ELECTROCHEMICAL REDUCTION OF CARBON DIOXIDE IN THE PRESENCE OF (Ni II -5,7,12,14-

Cyclic Voltammograms of [Ni(II)5,7,12,14-tetrametyldinaphtho[b,i] [1,4,8,11]tetraaza[14]annulene] ++ cation complex ([Ni(tmdnTAA)] 2+ hereafter) present two irreversible reduction peaks at -0.70 V y -1.50 V vs Ag/AgCl in N,N´-dimethylformamide (DMF), while in acetonitrile (MeCN) these peaks are at -0.93V. and -1.80 V vs Ag/AgCl. When DMF/H 2 O or MeCN/H 2 O are used as solvents, the peaks are also shifted with respect to those in pure DMF as solvent. For example, in DMF/ H 2 O they are -0.76 and -1.04 V respectively. Cyclic voltammograms of the cation complex in CO 2 saturated solutions exhibited the catalytic wave of the CO 2 reduction, E c p , at ~ -1.50 V in DMF/H 2 O and at ~ 1.80 V in MeCN/H 2 O. Under these conditions, the only product of the bulk electrolysis was hydrogen. Due to the formation of a stable product, the catalytic current for the CO 2 reduction of the second voltammetric cycle is 30% less intense than the current of the first cycle. The stable adduct, [Ni(II)tmdnTAA-CO] ++ , formed on the electrode was characterizated by spectroeletrochemistry and FT-IR spectroscopy.