多级孔结构石墨烯基复合材料的制备及其在氧气还原中的应用

The development of high-performance and low-cost oxygen reduction reaction(ORR) catalysts is very important for fuel cell that is one of the most effective devices to solve the energy crisis. However, the replacement of precious metal catalysts by low-cost non-precious metal catalysts often faces the problems of slow mass transfer, low activity and poor stability. This project studies the preparation of non-precious metal based composite catalysts with fast mass transfer, high activity and high stability by the structural design of graphene aerogels and optimization of composite system, and focuses on the related mechanism investigation: 1) By the introduction of hierarchically porous structure and heteroatom into the graphene aerogels, the novel supporting material with fast mass transfer and high activity can be obtained. 2) The novel graphene aerogels can be used to support non-precious metal catalysts to prepare the composite catalysts, exhibiting an enhanced mass transfer and increased activity. To further increase the stability of these composite catalysts and prevent the non-precious metal catalysts from peeling off and dissolution, the ultrathin porous carbon layer, which is carbonized from the polymer layer, is introduced throughout the aerogel networks to anchor the dispersed non-precious metal nanoparticles. Finally, the highly efficient and stable graphene-based ORR composite catalysts with a continuously interconnected sandwich structure (porous graphene skeleton–non-precious catalyst–porous carbon) are prepared.

非贵金属氧气还原反应（ORR）电催化剂，作为一种低成本催化剂材料，对发展燃料电池、解决能源危机问题具有重大意义。然而非贵金属ORR电催化剂往往面临着催化活性不高、稳定性差的问题。本项目拟通过石墨烯气凝胶载体的微观结构设计和复合体系的结构优化，开展兼具快传质、高活性和高稳定性非贵金属ORR复合电催化剂的制备及其机理研究：1）通过在大孔结构石墨烯气凝胶的骨架上引入介孔的结构设计和杂原子的掺杂，研究孔微观结构和杂原子掺杂对气凝胶内部传质和催化性能的影响，调控得到具有快传质和高活性的多级孔结构石墨烯气凝胶载体；2）通过与非贵金属催化剂复合，并引入多孔碳层，构筑石墨烯多孔骨架-非贵金属催化剂-多孔碳三明治结构。优化复合体系中各组分的微观结构，得到兼具快传质、高活性和高稳定性的非贵金属ORR复合电催化剂。探索出一条通过载体微观结构设计和复合体系结构优化制备高性能非贵金属ORR复合电催化剂的有效途径。

针对单一电催化剂材料面临的催化活性不高、稳定性差的问题，通过气凝胶骨架微观结构调控、多级孔结构构筑和复合体系设计优化制备了一系列兼具高活性、高稳定性和（较）低成本的气凝胶型电催化剂材料：.1）通过杂原子掺杂、气凝胶骨架的合金度调控和多级孔结构构筑等手段协同调控，制备了高合金度PtNi纳米框/掺氮石墨烯复合气凝胶。用作电催化甲醇氧化时，获得高活性的同时，实现酸性体系中电催化剂稳定性的突破。质量活性高达1647 mA/mgpt，是商用Pt/C的5.8倍；经过4000s的恒电位（0.56 V vs Ag/AgCl）催化过程后，其质量活性仍保持在381.2 mA/mgpt，是商用Pt/C的37倍；.2）利用复合体系优化和缺陷工程控制，实现气凝胶载体和电催化剂纳米颗粒之间的强相互作用，得到高性能、低成本的低铂/氧空位的氧化钨纳米线/石墨烯复合气凝胶（0.8 wt% Pt）。用作析氢反应时，在10 mA/cm2电流密度下，其过电位仅为42 mV，远远优于商用Pt/C。Tafel斜率低至30 mV/dec，50 mV过电位下的转换频率（TOF）高达26 s-1。即使在12000次加速衰减测试和40小时计时电位测量（10 mA/cm2）之后，电催化活性几乎保持不变，表现出了出色的稳定性；.3）在气凝胶骨架表面引入异种金属Bi，控制Bi在气凝胶骨架表面分布和引入量，实现气凝胶骨架表面电子结构的最优化，最终得到单原子Bi表面沉积的Ni97Bi3复合气凝胶。用作电催化甲醇氧化时，获得了远超其他非贵金属电催化剂的稳定性和活性。质量活性高达1833.8 mA/mg，特征活性高达200 mA/cm2。经历连续12小时（0.55 V vs. Ag/AgCl）耐久性测试，其活性保留率高达78%；.4）通过支撑体引入，使得具有丰富孔道结构的气凝胶材料可直接用作电催化电极材料，实现快速传质，获得高活性和高稳定性。结果发现，保留金属气凝胶原始结构的Pt50Ag50 AGs/CC的催化活性比传统超声滴涂的Pt50Ag50 AGs ink/CC高出了5倍，且耐久性显著增强。.揭示了气凝胶电催化剂微观结构（气凝胶骨架的合金化程度、复合体系的组成和微观结构）与电催化性能（反应物及其中间产物吸附能）之间的关系，提出了一条颇具特色的电催化剂高性能化和低成本化的气凝胶方案。