氮氧双掺杂介孔碳材料用作锂空气电池正极催化剂的研究

发布时间：2018-04-28 12:51

本文选题：锂空气电池 + 模板法　；参考：《哈尔滨工业大学》2017年硕士论文

【摘要】：现代社会对高能量密度储能设备的需求越来越强烈,因而具有极高理论能量密度的有机体系锂空气吸引了研究人员的的广泛关注。然而,要实现这种高能密度储能设备的实际应用,尚有很多问题需要解决。总体来说,目前锂空气电池面临着能量效率低、负反应严重、循环性能差等各种不足,针对这些问题和挑战,本论文从正极材料的设计和优化入手,探究了材料的结构特征和表面化学特性对电池性能的影响,并通过研究RuO_2/碳复合材料催化剂的电化学特性,明确了碳基体材料在高催化活性复合材料中的重要作用,并最终获得了一种能量效率高、循环寿命长的锂空气电池正极材料。首先以富含氮元素的三聚氰胺和甲醛作碳源,以不同质量的纳米SiO_2(Aerosil-200)做硬模板,采用水热聚合以及后续的高温煅烧获得了N、O双掺杂的单模板介孔碳泡沫材料。当三聚氰胺和SiO_2的质量比为7:4时获得的MCF-H7样本具有最高的比表(1028 m2 g-1)和最大的孔容(2.577 cm3 g-1)。电池测试结果显示,高比表、大孔容有利于电池获得高的放电比容量和好的氧还原反应(ORR)和氧析出反应(OER)催化活性,最终MCF-H7电极在100 m A g-1的电流密度下获得了高达13100 m Ah g-1的放电容量和低至1.08 V的充放电电压差,优于商业碳黑Super P的4600 m Ah g-1和1.55 V。在单模板介孔碳材料MCF-H7的基础上进一步引入不同质量的F127软模板剂,制备双模板介孔碳泡沫材料。电池测试结果显示MCF-H7-S2.5样本具有最佳的综合性能,其在保持材料具有较高比容量和ORR/OER催化活性的同时还具有较好的循环性能。最终,在200 m A g-1电流密度并限定500 m Ah g-1的放电比容量下能稳定循环25圈,高于单模板介孔碳泡沫样本MCF-H7的15圈。针对MCF-H7和MCF-H7-S2.5两种材料在电池性能上表现出来的差异,本论文从材料的结构特性和表面化学特性分析了其原因。结果表明,碳材料中高的O原子掺杂有利于电池获得更好的ORR和OER催化活性,但同时也会导致材料的循环性能较差;而低O高N的表面化学特性使材料保持一定的催化活性外,还能更好的抑制负反应的发生,从而提升材料的循环性能。该结果表明,同调控碳材料的结构特征一样,合理优化材料的表面化学特性也是改善碳材料电化学性能的有效手段。最后,以合成的介孔碳泡沫为基础,通过水热反应制备了RuO_2/碳复合材料。电池测试结果显示,在200 m A g-1的电流密度下复合材料显示出低至1.02 V的充放电过电势。在400 m A g-1的电流密度并限定放电比容量为500 m Ah g-1条件下进行循环性能测试,RuO_2/MCF-H7电极能稳定循环102圈,RuO_2/MCF-H7-S2.5电极则更是达到了160圈,该结果一方面显示了复合材料优越的电化学性能;另一方面也说明即使负载了高活性的电催化剂,碳基材料的性质仍然对锂空气电池性能有重要影响。
[Abstract]:In modern society, the demand for high energy density energy storage equipment is more and more intense, so lithium air with extremely high theoretical energy density has attracted extensive attention of researchers. However, there are still many problems to be solved to realize the practical application of this kind of high energy density energy storage equipment. Generally speaking, the lithium air battery is faced with many disadvantages, such as low energy efficiency, serious negative reaction, poor cycle performance and so on. In view of these problems and challenges, this paper starts with the design and optimization of cathode materials. The effects of the structure and surface chemical properties of the materials on the performance of the battery were investigated. The important role of the carbon matrix materials in the high catalytic activity composites was clarified by studying the electrochemical characteristics of the RuO_2/ carbon composite catalysts. Finally, a lithium air battery cathode material with high energy efficiency and long cycle life is obtained. Firstly, using nitrogen-rich melamine and formaldehyde as carbon source and different quality nano-SiO2Aerosil-200) as hard template, the single template mesoporous carbon foams doped with Nano O were obtained by hydrothermal polymerization and subsequent calcination at high temperature. When the mass ratio of melamine to SiO_2 is 7:4, the MCF-H7 samples obtained have the highest specific ratio of 1028 m ~ 2 g ~ (-1) and the maximum pore volume of 2.577 cm3 g ~ (-1). The results of the battery test showed that the high ratio meter and large pore volume were beneficial to obtain high discharge specific capacity and good catalytic activity of oxygen reduction reaction ORR and oxygen precipitation reaction. At the current density of 100mAg-1, the discharge capacity of the final MCF-H7 electrode was up to 13100 mAh g-1 and the charge-discharge voltage difference was as low as 1.08V, which was better than that of commercial carbon black Super P (4600 mAh g-1) and commercial carbon black (Super P) (4600 mAh g-1 and 1.55V). Based on the single template mesoporous carbon material (MCF-H7), the double template mesoporous carbon foams were prepared by introducing F127 soft template with different quality. The results of battery test showed that the MCF-H7-S2.5 sample had the best comprehensive performance, which kept the material with high specific capacity and catalytic activity of ORR/OER, and had good cycling performance at the same time. Finally, at the current density of 200mAg-1 and the specific discharge capacity of 500mAh g-1, the cycle can be stabilized for 25 cycles, which is higher than that of MCF-H7 of single template mesoporous carbon foam sample. In view of the difference between MCF-H7 and MCF-H7-S2.5 in battery performance, this paper analyzes the reasons from the structural characteristics and surface chemical characteristics of the materials. The results show that the high O atom doping in carbon materials is beneficial to obtain better catalytic activity of ORR and OER, but it also leads to poor cycling performance of the materials, while the surface chemical properties of low O and high N make the materials keep a certain catalytic activity. Can also better inhibit the occurrence of negative reactions, thereby improving the cycling performance of materials. The results show that the optimization of the surface chemical properties of carbon materials is also an effective means to improve the electrochemical properties of carbon materials as well as regulating the structural characteristics of carbon materials. Finally, based on the synthesized mesoporous carbon foam, RuO_2/ carbon composites were prepared by hydrothermal reaction. The results of the battery test show that the composite shows a charge-discharge overpotential of as low as 1.02 V at the current density of 200 mg ~ (-1). Under the condition of current density of 400mAg-1 and limited discharge capacity of 500mAh g-1, the cycle performance of Ruo 20 / MCF-H7 electrode can stabilize 102 cycles and Ruo / MCF-H7-S2.5 electrode reaches 160 cycles. On the one hand, the results show that the composite has excellent electrochemical performance, and on the other hand, the properties of carbon-based materials still have an important effect on the performance of lithium-air batteries even if the electrocatalysts are loaded with high activity.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM911.41

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