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 °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 COMn 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 COMn 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.