能源需求量的倍增，环境污染的日益严重均促使燃料电池等新型清洁能源转换技术的开发。其阴极氧还原反应（ORR）的动力学缓慢，导致消耗更多催化剂以提供反应发生所需的能量。目前为止，Pt基材料被认为是最具活性的ORR催化剂，但贵金属的价格高昂、储量匮乏及稳定性差等因素严重限制了其应用范畴。因此，探究高活性、价格低廉及稳定性和抗甲醇性能优异的非贵金属氧还原催化剂代替Pt基催化剂对于推动燃料电池的商业化应用具有非常重要的意义。金属有机骨架（MOFs）是由金属离子和有机配体通过配位键相互连接形成的一种网状骨架的多孔结构，由于其比表面积高、结构可控被广泛用作制备多孔碳的前驱体材料。本论文基于该材料的特殊优势，进行过渡金属元素的负载，研究催化剂的ORR活性和催化机理，具体研究内容和结论如下：

（1）以2-甲基咪唑作为有机配体通过自组装形成均匀的Co/Zn-MOFs，并与二维氧化石墨烯纳米片进行静电吸附，在高温氩气气氛下制备得到新型三维混合碳基导电网络材料（Co-CNTs@NCF_T）。通过对催化剂煅烧温度的调控，可以有效控制改善碳材料的氮构型和石墨化程度。优化后的Co-CNTs@NCF₉₀₀具有高度分散的金属颗粒、丰富的微介孔结构及高效的氮掺杂。热解过程中还原的Co纳米颗粒可以有效催化碳纳米管的生长，这种纵横交错的管状结构促进了电子的转移和物质的传输，从而提高催化性能。通过对比发现，石墨烯片层的引入促进了三维多孔结构的构成，丰富了催化活性物种及界面特性。电化学测试进一步表明，Co-CNTs@NCF₉₀₀在碱性介质中呈现出0.96 V的起始电位和0.84 V的半波电位，甚至可以与工业化应用的Pt/C催化剂媲美。

（2）在室温液相环境下，利用一锅法合成抗坏血酸修饰的Fe/Zn-MOFs，后通过“蒸发-碳化”与氧化石墨烯进行物理复合，制备得到Fe与N共掺杂的多孔碳材料（C-Fe/Fe₃O₄@NGF）。抗坏血酸的引入可以抑制大颗粒铁物种的形成，以此来增加催化剂的比表面积及促进缺陷碳的形成。反应过程中锌的挥发造就了更丰富的孔结构，为催化ORR提供了良好的场所。对材料的表征和测试表明所构筑的目标催化剂C-Fe/Fe₃O₄@NGF的比表面积高达675 m²/g，且其分级多孔结构有利于活性位点的暴露。电化学测试结果表明C-Fe/Fe₃O₄@NGF的ORR催化活性（半波电位为0.86 V）及稳定性均优于Pt/C催化剂。

（3）采用简单环保的超声辅助策略在酚醛树脂微球上合成双金属（BM）MOF，设计构筑了以氧化石墨烯为催化载体的MOFs衍生材料（UA-Co/RSC@NGF）。通过与传统方法制备MOFs的对比发现，超声波引起的声空化效应可以产生瞬时高压和高温，会加速成核过程，缩短合成时间，更易控制合成MOF的粒径。同时，在碳框架中掺杂氮可以提升碳基材料的导电性和电子亲和力，促进对O₂的快速吸附。得益于碳微球、石墨烯和BMMOF的强协同耦合效应，材料的内在活性被大幅度优化，从而显著提升ORR催化性能。在氧气饱和的氢氧化钾溶液中，UA-Co/RSC@NGF的半波电位可达0.90 V，从结果表明该材料遵循高效的四电子催化途径。在碱性介质中的电化学性能测试中，其表现出比工业化Pt/C催化剂更出色的稳定性和优异的抗甲醇毒蚀能力。

