【作者】 孙飞；

【导师】 秦裕琨； 高继慧；

【作者基本信息】 哈尔滨工业大学 ， 热能工程， 2017， 博士

【摘要】 发展大规模储能技术是解决传统电力工业峰谷差问题和新能源发电间歇性缺点的重要方向;燃煤发电支撑了中国的经济发展,但同时带来了严重的环境污染。无论对电化学储能,还是污染物控制,多孔碳同时具有物理和化学活性,是重要的气体分子或液相离子吸附储存介质。碳基电化学储能和污染物控制过程面临着共性关键问题:（1）揭示气体分子或液相离子在多孔碳内吸附转化及迁移过程的强化机制,是提升性能的关键问题;（2）高效要求活性发达,长寿命要求结构稳定,多孔碳活性与稳定性矛盾的协同是另一关键问题。本文抽提了四个当前制约多孔碳材料污染物控制与能量储存的关键问题为研究对象:（1）多孔碳纳孔结构内SO₂吸附转化及迁移机制;（2）多孔碳含氮缺陷定向构筑及离子吸附强化机制;（3）多孔碳含硼缺陷定向构筑及储锂活性与稳定性协同机制;（4）多孔碳介孔结构均匀构筑协同活性物质储锂活性及稳定性。通过上述四个关键问题的研究,逐步揭示多孔碳本征活性引导下气相分子吸附储存→电场/势协同作用下液相离子吸附储存的影响机制及强化方法。并在此基础提出了多种多孔碳活性与稳定性协同调控方法,为发展先进碳基污染物控制及能量储存技术奠定理论基础。本文首先以活性焦资源化脱硫过程为研究对象。活性焦纳孔结构内SO₂吸附转化过程涉及了气体分子SO₂吸附氧化、中间产物及终产物的迁移赋存等多个过程。通过固定床动力学实验及密度泛函理论（DFT）计算,研究了碳材料孔隙结构及含氮活性位对SO₂分子吸附的影响机制。研究结果表明,孔径小于0.7nm的微孔是SO₂物理吸附的主要场所。为准确获得含氮活性位对SO₂吸附的影响,本文基于分子自组装技术,制备了孔隙相同、含氮量不同的系列炭材料并用于SO₂吸附动力学研究。结合DFT计算,首次证明含氮活性位的引入改变了碳基面的电子分布,进而促进了SO₂的吸附,特别能够促进SO₂分子在碳基面、边缘的物理吸附,氮原子本身并非SO₂点对点相结合的化学活性位。在SO₂单独吸附研究基础上,本文进一步在固定床动力学实验系统中加入实际烟气组分O₂及H2O,研究了烟气中O₂及H2O对SO₂氧化及产物硫酸形成及迁移的影响机制。研究结果表明,相比于SO₂单独吸附,氧气与水存在条件下活性焦脱硫容量提高了7倍,具有分级孔结构的活性焦表现出最佳的脱硫性能,中孔及大孔的连通结构提供了反应产物SO3及H2SO4的迁移赋存空间。基于上述研究结果,本文考虑了活性焦内孔隙配组及官能团分布特性,提出了吸附质H2SO4/SO3“极性致迁移”机制:认为在活性焦脱硫过程中,分布在中孔内的极性官能团可成为极性分子的吸附中心,并通过极性作用或水合作用使吸附质SO3/H2SO4迁移出微孔并以液相赋存于中孔和大孔内。该机制是制备高性能活性焦,开发高性能吸附/解吸技术的重要理论基础。在多孔碳内气相分子吸附转化机制研究基础上,本文进一步以碳基双电层超级电容储能过程为研究对象,研究了外加电场/势引导下多孔碳内液相离子的吸附强化机制。碳材料内含氮缺陷的引入能够增强超级电容储能活性,但非均匀掺杂或表面掺杂会影响碳结构循环稳定性。针对这一问题,本文基于分子自组装原理,辅助于易于放大生产的气溶胶喷雾工艺,制备了形貌、孔隙及含氮缺陷三者协同可控的富氮碳纳米球,实现了含氮缺陷的高含量、分子尺度嵌入。通过关联结构表征结果、电化学储能特性以及DFT计算结果,揭示了含氮缺陷对液相离子输运及吸附的强化机制。研究结果表明,以富氮纳米碳球为电极材料,能量密度可达商用碳基双电层超级电容的3-5倍,循环寿命高达10000次;含氮缺陷引导了碳结构的表面极性及电子分布不均匀性、提高了液相离子扩散-吸附能力,从而增强了双电层电容行为。针对石墨负极嵌锂容量低及稳定性差的问题,本文进一步将分子自组装技术及气溶胶喷雾工艺用于制备硼掺杂纳米碳球,引入兼具高活性及高稳定性的硼碳结构（BC）,研究了含硼缺陷对锂离子吸附储存活性及稳定性的强化机制。研究结果表明,硼掺杂显著增强了碳材料的储锂容量、倍率性能以及循环寿命,高电流密度下循环充放电3000次后仍未发生容量衰减,代表了目前研究报道的最高水平。通过电化学阻抗测试、循环前后电极材料中含硼结构表征、DFT计算的相互印证,共同证明了含硼缺陷同时增强了碳材料的离子/电子传导性、锂离子吸附能力以及碳结构的化学稳定性,从而实现了储锂活性与稳定性的协同。针对活性金属及金属氧化物在充放电循环中体积应变问题,本文提出采用介孔碳骨架包覆纳米金属/金属氧化物颗粒。探究了活性物质在介孔碳骨架内的限域生长机制,分析了复合物的锂离子储存特性,结合反应前后电极形貌及结构表征,获得了介孔碳包覆对活性物质储锂活性及稳定性的强化机制。研究结果表明,碳骨架中均匀分布的介孔结构使复合物中氧化锌（ZnO）或锡（Sn）颗粒纳米化且分散均匀,实现了ZnO或Sn颗粒的限域生长,储锂容量及循环稳定性均达到现有报道的较高水平。碳骨架均匀介孔的构筑是抑制活性物质体积应变、提高电极利用率从而实现储锂活性与稳定性协同增强的关键。更多还原

【Abstract】 Development of large-scale energy storage technology is the direction for solving the peak and valley difference in traditional power industry and and the intermittent shortcoming of new energy power generation technologies.Coal-fired power generation supports China’s economic development,but at the same time brings serious environmental pollution.Carbon-based functional materials featuring both physical and chemical activity,are important adsorption media for gas molecules and liquid ion for both electrochemical energy storage and pollutant removal processes.Porous carbon-based electrochemical energy storage and contaminant control processes have a common scientific nature,namely,the adsorption,reaction,transport and storage of target species（molecules,ions,electrons）,the storage of material or energy in the pore structure of carbon materials is the common theme.High transport rate and storage capacity require well-developed activity;long cycle life requires high carbon structure stability;the contradiction between activity and stability is another key issue.This paper draws four key questions about the energy storage and pollut ant control of carbon materials:（1）Sulfur adsorption,conversion and