Synthesis and application of hexagonal perovskite BaNiO3 with quadrivalent nickel under atmospheric and low-temperature conditions

A hexagonal perovskite BaNiO3 with unusually high-valence nickel(IV) was synthesized under atmospheric and low-temperature conditions by an ethylenediamine-derived wet-chemical route. Secondary phases disappeared with increase in the pH value, and the singlephase BaNiO3 was successfully synthesized at pH 10. The specific surface area was similar to 32 m(2) g(-1), which is significantly enhanced compared to the BaNiO3 (0.3 m(2) g(-1)) synthesized by flux-mediated crystal growth. The BaNiO3 was used as an oxygen-evolution reaction (OER) catalyst, and the specific mass activity was similar to 5 times higher than that of the BaNiO3 synthesized by flux-mediated crystal growth. As a result, the ethylenediamine-derived sol-gel synthesis could be a simple technique to prepare crystalline compounds such as perov-skites and spinels, with unusually high-valence transition metals.