發(fā)布時間：2018-05-26 22:14

  本文選題：金屬有機框架化合物 + 類普魯士藍��； 參考：《中國科學技術大學》2017年博士論文

【摘要】：目前,世界上面臨的最嚴重的兩大問題是環(huán)境惡化和能源危機。氫能是一種清潔且可持續(xù)的能源,具有高能量密度、零排放和儲量豐富等優(yōu)點。為了應對上述兩大問題,氫能備受關注。在堿性電解池中電解水是目前最可能實現大規(guī)模產業(yè)化制氫的技術。然而電解水在動力學上需要越過較大的能壘,導致反應速率較慢,因此需要高活性的電催化劑來加速反應的進行。催化劑不僅僅改變反應動力學過程,還降低過電位從而減少電能消耗,進而降低制氫的成本。普魯士藍類似物早在1704年就已經被發(fā)現了,是一種最古老的且最簡單的金屬有機框架化合物。由于其在氣體吸附、儲能、催化及載藥等領域的廣泛應用,目前受到了廣泛的關注和大量的研究。類普魯士藍化合物是由作為金屬接頭的過渡金屬中心離子和作為有機連接器的氰根基團配體一起自組裝連接所形成的一種超分子結構。在類普魯士藍的框架結構中過渡金屬分別存在與碳原子相鄰以及與氮原子相鄰的兩種不同位置,并且這兩種位置上可以被不同的金屬離子所占據。這些金屬元素包含鐵、鈷、鎳、鋅和銅等過渡金屬。此外,可以使用少量的貴金屬離子取代框架結構中過渡金屬離子位置的過渡金屬,同時還能夠確保類普魯士藍的框架結構保持不變。這類類普魯士藍化合物中的金屬元素具有豐富的種類多樣性,因此非常適合用作制備過渡金屬、過渡金屬合金以及過渡金屬與貴金屬合金與碳復合的前驅體。合金化可以改變金屬原子間的鍵長從而改變表面的吸附能最終優(yōu)化電催化活性。而氰根基團是由氮原子和碳原子構成,可以作為C源和N源在合金粒子表面包覆上一層N摻雜的石墨烯層。這些包覆的石墨烯殼層可以促進合金核與石墨烯殼層之間的電子轉移,從而有利于提升電催化活性和循環(huán)穩(wěn)定性。因此,我們合成了一系列類普魯士藍化合物,并且以此為前驅體通過模板法熱解制備出了過渡金屬基電催化劑。并對制備的納米粒子在堿性電解液中析氫電催化性能和析氧電催化性能進行了研究。主要內容包含如下幾個方面:1.目前,析氫反應中最大的瓶頸是缺乏便宜的高活性電催化劑來取代鉑基電催化劑。我們使用釕摻雜的鈷氰酸鈷類普魯士藍粒子來作為前驅體制備了具有高活性和高穩(wěn)定性的電催化劑。該電催化劑是由核殼復合結構(RuCo@NC)構成,內部是釕和鈷的雙金屬合金納米粒子,外部是在合金表面原位包覆的氮摻雜的多層石墨烯。該復合材料在對堿性電解液中表現出優(yōu)異的析氫電催化活性。其析氫反應的電流密度達到10 mA cm-2和100 mA cm-2時,過電位分別只有28 mV和218 mV。并且循環(huán)反應10000次后活性無明顯下降,表現出極好的循環(huán)穩(wěn)定性。貴金屬Ru是最便宜的鉑族金屬,而該電催化劑中的釕含量只占催化劑總質量的3.58%,因此還具有很好的價格成本優(yōu)勢。通過密度泛函理論計算表明,在電催化劑的鈷核中引入釕可以增強電子從合金內核向外部石墨烯殼層的轉移,可以大幅度降低石墨烯表面上N摻雜近鄰處的C活性位點對氫的吸附自由能,因此有利于促進析氫反應的進行。2.析氧反應是電解水中另一個重要的半反應。然而,析氧反應在動力學上更加難以進行,需要高活性的析氧電催化劑來加速反應的進行。目前,Ru02和Ir02是性能最佳的析氧電催化劑。但是,它們在析氧反應中不夠穩(wěn)定且價格成本相對較高,無法在工業(yè)上大規(guī)模使用。過渡金屬以及它們的合金在理論上具有非常高的活性并且還具有更加便宜的價格成本,因此有很好的潛力來取代這些貴金屬基電催化劑在析氧反應中的應用。本章采用鐵氰酸鎳作為前驅體,簡便地制備出了氮摻雜的多層石墨烯包覆鐵鎳合金的復合材料(FeNi@NC)。該催化劑在堿性電解液中析氧電流密度達到10 mA cm-2時過電位只有299 mV,并且還在循環(huán)5000次后表現出較高的穩(wěn)定性�？梢钥闯�,該電催化劑在催化活性和循環(huán)穩(wěn)定性方面都超出了 RuO2電催化劑。因此,我們合成出的電催化劑在析氧領域中具有很好的潛在應用前景。3.析氧反應是電解水反應中陰極半反應,也是電解水制氫中一個關鍵的半反應。此外,析氧反應和它的逆反應氧還原反應是可再生燃料電池和金屬空氣電池的核心電化學反應。然而,析氧反應在動力學上速率較慢,因而需要高活性的電催化劑來降低反應的過電位從而降低能量損耗。非貴金屬基電催化劑被認為最有前景的材料之一,有潛力取代貴金屬基電催化劑在析氧反應中的應用。然而,這些非貴金屬電催化劑與貴金屬電催化劑相比活性和穩(wěn)定性還有不小的差距,因此需要研究加以提高。在此,我們通過一步法焙燒制備了高氮摻雜的多層石墨烯包覆碳化鈷鋅和金屬鈷組成的納米異質結復合材料(ZnCo3C/Co@NC)。我們制備的電催化劑在電流密度達到10 mAcm-2時過電位只有366 mV,其活性超過了商用RuO2電催化劑。此外,該電催化劑在氧還原反應中的起始電位和峰電流電位分別為0.912V和0.814V,該性能遠遠超過相應的金屬碳化物樣品。在異質結中金屬鈷與碳化鈷鋅的界面處,金屬Co作為電子施主具有更好的親電性,有利于促進OH-和反應中間體活性物質發(fā)生親核反應,從而加速析氧反應的進行;Co3ZnC作為電子受主具有更高的親核性,有利于促進反應中間體活性物質發(fā)生親電反應并將生成的OH-立即脫去,從而加速氧還原反應的進行。
[Abstract]:At present, the two most serious problems facing the world are environmental degradation and energy crisis. Hydrogen energy is a clean and sustainable energy, with the advantages of high energy density, zero emission and abundant reserves. In order to cope with the above two problems, hydrogen energy is paid much attention. In alkaline electrolysis pool, electrolysis water is the most likely to realize large-scale industry at present. The technology of hydrogen production. However, the electrolyzed water needs to cross a larger energy barrier in kinetics, resulting in a slower reaction rate. Therefore, a highly active electrocatalyst is needed to accelerate the reaction. The catalyst not only changes the reaction kinetics process, but also reduces the overpotential and reduces the energy dissipation, and then reduces the cost of hydrogen production. As early as 1704, it was discovered, the oldest and simplest metal organic frame compound. Due to its extensive application in the fields of gas adsorption, energy storage, catalysis