Single-step synthesis of nano-sized perovskite-type oxide/carbon nanotube composites and their electrocatalytic oxygen-reduction activities

Abstract

Composites of nano-sized perovskite-type oxides of La_1−xSr_xMnO₃ (LSMO) and carbon nanotubes (CNTs) were synthesized in a single step by the electrospray pyrolysis method, and their electrocatalytic activities for oxygen reduction were evaluated in an alkaline solution. The resulting LSMO nanoparticles with a diameter of less than 20 nm were well dispersed and deposited on the surface of CNTs. Elemental analysis showed that the metal-composition of LSMO/CNT composites was controlled by altering the concentrations of a precursor solution. Rotating-disk-electrode measurements revealed that the electrocatalytic activities of LSMO/CNT composites increased with an increase in a molar ratio of Sr element. Composites of LSMO nanoparticles and CNTs showed greater catalytic activities than conventional LSMO particles (1 µm) supported on carbon black for oxygen reduction. Moreover the LSMO/CNT catalyst showed larger oxygen-reduction currents even in the presence of ethylene glycol while a Pt disk electrode was affected by the oxidation currents of ethylene glycol. These results indicate that LSMO/CNT composites are a promising candidate as a cathode catalyst with a higher catalytic selectivity for oxygen reduction and a higher crossover-tolerance for use in anion-exchange membrane fuel cells.