新型载体上的钯—钆双金属催化剂在碱性溶液中对甲醇电氧化的催化性能研究

发布时间：2018-03-25 09:33

本文选题：钯-钆双金属　切入点：催化剂　出处：《中国科学院大学(中国科学院过程工程研究所)》2017年硕士论文

【摘要】：直接甲醇燃料电池(Direct methanol fuel cell,DMFC)是一种类型的质子交换膜燃料电池(PEMFC),它直接使用甲醇作为燃料,具有能量转化效率高、安全、环境友好等优点,有望成为运输和便携式设备的电源。然而,DMFC常用的阳极Pt/C催化剂的催化活性和稳定性不够优良,而且Pt金属价格昂贵,这些都成为限制其商业化发展的重要因素。DMFC的阳极催化剂材料由主催化剂和催化剂载体组成。主催化剂是催化材料的活性中心,其性能的提升是催化剂催化活性提高的基础;载体是主催化剂的依附材料,主催化剂均匀的分布在载体表面能够有效的提高主催化剂的利用面积,并且载体材料的特殊电子结构和性能也能够调控主催化剂的电子特性,从而促进催化剂的整体活性。本论文从主催化剂和催化剂载体两方面入手,设计并制备了具有高性能的钯(Pd)-钆(Gd)双金属催化剂,并且以Ti4O7和Mg-Al-LDH作为载体制备了钯基催化剂,以提升催化剂的催化活性。借助透射电子显微镜(TEM)、X射线衍射(XRD)、X射线光电子能谱(XPS)等技术对所制备的催化剂的结构、形貌进行表征。通过循环伏安(CV)、CO Stripping和计时电流法(CA)等测试技术对其电化学性能和稳定性进行了详细的对比和分析。在研究中采用NaBH4还原的方法制备了不同比例的Pd-Gd/C催化剂。XRD结果表明Pd与Gd以合金的形式存在于催化剂中。通过TEM对其结构和形貌进行表征,结果表明金属纳米粒子可以很好的分散在碳黑上,没有发现明显的团聚现象。电化学测试结果表明,20%Pd-10%Gd/C催化剂和其它的催化剂相比具有更高的催化活性。加入的Gd可以移除甲醇电氧化过程中产生的有毒物质CO,所以其促进作用可以用双功能原理进行解释。XPS结果表明,加入的Gd能够增加0价Pd的含量,起到金属化的作用。然后在钛黑载体上用硼氢化钠还原法分别合成了 20%Pd/Ti4O7和20%Pd-10%Gd/Ti4O7催化剂。实验结果发现,在钛黑载体上,Gd金属的添加依然可以提高催化剂的催化活性和抗一氧化碳中毒性,并促进催化剂的长时间作用的稳定性。然而与碳黑载体相比,在碱性介质中对甲醇的电氧化反应的催化性能对比中,钛黑载体的催化剂表现不如碳黑载体的,但是钛黑载体上的催化剂的抗一氧化碳中毒性能较好。与此同时,钛黑的失电子构型使得钛黑上的一些电子会有向Pd偏移的趋势,会导致金属态Pd含量的增加,理论上提高了催化剂的催化活性,而在甲酸溶液中的电化学分析结果正与该理论吻合。可能是由于Ti4O7是离子型晶体,有较强的极性,而甲酸水溶液中甲酸易电离,甲醇的解离很微软。所以在甲酸溶液环境中,钛黑载体性能比较优异,在甲醇溶液中性能则受到限制。最后以钯-镁铝层状氢氧化物为载体制备了 Pd/LDH催化剂。通过TEM对其结构和形貌进行表征,结果表明金属纳米粒子可以很好的分散在碳黑上,没有发现明显的团聚现象。通过XPS分析发现LDH能够增加催化剂中金属Pd的含量。电化学测试结果表明,Pd/LDH具有更高的催化活性。LDH载体能够吸附大量的羟基,可以有效地移除甲醇电氧化过程中产生的有毒物质CO,释放被CO毒化的活性位点,提高抗毒化性能。
[Abstract]:Direct methanol fuel cell (Direct methanol fuel cell, DMFC) is a type of proton exchange membrane fuel cell (PEMFC), which directly use methanol as fuel, has high energy conversion efficiency, safety, environment friendly and other advantages, is expected to become the transportation and portable equipment power supply. However, the common anode Pt/C catalyst DMFC the catalytic activity and stability is not good, but Pt metal is expensive, these have become the anode catalyst material.DMFC important factors to limit its commercial development by the main catalyst and catalyst carrier. The catalyst is the main active center of catalyst materials, the performance improvement is the basis for improving the catalytic activity of the catalyst carrier is attached; the main catalyst material, uniform distribution of main catalyst can effectively improve the utilization area of the main catalyst on the surface of the carrier, and the carrier materials of the special electronic structure and It can also control the electronic properties of the main catalyst, so as to promote the overall activity of the catalyst. This paper from the two aspects of the main catalyst and catalyst carrier, designed and fabricated with high performance palladium (Pd) - gadolinium (Gd) bimetallic catalyst, and using Ti4O7 and Mg-Al-LDH as the carrier prepared palladium base in order to enhance the catalytic activity of the catalyst, the catalyst. By means of transmission electron microscopy (TEM), X ray diffraction (XRD), X ray photoelectron spectroscopy (XPS) structure of the prepared