新型纳米阵列电极的构建及其在气体参与的电催化反应中的应用

发布时间：2018-04-30 02:40

本文选题：纳米阵列 + 表面浸润性　；参考：《北京化工大学》2017年博士论文

【摘要】：气体参与的电催化反应包括气体溢出反应(析氢、析氧、析氯反应)和气体消耗反应(氧还原和氢氧化反应),是涉及一些新型能源:电催化制氢、燃料电池(氢-氧,甲醇燃料电池等)和金属-空气电池的重要反应过程,提高这些电催化反应的效率和降低反应的过电位,对于提高新能源的转化和储存效率和降低反应能耗具有重要意义,为新能源技术取代传统能源提供更多的可能性。这些催化过程均涉及到气体的传质过程,方向性相反,即气体溢出反应需要气体尽快脱离电极表面向液相传质,而气体消耗反应则需要气体快速从液相向电极表面传输,因此对于气体参与的电催化反应不仅需要有廉价、优异的催化剂来降低催化反应的过电位来降低能耗,同时也需要构筑特殊浸润性的电极表面来加快气体在电极表面的传质过程,来提高催化反应效率。本论文通过构筑一系列纳米阵列与表面修饰相结合制备特殊浸润性的电极结构,研究气体、离子在结构化电极表面的传质状态及其相关的电化学性能,基于阵列的结构化优势,通过原位磷化阵列前驱体转化制备三元金属磷化物作为双功能催化剂,并研究这类新型且结构化的电极在气体参与的电催化反应中的性能,具体研究内容如下:1.超疏气的Pt纳米阵列的构筑及其水下的优异析氢活性通过恒电位和循环伏安的电化学沉积方法分别在钛片基底上制备得到不同形貌的纳米阵列和Pt纳米球,作为对比,通过离子溅射制备Pt平面电极,研究三种具有不同表面粗糙度结构的Pt电极,在水下的气泡粘附行为和气泡接触行为,以及在析氢电催化中的活性。研究表明,具有最高粗糙度的Pt纳米阵列表现出超疏气性质,与气泡的相互作用力最小,在电催化析氢过程中表现出最小气体溢出的尺寸和快的脱离速度,进而在催化活性和稳定性上也有很好的表现,揭示了通过构筑亲水阵列结构可以改变界面的浸润性进而改变气泡在界面的行为,在电催化中有利于改善气泡的溢出行为,为其他气体溢出反应提供了一种构筑有效电极的思路。2.阵列结构化的三元金属磷化物作为双功能催化剂在全水分解中的应用以Ni(N03)2和Co(N03)2分别为Ni源和Co源,以尿素为沉淀剂,以泡沫镍为基底,通过水热合成的方法制备Ni-Co前驱体纳米片阵列,并以此阵列结构为模板,通过CVD的方法原位磷化得到NiCoP纳米片阵列电极,通过掺杂改变单金属磷化物表面电子结构,提高其析氢催化活性,而且作为双功能催化剂的磷化物,在析氧催化过程中,过渡金属离子的变价在析氧起峰电位之前,金属磷化物的外侧先被氧化成相应的金属轻基氧化物或氧化物,核壳结构使其在析氧反应中也有不错的表现,另外,阵列结构的高度有序多孔结构增加了电极表面的粗糙度,提高了电极表面的疏气性,减少了气泡脱离时带来的扰动,增加了析氢析氧工作稳定性,在全水分解中也具有很好的表现。利用同样的水热合成方法制备多元金属纳米阵列跟后续原位磷化的方法,改变投料的金属盐溶液,在泡沫镍上合成了铁掺杂的Ni2P纳米片阵列,虽然在XRD中并未发现FeP的相,但是元素分布发现Fe均匀的分布在整个电极中,证明铁的均匀掺杂。铁的电负性相对于Ni较高,适量掺杂铁可能有利于减弱Ni-H之间的相互作用,加快Ni对氢原子的脱附过程,从而掺杂Fe原子占NiFe比为31.6 %的(Ni0.33Fe0.67)2P表现出最好的析氢活性。在OER中,Fe-掺杂的Ni2P作为NiFe-基催化剂,适度掺杂的铁有利于抑制Ni向高价态的转变,一定程度上有利于提高析氧活性。外加阵列结构在亲水的磷化物中引入的粗糙度,有利于减少气体在三维电极表面的粘附力,加快溢出速度,增加工作稳定性。在全水分解中也表现出与商业Pt/C、Ir/C可比拟的催化活性。3.半亲半疏的掺氮碳纳米阵列在氧还原反应中的应用。先利用水热合成的方法在碳纤维纸上生长Co(OH)2纳米片阵列,后以三聚氰胺为N源,以Co(OH)2纳米片阵列为催化剂,在碳纤维纸上直接生长N掺杂的碳纳米管阵列,表现出很高的亲水性,通过毛细力作用,使亲水碳纳米管的一侧为聚四氟乙烯(PTFE)修饰,在高温下焙烧,PTFE修饰部分表现出疏水性,得到半亲半疏的碳纳米管阵列。其中,亲水(疏气)部分有利于液体的传输,为电解质的快速通过通道同时作为反应区,疏水(亲气)部分可以形成气体通道,' 快速收集和传输气体,为反应区提供反应物,同时碳纳米管直接生长在导电集流体上保证了电子从集流体到催化剂的传输,有利于ORR的催化反应。随后通过调控PTFE在整个催化剂中所占比例,调控整个电极中亲气和疏气的比例优化气体和液体传输通道的部分,达到最优化的氧还原反应效率。半亲半疏电极不仅提供了气体快速传质而且保障液体和电子高速传输,为气体消耗电催化反应的电极结构化设计提供了一种思路。
[Abstract]:The electrocatalytic reactions involved in gas include gas spillover reactions (hydrogen evolution, oxygen evolution, chlorine evolution) and gas consumption reactions (oxygen reduction and hydrogen oxidation), which are important reactions involving some new energy sources: electrocatalytic hydrogen production, fuel cells (hydrogen oxygen, methanol fuel cells, etc.) and metal air batteries, to improve the efficiency of these electrocatalytic reactions. The rate and reduction of overpotential are of great significance for improving the conversion and storage efficiency of new energy and reducing the energy consumption of the reaction. It provides more possibilities for the new energy technology to replace the traditional energy. These catalytic processes involve the mass transfer process of gas and the opposite direction, that is, the gas spillover reaction requires gas to disconnect from the electrode table as soon as possible. In liquid phase mass transfer, gas consumption requires gas to rapidly transfer from the liquid to the surface of the electrode. Therefore, the electrocatalytic reaction of gas is not only necessary to reduce the overpotential of the catalytic