輕質(zhì)儲(chǔ)氫材料的改性研究
發(fā)布時(shí)間：2019-06-22 12:46
【摘要】：為了達(dá)到車載燃料電池應(yīng)用對(duì)氫源的要求,亟需一種高體積和重量能量密度的輕質(zhì)儲(chǔ)氫材料,為此國(guó)內(nèi)外開展了大量的研究工作。在輕質(zhì)儲(chǔ)氫材料中,硼氫化鋰(LiBH4)因其具有高達(dá)18.4wt.%的理論儲(chǔ)氫容量被認(rèn)為具有廣闊的應(yīng)用前景。然而,其脫氫溫度高且易釋放雜質(zhì)氣體、脫/加氫動(dòng)力學(xué)差和脫氫產(chǎn)物再加氫困難等問題制約了LiBH4的商業(yè)應(yīng)用。針對(duì)這些問題,本論文通過陽離子取代、陰離子取代、催化摻雜和失穩(wěn)體系構(gòu)建等方法逐步改善了LiBH4的儲(chǔ)氫性能,取得了一些創(chuàng)新性的研究成果：首先采用陽離子取代來改善LiBH4的脫氫性能。球磨LiBH4和MnCl2制備了陽離子取代的LiMn(BH4)3/2LiCl復(fù)合體系,研究了Mn離子取代對(duì)體系脫氫熱力學(xué)和動(dòng)力學(xué)性能的影響,闡明了其脫氫控速步驟,進(jìn)一步通過添加Ti基摻雜劑改善了復(fù)合體系的脫氫動(dòng)力學(xué)性能。其次,在陽離子取代基礎(chǔ)上,采用陰離子取代來進(jìn)一步改善LiBH4的脫氫性能。球磨LiBH4和MnF2制備了陰/陽離子取代的LiMn(BH4-xFx)3/2LiF復(fù)合體系,測(cè)試了復(fù)合體系的儲(chǔ)氫性能。通過與LiMn(BH4)3/2LiCl復(fù)合體系的儲(chǔ)氫性能進(jìn)行對(duì)比,闡明了陰離子取代對(duì)儲(chǔ)氫性能和動(dòng)力學(xué)控速機(jī)制的影響。然后,針對(duì)LiMn(BH4-xFx)3/2LiF復(fù)合體系的脫氫過程中存在的雜質(zhì)氣體問題,采用摻雜改性法優(yōu)化了復(fù)合體系的脫氫性能。通過球磨在LiMn(BH4-xFx)3/2LiF復(fù)合體系中摻雜一定量的LiNH2,摻雜后能夠顯著地抑制復(fù)合體系脫氫過程中雜質(zhì)氣體B2H6的生成,同時(shí)進(jìn)一步降低了體系的脫氫溫度。最后,針對(duì)LiMn(BH4-xFx)3/2LiF復(fù)合體系脫氫產(chǎn)物B單質(zhì)加氫困難的問題,采用與MgH2構(gòu)建失穩(wěn)體系來調(diào)制脫氫反應(yīng)的產(chǎn)物相。該失穩(wěn)體系在惰性氣體背壓下能夠穩(wěn)定地生成MgB2,且不存在明顯的成核孕育期,闡明了該失穩(wěn)體系中MgB2的形成機(jī)制。這一結(jié)果顯著改善了硼氫化物／金屬氫化物失穩(wěn)體系脫氫過程金屬硼化物成核期過長(zhǎng)的問題。本論文的研究開闊了對(duì)配位金屬氫化物性能進(jìn)行系統(tǒng)調(diào)制的思路,為配位氫化物的進(jìn)一步開發(fā)應(yīng)用奠定了理論基礎(chǔ)。論文的主要研究結(jié)果如下：(1) LiMn(BH4)3/2LiCl復(fù)合體系的物相結(jié)構(gòu)是由非晶態(tài)的LiMn(BH4)3和晶態(tài)的LiCl組成。其儲(chǔ)氫性能測(cè)試結(jié)果表明,LiCl復(fù)合體系的初始脫氫溫度從純LiBH4的400℃降低至135℃,在135-190℃區(qū)間內(nèi)失重為7.0wt.%。氣體成分分析表明釋放的氣體中H2占93.2 mol%, B2H6占6.8 mo1%。LiMn(BH4)3/2LiCl復(fù)合體系的脫氫反應(yīng)激活能Ea=114kJ/mol,脫氫過程受到三維界面的遷移擴(kuò)散控制。Ti基摻雜劑對(duì)LiMn(BH4)3體系脫氫性能改善的效果各異,具體表現(xiàn)在：TiN、TiC或TiO2不能有效催化LiMn(BH4)3/2LiCl復(fù)合體系的分解反應(yīng)；而TiF3摻雜的LiMn(BH4)3/2LiCl復(fù)合體系的初始脫氫溫度進(jìn)一步降低至125℃,其脫氫反應(yīng)激活能也由未摻雜前的114 kJ/mol下降為104 kJ/mol,推測(cè)原因?yàn)樵谇蚰诫s過程中TiF3與復(fù)合體系在局部形成了常溫脫氫的Ti(BH4)3。(2)使用MnF2替代MnCl2與LiBH4進(jìn)行球磨,制備了LiMn(BH4-xFx)3/2LiF復(fù)合體系。與LiMn(BH4)3/2LiCl復(fù)合體系相比,LiMn(BH4-xFx)3/2LiF復(fù)合體系不僅發(fā)生了陽離子Mn2+和Li+之間的取代,同時(shí)發(fā)生了陰離子F-和H-之間的取代,且F-離子取代后LiMn(BH4-xFx)3/2LiF復(fù)合體系的初始脫氫溫度進(jìn)一步從135℃下降至120℃,脫氫激活能Ea從114 kJ/mol降低至92 kJ/mol。 LiMn(BH4-xFx)3/2LiF復(fù)合體系失重為7.0wt.%。氣體成分分析表明釋放的氣體中H2占94.8 mol%,B2H6占5.2 mo1%,抑制了部分B2H6的產(chǎn)生。脫氫反應(yīng)由三維界面的遷移擴(kuò)散轉(zhuǎn)變?yōu)橐痪S形核長(zhǎng)大機(jī)制控制。脫氫性能和機(jī)制的改變均由F-對(duì)H-的部分取代造成B-H鍵失穩(wěn)所引起。(3)系統(tǒng)考察了LiNH2對(duì)LiMn(BH4-xFx)3/2LiF復(fù)合體系脫氫性能的影響。摻雜LiNH2會(huì)促進(jìn)LiMn(BH4-xFx)3/2LiF復(fù)合體系中硼氫化物與MnF2的置換反應(yīng),使得復(fù)合體系中的MnF2相逐漸轉(zhuǎn)變?yōu)長(zhǎng)iF相并形成非晶態(tài)的LiMn(BH4-xFx)3。相比于未摻雜的LiMn(BH4-xFx)3/2LiF復(fù)合體系,摻雜2.5、5、7.5、10和15wt.