catalysts, morphology were characterized by cyclic voltammetry (CV). CO, Stripping and chronoamperometry (CA) etc. test techniques were compared and analyzed on the electrochemical performance and stability. The method of NaBH4 reduction were used in the research to prepare Pd-Gd/C catalysts with different proportions of.XRD results showed that Pd and Gd exist in the alloy in the form of catalyst. Through the TEM of the node The structure and morphology were characterized. The results show that the metal nanoparticles can be well dispersed in carbon black, no obvious aggregation was found. The electrochemical test results show that compared with the 20%Pd-10%Gd/C catalyst and other catalyst has higher catalytic activity. The addition of Gd can be removed from the methanol electro oxidation process of CO toxic substances, so the promotion can use double function principle to explain the results of.XPS showed that the addition of Gd can increase the content of 0 at Pd, plays the role of metal. Then using sodium borohydride and 20%Pd/Ti4O7 20%Pd-10%Gd/Ti4O7 catalyst reduction method respectively in titanium black carrier. The experimental results show that the titanium black carrier, adding Gd metal still can improve the catalytic activity and resistance to carbon monoxide poisoning, and promote the stability of catalyst for long time. However, compared with the carbon black in the carrier. Comparison of electrocatalytic properties for methanol oxidation in alkaline medium, black titanium catalysts as the performance of the carbon black support, but resistance to carbon monoxide poisoning performance of the catalysts supported on titanium black better. At the same time, titanium black lost electron configuration makes the titanium black some electrons will have to offset Pd trend. Will cause the increase of Pd content of hot metal, theoretically improves the catalytic activity of the catalyst, and the electrochemical analysis in aqueous formic acid solution and the results are consistent with the theory. Ti4O7 is probably due to ionic crystals, with strong polarity, and formic acid aqueous solution of formic acid in methanol dissociation is easily ionized, so Microsoft. In the acid solution environment, the performance of titanium black carrier are excellent in methanol solution properties are limited. Finally the palladium catalyst Pd/LDH was prepared as the carrier. Magnesium hydroxide by TEM on the structure and The morphology was characterized, the results show that the metal nanoparticles can be well dispersed in carbon black, no obvious aggregation found. That LDH can increase content of metal Pd catalyst by XPS analysis. The electrochemical test results show that Pd/LDH has higher catalytic activity of.LDH carrier can adsorb many hydroxyl groups, can effectively remove methanol the electro oxidation process of toxic substances released by CO, the active site of CO poisoning, improve antitoxic properties.

【学位授予单位】：中国科学院大学(中国科学院过程工程研究所)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36;TM911.4

【相似文献】