一步法表面凹陷钯纳米多面体的可控制备及其电催化性能研究

As a superior catalyst, palladium nanocrystals have gained exceptional attention in recent years. To optimize their catalytic ability, a variety of shapes have been synthesized and investigated, including cube, octahedron, tetrahedron, decahedron, icosahedron, bipyramid, plate, bar, rod, and wire. Corresponding research has demonstrated that the particle catalytic activity and stability are correlated with their shapes. Particularly, because of the presence of lowcoordinate atomic steps and kinks at high densities, nanoparticles with concave surfaces have intrinsically higher catalytic ability than their convex counterparts. Thus, the research of Pd nanocrystals with concave surface has been of particular interest. However, due to their higher surface energy, concave surfaces are much harder to form than convex ones on nanoparticles. Despite recent progress, it remains a challenge to fabricate Pd concave nanocrystals by a simple and rapid route in seed-free aqueous solutions and control the degree and morphology of concavities. In this project, we propose to investigate one-step controllable synthesis of concave nanocrystals of palladium and their enhanced electrocatalytic performance. Various concave palladium nanocrystals with high quality and monodispersity, like cubes, octahedrons, right bipyramid and 5-fold twinned nanorods, will be synthesized kinetically from a fast one-step wet chemical method in an aqueous solution. We will focus on the modulation of surface curvature and morphology by controlling kinetically the reducing rate in the initial stage of reaction and during the reaction, respectively. It is expected that the high-efficiency palladium catalyst, which has superior catalytic activity and stability in formic acid and ethanol electrooxidation over the normal Pd nanocrystals and commercial Pd/C, will be achieved. This project has important sense in promoting the application of high-efficiency and low-cost concave palladium nanocrystals in catalysis.

近年来纳米钯催化剂的研究引起很大关注。相对于传统体材料催化剂，纳米钯的使用可以减小成本，同时提高催化效率。表面凹陷结构纳米颗粒富含低配位的台阶、扭结原子，展现更高效催化性能，有望成为新型高效纳米催化剂。但由于具有更高表面能，表面凹陷纳米颗粒合成困难，合成工艺的复杂性对应用和性能形成限制。本项目以发展低成本、高效表面凹陷纳米钯催化剂为目标，系统开展一步法表面凹陷钯纳米多面体的可控制备及电催化性能研究。利用一步湿化学合成方法，通过反应过程动力学控制，制备高质量、高单分散性的立方、八面、直角双锥，以及五次对称孪晶等纳米多面体。通过控制起始还原速度和反应中还原速度，精确调控多面体颗粒的凹陷程度与形貌。研究具有不同凹陷结构纳米多面体的电催化性能，建立凹陷结构与纳米多面体电催化性能的联系，指导具有高效电催化性能纳米颗粒的合成。本项目的开展，对于促进表面凹陷钯纳米多面体颗粒在催化领域的应用具有重要意义。

表面凹陷的贵金属钯纳米多面体具有大的比表面积，且它的高指数表面富含低配位的台阶原子和扭结原子，其在电催化应用中展现了优异的性能。然后由于高的表面能的限制，表面凹陷的钯纳米多面体的可控合成一直是个难点，通过合成表面凹陷的多面体来提高表面的电化学反应活性难以实现，因此阻碍了其应用的发展。在本项目的支持下，我们在表面凹陷的钯纳米多面体的可控制备及其电催化性能研究等方面取得重要进展：通过一步水相合成方法，我们实现了表面凹陷钯纳米立方体、表面凹陷钯纳米直角双锥体、表面凹陷钯纳米五次孪晶纳米棒等的制备；通过籽晶生长法，我们实现了表面凹陷钯立方八面体的制备。同时，我们通过控制反应动力学可以调制凹陷表面的形貌和凹陷程度；通过选用不同还原能力的还原剂选择性实现不同晶面的凹陷。我们提出一种动力学生长模型解释凹陷表面的形成机制，从而为其他表面凹陷多面体的可控合成提供了新的思路。在此基础上，我们优化了表面凹陷钯纳米多面体在甲酸、乙醇氧化反应中的催化活性，并对凹陷表面与性能提高展开了深入研究。我们的工作有力推动了金属钯纳米多面体在电催化领域的应用。