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

BaNiO3 and other Ba-Ni-O related phases are among the most active non-precious electrocatalysts towards the oxygen evolution reaction (OER) in basic media. In this work, we compare the electrocatalytic activities of the hexagonal perovskite BaNiO3 prepared by three different synthesis methods: sol-gel, metal nitrate decomposition and molten salts. We reveal by a combination of atomic-scale imaging and spectroscopic techniques how the choice of the synthesis method strongly influences the chemical, morphological and microstructural features of the products. Moreover, we demonstrate by Energy Electron Loss Spectroscopy and X-Ray Photoelectron Spectroscopy that previously reported electrocatalytic results concerning BaNiO3 prepared in molten salts are actually related to the presence of an unreported nickel hydroxide shell, which ultimately results in enhanced electrocatalytic activity. These results highlight the importance of acknowledging how the synthesis method strongly influences oxygen electrocatalysis performances and paves the way to further surface engineering.