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

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 (pi 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.