基于层状氢氧化物层间限域空间可控制备碳基纳米材料及其电化学性能研究
发布时间：2018-08-11 12:24
【摘要】：随着化石燃料的不断消耗,能源危机和环境污染越来越严重,对人类健康、能源安全和环境保护提出了更为严峻的挑战,因此迫切需要发展新型清洁能源。燃料电池和锂离子电池具有环境污染小、能量转换效率高等优点,作为有效的清洁电源有望解决上述问题,但提高燃料电池和锂离子电池电化学性能的关键在于开发具有优异性能的电极材料。本论文利用层状氢氧化物的层间限域空间可控制备了一系列掺杂碳基纳米材料,考察了合成工艺与材料结构之间的关系规律,对其氧还原(ORR)电催化和锂存储性能进行了测试和评估,并深入地研究了材料结构和电化学性能之间的内在关系。主要研究内容如下:1、基于镁铝水滑石(MgAl-LDH)层间二维限域效应,制备了选择性氮硫双掺杂碳纳米片(NSCNs),并对其氧还原电催化和锂存储性能及机制进行了研究。首先将间氨基苯磺酸根阴离子通过一步水热法插入MgAl-LDH层间,再通过高温碳化和酸化刻蚀实现了 NSCNs的可控制备,获得的NSCNs由大量相互连接的纳米片组成,呈现出丰富的多级微介孔和高的比表面积。LDH的层间二维限域效应不仅促进了具有平结构的吡啶N和吡咯N的形成(达到90.3%),而且有效地缓解了高温下N原子和S原子的损失,提高了杂原子掺杂量。用作ORR电催化剂,NSCNs在碱性介质中表现出高的催化活性,与商业Pt/C催化剂相比,具有更好的抗甲醇毒化能力和稳定性。用作锂离子电池负极材料,NSCNs表现出超高的比容量(在电流密度0.2 A·g-1下循环110周后比容量可达2240 mAh·g-1),优异的倍率性能(在电流密度4.0A·g-1下比容量为983 mAh·g-1)和长久的稳定性(在电流密度4.0 A·g-1下循环500周后的可逆比容量仍达到950mAh·g-1)。此外,XPS结果和DFT理论计算结果表明在循环过程中掺杂的吡咯N原子能够和Li+结合形成Li3N并从掺杂碳上脱落,同时在邻近吡咯N原子的位点形成更多的边缘C原子用于储锂,而吡啶N和季N原子不能发生像吡咯N原子那样的脱落。2、基于CoAl-LDH层间二维限域效应,制备了 Co9S8/氮掺杂碳纳米片基空心球复合物(Co9S8/NHCS),并对其氧还原催化活性进行了研究。首先将间氨基苯磺酸根阴离子通过一步水热法插入CoAl-LDH层间,再通过高温碳化和选择性酸化刻蚀制备了 Co9S8/NHCS,获得的Co9S8/NHCS具有由大量纳米片组成的空心球状结构,其中单分散的Co9S8植入碳纳米片中。此结构主要有以下优势:基于层间二维限域方法获得了单分散的Co9S8颗粒,使Co9S8的催化活性位点能够被充分地暴露和利用,因而具有高的催化活性;间氨基苯磺酸根阴离子的分解碳化和Co9S8的生成同时发生,使得生成的Co9S8纳米颗粒能够植入碳纳米片中,因而具有高的稳定性;前驱体的空心球状结构使得制备的Co9S8/NHCS也具有独特的空心球状结构和多级孔结构,有助于在催化过程中促进电解质离子、反应中间体和产物的快速传输。此外,本工作系统地研究了焙烧温度和空心球状结构对催化剂结构(如比表面积、孔分布、氮掺杂类型、Co9S8的尺寸大小等)和催化活性的影响,结果表明900 ℃是优化的焙烧温度且空心球状结构对ORR催化活性的提高具有非常重要的作用。电化学测试表明在900℃下制备的Co9S8/NHCS催化剂在碱性和酸性介质中均具有最高的ORR催化活性、持久的稳定性和优异的抗甲醇毒化能力。3、基于CoAl-LDH层间二维限域效应,制备了含有Co-Nx组分的碳纳米片基空心球复合物(Co-N/C),并对其在不同pH介质中的氧还原催化活性和活性位点进行了研究。首先将间氨基苯磺酸根阴离子通过一步水热法插入CoAl-LDH层间,再通过高温碳化和酸化刻蚀制备了 Co-N/C。获得的Co-N/C具有由大量含有Co-Nx组分的碳纳米片组成的空心球状结构,呈现出丰富的微介孔和高的比表面积。作为ORR电催化剂,对其在不同pH介质中的催化活性进行了测试,电化学数据表明在900℃下制备的Co-N/C催化剂具有最高的ORR催化活性,在碱性和中性介质中表现出高的半波电位和大的极限扩散电流,该性能和商业Pt/C催化剂相当,同时表现出优异的稳定性和抗甲醇毒化能力。通过在不同pH介质中研究掩蔽离子(SCN-和F-)对Co原子中心进行毒化前后的ORR催化活性以及比较Co-N/C催化剂的Co-Nx位点破坏前后的ORR催化活性,发现在碱性介质中,Co-N/C催化剂的催化活性没有明显地变化,而在中性和酸性介质中,Co-N/C催化剂的催化活性明显地降低,说明Co-N/C催化剂中的Co-Nx位点在中性和酸性介质中直接作为ORR催化活性位点,而在碱性条件下对催化活性的影响是可忽略的。4、基于Co(OH)2层间二维限域效应,制备了硫化钴和氮掺杂碳纳米片基花状复合物(Co9S8/CO1-xS@]NC),并对其形成机理和锂存储性能进行了研究。首先将间氨基苯磺酸根阴离子通过一步水热法插入Co(OH)2层间,再将具有插层结构的Co(OH)2前驱体与硫粉均匀混合后在N2气氛下焙烧得到Co9S8/Co1-xS@NC。获得的Co9S8/Co1-xS@NC具有由大量植入小尺寸硫化钴纳米颗粒的氮掺杂碳纳米片组成的花状形貌,并且在硫化钴颗粒外表面覆盖有几层石墨烯。通过对插层结构的Co(OH)2前驱体的碳化/硫化机理进行详细地研究,发现间氨基苯磺酸根离子分解碳化形成碳纳米片发生在约200 ℃-400 ℃,在这个过程中伴随着S的升华、Co(OH)2层的分解和Co1-xS纳米颗粒的生成,所以Co1-xS纳米颗粒可以植入在碳纳米片中。随着焙烧温度的增加,部分Co1-xS逐渐向Co9S8转变,同时碳纳米片的石墨化程度进一步提高。此结构主要有以下优势:具有小尺寸的硫化钴能够缩短锂离子的传输距离和缓解脱嵌锂过程中产生的体积应力,这有助于提高电极的循环稳定性和倍率性能;氮掺杂的碳基质和硫化钴外表面覆盖的几层石墨烯不仅可以防止颗粒之间的聚集和减小颗粒之间的电阻,而且可以有效地缓解在充放电循环过程中硫化钴的体积膨胀和多硫化物在电解液中的溶解,因此有助于提高电极的循环稳定性;薄的颗粒-纳米片结构可以减少离子和电子的传输距离,使得硫化钴纳米颗粒被充分地利用,因此有助于获得高的比容量;具有大比表面积的花状形貌和多级孔结构能够促进电解液进入电极内部,加快锂离子的传递。此外,通过调变前驱体和硫粉的比例或焙烧温度可有效地控制硫化钴的组成。作为锂离子电池负极材料,电化学测试表明在900 ℃,且前驱体和硫粉的质量比为1:0.75时制备的Co9S8/Co1-xS@NC表现出高的比容量和优异的倍率性能。本论文提出的基于层状氢氧化物层间限域合成方法可拓展到制备其它具有优异性能的功能性掺杂碳基纳米材料,并在超级电容器、太阳能电池、传感器、环境保护、催化等领域表现出广阔的应用前景。
