石墨烯负载镍基复合材料氧还原催化剂的研究

发布时间：2018-12-20 07:10

【摘要】：由于环境污染和能源紧张的加剧,科学家正努力研究新型的清洁能源来减少对传统化石燃料的消耗。燃料电池,由于其高的电流密度,低的操作环境要求以及污染物排放量而广泛被人们关注,但是,高成本的铂基催化剂阻碍了燃料电池的大规模推广,另外,在催化过程中产生的CO容易引起金属铂中毒,从而失去催化活性。因此,为了降低燃料电池催化剂的成本并促进其商业化应用,对非贵金属催化剂的研究一直都是人们关注的重点,例如,以多组分合金以及以石墨烯为载体的金属催化剂。鉴于氧还石墨烯在各领域表现出的优异的性能,本文以其为载体材料,与过渡金属化合物相复合来制备复合材料催化剂,旨在探索制备高活性高稳定性的氧还原催化剂。在本文中,将Ni O作为研究对象,GO负载的Ni(OH)_2为前驱体制备不同形貌的复合材料催化剂,所制备催化剂的结构和形貌主要由X-射线衍射仪(XRD),Raman光谱,扫描电镜(SEM)以及透射电镜(TEM)测试与表征,其电化学性能主要由循环伏安法(CV)、线性扫描伏安法(LSV)、塔菲尔曲线(Tafel)以及电流-时间曲线(i-t)表示,而氧还原过程的催化机理可由旋转圆盘电极(RDE)、交流阻抗谱图(EIS)和旋转环盘电极(RRDE)测试来说明。具体内容概括为以下几个部分:(1)首先,本文研究了在不同气体氛围下(空气、氩气和氨气)热解Ni(OH)_2/GO得到的s-NiO/rGO、g-NiO/rGO和g-NiO/N-rGO三种催化剂结构形貌以及电化学性能的差异,结果表明,在空气下热解Ni(OH)_2/GO得到了片状的NiO负载在rGO上,而在氩气和氨气气氛下则得到了球形的NiO,并且在氨气气氛处理下有一部分的N原子掺杂到还原的氧化石墨烯上。电化学测试表明,g-NiO/N-rGO的电流密度和初始电压(-0.13 V)都接近于商业Pt/C(20%)电极,而NiO/rGO催化活性提高的原因主要是在氨气氛围下热解而引入了氮原子的原因,形貌对氧还原催化过程影响较小一些,RDE和RRDE测试都证明了g-NiO/N-rGO主要发生四电子反应。(2)其次,为获得催化活性更高的催化剂,使用金属Pd对NiO/rGO进行修饰,主要方法是使用NaBH_4进行还原,将Pd还原到NiO/rGO上。研究表明,NiO和Pd颗粒均匀的负载在石墨烯上,金属Pd的颗粒较大一些,主要是NaBH_4的还原性太强所导致的。通过电化学测试可得知,Pd修饰NiO/rGO后,无论是在起始电压还是电流密度方面都有一定的提高,主要是Pd负载在还原氧化石墨烯上后提高了其导电性并减小了电极与溶液的接触电阻,提高了其氧还原催化活性。而旋转圆盘法和旋转环盘法则从两方面证明在催化氧化过程Pd@NiO/rGO主要发生四电子反应,并伴随少量二电子反应发生。
[Abstract]:As environmental pollution and energy tensions intensify, scientists are working on new clean energy sources to reduce the consumption of traditional fossil fuels. Fuel cells, due to their high current density, low operating environment requirements and pollutant emissions, have attracted widespread attention. However, the high cost of platinum-based catalysts has hindered the large-scale promotion of fuel cells. CO produced in the catalytic process is prone to lead to platinum poisoning, thus losing the catalytic activity. Therefore, in order to reduce the cost of fuel cell catalysts and promote their commercial application, the research of non-noble metal catalysts has been the focus of attention, such as multi-component alloys and graphene supported metal catalysts. In view of the excellent performance of Oxygenene in various fields, the composite catalyst was prepared by using it as the support material and the transition metal compound phase. The aim of this paper was to explore the preparation of oxygen reduction catalyst with high activity and stability. In this paper, Ni O was used as the research object and Ni (OH) _ 2 supported on GO was used as precursor to prepare composite catalysts with different morphologies. The structure and morphology of the catalysts were mainly determined by (XRD), Raman spectra of X-ray diffractometer. The electrochemical properties of SEM (SEM) and TEM (TEM) were characterized by cyclic voltammetry (CV), linear scanning voltammetry (CV), (LSV), Tafel curve (Tafel) and current-time curve (i-t). The catalytic mechanism of oxygen reduction can be explained by (RDE), impedance spectroscopy (EIS) and (RRDE) measurement. The specific contents are summarized as follows: (1) at first, we study the s-Nio / rGO. obtained by pyrolysis of Ni (OH) _ 2/GO in different atmosphere (air, argon and ammonia). The structural morphology and electrochemical properties of the three catalysts g-NiO/rGO and g-NiO/N-rGO were different. The results showed that the NiO supported on rGO was obtained by pyrolysis of Ni (OH) _ 2/GO in air. The spherical NiO, was obtained in argon and ammonia atmosphere, and some N atoms were doped into the reduced graphene oxide in ammonia atmosphere. Electrochemical measurements show that the current density and initial voltage (-0.13 V) of g-NiO/N-rGO are close to those of commercial Pt/C (20%) electrodes. The main reason for the increase of catalytic activity of NiO/rGO is the introduction of nitrogen atoms in the pyrolysis of ammonia atmosphere, and the morphology has less influence on the catalytic process of oxygen reduction. RDE and RRDE tests show that g-NiO/N-rGO mainly occurs four-electron reaction. (2) secondly, in order to obtain the catalyst with higher catalytic activity, the metal Pd is used to modify the NiO/rGO. The main method is to reduce NiO/rGO by using NaBH_4. Restore Pd to NiO/rGO. The results show that the particles of NiO and Pd are uniformly loaded on graphene, and the particles of metal Pd are larger, which is mainly caused by the too strong reduction of NaBH_4. The electrochemical measurements show that the initial voltage and current density of NiO/rGO modified by Pd can be improved to a certain extent. The main reason is that the Pd supported on the reduced graphene can improve the electrical conductivity, decrease the contact resistance between the electrode and the solution, and improve the catalytic activity of oxygen reduction. The rotating disk method and the rotating ring disk rule show that Pd@NiO/rGO mainly occurs in the catalytic oxidation process with a small number of two-electron reactions.
【学位授予单位】：济南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36;TB333

【参考文献】