migration mechanism in the nanopores of porous carbons;（2）Construction of nitrogen-containing defects in carbon materials and mechanism of ion adsorption enhancement;（3）Construction of boron-containing defects in carbon materials and mechanism of lithium ion storage enhancement;（4）Mesoporous structure homogeneously construction in carbon materials for synergistically enhancing the activity and stability of active lithium storage materials.Through studying the above four key issues,this paper aims to step-by-step reveal the influence mechanism and strengthening method for carbon based ion adsorption and storage,molecule adsorption and storage and multiphase adsorption catalysis.Based on the above studies,this paper proposes several strategies for synergistically enhancing the activity and stability of porous carbons,which lays the theoretical foundation for the development of advanced carbon-based pollutant control and energy storage technology.The adsorption process of SO₂ in actived coke involves the process of adsorption and oxidation of SO₂,the migration of intermediates and final products.In this paper,the effects of the pore structure and nitrogen-containing active sites on the adsorption of SO₂ molecules were firstly studied.The results show that micropores with pore size less than 0.7 nm are the main space for SO₂ physical adsorption.In order to accurately obtain the effect of nitrogen-containing active sites on the adsorption of SO₂,a series of carbon materials with the same pore structure parameters and different nitrogen contents were prepared and studied for the adsorption of SO₂.Combining the DFT calculation,this paper for this time reveals the enhancing mechanism of nitrogen-containing active sites on the SO₂ adsorption process.The calculation results indicate that the introduction of nitrogen-containing active sites changes the electron distribution of the carbon-based surface,which promotes the adsorption of SO₂ on the carbon-based surface,in particular,can promote the physical adsorption of SO₂ molecules on the carbon-based surface and the edge of carbon surface.Nitrogen atom itself is not the SO₂ point-to-point combination site.Based on the study of SO₂ separate adsorption,this paper further studied the mechanism of O₂ and H2 O in flue gas on SO₂ oxidation and sulfuric acid formation and migration.The results show that the SO₂ removal capacity in the presence of O₂ and H2 O is 7 times higher than that of SO₂ separate adsorption;the activated coke with hierarchically pore gives the best desulfurization performance;the mesopore and macropore connected structures provide the migration and storage space for desulfurization products SO3 and H2SO4.On the basis of the above research,this paper creatively proposed the SO3/H2SO4 polarity-induced migration mechanism.It is considered that the polar functional groups,distributing in mesopores of activated coke play a significant role in the SO₂ removal process.Polar functional groups act as the adsorption centers of polar molecules.Relying on polar effect or hydration,the byproduct SO3 or H2SO4 forming in micropores are able to migrate out of micropores and into mesopores or macropores in the form of liquid.The introduction of nitrogen defects in the carbon material could enhance the supercapacitor activity,however,non-uniform doping or surface doping can