[Abstract]:With the continuous consumption of fossil fuels, the energy crisis and environmental pollution are becoming more and more serious, which poses a more serious challenge to human health, energy security and environmental protection. Therefore, it is urgent to develop new clean energy sources. Fuel cells and lithium-ion batteries have the advantages of less environmental pollution, high energy conversion efficiency, and so on, as an effective cleaner. In this paper, a series of doped carbon-based nanomaterials were synthesized by controlling the interlayer confinement space of layered hydroxides, and the relationship between the synthesis process and the structure of the materials was investigated. The main research contents are as follows: 1. Selective Nitrogen-Sulfur double-doped carbon nanosheets (NSCNs) were prepared based on the two-dimensional confinement effect between MgAl-LDH layers, and their oxygen content was determined. The reductive electrocatalysis and lithium storage properties and mechanisms were studied. The m-aminobenzenesulfonate anion was first inserted into the MgAl-LDH interlayer by one-step hydrothermal method, and then controlled preparation of NSCNs was realized by high temperature carbonization and acidification etching. The obtained NSCNs consisted of a large number of interconnected nanosheets, showing rich multistage mesoporous and high-level. Specific surface area. The two-dimensional interlayer confinement effect of LDH not only promotes the formation of pyridine N and pyrrole N with flat structure (up to 90.3%), but also effectively alleviates the loss of N and S atoms at high temperature and increases the amount of heteroatom doping. As an ORR electrocatalyst, NSCNs exhibit high catalytic activity in alkaline medium and commercial Pt/C catalyst. NSCNs, as anode materials for lithium-ion batteries, exhibit super-high specific capacity (after 110 weeks of cycling at current density of 0.2 A g-1), excellent rate performance (at current density of 4.0 A g-1, specific capacity of 983 mAh g-1) and long-term stability (at current density of 4.0 A g-1). In addition, XPS and DFT calculations show that the doped pyrrole N atoms can bind to Li + to form Li3N and fall off the doped carbon during the cycling process. At the same time, more edge C atoms are formed at the sites adjacent to the pyrrole N atoms for lithium storage. Pyridine N and quaternary N atoms can not fall off like pyrrole N atoms. 2. Co9S8/N-doped carbon nanosheet-based hollow sphere composite (Co9S8/NHCS) was prepared based on CoAl-LDH interlayer two-dimensional confinement effect, and its catalytic activity for oxygen reduction was studied. Firstly, m-aminobenzenesulfonate anion was inserted into CoAl-LDH by one-step hydrothermal method. Co9S8/NHCS was prepared by high temperature carbonization and selective acidification etching. The obtained Co9S8/NHCS has a hollow spherical structure consisting