基于MOFs结构的‘过渡金属-氮-碳’分级多孔氧还原电催化材料的结构设计及功能调控

One of the key scientific issues in the field of fuel cells is the research and development of high-performance and cost effective non-precious metal electrocatalysts for oxygen reduction. Taking advantage of their intrinsic transition metal-nitrogen coordination (Me-N4) and abundant micropores, this proposal intends to adopt metal-organic frameworks, especially the zeolite imidazolate frameworks (ZIFs), as the precursor to prepare the transition metal-nitrogen-carbon (Me-N-C) catalysts with increased active sites and enhanced mass transport. The structure-controlled synthesis of ZIFs will be first investigated by selecting the central metal and imidazolate ligand to optimize the Me-N4 structure and pore diameter. Then, the pyrolysis mechanism of ZIFs with or without the addition of metal, nitrogen and carbon sources will be studied to establish the controllable formation of the hierarchically porous structure for Me-N-C catalysts. Finally, the effect of pore structure and chemical composition on the activity and electrochemical stability of Me-N-C will be investigated to provide informative conclusions to further improve the oxygen reduction performances.

研究开发高性能、低成本的非贵金属氧还原电催化材料是燃料电池领域迫切需要解决的科学问题。本项目以金属-有机骨架化合物（MOFs）中代表性的一类沸石咪唑酯（ZIFs）作为前驱体，利用其独特的金属-氮配位结构（Me-N4）和较大的微孔比表面积，通过调控热解过程构筑微孔-介孔-大孔的分级多孔过渡金属-氮-碳（Me-N-C）氧还原电催化材料，促进Me-N-C催化性能的提升，推动燃料电池氧还原催化剂的低成本化。项目从ZIFs的制备工艺入手，通过调控金属离子半径和咪唑配体长度，从分子层面实现ZIFs组成和孔道结构的有效调控；以ZIFs为前驱体热解制备分级多孔Me-N-C催化剂，优化热解条件，建立ZIFs构筑分级多孔Me-N-C催化剂的调控方法；通过系统的电化学测试，阐明Me-N-C催化剂的氧还原催化性能影响机制，探究分级多孔Me-N-C催化剂的催化机理，为设计和制备高活性的Me-N-C催化剂提供理论依据

项目旨在开发高性能低成本非贵金属氧还原催化剂，以推动燃料电池关键材料氧还原催化剂的低成本化。项目利用含有过渡金属-氮配位结构（Me-N4）且孔道可调的沸石咪唑酯类金属有机骨架材料（ZIFs）作为前驱体，通过调控热解过程构筑微孔-介孔-大孔的分级多孔过渡金属、氮共掺杂炭电催化材料用于氧还原反应，促进了活性位点形成和高分散分布，提高了催化剂孔道的传质能力，从而实现了催化剂催化性能的提升。项目从ZIFs的制备工艺入手，通过调控金属离子和咪唑配体种类，从分子层面实现了ZIFs组成和孔道结构的有效调控，成功制备了核壳结构的ZIF-8@ZIF-67、多面体形貌的双金属Fe,Co-ZIF以及元素梯度分布的圆柱形Fe,Zn-ZIF；以其为前驱体制备了具有分级孔结构的钴、氮共掺杂炭（Co,N-HCNP）、双活性位点的铁、钴、氮共掺杂炭（Fe,Co,N-CNP）以及Fe-N4活性位高度暴露的铁、氮共掺杂炭（Fe,N-HPCC）催化剂。制备的催化剂表现出优异的电催化性能，在0.1 M KOH电解质中，催化剂半波电位最高达到0.898 V，优于商业化Pt/C 51 mV；在0.1 M HClO4电解质中，催化剂半波电位最高为0.76 V，有望应用于质子交换膜燃料电池。