Changing the Selectivity of O2 Reduction Catalysis with One Ligand Heteroatom

The development of catalytic systems that selectively reduce O2 to water is needed to continue the advancement of fuel cell technologies. As an alternative to platinum catalysts, derivatives of iron (Fe) and cobalt (Co) porphyrin molecular catalysts provide one benchmark for catalyst design, but incorporation of these catalysts into heterogeneous platforms remains a challenge. Co-porphyrins can be heterogeneous O2 reduction catalysts when immobilized on to edge plane graphite (EPG) electrodes, but their selectivity for the desired four-electron reduction of O2 to H2O is often poor. Herein, we demonstrate substantial improvements in the O2 reduction selectivity using a Co-porphyrin that incorporates a 2-pyridyl group at one of the meso-positions of a Co-tetraarylporphyrin (cobalt(II) 5-(2-pyridyl)-10,15,20-triphenylporphyrin, CoTPPy). The properties of CoTPPy immobilized on EPG were investigated using cyclic voltammetry, rotating disk, and rotating ring-disk electrochemistry. The presence of a single 2-pyr...