吡啶氮主导的高密度、单原子分散Fe-N-C高效氧还原催化剂的可控制备及性能研究

Fe-N-C carbon-based non-precious metal catalysts have attracted much attention because of their high oxygen reduction catalytic performance in acidic media. However, carbon based catalysts usually suffer from (1) low density, accessibility and specific activity of active sites; (2) the lack of a reasonable hole structure will impede mass and electron transfer, and reduce areas of reaction interface. Here, in this project, high concentration of single-atom dispersed Fe-Nx and pyridinic nitrogen modified carbon-based non-precious metal catalysts with three-dimensionally ordered interconnected meso-macroporous hollow shell structure were design and prepared using complexs chelated by pyridine polymer and Fe as sole precursor and “interconnected two types of SiO2 nanospheres templates (meso-/macroporous)” as templates. Analyzing the influence of the density and distribution of the active sites and pore structural parameters on the oxygen reduction reaction performance; and elucidating the composition–structure–activity relationships for Fe-N-C carbon-based non-precious metal catalysts in oxygen reduction reaction. The research results are expected to provide theoretical basis and technical support for the design of high performance carbon-based non-precious metal catalysts.

Fe-N-C碳基催化剂由于在酸性介质中具有较高的氧还原反应（ORR）催化性能，被认为是最有前景的一类非贵金属氧还原催化剂。针对目前碳基催化剂存在活性位密度、利用率低及单点催化活性低；缺乏合理的孔结构，由此带来传质、传荷受限以及有效反应界面减少等问题，本项目采用吡啶类高分子聚合物螯合Fe作为单一前驱体，以无机盐（MgCl2、LiCl等）为Fe原子隔离剂，部分黏连的介孔、大孔SiO2纳米球双模板为模板剂，可控制备含有高密度、高暴露率的单原子分散Fe-Nx和吡啶氮高活性活性位，和3D内部连通、高电导率、高石墨化的有序介孔-大孔碳空心壳框架结构Fe-N-C高效氧还原催化剂。经过系统的研究和分析，揭示活性位的密度、分布和有序多级孔孔结构参数对催化剂ORR催化性能的影响规律；阐明催化性能与原子组成、电子构型、孔结构之间的构效关系；为碳基非贵金属催化剂的设计、制备及应用提供理论依据和技术支撑。

本项目针对质子交换膜燃料电池中阴极氧还原用铂基催化剂存在资源稀缺和价格昂贵等问题，研制开发新型高效非贵金属阴极催化剂。拟通过硬模板纳米构筑方法，以介孔、大孔SiO2等为模板剂，富含金属-氮（M-Nx)配位结构的吡啶基金属螯合物、配位金属有机骨架等作为金属、氮和碳的前驱体，通过控制这些前驱体在介孔大孔二氧化硅等限域孔道内热解或进行直接热解，实现大量M-Nx和吡啶氮可接触氧还原活性位在M-N-C催化剂中的原位生成。通过优化合成条件，调控煅烧温度、前驱体的组成比例、有序多级孔孔结构等，构建出高电导率、高石墨化和富含大量可接触活性位的多级孔M-N-C氧还原催化剂。环盘电极测试表明，在0.1MKOH介质中，催化剂的ORR半波电位比商业Pt/C正40-10mV，在0.1MHClO4中，部分催化剂ORR半波电位接近商业Pt/C催化剂，同时在酸性和碱性介质中，催化剂的稳定性均超过了商业Pt/C。其中我们制备的Fe单原子和氮共掺杂的空心碳多面体催化剂在H2/O2质子交换膜燃料电池（PEMFC）中表现出超高性能，在0.7V时电流密度为400mAcm-2，在0.8V时为133mAcm-2，最大功率密度为628mWcm-2，这是据报道的非铂基金属阴极的最佳PEMFC性能之一。该项目的研究，对于降低PEMFC燃料电池的成本，加速燃料电池的商业化进程具有重大意义。..