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燃料电池是一种可将化学能通过电催化反应直接转化成电能的装置,具有能量密度高和清洁无污染等优点.燃料电池阴极氧还原反应(ORR)的动力学较迟缓,是电池能量效率损失的主要原因.目前ORR催化活性最高的是铂基催化剂,但由于贵金属铂价格昂贵,储量稀少,且对燃料小分子渗透的抗性较差,严重制约了燃料电池的大规模应用.因此,高性能、低成本的非贵金属催化剂成为燃料电池领域的研究热点.本文选用含氮量高达45%的三聚氰胺-甲醛树脂为碳源和氮源,Fe(SCN)_3为铁源和硫源,以CaCl_2为模板,在高温和铁的催化作用下将树脂碳化,经酸洗和二次热处理工艺,制备出铁、氮、硫共掺杂的多孔碳(FeNS-PC).干燥后的CaCl_2颗粒可防止树脂在高温下交联形成块状碳颗粒,同时起到造孔模板的作用.CaCl_2颗粒在温和条件下即可除去,无需强腐蚀性条件,因此不会对催化活性中心造成破坏.在Fe/N/C催化剂中掺杂S可进一步提高催化活性,不添加碳载体可避免低活性的碳载体降低质量活性,多孔结构可促进传质,充分利用活性位点.我们优化了热处理温度,并对催化剂的结构、组分及催化性能等进行了表征分析.结果表明,热处理温度为900℃时,可将树脂完全转化成多孔碳,并获得较高的杂原子掺杂量,可达到最优活性.CaCl_2为模板剂可避免使用强腐蚀性试剂去除模板,有利于保留活性位,并得到多孔结构.FeNS-PC-900的比表面积可达775 m~2/g.得益于原位掺杂的合成工艺,各掺杂元素在多孔碳表面均匀分布.在酸性介质中,FeNS-PC-900的半波电位可达到0.811V,仅比商业Pt/C催化剂低78mV;在0.8V电位下的质量活性为10.2A/g,表现出优异的催化活性.经过10000圈加速衰减测试后,其半波电位仅下降了20mV,在0.75V电位下持续放电10000s后,其ORR电流仍保持初始电流的84.4%,具有比Pt/C更加优异的稳定性.以FeNS-PC-900为阴极催化剂的质子交换膜燃料电池的最大功率密度可达到0.49 W/cm~2,并在0.6 V电压下持续放电10h后,其电流仍可保持初始电流的65%,表现出良好的应用潜力.FeNS-PC-900具有高掺杂含量、高比表面积和多孔结构,并且杂原子在催化剂表面均匀分散,在半电池和燃料电池测试中都表现出优异的催化活性和稳定性,表明其是一种非常有潜力应用于燃料电池的非贵金属氧还原催化剂.
Fuel cell is a device that can directly convert chemical energy into electricity by electrocatalytic reaction, has the advantages of high energy density and clean and pollution-free etc. The kinetics of oxygen reduction reaction (ORR) in fuel cell is relatively slow, which is the result of battery energy efficiency The main reason for the loss of the ORR catalyst activity is currently the highest catalytic activity of platinum-based catalysts, but because of expensive platinum platinum, reserves scarce, and poor resistance to fuel small molecule penetration, severely restricted the large-scale fuel cell applications.Therefore, High-performance and low-cost non-precious metal catalysts have become the hot topics in fuel cell field.In this paper, melamine-formaldehyde resin with 45% nitrogen as carbon source and nitrogen source, Fe (SCN) 3 as iron source and sulfur source CaCl 2 as template, the resin was carbonized under high temperature and iron catalysis, and FeNS-PC co-doped porous carbon (FeNS-PC) was prepared by acid pickling and secondary heat treatment. The dried CaCl 2 particles were Prevent the resin from cross-linking to form massive carbon particles at high temperature, and at the same time play the role of pore-forming template .CaCl 2 particles can be removed under mild conditions without strong corrosive conditions and therefore will not cause catalytic activity center Bad.Doping S with Fe / N / C catalyst can further improve the catalytic activity, without adding carbon carrier to avoid low activity of carbon carrier to reduce the mass activity, porous structure can promote mass transfer, make full use of the active site.We optimized The results show that the resin can be completely converted into porous carbon and the higher doping amount of heteroatoms can be obtained when the temperature is 900 ℃, CaCl2 can be used as a template to avoid using strong corrosive reagents to remove the template, which will help retain active sites and obtain porous structure .FeNS-PC-900 has a specific surface area of 775 m 2 / g. In the in-situ doping synthesis process, the doping elements are uniformly distributed on the surface of porous carbon, the half-wave potential of FeNS-PC-900 can reach 0.811V in acidic medium, which is only 78mV lower than that of commercial Pt / The mass activity at 0.8V was 10.2 A / g, showing excellent catalytic activity.After 10000 cycles of accelerated decay test, the half-wave potential decreased only 20mV, and at 10000V, the ORR current Still maintain 84.4% of the initial current, has more excellent than Pt / C Different stability. The proton exchange membrane fuel cell with FeNS-PC-900 cathode catalyst can reach a maximum power density of 0.49 W / cm ~ 2 and discharge at 0.6 V for 10 h, Current of 65%, showing good potential applications.FeNS-PC-900 with high doping content, high specific surface area and porous structure, and the heteroatom in the catalyst surface uniformly dispersed in the half-cell and fuel cell tests have shown Excellent catalytic activity and stability, indicating that it is a very potential for non-noble metal oxygen reduction catalyst for fuel cells.