鈷基金屬有機框架結(jié)構(gòu)材料的合成及其電化學(xué)性能研究
發(fā)布時間：2019-05-22 23:12
【摘要】：隨著能源材料的發(fā)展,氫氣由于其清潔、零污染等優(yōu)點被視為一類高效的新型能源載體。而堿性條件下的水分解被認為是一種非常具有應(yīng)用前景的制氫方法,它包括兩個半反應(yīng),即在陰極發(fā)生的析氫反應(yīng)和在陽極發(fā)生的析氧反應(yīng)。但是,在整個水分解系統(tǒng)中,由于電催化析氧反應(yīng)是一個4電子反應(yīng)過程,因此,析氧反應(yīng)的發(fā)生需要克服更大的動力學(xué)能壘。所以,發(fā)展高效的析氧電催化劑成為提高全水分解性能的一個主要研究方向。近年來,金屬有機框架結(jié)構(gòu)材料(metal-organic frameworks)由于其較好的物理穩(wěn)定性、化學(xué)穩(wěn)定性以及規(guī)則有序的孔道、骨架結(jié)構(gòu),逐漸代替了傳統(tǒng)的多孔材料并廣泛地應(yīng)用于各類反應(yīng)中。鑒于現(xiàn)有的析氧電催化劑仍然具有析氧過電位大,制備方法復(fù)雜等缺點,本論文結(jié)合金屬有機框架結(jié)構(gòu)材料(MOFs)的結(jié)構(gòu)優(yōu)點和應(yīng)用基礎(chǔ),創(chuàng)新性地合成了不同的鈷基金屬有機框架結(jié)構(gòu)材料(MOFs)和其衍生物并將獲得的MOFs材料應(yīng)用于電催化析氧反應(yīng)中,同時研究其在析氧反應(yīng)中的理論意義和實際應(yīng)用價值。本文主要分為以下幾個工作:1.近年來,鑒于MOFs-基材料的大的比表面積和可調(diào)的孔道結(jié)構(gòu)等優(yōu)點,MOFs-基材料被逐步應(yīng)用在電催化析氧反應(yīng)中。然而,通常的MOFs-基催化劑的制備方法是使用Nafion將電極材料涂覆在玻璃碳電極上以待測試。這就使得電極材料在析氧反應(yīng)中的電子和質(zhì)子傳輸被Nafion膜阻礙,因而導(dǎo)致MOFs-基催化劑的有效催化活性降低。因此,優(yōu)化活性材料的電荷傳輸性能成為了設(shè)計MOFs-基析氧電催化劑的關(guān)鍵。在本工作中,我們合成了超薄的MOFs材料(ZIF-67)納米片并將其原位生長在高導(dǎo)電的Ti@TiO_2/Cd S基底上以此來優(yōu)化整個電極的電荷傳輸能力。所獲得的Ti@TiO_2/Cd S/ZIF-67電極具有的獨特的三維結(jié)構(gòu),不僅提高了電子轉(zhuǎn)移的速率而且提高了ZIF-67材料的穩(wěn)定性。而ZIF-67作為一類由Co鹽和2-甲基咪唑配位形成的多孔材料,由于咪唑配體中所含的高電負性的N原子產(chǎn)生的誘導(dǎo)效應(yīng),使得Co離子的價態(tài)升高,從而進一步提高了Ti@TiO_2/Cd S/ZIF-67電極的析氧反應(yīng)的能力。鑒于以上結(jié)論,我們將合成的Ti@TiO_2/Cd S/ZIF-67電極應(yīng)用于堿性條件下的析氧反應(yīng),與其他MOFs-基的電催化劑相比,它展示了一個非常小的Tafel斜率(42m V/dec)及良好的穩(wěn)定性,這進一步說明了Ti@TiO_2/Cd S基底良好的導(dǎo)電性。這些實驗數(shù)據(jù)及結(jié)論為研究高效的析氧電化學(xué)催化劑開辟了一條新的研究思路。2.電催化水分解作為一種高效的、大規(guī)模的產(chǎn)氫方式,日益受到科研工作者的廣泛關(guān)注。然而,作為電催化水分解的一個半反應(yīng),析氧反應(yīng)的發(fā)生需要克服更大的動力學(xué)能壘。因此,發(fā)展高效的析氧電催化劑成為提高電催化全水分解性能的一個主要研究方向�？紤]到金屬有機框架材料(metal-organic frameworks,MOFs)規(guī)則有序的孔道結(jié)構(gòu)、穩(wěn)定的骨架及大的比表面積等優(yōu)點,在本工作中,我們采用一步磷化法在N2氣氛下將水熱合成的雙金屬有機框架結(jié)構(gòu)材料(Co Fe-MOFs)轉(zhuǎn)化生成Co-Fe-P復(fù)合物,并把它作為新的電催化劑應(yīng)用于電催化析氧反應(yīng)中。通過對鈷、鐵比例的進一步優(yōu)化,我們所得到的Co-Fe-P-1.7電極具有比鈷鐵層狀雙氫氧化物(Co Fe-LDH)以及Co Fe-MOFs-1.7電極更優(yōu)越的析氧性能。同時,我們將造成這一結(jié)果的原因進行了詳細的分析并得出以下結(jié)論:正是由于Co和Fe兩種金屬之間的協(xié)同效應(yīng)、Co-Fe-P-1.7中高價態(tài)的Co離子的存在、大的電化學(xué)活性表面積(ECSA)以及暴露在Co/Fe磷化物表面上的納米線,使得Co-Fe-P-1.7在1.0 M KOH中展示了優(yōu)異的電催化析氧性能,包括:在10 m A/cm~2處的過電位為244 m V、小Tafel斜率(58 m V/dec)以及良好的穩(wěn)定性。此外,在1.0 M KOH溶液中,我們將所獲得的Co-Fe-P-1.7修飾在Ni網(wǎng)上并作為在二電極體系下水分解的陽極和陰極,其在10 m A/cm~2的電流密度下的全水分解電壓為1.60 V,以上研究都為發(fā)展高效的MOFs-基雙功能化的催化劑提供了實驗借鑒和研究思路。3.通過水熱法合成了鈷/鐵雙金屬有機框架結(jié)構(gòu)(Co Fe-MOF-74),同時比較了不同的Fe摻入量對Co Fe-MOF-74的析氧性能的影響;繼而將所得到的Co Fe-MOF-74電極和商業(yè)的Pt/C負載在Ni網(wǎng)上進行了全水分解實驗,發(fā)現(xiàn)組合的催化劑具有良好的水分解性能,這為發(fā)展高效的MOFs-基析氧催化劑提供了實驗借鑒和研究思路。
