原位还原法制备碳纳米管负载钯基纳米复合物及其对C2-C4醇氧化的电催化活性

It has important theoretical and practical significance for the study on the direct alcohol fuel cells using ethanol, 1-propanol and 1-butanol (C2-C4 alcohols) as fuels which are called the renewable resources. It is difficult for the complete electro-oxidation of the C2-C4 alcohols to carbon dioxide because of the stable C-C bonds in their molecules. However, in alkaline media, the main electro-oxidation products of the C2-C4 alcohols on the Pd-based electrocatalysts are carboxylic acids (carboxylates). In view of this, we intend to obtain the covalent (or non-covalent) functionalized MWCNTs, which then integrate with Pd ion and other metal ions. After being reduced, the formed metal nanoparticles are in situ immobilized on the MWCNT surface, leading to the synthesis of the Pd-based/MWCNT composite nano-electrocatalysts. The prepared composite electrocatalysts possess the high selectivity for the electro-oxidation of the C2-C4 alcohols to the corresponding carboxylic acids. The direct alcohol (C2-C4) fuel cells using these novel composite catalysts as the anodic materials can not only outpput electricity, but also obtain the valuable products of carboxylic acids (carboxylates). This project will systematically study the effect of the various functionalization treatments of MWCNTs including different carboxylating methods, different extents of amidization and molecule modifications, etc., on the stability and dispersivity of the metals nanoparticles, and also study the effect of the compositions of the Pd-based composite nano-catalysts on the selectivity, reaction mechanism and catalytic activity for the electro-oxidation of the C2-C4 alcohols. It will be of great significance on science for the research of this project on the electro-oxidation mechanism of alcohols, the preparation of novel electrocatalysts and the development of new-style direct alcohol fuel cells.

研究以乙醇、正丙醇和正丁醇(C2-C4)等可再生醇为燃料的直接醇燃料电池具有重要的意义。C2-C4醇难以完全电氧化为CO2,而在碱性溶液中，它们在钯类催化剂上电氧化的主要产物是羧酸(盐)。鉴于此，我们对多壁碳纳米管(MWCNT)进行共价或非共价功能化处理，使其与钯和其它金属离子以配位键或物理吸附方式结合，再将它们还原成纳米颗粒并原位沉积于MWCNT表面，从而制备钯基/MWCNT复合纳米材料，使其能选择性电氧化C2-C4醇为相应羧酸。以此复合催化剂为阳极组成的直接醇(C2-C4)/空气燃料电池不仅可以输出电能，还能回收产物羧酸(盐)。通过系统研究MWCNT的各种功能化方法(羧酸化,不同程度酰胺化,不同分子的修饰等)对稳定与分散金属纳米颗粒的影响，研究钯基复合纳米颗粒的组成对C2-C4醇电氧化的选择性、反应机理与催化活性的影响,为开发新颖的直接醇类燃料电池提供科学依据.

研究以乙醇、正丙醇和正丁醇(C2-C4)等可再生醇为燃料的直接醇燃料电池具有重要的意义. 而在碱性溶液中，钯是电化学催化C2-C4醇氧化优异的催化剂。为了提高纳米钯催化剂的电催化活性与稳定性，将钯纳米颗粒固定并分散在多壁碳纳米管(MWCNT)表面是一种有效的方法。本项目主要研究内容有：在MWCNT上，或功能化MWCNT上原位沉积钯、钯基双金属或三金属纳米颗粒；制备新型钯基多金属/MWCNT纳米复合电催化剂；测定这些催化剂对C2-C4醇氧化的电活性与稳定性；以这些新颖的钯基电催化剂为阳极、以非铂（或非钯）金属掺杂的C-N复合物为阴极，设计出无膜的直接醇-空气燃料电池并考察其性能。结果表明：（1）在阳离子表面活性剂修饰的MWCNT表面上，氯化钯能自发还原形成钯纳米颗粒，后者原位沉积在MWCNT表面，形成的催化剂对醇氧化具有优异的电活性；（2）在EDTA和-环糊精修饰后的MWCNT上,所形成的Pd纳米颗粒的粒径更小,分散度更高，在碱性溶液中对乙醇氧化的电化学活性更强；（3）首先制备负载于碳纳米管上的纳米镍和纳米镍钴颗粒. 以它们为还原剂与PdCl2溶液反应, 原位还原Pd2+得到负载在多壁碳纳米管表面的Pd-Ni/MWCNT和Pd-Ni-Co/MWCNT催化剂，它们的钯负载量小，且它们对醇氧化表现出极高的电活性；（4）将金属盐、碳纳米管（CNT）与Nafion溶液混合后，再均匀地涂覆在碳纸（CP）表面，随后将该碳纸浸没在NaBH4溶液中，形成的金属纳米颗粒直接原位沉积在CNT表面。这样形成的钯基复合纳米颗粒对乙醇氧化的电活性与稳定性都远高于通常的Pd/CP；（5）采用化学还原法，制备了一系列MWCNT负载的钯基复合多金属纳米催化剂：Pd-Ni, Pd-Sn, Pd-Sn-Ni, Pd-Ag, Pd-Ag-Sn等，它们对醇氧化的电活性远远高于Pd/MWCNT；（6）设计的无膜醇-空气燃料电池能稳定放电，并具有较大的功率密度；（7）为配合这种无膜醇-空气电池的设计，制备了一系列非贵金属掺杂的C-N复合物，它们对氧还原反应具有优异的电催化活性，并且对醇氧化呈惰性，保证了这种无膜燃料电池的正常放电；（8）钯基复合催化剂对醇氧化的高活性是由钯与其它金属的双功能效应所引起的。