【作者】 崔凯；

【导师】 唐晓亮； 徐宇曦；

【作者基本信息】 兰州大学 ， 化学·无机化学， 2025， 博士

【摘要】 单原子催化剂（SACs）具有较高的原子利用率,出色的活性、选择性和稳定性等优异特性,使其被广泛的应用于许多领域。但是,由于其制备方法的局限性,导致其存在负载量低、容易团聚以及催化机制不明确等问题,从而在催化反应中存在一定的局限性。然而,在分子水平上设计并可控地制备可设计性和可调控性的多孔有机框架材料作为SACs的支撑平台已经展现出广阔的发展前景,但是其在电催化反应过程中依然受到了自身催化活性低、电子传输能力差以及活性位点数量稀少等问题的限制。基于此,本论文重点围绕有机框架基SACs材料目前在电催化反应中面临的问题,分别从分子水平上框架结构的设计、超薄纳米片的制备以及二维纳米片异质结的构建,合成了三种性能优异的有机框架基SACs。根据三种有机框架基SACs材料的特性,分别考察了三种催化剂材料电催化二氧化碳（CO₂）还原性能和电催化氧还原（ORR）性能,并初步探索三种催化剂分别在CO₂流动池、锌-空电池以及阴离子交换膜燃料电池（AEMFC）中的应用。论文共分为五章:第一章:简要介绍了有机框架基SACs材料的结构特性以及合成方法策略,进一步重点调研了有机框架基SACs材料在电催化领域的应用研究。第二章:通过在分子水平上调整单体的结构,合成了三种新型乙烯基连接的具有连续可调的D-π-A相互作用的金属共价有机框架（TMT-CH₃-MCOF、TMP-CH₃-MCOF和TMP-MCOF）,实现了高效的CO₂还原产甲酸盐性能。其中,与TMT-CH₃-MCOF和TMP-MCOF相比,TMP-CH₃-MCOF在1.0 V vs.RHE电压下的甲酸盐法拉第效率(FE_HCOO-)最高,达到95.6%,在1.0至1.2 V vs.RHE电压范围内的FE_HCOO-均高于90%。原位实验和理论计算进一步表明,TMP-CH₃-MCOF中的催化位点具有独特的适中D-π-A相互作用,对反应中间体具有合适的结合能力,有利于*HCOO的形成和*HCOOH的解吸,从而有效的促进电催化CO₂还原产甲酸盐。第三章:采用无水Fe Cl₃催化2,6-氰基吡啶（DCP）聚合,首次合成了一种结晶、双孔吡啶基共价三嗪框架（Fe-CTF）。其中Fe Cl₃不仅可以作为高活性路易斯酸催化剂促进DCP单体的二维有序聚合,还能通过与吡啶和三嗪基团配位在CTF内产生独特的Fe-N₃单原子活性位点。通过简单的球磨法将块体层状Fe-CTF剥离成的少层纳米片（Fe-CTF NSs）,在ORR中表现出优异的电催化性能。其半波电位和起始电位分别高达0.902 V和1.02 V,同时还具有超高的锌-空气电池性能,比容量和功率密度分别达到811 m Ah g^-1和230 m W cm^-2。将原位X射线吸收精细结构谱与理论计算相结合,揭示了在电催化过程中Fe-N₃向Fe-N₂再到Fe-N₃的动态可逆演化,从而进一步加速了电催化反应。第四章:将负载Fe单原子的单层CTF纳米片和化学转化石墨烯通过一步π-π堆积形成二维异质结纳米片电催化剂。不但其活性位点能够得到极大的暴露,其催化活性、电子传输能力以及电催化稳定性均能同时得到进一步优化,实现了对催化剂性能全方位优化。得益于该策略独特的优势,其半波电位和起始电位分别高达0.94 V和1.057 V,CV循环10 W圈后仅衰减10 m V。进一步组装了AEMFC,其功率密度在4.9 m A cm^-2达到1.97 W cm^-2,并且可以持续稳定运行150 h。原位实验与理论计算相结合揭示了在电催化过程中活性中心由Fe-N₃O向Fe-N₂O的变化,导致其Fe单原子的3d轨道由适中自旋转变为高自旋,进一步展现出优异的电催化性能。最后,我们将该策略进一步扩展到二维MOF和COF材料中,其电催化活性和稳定性均得到了显著的提升,表明其具有广泛的普适性。第五章:对本论文的工作做了系统的总结和展望。更多还原

