Terbium-induced cobalt valence-band narrowing boosts electrocatalytic oxygen reduction

Rare-earth (RE)-based materials are evolving as a promising paradigm for the electrocatalytic oxygen reduction reaction (ORR) to lead the practical application in energy conversion technologies. However, the systematic comprehension of the catalytic role of RE in the enhanced ORR is still limited. Herein, we develop a novel RE-based catalyst consisting of atomic Co species coupled with Tb2O3 (Co@Tb2O3) to unveil the role of RE in enhanced ORR performance. Co@Tb2O3 delivers satisfactory ORR activity with an onset potential and half-wave potential of 1.02 VRHE and 0.85 VRHE, respectively, outperforming the Pt/C benchmark and many reported Co-based catalysts. Quasi-operando X-ray photoemission spectroscopy exhibits potential-dependent shifts of binding energy and full width at half maximum for Co 2p and Tb 3d/4d, demonstrating the successful coverage and transformation of oxygen intermediates during the ORR. Theoretical calculations uncover that the constructed [Co-O-Tb] unit site in Co@Tb2O3 endows Co 3d with a narrow band and appropriate band location via the gradient orbital coupling of Co 3d-O 2p-Tb 4f. Such narrow-band behavior in the [Co-O-Tb] unit site makes the interaction between the Co site and oxygen intermediates in the form of an ideal sigma/pi bond mixing type, which provides flexible binding strength of oxygen intermediates, thus breaking the scaling relation of *OOH and*OH to be closer to optimal conditions. We believe that this work would set a new understanding for the design of high-efficiency RE-based materials towards the ORR. Tb2O3 endows Co 3d with a narrow band and appropriate band location via Co 3d-O 2p-Tb 4f gradient orbital coupling to efficiently enhance the oxygen reduction reaction.