AMINOPYRIDYL CATION-RADICAL METHOD FOR BRIDGING BETWEEN METAL-COMPLEXAND GLASSY-CARBON - COBALT(II) TETRAPHENYLPORPHYRIN BONDED ON GLASSY-CARBON FOR ENHANCEMENT OF CO2 ELECTROREDUCTION

Aminopyridyl compound immobilization on glassy carbon (GC) was carried out by amine cation radical formation through electro-oxidation at GC in ethanol solution, and subsequently by chemical bonding of the radi cal to GC. The aminopyridyl group immobilized on GC takes part as a br idge between cobalt tetraphenylporphyrin (Co(II)TPP) and GC, where the nitrogen of the pyridyl group is coordinated as a fifth ligand of Co( II)TPP, being perpendicular to the porphyrin plane. The Co(II)TPP modi fied GC electrode was thus prepared by a bridging amine of 4-aminopyri dine, 4-aminoethylpyridine, or imidazole in the electrochemical and ch emical processes, which is denoted 'CoTPP bonded GC'. Whereas Co(II)TP P physically attached to GC, denoted CoTPP/GC, was not able to reduce CO2 at E = -1.1V(SCE) in pH 6.3 phosphate buffer solution, 'CoTPP bond ed GC' gave CO from CO2 electroreduction at that potential with 60% cu rrent efficiency. By polarization of 'CoTPP bonded GC' at hydrogen evo lution potentials, Co(II)TPP stacked on 'CoTPP bonded GC' is suggested to be converted to HCo(II)TPP, but Co(II)TPP on CoTPP/GC remains the same. Hydrogenated 'CoTPP bonded GC' is suggested to play an important role as one of the intermediates of CO2 electroreduction. (C) 1997 El sevier Science S.A.