CATALYSIS ON IMMOBILIZED CO(II)TPP MODIFIED GLASSY-CARBON ELECTRODE - CO2 ELECTROREDUCTION

Cobalt tetraphenylporphyrin (Co(II)TPP) was fabricated on glassy carbon (GC) through 4-pyridyl-NH-CO- (1), 4-pyridyl-CH2-NH-CO- (II), and 4-piperidyl-CH2-NH-CO- (III), where N of pyridyl or piperidyl coordinates to Co of Co(II)TPP. The Co(II)TPP immobilized through bridging species of I only gave an anodic hump at -0.6 V (SCE) in Ar atmosphere buffer solution (pH7) by cyclic voltammogram when the electrode firstly polarized to potentials where hydrogen evolution reaction takes place. The hump disappeared under CO2 atmosphere and this electrode only gave quite high current efficiency of CO production at -1.1 V(SCE), which corresponds to -0.5 V(RHE), while the other electrodes including Co(II)TPP physically fixed GC did not give any anodic hump at -0.6 V(SCE). Such difference is discussed in correlation with formation of HCo(II)TPP on the former electrode, which is likely to be oxidized to Co(II)TPP at -0.6 V(SCE) as hump.