【Abstract】 Single-atom catalysts（SACs）possess remarkable properties,including high atom utilization,exceptional activity,selectivity,and stability,which make them widely applicable across various fields.However,the limitations of their preparation methods have resulted in challenges such as low loading,susceptibility to agglomeration,and unclear catalytic mechanisms.However,the design and controllable fabrication of SACs at the molecular level based on designable and tunable porous organic framework materials as a suitable support platform for SACs has shown great promise,but they are still limited by their own low intrinsic activity,poor electron transport capacity,and sparse number of active sites during electrocatalytic reactions.Based on this,this thesis focuses on the current problems faced by organic framework-based SACs materials in electrocatalytic reactions,and three organic framework SACs with excellent performances were synthesized from the design of the building monomers at the molecular level,the preparation of ultrathin nanosheets,and the construction of two-dimensional nanosheet heterojunctions,respectively.Based on the properties of the three organic framework-based SACs materials,the three catalyst materials were investigated for electrocatalytic CO₂ reduction reaction performance and electrocatalytic oxygen reduction reaction（ORR）performance,respectively,and further extended them to CO₂ flow cell,Zn-air battery,and anion-exchange membrane fuel cell（AEMFC）.The thesis is divided into five chapters:Chapter 1:The structural properties and synthesis strategies of organic framework-based SACs materials are briefly introduced,with a particular emphasis on exploring the application of these materials in electrocatalysis.Chapter 2:we report three new kinds of vinylene-linked metal-covalent organic frameworks（TMT-CH₃-MCOF,TMP-CH₃-MCOF and TMP-MCOF）with continuously tunable D-π-A interactions by adjusting the structure of the monomers at the molecular level for realizing efficient electroreduction of CO₂ to formate.Interestingly,compared with TMT-CH₃-MCOF and TMP-MCOF,the TMP-CH₃-MCOF exhibited the highest formate Faradaic efficiency(FE_HCOO-)of 95.6%at 1.0 V vs RHE and displayed the FE_HCOO-above 90%at the voltage range of 1.0 to 1.2 V vs.RHE.Theoretical calculations further reveal that the catalytic sites in TMP-CH₃-MCOF with unique moderate D-π-A interactions have suitable binding ability towards the reaction intermediate,which is beneficial for the formation of*HCOO and desorption of*HCOOH,thus effectively promoting the electroreduction of CO₂ to formate.Chapter 3:we report a novel solvent-free Fe Cl₃-catalyzed polymerization of 2,6-pyridinedicarbonitrile（DCP）to achieve the first synthesis of crystalline,dualporous,pyridine-based CTF（Fe-CTF）.The Fe Cl₃ could not only act as a highly active Lewis acid catalyst for promoting the two-dimensional ordered polymerization of DCP monomers,but also in situ coordinate with the tridentate chelators generated between pyridine and triazine groups to yield unique Fe-N₃ single-atom active sites in Fe-CTF.Abundant few-layer crystalline nanosheets（Fe-CTF NSs）could be prepared through simple ball-milling exfoliation of the bulk layered Fe-CTF and exhibited remarkable electrocatalytic performance for oxygen reduction reaction（ORR）with a half-wave potential and onset potential up to 0.902 and 1.02 V respectively,and extraordinary Zn-air battery performance with an ultrahigh specific capacity and power density of 811m Ah g^-1 and 230 m W cm^-2 respectively.By combining operando X-ray absorption spectroscopy with density functional theory calculations,we revealed a dynamic and reversible evolution of Fe-N₃→Fe-N₂→Fe-N₃ during the electrocatalytic process,which could further accelerate the electrocatalytic reaction.Chapter 4:We developed two-dimensional nanosheet heterojunction catalysts through a one-stepπ-πstacking process involving monolayer CTF nanosheets loaded with Fe single atoms and chemically converted graphene.The active sites of these 2D heterojunction nanosheet catalysts were not only significantly exposed,but their intrinsic catalytic activity,electron transport capacity,and electrocatalytic stability were also optimized simultaneously,resulting in outstanding electrocatalytic performance for the same time,achieving the optimization of all aspects of the catalyst performance.The half-wave potential and onset potential reached impressive values of 0.940 V and1.057 V,respectively.Additionally,the CV decayed by 10 m V after 10,000 cycles.An anion-exchange membrane fuel cell was assembled,achieving a power density of 4.9m A cm?2,which corresponds to 1.97 W cm?2,and it demonstrated stable operation for150 h.Through a combination of in situ experiments and theoretical calculations,we observed that the active centers transitioned from Fe-N₃O to Fe-N₂O during the electrocatalytic process,enhancing the electrocatalytic stability of Fe-N₂O.Furthermore,it was revealed that the active center shifted from Fe-N?O to Fe-N?O during the electrocatalytic process,leading to a transformation of its Fe 3d orbital from low spin to high spin,which further underscored its excellent electrocatalytic performance.Finally,we further extended the strategy to 2D MOF and COF materials,and their electrocatalytic activity and stability were significantly improved,indicating the broad generalizability of our strategy.Chapter 5:The work of this paper is systematically summarized and prospected.更多还原