A Dual-Atom La2 Catalyst for the Oxygen Reduction Reaction.

Rare earth lanthanum element has large atomic radius, multi-shell orbital electrons, and Fenton-like reaction inertia, on which a localized high-coordination structure can be easily formed for the favorable adsorption of reaction intermediates. However, for single-atom lanthanum sites, due to the loss of all the outmost s and d electrons, the practically vacuous outmost orbitals are stable but sleepy for the oxygen reduction reaction (ORR). Here, we synthesize a novel dual-atom La catalyst onto N-doped graphene (La2-NG) by a Joule ultrafast heating method, which shows a half-wave potential of 0.893 V for the ORR. The La2-NG-assembled zinc-air battery demonstrates a great open circuit voltage of 1.52 V and a maximal power density of 192 mW cm-2. Operando X-ray absorption spectra reveal the change of valence states of La and the dynamic structural evolution of La2-N6 moiety embedded onto the graphene during the ORR, through which the adsorption/desorption of oxygen reduction intermediates can be reasonably regulated. Theoretical calculations further demonstrate that the La2-N6 structure can decrease the reaction energy barrier and promote charge transfer.