Advances in the Molecular Catalysis of Dioxygen Reduction
Charles W. Machan
Abstract
The reduction of dioxygen (O2) is of vital importance to energy-related reactions. In biology, respiration uses O2 reduction as a thermodynamic sink, whereas fuel cells pair the oxygen reduction reaction (ORR) to H2O as a proton-dependent half-reaction to the oxidation of chemical fuels. Catalytic ORR processes mediated by molecular inorganic species continue to garner interest as models for heterogeneous systems. The ability to directly observe, quantify, and synthesize relevant intermediates from proposed reaction mechanisms renders molecular species readily optimizable, relative to the distribution of active sites within the nanoscale and mesoscale morphologies of heterogeneous systems. The development of next-generation cathode materials to displace platinum (Pt) for ORR will require improvements in the fundamental understanding of how O2 behaves as a substrate, which well-defined homogeneous systems are uniquely positioned to provide. This Perspective provides a summary of recent advances in the area of homogeneous catalytic O2 reduction, with a particular emphasis on improvements in activity and selectivity aided by mechanistic understanding.