钯基复合纳米催化剂的合成及催化应用

发布时间：2018-10-10 15:12

【摘要】：乙醇是可以通过农产品大量生产的可再生清洁燃料,使得直接乙醇燃料电池(DEFC)具有广阔的实际应用前景。当前,制约直接乙醇燃料电池发展的瓶颈是阳极电催化剂的活性和稳定性仍然不够,与实际使用要求存在较大差距,阻碍了直接乙醇燃料电池的商业化进程,所以设计和制备高效的阳极催化剂具有重要意义。目前,活性最高的铂(Pt)基纳米催化剂存在易于中毒失活、成本高昂和Pt资源紧缺等问题,研究和开发Pt的替代催化剂成为燃料电池技术发展的重要方向。钯(Pd)基纳米催化剂由于其优异的催化性能、更丰富的资源和更低的价格等优势,已被广泛研究和用作小分子(甲醇、甲酸、乙醇等)燃料电池的电催化剂。通过向Pd基催化剂中引入第二种金属形成合金或制备异质结纳米晶,都可有效改善催化剂性能,但催化剂表面不同金属活性位点间距对催化反应的影响还尚待研究。本论文发展了一种调控Pd-Ni-P三元纳米催化剂中Pd与Ni两种活性位点的间距的新方法,从而显著改善乙醇直接电催化氧化性能,实现了催化剂性能的“表面原子工程”调控。通过液相法制备了不同形貌结构的Pd-Ni-P三元纳米晶,随着Pd/Ni-P哑铃型异质结构逐步转化为Pd-Ni-P复合纳米颗粒,使Pd在Ni-P中逐渐分散为超小的团簇,逐渐减小了 Pd(乙醇催化氧化活性位点)与Ni(羟基自由基形成位点)两种活性位点的间距,降低了两种反应物中间体的距离,增加了其有效碰撞反应几率,从而显著提高乙醇的电催化氧化活性。同时,P的引入可有效防止Ni的流失,从而显著改善催化的稳定性。在1.0 M NaOH和1.0 M C2H5OH的溶液体系中,Pd-Ni-P三元纳米催化剂催化乙醇氧化反应(EOR)的活性提高至4.95A/mgPd,是商业Pd/C催化剂活性的6.88倍,展现了优异的催化活性和稳定性。相关实验结果与密度泛函理论(DFT)计算分析一致,为燃料电池电催化剂的设计合成提供了新思路。
[Abstract]:Ethanol is a renewable and clean fuel that can be produced in large quantities by agricultural products, which makes direct ethanol fuel cell (DEFC) have a broad application prospect. At present, the bottleneck that restricts the development of direct ethanol fuel cell is that the activity and stability of anode electrocatalyst are still not enough, and there is a big gap with the actual application requirement, which hinders the commercialization process of direct ethanol fuel cell. Therefore, it is of great significance to design and prepare efficient anode catalysts. At present, platinum (Pt) based nano-catalysts with the highest activity are prone to deactivation, high cost and shortage of Pt resources. Therefore, the research and development of alternative catalysts for Pt has become an important direction of fuel cell technology development. Palladium (Pd) based nanocatalysts have been widely studied and used as electrocatalysts for fuel cells with small molecules (methanol, formic acid, ethanol, etc.) due to their excellent catalytic performance, abundant resources and lower price. By introducing a second metal into the Pd catalyst to form alloys or preparing heterojunction nanocrystals, the performance of the catalyst can be improved effectively. However, the effect of different metal active site spacing on the catalytic reaction remains to be studied. In this paper, a new method is developed to regulate the distance between the active sites of Pd and Ni in Pd-Ni-P ternary nanocatalysts, which can significantly improve the direct electrocatalytic oxidation of ethanol and realize the "surface atomic engineering" regulation of the performance of the catalysts. Pd-Ni-P ternary nanocrystals with different morphologies were prepared by liquid phase method. With the transformation of Pd/Ni-P dumbbell-shaped heterostructures into Pd-Ni-P composite nanoparticles, Pd was gradually dispersed into ultrasmall clusters in Ni-P. The distance between two active sites of Pd (ethanol catalytic oxidation active site) and Ni (hydroxyl radical forming site) was gradually reduced, the distance between the two reactants was decreased, and the probability of effective collision reaction was increased. Therefore, the electrocatalytic oxidation activity of ethanol was improved significantly. At the same time, the introduction of P can effectively prevent the loss of Ni, thus significantly improving the stability of the catalyst. In the solution system of 1.0 M NaOH and 1.0 M C2H5OH, the catalytic activity of Pd-Ni-P ternary nanometer catalyst for ethanol oxidation of (EOR) was increased to 4.95 A / mg PD, which was 6.88 times of that of commercial Pd/C catalyst, showing excellent catalytic activity and stability. The experimental results are consistent with the density functional theory (DFT) (DFT) calculation and analysis, which provides a new idea for the design and synthesis of fuel cell electrocatalysts.
【学位授予单位】：北京化工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36

【相似文献】