In situ generation of highly active sites by chemical vapor deposition of C2H4 over the LaMn0.7Co0.3O3 perovskite for the oxygen reduction reaction

Abstract

The LaMn_0.7Co_0.3O₃ perovskite was used as a substrate to deposit carbon via Chemical Vapor Deposition (CVD) to form composites active for the oxygen reduction reaction (ORR). The presence of carbon material is important to improve the electrical conductivity of the metal oxide. The composites were characterized by different physicochemical methods. During the CVD process and regardless of the time of carbon deposition, the perovskite structure is decomposed into other crystallite structures including MnO, Co, La₂O₃ and La(OH)₃. In addition, carbon nanotubes are formed over the metal oxides due to the presence of cobalt in the perovskite, especially after 20 min of CVD carbon deposition. The electrocatalytic activity towards ORR was assessed using a rotating ring-disk electrode in an alkaline liquid medium. The strong interactions between the carbon material and the metal-based compounds through C–O–M covalent bonds, which are highly active sites for ORR, considerably improve the catalytic performance. Moreover, new crystal phases are formed, which lead to the formation of the MnO/Co heterointerfaces that are also important sites for ORR. However, it was demonstrated that the presence of lanthanum-based compounds limits the number of active sites available for the ORR due to La segregation on the surface of the samples. Finally, the presence of carbon defects in the carbon nanotubes, especially the edge sites, can also produce a synergistic effect with the other active sites, enhancing the overall ORR reaction.