%LiNH2的復(fù)合物的起始脫氫溫度分別下降至101、96、94、78和77℃,失重分別為6.8、5.0、4.8、6.5和9.3wt.%。質(zhì)譜分析表明大于5wt.%的LiNH2即可顯著抑制LiMn(BH4-xFx)3/2LiF復(fù)合體系脫氫過程中所生成的B2H6,但過多的LiNH2也會(huì)生成NH3,影響釋放氫氣的純度。實(shí)驗(yàn)證明,添加5 wt.%LiNH2可以獲得純氫氣的釋放,此時(shí)摻雜后的復(fù)合物在100-140℃分解,放出約5.0 wt.%純氫氣,脫氫反應(yīng)的激活能Ea為91.0 kJ/molc具體改善機(jī)制為[BH4]-基團(tuán)中Hδ-和[NH2]-中H5-結(jié)合致使H2在低溫下逸出,類似地,抑制B2H6產(chǎn)生的機(jī)制為[BH4]-基團(tuán)中Bδ+被[NH2]-中Nδ-固定,阻斷了游離態(tài)的BH3或者BH3帶電基團(tuán)的產(chǎn)生和進(jìn)一步結(jié)合。(4)研究了MgH2與LiMn(BH4-xFx)3/2LiF構(gòu)建的失穩(wěn)體系的脫氫性能。升溫實(shí)驗(yàn)表明,復(fù)合體系中LiMn(BH4-xFx)3/2LiF在120-160℃分解,失重為4.9Wt.%; MgH2在350～500℃分解,失重為2.1 wt.%。隨后的物相分析顯示,LiMn(BH4-xFx)3/2LiF分解產(chǎn)生的B伴隨著MgH2的分解最終轉(zhuǎn)化為MgB2。該體系能在惰性氣體中生成MgB2,且不存在明顯的成核孕育期,明顯改善了MgH2-LiBH4體系中MgB2形成條件苛刻且孕育期長(zhǎng)等問題。改善得益于：首先伴隨MgH2分解,Mg原子逸出表面能量不斷降低,可動(dòng)性增強(qiáng),進(jìn)而加速了與B形成MgB2的成核動(dòng)力學(xué)；其次,Mn元素附著于MgB2晶核周圍,加速了Mg原子在MgB2晶格中的擴(kuò)散,進(jìn)而促進(jìn)了MgB2晶核生長(zhǎng)過程。
[Abstract]:In order to meet the requirements of the on-board fuel cell application to the hydrogen source, a light hydrogen storage material with high volume and energy density is needed, and a great deal of research has been carried out at home and abroad. In the light hydrogen storage material, lithium borohydride (LiBH4) has a capacity of up to 18.4% by weight. The theoretical hydrogen storage capacity of% is considered to have a wide application prospect. However, that problem of high dehydrogenation temperature and easy release of the impurity gas, the dehydro-kinetic difference and the re-hydrogenation of the dehydrogenation product, and the like, has restricted the commercial application of the LiBH4. In view of these problems, this paper has gradually improved the hydrogen storage performance of LiBH4 by the method of cation substitution, anion substitution, catalytic doping and instability system, and has obtained some innovative research results: firstly, the cation substitution is adopted to improve the dehydrogenation performance of the LiBH4. LiMn (BH4)3/ 2LiCl composite system with cation substitution was prepared by ball-milling LiBH4 and MnCl2, and the effect of the substitution of Mn ions on the thermodynamic and kinetic properties of the system was studied. Second, on the basis of cation substitution, anion substitution is used to further improve the dehydrogenation performance of LiBH4. LiMn (BH4-xcarbon)3/ 2LiF composite system with negative/ cationic substitution was prepared by ball-milling LiBH4 and MnF2, and the hydrogen storage performance of the composite system was tested. The hydrogen storage performance of LiMn (BH4)3/2 LiCl composite system is compared, and the effect of the anion substitution on the hydrogen storage performance and the dynamic