ELECTROCATALYTIC REDUCTION OF CO2 BY NICKEL(II) CYCLAM - STUDY OF THE REDUCTION-MECHANISM ON MERCURY BY CYCLIC VOLTAMMETRY, POLAROGRAPHY AND ELECTROCAPILLARITY

The electrocatalytic reduction of CO2 on mercury with Ni(II)-cyclam was studied in detail by cyclic voltammetry, polarography and electrocapillarity of aqueous solutions with and without the catalyst under N2, CO and CO2. It is concluded from these electrochemical measurements that (i) the adsorbed complex (Ni(I)-cyclamad) on Hg, not the reduced complex in solution Ni(I)-cyclam, is the active catalyst for the CO2 reduction; (ii) both Ni(II)- and Ni(I)-cyclam can adsorb on Hg, and the oxidation states of the adsorbed complexes depend on the electrode potentials; (iii) Ni(I)-cyclam adsorbs on Hg even at -2.0 V (vs. SCE) under N2, but the surface concentration of Ni(I)-cyclamad decreases gradually with a decrease in the potential and desorbs completely at potentials more negative than -1.7 V under CO or CO2; and (iv) the desorption of Ni(I)-cyclamad under CO or CO2 is due to the formation of unadsorbable Ni(I)-cyclam-CO by the reaction of Ni(I)-cyclam in solution with dissolved CO or electrocatalytically generated CO from CO2. © 1990.