B Rezaei, Maryam Mokhtarianpour, Hassan Hadadzadeh, Ali A. Ensafi, J. Shakeri,

A mononuclear Re(I) complex, [ReCl(CO)3(phen-dione)], was investigated as a new electrocatalyst for the reduction of CO2 in two catalytic systems (homogeneous and heterogeneous) by voltammetry experiments. A modified pencil graphite electrode with carboxylated multiwall carbon nanotubes (CMWCNTs-PGE) was used as a working electrode for both catalytic systems. In the homogeneous system, the Re(I) complex revealed the catalytic activity for the reduction of CO2 to CO in an acetonitrile solution at the onset potential of 
545 mV vs. NHE. Also, the results showed that the presence of methanol as a weak Bronsted acid enhanced the rate of the catalytic process for the reduction of CO2 in the homogenous condition. In the heterogonous condition, the Re(I) complex was simply casted on the CMWCNTs-PGE and then investigated for the reduction of CO2 in an acidic solution of MeOH. The results also revealed that the onset potential for the heterogeneous catalyst was more positive than the homogenous condition. Also, the cathodic current density for the heterogeneous catalyst was higher in
an acidic solution of MeOH. Adding sulfuric acid shifted the onset potential about 477 mV toward the more positive potential (at the onset potential of 
390 mV vs. NHE) and increased the cathodic current about 10.7 times in the heterogeneous reduction of CO2.

Keywords:
Carbon dioxide, Rhenium(I) complex, Heterogeneous catalyst, Homogeneous catalyst