and drug loading, the Prussian blue compound is a central ion of transition metal as a metal joint. A supramolecular structure formed by a self-assembly connection with the ligands of the cyanogen group as the organic connector. In the framework of Prussian blue, the transition metals are adjacent to the carbon atoms and two different positions adjacent to the nitrogen atom, and these two positions can be occupied by different metal ions. The elements contain transition metals such as iron, cobalt, nickel, zinc and copper. In addition, a small amount of precious metal ions can be used to replace transition metals in the transition metal ions in the frame structure, while the frame structure of the Prussian blue can be kept constant. The metal elements in the Prussian blue complex are rich in variety, So it is very suitable for the preparation of transition metal, transition metal alloy and precursor of transition metal and metal alloy and carbon composite. Alloying can change the bond length between metal atoms and change the surface adsorption energy to optimize the electrocatalytic activity. The cyanogen group is made up of nitrogen source and carbon atom, which can be used as the source of C and the source of N. A layer of N doped graphene is coated on the surface of the alloy particles. These coated graphene shells can promote electron transfer between the alloy core and the graphene shell. Thus, the electrocatalytic activity and the cyclic stability are promoted. Therefore, a series of Prussian blue compounds have been synthesized and used as precursors through the template. Transition metal based electrocatalysts were prepared by pyrolysis. The electrocatalytic properties of hydrogen evolution and oxygen evolution in alkaline electrolyte were studied. The main contents include the following aspects: 1. the biggest bottleneck in the process of hydrogen evolution is the lack of cheap and highly active electrocatalysts to replace platinum based electrocatalysis. We use ruthenium doped cobalt cyanate Prussian blue particles as precursors to prepare an electrocatalyst with high activity and high stability. The electrocatalyst is composed of a nuclear shell composite structure (RuCo@NC), a bimetallic alloy nanoparticle with ruthenium and cobalt, and a nitrogen doped multilayer stone coated on the surface of the alloy. The composites exhibit excellent hydrogen evolution electrocatalytic activity in the alkaline electrolyte. When the current density of the hydrogen evolution reaction reaches 10 mA cm-2 and 100 mA cm-2, the overpotential is only 28 mV and 218 mV., respectively, and the activity has no obvious decrease after 10000 cycles, and the noble metal Ru is the cheapest. The content of ruthenium in the electrocatalyst is only 3.58% of the total mass of the catalyst, so it has a good price cost advantage. The density functional theory shows that the introduction of ruthenium in the cobalt core of the electrocatalyst can enhance the transfer of electrons from the alloy core to the external graphene shell, which can greatly reduce the surface of the graphene surface. The N doped C active site in the near neighbour is free energy for hydrogen adsorption. Therefore, it is beneficial to promote the hydrogen evolution reaction to promote the hydrogen evolution reaction is another important half reaction in the electrolysis