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 but the relationships between the synthesis conditions and the electrochemical properties have not been thoroughly investigated, which prevents further optimization of the materials performances. 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.