镍钴基电催化剂的制备及氧电极催化性能研究

发布时间：2018-07-20 15:23

【摘要】：随着人类社会和世界经济的飞速发展,能源的不断消耗和环境的不断恶化成为人类面临的严峻问题,人们迫切的需要发展新型与可再生能源以此减少对有限的传统化石能源的依赖。其中电化学能量转换与存储技术(如燃料电池、金属-空气电池和电解水等),因能量转化效率高和环境友好等优点成为了各国科学家的研究方向和热点。电化学能量转换与存储技术的核心是一系列的电化学反应过程:氧还原反应、氢气氧化反应和氢气、氧气析出反应。一般而言,动力学非常缓慢的氧还原和氧析出反应制约着整个电化学装置的综合性能和商业化进程。合成和设计优良活性的电催化剂是加速这些反应进程的关键。目前,商用电催化剂都为贵金属基材料(如:铂基、钯基、铱基等),其高昂的价格和稀缺性成为上述电化学技术商业化应用的制约因素。近年来,为提高电催化反应的效率,开发价格低廉、地球资源丰富的非贵金属纳米电催化剂替代贵金属纳米电催化剂已经得到广泛的关注。基于此,本文主要内容包括合成了催化活性高、稳定性好和价格低廉的氧气电催化剂。主要内容包括以下几个方面:1,我们提出一种"自上而下"的合成策略,通过简单的原位高温热解方法制备了一种负载量超过4%的氮掺杂的多孔碳负载Co单原子催化剂。以ZnCo-BMOF为前驱体,在超过800℃高温热解还原的过程中,Co离子被配体热解形成的碳还原并伴随着Zn的挥发。掺杂的Zn起着"栅栏"的作用增加了相邻Co离子在空间上的距离,不发生Co-Co键的生成。合成的Co单原子催化剂在0.1M KOH溶液中表现出优越的氧还原催化活性和稳定性,半波电位达到0.881V,远远超过Pt/C和大部分报道的非贵金属纳米电催化剂。在研究过程中,我们利用球差矫正电镜,X射线精细吸收谱等表征手段,在原子水平上对催化剂的结构给出了较为清晰的图像,从而为探索催化剂的构效关系奠定了良好的基础。此反应策略可以推广到其它金属(如Ni,Cu,Fe,Ru)等一系列单原子催化剂的合成,为以后其他单原子催化剂的制备提供了新的策略和思路。2,电催化剂的设计和合成在电化学可再生能源转换技术中占据非常重要的地位。利用氧化石墨烯(GO)直接分散未经处理的碳纳米管作为基底,通过简单温和的水解方法负载具有一定氧析出活性的NiCo层状双氢氧化物(NiCo-LDH)。氧化石墨烯被认为具有类表面活性剂的性质,含有疏水性的芳香碳环和亲水性的羟基、羧基等边缘基团。氧化石墨烯可以与碳纳米管通过π-π键相互作用而直接分散碳纳米管(CNT),无需对碳纳米管表面进行功能化或表面活性剂处理,氧化石墨烯与碳纳米管的表面可通过π-π键相互作用而结合。这种方法不仅保留了氧化石墨烯的水溶性,并且碳纳米管也无需经过任何功能化修饰处理,能保留完整的电子结构。与此同时,碳纳米管阻止了氧化石墨烯的聚集并且提高了氧化石墨烯的导电性。通过改变GO与CNT的比例,当GO与CNT的比例为1:1时,得到OER活性最优的复合材料。在0.1 M KOH溶液中,NiCo-LDH/GO-CNT的OER电催化的起始电位仅为1.42V,比其他催化剂的起始电位要负得多。稳定性测试表明循环1000圈后电流密度仍能保持90%以上。该复合材料具有高催化活性和良好稳定的主要原因是LDH和GO-CNT对OER催化的协同效应。
[Abstract]:With the rapid development of human society and the world economy, the continuous consumption of energy and the deterioration of the environment have become a serious problem faced by mankind. People urgently need to develop new and renewable energy to reduce the dependence on the Limited traditional fossil energy. The core of the electrochemical energy conversion and storage technology is a series of electrochemical reaction processes: oxygen reduction reaction, hydrogen oxidation reaction, hydrogen oxidation and oxygen precipitation reaction. Generally speaking, kinetics is very important. Slow oxygen reduction and oxygen precipitation restrict the comprehensive performance and commercialization of the entire electrochemical device. The key to the acceleration of these processes is the synthesis and design of excellent active electrocatalysts. At present, commercial electrocatalysts are precious metal based materials (such as platinum, palladium, iridium, etc.), with high prices and scarcity. In recent years, in order to improve the efficiency of the electrocatalytic reaction and to develop the low price, the non noble metal nanoselectrocatalyst has been widely concerned in recent years to replace the noble metal nanoscale electrocatalyst. Based on this, the main contents of this paper include the synthesis of high catalytic activity, good stability and good stability. Low price oxygen electrocatalysts. The main contents include the following aspects: 1, we propose a "top-down" synthesis strategy to prepare a Co monatomic catalyst with a load of more than 4% of the nitrogen doped porous carbon supported by a simple in situ high-temperature pyrolysis method. With ZnCo-BMOF as a precursor, high temperature pyrolysis over 800 degrees centigrade. In the original process, the Co ions were reduced by the carbon formed by the ligand and accompanied by the volatilization of Zn. The doping Zn played a "fence" role to increase the distance of adjacent Co ions in the space and did not produce the Co-Co bond. The synthesized Co single atom catalyst showed superior oxygen reduction catalytic activity and stability in the 0.1M KOH solution and half wave electricity. 0.881V, far more than Pt/C and most of the non noble metal nanoscale catalysts reported, in the study process, we use spherical aberration electron microscopy, X ray fine absorption spectrum and other characterization means to give a more clear image on the structure of the catalyst at the atomic level, which is good for the exploration of the structure effect relationship of the catalyst. The reaction strategy can be extended to the synthesis of a series of single atomic catalysts, such as Ni, Cu, Fe, Ru, etc., which provide a new strategy and thought.2 for the preparation of other single atom catalysts in the future. The design and synthesis of the electrocatalyst occupy a very important position in the electrochemical renewable energy transfer technology. GO directly disperses untreated carbon nanotubes as substrates and loads NiCo layered double hydroxides (NiCo-LDH) with a certain oxygen precipitation activity through simple and mild hydrolysis. Graphene oxide is considered to have the properties of the surface active agent, containing hydrophobic aromatic carbon rings, hydrophilic hydroxyl groups, carboxyl groups and other marginal groups. Fossil graphene can disperse carbon nanotubes (CNT) directly with carbon nanotubes through the interaction of pion bonds. The surface of carbon nanotubes is not required to be functionalized or treated by surfactant. The surface of graphene oxide and carbon nanotubes can be combined by the interaction of pi - pi bonds. This method not only preserves the water solubility of graphene oxide, but also the surface of carbon nanotubes. At the same time, carbon nanotubes prevent the aggregation of graphene oxide and increase the conductivity of graphene oxide. By changing the ratio of GO to CNT, when the ratio of GO to CNT is 1:1, the composite with the best activity of OER is obtained. In the 0.1 M KOH solution. In the liquid, the starting potential of NiCo-LDH/GO-CNT's OER electrocatalysis is only 1.42V, which is much more negative than the starting potential of other catalysts. The stability test shows that the current density can remain above 90% after 1000 cycles. The main reason for the high catalytic activity and good stability of the composite is the synergistic effect of LDH and GO-CNT on OER.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O643.36;O646

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