High-Performance Electrocatalysis on Palladium Aerogels
High-Performance Electrocatalysis on Palladium Aerogels
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DOI：
10.1002/anie.201108575
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发表时间：
2012-01-01
影响因子：
16.6
通讯作者：
Eychmueller, Alexander
中科院分区：
文献类型：
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作者：
Liu, Wei;Herrmann, Anne-Kristin;Eychmueller, Alexander
新型的自组装结构是纳米化学和纳米技术的研究热点。气凝胶是一类独特的无机聚合物，具有低密度、大的开孔和高的内表面积，以其上级的物理和化学性质而闻名，这与其通过宏观尺度上的自组装放大的纳米材料的特定性质的组合有关。到目前为止，已经对氧化物基气凝胶进行了大量的研究，其中传统的二氧化硅、氧化铝和二氧化钛气凝胶是研究最广泛的系统之一。这些材料已经发现有吸引力的应用，例如作为热绝缘体和电化学装置的组件。[1]还对气凝胶（二氧化硅、二氧化钛、氧化铝、碳等）上负载的金属纳米颗粒（例如铂）的混合气凝胶进行了大量研究，该联合收割机结合了金属纳米颗粒的催化性能和气凝胶的高度多孔结构。[2]近年来，溶胶-凝胶法在硫系气凝胶制备中的应用得到了发展。[3]最近，Leventis等人通过碳热法开发了金属气凝胶（包括Fe、Co、Ni、Cu）。[4]我们的团队已经开发了非负载的monoclonal（Pt，Au和Ag）和monoclonal（PtAg和AuAg）气凝胶，[5]并且半导体和金属纳米颗粒的复合气凝胶已经成功实现。[6]这些由硫族化物半导体或金属纳米晶体形成的气凝胶构成了一类不断发展的材料，由于其光学和催化性能而具有巨大的潜力;[3-6]然而，这些材料的应用仍有待于在广度和深度上进行探索。[3e]此外，通过简单的策略开发具有高孔隙率、大比表面积和高活性的新型纳米结构金属气凝胶具有极大的兴趣。以前，已经开发了其他重要的策略来生成多孔金属纳米结构，例如，通过模板化，脱合金，电沉积方法;[7]最近，Krishna等人也报道了通过简单地混合前体和还原剂快速合成高表面积的贵金属纳米海绵。[8]环糊精（CD）是一类易于获得的水溶性无毒环状低聚糖，具有疏水的内腔和亲水的外部，在主客体相互作用，分子识别和药物递送的研究中非常重要。[9]它们在金属纳米材料领域也引起了人们的关注，主要是因为它们可以提高水溶性和控制纳米颗粒的粒径。相比之下，没有太多的注意，通过利用环糊精和目标分子之间的主客体相互作用来提高金属纳米颗粒的催化活性。[10]本文报道了一种制备a-、B-或g-环糊精（PdCD）修饰的纳米结构Pd气凝胶的简便方法。当在a-、B-或g-CD存在下用硼氢化钠（NaBH 4）还原四氯钯酸钾（K2 PdCl 4）时，PdCD水凝胶自发形成而无需额外处理，随后用超临界CO2干燥后，得到PdCD气凝胶。使用这种简单的方法，我们生产了具有高孔隙率和大表面积的PdCD气凝胶。PdCD气凝胶对乙醇的电氧化具有很高的催化活性，其中Pda-CD和Pdb-CD气凝胶是最好的上级催化剂。由于该气凝胶制备工艺简单、环境友好、催化活性高，有望实现工业化生产。
Novel self-assembled architectures are currently of great interest for nanochemistry and nanotechnology. Aerogels, a unique class of inorganic polymers with low densities, large open pores, and high inner surface areas, are well known for their superior physical and chemical properties, which are linked to their combination of specific properties of the nanomaterials magnified by self-assembly on the macroscale. Up to now, a wealth of research has been carried out on oxidebased aerogels, with the traditional silica, alumina, and titania aerogels amongst the most widely studied systems. These materials have found attractive applications, for example as thermal insulators and components of electrochemical devices.[1] A great deal of research has also been conducted on hybrid aerogels of metal nanoparticles (eg platinum) supported on aerogels (silica, titania, alumina, carbon, etc.), which combine both the catalytic properties of the metal nanoparticles and the highly porous structures of the aerogels.[2] Recently, the extension of sol–gel methods to the preparation of chalcogenide aerogels was realized.[3] Most recently, Leventis et al. has developed metal aerogels (including Fe, Co, Ni, Cu) by a carbothermal method.[4] Our group has developed nonsupported monometallic (Pt, Au, and Ag) and bimetallic (PtAg and AuAg) aerogels,[5] and composite aerogels of both semiconductor and metal nanoparticles have been successfully realized.[6] These aerogels formed from chalcogenide semiconductor or metal nanocrystals constitute an evolving class of materials with enormous potential on account of their optical and catalytic properties;[3–6] however, applications of these materials are still to be explored in width and depth.[3e] In addition, it is of great interest to develop new nanostructured metallic aerogels with high porosity, large surface area, and high activity by simple strategies. Previously, other important strategies have been developed to generate porous metal nanostructures, for example, by templating, dealloying, electrodepositing approaches;[7] recently, Krishna et al. have also reported a rapid synthesis of high-surface-area noble metal nanosponges by simply mixing the precursors and reducing agent.[8]Cyclodextrins (CDs), a class of readily available, watersoluble, and nontoxic cyclic oligosaccharides with a hydrophobic inner cavity and a hydrophilic exterior, are of great importance in studies of host–guest interactions, molecular recognition, and drug delivery.[9] They have also drawn attention in the area of metal nanomaterials, mainly because they can enhance water-solubility properties and control particle size of nanoparticles. In contrast, not much attention has been paid to improving the catalytic activity of the metal nanoparticles by utilizing the host–guest interactions between cyclodextrin and the target molecules.[10] Herein, we report a facile method to prepare nanostructured Pd aerogels modified by a-, b-, or g-cyclodextrins (PdCD). When potassium tetrachloropalladate (K2PdCl4) was reduced with sodium borohydride (NaBH4) in the presence of a-, b-, or g-CD, the PdCD hydrogels formed spontaneously without additional treatment, and after subsequent drying with supercritical CO2, PdCD aerogels were obtained. Using this simple approach, we produced PdCD aerogels with high porosities and large surface areas. The PdCD aerogels exhibit very high activities towards the electrooxidation of ethanol, with Pda-CD and Pdb-CD aerogels as the superior catalysts. Because of the simple and environmentally friendly preparation process together with the high catalytic activity, upscaling production of the Pd aerogels for commercial use …