[Abstract]:With the development of energy materials, hydrogen is considered as a new type of new energy carrier because of its cleaning and zero pollution. The decomposition of water under alkaline conditions is considered to be a very promising method of hydrogen production, which consists of two half-reactions, the hydrogen evolution reaction at the cathode and the oxygen evolution reaction at the anode. However, in the whole water decomposition system, since the electrocatalytic oxygen evolution reaction is a 4-electron reaction process, the occurrence of the oxygen evolution reaction needs to overcome the larger kinetic energy barrier. Therefore, the development of efficient oxygen-evolution catalyst is one of the main research directions to improve the whole-water decomposition property. In recent years, metal-organic framework has been widely used in various reactions due to its good physical stability, chemical stability and regular and ordered pore and framework structure. In view of the defects of the existing oxygen evolution electrocatalyst still has the defects of large oxygen evolution potential, complex preparation method and the like, the present paper combines the structural advantages and the application foundation of the metal organic framework structure material (MOFs), The organic framework material (MOFs) and its derivatives are synthesized and the obtained MOFs material is applied to the electrocatalytic oxygen evolution reaction, and the theoretical and practical application value in the oxygen evolution reaction is also studied. This paper is mainly divided into the following work:1. In recent years, with the advantages of large specific surface area and adjustable pore structure of the MOFs-based materials, the MOFs-based materials are gradually applied in the electrocatalytic oxygen evolution reaction. However, the usual method for preparing the MOFs-based catalyst is to use Nafion to coat the electrode material on the glassy carbon electrode for testing. This allows the electron and proton transport of the electrode material in the oxygen evolution reaction to be blocked by the Nafion membrane, thus leading to a reduction in the effective catalytic activity of the MOFs-based catalyst. Therefore, the charge transfer performance of the optimized active material becomes the key to the design of MOFs-based oxygen-based electrocatalyst. In this work, we synthesized ultra-thin MOFs (ZIF-67) nanosheets and grown them in situ on a highly conductive Ti@TiO_2/ Cd S substrate to optimize the charge transport capacity of the entire electrode. The obtained Ti@TiO_2/ Cd S/ ZIF-67 electrode has a unique three-dimensional structure, not only improves the rate of electron transfer, but also improves the stability of the ZIF-67 material. ZIF-67 is a kind of porous material which is formed by co-salt and 2-methyl detomidine, and because of the induced effect of the high electronegativity of N atoms, the valence state of Co ion is increased, thus further improving the oxygen evolution reaction capability of the Ti@TiO_2/ Cd S/ ZIF-67 electrode. In view of the above conclusion, we apply the