【作者】 王光彬；

【导师】 黄柏标； 郑昭科；

【作者基本信息】 山东大学 ， 材料学， 2021， 硕士

【摘要】 二氧化锰（MnO₂）作为地表丰度最大的金属氧化物之一,不仅存量可观、价格低廉和绿色无毒,还具有多样的晶体结构和氧化态。这些独特优势使MnO₂在光电催化、污染物降解、电化学以及超级电容器等领域成为热点材料,并取得了飞速的进展。随着研究的深入,科研人员发现MnO₂的催化活性主要取决于其独特的隧道结构,而晶体结构的多样性使得隧道结构的尺寸和种类更加丰富。因此,MnO₂形态学的结构控制和设计成为纳米材料发展的热点。近年来,电催化技术的飞速发展成为解决当前能源短缺和环境污染的潜在策略,丰富多样的纳米材料催化剂也为电催化技术的发展增添了更加持久的动力。MnO₂丰富的晶体结构及其多价态特性,更易于参加活性的电化学氧化还原反应,是一种具有应用潜力的电催化剂。然而MnO₂材料本身具有导电性低和活性位点不足等缺陷,使其电催化活性受到了一定的限制。目前,通过调控形貌、尺寸控制以及增加比表面积等方式取得了一定的进展,但是还未从本质上提升MnO₂的电催化活性。如何采用有效手段对MnO₂材料的结构进行调控、设计和改性,对于提升其电催化效率进而加快工业化应用具有重大意义。本论文采用晶相调控、过渡金属阳离子掺杂及微结构设计三种手段来优化MnO₂材料的微结构,进而提升其电催化活性。通过对所制备催化剂的形态结构和电化学性质进行测试,探究了其活性增强的原因和机理。具体研究内容如下:第一章中,系统分析了 MnO₂材料常见的晶体结构,详细介绍了其制备方法和应用方向,然后针对在电催化领域,MnO₂当前存在的核心问题进行了分析,并提出相应的解决策略。最后对结构调控以及探索新型高效电催化剂的方式进行总结,进而引出本文的选题内容和研究意义。第二章中,以OER为目标反应,理论上提出了具有活性的晶体结构。对四种不同晶相MnO₂的形貌特征和电化学性质进行了系统的测试,研究了 OER活性与其晶体结构的内在关系,确定了具有活性的最佳晶体结构,揭示了 MnO₂的OER活性强烈依赖其晶体结构的特征。第三章中,基于过渡金属阳离子掺杂的思路,通过水热法制备了五种不同过渡金属阳离子掺杂的MnO₂,对其结构特征和化学性质进行详细测试,对比了它们的OER性能,其中Fe-MnO₂展现出最佳活性。并通过EIS和ECSA等测试对其性能增强的机理进行了讨论。结果表明,过渡金属阳离子的引入不仅能改善MnO₂电极的界面电子传输能力和电导率,还会改变MnO₂本身的活性结构,提供更加高效稳定的活性位点,加快水氧化过程的反应效率。第四章中,采用微结构设计的策略,通过一步水热法成功制备了一种具有氧空位的MnO₂超长纳米线。对其晶体结构和微观形貌进行系统的表征,证实超长纳米线结构以及氧空位的存在,然后通过一系列NRR活性测试,评价了 MnO₂超长纳米线电化学性质。结果表明,MnO₂超长纳米线是一种具备优良NRR活性的催化剂,而且具备良好的耐久性和选择性。确定了微结构设计、形貌调控和引入氧空位是一种提升NRR活性的有效策略。第五章中,我们对整篇论文进行总结,评价与讨论了论文的主要创新点。针对当前存在的不足,有计划进行解决,并对以后的工作进行了展望。更多还原

【Abstract】 As one of the most abundant metal oxides on the earth’s surface,MnO₂ not only has considerable reserves,is　inexpensive and environmentally friendly,but also has a variety of crystal structures and oxidation states.These unique advantages make MnO₂ become a hot material in the fields of photocatalysis,pollutant degradation,electrochemistry and supercapacitors,and have made rapid progress.With the deepening of research,researchers found that the catalytic activity of MnO₂ mainly depends on its unique tunnel structure,and the diversity of crystal structures makes the size and types of tunnel structures more abundant.Therefore,the structure control and design of MnO₂ morphology has become a hot topic in the development of nanomaterials.In recent years,the rapid development of electrocatalysis technology has become a potential strategy to solve the current energy shortage and environmental pollution,and a variety of nanomaterial catalysts have also added a more lasting impetus to the development of electrocatalysis technology.Because of its rich crystal structure and polyvalence,MnO₂ is more likely to participate in active electrochemical oxidation-reduction reactions,which makes it an electrocatalyst with potential application.However,the MnO₂ material itself has the defects of low conductivity and insufficient active sites,which limits its electrocatalytic activity.At present,some progress has been made by controlling morphology,size and increasing specific surface area,but the electrocatalytic activity of MnO₂ has not been substantially improved.How to adopt effective means to regulate,design and modify the structure of MnO₂ material is of great significance for improving its electrocatalytic efficiency and accelerating its industrial application.In this paper,three methods of crystal phase control,transition metal cation doping and microstructure design are used to adjust the structure of MnO₂ materials and improve their electrocatalytic activity.Through the test and characterization of the crystal structure,microscopic morphology and electrochemical properties of the prepared catalyst,the reason and mechanism of its enhanced activity were further explored.The specific research content is as follows:In the first chapter,the common crystal structures of MnO₂ materials are systematically analyzed,and the preparation methods and application directions are introduced in detail.Then,the existing core problems of MnO₂ in the field of electrocatalysis are analyzed,and the corresponding solutions are proposed.Finally,the structure regulation and the way to explore new efficient electrocatalyst are summarized,and then the topic and research significance of this paper are introduced.In the second chapter,an active crystal structure is theoretically proposed with OER as the target reaction.The morphology and electrochemical properties of four different crystal phases of MnO₂ were systematically tested.The intrinsic relationship between OER activity and its crystal structure was studied.The best crystal structure with activity was determined,which revealed that the OER activity of MnO₂ strongly depended on its crystal structure.In the third chapter,based on the idea of transition metal cation doping,five different transition metal cation doped MnO₂ were prepared by hydrothermal method.Their structural characteristics and chemical properties were tested in detail,and their OER performance was compared.Among them,Fe-MnO₂ showed the best activity.The mechanism of its performance enhancement was discussed by EIS and ECS A tests.The results show that the introduction of transition metal cation can not only improve the interfacial electron transport capacity and conductivity of MnO₂ electrode,but also change the active structure of MnO₂ itself,provide a more efficient and stable active site,and accelerate the reaction efficiency of water oxidation process.In the fourth chapter,a kind of ultralong MnO₂ nanowires with oxygen vacancy was successfully prepared by one-step hydrothermal method using the microstructural design strategy.The crystal structure and micro structure of the ultralong MnO₂ nano wires were characterized systematically,and the existence of oxygen vacancy was confirmed.Then,the electrochemical properties of the ultralong MnO₂ nano wires were evaluated by a series of NRR activity tests.The results show that MnO₂ nanowires is a kind of catalyst with excellent NRR activity,and has good durability and selectivity.Microstructure design,morphology control and the introduction of oxygen vacancies are effective strategies to enhance the activity of NRR.In the fifth chapter,we summarize the whole paper,evaluate and discuss the main innovation points of the paper.In view of the existing inadequacies,we plan to solve them and look forward to the future work.更多还原