Studies of soluble molecular electrocatalysts can provide new insights into optimization of complex multi-electron/multi-proton electrocatalytic processes. Our continuing studies of iron porphyrin electrocatalysts for the oxygen reduction reaction (ORR) have shown that the rates and efficiencies (overpotentials) can be closely correlated with the fundamental properties of the catalytic system: the E1/2 of the catalyst and the pKa of the acid (in organic solvents). In particular, we have found that the polycationic iron (ortho-trimethylanilinium)porphyrin (Fe-o-TMA), reported to be an exception CO2 reduction electrocatalyst,1 is also very effective for the ORR. When using an acetic acid/acetate buffer, this catalyst exhibits high turnover at low overpotentials. The exceptional activity has been shown to result from a combination of the binding of axial ligands and the use of a weak acid. These results can be quantitatively explained – and predicted – as the result of the combination of multiple scaling relationships. Ongoing studies are exploring how other coulombic interactions can be harnessed to improve ORR catalysis and how the scaling relationships may be extended to understand catalytic selectivities as well.

Developing scaling relationships to understand and improve molecular electrocatalysis

2019 Spring National Meeting

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