自组装合成Fe-N-C-PANI有序介孔结构催化剂及其在酸性条件下的氧还原活性

Synthesis of Ordered Mesoporous Fe-N-C-PANI Catalyst via Self-assembly and Its Oxygen Reduction Reaction Activity in Acid Medium

采用乙醇挥发自组装法,以F127为模版,甲阶酚醛树脂为碳源,聚苯胺为配体,加入硝酸铁和硅酸盐,制备了有序多级孔的Fe-N-C-PANI催化剂.催化剂的成分和形貌表征结果表明,在热处理温度为800℃时,有序介孔的结构最清晰,拥有整齐的孔道和最高的比表面积(1007 m^2/g);XPS分析结果表明,吡啶氮原子和石墨氮原子含量(摩尔分数)为3.86%.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,提高了催化剂的氧还原反应(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 V,半波电势为0.81 V.有序介孔结构使催化剂更易石墨化,提高了材料的稳定性.

Highly ordered mesoporous Fe-N-C-PANI electrocatalysts were synthesized by ethanol evaporation induced self-assembly using triblock copolymer Pluronic F127 as template, phenol-formaldehyde resin as carbon precursor and polyaniline as the N precursor. XRD, TEM, BET, XPS and RDE techniques were used to characterize the composition, morphology and electrocatalytic activity of the catalysts. The results show that the catalyst pyrolyzed at 800℃ has distinctly ordered mesoporous structure and straightest channel, and its speci-fic surface area is as high as 1007 m^2/g. The results of XPS show that the percentage of pyidinic N and Graphitic N of Fe-N-C-PANI-800 is 3.86% （molar fraction）. In the process of heat treatment, Fe （Ⅲ） was reduced to metallic Fe, and the introduction of N was facilitated, which made iron carbide turn into Fe-Nx active sites, and enhanced the ORR catalytic performance of catalysts. But when the temperature rise to 900℃, the formation of metallic Fe decreases its ORR activity. In the acid medium, Fe-N-C-PANI-800 has an onset potential of 0. 89 V （vs. RHE） and a half-wave potential of 0. 81 V （vs. RHE）. Ordered mesoporous catalyst had higher graphitization structure, which improved its stability.