Electrocatalytic CO2 reduction by cobalt octabutoxyphthalocyanine coated on graphite electrode

Electrocatalytic CO2 reduction was studied by using a modified graphite electrode coated with cobalt octabutoxyphthalo-cyanine (CoPc(BuO)(8)) and dipped in an aqueous electrolyte. The CoPc(BuO)(8) worked as a catalyst to produce CO with higher activity and selectivity than the non-substituted CoPc. Under typical conditions at pH 4.4, the most active and selective CO2 reduction was achieved at -1.30 V with turnover number 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 from the complex to the coordinated CO2 molecule. The use of a poly(4-vinylpyridine) membrane to disperse the complex decreased the activity. The mechanism was investigated by the use of in situ potential-step chronoamperospectroscopy (PSCAS) in a homogeneous CoPc(BuO)(8)/pyridine solution. In the absence of CO2, distinct two-steps visible spectral changes 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.