铂基纳米晶晶体有序程度对其氧还原催化性能的影响

Advanced polymer electrolyte membrane fuel cells (PEMFCs) demand oxygen reduction reaction (ORR) catalysts that demonstrate high activity, good durability and affordable precious group metal (PGM) loading. To achieve the goal will require further improvements of the current platinum (Pt) based cathodes in terms of catalyst mass activity at high potentials and better catalyst durability. PtM alloy nanocrystal (NC) catalysts with M being a first row transition metal (M), such as Fe, Co, or Ni have a disordered face-centered cubic (fcc) solid-solution structure in which M and Pt are randomly distributed. When these MPt NPs are exposed to the corrosive conditions in acid-based fuel cells, M is subject to fast etching that leaves a defective Pt surface with low-coordination Pt, which reduces ORR activity and stability. The M stability in the MPt alloy and the activity of MPt catalysts can be dramatically improved once the M and Pt are in an ordered intermetallic structure. The ordered intermetallic structure is formed when there is a strong 3d-5d orbital interaction between M and Pt, which do not exist in the disordered solid-solution counterpart. Due to this strong interaction, M is stabilized much better by Pt in the more close-packed structure, resulting in less M etching under acidic fuel cell conditions. My previous work demonstrated the synthesis of 9 nm fully-ordered fct-PtFe NCs and its excellent catalytic performance for ORR. The primary goal of this project is to develop fully-ordered PtM NC electro-catalysts for ORR in acid media. The effect of NC size, surface micro-profile and the fcc PtM precursor on their phase transformation and catalysis will be investigated. Successful completion of research in these tasks will overcome the grand cathode challenge and lay the foundation for a sustainable, high-energy-density, and low-cost PEMFCs as a prime electrochemical energy conversion system.

质子交换膜燃料电池的商业化应用需要开发具有高活性，高稳定性和低贵金属铂(Pt)用量的氧还原反应催化剂。为了达到这一目标需要显著提高当前铂基阴极催化剂的表现，特别是在高电压时的活性和催化剂稳定性方面。普通PtM合金纳米晶催化剂(M = Fe，Co，Ni)在电池的酸性环境中由于M被腐蚀稳定性较差。将其由无序的面心立方(fcc)转化为面心四方(fct)的金属间有序结构能够利用3d-5d电子轨道间的作用极大的增强M的稳定性从而提高催化剂表现。在前期工作中，本人制备了9 nm完全有序的PtFe纳米晶催化剂。本课题在此基础上，试图进一步研究完全有序PtM纳米晶的制备，尺寸控制和表面微观结构的精细调控。同时研究PtM前驱体结构对fcc-fct相转化的影响，提出促进相转化的有效方式。以期能够加深有序结构纳米晶对电催化性能影响的理解，在此基础上研发有潜力的下一代燃料电池阴极催化剂。

申请人在结构有序的铂基纳米晶催化剂的可控制备及氧还原电催化性能研究方面方面取得了以下成果：（1）发现前驱体氧空位能够促进纳米晶相转化的机制，构筑Pt/MOx核/壳结构前驱体，成功制备3-6 nm的高度/完全有序的L10-PtNi和PtCo高性能铂基纳米晶；（2）对高度有序二元铂基纳米晶进行第三种过渡金属掺杂，进一步对纳米晶的表面应力和表面能进行精细调控，优化其氧还原活性/稳定性，表现出在质子交换膜燃料电池中的应用前景。在Joule, Adv. Energy Mater., Angew. Chem. Int. Ed.等SCI期刊发表论文22篇，申请专利1项。本项目主要研究了结构有序纳米晶晶体有序程度对其氧还原电催化活性的影响，并在理解氧空位对促进纳米晶相转化的机制和设计结构可控的金属催化剂方面提供了一定的参考意义。