基于有序多级孔结构构建高活性的M-N/C型燃料电池阴极催化剂及其构效关系

Developing oxygen reduction catalysts with high performance and low cost has been one of the major challenges for the commercialization of proton exchange membrane fuel cell (PEMFC). Transition metal based nitrogen complexes M-N/C(M=Fe、Co) is one of the most promising alternative non-noble metal catalyst of Pt catalysts. However, its catalytic activity is still at a low level compared to Pt-based catalysts. In this application, aiming at the low active site density and utilization of M-N/C type non-noble metal oxygen-reduction catalyst, M-N/C (M=Fe、Co) type oxygen-reduction catalyst with ordered mesostructure and hierarchical porosity have been synthesized via a direct triblock copolymer-templating process by using nitrogen-containing polymers as a N precursor, and its oxygen reduction catalysis and mass transfer mechanisms were investigated. The geometrical and electronical structure of catalysts are optimized by modulating the size and morphology of ordered mesostructure and hierarchical porosity, the content of polyaniline and transition metal, and the heat-treatment temperature to synthesize M-N/C type non-precious metal catalyst with high catalytic activity for oxygen reduction reaction (ORR) in acidic solution. This kind of catalyst with low cost and high property is promising to meet the needs of practical application of the PEMFC cathode and promote the commercial application of PEMFC-one of the most clean energy conversion technologies.

开发高效、低成本的氧还原催化剂是实现质子交换膜燃料电池商业化应用的关键问题。其中M-N/C(M=Fe、Co) 过渡金属复合型催化剂是有可能替代Pt催化剂的非贵金属催化剂之一，但目前其氧还原催化活性还远不能和Pt基催化剂相比。本申请针对M-N/C型非贵金属氧还原催化剂活性点密度和利用率低的问题，以三嵌段共聚物为模板，含氮聚合物为N源合成具有有序多级孔结构的M-N/C(M=Fe、Co) 型氧还原催化剂，并研究其氧还原催化和传质机理。通过调控有序多级孔的孔径大小和形貌，并结合调节聚苯胺的用量、过渡金属的含量、烧结温度等调节催化剂的几何、电子构型，合成在酸性溶液中具有高效氧还原催化活性的M-N/C型非贵金属催化剂；从而降低催化剂成本，推进质子交换膜燃料电池这一清洁能量转换技术的商业化。

本课题分别以尿素酚醛树脂（UPF）和聚苯胺为含氮配体，以三嵌段聚合物F127为模版，甲阶酚醛树脂为碳源，成功合成了具有有序分级孔结构的M-N/C型非贵金属氧还原催化剂。利用XRD，TEM，BET，XPS等方法对催化剂的成分、形貌和电化学催化活性进行了表征。结果表明以聚苯胺为配体制备的催化剂具有清晰的有序介孔结构，拥有整齐的孔道和高的比表面积，达到1007 m2•g-1。XPS结果表明吡啶氮原子和石墨氮原子为3.86 at.%。热处理温度升高过程中Fe（Ⅲ）被还原，向单质Fe转化，并促进了N的掺杂，使碳化铁转化为Fe-Nx活性位点，提高了催化剂的ORR催化活性，热处理温度达到900℃时，过多的单质铁使其氧还原活性下降。在酸性溶液中，Fe-N-C-PANI-800催化剂的起始电位可达0.89 Vvs.RHE，半波电势为0.81 Vvs.RHE。有序介孔结构使催化剂更易石墨化，提高了材料的稳定性。