Vector substrate design for grain boundary engineering: boosting oxygen evolution reaction performance in LaNiO3.

The realization and subsequent control of emerging structural and electronic phases in solid materials has significantly enhanced their functionalities, thereby benefiting both fundamental research and practical applications. The grain boundary (GB), as a transitional region within the crystal lattice, exhibits atomic shifts and distinct energy profiles. These unique characteristics offer a promising avenue for the discovery of advanced active catalytic phases for carbon, oxygen, hydrogen, and nitrogen evolution/reduction reactions. However, the challenge lies in isolating and controlling the quantity of grain boundaries in conventional catalysts, which hinders the identification of their functional attributes. In this study, we successfully engineered the (001)/(110), (001)/(111), and (110)/(111) GBs in LaNiO₃ (LNO) using a vector substrate design approach. Subsequent evaluation of these GBs in the oxygen evolution reaction (OER) revealed that LNO (110)/(111) exhibited the fastest surface reconstruction into Ni oxyhydroxide and the most superior OER performance, achieving 2.36 mA cm^-2 at η = 400 mV. This outstanding performance is attributed to its strongest Ni-O covalency and the proximity of the O 2p-band center to the Fermi level. This research aims to address the challenges associated with isolating and controlling GBs for optimized OER performance, while also providing comprehensive insights into the relationship between GBs and surface reconstruction behaviors.