Directly visualizing and exploring local heterointerface with high electro-catalytic activity

Oxide heterostructures of perovskite/Ruddlesden-Popper exhibit exceptionally high oxygen reduction/evolution reaction (ORR/OER) activity and can be used in next-generation energy storage materials. To make clear the real highly-active centers in the heterostructured material and obtain direct evidence to further understand the origin of the enhanced ORR/OER kinetics accurately, here we prepared a surface-patterned heterostructured thin-film of typical Ln1-xSrxCoO3/Ln2-xSrxCoO4 (Ln is lanthanide) using designed pulsed laser deposition (PLD), exposed the local heterointerface and visualized its enhanced performance using three-dimensional time of flight secondary ion mass spectrometry (3D TOF-SIMS) after 18O2/16O2 isotope exchange. Additionally, a multiple-layered heterostructured thin-film was constructed by PLD with switched targets, and the atomic-resolution crystal structures of local heterointerface were observed via scanning transmission electron microscopy after focused ion beam milling. Moreover, the origin of ORR/OER enhancement at local heterointerface was further studied directly, the results demonstrate that ORR/OER process is accelerated due to the decrease of Co valance state and generated oxygen vacancies. This study gives an effective strategy to precisely investigate the heterostructured materials for energy storage technologies such as batteries and fuel cells.