence of various experimental factors on the course of the reaction has been investigated. Under given conditions, Ni cyclam/sup 2 +/ is remarkably efficient and selective for electroreduction of CO/sub 2/ into CO, even in water. The stability of the system has been tested in long range electrolysis, showing that even after thousands of catalytic cycles no deactivation occurs. The mechanistic investigation presently described points to the importance of molecular species adsorbed on the cathode surface. The contribution of reduced species in the bulk is marginal. In addition, during the electrocatalytic process, a nickel(I) carbonyl complex is present: (Ni(cyclam)(CO))/sup +/. The latter complex may be involved in the catalytic reaction leading to CO evolution. Surprisingly, the behavior of Ni cyclam/sup 2 +/ as electrocatalyst is unique. Among the numerous complexes investigated, only Ni cyclam/sup 2 +/ shows such a large selectivity for the electroreduction of CO/sub 2/ over the electroreduction of water. The size of the cyclam ligand and the presence of secondary amine groups (NH) might account for the very special properties of the electrocatalyst.