The spin-state effect on the oxygen evolution reaction of LaCoO3 perovskites

Efficient, stable and low-cost oxygen evolution reaction (OER) electrocatalysts are critical for energy conversion and storage. Spin-state regulation is an innovative strategy to enhance electrocatalytic activity, but current studies focus on bulk materials, neglecting the spin states of surface-active sites. In this work, taking the typical multi-spin-state perovskite LaCoO3 as a model system, we systematically investigated the spin states of Co ions in both surface and bulk regions, as well as their respective effects on OER performance. Our results reveal that the surface Co ions are exclusively confined to the high spin state, even though the spin states of bulk Co ions can be tuned to low spin, intermediate spin, and high spin configurations. Notably, the spin state of bulk Co has a negligible impact on catalytic activity. To modulate the orbital occupation of surface-active Co ion, we changed its coordination environment and found that the spin state of surface-active Co has a more significant impact on catalytic activity than that of bulk Co. Our findings demonstrate that the spin state of surface-active sites is a more reliable descriptor for OER catalysis, offering profound mechanistic understanding of spin-state regulation and a new pathway for developing high-performance catalysts via spin-state engineering.