杂原子掺碳催化剂介尺度表界面结构调控与构建

Heteroatom doped carbon, such as N, B and P atoms doped carbon, have attracted much attention in catalysis because of the band gap opening and structure activation with the doping. However, its catalytic activity is not as good as precious catalysts due to their intrinsic property and insufficient active sites. In this project, we propose to regulate the mesoscale geometric morphology and surface structure of heteroatom-doped carbon catalysts, and then to introduce adequate active-sites at triple-phase boundaries. Self-assembled heteroatom-containing polymer is fixed and fully sealed inside salt via recrystallization of salt solution. During carbonization, the salt crystal functions as a fully sealed nanoreactor, facilitating heteroatom incorporation and graphitization. The gasification in such a closed nanoreactor creates a large number of pores in the resultant samples. Such a mesoscale structure has linkages of various species-transport channels to the active sites: voids for O2 and water transport, a carbon framework for electron transport, and proton polymer modified subsequently on the walls of the pores for proton transport. It is conducive to mass transport and high utilization of active sites. The mesoscale structure of the heteroatom-containing polymer can be accurately transferred to the final heteroatom doped carbon materials, after dissolution of the salt just in a hot water. The “shape fixing via salt recrystallization” method can effectively prevent the collapse, sintering and deformation of the polymer during carbonization.

杂原子掺碳材料因带隙打开和结构活化成为非贵金属碳基催化剂的研究热点。然而，杂原子掺碳催化剂还存在活性低、活性位少、体积密度小等缺点。据此，本申请提出：“杂原子掺碳催化剂介尺度表界面结构调控与构建”的解决方案。采用密度泛函理论与分子动力学相结合的方法，构建介尺度杂原子掺碳催化剂聚集体模型，对表界面结构和孔道结构进行理论模拟，揭示介观结构对活性以及传质效率的影响机制；通过软、硬模板法，自组装、原位聚合等手段，合成特定结构形貌的有机聚合物；利用我们首创的“盐溶液重结晶固形高温炭化法”，将炭化时结构形貌可能坍塌、烧结、变形的聚合物封装在重结晶的盐晶体中，利用盐晶体的固形、封闭和限域效应，调控聚合物高温炭化时的介观形貌；利用“混合盐熔融相变法”，通过调节高温炭化时产生的水、气调控表界面产生的缺陷、孔隙和掺杂类型，确保杂原子掺碳催化剂活性位点尽可能地处在有效孔道中，实现催化中心利用率的全面提升。

由于杂原子掺碳非贵金属氧还原催化剂存在的活性位数量少、体积密度低、孔道结构不够丰富等缺点，使得其氧还原活性低、稳定性差。本课题组从催化剂介尺度表界面活性位构筑，多级孔互传网络结构以及介尺度结构构筑策略三方面提升杂原子掺碳催化剂氧还原活性，主要成果包括：1）利用“气化与热熔”的高温双相变法、软硬模板法等法构筑出“大孔-介孔-微孔”多级互穿网络型掺碳催化剂，实现气体多孔电极催化与物质传递双功能的精确调控。2）提出利用双阴离子的协同调控催化剂表界面介尺度区域配体结构，使其兼具了两极端单一配体催化剂各自单一的高稳定性和高活性优势，实现了催化活性和稳定性的同步提升。3）提出“中心原子异化效应”和金属/氧化物界面“析氢烟囱效应”理论，阐明介尺度晶体结构反转和界面组分突变导致催化活性差异的理论化学基础，并成功的指导了高效催化剂的设计。4）利用具有埃级高度扁平反应器的空间限域效应，实现反应器内物质传递和反应过程的分步解耦，强化二维平面方向原子间的有效碰撞，制备出自支撑单原子层催化剂，发现二维平面材料d轨道异于单原子和三维纳米颗粒材料的分裂是其兼具稳定和高活性的关键。