Mechanical Interlocking Enhances the Electrocatalytic Oxygen Reduction Activity and Selectivity of Molecular Copper Complexes

Efficient O2 reduction reaction (ORR) for selective H2O generation enables advanced fuel cell technology. Non-precious metal (NPM) catalysts are viable and attractive alternatives to state-of-the-art Pt-based materials that are expensive. Cu complexes inspired by Cu-containing O2 reduction enzymes in nature have yet to reach their desired ORR catalytic performance. Here, the concept of mechanical interlocking is introduced to the ligand architecture to enforce dynamic spatial restriction on the Cu coordination site unachievable using other structural means. The utility of the kinetic effects from mechanical bond in transition metal catalysis is just about to emerge, and here the catenane ligands govern the O2 adduct binding mode, thereby steering the selectivity to generate H2O as the major product via the 4e– pathway, rivaling the selectivity of Pt. The kinetic effects from the interlocked catenane ligand also promotes product elimination and boosts the onset potential by 130 mV, the mass activity by 1.8 times, and the turnover frequency (TOF) by 1.5 folds as compared to the non-interlocked counterpart. Our Cu catenane complex represents one of the first examples to take advantage of mechanical interlocking to afford electrocatalysts with enhanced activity and selectivity. The mechanistic insights gained through this integrated experimental and theoretical study are envisioned to be of practical value not just to the area of ORR energy catalysis, but also with broad implications on interlocked metal complexes that are of critical importance to the general fields in redox reactions involving proton-coupled electron transfer (PCET) steps