燃料电池阴极Pt-Fe/C纳米线粒体网络电催化剂研究

The project is to overcome several factors including the high costs of the traditional electrocatalysts, the sluggish kinetics of oxygen reduction reaction (ORR) and the relatively low durability for proton exchange membrane fuel cells (PEMFCs), and it also investigate the preparation methods and the scientific problems of the Pt-Fe/C alloy nanowires networks structure catalyst (Pt-Fe/C NWNs). This project will be employed two aspects to improve electrocatalytic activity, e.g., by the incorporation of a second element (alloying) and through nanostructure control strategies, and we adopt the synthesis of platinum-iron alloy nanowire networks (Pt-Fe/C NWNs) using a simple and inexpensive surfactant cetyltrimethylammonium bromide (CTAB) based soft-template procedure. Through the unique morphology and structure of catalyst were controlled, in order to realize high mass transfer, electron transport, precious metals utilization efficiency and durability. Investigation of synthesis conditions affect catalyst structures and performance, so as to determine the best preparation conditions; The Pt-Fe/C NWNs prepared under the best synthesis condition act as cathode catalyst, and study the cell performance and durability, and analyzes highly activity and long durability mechanism of Pt-Fe/C NWNs. The studies in the project will not only to fuel cell technology plays a positive role in promoting the progress, but also will understand Pt-Fe/C NWNs forming mechanism and the control strategy, and understand deeply the fuel cell catalyst complicated system and relationship of "preparation-structure-performance" understanding of the relationship.

本项目以克服质子交换膜燃料电池传统阴极催化剂的氧还原动力学较慢，耐久性偏低以及成本较高等问题为出发点，研究Pt-Fe/C合金纳米线立体网络电催化剂(Pt-Fe/C NWNs)的制备方法及其中的科学问题。本项目将从催化剂组成和结构调变两个方面来进行，拟用阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)为软模板合成Pt-Fe/C NWNs。通过对该催化剂独特形态和结构的控制，以期实现较高的传质、电子传输、贵金属利用率和耐久性。考察合成条件对催化剂结构和性能影响，从而确定最佳的制备条件；以最佳的条件合成Pt-Fe/C NWNs作为燃料电池阴极，研究其发电性能和耐久性，并分析Pt-Fe/C NWNs的高活性和长耐久性机理。本项目研究不仅会对燃料电池技术进步起到积极推动作用，还会增进对Pt-Fe/C NWNs形成机制和控制策略理解，从而加深对燃料电池催化剂复杂体系"制备-结构-性能"关系的认识。

本项目主要涉及四大部分研究内容，即甲酸还原法合成PtNWs/C的制备条件优化；软模板法合成Pt-Fe NWNs/C和Pt-Co NWNs/C的制备条件优化、PtNWs/C在千瓦级电堆上的应用及耐久性研究。结论如下：(1) 当还原剂用量和反应时间分别为30 ml和72h时，形成均一的纳米线结构PtNWs/C，其电化学活性最好；其最大率密度达到748.8mWcm-2，高于商业Pt/C (715.4mWcm-2)。(2) 商业Pt/C和PtNWs/C催化剂经过1500 cycles加速老化后，Pt/C的ECSA衰退率为23.3%，而PtNWs/C的ECSA衰退率仅为3.1%，说明PtNWs/C的耐久性好于Pt/C。也对Pt/C和PtNWs/C制成的MEA进行14 h高电势下(1.5 V)加速老化测试，结果显示Pt/C制成MEA的ECSA发生了很明显衰退，而Pt NWs/C的 ECSA衰退很少。(3) 由15片250cm2的MEA组成1.5kW电堆，经过420h动态工况运行，电堆平均单片电池平均衰退率14.4%。(4) 采用软模板法合成Pt-Fe NWNs/C催化剂。当还原剂用量为0.4g时，Pt-Fe/C形成纳米线立体网络结构(Pt-Fe NWNs/C)。CV和LSV结果表明，当还原剂用量为0.4g时，其ORR活性最好，优于商业Pt/C催化剂。(5) 考察了制备条件对Pt-Co结构和性能影响。研究表明：当还原剂用量为0.4g NaBH4，搅拌速度为1000rpm，表面活性剂CTAB浓度为40mM时，Pt-Co形成纳米线网络结构，表现出最佳的电化学性能，优于商业Pt/C催化剂。 (6) 探索了Pt-Co NWNs/C的不同制备流程。Pt-Co NWNs的比质量活性为商业Pt/C的1.5倍。3000圈测试之后，Pt/C的ECSA下降了34.2%，而Pt-Co NWNs/C仅为14.7%。 (7) Pt-Co NWNs/C和Pt/C的最高比质量功率分别为1.29和1.23 kW gPt-1；表明Pt-Co NWNs/C发电性能优于Pt/C。在电流密度恒定为1000 mAcm-2运行100 h后，以Pt/C和Pt-Co NWNs/C制备MEA的最大功率密度分别衰减了99.4 mWcm-2和71.4mWcm-2。结果显示Pt-Co NWNs/C表现较好的稳定性。