ELECTROCATALYTIC CO2 REDUCTION BY COBALT OCTABUTOXYPHTHALOCYANINE COATED ON GRAPHITE ELECTRODE

Electrocatalytic CO2 reduction was studied by using a modified graphit e electrode coated with cobalt octabutoxyphthalo-cyanine (CoPc(BuO)(8) ) and dipped in an aqueous electrolyte. The CoPc(BuO)(8) worked as a c atalyst to produce CO with higher activity and selectivity than the no n-substituted CoPc. Under typical conditions at pH 4.4, the most activ e and selective CO2 reduction was achieved at -1.30 V with turnover nu mber of the catalyst similar to 1.1 x 10(6) h(-1) and the selectivity of the produced CO/H-2 similar to 4.2. The high activity was ascribed to the electron-donating BuO substituents of the complex, which would facilitate the coordination of CO2 as well as the electron transfer fr om the complex to the coordinated CO2 molecule. The use of a poly(4-vi nylpyridine) membrane to disperse the complex decreased the activity. The mechanism was investigated by the use of in situ potential-step ch ronoamperospectroscopy (PSCAS) in a homogeneous CoPc(BuO)(8)/pyridine solution. In the absence of CO2, distinct two-steps visible spectral c hanges were observed following the first and second reductions of the complex, However, under CO2 atmosphere, only the one-electron reduced species was present under steady state. It was proposed that the third reduction of a CO2-coordinated CoPc(BuO)(8) should take place for CO production.