Catalytic Activity of LaBO3 for OER in HClO4 Medium: An Approach to the Molecular Orbital Theory

The electrocatalytic activity of transition-metal-based perovskites, LaBO3 (B = Ni, Mn, Cr, and Co), toward an oxygen evolution reaction (OER) was investigated in HClO4 medium by linear polarization and electrochemical impedance measurements. X-Rays Diffraction characterization showed that single perovskite phases were formed. Field-emission scanning electron microscopy showed that changing the type of B-site metal ion affected the morphology of the prepared perovskites. High-resolution transmission electron microscopy confirmed the formation of orthorhombic phase laCrO(3) and of the rhombohedral phases of LaNiO3, LaMnO3, and LaCoO3. Results were compared with LaFeO3 and the order of the electrocatalytic activity was found to be LaNiO3 > LaFeO3 > LaMnO3. This trend agrees with the calculated activation energy values, 11.38, 20.13, and 22.01 kJ mol(-1) for LaBO3 (B = Ni, Fe and Mn), respectively and is explained based on molecular orbital principles. LaCrO3 and LaCoO3 showed no catalytic activity toward OER due to the dissolution of LaCrO3 and the formation of a passive layer of Co3O4 when tested in HClO4. Ternary La1-xSrxNiO3 perovskites have higher catalytic activity for OER compared to LaNiO3, which is promoted by increasing the Sr ratio. (C) 2015 The Electrochemical Society.