基于非贵金属内核-PtRu合金壳层的核壳结构催化剂抗中毒性能研究

An important challenge for the commercialization of proton exchange membrane fuel cell (PEMFC) is the high cost and low anti-poisoning capability of Pt-based noble metal catalysts. Catalysts with core-shell structure can reduce the amount of noble metal. At the same time, the property and composition of the core affect the electronic structure of the shell metal, adjusting the anti-poisoning capability. Under the low potential and reducing atmosphere in the anode, noble metals prefer to surface enrichment, and the non-noble metal core will be stabilized. Therefore, it is possible to reduce the amount of noble metal greatly using non-noble metal as the core for anode core-shell structured catalysts. Combining the superior CO tolerance of PtRu alloy, this project aims to investigate the anti-poisoning capability of core shell structured catalysts using non-noble metals with different properties (Cu, Ni and SnOx) as the core and PtRu alloy as the shell. Electrochemical methods and in situ spectroscopic characterization techniques are used to investigate the effect of ligand and strain effect of the core and the synergistic effect between the shell components on anti-poisoning capability of core-shell structured catalyst, and the anti-poisoning mechanisms of core-shell structured catalyst with different cores will be clarified. Based on these results, the relationship among the composition and structure of core, electronic structure of shell metal, and anti-poisoning capability of core-shell structured catalysts will be established, providing a theoretical basis for further design and preparation of novel anode catalysts with low amount of noble metal and high anti-poisoning capability for PEMFC.

铂基催化剂价格昂贵且易被毒化是质子交换膜燃料电池(PEMFC)商业化面临的重要挑战。核壳结构催化剂不仅可降低贵金属用量，而且内核组成也会影响壳层金属的电子结构，进而调变其抗中毒性能。在阳极低电势和还原性气氛下，贵金属倾向于向表面富集，非贵金属内核不易流失，这为大幅度降低阳极催化剂的贵金属用量提供了可能。结合PtRu合金优越的抗CO性能，本项目旨在研究基于三种不用性质和组成的非贵金属内核(Cu，Ni和SnOx)-PtRu合金壳层核壳结构催化剂的抗中毒性能：通过电化学方法和原位谱学表征技术等研究内核的配体和应力效应以及壳层组分间的协同效应等对核壳结构催化剂抗中毒性能的影响，阐明基于不同内核组成的核壳结构催化剂的抗中毒机理；建立核壳结构催化剂组成和结构、表面电子性质与抗中毒性能之间的关联，为设计和制备新型低贵金属用量和高效抗中毒PEMFC阳极催化剂提供理论依据。

本项目针对燃料电池电催化剂性能和成本的局限，结合研究组和申请人分别在新型纳米多孔材料和燃料电池领域的多年研究基础，开展了以非贵金属为内核、外层富Pt或PtRu的核壳结构催化剂的可控合成和电催化特性及机理研究：通过调控实验参数如气氛组成、温度、加热方式及时间等热力学和动力学因素，多元醇法结合还原热处理和碱溶方法成功合成表面富PtRu内核为SnO2的核壳结构催化剂，经过碱溶处理后的催化剂的电化学催化活性明显高于原始制备的催化剂和H2还原处理的催化剂，主要源于PtRu合金的表面聚集和PtRu与SnO2间的协同作用。利用金属置换反应和退火处理，成功合成了以PtRu合金为壳层，PtNi合金为内核的核壳结构催化剂，研究了置换时间、浓度和pH值等条件对壳层合金度的影响，及其对电化学性能及PEMFC电池性能和抗CO中毒性能的影响，300 oC H2气氛中进行退火处理，可以提高表面PtRu的合金度，进而提高催化性能CO电催化剂活性，原因归结为低电位下催化剂表面Ru的亲氧性能和吸附态CO与Pt活性位的弱吸附能。利用不同Fe前体浸渍Pt/C催化剂，经过高温还原、酸溶和退火处理得到表面富Pt的PtFe@Pt/C催化剂，可有效抑制催化剂在酸性环境中溶解，提高催化剂的电化学活性，研究了Fe前体和还原温度对催化剂结构和性能的影响，由柠檬酸铁铵和氯化铁前体制备的催化剂电化学活性表面积较大，氧还原活性较高。以ZIF系列金属有机框架材料为前躯体进行高温碳化，原位制备出了氮掺杂多孔碳材料担载Co纳米粒子，测试了不同Co/Zn比例的Co/N-C系列催化剂的结构组成和电化学氧还原活性，不同Co/Zn比例得到的氮掺杂多孔碳材料担载Co纳米粒子的氧还原活性存在较大差别，Co/Zn为0.75的催化剂在室温下的氧还原活性最高，接近商品化40 wt.% Pt/C催化剂，是具有潜力的贵金属替代品。