reaction to reduce the energy consumption, but also to build a special infiltrative electrode surface to speed up the gas in the electrode. In this paper, a series of nanoscale arrays and surface modification are constructed to prepare a special infiltrative electrode structure. The mass transfer state and the related electrochemical properties of the gas and ions on the surface of the structured electrode are studied based on the structural advantage of the array, through the in-situ phosphating array. The precursor transformation is used to prepare three element metal phosphide as a bifunctional catalyst, and the properties of these new and structured electrodes in the electrocatalytic reaction of gas are studied. The specific contents are as follows: 1. the construction of Pt nanoscale arrays of super sparse gas and the electrochemical deposition of excellent hydrogen evolution under the constant potential and cyclic voltammetry under water The nano arrays and Pt nanospheres with different morphologies were prepared on the titanium substrate. As a contrast, Pt planar electrodes were prepared by ion sputtering. Three kinds of Pt electrodes with different surface roughness structures were studied. The adhesion behavior of bubbles and the contact behavior of bubbles under water and the activity in the electrocatalysis of hydrogen evolution were investigated. The Pt nanoarray with the highest roughness shows the properties of super sparse gas, the smallest interaction force with the bubble. In the process of electrocatalytic hydrogen evolution, it shows the size of the minimum gas overflow and the fast disengagement speed, and then the catalytic activity and stability also have good performance. It reveals that the interface can be changed by constructing the hydrophilic array structure. Wettability and then change the behavior of bubbles in the interface, in the electrocatalysis, it is beneficial to improve the spillover behavior of the bubbles and provides a way of building effective electrodes for other gas spillovers..2. array structured three metal phosphide is used as a bifunctional catalyst in the whole water decomposition, and Ni (N03) 2 and Co (N03) 2 are Ni sources, respectively. Co source, Ni-Co precursor nanoscale array was prepared by hydrothermal synthesis using urea as precipitant and nickel foam as the substrate. The array structure was used as template. The NiCoP nanoscale array electrode was obtained by in situ phosphating by CVD method. The electronic structure of the surface of mono metal phosphide was changed by doping, and the catalytic activity of hydrogen evolution was improved. Moreover, the catalytic activity of hydrogen evolution was improved. For the phosphide of a bifunctional catalyst, in the process of oxygen evolution, the valence of the transition metal ions is oxidized to the corresponding metal oxide or oxide before the peak potential of oxygen evolution, and the core and shell structure makes it good in the oxygen evolution reaction, and the highly ordered porous junction of the array structure. The roughness of the electrode surface is increased, the sparsely on the surface of the electrode is increased, the disturbance caused by