四氧化三锰纳米晶/石墨烯复合电极材料制备及其电化学性质

【作者】 杨小帆；

【导师】 刘宗怀；

【作者基本信息】 陕西师范大学 ， 无机化学， 2016， 硕士

【摘要】 电化学电容器作为一种新型的储能器件因其充放电速率快、功率密度高及循环稳定性好等特点而备受人们的关注。影响电化学电容器性能的主要因素有组装方法、电解液及电极材料,其中电极材料是最为重要的因素。因此研发具有高电容性质的电极材料是提高电化学电容器性能的主要途径之一。Mn₃O₄具有储量丰富、环境友好和理论比电容高等特点,已经广泛的用作超级电容器电极材料。但是Mn₃O₄导电性差,块体材料比表面积小,使得与电解液反应的活性位点减少,导致Mn₃O₄材料电容性质无法得到充分发挥。为了克服这些问题,将Mn₃O₄纳米化并与具有优异导电性的碳材料如石墨烯复合,期待制备具有良好导电性及高电容性质的Mn₃O₄纳米晶／石墨烯复合电极材料。本研究工作通过通过离子交换反应、石墨烯纳米层孔洞化处理及高温煅烧过程,分别制备了Mn₃O₄纳米晶／还原石墨烯（孔洞化石墨烯）复合电极材料,对制备复合电极材料进行了系统表征,研究了制备材料的电化学性质。全文包括四章内容,第1章为绪论部分,第^2-3章为实验部分,第4章是全文总结。绪论部分论述了电化学电容器的结构、储能机理和电化学电容器电极材料及其在商业中的应用,讨论了石墨烯,Mn₃O₄及由二者所构成的复合材料的结构、制备方法及应用。在第2章实验部分,通过离子交换及热处理的方法制备了Mn₃O₄纳米晶／还原石墨烯复合电极材料（Mn3O4/RGO）,并对其结构、形貌及电化学性质进行了系统表征；第3章通过H₂O₂对氧化石墨烯（GO）进行孔洞化处理,再使用离子交换及热处理方法制备了Mn₃O₄纳米晶／孔洞还原石墨烯复合材料（Mn3O4/HRGO）,并对其结构,形貌及电化学性质进行了分析表征。第4章为全文总结。（1）以Mn（NO₃）₂为锰源,通过离子交换方法制备中间产物吸附锰离子氧化石墨烯GO-Mn2+。氧化石墨烯中间产物GO-Mn2+在不同温度氮气气氛中煅烧4 h,得到MnOx纳米晶/还原石墨烯复合电极材料。比较分析复合材料中锰氧化合物的价态、纳米晶的大小及复合材料中还原石墨烯的还原程度与煅烧温度及气氛影响关系。氧化石墨烯中间产物GO-Mn2+在450℃ N2气氛下煅烧4 h,得到Mn₃O₄纳米晶均匀分散在RGO片层上的复合电极材料Mn3O4/RGO-450。在三电极体系下,以Mn3O4/RGO为工作电极,Ag/AgCl为参比电极,Pt为对电极,在1M KOH电解液中对复合材料的电化学性质进行了系统表征,复合材料的电化学性质与其结构及Mn₃O₄的活性位点利用率密切相关。在电势窗口为-0.9到0.1 V,在1 Ag^-1的电流密度下,测定Mn3O4/RGO-450复合电极材料的质量比电容,其质量比电容为519 F g^-1。该值高于纯Mn3O4纳米晶及纯RGO电极的比电容,且复合材料的阻抗值也小于纯Mn₃O₄电极。（2）采用H₂O₂对GO片层在反应温度100℃水热处理4 h,实现石墨烯纳米层的孔洞化处理,制备孔洞化氧化石墨烯（HGO）。 HGO与Mn2+进行离子交换反应,生成吸附锰离子的孔洞氧化石墨烯中间产物Mn2+-HG O。中间产物Mn2+-HGO在N2气氛中煅烧4 h,制备MnOx纳米晶/孔洞还原石墨烯（HRGO）复合电极材料。通过对制备材料的形貌和结构表征,讨论MnOx纳米晶/HRGO的结构和形貌与煅烧温度的关系。与Mn3O4/RGO-450电极材料进行比较,研究孔洞化处理对于制备材料形貌、结构及电化学性质影响。通过对MnOx纳米晶/HRGO复合电极材料的电化学性质系统研究,讨论孔洞化处理对于制备材料电极电容量、循环稳定性及倍率性能的影响,研究孔洞化处理技术对于石墨烯复合电极材料电化学性质和导电率之间的平衡关系。更多还原

