Circumventing Scaling Relations in Oxygen Electrochemistry Using Metal–Organic Frameworks

It
has been well-established that unfavorable scaling relationships
between *OOH, *OH, and *O are responsible for the high overpotentials
associated with oxygen electrochemistry. A number of strategies have
been proposed for breaking these linear constraints for traditional
electrocatalysts (e.g., metals, alloys, metal-doped carbons); such
approaches have not yet been validated experimentally for heterogeneous
catalysts. Development of a new class of catalysts capable of circumventing
such scaling relations remains an ongoing challenge in the field.
In this work, we use density functional theory (DFT) calculations
to demonstrate that bimetallic porphyrin-based MOFs (PMOFs) are an
ideal materials platform for rationally designing the 3-D active site
environments for oxygen reduction reaction (ORR). Specifically, we
show that the *OOH binding energy and the theoretical limiting potential
can be optimized by appropriately tuning the transition metal active
site, the oxophilic spectator, and the MOF topology. Our calculations
predict theoretical limiting potentials as high as 1.07 V for Fe/Cr-PMOF-Al,
which exceeds the Pt/C benchmark for 4e ORR. More broadly, by highlighting
their unique characteristics, this work aims to establish bimetallic
porphyrin-based MOFs as a viable materials platform for future experimental
and theoretical ORR studies.