water. However, the oxygen evolution reaction is more difficult to carry out in kinetics, and the high active oxygen evolution electrocatalyst is needed to accelerate the reaction. At present, Ru02 and Ir02 are the nature of the reaction. The best oxygen evolution electrocatalysts are available. However, they are not stable in the oxygen evolution reaction and have relatively high price costs and can not be widely used in industry. Transition metals and their alloys have very high activity in theory and have cheaper price costs, so there is a great potential to replace these precious metals. The application of electrocatalyst in the oxygen evolution reaction. This chapter uses nickel ferricyanate as a precursor to prepare a nitrogen doped multilayer graphite coated iron nickel alloy composite (FeNi@NC). The catalyst is only 299 mV when the oxygen evolution current density reaches 10 mA cm-2 in the alkaline electrolyte, and is also performed after 5000 cycles. It can be seen that the electrocatalyst has exceeded the RuO2 electrocatalyst in both catalytic activity and cyclic stability. Therefore, our synthesized electrocatalyst has a good potential application prospect in the field of oxygen evolution. The.3. oxygen evolution reaction is the cathode semi reaction in the electrolysis water reaction, and is also a key to the hydrogen production of the electrolysis water. In addition, the oxygen evolution reaction and its reverse redox reaction are the core electrochemical reactions of the renewable fuel cell and the metal air battery. However, the kinetic rate of the oxygen evolution reaction is slower, so the highly active electrocatalyst is needed to reduce the overpotential of the reaction and reduce the energy loss. One of the most promising materials has the potential to replace the application of the noble metal based electrocatalysts in the oxygen evolution reaction. However, these non noble metal electrocatalysts have no small gap between the activity and stability of the noble metal electrocatalysts. Therefore, it is necessary to study it. In this case, we have prepared high nitrogen doping by one-step roasting. A nano heterojunction composite (ZnCo3C/Co@NC) consisting of cobalt zinc and metal cobalt (ZnCo3C/Co@NC) is coated with multilayer graphene. The electrocatalyst prepared by us has a over potential of only 366 mV when the current density reaches 10 mAcm-2, and its activity exceeds the commercial RuO2 electrocatalyst. In addition, the starting potential and peak current potential of the electrocatalyst in the oxygen reduction reaction are in addition. Unlike 0.912V and 0.814V, the performance is far more than the corresponding metal carbide samples. In the heterojunction, the metal cobalt and cobalt carbide at the interface, metal Co as the electron donor has better electrophilic property, is beneficial to promote the nucleophilic reaction of the active substances of the OH- and the reaction intermediates, and accelerate the oxygen evolution reaction; Co3ZnC is the electron acceptor. The host has a higher nucleophilic activity, which helps to promote the reaction of reactive intermediates and remove the generated OH- immediately, thus accelerating the oxygen reduction reaction.
【學位授予單位】：中國科學技術大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：O643.36;TQ116.2

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