【摘要】 以Vulcan XC-72炭黑为载体,通过对炭载体石墨化处理和表面化学修饰,将其与化学沉淀法制备的纳米级LaMnO3颗粒共混,再经特定温度下煅烧,制备出改性炭黑-LaMnO3复合材料.X射线光电子能谱和热重分析表明,当煅烧温度在300°C时,炭载体与LaMnO3纳米颗粒之间形成了大量C–O–M(M=La,Mn)化学键.扫描电子显微镜和高分辨透射电子显微镜分析发现,纯相LaMnO3纳米颗粒主要呈现短棒、三支棒或竹节棒的形貌特征,炭载体则为具有完整石墨层的空心球结构,LaMnO3均匀分散在炭载体上.在25°C,1 mol/L NaOH溶液中的电化学测试结果表明,成分比(LaMnO3:C)为2:3的复合材料具有很高的氧还原电催化活性,氧还原反应电子数为3.81,中间产物H2O2产率为9.5%,其活性接近商业Pt/C催化剂(E-TEK).高的氧还原电催化活性主要归因于LaMnO3纳米颗粒与炭载体之间形成了大量共价键.更多还原

【Abstract】 Covalent coupling between LaMnO3 nanoparticles and carbon black to produce a composite catalyst for oxygen reduction reaction(ORR) was achieved by physical mixing of modified carbon and perovskite-type LaMnO3 nanoparticles, followed by sintering at different temperatures. Perovskitetype LaMnO3 nanoparticles were first synthesized via chemical precipitation, and the carbon support(Vulcan XC-72) was modified using graphitization, followed by HNO3 and ammonia treatments. The morphology and electronic states of the carbon black-LaMnO3 hybrid catalyst were characterized by scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The loaded LaMnO3 particles featured rod-like, three bars-like, and bamboo rod-like structures and were homogeneously dispersed in the carbon matrix that featured a hollow spherical structure. At a sintering temperature of about 300 °C, C–O–M(M = La, Mn) bonds formed at the interface between the carbon and LaMnO3 nanoparticles. Electrochemical measurements in 1 mol/L NaOH showed that the carbon-LaMnO3 hybrid prepared at a LaMnO3/GCB mass ratio of 2:3 displayed the highest electrocatalytic activity towards ORR among all the synthesized hybrid catalysts. The electrocatalytic activity was comparable with that obtained by commercial Pt/C catalyst(E-TEK). The average electron transfer number of ORR was ~3.81, and the corresponding yield of the hydrogen peroxide intermediate was ~9.5%. The remarkably improved electrocatalytic activity towards ORR was likely because of the formation of covalent bonds(C–O–M) between the LaMnO3 nanoparticles and carbon that can effectively enhance the ORR kinetics. This information is important to understand the physical origin of the electrocatalytic activity of carbon-supported rare earth oxides as catalysts for ORR.更多还原