Toward synergy of carbon and La2O3 in their hybrid as an efficient catalyst for the oxygen reduction reaction

Abstract

Investigating the synergy in hybrids between rare earth (La, Ce, Y) oxides and carbon may be an effective way to develop new efficient and cheap catalysts for catalyzing the oxygen reduction reaction (ORR). In this work, a set of La₂O₃/C hybrids with different La₂O₃ loadings were prepared by chemical precipitation in alkaline solution, followed by calcination treatment. The prepared La₂O₃ nanoparticles with hexagonal structure covered uniformly on the carbon surface. X-ray photoelectron spectroscopy (XPS) indicated different contents of covalent C–O–La bonds at the interface between the La₂O₃ and carbon in these hybrids. The electrochemical experiments in alkaline solution show that the catalyst with 80 wt% of La₂O₃ exhibits the highest electrochemical activity in catalyzing ORR and the lowest production of hydrogen peroxide among the synthesized hybrids. The remarkably enhanced ORR activity is attributed to the maximum content of the C–O–La bonds formed in the hybrid. Interestingly, the above C–O–La covalent bonds can promote the electron transfer from the supported carbon (π electron) to the La₂O₃ phase, and the transferred electron can fill the unoccupied e_g orbital splitted by the La 5d orbital of La₂O₃, which should be responsible for the improved ORR performance.