synthesized Ti@TiO_2/ Cd S/ ZIF-67 electrode to the oxygen evolution reaction under alkaline conditions, which shows a very small Tafel slope (42 m V/ dec) and good stability as compared to the other MOFs-based electrocatalysts. This further illustrates the good electrical conductivity of the Ti@TiO_2/ Cd S substrate. These experimental data and conclusions have opened up a new way to study the efficient oxygen evolution electrochemical catalyst. Electrocatalytic water decomposition is an efficient and large-scale method of hydrogen production, and is increasingly concerned by scientific researchers. However, as one and a half of the electrocatalytic water decomposition, the occurrence of oxygen evolution reaction needs to overcome the larger kinetic energy barrier. Therefore, the development of an efficient oxygen-evolution catalyst is one of the main research directions to improve the whole-water decomposition property of electrocatalysis. in consideration of that well-ordered pore structure of the metal-organic framework material (MOFs), the stable skeleton and the large specific surface area and the like, The Co-Fe-P composite was synthesized by a one-step phosphorization method in the atmosphere of N2, and the Co-Fe-P composite was transformed into a new electrocatalyst. By further optimizing the ratio of cobalt and iron, the Co-Fe-P-1.7 electrode obtained has better oxygen evolution performance than that of the cobalt-iron layered double hydroxide (Co Fe-LDH) and the Co Fe-MOFs-1.7 electrode. At the same time, the cause of this result is analyzed in detail and the conclusion is drawn that Co-Fe-P-1.7 has the Co-Fe-P-1.7 high valence Co ion in the co-Fe-P-1.7 due to the synergistic effect between the two metals of Co and Fe. The large electrochemically active surface area (ECSA) and the nanowires exposed to the Co/ Fe phosphide surface, such that the Co-Fe-P-1.7 exhibited excellent electrocatalytic oxygen evolution performance in 1.0 M KOH, including an overpotential at 10 m A/ cm-2 of 244 m V, a small Tafel slope (58 m V/ dec), and good stability. in addition, in a 1.0 M KOH solution, we modify the obtained Co-Fe-P-1.7 on the Ni line and act as an anode and a cathode for water decomposition in a two-electrode system, with a full water decomposition voltage of 1.60 V at a current density of 10 m A/ cm-2, The above research has provided the experimental reference and the research thinking for the development of efficient MOFs-based bifunctional catalyst. Co Fe-MOF-74 (Co Fe-MOF-74) was synthesized by hydrothermal method, and the effect of different Fe doping amount on the oxygen evolution of Co Fe-MOF-74 was compared. It is found that the combined catalyst has good water decomposition property, which provides the experimental reference and the research idea for the development of efficient MOFs-based oxygen evolution catalyst.
