Metal-Triazolate-Framework-Derived FeN4 Cl1 Single-Atom Catalysts with Hierarchical Porosity for the Oxygen Reduction Reaction.

The construction of single-atom catalysts (SACs) with high single atom densities, favorable electronic structures and fast mass transfer is highly desired. We have utilized metal-triazolate (MET) frameworks, a subclass of metal-organic frameworks (MOFs) with high N content, as precursors since they can enhance the density and regulate the electronic structure of single-atom sites, as well as generate abundant mesopores simultaneously. Fe single atoms dispersed in a hierarchically porous N-doped carbon matrix with high metal content (2.78 wt %) and a FeN4 Cl1 configuration (FeN4 Cl1 /NC), as well as mesopores with a pore:volume ratio of 0.92, were obtained via the pyrolysis of a Zn/Fe-bimetallic MET modified with 4,5-dichloroimidazole. FeN4 Cl1 /NC exhibits excellent oxygen reduction reaction (ORR) activity in both alkaline and acidic electrolytes. Density functional theory calculations confirm that Cl can optimize the adsorption free energy of Fe sites to *OH, thereby promoting the ORR process. The catalyst demonstrates great potential in zinc-air batteries. This strategy selects, designs, and adjusts MOFs as precursors for high-performance SACs.