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目前,开发高效的阴极氧还原反应(ORR)电催化剂是实现燃料电池和金属-空气电池商业化发展急需完成的目标.在过去的几十年中,人们在探索廉价高效的ORR电催化剂(如N掺杂的非金属及非铂电催化剂)领域做了广泛的研究.在N掺杂的碳基ORR催化剂中,已知的N基活性位点主要分为四类,即吡啶类氮(P-N)、吡咯类氮(Py-N)、石墨化氮(G-N)和氧化类氮(O-N).尽管人们对这四种类型氮的活性位点做了大量的研究,但是它们在催化反应中起到的ORR催化作用以及催化机理和活性位点本身结构的关系仍不够明确.早期的研究中有人认为P-N或者Py-N是ORR催化活性位点,也有人认为是G-N起作用.最近也有研究表明,P-N和G-N都是ORR催化活性位点,只是在ORR中所起的催化能力不同.因此,很有必要认清这些问题.本文通过Hummer法酸性氧化一次和两次碳黑Vulcan XC-72(VXC-72)以及随后高温热处理,制备了一系列ORR催化剂VXCO-1,VXCO-2,VXCO-1(900)和VXCO-2(900),采用场发射扫描电子显微镜(SEM),N_2吸附脱附法,元素分析仪(EA),X射线光电子能谱(XPS),拉曼光谱仪(Raman),X射线衍射能谱(XRD),电化学循环伏安法和线性伏安法测试等手段研究Hummers法酸氧化和高温热处理对VXC-72形貌组成的影响,以及这些碳基中成分和其催化ORR能力的关系.SEM结果表明,Hummer法酸性氧化处理VXC-72一次和两次后可以逐层剥落其最外边的碳层结构,最终得到表面光滑的类片层状结构的碳材料(VXCO-1和VXCO-2).这种表面光滑的类片层状结构的碳材料比表面积大于处理前的VXC-72,而高温热处理之后的碳材料(VXCO-1(900)和VXCO-2(900))由于类石墨层碎片结构蒸发损失暴露出更多内部的微孔和介孔结构使比表面积增加.Raman和XRD结果表明,氧化处理使碳材料的石墨化程度增加,而高温热处理则降低了其石墨化程度.EA和XPS结果表明,Hummer法酸性氧化处理可以使在碳材料中掺入的N以石墨化的为主,高温热处理却使得石墨化氮转变为吡啶类的氮.ORR结果发现,活性的石墨化氮倾向于使ORR反应经历两电子过程,从而生成H2O2为主要产物;而吡啶类氮的活性位点更倾向于使ORR反应经过四电子过程,主产物是水.该结果有助于新型碳基氧还原催化剂的设计和分析.
At present, the development of highly efficient cathodic oxygen reduction (ORR) electrocatalysts is a much needed goal to realize the commercialization of fuel cells and metal-air batteries.In the past few decades, people have been exploring the cheap and efficient ORR electrocatalysts N-doped non-metallic and non-platinum electrocatalysts.) Among N-doped carbon-based ORR catalysts, there are four main classes of known N-based active sites, namely, pyridine nitrogen Py-N, GN, and ON Although a large number of studies have been conducted on the active sites of these four types of nitrogen, they have been used in catalytic reactions However, the relationship between the catalytic mechanism of ORR and the structure of the active site is still unclear. In the early studies, it was suggested that PN or Py-N is the active site of ORR and some people think that GN plays a role.Recently, , Both PN and GN are ORR catalytic active sites, but only have different catalytic capacities in ORR.Therefore, it is necessary to recognize these problems.In this paper, one and two carbon black Vulcan XC-72 VXC-72) followed by high temperature heat treatment The ORR catalysts VXCO-1, VXCO-2, VXCO-1 (900) and VXCO-2 (900) were characterized by field emission scanning electron microscopy (SEM), N 2 adsorption and desorption, elemental analysis X-ray diffraction (XPS), Raman spectroscopy, X-ray diffraction (XRD), cyclic voltammetry and linear voltammetry were used to investigate the effects of acid oxidation and high temperature heat treatment on the morphology of VXC-72 Composition and the relationship between these carbon-based components and their ability to catalyze ORR.SEM results show that the Hummer acidic oxidation treatment of VXC-72 once or twice can be stripped of its outermost layer of carbon layer structure, and ultimately get the surface (VXCO-1 and VXCO-2) with a smooth lamellar structure.The surface area of the carbon material with the smooth surface of the lamellar structure is larger than that of the VXC-72 before the treatment, and the carbon material after the high-temperature heat treatment (VXCO-1 (900) and VXCO-2 (900)) increase the specific surface area due to the evaporation loss of the graphite-like layer fragments exposed to more internal micropores and mesoporous structures.The results of Raman and XRD show that the oxidation treatment makes the carbon The degree of graphitization of the material increases, while the high temperature heat treatment reduces the degree of graphitization.EA and XPS results show that the Hummer method Oxidation of the carbon material can lead to the main graphitization of N, which leads to the conversion of graphitized nitrogen to pyridine-based nitrogen.ORR results show that the activity of graphitized nitrogen tends to make the ORR reaction undergo two Electronic processes to generate H2O2 as the main product, while the active site of pyridine nitrogen is more likely to undergo ORR reaction through the four-electron process and the main product is water, which contributes to the design and analysis of novel carbon-based oxygen reduction catalysts.