Composition-dependent electro-catalytic activities of covalent carbon-LaMnO3 hybrids as synergistic catalysts for oxygen reduction reaction

Through in-situ nucleation and growth of perovskite-type LaMnO3 nanocrystals on a modified carbon black, a set of LaMnO3/C hybrids with different LaMnO3 loadings (40 wt%, 80 wt%, 100 wt% and 140 wt%, relative to carbon) were facilely fabricated via hydrolysis and precipitation in an ethanol solution, followed by calcination at 700 degrees C. The obtained LaMnO3 nanoparticles feature perovskite-type structure and are dispersed uniformly on the carbon surface. The electrochemical experiments in 1 mol L-1 NaOH solution illustrate that the hybrid catalyst (100 wt% of LaMnO3) exhibits the highest ORR electrocatalytic activity and the lowest hydrogen peroxide yield. X-ray photoelectron spectroscopy (XPS) reveals that the catalyst with the best catalytic activity has the highest content of covalent C-O-Mn bonds formed at the interface between the LaMnO3 and carbon, which implies a close correlation between the loading and the covalent bond content within the hybrids. The synergy between the oxide and carbon, raised by the formed C-O-Mn bonds in their hybrid, is responsible for the remarkably improved ORR activity. This information is important to achieve synergy between non-noble metal oxides and carbon in their composites as efficient and economical ORR catalysts. (C) 2016 Published by Elsevier Ltd.