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聚合物衍生的多维度氮掺杂碳基材料及电催化氧还原性能研究
中文摘要

能源短缺的压力推动了高效、清洁的能量存储和转换装置的开发和利用。作为重要的阴极电极反应,氧气还原反应(ORR)涉及多步复杂的反应,属于动力学缓慢过程,决定这些能量转换技术和储存装置的转换效率。因此,需要研究和开发成本低、催化活性高、长循环性能稳定的ORR催化剂降低ORR反应过电位,提高能量转换效率。铂基催化剂是目前商用的ORR催化剂,但存在资源有限、价格昂贵、稳定性差的问题。理想的ORR催化剂要求在低过电位下产生高催化电流,还需具备电化学稳定性优异、低成本、易制备的特点。碳基材料因其电压窗口宽、导电性好、稳定性优异被认为是具有发展前景的ORR催化剂。但是碳基催化剂的催化效率通常较低,原因是催化活性位点被掩埋,无法暴露出来进行有效的介质传递和电子转移。基于此,本论文以构建高活性ORR催化剂为研究目标,利用化学改性、物理吸附等设计手段制备多维度氮掺杂碳基材料,对催化剂的结构及ORR性能进行系统研究,主要要点如下: (1)零维血红细胞状氮掺杂扁形碳球。首先将聚苯乙烯空心球通过交联、磺化等功能化修饰,制备表面带有负电荷的交联磺化聚苯乙烯扁球,利用静电吸附作用将聚苯胺均匀地诱导生长在磺化聚苯乙烯扁球上,经过高温热处理后形成具有介孔结构、氮掺杂碳位点均匀分布的氮掺杂扁形碳球。系统地研究交联磺化反应、氮掺杂方式、煅烧温度等因素对催化剂的结构和性能的影响,证明氮和铁掺杂对ORR催化活性的协同增强作用机制。 (2)一维氮掺杂CNTs。利用磺化聚苯乙烯的凝胶诱导作用在经磺化聚苯乙烯层修饰的碳纳米管(CNTs)上可控生长了聚苯胺,经过高温热处理制备氮掺杂碳位点均匀分布的氮掺杂CNTs。充分结合CNTs的导电性和氮掺杂碳活性位点的优势,在CNTs层和氮掺杂碳层形成稳定的键合作用,系统地考查了 CNTs导电载体、氮掺杂碳、磺化聚苯乙烯层对ORR催化活性和电化学稳定性的贡献。 (3)三维氮掺杂介孔碳。通过简单的物理吸附和原位聚合法制备氮掺杂碳位点均匀分布的氮掺杂介孔碳。通过系统地研究介孔碳基底、氮掺杂碳等对ORR性能的影响,明确了ORR性能提升的机制:介孔碳骨架提高了电子传输能力,提供有效的气体吸附和扩散通道,高比表面积有利于与电解液充分浸润,增加了活性位点。经化学改性也能够实现氮掺杂碳位点的均匀分布,但是利用多孔碳结构的物理吸附作用的原位聚合法更加具有实用推广性。 (4)三维氮掺杂超级多孔碳。利用一种简单、普适的方法合成了具有三维网络结构的超交联聚合物,经过活化处理后制备三维氮掺杂超级多孔碳。超交联结构使多孔碳骨架在热解过程中避免坍塌。研究了单体类型、活化温度对氮掺杂超级多孔碳的比表面积、孔结构、氮掺杂含量和氮掺杂的方式对三维氮掺杂超级多孔碳的ORR性能的作用机制。 (5)在三维碳毡上原位生长聚苯胺,通过简便的微波法制备氮掺杂碳纤维,研究碳化处理方式、微波处理时间等因素对碳材料结构和ORR性能的影响规律,证明微波法不但能够明显缩短反应时间,且氮含量、吡啶氮比例以及石墨型碳的含量均优于传统热解法制备的样品,该合成手段可推广用于制备其他杂原子掺杂的多功能碳基材料。 关键词:电催化;氧气还原反应;氮掺杂碳;介孔碳;导电高分子 论文类型:应用研究

英文摘要

Fuel cells and metal-air batteries are under serious consideration as the promising energy storage and conversion devices due to the energy dilemma. As the important cathode reaction, oxygen reduction reaction (ORR) greatly dominates the energy conversion efficiency due to its sluggish kinetics. Although platinum (Pt)-based materials are regarded as the most efficient electrocatalysts for ORR, high cost, poor stability and durability of Pt-based catalysts significantly impede the large-scale implementation for these electrochemical energy storage and conversion devices. Carbon-based materials have been well-established as promising alternatives with wide voltage window, benign conductivity, enhanced stability and competitive cost. However, the low catalytic efficiency of carbon-based catalysts is generally attributed to low specific surface area and invalid active sites, which fail to be exposed for efficient media transfer and electron transfer. Herein, this dissertation is aimed at constructing efficient and robust ORR electrocatalysts by rational design and modification of carbon-based materials. (1)Nitrogen-doped carbon spheres with mesoporous structure and uniformly distributed nitrogen-doped carbon sites have been prepared, derived from PANI@PS composites of which polyaniline uniformly supported on PS after crosslinking and sulfonation modifications of PS spheres. By systematically studying structures and properties of different catalysts, it could be demonstrated the synergistic enhancement to catalytic activity of N and Fe. (2)Nitrogen-doped CNTs with uniform hierarchical structures have been achieved through sulfonated polystyrene modified CNTs to asssist uniform distribution of PANI covered on CNTs matrix.The unique design of sulfonated polystyrene layer between the CNTs and PANI facilitate: 1) uniform distribution of PANIdue to electrostatic adsorption between the sulfonate ion andaniline salt; 2)excellent chemical affinity between the N-carbon layer and CNTs skeleton; 3) nitrogen sites to distribute uniformly after pyrolysis treatment. The unique architecture of PANI@CNTs-SPS composites ensures the nitrogen-doped catalyst with rich active sites, efficient electronic transfer pathway and enhanced electrochemical stability. (3)Nitrogen-doped mesoporous carbons with uniformly distributed nitrogen-doped carbon sites have been prepared by simple physical adsorption and in-situ polymerization. The mesoporous structures and high specific surface area of NCMK-900 provide effective gas adsorption and diffusion channels, rich active sites and sufficient contact with electrolyte. In-situ polymerization by physical adsorption of porous structures is more practical than chemical modification to achieve uniform distribution of nitrogen-doped carbon sites. (4)Three-dimensional hierarchical micro-/mesoporous nitrogen doped carbon materials have been synthesized derived from hypercrosslinked polymers by a simple and universal method. The hypercrosslinked structures avoid collapse of porous carbon skeletons during pyrolysis. The effects of specific surface area, pore structure, nitrogen doping content and nitrogen doping type of nitrogen-doped hyperporous carbon materials on ORR electrocatalytic performance have been systematacially studied. (5)Nitrogen-doped carbon fibers are prepared through a simple microwave assisted heatingmethod. The effects of different microwave heating time and heat treatment methods on structures and ORR performance of nitrogen-doped carbon fibers have been studied. It proves that microwave assisted heating method shows clear superiority over other traditional pyrolysis methods by shortening heating time, andenhancing the content of doped nitrogen, proportion of pyridine nitrogen and degree of graphitization. KEYWORDS: Electrocatalysts; Oxygen Reduction Reaction; Nitrogen-Doped Carbon; Porous Carbon; Conducting Polymers TYPE OF DISSERTATION: Application Research

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