affect the carbon structure cycling stability.To solve the problem,this paper reports a novel nitrogen-rich carbon sphere（NRC）based on molecular self-assembly process assisted with aerosol spray process which is easy to amplify the production.The morphology,porosity and nitrogen defects can be synergistically regulated,which achieves molecule-scale embedding of nitrogen species into carbon structure with a high content.Through the correlation analysis between structure characterization results,electrochemical properties and the quantum chemical calculation results,this paper reveals the strengthening mechanism of nitrogen defects on ion transport and adsorption.The results indicate that the energy density of NRC-based supercapacitor is 3-5 times that of the commercial carbon-based double-layer supercapacitor and the cycling life is up to 10,000 times;nitrogen defects induce the surface polarity and non-uniform electron distribution and thus improve the ion diffusion and adsorption capability which leads to enhanced double-layer supercapacitive behavior.In view of the problem that the graphite anode has low lithium capacity and poor stability,this paper further employs molecular self-assembly technique and aerosol spray process to prepare boron-doped nanocarbon sphere by which the highly active and highly stable BC structure can be introduced into carbon structure.Strengthening mechanism of boron doping on lithium storage Activity and stability was systematically studied.The results indicate that boron doping greatly enhance the carbon based anode properties in terms of high lithium storage capacity,excellent rate capability and long lifespan.The constructed anode exhibits no capacity decay at high current density even after 3000 cycles,which represents the highest level among the reported carbon based anode materials.Through the correlation analysis between structure characterization results,electrochemical properties and the quantum chemical calculation results,the enhancing effect of boron doping on ion/electron conductivity,lithium ion adsorption capability and carbon structure stability were elucidated.The synergistic effects endow the boron-doped nanocarbon spheres with both high lithium storage activity and stability.Aiming at the problem of volume strain of active metal and metal oxide during charge and discharge cycles,this paper adopted a mesoporous carbon skeleton for coating with nano metal/metal oxide particles.The nano-confined growth mechanism of active materials in carbon framework was studied.The lithium storage characteristic of prepared nanocomposite was tested.Combing the morphology and structure characterizations,the enhancing mechanis m of mesoporous carbon coating on lithium storage activity and stability was obtained.The results indicate that the uniformly distributed mesoporous structure in carbon framework the ZnO or Sn particles in the composite to be nanocrystalline and dispersed uniformly.The lithium storage capacity and cycling property reach the highest level among reported similar metal/metal oxide based anode materials.The construction of homogeneous mesopores of carbon skeleton is the key to suppress the volumetric strain of active substances and improve the utilization of electrode in order to realize the synergistic enhancement of lithium storage activity and stability.更多还原