【作者】 李军；

【导师】 张磊；

【作者基本信息】 华南理工大学 ， 化学工程与技术， 2024， 博士

【摘要】 碳基材料具有独特的物理和化学性质,主要包括:（1）碳基材料中的石墨碳原子构成平面六边形网络结构而形成可自由移动的π电子,使其具有良好的导电性;（2）碳基材料中的碳-碳共价键具有较大的键能,保证了其较高的结构稳定性;（3）碳基材料较大的比表面积和丰富的孔隙结构可以提供大量的负载/催化位点和传质通道,有利于提高催化效率;（4）碳基材料中的缺陷可以改变局域电荷和自旋密度分布,优化电子结构,进而使其获得催化活性。基于上述特征,碳基材料被广泛应用于电催化剂的开发。然而,高性能碳基电催化剂的发展仍然面临着挑战,主要包括碳基电催化剂的可控制备、活性位点和形貌结构的精确设计与调控等。针对以上挑战,本论文以化学组分和形貌结构易于调控的金属-有机框架（MOFs）及其复合物衍生碳基材料分别作为电催化剂载体和直接作为电催化剂。一方面,通过杂原子掺杂策略调控活性位点的电子结构,实现了碳基材料和催化主体材料（Pt纳米团簇或硫物种）之间的耦合调控,从而改善了相关电催化还原反应的能垒和动力学;另一方面,通过对形貌结构的调控,实现了反应动力学的进一步改善。同时,揭示了所制备碳基电催化剂的结构和性能之间的内在关系。具体工作如下:1.通过N掺杂实现了碳基材料与Pt纳米团簇之间的耦合调控。针对碱性析氢反应动力学缓慢和Pt的高成本问题,本论文通过聚苯乙烯球模板法结合浸渍法将低载量（3.39 wt%）的Pt纳米团簇（～1.6 nm）均匀分散地锚固在MOFs衍生N掺杂有序大孔碳载体上（Pt-30/NCM）,作为高效的碱性析氢电催化剂。该碳基电催化剂设计的创新思路在于:i)碳载体上的N掺杂有助于其与Pt纳米团簇形成金属-载体相互作用而优化Pt活性位点的电子结构,从而实现对碱性环境下H₂O分子解离的高效催化;ii)在碳载体上构筑相互联通的有序大孔结构有利于暴露更多的活性位点并改善碱性析氢反应中的传质和电荷转移。研究结果表明,Pt-30/NCM在1 M KOH电解液中比没有有序大孔结构的实心对比样品（Pt-30/NCS）和商业化20 wt%Pt/C具有更好的析氢反应性能。密度泛函理论计算结果证实了N掺杂有助于碳载体向Pt纳米团簇转移电子而形成强耦合效应,从而降低碱性溶液中H₂O分子解离的能垒,加速析氢反应动力学。2.通过S/N共掺杂实现了碳基材料与硫物种之间的耦合调控。针对水系Zn-S电池正极硫还原反应动力学缓慢的问题,本论文以聚合物包覆MOFs复合纤维为前驱体,设计MOFs原位衍生的S纳米颗粒限域在聚合物热解衍生的S/N共掺杂碳纤维的纳米孔中（S@S,N-CNF）,作为高性能水系Zn-S电池的正极材料。本工作的创新思路在于:i)碳基材料上的S/N双掺杂可以协同调控活性位点电子结构,从而实现对硫还原反应的高效催化;ii)将S纳米颗粒封装在具有多孔结构的碳材料中形成对S具有限域作用的S@C核-壳结构,可以改善电荷转移并降低活化能,从而进一步促进硫还原反应动力学。研究结果表明,与其他对比硫正极相比,S@S,N-CNF正极具有最高的放电电压和比容量,CS/S,N-CNF正极（无S@C核-壳结构）次之,CS/N-CNF（单一N掺杂且无S@C核-壳结构）最低。此外,S@S,N-CNF正极（S:41 wt%）在0.2 A g^-1的电流密度下具有高达607 m Ah g^-1的放电比容量和379 Wh kg^-1的能量密度（基于硫和碳的总质量）。密度泛函理论计算证实了S/N共掺杂可以协同调控活性位点的电子结构而实现对重要多硫化物中间体（*Zn S₄）的耦合调控,从而优化活性位点对*Zn S₄的吸附强度,有效地降低硫还原反应能垒和促进硫还原反应动力学。3.为了证明杂原子掺杂策略对优化水系Zn-S电池硫还原反应性能的适用性,本论文继续以聚合物包覆MOFs复合纤维为前驱体,在衍生的碳基材料上设计P/N共掺杂作为催化活性中心以改善硫还原反应动力学。制备的P/N共掺杂多孔碳纳米纤维（P,N-CNF）作为水系Zn-S电池硫正极电催化剂时,在相同测试条件下,相比于工作2中的S/N共掺杂多孔碳纳米纤维（S,N-CNF）具有更高的硫还原反应活性。根据密度泛函理论计算结果分析,这可能是由于P/N共掺杂可以更有效地降低硫还原反应能垒。此外,将绝缘性质的硫单质与导电的一维多孔碳纳米纤维均匀复合,有利于促进硫还原反应过程中的电子转移。得益于上述优势,P,N-CNF与硫单质（S:60 wt%）复合后得到的P,N-CNF/S60作为硫正极材料时,在0.3 A g^-1的电流密度下具有高达800 m Ah g^-1的放电比容量和510Wh kg^-1的能量密度（基于硫和碳的总质量）。更多还原

