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MOFs基碳材料的制备及催化性能研究
Study on Preparation and Catalytic Performance of MOFs-Based Carbon Materials
【作者】 张亮;
【导师】 温娜;
【作者基本信息】 福州大学 , 材料工程(专业学位), 2021, 硕士
【摘要】 氧还原反应(Oxygen Reduction Reaction,ORR)和析氧反应(Oxygen Evolution Reaction,OER)是各种新型电化学装置核心反应。但是,它们过电位高,动力学迟滞,需要催化剂的帮助来促进反应的进行。传统贵金属基催化剂成本高,稳定性差,因此,迫切需要开发兼顾成本和性能的电催化剂。过渡金属碳基催化剂价格低廉、催化活性和稳定性出色,被视为最具潜力的候选材料。研究表明,过渡金属可作为活性中心,多孔结构有利于活性位点的暴露,从而对物质传递和电子传输的过程进行促进,掺杂杂原子能够进一步提升催化活性。本文以生物小分子鸟嘌呤和金属有机框架材料ZIFs(Zeolitic Imidazolate Frameworks,ZIFs)材料为主要原料,通过高温热解的方法制备了Co-N-C、Co-NP@C和Co Fe-N@C等碳基催化剂材料,研究和表征了这些材料的形貌结构,并测试了它们作为ORR/OER催化剂的催化活性及稳定性等指标。具体内容如下:(1)通过高温热解鸟嘌呤包覆ZIF-67的复合材料,制备了镶嵌Co纳米颗粒的氮掺杂碳基催化剂Co-N-C材料,使用多种方法表征并分析了其形貌结构及元素组成。在碱性条件下,Co-N-C-800具有系列样品中最优的ORR催化活性,其半波电位(0.83 V vs.RHE)和起始电位(0.92 V vs.RHE)均能够媲美于商业Pt/C,且表现出了更加优秀的甲醇耐受能力和稳定性能。(2)仅有N掺杂的碳基催化剂的OER催化活性不够理想,但是N、P共掺杂能够更好地提升材料的OER催化活性。基于此,以鸟嘌呤在空气中高温活化得到的产物G-600和Co Zn-ZIFs为前驱体,掺杂P元素,合成了含过渡金属的氮磷共掺杂的碳基催化剂Co-NP@C。在碱性条件下,制备得到的Co-NP@C-2催化剂催化OER反应电流密度达到10 m A·cm-2时的过电位为330 m V,Tafel斜率为72.5·dec-1,非常接近Ru O2。且该催化剂稳定性出色,经过1000次循环后,性能仅有8 m V的衰减。(3)不同过渡金属间的协同作用能够进一步提升ORR催化活性,而鸟嘌呤自组装制备的二维碳纳米片材料具有多级孔隙结构和较多的缺陷位点,为负载过渡金属提供丰富的N掺杂位点。因此,通过原位合成法,以N掺杂纳米片为载体,负载核壳结构的Co Zn-ZIFs,并通过浸渍法引入Fe元素,使用一步热解法制备双金属掺杂的含氮碳基催化剂Co Fe-N@C。实验结果表明,在碱性条件下,Co Fe-N@C-800拥有超越商业Pt/C的性能,抗甲醇性能和稳定性也非常出色。
【Abstract】 Oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)are the key reactions in advanced electrochemical devices.However,they are commonly associated with high overpotentials and slow kinetics,so efficient catalysts are needed to facilite the reactions.Suffering from the high cost and poor stability of tranditional noble metal-based catalysts,there is an urgent need to develop electrocatalysts taking into account both low cost and high performance.Transition metal carbon-based catalysts are viewed as the most promising alternatives due to their low price,excellent catalytic activity and outstanding stability.According to the research results,the transition metals can act as active centres,the porous structure facilitates the exposure of more active sites to promote mass transfer and electron transport,and the introduction of heteroatoms can further enhance the catalytic activity.In this paper,biomolecules guanine and zeolitic imidazolate frameworks(ZIFs)were used as the main raw materials to prepare carbon-based catalyst materials such as Co-N-C,Co-NP@C and Co Fe-N@C by high-temperature pyrolysis,and their morphological structures were studied and characterized.Furthermore,we have tested their catalytic activities and stability as ORR/OER catalysts.The specific research content is as follows:(1)Nitrogen-doped carbon-based catalysts Co-N-C inlaid with Co nanoparticles were prepared by high-temperature pyrolysis of guanine-coating ZIF-67 composites.Their morphological structures,elemental compositions were characterized by various methods.Among series samples,Co-N-C-800 exhibited the best catalytic activity toward ORR with a half-wave potential of 0.83 V(vs.RHE)and an onset potential of0.92 V(vs.RHE).These two indexes are close to commmercial Pt/C.Co-N-C-800 also demonstrated better tolerance for methanol and stability.(2)Carbon-based catalysts Co-NP@C with only N-doped may not show satisfactory catalytic activity toward OER,we could improve their performance by N,S co-doping.On this basis,nitrogen and phosphor co-doped carbon-based catalysts containing transition metal were synthesised by using the products G-600(obtained by high temperature activation of guanine in air)and Co Zn-ZIFs as precursors.The doping of P element is involved in the preparation process.Under the alkaline condition,when the current density is up to 10 m A·cm-2,its overpotential is only 330 m V with a Tafel slope of 72.5·dec-1,which is very close to that of Ru O2.Co-NP@C-2 exhibited excellent stability,with only an 8 m V degradation afer 1000 cycles.(3)Synergistic interactions between different transition metals can further enhance ORR catalytic activity,and the two-dimension carbon nanosheets prepared by guanine self-assembly have hierarchical pore structure and many defect sites,which provide abundant N-doping sites for loading transition metals.The bimetal-doped nitrogen-containing carbon-based catalysts Co Fe-N@C were prepared by in-situ synthesis,with N-doped nanowires as substrates,loading core-shell structure Co Zn-ZIFs,and introducing Fe element by impregnation.The experimental results showed that,under alkaline conditions,Co Fe-N@C-800 had better performance toward ORR than commercial Pt/C.It also demonstrated excellent tolerance for methanol and superior stability.
【Key words】 electrocatalyst; guanine; zeolitic imidazolate frameworks; oxygen reduction reaction; oxygen evolution reaction;
- 【网络出版投稿人】 福州大学 【网络出版年期】2024年 10期
- 【分类号】TQ426;TM911.4