of a large number of nanosheets, in which monodisperse Co9S8 was implanted into carbon nanosheets. The structure has the following advantages: monodisperse Co9S8 particles were obtained based on the two-dimensional finite-region method, which prompted the formation of Co9S8 particles. The decomposition and carbonization of m-aminobenzenesulfonate anion and the formation of Co9S8 occur simultaneously, which makes the Co9S8 nanoparticles implanted into carbon nanosheets and thus has high stability. The hollow spherical structure of the precursor makes the prepared Co9S8/NHCS highly stable. In addition, the effects of calcination temperature and hollow spherical structure on the structure of the catalysts (such as specific surface area, pore distribution, nitrogen doping type, size and size of Co9S8) and The results showed that 900 C was the optimum calcination temperature and the hollow spherical structure played a very important role in enhancing the catalytic activity of ORR. Electrochemical tests showed that the CO9S8/NHCS catalysts prepared at 900 C had the highest ORR catalytic activity in both alkaline and acidic media, long-term stability and excellent anti-A activity. Alcohol toxicity. 3. Carbon nanosheet-based hollow sphere composites (Co-N/C) containing Co-Nx components were prepared based on the two-dimensional confinement effect of C oAl-LDH layers. The catalytic activity and active sites of the hollow sphere composites in different pH media were studied. The anions of m-aminobenzenesulfonate were firstly inserted into the layers of C oAl-LDH by one-step hydrothermal method and then recanalized. Co-N/C was prepared by carbonization and acidification etching at high temperatures. The obtained Co-N/C has a hollow spherical structure consisting of a large number of carbon nanosheets containing Co-Nx components, showing abundant mesopores and high specific surface area. As an ORR electrocatalyst, its catalytic activity in different pH media was tested. The electrochemical data showed that the Co-N/C had a hollow spherical structure at 900 C. The prepared C o-N/C catalyst exhibited the highest ORR activity, high half-wave potential and high limiting diffusion current in alkaline and neutral media. The performance of the catalyst was similar to that of commercial Pt/C catalyst, and showed excellent stability and anti-methanol toxicity. The ORR catalytic activity of Co-N/C catalyst before and after poisoning and the ORR catalytic activity of Co-N/C catalyst before and after destruction of Co-Nx site were compared. It was found that the catalytic activity of Co-N/C catalyst did not change significantly in alkaline medium, but in neutral and acidic medium, the catalytic activity of Co-N/C catalyst decreased significantly, indicating that the Co-N catalytic activity of Co-N/C catalyst decreased significantly. The x site acts as ORR active site directly in neutral and acidic media, but the effect on ORR catalytic activity is negligible under alkaline conditions. 