本文關(guān)鍵詞：Ag-Cu和TiO_2催化材料的制備、相變以及性能研究　出處：《西北工業(yè)大學(xué)》2015年博士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： Ag-Cu納米合金 氧還原催化劑 鋅-空氣電池 TiO_2納米纖維 Ti_nO_(2n-1)納米纖維 晶體學(xué) 異質(zhì)界面 相變 納米凹坑

【摘要】：氫燃料電池是先進(jìn)的能源利用方式,能夠把氫燃料中的化學(xué)能通過(guò)電化學(xué)反應(yīng)直接轉(zhuǎn)化為電能。然而在實(shí)際應(yīng)用中,光催化制氫效率較低,而且氫的儲(chǔ)存和運(yùn)輸成本較高,阻礙了氫燃料電池的大規(guī)模生產(chǎn)。在這種背景下,鋅-空氣燃料電池因使用豐富易獲取的金屬鋅代替氫做為燃料,同時(shí)具有能量密度高和環(huán)保的優(yōu)勢(shì),成為清潔能源領(lǐng)域的研究熱點(diǎn)。針對(duì)鋅-空氣燃料電池的研究工作主要集中在尋求可替代Pt/C、Pd等貴金屬的高效且成本低廉的氧還原電催化劑方面。另一方面,人們也在不懈的尋求低成本的制氫技術(shù)。作為光催化劑材料的代表,納米TiO2因具備比表面積大、光催化及吸收性能好、表面活性高以及無(wú)毒無(wú)害等優(yōu)勢(shì),不僅在光催化制氫領(lǐng)域,而且在環(huán)境污染治理領(lǐng)域有著廣泛的應(yīng)用前景。研究表明,由于混晶納米TiO2具有比單相TiO2材料更好的光催化特性,因此合成TiO2混相納米晶是高效光催化制氫以及有效治理環(huán)境污染的重要途徑之一。本文采用脈沖激光沉積(Pulsed Laser Deposition,PLD)法,制備了高性能的Ag-Cu合金型氧還原催化劑。通過(guò)電化學(xué)性能測(cè)試并結(jié)合TEM表征,證實(shí)了薄膜內(nèi)的Ag-Cu固溶體合金納米顆粒是高催化活性的主要原因。當(dāng)電流密度為20 mA cm-2,用該催化劑組裝的組裝的一次鋅-空電池的比容量以及比能量密度分別升高至678 mAh g-1和725.5 mWh g-1,而采用該催化劑組裝的二次鋅-空氣電池在經(jīng)過(guò)400個(gè)充放電循環(huán)之后,電池的充放電電壓基本保持不變,其電池能量效率僅由55%降低至52.7%,表明電池具有很好的穩(wěn)定性。另外,采用電化學(xué)沉積法(Electrochemcial Deposition Method,EDM)制備了Ag-Cu納米合金枝晶,獲得了枝晶的晶體學(xué)特征和生長(zhǎng)機(jī)制,TEM結(jié)果表明,所得的Ag-Cu納米枝晶是Ag3Cu(L12)枝晶,其主枝和側(cè)枝的生長(zhǎng)方向均為?110?,即面心立方結(jié)構(gòu)的密排方向�；趯�(shí)驗(yàn)結(jié)果,提出了由定向附著機(jī)制和奧斯瓦爾德熟化機(jī)制控制的枝晶生長(zhǎng)的機(jī)理模型。針對(duì)混相TiO2光催化劑方面的研究只要集中在以下三個(gè)部分。首先,利用TEM原位加熱方法研究了水熱法制備的H2Ti3O7(HT)至TiO2(B)(TB)以及TB至銳鈦礦(TA)納米纖維的相變過(guò)程中線形貌的變化規(guī)律和兩相界面的原子結(jié)構(gòu),并采用不變應(yīng)變單元原理(Invariant Deformation Element,IDE)模型計(jì)算了兩個(gè)相變過(guò)程的晶體學(xué)特征。結(jié)果表明,HT/TB和TB/TA兩相相變的晶體學(xué)取向關(guān)系分別為HT T B[001]//[001]、HT TB(020)//(020)及HT TB(200)//(200)和TB TA[001]//[100]、TB TA(200)//(002)以及TB TA(020)//(020)。由于結(jié)構(gòu)非常相似,因而HT/TB的相界面呈完全共格狀態(tài),而TB/TA相變體系中存在一種共格界面和兩種非共格界面,其界面類型和形態(tài)與煅燒溫度密切相關(guān)。另外,通過(guò)基本構(gòu)建塊(Fundamental Building Block,FBB)模型揭示了兩種相變的原子機(jī)制,并在此基礎(chǔ)上利用IDE模型計(jì)算了兩種相變的晶體學(xué)特征,計(jì)算結(jié)果與實(shí)驗(yàn)觀察結(jié)果吻合。通過(guò)在大氣和真空兩種條件下煅燒TB納米纖維,獲得了不同煅燒氣氛對(duì)相變產(chǎn)物的影響規(guī)律,基于TEM觀察結(jié)果,揭示了TB至TinO2n-1的相變?cè)訖C(jī)制,并同時(shí)提出了一種制備新型TiO2基復(fù)相納米材料的方法。結(jié)果表明,在空氣中在650°C下煅燒1小時(shí)的TB納米纖維中存在與TB具有相同空間群的兩種中間相Ti3O5(T-I)和Ti6O11(T-II),而在真空下,當(dāng)煅燒溫度為650°C左右時(shí),TB納米纖維中僅發(fā)現(xiàn)有T-I相,可能是由于高真空下納米纖維表面張力較大使得T-I無(wú)法進(jìn)一步轉(zhuǎn)變?yōu)門-II相。根據(jù)不同氣氛下煅燒樣品的結(jié)果,提出了TB?T-I?T-II?TA的相變順序及相應(yīng)的化學(xué)反應(yīng)方程式。此外,利用高分辨TEM方法揭示了TB至TA相變過(guò)程中出現(xiàn)的TB/T-I、TB/T-II、T-II/TA及TB/TA4種共格相界面的晶體學(xué)位相關(guān)系:TB T-I[100]//[001]、TB T-II[100]//[100]、T-II TA[100]//[100]和TB TA[100]//[100],同時(shí)提出了一種新型的Ti3O5和Ti6O11相的制備方法。在TB納米纖維發(fā)生相變的過(guò)程中,利用TEM觀察得到了煅燒氣氛對(duì)線表面納米凹坑形態(tài)和分布的影響規(guī)律,探討了納米凹坑的存在對(duì)TB至TA和TA至TR兩類相變過(guò)程的影響機(jī)制。結(jié)果表明,納米凹坑是在TB至TA的相變過(guò)程中生成的,在大氣和真空下產(chǎn)生的納米凹坑形態(tài)和分布狀態(tài)有所不同。在大氣中煅燒的納米纖維中出現(xiàn)的納米凹坑較多,其形態(tài)呈六棱柱形,底面平行于TA{100},柱面分別平行于TA{011}和TA{010},而真空中生成的納米凹坑數(shù)量很少,形態(tài)不規(guī)則。另外,當(dāng)加熱溫度超過(guò)700°C后,TA表面納米凹坑的數(shù)量急劇減少,同時(shí)形狀向圓形變化。通過(guò)對(duì)比大氣和真空下的相變進(jìn)程發(fā)現(xiàn),無(wú)論對(duì)于TB至TA還是TA至TR相變,納米凹坑的存在均會(huì)阻礙相變的發(fā)生,其原因是由于納米纖維的表面重構(gòu)使得納米凹坑消失,同時(shí)消耗了能量,使得相變點(diǎn)升高。
