BaNiO₃ Electrocatalysts for Oxygen Evolution Reaction: The Role of Synthetic Methods

BaNiO₃ and other Ba-Ni-O-related phases are among the most active nonprecious electrocatalysts toward the oxygen evolution reaction (OER) in basic media, but the relationships between the synthesis conditions and the electrochemical properties have not been thoroughly investigated, which prevents further optimization of the materials' performance. In this work, we compare the electrocatalytic activities of hexagonal perovskite BaNiO₃ prepared by three different synthesis methods: sol-gel, metal nitrate decomposition, and molten salts. We show by combining atomic-scale imaging and spectroscopic techniques how the choice of the synthesis method influences the chemical, morphological, and microstructural features of the materials. We especially 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 how the synthesis method can strongly influence oxygen electrocatalysis, which paves the way to further surface engineering of other energy materials.