New Heterometallic Zirconium Metalloporphyrin Frameworks and Their Heteroatom-Activated High-Surface-Area Carbon Derivatives

Four cubic zirconium-porphyrin frameworks,
CPM-99­(H2, Zn, Co, Fe), were synthesized by a molecular-configuration-guided
strategy. Augmentation of meso-substituted side arms
(with double-torsional biphenyl rings) of tetratopic porphyrin linkers
leads to a successful implementation of zirconium-carboxylate frameworks
with cubic 2.5 nm cage. The hard-templating effect of Zr6-polyoxo-cluster and uniformly embedded (metallo)­porphyrin centers
endow CPM-99 with highly desirable properties as precursors for oxygen
reduction reaction (ORR) catalysts. The pyrolytic products not only
retain the microcubic morphology of the parent CPM-99 but also possess
porphyrinic active sites, hierarchical porosity, and highly conducting
networks. CPM-99Fe-derived material, denoted CPM-99Fe/C, exhibits
the best ORR activity, comparable to benchmark 20% Pt/C in alkaline
and acidic media, but CPM-99Fe/C is more durable and methanol-tolerant.
This work demonstrates a new route for the development of nonprecious
metal ORR catalysts from stable metalloporphyrinic MOFs.