钯基金属间化合物纳米晶的可控制备及氧还原反应中的构效关系

Pd-based intermetallic nanocrystals have been regarded as a promising substitute for Pt-based catalysts towards oxygen reduction reaction (ORR) due to their superior catalytic performance and lower cost. However, it remains a tremendous challenge to controllably synthesize Pd-based intermetallic nanocrystals through a wet-chemistry approach. In addition, the issues associated with disorder-order transition mechanism in the synthesis and structure-property relationship during the catalytic reaction still need to be addressed clearly. In this proposal, Pd-based intermetallic nanocrystals with controlled shapes, structures, and compositions are synthesized through a wet-chemistry approach by manipulating the reaction thermodynamics and kinetics in aim to decrease their disorder-order transition temperature and accelerate the diffusion rate of atoms. The ORR properties catalyzed by Pd-based intermetallic nanocrystals are expected to be substantially enhanced by tailoring the shape, structure and composition in combination with modification of ordering alloy shell on the surface. In-situ liquid-cell transition electron microscopy (TEM) technique is employed to investigate the disorder-order transition process in the atomic level and dynamic, real-time fashion during the wet-chemistry synthesis of Pd-based intermetallic nanocrystals. Based on this study, the critical thermodynamic and kinetic conditions for disorder-order transition are clarified and a general mechanism or method for the formation of intermetallic nanocrystals is constructed. In addition, in-situ electrochemical cell TEM technique is developed to monitor the evolution of shape, structure and composition of Pd-based intermetallic nanocrystals during the catalytic process in the dynamic and real-time fashion. In the atomic level, the effect of shape, structure, composition of Pd-based intermetallic nanocrystals on the ORR properties is investigated and revealed, thereby constructing the structure-property relationship and clarifying the physical-chemistry relative mechanism. As such, these results will provide the key material and theory fundament for the exploitation and development of fuel cells. The successful enforcement of this grant will have scientific significance and commercial value for the development of fuel cells.

钯基金属间化合物纳米晶由于其优越的氧还原性能和更低的材料成本，被认为是铂基催化剂的理想替代材料，但是它们的湿化学法可控制备是目前面临的科学难题。此外，纳米晶形成过程中的无序-有序转化机理以及催化反应中的构效关系还缺乏深入的研究。本项目提出通过调控反应热力学和动力学，降低其无序-有序转变温度，提高原子扩散速度，实现钯基金属间化合物纳米晶的可控制备。通过形貌、结构、成分调控及有序合金化改性提高其氧还原性能。利用液相原位透射电镜技术在原子尺度，实时、动态研究钯基金属间化合物纳米晶无序-有序转化过程，阐明转化的热力学和动力学临界条件，构建普适性原理和方法。进一步利用电化学功能原位电镜技术研究纳米晶在催化过程中形貌、结构、成分的演变过程，在原子尺度揭示它们对氧还原催化性能的影响规律，建立构效关系，阐明相关物理化学机制。为燃料电池的开发和应用提供关键材料与理论支撑，具有重要科学意义和商业价值。

Pd基金属间化合物纳米晶由于具有有序的原子排列，固定的晶体结构，负的形成焓以及强的电子耦合作用，被认为是一类有前景的燃料电池反应催化剂，也是Pt基催化剂的理想替代材料。然而，金属间化合物的形成常需要克服较大的势垒，其湿化学法制备是一个难题。同时，Pd基金属间化合物的活性和稳定性提升以及催化反应机理还需要深入研究。本项目首先发明了修饰剂辅助的热力学和动力学调控新方法，促进原子间的互扩散，可控制备了Pd3Pb方形纳米片和超薄花状金属间化合物纳米晶，显著提高了氧还原反应性能，揭示了晶面效应，电子耦合效应及位点效应对性能提升的作用。其次发明了Au、Ga掺杂改性提升Pd基金属间化合物氧还原性能的新方法，制备了Au掺杂的Pd3Pb纳米线与Ga掺杂的Pd3Pb方形纳米片，阐明了电子耦合效应对氧还原催化性能的影响规律并建立了构效关系，显著提升了其性能。然后构建了Pd基金属间化合物核壳纳米结构，可控制备了Pd3Pb@PtmPb核壳立方体，显著提升了氧还原和甲醇氧化性能，阐明了特异配体效应和双功能效应的作用。最后发展和利用原位电镜技术揭示了Pd基催化剂的刻蚀机理，阐明了应力大小、类型和曲率对催化剂稳定性的影响规律，为设计高性能的氧还原催化剂提供了新思路和方法。通过本项目的研究，为Pd基金属间化合物纳米晶的发展和应用提供了理论数据和关键基础，具有重要的科学意义和商业价值。