【作者】 高扬；

【导师】 智林杰； 杨全红；

【作者基本信息】 天津大学 ， 应用化学， 2020， 博士

【摘要】 随着新型电化学能量转换装置的发展,开发低成本和高活性的电催化剂材料在学术界和工业界引起了广泛关注。碳基纳米材料具有来源广泛、成本低廉、高导电性、良好的化学稳定性以及结构和功能可调控性等优点,因此在能源转换技术的实用化开发中具有很大的应用前景。本论文从碳基纳米材料结构设计的角度出发,通过构建合适的模型体系,采用实验和理论模拟相结合的方法,研究了一系列与碳基纳米材料相关的科学问题。比如,传质效应和双掺杂效应对于电催化活性的影响,材料的石墨化结构、孔结构和化学结构的协同调控在电催化反应中的重要性,结构设计对于电合成过氧化氢的影响,主要研究成果如下:利用同轴静电纺丝技术和高温热解方法,设计制备了具有多级次孔结构、一维电解液/反应物传输通道和丰富的催化活性位点的一维N,P共掺杂中空碳纳米纤维。该材料在氧还原反应、析氧反应和析氢反应中均具有催化活性,表现出明显的三功能催化活性。其中,该材料在氧还原反应中的半波电位与析氧反应达到10 mA cm-2电流密度时的电位之间的差值ΔE为0.73 V,表现出对氧电催化反应优异的催化性能。采用该类材料作为模型体系,以氧还原反应为例,研究了传质效应对电催化反应性能的作用机理。利用同轴静电纺丝技术的灵活性,通过调控同轴静电纺丝过程中芯层溶液的组成,设计制备了不同双杂原子共掺杂的碳亚微米管。采用该类材料作为模型体系,研究了碳基纳米材料的双掺杂效应对于氧还原反应催化活性的影响。实验结果表明,N,P共掺杂时具有最佳的氧还原反应催化活性和催化动力学,N,S共掺杂时次之,而N,B共掺杂表现出较差的催化活性。密度泛函理论计算表明,N和P的共掺杂能够协同调控催化反应路径和碳网络的电子特性,产生位于氧化态的P和石墨化态的N附近的边缘C活性位点。采用一步简单的溶液反应制备了不同金属比例的双金属沸石咪唑骨架颗粒,后经碳化处理得到Co-N-C材料。以该类材料为模型体系,研究了 Co-N-C材料中石墨化结构、多级次孔结构和活性物种分布的协同调控对于氧电催化反应性能的影响。密度泛函理论计算表明,N掺杂石墨烯与Co之间的相互作用能够调变N掺杂石墨烯的电荷分布,在吡啶态N周围产生活性C位点。采用聚丙烯腈基的聚合物干凝胶作为前驱体,经过高温热解处理得到了 N,O共掺杂的碳干凝胶。随后,研究了结构设计对于电合成过氧化氢的重要性,结果表明,N,O共掺杂的碳干凝胶具有优异的电合成过氧化氢性能,其在0.15-0.6 V具有高于90%的过氧化氢选择性。通过结合密度泛函理论计算研究了 N,O共掺杂的碳网络在两电子路径的氧还原反应中的催化活性位点。更多还原

【Abstract】 With the development of new electrochemical energy conversion devices,the development of low-cost and highly active electrocatalyst materials has attracted widespread attention in academia and industry.Carbon-based nanomaterials have the advantages of wide sources,low cost,high electrical conductivity,good chemical stability,and controllability of structures and functions,and therefore have great application prospects in the practical development of energy conversion technologies.From the perspective of structural design of carbon-based nanomaterials,this paper studies a series of scientific issues related to carbon-based nanomaterials by constructing suitable model systems and using a combination of experiments and theoretical simulations.For example,the effects of mass transfer and dual-doping on the electrocatalytic activity,the importance of the synergistic engineering of the graphitized structure,pore structure,and chemical structure of the material in the electrocatalytic reaction,and the effect of structural design on the electrosynthesis of hydrogen peroxide.The main research results are as follows:One-dimensional N,P co-doped hollow carbon nanofibers with hierarchical porous structure,one-dimensional electrolyte/reactant transport channels,and abundant catalytic active sites were designed and prepared via coaxial electrospinning technology,followed by high-temperature pyrolysis treatment.The as-prepared carbon nanomaterial exhibits an excellent trifunctional electrocatalytic activity for oxygen reduction reaction,oxygen evolution reaction,and hydrogen evolution reaction.Impressively,the as-obtained material shows particularly excellent catalytic performance for oxygen electrocatalytic reactions as characterized by a low potential deviation(ΔE)of 0.73 V between the half-wave potential of oxygen reduction reaction and the potential reaching 10 mA cm-2 for oxygen evolution reaction.Subsequently,using this type of material as a model system,the effect of mass transfer on the performance of oxygen reduction reaction was studied.Considering flexibility of coaxial electrospinning technology,a series of dual-doped carbon submicrotubes were designed and prepared by adjusting the composition of the core solution during the coaxial electrospinning process.The effect of dual-doping on the catalytic activity of carbon-based nanomaterials for oxygen reduction reaction was studied by using this type of material as a model system.It was found that N,P co-doping shows the best catalytic activity and catalytic kinetics of oxygen reduction reaction over N,S and N,B co-doping.Density functional theory calculations revealed that N,P co-doping could synergistically modulate catalytic reaction pathways and the electronic structure of carbon network,thus generating the active edge C site situated around the oxidized P site nearby a graphitic N atom.Bimetallic zeolitic imidazolate frameworks with different metal ratios were prepared by a simple one-step solution reaction,and then carbonized to obtain Co-N-C materials.Subsequently,the effect of the synergistic engineering of graphitized structure,hierarchical porous structure,and active species distribution on the performance of oxygen electrocatalytic reactions in Co-N-C materials were studied.Density functional theory calculations revealed that the interaction between N-doped graphene and Co could modulate the charge distribution of N-doped graphene,thus generating the active C sites near pyridinic N.A N,o co-doped carbon xerogel was obtained by the pyrolysis treatment of a polyacrylonitrile-based polymer xerogel as the precursor.Subsequently,the importance of structural design for the electrosynthesis of hydrogen peroxide was investigated.It was found that the N,o co-doped carbon xerogel shows an excellent performance for the electrosynthesis of hydrogen peroxide as revealed by the hydrogen peroxide selectivity of more than 90%at the potential range of 0.15-0.6 V.Then,density functional theory calculations were used to study the catalytic active site of N,O co-doped carbon networks for the two-electron pathway oxygen reduction reaction.更多还原