Tailoring the Electronic Structures of the La2NiMnO6 Double Perovskite as Efficient Bifunctional Oxygen Electrocatalysis

Double perovskite oxides are one of the most promising bifunctional electrocatalysts for efficient oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) due to their adjustable electronic structures via doping with different metal cations or engineering of defects. Herein, we report a systematic study on the tuning of the electronic structure of La2-xSrxNiMnO6 with 0 ≤ x ≤ 1.0 to promote the bifunctional OER/ORR activity. The bifunctional index (ΔE) is substantially reduced with increasing of Sr contents and achieves an optimal value of 0.85 V for La1.4Sr0.6NiMnO6, exceeding that of widely studied LaNiO3. Our study on electronic structures reveals that the enhancement of the ORR and OER activities strongly correlates with the appearance of Ni3+ oxidation states and the upshift of the O 2p-band center promoted by Sr doping. Furthermore, an increase of hole states, derived from Ni3+ states, reduces the energy barrier for the electron transfer from 0.44 to 0.12 eV and hence improves the intrinsic OER activities. The tuning of the electronic structure that leads to higher OER and ORR activities in La2-xSrxNiMnO6 can be extended to other materials for the design of active bifunctional electrocatalysts.