【作者】 刘虹；

【导师】 王晓敏；

【作者基本信息】 太原理工大学 ， 材料学， 2010， 硕士

【摘要】 金属铂是迄今为止发现的最有效的直接甲醇燃料电池（DMFC）电极催化剂。提高催化剂的电化学活性和抗CO中毒的能力是DMFC催化剂性能研究的热点。由于甲醇氧化过程中生成的中间产物CO会使Pt中毒,降低Pt的催化活性,而且铂作为贵金属,成本相对较高,因此研究Pt-M二元催化剂以克服一元催化剂的不足是当前的的研究趋势。Pt-Sn二元催化剂由于金属Sn成本较低,Pt-Sn催化剂的催化活性好而备受关注。但有关Pt-Sn/CMS结构对催化活性的影响机理的报道很少。本研究在CVD法制备得到粒径均匀,分散度好的碳微球的基础上,利用浸渍还原法合成了Pt-Sn/CMS,采用X-射线光电子能谱（XPS）、X-射线衍射（XRD）、高分辨透射电子显微镜（HRTEM）等手段对其结构、形貌等进行表征,通过电化学工作站对其电化学性能进行了测试,并与Pt/CMS进行比较,以确定Sn元素对Pt/CMS电催化活性的影响,进一步探索担载型Pt-Sn/CMS结构对催化活性的影响机理。实验结果表明:1.采用化学气相沉积法制备出粒径均匀,分散性好,尺寸在300nm左右的碳微球。通过浸渍还原法制备了Pt-Sn/CMS,金属颗粒的平均粒径为4.6nm。2.Pt-Sn/CMS催化剂中的Sn元素,以PtSn合金和SnO₂的形式存在。XPS、XRD、TEM均表明,随着Sn元素的加入,出现SnO₂,且金属态Pt的含量下降,形成PtSn合金。3.采用循环伏安法和交流阻抗法得到的Pt-Sn/CMS催化剂的电催化活性优于Pt /CMS。从结构上分析可知,Sn进入Pt晶格后,改变了Pt的面心立方晶格中的d电子结构,使CO在合金表面的吸附状态有所改变,降低了吸附能,起到了活化吸附态（CO）ads作用,使CO容易被氧化形成CO₂,从而提高Pt的催化活性。同时,生成的SnO₂能够在较低电位下提供OHads,OHads与反应中生成的CO进行反应,使Pt活性位得以释放,最终减轻催化剂的中毒。更多还原

【Abstract】 Platinum is the most effective catalyst of direct methanol fuel cells （DMFC） electrode so far. The improvement of electrocatalysis activity and CO oxidation are key points for electrocatalysis of DMFC. On one hand, intermediate（CO） will be strongly adsorbed on Pt in methanol oxidation so that the catalytic activity of Pt reduces. On the other hand, Pt is comparatively expensive as noble metal. So many scholars are studying Pt-M binary catalyst in order to overcome insufficiency of monobasic catalyst. The cost of Sn is cheap, and electrochemical activity of Pt-Sn/C is better, so it is a hot topic in research field.In this paper, PtSn nanoparticles were loaded on Carbon Microspheres（CMS） with impregnation-reduction method. Compare with Pt/CMS, the composition was characterized by X-ray photoelectron spectroscopy （XPS）, Scanning electron microscope （SEM）, X-ray diffraction （XRD）, High resolution transmission electronmicroscopy （HRTEM） and cyclic voltammetry （CV）.The results show that:1.Pt-Sn/CMS catalyst was perpared by impregnation-reduction method. The nanoparticles are well dispersed on the surface of the CMS, and mean particle diameter is 4nm. 2. XRD, XPS indicated that the addition of Sn was mostly in form of both PtSn alloy and SnO₂ in Pt-Sn/CMS catalyst.3. The cyclic voltammetry shows electrocatalysis activity of Pt-Sn/CMS is better than that of Pt/CMS. The results suggest that the presence of Sn, which changes the Pt lattice parameter, allows methanol to be adsorbed and dissociated at lower potentials than that observed on the commercial Pt/CMS catalyst. The Sn sites are always free to adsorb OHads, which prefer to be adsorbed mostly onto Sn sites rather than on Pt sites. Moreover, Sn or Sn oxide are able to form oxygen-containing species at lower overpotentials than Pt. Therefore, Sn or Sn oxide improves the methanol oxidation at lower potentials and increases the reaction rate.更多还原