La₂O₂CO₃ Encapsulated La₂O₃ Nanoparticles Supported on Carbon as Superior Electrocatalysts for Oxygen Reduction Reaction

ACS Appl. Mater. Interfaces 2015, 7, 26914−26922

Weiwei Gu, Jingjun Liu,* Mingan Hu, Feng Wang,* and Ye Song

ABSTRACT: Constructing nanoscale hybrid materials with unique interfacial structures by using various metal oxides and carbon supports as building blocks are of great importance to develop highly active, economical hybrid catalysts for oxygen reduction reaction (ORR). In this work, La₂O₂CO₃ encapsulated La₂O₃ nanoparticles on a carbon black (La₂O₂CO₃@La₂O₃/C) were fabricated via chemical precipitation in an aqueous solution containing different concentrations of cetyltrimethyl ammonium bromide (CTAB), followed by calcination at 750 °C. At a given CTAB concentration 24.8 mmol/L, the obtained lanthanum compound nanoparticles reach the **allest particle size (7.1 nm) and are well-dispersed on the carbon surface. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results demonstrate the formation of La₂O₂CO₃ located on the surface of La₂O₃ nanoparticles in the hybrid. The synthesized La₂O₂CO₃@La₂O₃/C hybrid exhibits a significantly enhanced electrocatalytic activity in electrocatalysis experiments relative to pure La₂O₃, La₂O₂CO₃, and carbon in an alkaline environment, by using the R(R)DE technique. Moreover, its long-term stability also outperforms that obtained by commercial Pt/C catalysts (E-TEK). The exact origin of the fast ORR kinetics is mainly ascribed to the La₂O₂CO₃ layer sandwiched at the interface of carbon and La₂O₃, which contributes favorable surface-adsorbed hydroxide (-OH^- _ad) substitution and promotes active oxygen adsorption at the interfaces. The unique covalent -C-O-C(=O)-O-La-O- bonds, formed at the interfaces between La₂O₂CO₃ and carbon, can act as active sites for the improved ORR kinetics over this hybrid catalyst. Therefore, the fabrication of lanthanum compound-based hybrid material with an unique interfacial structure maybe open a new way to develop carbon supported metal oxides as next-generation of ORR catalysts.