4. Based on the two-dimensional confinement effect between CO(OH)2 layers, cobalt sulfide and nitrogen-doped carbon nano-flake-based flower composite (Co9S8/CO1-xS@) NC were prepared, and its formation mechanism and lithium storage properties were studied. Co9S8/Co1-xS@NC was prepared by mixing the intercalated Co(OH)2 precursor with sulfur powder and calcining it in N2 atmosphere. The obtained Co9S8/Co1-xS@NC consisted of a large number of nitrogen-doped carbon nanosheets embedded in small size cobalt sulfide nanoparticles. The intercalated Co (OH) 2 precursor was carbonized and vulcanized. It was found that the carbonization of m-Aminobenzene sulfonate ion to form carbon nanosheets occurred at about 200 ~400 ~C, accompanied by S sublimation and Co (OH) 2 layer. Co1-xS nanoparticles can be implanted in carbon nanosheets because of the decomposition and the formation of Co1-xS nanoparticles. With the increase of calcination temperature, some of Co1-xS is gradually transformed to Co9S8, and the graphitization degree of carbon nanosheets is further improved. Separation and relaxation of the volume stress produced in the process of lithium removal are helpful to improve the cyclic stability and rate performance of the electrode; nitrogen-doped carbon matrix and several layers of graphene coated on the outer surface of cobalt sulfide can not only prevent the aggregation of particles and reduce the resistance between particles, but also effectively alleviate the charge-discharge cycle process. The volume expansion of medium cobalt sulfide and the dissolution of polysulfide in electrolyte are helpful to improve the cyclic stability of the electrode; the thin particle-nanosheet structure can reduce the ion and electron transport distances, making the cobalt sulfide nanoparticles fully utilized, thus contributing to high specific capacity; the flower-like structure with large specific surface area The morphology and pore structure can promote the electrolyte to enter the electrode and accelerate the transfer of lithium ions. In addition, the composition of cobalt sulfide can be effectively controlled by changing the ratio of the precursor and sulfur powder or calcination temperature. As the anode material of lithium-ion batteries, the electrochemical tests show that the electrolyte is at 900 C and the mass ratio of the precursor and sulfur powder is 1:0.75. The prepared Co9S8/Co1-xS@NC exhibits high specific capacity and excellent rate performance. The method based on interlayer limiting synthesis of layered hydroxides proposed in this paper can be extended to prepare other functionally doped carbon-based nanomaterials with excellent properties, and can be used in supercapacitors, solar cells, sensors, environmental protection, catalysis and other fields. It has broad application prospects.
