改性炭黑-LaMnO3复合材料的制备及其共价复合效应对氧还原性能的影响

以VulcanXC-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℃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℃，1mol/LNaOH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.

Facile preparation of modified carbon black-LaMnO3 hybrids and the effect of covalent coupling on the catalytic activity for oxygen reduction reaction

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. Perovskite-type 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-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 intermediatewas ~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.