The doubling of energy demand and the increasingly serious environmental pollution have prompted the development of new clean energy conversion technologies, such as fuel cells. The slow kinetics of cathodic oxygen reduction reaction (ORR) requires more catalysts to provide the energy required for the reaction. Up to now, Pt-based catalyst has been considered the most active ORR catalyst, but the high cost of precious metals, lack of reserves and poor stability limit its application. Therefore, it is of great significance to explore non-noble metal oxygen reduction catalysts with high activity, low price, excellent stability and methanol resistance to replace traditional Pt-based catalysts for promoting the commercial application of fuel cells. Metal-organic-frameworks (MOFs) are porous structures widely used as precursor materials for the preparation of porous carbon due to their high specific surface area and controllable structure. Based on the special advantages of this material, this paper doped transition metal elements to study the ORR activity and catalytic mechanism of the catalyst. The specific research contents and conclusions are as follows:

(1) Homogeneous Co/Zn-MOFs were formed by self-assembly using 2-methylimidazole as an organic ligand and were electrostatically adsorbed onto two-dimensional graphene oxide nanosheets. A novel three-dimensional hybrid carbon-based conductive network material was prepared under a high-temperature argon atmosphere (Co-CNTs@NCF_T). The nitrogen configuration and graphitization degree of carbon materials can be effectively controlled and improved by controlling the calcination temperature of catalysts. The optimized Co-CNTs@NCF₉₀₀ has highly dispersed metal particles and efficient nitrogen doping. The reduced Co nanoparticles produced in the pyrolysis process can effectively catalyze the growth of carbon nanotubes. This crisscross tubular structure promotes the transfer of electrons and the transport of substances. It was found that the introduction of graphene lamellae promoted the formation of a three-dimensional porous structure, and enriched the catalytic active species and interface properties. Electrochemical tests further show that Co-CNTs@NCF₉₀₀ exhibits an initial potential of 0.96 V and a half-wave potential of 0.86 V in alkaline media, which can even be compared with the industrial Pt/C catalyst.

(2) The ascorbic acid modified Fe/Zn-MOFs were synthesized by the one-pot method in the liquid phase at room temperature, and then were physically combined with graphene oxide by evaporation-carbonization, resulting in Fe and N co-doped porous carbon species materials (C-Fe/Fe₃O₄@NGF) were prepared. The introduction of ascorbic acid can inhibit the formation of large-particle iron species，so as to increase the specific surface area of the catalyst and promote the formation of defective carbon. The volatilization of zinc in the reaction process creates a richer pore structure, which provides a good place for catalytic ORR. The characterization and testing showed that the specific surface area of the constructed catalyst C-Fe/Fe₃O₄@NGF was 675 m²/g, and its hierarchical porous structure was conducive to the exposure of active sites. The electrochemical test results showed that the half-wave potential (0.86 V) and stability of C-Fe/Fe₃O₄@NGF were better than Pt/C catalysts.

(3) BMMOF was synthesized on phenolic resin microspheres using a simple and environmentally friendly ultrasonic-assisted strategy. MOFs-derived materials (UA-Co/RSC@NGF) using graphene oxide as catalytic carrier were designed and constructed. Compared with traditional methods for preparing MOFs, it was found that the acoustic cavitation effect caused by ultrasound can generate instantaneous high pressure and temperature, accelerate the nucleation process, shorten the synthesis time, and more easily control the particle size of synthesized MOFs. Concurrently, nitrogen doping in the carbon frame can improve the conductivity and electron affinity of carbon-based materials, promoting rapid adsorption of O₂. Benefiting from the strong synergistic coupling effect of carbon microspheres, grapheme and BMMOF, the intrinsic activity of the material is greatly optimized, thereby significantly improving the ORR performance. The half-wave potential of UA-Co/RSC@NGF can reach 0.90 V in an oxygen-saturated potassium hydroxide solution. The results show that the material follows an efficient four-electron transfer catalysic pathway. In the electrocatalytic test in an alkaline medium, it exhibits higher stability and excellent methanol corrosion resistance than commercial Pt/C catalysts.

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