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

Abstract

Constructing nanoscale hybrid materials\nwith unique interfacial structures by using various metal oxides and\ncarbon supports as building blocks are of great importance to develop\nhighly active, economical hybrid catalysts for oxygen reduction reaction\n(ORR). In this work, La₂O₂CO₃ encapsulated\nLa₂O₃ nanoparticles on a carbon black (La₂O₂CO₃@La₂O₃/C)\nwere fabricated via chemical precipitation in an aqueous solution\ncontaining different concentrations of cetyltrimethyl ammonium bromide\n(CTAB), followed by calcination at 750 °C. At a given CTAB concentration\n24.8 mmol/L, the obtained lanthanum compound nanoparticles reach the\nsmallest particle size (7.1 nm) and are well-dispersed on the carbon\nsurface. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy\n(XPS) results demonstrate the formation of La₂O₂CO₃ located on the surface of La₂O₃ nanoparticles in the hybrid. The synthesized La₂O₂CO₃@La₂O₃/C hybrid exhibits\na significantly enhanced electrocatalytic activity in electrocatalysis\nexperiments relative to pure La₂O₃, La₂O₂CO₃, and carbon in an alkaline environment,\nby using the R­(R)­DE technique. Moreover, its long-term stability also\noutperforms that obtained by commercial Pt/C catalysts (E-TEK). The\nexact origin of the fast ORR kinetics is mainly ascribed to the La₂O₂CO₃ layer sandwiched at the interface\nof carbon and La₂O₃, which contributes favorable\nsurface-adsorbed hydroxide (OH^–_ad) substitution and promotes active oxygen adsorption at the interfaces.\nThe unique covalent COC­(O)OLaO\nbonds, formed at the interfaces between La₂O₂CO₃ and carbon, can act as active sites for the improved\nORR kinetics over this hybrid catalyst. Therefore, the fabrication\nof lanthanum compound-based hybrid material with an unique interfacial\nstructure maybe open a new way to develop carbon-supported metal oxides\nas next-generation of ORR catalysts.