the bubble separation is reduced, the stability of the oxygen evolution is increased, and the performance of the hydrogen evolution is also very good. The same method of hydrothermal synthesis is used to prepare the multi metal nanometers array and the subsequent in-situ phosphating method to change the feeding material. In the metal salt solution, iron doped Ni2P nanoscale arrays are synthesized on the foamed nickel. Although the phase of FeP is not found in XRD, the distribution of Fe is uniformly distributed in the whole electrode, which proves that the iron is even doped. The electronegativity of iron is higher than that of Ni. A proper doping of iron may help to weaken the interaction between Ni-H and accelerate N. I has the best hydrogen evolution activity for the desorption of hydrogen atoms, and the doping of Fe atoms with NiFe ratio of 31.6% (Ni0.33Fe0.67) 2P shows the best hydrogen evolution activity. In OER, Fe- doped Ni2P is a NiFe- based catalyst, and the moderately doped iron is beneficial to inhibit the transition of Ni to high valence state, to a certain extent, to improve the activity of oxygen evolution. The added array structure is hydrophilic. The roughness introduced in the phosphide is beneficial to reduce the adhesion of gas on the surface of the electrode, speed up the spillover speed and increase the stability of the work. In the whole water decomposition, the application of the catalytic activity.3., which is comparable to the commercial Pt/C, Ir/C, is used in the oxygen return. Co (OH) 2 nanoscale arrays were grown on carbon fiber paper, then melamine was used as N source and Co (OH) 2 nanoscale array was used as catalyst to direct the growth of N doped carbon nanotube arrays on carbon fiber paper, showing high hydrophilicity. By capillary force, the side of the hydrophilic carbon nanofilm was modified by polytetrafluoroethylene (PTFE) and roasted at high temperature. The PTFE modified part shows a hydrophobic and semi hydrophobic carbon nanotube array, in which the hydrophilic (sparsely) part is beneficial to the transmission of the liquid, the rapid passage of the electrolyte through the channel as the reaction zone, the hydrophobic (pro gas) part can form a gas channel, 'the gas is quickly collected and transmitted, and the reactant is provided for the reaction zone, and the carbon is also absorbed. The direct growth of the rice tube on the conductive collector ensures the transmission of the electron from the collector to the catalyst, and is beneficial to the catalytic reaction of ORR. Then the optimum oxygen reduction reaction efficiency is achieved by regulating the proportion of the PTFE in the whole catalyst and regulating the proportion of the gas and the liquid transmission channel in the proportion of the whole electrode. The semi parent and semi sparse electrode not only provides rapid mass transfer of gas but also ensures high speed transmission of liquid and electrons. It provides a way of thinking for the structural design of the electrode for the electrocatalytic reaction of gas consumption.

【学位授予单位】：北京化工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O643.32;O646.5

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