【作者】 徐佳；

【导师】 方莉；

【作者基本信息】 山西大学 ， 物理化学， 2010， 硕士

【摘要】 铂催化剂是一种具有较高电催化活性的燃料电池催化剂,但是甲醇的解离吸附产物CO容易使铂中毒。目前抗CO中毒能力最强的双金属催化剂是PtRu合金,但在阳极反应中发生的Ru溶出损失一直是一个难题。而作为最有前景的双金属阳极催化剂PtRh,相关的研究报道大都局限于Rh修饰Pt电极的制备与应用,很少涉及表面合金和实质性催化剂的制备与应用。本论文以Pt网为模型电极催化剂,以甲醇的电化学氧化作为探针反应,采用强迫沉积法在铂网表面制备了沉积结构及Pt、Rh含量不同的沉积层,通过循环伏安法对催化剂进行了表征,并研究了甲醇的电催化氧化行为。在此基础上,以石墨为载体,通过在超声波作用下化学还原制备了5%Pt(记作：Pts／C)催化剂基底,考察了不同焙烧温度、还原温度对Pts／C催化剂基底的影响；然后,通过强迫沉积法制备了不同的PtxRhy/Pt5/C、PtxRhyPtz/Pt5/C“三明治”式沉积层,采用循环伏安法研究了Pt、Rh沉积结构和沉积量改变,以及焙烧还原气氛对负载PtRh合金催化剂制备的影响,采用X-射线衍射(XRD)手段对催化剂表面的形态和组成进行了表征,并考察了催化剂在甲醇电化学氧化中的催化活性。结果表明：(1)采用强迫沉积法均可以使纯Rh和PtRhPt“三明治”式结构沉积在Pt网上形成取向附生的沉积层。对于纯Rh沉积层而言,甲醇氧化起始电势没有下降,但峰顶电势略降低了40mV；随着Rh覆盖度增大,使得甲醇氧化电流密度大幅度减小。而PtxRhyPtz“三明治”结构沉积层在沉积过程中形成了部分合金,改变了催化剂表面特性,从而提高了催化剂的催化活性和稳定性。甲醇在Pt1Rh8Pt1“三明治”结构沉积层的氧化电势比纯Pt表面降低了45 mV,氧化电流密度提高了40%。(2)采用400℃下焙烧的Pt5／C作为催化剂基底,对比不同焙烧温度下制备的Pt5／C基底,起始氧化电势和峰顶电势几乎没有变化,但是从峰电流来看,在400℃下焙烧制备的Pts／C催化剂基底峰电流最高。(3)采用强迫沉积法将不同含量的Pt、Rh沉积在Pts／C基底上制备了三明治式沉积层,在300℃下焙烧、150℃还原后形成了很好的合金,由Pt0.1Rh2/Pt5/C“三明治”式沉积层形成的PtRh/Pt5/C合金催化剂表现出较好的催化活性。甲醇在PtRh/Pt5/C催化剂表面的氧化峰顶电势与Pt5／C基底相比起来降低了60 mV。更多还原

【Abstract】 It is well known that Platinum is the most efficient catalyst in the direct methanol fuel cells. However, Platinum is easily poisoned by chemisorption of CO produced by dissociative adsorption of methanol. By far, PtRu bimetallic catalysts are the most acceptable catalysts to tolerate CO. Nevertheless, the ruthenium loss during the anode reaction at working condition is a severe problem, due to the unstablilty and solublility of ruthenium. Pt-Rh catalysts are considered to be the most promising bimetallic anode catalyst candidate. And recent research has mostly focused on the preparation, characterization of rhodium modified platinum single crystals and their applications in electro-oxidation of CO, CH3OH, CH3CH2OH, etc. There have been few papers concerning the formation and characterization of surface alloys, the preparation of actual supported PtRh alloy catalysts.Firstly, the preparation and characterization of PtRh bimetallic film on the Pt mesh with different content of Pt, Rh by force deposition were studied and the effects of the variation of the deposit structure and the catalytic in the methanol electrooxidation were investigated by means of cyclic voltammetry (CV). Then, using graphite as the carrier, Pt5/C substrate was prepared by formaldehyde reduction at ultrasonic enviroument. The effects of different calcination temperature and different reduction temperature to the catalytic properties of Pt5/C were studied. On the Pt5/C substrate, PtxRhy/Pt5/C、PtxRhyPtz/Pt5/C "sandwich structure" layers were deposited by force deposit method. The effects of the variation of the deposit structure, the amount of Pt, Rh and reduction atmosphere on the formation of supported PtRh alloy were studied via CV and X-ray diffraction (XRD), and the methanol catalytic electrooxidation on the surface fo above catalysts were studied as well.The results are as follows:(1) It is observed that both pure Rh and PtRhPt sandwich structure deposit growth are epitaxial on the Pt mesh by force deposition. For pure Rh deposits, there is no siganificant change for the onset potentials of methanol oxidation, but the peak potential of methanol oxidation on the reduced catalysts was 40mV lower than that on the pure Pt mesh, with the Rh coverage increases, the current density of methanol significantly reduced. The PtRhPt sandwich structure deposit on Pt mesh formed partial alloy during the deposition process, which showed better catalytic activity and stability. The peak potential of methanol oxidation at Pt1Rh8Pt1 was 45mV more negative than that on pure Pt mesh, while the oxidation peak current intensity increased by 40%.(2) The self-made Pt5/C substrate possesses similar properties as Pt polycrystal electrode. The calcination temperature has less effect on the catalytic activity of the Pt5/C substrate. The only difference is the current density of methanol oxidation on Pt5/C calcined at 400℃was higher than on those calicned at other ptemoratures.(3) Similar to PtRh alloy formed on Pt mesh, epitaxial PtRh alloy formation are observed on Pt5/C substrate. Therein, PtRh surface alloy derived from Pt0.1Rh2/Pt5/C sandwich structure shows better catalytic activity in methanol electrooxidation, which the oxidation potential was 60mV negative shift compared to that on pure Pt5/C.更多还原