[Abstract]:Hydrogen fuel cell is an advanced way of energy utilization, which can directly convert chemical energy in hydrogen fuel into electric energy by electrochemical reaction. However, in practical applications, the efficiency of photocatalytic hydrogen production is low, and the storage and transportation cost of hydrogen is high, which hinders the large-scale production of hydrogen fuel cells. Under this background, zinc air fuel cell is a hot topic in clean energy area because of its high energy density and environmental protection. The research work of zinc air fuel cell is mainly focused on searching for efficient and inexpensive oxygen reduction electrocatalysts that can replace Pt/C, Pd and other precious metals. On the other hand, people are unremitting seeking low cost hydrogen production technology. As the representative of photocatalyst materials, nano TiO2 has wide application prospects in the field of photocatalytic hydrogen production and environmental pollution control because of its large specific surface area, good photocatalytic and absorption properties, high surface activity and innocuity and harmlessness. Research shows that, due to mixed crystal TiO2 nanoparticles have better photocatalytic properties than single-phase TiO2 material, so the synthesis of TiO2 mixed phase nanocrystalline high photocatalytic hydrogen production, is one of the important ways to effectively control environmental pollution. A high performance Ag-Cu alloy oxygen reduction catalyst was prepared by pulsed laser deposition (Pulsed Laser Deposition, PLD). The main reason for the high catalytic activity of the Ag-Cu solid solution alloy nanoparticles in the film was confirmed by the electrochemical performance test and TEM characterization. When the current density is 20 mA cm-2, a zinc - assembly with the catalyst of air battery capacity and energy density were increased to 678 mAh g-1 and 725.5 mWh g-1, while the two zinc air battery assembly of the catalyst after 400 charge discharge cycles, discharge voltage the pool remained basically unchanged, the battery energy efficiency only decreased from 55% to 52.7%, indicates that the battery has good stability. In addition, the electrochemical deposition method (Electrochemcial Deposition Method, EDM) Ag-Cu nano alloy dendrite was prepared and obtained crystallographic characteristics and growth mechanism of dendrite, TEM results show that the Ag-Cu nano dendrite is Ag3Cu (L12) dendrite growth direction, its main branches and lateral branches are? 110,? The direction of close packed face centered cubic structure. Based on the experimental results, a mechanism model for dendrite growth controlled by directional attachment mechanism and Oswald ripening mechanism is proposed. The research on the mixed phase TiO2 photocatalyst is focused on the following three parts. First of all, the study of hydrothermal synthesis method using TEM in situ heating H2Ti3O7 (HT) to TiO2 (B) (TB) and TB (TA) atomic structure to anatase nano fiber morphology midline phase change process and change rule of the interface, and the constant strain element principle (Invariant Deformation Element, IDE) model calculate the two crystallographic characteristics of phase change process. The results show that the relationship between the crystallographic orientation and TB/TA phase transformation in HT/TB