PEMFC新型氧化物与铂基金属的梯级核壳结构催化剂之构筑及作用机理研究

Proton exchange membrane fuel cells (PEMFCs) are being considered as high-efficiency and low-emission alternative power sources for stationanry and transportion applications. Before mass-market penetration, however, the high-cost and low-life problems of PEMFCs must be addressed, which is mainly due to the usage of platinum (Pt) as the cathode catalyst for oxygen reduction reaction (ORR). To develop highly active and stable ORR catalysts, we propose the novel concept of hierarchical core-shell catalysts (MOx@[M'@Pt]) that consist of metal oxides (MOx) uniformly decorated by Pt-based core-shell (M'@Pt) metal nanoparticles. This project will explore efficient synthetic strategies for the hierarchical MOx@[M'@Pt] catalysts, and clarify their ORR activity (including the tolerance to impurity poisoning) and electrochemical stability. At first, an efficient approach is proposed and thoroughly investigated to synthesize the MOx@[M'@Pt] catalysts with controlled shapes and compositions. On the basis of thus obtained catalysts,the catalytic activity towards the ORR, the tolerance to poisoning and the electrochemical stability of such MOx@[M'@Pt] catalysts are evaluated. Further, by combining the in-situ and ex-situ experimental techniques as well as quantum chemistry computations, the interactions (e.g., electronic effect and geometric effect）between metal oxides and Pt-based core shell metal nanoparticles, and their underlying relationships with the activity and stability enhancement are analyzed in great details. Finally, the design principle of the MOx@[M'@Pt] catalysts will be theoretically established, and the highly active and stable MOx@[M'@Pt] catalysts will be the constructed and optimized, accordingly. The implementation of this project will broaden and enrich the electrocatalytic theories of fuel cells, and provide new strategies for the design and controlled synthesis of the ORR catalysts with high activity and durability, which is significantly beneficial to the development of PEMFCs.

氧还原（ORR）催化剂的活性和稳定性是决定质子交换膜燃料电池成本和寿命的关键因素。本项目结合氧化物（MOx）与Pt基金属核壳（M'@Pt）催化剂的各自优点提出了梯级核壳结构MOx@[M'@Pt]催化剂的新思路，考察该催化剂的可控制备并重点研究其工作原理，旨在探索提高ORR催化剂活性和稳定性的新途径。项目首先研究MOx@[M'@Pt]催化剂的可控构筑方法和原理，有效调控其组成、结构；在此基础上，系统考察催化剂的ORR活性（含耐毒化能力）和稳定性，重点结合原位、非原位实验和量子化学计算等技术研究氧化物和Pt基金属核壳颗粒的相互作用对催化活性、稳定性的影响及机制；最后建立高活性、高稳定MOx@[M'@Pt]催化剂的设计原则，并据此构筑和优化该催化剂。本项目的实施有助于丰富和完善燃料电池电催化的理论基础，为构筑高活性、高稳定ORR催化剂提供新的突破口和理论依据，对促进燃料电池的研发具有重要意义。

燃料电池电催化剂的活性与稳定性是决定质子交换膜燃料电池成本和寿命的关键因素。本项目针对ORR、MOR等电催化剂存在的关键科学问题，通过构筑核壳结构、合金化、掺杂等手段制备了M'@Pt、M'Pt/C和MOx@Pt/C等电催化剂，通过评价其催化活性、稳定性来调控其结构、组成。制备了梯级核壳Pd-Ir-Ni纳米粒子，发现该材料的ORR比活性相对于Pd/C得到了极大改善，通过分析发现特殊的结构诱导Pd表面产生压缩的晶格应变，晶格应变的产生有助于提高ORR性能，同时，该结构也防止了Ni的溶出，进而提高了该材料的稳定性。纳米合金化同样有助于改善材料的ORR活性，制备了Pd3Fe金属间合金纳米粒子，研究其ORR活性发现材料在0.8 V下的比活性是Pd/C的2.6倍，经分析表面金属间合金的形成有助于调控晶格应变能以及彼此间的电子结构，进而改善ORR活性。为了改善阳极电氧化催化剂存在的问题，制备了Pd-CeO2@C纳米复合催化剂，显著提高了其乙醇氧化活性及稳定性，研究发现在催化剂表面丰富的含氧物种有助于氧化去除CO等毒性中间产物，并且独特的结构也有利于改善其稳定性。总之，本项目的研究工作主要是通过物理表征并结合电化学测试手段，深入分析了氧气、甲醇分子等在阴极、阳极的反应过程，揭示了O2分子在ORR过程中O-O键的变化情况及MOR过程中吸附在活性位表面的含氧中间产物类型及吸附强度，阐明了ORR、MOR在催化剂表面的反应机理，最终得出ORR、MOR等在催化剂表面活性增强的内在反应机制，并据此构筑和优化催化剂结构。本项目开展的研究工作有助于丰富和完善燃料电池电催化的理论基础，为构筑高活性、高稳定的电催化剂提供新的突破口和理论依据，对促进燃料电池的研发具有重要意义。

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