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基于羧酸类配体的金属有机框架(MOFs)材料的合成及其电化学性能研究

作者:完美论文网  来源:www.wmlunwen.com  发布时间:2019/10/24 9:40:40  

摘要:超级电容器作为一种高效新型的储能设备,其具有快速充放电能力,稳定的循环寿命,同时能量密度高。电极材料的性能是决定超级电容器比电容的因素之一。常用的电极材料主要有碳材料、金属(氢)氧化物和导电聚合物。

金属有机框架结构材料(MOFs)是一种新型的多孔材料,具有大表面积、可调的孔径和掺入能够发生氧化还原反应的金属中心离子。MOFs自身携带的孔或通道对于超级电容器充电和放电过程中离子的快速转移和扩散是非常是有利的,被认为是用于超级电容器电极材料研究的非常有希望的电极材料。本论文通过合成导电性能较好的MOFs材料来提高电子传输效率,进而实现高容量和倍率性能。选用了不同的羧酸类以及含氮杂环类有机物分别作为有机配体,合成了不同纳米结构的金属有机材料,进而组装成超级电容器,详细讨论并测试了其电化学性能。具体研究内容如下:

1、选用1,3,5-苯三甲酸作为有机配体,硝酸锰作为金属离子,采用水热法合成了棒状的Mn-MOFs。电化学测试表明Mn-MOFs在0.5 A g-1电流密度下具有371 F g-1的优异比电容,并且具有高的倍率性能(在10 A g-1电流密度下的容量保持率为67%)。此外,设计的混合超级电容器在1 A g-1电流密度下, 2000次循环后能够保留初始比电容的96.2%,具有优良的循环稳定性。

2、分别利用2,5-吡嗪二羧酸和2,3-吡嗪二羧酸为有机配体,四水合硝酸锰为原料,在高温反应釜中合成出不同的Mn-MOFs用于超级电容器电极材料。以2,5-吡嗪二羧酸为有机配体合成的Mn-MOFs-1在0.5 A g-1电流密度下比电容达到384 F g-1,组装的相应的非对称电容器在1000次循环充放电后依旧保持着初始比电容的92.4%。以2,3-吡嗪二羧酸为有机配体合成的Mn-MOFs-2在电流密度为0.5 A g-1时测得其比电容为323 F g-1, 组装成非对称电容器时,1000次循环充放电后还保持着初始比电容的87.4%。比较而言,羧酸位于对位的配体更加有利于获得优良的电化学性能。

3、采用6-喹喔啉羧酸作为有机配体,硝酸锰和硝酸镍为原料,合成出Ni/Mn双金属MOFs。Ni/Mn-MOFs在0.5A g-1电流密度下比电容达到了1015 F g-1,组装成的非对称电容器时在1 A g-1电流密度下比电容为154 F g-1。其在1000次循环充放电之后的比电容保持率是74.1%, 说明该材料具有较好的电化学性能。

As a highly efficient new energy storagedevice, supercapacitor has rapid charge-discharge capability, stable cycle lifeand high energy density. The performance of the electrode materials are onecrucial factor to determine the specific capacitance of thesupercapacitor.  The frequently usedelectrode material mainly includes carbon nanomaterial, metal (hydr)oxides andconductive polymer.

Metal organic frameworks (MOFs) material isa new type of porous material with large surface area, adjustable pore size andmetal center ions that are capable of undergoing redox reaction. The pores andholes in MOFs help to the fast transfer and diffusion of ions during thecharge-discharge process of supercapacitors. Therefore, MOFs have beenconsidered as a promising electrode material for supercapacitor.

In this article, electronically conductiveMOFs were synthesized to improve the transfer rate of electrons and bring abouthigh capacitance and rate capability. Various carboxylic acids andnitrogen-containing heterocyclic organic compounds were utilized as organicligands to synthesize different metal organic materials. Furthermore,corresponding asymmetrical supercapacitors were assembled based on these MOFselectrode materials and their electrochemical performances were detailedlyinvestigated.  The specific researchcontent is listed as follows:

1. Rod-shaped manganese based metal-organicframeworks (Mn-MOFs) were prepared through a facile solvothermal method using1,3,5-benzentricarboxylic acid as organic linker and manganese nitrate was usedas the metal ion salt.  The Mn-MOFsexhibited a high specific capacitance of 371 F g-1 at 0.5 A g-1 and anexcellent rate capability (capacity retention rate is 67% at a current of 10 Ag-1).  Besides, the fabricated hybridsupercapacitors have an excellent cycle stability (retained 96.2% of theinitial capacitance after successive 2,000 charge-discharge cycles at a currentdensity of 1 A g-1).

2. Various Mn-MOFs were synthesized inhigh-temperature reactor using 2,5-pyrazinedicarboxylic acid and2,3-pyrazinedicarboxylic acid as organic ligands and manganese nitratetetrahydrate as raw materials.  Thespecific capacitance of Mn-MOFs-1 that were synthesized using2,5-pyrazinedicarboxylic acid as an organic ligand reaches 384 F g-1 at acurrent density of 0.5 A g-1.  Whenassembled into an asymmetric capacitor, the supercapacitor still maintains aninitial specific capacitance of 92.4% after 1000 cycles of charge anddischarge.  Furthermore, Mn-MOFs-2 thatwere synthesized using 2,5-pyrazinedicarboxylic acid as an organic ligand has aspecific capacitance of 323 F g-1 at a current density of 0.5 A g-1 and theassembled asymmetric capacitor also maintained 87.4% of the initial specificcapacitance after 1000 cycles of charge and discharge.  Comparatively speaking, the carboxylic acidligands in the opposite position are more favorable to obtain excellentelectrochemical performances. 

3.Ni/Mn bimetallic MOFs were synthesized byusing 6-quinoxaline carboxylic acid as an organic ligand and manganese nitrateand nickel nitrate as raw metal salt. Ni/Mn-MOFs have a specific capacitance of 1015 F g-1 at a currentdensity of 0.5 A g-1 and the assembled asymmetric supercapacitor shows aspecific capacitance of 154 F g-1 at a current density of 1 A g-1. After 1000cycles of charge and discharge, the specific capacitance retention rate was74.1%, indicating that the material has good electrochemical performances.

关键词:金属有机框架材料;羧酸;电化学性能;超级电容器

Metal-organic framework materials;Carboxylic acid; Electrochemical performance; Supercapacitor

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