Nafion基纳米纤维三维网络结构膜电极的可控构筑及在DMFC中的应用研究

The relatively low utilization of noble catalyst and disordered catalyst layer are the remaining issues limiting the performance improvement of the membrane electrode assembly (MEA) for a DMFC. Three-dimensional nanostructured components are introduced in MEA as an attractive solution to improve the performance, promising to maximize the three-phase boundary, to enhance the electrochemical reactivity and to reduce the noble metal loading. In the project, a novel MEA with three-dimensional nanofibrous structure will be fabricated by an electrospinning technique, expecting above advantages. The relationships between the nanostructures (such as morphologies, nano sizes, arrangement manner and uniformity of nanofibers, the loading sites and distribution of the catalysts, the homogeneity of the Nafion resin, etc.) with the MEA properties (such as the efficiency of mass, proton and electron transportation, the utilization of catalyst) will be investigated internally. A new approach will be pursued to load the noble catalyst only on the surface layer of the nanofibers, promising the maxim catalyst utilization. The lifetime of the MEAs will be prolonged by boundary modification and structure regulation, due to their enhanced interface compatibility between the gas diffusion layer, the Nafion membrane with the catalyst layer. Therefore, such nanofiber network structure and corresponding nanofabricating approach is desired to achieve superior performance and lower catalyst loading in MEAs, promoting the commercial viability of DMFCs.

集成催化剂和质子交换膜的膜电极存在催化剂利用率低、催化层结构无序等问题，制约了DMFC性能提高和成本降低，因而迫切需要发展三维网络纳米结构膜电极，最大化三相反应界面，实现电池性能的提高和催化剂用量的降低。本项目借助静电纺技术工艺成熟、纳米纤维尺寸和形貌可控等特点，构筑纳米纤维三维网络结构膜电极，研究纳米结构的形貌、尺寸、取向、分布、催化剂负载方法和催化剂粒子分布以及树脂分散度等对膜电极内分子、质子和电子的高效输运及催化剂利用率的影响，重点探索仅纳米纤维表层含催化剂粒子的制备方法，阐明纳米纤维三维网络结构膜电极的可控构筑规律，实现膜电极三相界面电催化活性、传质效率和结构稳定性的提高。通过纳米纤维网络的表面修饰和结构调控，探索实现三维网络结构催化层与扩散层及膜之间界面兼容性提高的方法，提升膜电极寿命。发展低催化剂用量、高性能纳米纤维网络结构膜电极制备方法，推进DMFC的实用化进程。

课题针对DMFC膜电极存在的催化剂利用率低、催化层结构无序等问题，借助静电纺技术工艺成熟、纳米纤维尺寸和形貌可控等特点，构筑了多种纳米纤维三维网络结构膜电极，最大化膜电极三相反应界面，实现了电池性能的提高和催化剂Pt用量的大幅降低，实现了预定的研究目标。通过纳米纤维网络结构、多孔微球等催化层结构的构筑，直接甲醇燃料电池的性能得到显著提升(在PtRu载量为2.0 mg cm-2时，最大功率密度43.0±0.9 mW cm-2)，在同比性能情况下，阴阳极催化剂载量均可降低至1mgcm-2，是原来的1/2~1/4，显著降低了成本；通过静电纺丝及热处理技术制备了Co/N/C纳米棒氧还原催化剂在酸性条件下具有较好的ORR活性，起始还原电位在0.8V (vs RHE)，半波电位为0.62V（vs RHE），应用于DMFC阴极催化剂，在25oC、空气自呼吸模式条件下，DMFC的最大功率密度可达8 mWcm-2，表明该类催化剂具有良好的应用前景。发展低催化剂用量、高性能纳米纤维网络结构膜电极制备方法，推进DMFC的实用化进程。