【Abstract】 Carbon-based materials have unique physical and chemical properties,mainly including the following aspects:（1）The graphite carbon atoms in carbon-based materials form a planar hexagonal network with freely movableπelectrons,endowing them with good conductivity;（2）The covalent bonds in carbon-based materials possess high bond energies,ensuring the high structural stability;（3）The large specific surface area and rich pore structure of carbon-based materials can provide a large number of anchoring/catalytic sites and mass transfer channels,facilitating the catalytic efficiency;（4）Defects in carbon-based materials can regulate local charge and spin density distributions,optimize electronic structure,and thereby enhance the catalytic activity.Based on the above characteristics,carbon-based materials are widely used in the development of electrocatalysts.However,the development of high-performance carbon-based electrocatalysts still faces challenges,mainly including controllable preparation of carbon-based electrocatalysts,accurate design and regulation of active sites and morphological structures.In view of the above challenges,this paper takes metal–organic frameworks（MOFs）and their composites derived carbon-based materials that are easily controllable in terms of chemical composition and morphological structures as electrocatalyst supports or electrocatalysts,respectively.For one thing,the electronic structure of active sites was regulated through the heteroatom-doping strategy,achieving coupling regulation between carbon-based materials and catalytic host materials（Pt nanoclusters or sulfur species）,and then improving the energy barrier and kinetics of related electrocatalytic reduction reactions.For another,the morphology engineering was adopted to further improve the reaction kinetics.Meanwhile,the intrinsic relationship between the structure and performance of the as-prepared carbon-based materials was revealed.The specific research content is as follows:1.The coupling regulation between carbon-based materials and Pt nanoclusters is realized by N doping.In view of the sluggish kinetics of the hydrogen evolution reaction（HER）in alkaline media and the high cost of Pt,in this paper,Pt nanoclusters（～1.6 nm）uniformly anchored on MOF-derived ordered macroporous nitrogen-doped carbon support（Pt-30/NCM）with only 3.39 wt%Pt loading is rationally constructed via a polystyrene spheres template method followed by an impregnating method as a highly enhanced electrocatalyst for alkaline HER.The innovative ideas of the design of this carbon-based material are as follows:i)nitrogen-doping facilitates the establishment of metal–support interactions between Pt nanoclusters and carbon support,optimizing the electronic structure of the Pt active site and achieving efficient alkaline water dissociation;ii)the construction of interconnected ordered macroporous structures on carbon supports can enhance the exposure of active sites and facilitate efficient alkaline hydrogen evolution reaction.The results show that Pt-30/NCM exhibits superior intrinsic activity and operation stability compared to the solid counterpart without ordered macropores（Pt-30/NCS）and commercial 20 wt%Pt/C.The density functional theory（DFT）calculations reveal that N-doping contribute to transfer electrons from carbon carriers to Pt nanoclusters to form a strong coupling effect,thereby reducing the energy barrier for H₂O molecule dissociation and accelerating the alkaline HER kinetics.2.The coupling regulation between carbon-based materials and sulfur species is realized by S/N co-doping.In view of the sluggish sulfur reduction reaction（SRR）kinetics in aqueous Zn-S batteries,in this paper,MOFs@polymer composite fibers were used as the precursors to design and fabricate S nanoparticles derived from MOFs confined in situ within the nanopores of electrospun fibers derived S and N co-doped carbon nanofibers（S@S,N-CNF）composite as a cathode material for high-performance aqueous Zn-S batteries.The innovative ideas of this work are as follows:i)S/N dual doping can synergistically regulate the electronic structure of active sites,thereby achieving efficient catalysis for SRR;ii)encapsulating S nanoparticles in carbon materials with porous structures to form a S@C core–shell structure with spatially confined S nanoparticle yolks can improve charge transfer and lower activation energy,thus further promoting SRR kinetics.The results show that S@S,N-CNF cathode possesses the highest discharge voltage and specific capacity,followed by CS/S,N-CNF（without S@C core–shell structure）,while CS/N-CNF（single N doping）exhibits the lowest performance.Moreover,the S@S,N-CNF（S:41 wt%）cathode displays a high specific capacity of 607 m Ah g^-1 with a high energy density of 379 Wh kg^-1 at 0.2 A g^-1（based on the toal mass of sulfur and carbon）.Furthermore,DFT calculations reveal that S/N dual-doping can synergistically tune the electronic structure of active sites and achieve coupling regulation of important polysulfide intermediates（i.e.,*Zn S₄）,thereby optimizing the adsorption strength of*Zn S₄ on active sites,effectively reducing the activation energy barrier and significantly accelerating SRR kinetics.3.To demonstrate the applicability of heteroatom doping strategy in optimizing the SRR performance in aqueous Zn-S batteries,MOFs@polymer composite fibers were still used as the precursors to design and fabricate P and N co-doped carbon nanofibers（P,N-CNF）for promoting SRR.When served as sulfur cathode electrocatalysts for aqueous Zn-S batteries,P,N-CNF exhibit higher SRR activity compared to the S and N co-doped porous carbon nanofibers（S,N-CNF）in Study 2 at the same test conditions.According to the results of DFT calculations,the reason may be attributed to the fact that the P and N co-doping can more effectively lower the energy barrier of the SRR.In addition,conductive one-dimensional carbon nanofibers are beneficial for facilitating electron transfer during the SRR process.Benefiting from these advantage,the P,N-CNF/S60（S:60 wt%）cathode exhibits a high specific capacity of 800 m Ah g^-1 with a high energy density of 510 Wh kg^-1 at 0.3 A g^-1（based on the toal mass of sulfur and carbon）.更多还原