ELECTROCHEMICAL-BEHAVIOR OF [OCTAETHYLPORPHYRIN IRON(III)-SIGMA-BONDED PYRROLE] AND ITS ELECTROCATALYTIC ACTIVITY FOR THE REDUCTION OF DIOXYGEN

The electrochemistry of [octaethylporphyrin iron(III)-sigma-bonded pyr role] (abbreviated as (OEP)Fe(II)(Pyr)) was investigated in CH2Cl2 + T BAP solution by cyclic voltammetry (CV) and in situ UV-visible electro nic absorption spectrometry. It was found that (OEP)Fe(III)(pyr) can u ndergo a quasi-reversible one-electron reduction step to form (OEP)Fe( II)(Pyr), and two sorts of irreversible one-electron oxidation step: o ne was the formation of [(OEP)Fe(II)(Pyr)]+ firstly, followed by loss of the sigma-bonded pyrrole to produce [(OEP)Fe(III)]+] the other was probably the direct formation of [(OEP)Fe(III)]+ with simultaneous los s of the sigma-bonded pyrrole. It was also found that (OEP)Fe(III)(Pyr ) adsorbed on the surface of glassy cardon (GC) exhibited high activit y for the electrocatalytic reduction of dioxygen, but this activity wa s not stable. However, this catalyst can be buried in polypyrrole (PPy r) film, resulting in more stable activity. Rotation ring-disk experim ents (RRDE) demonstrated that (OEP)Fe(II)(Pyr) whether adsorbed on a G C surface or buried in PPyr film could catalyze the reduction of dioxy gen to give water predominantly. In these two cases, the catalytic mec hanisms were found to be the same and the water production efficiencie s were nearly 90% in the potential region -0.30 to 0.35 V (vs. SCE) in O2 saturated 0.05 M H2SO4 solution. The slope of the Tafel curve sugg ested that the one-electron transfer from [(OEP)Fe(II)(Pyr)-O2] to [(O EP)Fe(III)(Pyr)-O2-] was the rate-controlling step before the limiting disk current was reached.