PNNL

Abstract

Fe(III)meso-tetra(2-carboxyphenyl)porphine chloride (1) was investigated as an electrocatalyst for the oxygen reduction reaction (ORR). Rotating ring-disk voltammetry and independent reactions with hydrogen peroxide indicate that 1 has very high selectivity for reduction of O2 to H2O, without forming significant amounts of H2O2. Cyclic voltammetric measurements at high substrate/catalyst ratios allowed the determination of the turnover frequency (TOF) of 1, TOF = 103 s-1. The 4-carboxyphenyl isomer of 1, in which the carboxylic acids point away from the iron center, is a substantially slower and less selective catalyst. This direct comparison demonstrates that the value of the carboxylate groups positioned to act as proton delivery relays to enhance both the TOF and selectivity of 1 as a catalyst for the ORR. This research was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center, funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.