speed control mechanism is clarified. In the process of dehydrogenation of LiMn (BH4-xn)3/ 2LiF composite system, the dehydrogenation performance of the composite system was optimized by the doping modification method. By ball-milling, a certain amount of LiNH2 is doped in the LiMn (BH4-xn)3/ 2LiF composite system, and after doping, the generation of the impurity gas B2H6 in the dehydrogenation process of the composite system can be remarkably inhibited, and meanwhile, the dehydrogenation temperature of the system is further reduced. In the end, the product phase of the dehydrogenation reaction was prepared by the formation of the instability system with MgH2, in the light of the difficult problem of the simple substance hydrogenation of the dehydrogenation product B of the LiMn (BH4-xn)3/2 LiF composite system. MgB2 can be stably generated under the back pressure of inert gas, and no obvious nucleation period is present, and the formation mechanism of MgB2 in the unstable system is illustrated. This result significantly improves the problem of the too long nucleation period of the metal boride during the dehydrogenation process of the borohydride/ metal hydride unstable system. The research of this thesis is open to the idea of system modulation for coordination metal hydride performance, which lays a theoretical foundation for the further development and application of coordination hydride. The main results of this paper are as follows: (1) The phase structure of LiMn (BH4)3/2 LiCl composite system is composed of amorphous LiMn (BH4)3 and crystalline LiCl. The results of the hydrogen storage performance test show that the initial dehydrogenation temperature of the LiCl composite system is reduced from 400 鈩，
本文編號(hào)：2504593
[Abstract]:In order to meet the requirements of the on-board fuel cell application to the hydrogen source, a light hydrogen storage material with high volume and energy density is needed, and a great deal of research has been carried out at home and abroad. In the light hydrogen storage material, lithium borohydride (LiBH4) has a capacity of up to 18.4% by weight. The theoretical hydrogen storage capacity of% is considered to have a wide application prospect. However, that problem of high dehydrogenation temperature and easy release of the impurity gas, the dehydro-kinetic difference and the re-hydrogenation of the dehydrogenation product, and the like, has restricted the commercial application of the LiBH4. In view of these problems, this paper has gradually improved the hydrogen storage performance of LiBH4 by the method of cation substitution, anion substitution, catalytic doping and instability system, and has