“过渡金属-氮”共掺杂碳基铝空气电池催化剂的结构调控及氧还原催化特性

In this project, a facile and systematical preparation methodology is introduced to develop high performance Fe-N-C catalysts for oxygen reduction reaction. Four kinds of carbon based catalysts with different morphologies and structures (Fe-N doped porous graphene, Fe-N doped mixture of graphene and carbon nanotube, bamboo-like Fe-N doped carbon nanotube and N-doped graphene) will be obtained by tuning the content of iron source and the incorporation of carbon source and nitrogen source. The formation mechanisms of these catalysts will be discussed and the effect of different iron and nitrogen sources will be investigated. For further improving the catalytic performance, novel Cu-Fe-N-C and Co-Fe-N-C compounds are designed by a double transitional metal doping strategy. Several preparation methods will be introduced and the ratios of Cu/Fe and Co/Fe will be optimized. Meanwhile, the difference of electrochemical performance because of the incorporation of Cu and Co will be well compared. Theoretical calculations of oxygen molecules absorption on these catalysts will be carried out by the first principles method. And the effect of electronic and geometrical structures of the carbon due to the Fe-N doping and double metal doping will be studied, respectively. The mechanism of oxygen reduction reactions and their kinetic processes will be also studied. The synergistic electrocatalytic mechanism towards ORR of as-constructed Fe-N-C and Cu-Fe-N-C composite catalysts will be highlighted. This project will provide important guidance to develop low-cost and high performance ORR catalysts for Al-air batteries.

本项目提出了一套相对系统的制备方法，通过控制铁含量和氮碳源的选择加入，可分别得到高催化活性的Fe-N共掺杂多孔石墨烯，Fe-N掺杂石墨烯/碳纳米管，竹节状Fe-N掺杂碳纳米管和氮掺杂石墨烯四类具有不同结构与形貌的碳材料，研究相关材料形成机理；考察不同铁源和氮源对电催化性能的影响；通过对比分析有望明确Fe-N-C的主导催化活性中心。引入双金属掺杂技术，分别制备Cu-Fe-N-C和Co-Fe-N-C材料，优化合成条件，获得Cu/Fe, Co/Fe的最佳配比，对比Cu和Co掺杂对电催化活性的影响规律。采用第一性原理对掺杂类碳材料的氧吸附能及吸附方式进行模拟，研究铁氮掺杂和双金属掺杂对碳材料几何结构与电子结构的影响；深入研究相关催化剂的氧还原反应机理及动力学过程，计算动力学参数，深入剖析Fe-N-C和Cu-Fe-N-C的协同催化作用，为低成本、高活性和长寿命铝空气电池催化剂开发提供规律性认识。

铝空气电池是用铝代替氢而构建的一种金属燃料电池，具有能量密度高、安全、成本低、无污染、放电电压平稳等优点，且铝资源丰富，能再生利用，可更换铝电极进行机械充电，是很有发展前景的电池技术。然而，空气电极中的氧还原催化剂仍然是制约铝空气电池大规模商业应用的关键因素。. 基于开发高催化活性、高稳定性、价格低廉的氧还原催化剂的目的，本项目通过相对系统的制备方法，制备了一系列过渡金属-氮共掺杂碳催化剂，如四种具有不同典型形貌的热解类Fe-N-C氧还原催化剂材料，石墨烯状碳片Fe3C@Fe/N-C等，不同类型的Fe源制备得的Fe-N-C氧还原催化剂，以及Cu-Fe-NC，Co-N-C， Cu-N-C以及NC等催化剂。通过研究相关材料及形貌的形成机理，考察不同掺杂铁源和氮源对催化剂的影响， 明确了Fe-N-C的主导催化活性中心，并通过Cu，Fe共掺杂的方式进一步研究了铁氮掺杂和双金属掺杂对碳材料几何结构与电子结构的影响；深入研究相关催化剂的氧还原反应机理及动力学过程。得到的Cu-Fe-N-C比原始Fe-N-C表现出更好的催化活性，起始电位正移20 mV，约为0.967 V vs RHE，半波电位正移25 mV（0.864 V vs RHE），极限电流密度也得到了提高。并且通过实验结果和DFT计算，进一步证实了 Cu-Fe-N-C催化剂中双金属掺杂的协同效应是其性能显著提高的主要原因。此外，本项目还研究了氮掺杂碳中氮对周边碳原子的影响，理论计算结果表明暴露出来的靠近吡啶N的边缘碳原子是材料中的高活性位点。. 本项目对过渡金属-氮共掺杂碳催化剂进行了系统和深入的研究，相关结论将为低成本、高活性和长寿命铝空气电池催化剂开发提供规律性认识。