【学位授予单位】：北京化工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB383.1
，
本文编号：2176984
[Abstract]:With the continuous consumption of fossil fuels, the energy crisis and environmental pollution are becoming more and more serious, which poses a more serious challenge to human health, energy security and environmental protection. Therefore, it is urgent to develop new clean energy sources. Fuel cells and lithium-ion batteries have the advantages of less environmental pollution, high energy conversion efficiency, and so on, as an effective cleaner. In this paper, a series of doped carbon-based nanomaterials were synthesized by controlling the interlayer confinement space of layered hydroxides, and the relationship between the synthesis process and the structure of the materials was investigated. The main research contents are as follows: 1. Selective Nitrogen-Sulfur double-doped carbon nanosheets (NSCNs) were prepared based on the two-dimensional confinement effect between MgAl-LDH layers, and their oxygen content was determined. The reductive electrocatalysis and lithium storage properties and mechanisms were studied. The m-aminobenzenesulfonate anion was first inserted into the MgAl-LDH interlayer by one-step hydrothermal method, and then controlled preparation of NSCNs was realized by high temperature carbonization and acidification etching. The obtained NSCNs consisted of a large number of interconnected nanosheets, showing rich multistage mesoporous and high-level. Specific surface area. The two-dimensional interlayer confinement effect of LDH not only promotes the formation of pyridine N and pyrrole N with flat structure (up to 90.3%), but also effectively alleviates the loss of N and S atoms at high temperature and increases the amount of heteroatom doping. As an ORR electrocatalyst, NSCNs exhibit high catalytic activity in alkaline medium and commercial Pt/C catalyst. NSCNs, as anode materials for lithium-ion batteries, exhibit super-high specific capacity (after 110 weeks of cycling at current density of 0.2 A g-1), excellent rate performance (at current density of 4.0 A g-1, specific capacity of 983 mAh g-1) and long-term stability (at current density of 4.0 A g-1). In addition, XPS and DFT calculations show that the doped pyrrole N atoms can bind to Li + to form Li3N and fall off the doped carbon during the cycling process. At the same time, more edge C atoms are formed at the sites adjacent to the pyrrole N atoms for lithium storage. Pyridine N and quaternary N atoms can not fall off like pyrrole N atoms. 2. Co9S8/N-doped carbon nanosheet-based hollow sphere composite (Co9S8/NHCS) was prepared based on CoAl-LDH interlayer two-dimensional confinement effect, and its catalytic activity for oxygen reduction was studied. Firstly, m-aminobenzenesulfonate anion was inserted into CoAl-LDH by one-step hydrothermal method. Co9S8/NHCS was prepared by high temperature carbonization and selective acidification etching. The obtained Co9S8/NHCS has a hollow spherical structure consisting of a large number of nanosheets, in which monodisperse Co9S8 was implanted into carbon nanosheets. The structure has the following advantages: monodisperse Co9S8 particles were obtained based on the two-dimensional finite-region method, which prompted the formation of Co9S8 particles. The decomposition and carbonization of m-aminobenzenesulfonate anion and the formation of Co9S8 occur simultaneously, which makes the Co9S8 nanoparticles implanted into carbon nanosheets and thus has high stability. The hollow spherical structure of the precursor makes the prepared Co9S8/NHCS highly stable. In addition, the effects of calcination temperature and hollow spherical structure on the structure of the catalysts (such as specific surface area, pore distribution, nitrogen doping type, size and size of Co9S8) and The results showed that 900 C was the optimum calcination temperature and the hollow spherical structure played a very important role in enhancing the catalytic activity of ORR. Electrochemical tests showed that the CO9S8/NHCS catalysts prepared at 900 C had the highest ORR catalytic activity in both alkaline and acidic media, long-term stability and excellent anti-A activity. Alcohol toxicity. 