Metalloid-Cluster Ligands Enabling Stable and Active FeN₄ -Te_n Motifs for the Oxygen Reduction Reaction.

Abstract

In nature, the oxygen reduction reaction (ORR) is catalyzed by cytochrome P450 (CYP) enzymes containing heme iron centers with an axial thiolate ligand (FeN₄ -S), which are among the most finely developed catalysts by natural selection. However, the exceptional ORR activity and selectivity of CYP enzymes originate from their non-rigid and self-adaptive coordination network with molecular ligands, which sacrifices the stability of the active motifs under electrochemical reaction conditions. Here, a design strategy to circumvent this dilemma by incorporating Fe-N₄ motifs into carbon matrices instead of the protein scaffold and replacing the axial molecular thiolate ligand with a stable tellurium cluster (Te_n ) is demonstrated. Theoretical calculations indicate a moderate interaction between Fe 3d and Te 5p orbitals once n > 2, allowing the FeTe bond to dynamically change its strength to adaptively facilitate the intermediate steps during the ORR process, which renders FeN₄ -Te_n active sites with superior ORR activity. This adaptive behavior mimics the conformational dynamics of an enzyme during the reaction, but retains the stability nature as a heterogeneous catalyst. The experiments validate that the as-designed catalyst with a characterized FeN₄ -Te_n structure outperforms the commercial Pt/C catalyst both on activity and stability.