Coordination chemistry of large-size yttrium single-atom catalysts for oxygen reduction reaction.

Although being transition metals, the Fenton-inactive group 3-4 elements (Sc, Y, La, Ti, Zr, and Hf) could easily lose all the outermost s and d electrons, leaving behind ionic sites with nearly empty outermost orbitals that are stable but inactive for oxygen involved catalysis. We demonstrate here that the dynamic coordination network could turn these commonly inactive ionic sites into platinum-like catalytic centers for oxygen reduction reaction (ORR). Using density functional theory calculations, we identify a macrocyclic ligand coordinated yttrium single-atom (YN 4 ) moiety, which is originally ORR inactive because of the too strong binding of hydroxyl intermediate, while it could be activated by an axial ligand X through the covalency competition between Y-X and Y-OH bonds. Strikingly, it is also found that the binding force of the axially coordinated ligand is an effective descriptor, and the chlorine ligand is screened out with an optimal binding force that behaves self-adaptively to facilitate each ORR intermediate steps by dynamically changing its Y-Cl covalency. Our experiments validate that the as-designed YN 4 -Cl moieties embedded within the carbon framework exhibit a high half-wave potential (E 1/2 = 0.85 V) in alkaline media, the same as that of the commercial Pt/C catalyst, and it delivers a maximum power density of 162 mWcm -2 in a zinc-air cell, outperforming the commercial Pt/C (152 mW cm -2 ). This article is protected by copyright. All rights reserved.