石墨烯负载新型铂基核壳凹型纳米晶的可控制备及其催化性能研究

Platinum (Pt) as a noble-metal is the most widely used electrocatalyst in low-temperature fuel cell. However, the extremely precious price and scarce resource of Pt together with the slow reaction kinetics of cathode are the major obstacles to fuel cell for widespread commercialization. As such, synthesizing the electrocatalysts with features of high activity, good stability, and low percentage of Pt is of great importance for promoting the commercialization development of fuel cell. In this proposal, graphene-supported Pt-based core-shell concave nanocrystals will be controllably constructed by several strategies including shape control, structure design, and composition tuning, which is expected to solve the scientific problems in fuel cell such as low catalytic activity and poor stability for oxygen reduction reaction (ORR) as well as low Pt usage. A kinetically-controlled strategy is proposed to controllably synthesize Pt concave nanocrystals with high-index faced exposed on the surface. The kinetic growth mechanism for producing these concave nanocrystals is clarified by in-situ TEM technique. The general method presented here can be extended to synthesize concave nanocrystals made of other materials. The catalytic properties for ORR are substantially optimized and enhanced by varying the shape and exposed facets of Pt concave nanocrystals. A seeded epitaxial growth is exploited to synthesize Pt-based core-shell concave nanocrystals. In addition, the scientific problems of Pt-based electrocatalysts such as low activity, stability, and Pt usage are further solved by alloying with transitional metals such as Ni and Co, and compositing with graphene. The physical and chemical mechanisms presented in the formation of these nanocomposites and enhancement of ORR performances are also clearly revealed. The successful enforcement of this grant will have scientific significance and commercial value for the development of fuel cell.

低温燃料电池主要采用贵金属铂作为电催化剂，其高昂的成本、资源的稀缺性以及缓慢的阴极氧还原速度已成为限制燃料电池商业化推广的主要障碍。因此，研制高活性、高稳定性、低铂含量的电催化剂对推动燃料电池的发展具有重要意义。本项目通过形貌调控、结构设计、成分优化等手段构建石墨烯负载铂基核壳凹形纳米晶复合结构，期望解决低温燃料电池中氧还原催化剂活性不高、稳定性差，铂利用率低和使用量高等科学问题。提出动力学控制的方法制备高指数晶面外露的铂凹形纳米晶，利用原位透射电镜技术揭示其动力学形成机理，并形成普适性方法。通过调控铂凹形纳米晶的形貌和外露晶面，优化并提高其氧还原活性。利用种子辅助外延生长技术实现铂基核壳凹形纳米晶的可控制备，并通过镍、钴等过渡金属的合金化改性以及与石墨烯的复合协同作用进一步提高催化剂的活性和稳定性、降低铂的使用量，同时揭示相关的物理化学机制，具有重要的科学意义和商业价值。

低温燃料电池主要采用贵金属Pt作为电催化剂，其高昂的成本、资源的稀缺性、易被CO中毒以及缓慢的阴极氧还原速度已成为限制燃料电池商业化推广的主要障碍。因此，研制高活性、高稳定性、低Pt含量的电催化剂对推动燃料电池的发展具有重要意义。我们基于热力学和动力学调控的原理，构建了两类合成Pt基凹形纳米结构的新方法。基于修饰剂辅助的热力学调控的原理，成功制备了Au@Pt核壳五角星和Pd@Pt核壳六角和八角等凹形纳米结构。基于动力学原理，通过调控原子的沉积速率和反应速率的比例，成功制备了PtCu合金和PtPd合金凹形立方体等凹形纳米结构。系统研究了上述凹形纳米结构的氧还原、甲醇氧化和甲酸氧化性能，与商用的催化剂相比，其催化性能获得了显著的提高。阐明了晶面效应、应力效应、电子耦合效应和双功能效应等对催化性能提高的作用和贡献，为设计新型高性能的催化剂提供了新思路和方法。利用原位透射电镜等技术系统研究了PtCu等凹形纳米结构的动力学形成机理，揭示了欠电位沉积过程、置换反应以及相分离对形成凹形纳米结构的作用，为制备新型凹形纳米结构提供了途径。研究了Au、Pd、Cu等金属改性以及与石墨烯复合对Pt基凹形纳米晶催化性能的影响，建立了构效关系，显著提高了催化剂的活性与稳定性。通过本项目的研究，为研发高性能的燃料电池催化剂提供了理论基础和关键材料，具有重要的科学意义和商业价值。