Hidden Hydroxides in KOH-Grown BaNiO₃ Crystals: A Potential Link to Their Catalytic Behavior

Abstract

The hexagonal perovskite BaNiO3, prepared via nonceramic approaches, is known to act as a good catalyst for the oxygen evolution reaction (OER) in alkaline media. Here, we report our observation that BaNiO3 synthesized via KOH flux growth and high-pressure ceramic synthesis with high O2 pressure have different magnetic properties. We show that this is because the KOH flux-grown crystals made in open air are actually a hydroxide-containing form of BaNiO3 that can be “dried” upon annealing in an O2 flow. This work not only unveils a previously unknown aspect of the BaNiO3 OER catalyst and offers some insights into the underlying mechanism, but also suggests that hydroxide ions may be present in other hexagonal perovskite oxides prepared in wet conditions.

BaNiO3 electrocatalysts for oxygen evolution reaction: the role of synthetic methods

“…The resulting solid was washed thoroughly with deionized water by centrifugation until the conductance of the supernatant matched the one of deionized water. A single crystal sample was also prepared by the molten salts method following the procedure previously described by L. Jin et al 33 .…”

“…Surface carbonation is common for materials containing barium, due to its basicity. MS-BaNiO3 Ba 3d signals (Figure S4a Recent studies have hypothesized the presence of hydroxides in BaNiO3 samples prepared using potassium hydroxide as a flux 33 . Our findings confirm the presence of these hydroxides at the surface of the perovskite particles in the MS-BaNiO3 sample, rather than within the BaNiO3 structure as previously suggested 26 .…”

“…Recent studies regarding BaNiO3 preparation focus on the molten salts method, as it seems to be appropriate to control single crystal morphology 25 . On the other hand, it has been recently suggested that the phase obtained by this method is not BaNiO3, but rather a barium and nickel oxyhydroxide (BaNiO2.45(OH)0.55) 26 .…”