【Abstract】 As a new energy storage device, electrochemical capacitor has attracted a great deal attention because of its rapid charge-discharge ability, long cycle life and high power density. Research results indicate that the capacitive property of electrochemical capacitor is influenced by the electrode materials, electrolyte, and the assembled devices, with the most important factor being the electrode materials. Therefore, what is a way to improve the capacitance of electrochemical capacitor is developing a kind of electrode materials with good capacitance. Mn₃O₄ has been widely used as electrode materials for electrochemical capacitor, which has a lot of advantages, such as high theoretical capacitance, environment-friendly and nature abundance. However, its electrochemical performance is limited due to its poor electrical conductivity, small surface area and low active utilization. In order to overcome these problems, the Mn₃O₄ can be made into nano-size and hybridized with carbon-based materials which have excellent electrical conductivity, like graphene. Therefore, the Mn₃O₄/graphene hybrid electrode materials with high capacitance are expected to be prepared. In this thesis, by using ion-exchange reaction, graphene nano-layer holey processing and high-temperature calcination process, manganese tetroxide nanocrystalline/reduced graphene （holey graphene） hybrid electrode materials are prepared, and their morphology, structure and electrochemical peorperty are systematically investigated.The whole thesis consists of four chapters. The structure, energy storage principle, the electrode materials, and the application of the electrochemical capacitor are systematically reviewed, and also the structure, preparation methods and applications of graphene, Mn₃O₄, and Mn₃O₄/graphene hybrid materials are discussed in Chapter 1. The second part is the experimental parts and result discussion. By using ion exchange method and heat treatment, the nanocrystalline manganese tetroxide/reduced graphene electrode material （Mn₃O₄/RGO） are prepared, and their structure, morphology and electrochemical properties are systematically investigated in Chapert 2. By using H₂O₂ as etchant and oxidant, nanoporous is introduced into graphene oxide nanosheets and holey graphene oxide is obtained, then the nanocrystalline manganese tetroxide/holey reduced graphene electrode material （Mn₃O₄/HRGO） are prepared, and their structure, morphology and electrochemical properties are systematically investigated in Chapert 3. The conclusion of this thesis is given in Chapter 4.（1） The MnOx/graphene hybrid material is prepared by exchanging GO with Mn2+ ions and followed by calcining the Mn2+-exchanged material at different temperatures for 4 h in N2 atmosphere. The effect of the calcination temperatures on the phase and morphology of the obtained materials is investigated. The phase and size of MnOx nanocrystalline and reduction degree of GO in the hybrid material are affected by calcining temperature. The Mn₃O₄/RGO hybrid sample can be obtained at 450℃, in which Mn₃O₄ nanocrystalline with average size of 13.5 nm are homogeneously distributed on the surface of RGO. The electrochemical properties of Mn₃O₄ nanocrystalline/RGO are investigated by cyclic voltammetry and galvanostatic charge-discharge in 1 M KOH electrolyte. Their electrochemical performance is highly structure dependent and highly utilization of Mn₃O₄ nanocrystalline. The Mn₃O₄ nanocrystalline/RGO hybrid electrode exhibits a high specific capacitance of 519 F g-at a current density of 1 A g^-1. This method can be expanded to control the size of other transition-metal oxide nanocrystalline on the graphene nanosheets and improve the capacitance and urilization of the metal oxide-graphene nanohybrids.（2） By using H₂O₂ as etchant and oxidant, nanoporous is introduced into graphene oxide nanosheets and holey graphene oxide is obtained （HGO） at 100℃ for 4 h. Then the nanocrystalline manganese tetroxide/holey reduced graphene electrode material （Mn₃O₄/HRGO） is prepared by exchanging HGO with Mn2+ ions and followed by calcining the Mn2+-exchanged material at different temperatures for 4 h in N2 atmosphere. The effect of the calcining temperatures on the phase and morphology of the obtained materials is investigated. The phase and size of MnOx nanocrystalline and reduction degree of HGO in the hybrid material are affected by calcining temperature, by which the Mn₃O₄/HRGO hybrid sample can be obtained at 450℃. By comparing with Mn₃O₄/RGO-450 electrode material, the effect of the holey treatment for graphene oxide on the electrode capacity, cycling stability and rate performance of the obtained MnOx/HRGO hybrid electrodes are investigated, and their electrochemical properties are also discussed.更多还原