were HT T B[001]//[001], HT TB (020) / (020) HT and TB (200) / (200) and TB TA[001]//[100], TB TA (200) / (002) TB and TA (020) / (020). Because the structure is very similar, the interface of HT/TB is perfectly coherent. However, there exists a coherent interface and two kinds of non coherent interfaces in TB/TA phase change system. Its interface type and morphology are closely related to calcination temperature. In addition, the atomic mechanism of two kinds of phase transitions is revealed by Fundamental Building Block (FBB) model. Based on that, the crystallographic characteristics of two phase transitions are calculated by IDE model, and the calculated results are in agreement with the experimental observations. Through the air and vacuum under the two conditions of calcination of TB nanofibers, obtaining the effect of different calcination atmosphere on transformation products, based on the TEM results, reveals the transformation mechanism of TB atoms to TinO2n-1, and also puts forward a new preparation method of TiO2 based nanocomposite materials. The results show that the TB has two kinds of intermediate same space group Ti3O5 exists in the air at 650 DEG C calcined under 1 hours of TB nanofibers (T-I) and Ti6O11 (T-II), and under vacuum, when the calcination temperature is about 650 DEG C, TB nano fibers found only T-I that may be due to a high vacuum surface tension nano fiber makes T-I cannot be further transformed into T-II phase. According to the results of the calcined samples under different atmospheres, the order of phase transition and the corresponding chemical reaction equation of TB? T-I? T-II? TA were put forward. In addition, the use of high resolution TEM method reveals TB to TA phase transition in TB/T-I, TB/T-II, T-II/TA and TB/TA4 phase interface crystallographic phase relationship: TB T-I[100]//[001], TB T-II[100]//[100], T-II TA[100]//[100] and TB TA[100]//[100] Ti3O5 and Ti6O11, and proposed a new phase preparation method. In the process of phase transformation of TB nanofibers, the influence of calcination atmosphere on the morphology and distribution of nano pits on the line surface was observed by TEM. The mechanism of the existence of nano pits on the two phase transformation processes from TB to TA and TA to TR was discussed. The results show that the nano pits are formed during the phase transition from TB to TA, and the morphology and distribution of the nanoscale in the atmosphere and the vacuum are different. There are more nano pits in the nanofibers calcined in the atmosphere, the morphology is six prism, the bottom surface is parallel to TA{100}, the cylinders are parallel to TA{011} and TA{010}, and the number of nano pits in vacuum is very small. In addition, when the heating temperature is over 700 C, the number of nanoscale pits on the surface of TA decreases sharply, and the shape changes to the circle. By comparing the transformation process in atmosphere and vacuum, it is found that the existence of nano pits will impede the occurrence of phase transition, no matter for TB to TA or TA to TR phase transition.
【學(xué)位授予單位】：西北工業(yè)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TQ426

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本文編號(hào)：1338004