3. Carbon nanosheet-based hollow sphere composites (Co-N/C) containing Co-Nx components were prepared based on the two-dimensional confinement effect of C oAl-LDH layers. The catalytic activity and active sites of the hollow sphere composites in different pH media were studied. The anions of m-aminobenzenesulfonate were firstly inserted into the layers of C oAl-LDH by one-step hydrothermal method and then recanalized. Co-N/C was prepared by carbonization and acidification etching at high temperatures. The obtained Co-N/C has a hollow spherical structure consisting of a large number of carbon nanosheets containing Co-Nx components, showing abundant mesopores and high specific surface area. As an ORR electrocatalyst, its catalytic activity in different pH media was tested. The electrochemical data showed that the Co-N/C had a hollow spherical structure at 900 C. The prepared C o-N/C catalyst exhibited the highest ORR activity, high half-wave potential and high limiting diffusion current in alkaline and neutral media. The performance of the catalyst was similar to that of commercial Pt/C catalyst, and showed excellent stability and anti-methanol toxicity. The ORR catalytic activity of Co-N/C catalyst before and after poisoning and the ORR catalytic activity of Co-N/C catalyst before and after destruction of Co-Nx site were compared. It was found that the catalytic activity of Co-N/C catalyst did not change significantly in alkaline medium, but in neutral and acidic medium, the catalytic activity of Co-N/C catalyst decreased significantly, indicating that the Co-N catalytic activity of Co-N/C catalyst decreased significantly. The x site acts as ORR active site directly in neutral and acidic media, but the effect on ORR catalytic activity is negligible under alkaline conditions. 4. Based on the two-dimensional confinement effect between CO(OH)2 layers, cobalt sulfide and nitrogen-doped carbon nano-flake-based flower composite (Co9S8/CO1-xS@) NC were prepared, and its formation mechanism and lithium storage properties were studied. Co9S8/Co1-xS@NC was prepared by mixing the intercalated Co(OH)2 precursor with sulfur powder and calcining it in N2 atmosphere. The obtained Co9S8/Co1-xS@NC consisted of a large number of nitrogen-doped carbon nanosheets embedded in small size cobalt sulfide nanoparticles. The intercalated Co (OH) 2 precursor was carbonized and vulcanized. It was found that the carbonization of m-Aminobenzene sulfonate ion to form carbon nanosheets occurred at about 200 ~400 ~C, accompanied by S sublimation and Co (OH) 2 layer. Co1-xS nanoparticles can be implanted in carbon nanosheets because of the decomposition and the formation of Co1-xS nanoparticles. With the increase of calcination temperature, some of Co1-xS is gradually transformed to Co9S8, and the graphitization degree of carbon nanosheets is further improved. Separation and relaxation of the volume stress produced in the process of lithium removal are helpful to improve the cyclic stability and rate performance of the electrode; nitrogen-doped carbon matrix and several layers of graphene coated on the outer surface of cobalt sulfide can not only prevent the aggregation of particles and reduce the resistance between particles, but also effectively alleviate the charge-discharge cycle process. The volume expansion of medium cobalt sulfide and the dissolution of polysulfide in electrolyte are helpful to improve the cyclic stability of the electrode; the thin particle-nanosheet structure can reduce the ion and electron transport distances, making the cobalt sulfide nanoparticles fully utilized, thus contributing to high specific capacity; the flower-like structure with large specific surface area The morphology and pore structure can promote the electrolyte to enter the electrode and accelerate the transfer of lithium ions. In addition, the composition of cobalt sulfide can be effectively controlled by changing the ratio of the precursor and sulfur powder or calcination temperature. As the anode material of lithium-ion batteries, the electrochemical tests show that the electrolyte is at 900 C and the mass ratio of the precursor and sulfur powder is 1:0.75. The prepared Co9S8/Co1-xS@NC exhibits high specific capacity and excellent rate performance. The method based on interlayer limiting synthesis of layered hydroxides proposed in this paper can be extended to prepare other functionally doped carbon-based nanomaterials with excellent properties, and can be used in supercapacitors, solar cells, sensors, environmental protection, catalysis and other fields. It has broad application prospects.
【学位授予单位】：北京化工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB383.1
，
本文编号：2176984
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