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

Four cubic zirconium-porphyrin frameworks, CPM-99(H-2, 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.