单原子层贵金属修饰的钯基核壳结构纳米粒子的可控制备及电化学性能

Pt is currently one of the key components for fuel cell catalysts. In this regard, it is of great interest to enhance the utilization efficiency of Pt or explore non-Pt catalysts for fuel cell application. Recently, Pd-based nanomaterials as catalysts for oxygen reduction reaction (ORR) have attracted much attention because their unique properties, such as the similar properties to Pt, and the relatively low cost compared with Pt. We are planning to synthesize Pd-based core-shell structure nanoparticles by using a simple, effective and mass-producible method. Different from conditional wet chemical reducing method, which need to add plenty of surfactant to form the core-shell structure. The prepared Pd-based core-shell structure nanoparticles will be used as electrocatalysts for the ORR. The electronic structure of the catalysts could be tuned by adding different 3d-transition metals, or choose different temperature and atmosphere, which would change the adsorption energy of oxygen, and thus affect their electrocatalytic activities for the ORR. XRD, HRTEM, and XPS techniques will be used to characterize the physical properties of the as-prepared nanoparticles. We can get structure-activity relationship between the physical properties and the electrochemical performance, which will guide the synthesis of the best nanocatalyst. The electrocatalytic activity and stability of Pd-based core-shell structure nanoparticles could be further enhanced by a monolayer of Pt or Au decoration on the surface by using a spontaneous displacement method.

贵金属铂（Pt）是目前质子交换膜燃料电池阴、阳极催化剂均不可缺少的关键元素之一，提高Pt的利用率和发展非Pt催化剂是燃料电池催化剂研究的重要课题。近年来，钯（Pd）基合金纳米材料由于其特殊的性质被用于氧还原催化剂的研究备受关注。本项目拟以Pd基合金纳米粒子为研究对象，采用简单易操作的制备方法，大批量制备Pd表面富集的核壳结构的纳米粒子用于燃料电池电催化剂。拟通过加入不同的3d过渡金属元素和控制后处理的温度和气氛来调制核中Pd的电子结构，从而影响壳层Pd对氧的吸附能，进而提高其对氧还原反应的电催化活性。拟采用XRD、HRTEM、XPS等测试技术，对催化剂进行全面的物理特性表征。拟将催化剂纳米粒子的物理性质与电化学性能相关联，找出其构效关系，从而指导最优催化剂的合成方向。最后拟在所选出的最优催化剂纳米粒子表面采用自发置换的方法在其表面修饰单原子层的Pt或者Au以进一步提高催化剂的活性及稳定性。

基于Pd与Pt相似的结构、物理化学性质以及储量和价格方面的优势，研究和开发Pd基催化剂有重要的理论和实际的应用价值。本项目采用浸渍-还原法，向Pd催化剂中加入3d-过渡金属（Co, Zn, Cu, V, Fe），通过调控过渡金属元素的种类、原子的比例和后处理温度，制备了Pd-V/C、Pd-Fe/C、Pd-Co-Zn/C、Pd-Co-Cu/C系列催化剂。实验结果表明，Pd3V/C、Pd8CoZn/C、Pd6CoCu/C和O-PdFe/C表现出良好的氧还原催化活性，这主要归功于3d-过渡金属的存在能改变Pd的电子结构，从而降低Pd对氧的吸附能，进而提高对氧还原反应的催化活性。为了进一步提高催化剂的性能，采用自发取代的方法，将少量的Pt或者Au修饰在Pd-基催化剂表面。实验结果表明：Pt修饰后催化剂的活性和稳定性均有明显提高，但是，Au修饰只能提高催化剂的稳定性不能提高催化剂的活性。最后，将Pd6CoCu@Au/C催化剂用于燃料电池系统进行实际燃料电池测试，表现出了较高的功率密度和较好的稳定性。