碳基纳米笼包裹铂催化剂构建及其抗醇氧还原催化性能研究

发布时间：2018-02-25 21:01

本文关键词： 碳基纳米包裹催化剂构建及其抗醇还原催化性能研究　出处：《南京大学》2016年硕士论文　论文类型：学位论文

【摘要】：直接甲醇燃料电池(DMFC)具有能量转换效率高、环境友好、低温启动速度快、燃料甲醇易输运且来源广泛、电池结构简单等优点,在便携式电源等方面有广阔应用前景,因而备受关注。其核心是高性能的电催化剂,到目前为止,最常用的Pt/C催化剂的活性高,但存在稳定性差、抗CO中毒能力低等不足。就阴极氧还原(ORR)而言,还存在抗醇能力差的不足,因此,开发催化活性高、抗CO中毒和抗醇能力强、稳定性好的Pt基催化剂尤显重要。人们发展了Pt单原子化、合金化和包裹这三种策略提高其抗醇性能。我们课题组开发出了具有高比表面积、微孔-介孔-大孔共存、高导电性等特征的空心碳基纳米笼。利用其约0.6 nm的微孔和空心纳米笼状结构特征,本论文围绕碳基纳米笼包裹铂催化剂的设计、可控合成及抗醇ORR性能开展了较为系统深入的研究工作,主要进展包括：1.可控地制备出碳基纳米笼包裹或负载的铂催化剂：以具有三维分级结构的碱式碳酸镁为前驱物,苯或吡啶为碳源,制备出具有高比表面积、高导电性、微孔-介孔-大孔共存等特征的三维分级结构碳纳米笼(CNC)和氮掺杂CNC(NCNC)。利用简单的真空-填充方法,将约1.3 nm的Pt粒子填装到CNC和NCNC的纳米空腔内,可控地制备出具有包裹结构的Pt@CNC与Pt@NCNC催化剂。借助微波辅助乙二醇还原法,将约2.6 nm的Pt粒子负载在CNC和NCNC的纳米笼外表面,可控地制备出负载型的Pt/CNC与Pt/NCNC对照组催化剂。2. Pt@CNC 与 Pt@NCNC具有优异的ORR活性、稳定性和抗醇性能：Pt@CNC与Pt@NCNC均展现出了良好的ORR活性,如Pt@NCNC的起始电位为650mV (vs.Ag/AgCl),略低于对照组Pt/NCNC和商业Pt/C的680 mV；二者均表现出完全的抗醇性能,而Pt/C和对照组催化剂完全不抗醇；二者均表现出远优于Pt/C和对照组催化剂的ORR稳定性。通过CO2扩孔和再沉积碳层封孔的方法调变纳米笼壁上微孔的尺寸和数量,发现：当微孔尺寸变大时,Pt@NCNC的ORR性能提高而抗醇性能劣化；当微孔尺寸和数量减小,其ORR性能呈下降趋势,最终与NCNC载体的ORR性能相当。可见,微孔对Pt@NCNC催化剂的电化学性能起关键作用。换句话说,纳米笼壁上的约0.6nm的微孔具有分子筛分效应,允许尺寸相对较小的氧分子和离子通过笼壁进入纳米空腔,而阻碍大尺寸的分子如醇穿过微孔进入笼内。这为开发新颖的抗醇的Pt基ORR电催化剂提供思路。3.原位合成Pt@NCNC催化剂及其ORR性能：通过微波辅助乙二醇还原法将Pt纳米粒子负载在纳米MgO粒子表面,浸渍醋酸镁后热解形成新的MgO层,以吡啶为碳源,得到包裹型Pt@NCNC催化剂。初步的结果表明,在酸性介质中,其具有完全的抗醇性能,但ORR性能不够好。通过优化制备条件,有望开发出高性能的抗醇的Pt基ORR电催化剂。
[Abstract]:Direct methanol fuel cell (DMFC) has the advantages of high efficiency of energy conversion, friendly environment, fast start-up speed at low temperature, easy transportation of fuel methanol from a wide range of sources, simple structure of the battery, and so on. It has a broad application prospect in portable power supply and so on. The core of the catalyst is high performance electrocatalyst. By far, the most commonly used Pt/C catalyst has high activity, but its stability is poor, and its ability to resist CO poisoning is low. Therefore, it is very important to develop Pt catalyst with high catalytic activity, strong ability to resist CO poisoning and alcohol, and good stability. Alloying and encapsulation are three strategies to improve their alcohol resistance. Our team has developed a high specific surface area, micropore-mesoporous and macroporous coexistence. Hollow carbon based nano-cages with high electrical conductivity and so on. Based on its 0.6 nm micropore and hollow nano-cage structure, this paper focuses on the design of carbon based nano-cages coated with platinum catalysts. Systematic and in-depth research work has been carried out on the properties of controllable synthesis and alcohol-resistant ORR. The main progress includes: 1. Controllable preparation of carbon based nano-cage encapsulated or supported platinum catalysts: the basic magnesium carbonate with a three-dimensional hierarchical structure is used as the precursor. Using benzene or pyridine as carbon source, three dimensional graded structure carbon nanocage (CNC) and nitrogen-doped CNC (NCNC) with high specific surface area, high conductivity and coexistence of micropore-mesoporous and macroporous were prepared. The Pt particles of about 1.3 nm were filled into the nano-cavity of CNC and NCNC, and the Pt@CNC and Pt@NCNC catalysts with encapsulated structure were prepared under controlled control. By microwave-assisted ethylene glycol reduction, the Pt particles of about 2.6nm were loaded on the outer surfaces of CNC and NCNC nanometers. The supported catalysts of Pt/CNC and Pt/NCNC were prepared under controlled control. 2.The catalysts of Pt@CNC and Pt@NCNC showed excellent ORR activity, stability and anti-alcohol-resistant properties. Both Pt@CNC and Pt@NCNC exhibited good ORR activity. For example, the initial potential of Pt@NCNC was 650mV / v / AgAgClN, which was slightly lower than that of Pt/NCNC and commercial Pt/C (680mV), both of which showed complete alcohol-resistance, but Pt/C and control catalyst were not resistant to alcohols at all. Both of them showed much better ORR stability than Pt/C and the control catalyst. The size and number of micropores on the wall of the nanocage were adjusted by means of CO2 pore expansion and redeposited carbon layer sealing. It was found that when the size of micropore became larger, the ORR performance of PTN NCNC improved and its anti-alcohol performance deteriorated, and when the size and number of micropores decreased, the ORR performance showed a downward trend, and finally the ORR performance of NCNC carrier was similar to that of NCNC carrier. Micropores play a key role in the electrochemical performance of Pt@NCNC catalysts. In other words, about 0.6 nm micropores on the wall of nanospheres have molecular sieve separation effects, allowing relatively small oxygen molecules and ions to enter the nano-cavity through the cage wall. This provides a way to develop novel Pt based ORR electrocatalysts for alcohol resistance. 3. In situ synthesis of Pt@NCNC catalyst and its ORR performance: microwave assisted ethylene glycol reduction method to Pt. Nanoparticles are loaded on the surface of nanometer MgO particles. After impregnating magnesium acetate, a new MgO layer was formed, and the encapsulated Pt@NCNC catalyst was obtained by using pyridine as carbon source. The preliminary results showed that it had complete alcohol-resistant property in acid medium, but the ORR performance was not good enough. It is expected to develop high performance Pt-based ORR electrocatalyst for alcohol resistance.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：O643.36

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