【學(xué)位授予單位】：蘭州大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：O643.36;TQ116.2
本文編號：2483360
[Abstract]:With the development of energy materials, hydrogen is considered as a new type of new energy carrier because of its cleaning and zero pollution. The decomposition of water under alkaline conditions is considered to be a very promising method of hydrogen production, which consists of two half-reactions, the hydrogen evolution reaction at the cathode and the oxygen evolution reaction at the anode. However, in the whole water decomposition system, since the electrocatalytic oxygen evolution reaction is a 4-electron reaction process, the occurrence of the oxygen evolution reaction needs to overcome the larger kinetic energy barrier. Therefore, the development of efficient oxygen-evolution catalyst is one of the main research directions to improve the whole-water decomposition property. In recent years, metal-organic framework has been widely used in various reactions due to its good physical stability, chemical stability and regular and ordered pore and framework structure. In view of the defects of the existing oxygen evolution electrocatalyst still has the defects of large oxygen evolution potential, complex preparation method and the like, the present paper combines the structural advantages and the application foundation of the metal organic framework structure material (MOFs), The organic framework material (MOFs) and its derivatives are synthesized and the obtained MOFs material is applied to the electrocatalytic oxygen evolution reaction, and the theoretical and practical application value in the oxygen evolution reaction is also studied. This paper is mainly divided into the following work:1. In recent years, with the advantages of large specific surface area and adjustable pore structure of the MOFs-based materials, the MOFs-based materials are gradually applied in the electrocatalytic oxygen evolution reaction. However, the usual method for preparing the MOFs-based catalyst is to use Nafion to coat the electrode material on the glassy carbon electrode for testing. This allows the electron and proton transport of the electrode material in the oxygen evolution reaction to be blocked by the Nafion membrane, thus leading to a reduction in the effective catalytic activity of the MOFs-based catalyst. Therefore, the charge transfer performance of the optimized active material becomes the key to the design of MOFs-based oxygen-based electrocatalyst. In this work, we synthesized ultra-thin MOFs (ZIF-67) nanosheets and grown them in situ on a highly conductive Ti@TiO_2/ Cd S substrate to optimize the charge transport capacity of the entire electrode. The obtained Ti@TiO_2/ Cd S/ ZIF-67 electrode has a unique three-dimensional structure, not only improves the rate of electron transfer, but also improves the stability of the ZIF-67 material. ZIF-67 is a kind of porous material which is formed by co-salt and 2-methyl detomidine, and because of the induced effect of the high electronegativity of N atoms, the valence state of Co ion is increased, thus further improving the oxygen evolution reaction capability of the Ti@TiO_2/ Cd S/ ZIF-67 electrode. In view of the above conclusion, we apply the synthesized Ti@TiO_2/ Cd S/ ZIF-67 electrode to the oxygen evolution reaction under alkaline conditions, which shows a very small Tafel slope (42 m V/ dec) and good stability as compared to the other MOFs-based electrocatalysts. This further illustrates the good electrical conductivity of the Ti@TiO_2/ Cd S substrate. These experimental data and conclusions have opened up a new way to study the efficient oxygen evolution electrochemical catalyst. Electrocatalytic water decomposition is an efficient and large-scale method of hydrogen production, and is increasingly concerned by scientific researchers. However, as one and a half of the electrocatalytic water decomposition, the occurrence of oxygen evolution reaction needs to overcome the larger kinetic energy barrier. Therefore, the development of an efficient oxygen-evolution catalyst is one of the main research directions to improve the whole-water decomposition property of electrocatalysis. in consideration of that well-ordered pore structure of the metal-organic framework material (MOFs), the stable skeleton and the large specific surface area and the like, The Co-Fe-P composite was synthesized by a one-step phosphorization method in the atmosphere of N2, and the Co-Fe-P composite was transformed into a new electrocatalyst. By further optimizing the ratio of cobalt and iron, the Co-Fe-P-1.7 electrode obtained has better oxygen evolution performance than that of the cobalt-iron layered double hydroxide (Co Fe-LDH) and the Co Fe-MOFs-1.7 electrode. At the same time, the cause of this result is analyzed in detail and the conclusion is drawn that Co-Fe-P-1.7 has the Co-Fe-P-1.7 high valence Co ion in the co-Fe-P-1.7 due to the synergistic effect between the two metals of Co and Fe. The large electrochemically active surface area (ECSA) and the nanowires exposed to the Co/ Fe phosphide surface, such that the Co-Fe-P-1.7 exhibited excellent electrocatalytic oxygen evolution performance in 1.0 M KOH, including an overpotential at 10 m A/ cm-2 of 244 m V, a small Tafel slope (58 m V/ dec), and good stability. in addition, in a 1.0 M KOH solution, we modify the obtained Co-Fe-P-1.7 on the Ni line and act as an anode and a cathode for water decomposition in a two-electrode system, with a full water decomposition voltage of 1.60 V at a current density of 10 m A/ cm-2, The above research has provided the experimental reference and the research thinking for the development of efficient MOFs-based bifunctional catalyst. Co Fe-MOF-74 (Co Fe-MOF-74) was synthesized by hydrothermal method, and the effect of different Fe doping amount on the oxygen evolution of Co Fe-MOF-74 was compared. It is found that the combined catalyst has good water decomposition property, which provides the experimental reference and the research idea for the development of efficient MOFs-based oxygen evolution catalyst.
【學(xué)位授予單位】：蘭州大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：O643.36;TQ116.2
【參考文獻】
相關(guān)期刊論文 前1條
1 宋國強;王志清;王亮;李國儒;黃敏建;銀鳳翔;;MOF(Fe)的制備及其氧氣還原催化性能[J];催化學(xué)報;2014年02期
，本文編號：2483360
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