obtained some innovative research results: firstly, the cation substitution is adopted to improve the dehydrogenation performance of the LiBH4. LiMn (BH4)3/ 2LiCl composite system with cation substitution was prepared by ball-milling LiBH4 and MnCl2, and the effect of the substitution of Mn ions on the thermodynamic and kinetic properties of the system was studied. Second, on the basis of cation substitution, anion substitution is used to further improve the dehydrogenation performance of LiBH4. LiMn (BH4-xcarbon)3/ 2LiF composite system with negative/ cationic substitution was prepared by ball-milling LiBH4 and MnF2, and the hydrogen storage performance of the composite system was tested. The hydrogen storage performance of LiMn (BH4)3/2 LiCl composite system is compared, and the effect of the anion substitution on the hydrogen storage performance and the dynamic speed control mechanism is clarified. In the process of dehydrogenation of LiMn (BH4-xn)3/ 2LiF composite system, the dehydrogenation performance of the composite system was optimized by the doping modification method. By ball-milling, a certain amount of LiNH2 is doped in the LiMn (BH4-xn)3/ 2LiF composite system, and after doping, the generation of the impurity gas B2H6 in the dehydrogenation process of the composite system can be remarkably inhibited, and meanwhile, the dehydrogenation temperature of the system is further reduced. In the end, the product phase of the dehydrogenation reaction was prepared by the formation of the instability system with MgH2, in the light of the difficult problem of the simple substance hydrogenation of the dehydrogenation product B of the LiMn (BH4-xn)3/2 LiF composite system. MgB2 can be stably generated under the back pressure of inert gas, and no obvious nucleation period is present, and the formation mechanism of MgB2 in the unstable system is illustrated. This result significantly improves the problem of the too long nucleation period of the metal boride during the dehydrogenation process of the borohydride/ metal hydride unstable system. The research of this thesis is open to the idea of system modulation for coordination metal hydride performance, which lays a theoretical foundation for the further development and application of coordination hydride. The main results of this paper are as follows: (1) The phase structure of LiMn (BH4)3/2 LiCl composite system is composed of amorphous LiMn (BH4)3 and crystalline LiCl. The results of the hydrogen storage performance test show that the initial dehydrogenation temperature of the LiCl composite system is reduced from 400 鈩，
本文編號(hào)：2504593
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