【摘要】：氫能作為一種極具發(fā)展?jié)摿Φ睦硐肭鍧嵞茉炊鴱V受關注,而安全、高效和低成本的儲氫技術是目前氫能開發(fā)應用亟需解決瓶頸技術。硼氫化鋰(LiBH4)因具有18.5 wt%的質量儲氫密度和121 kg H2/m3的體積儲氫密度,成為目前高容量儲氫材料的研究熱點之一。然而,LiBH4熱力學穩(wěn)定性較高,吸放氫動力學性能較差,可逆吸氫的條件過于苛刻,嚴重阻礙了其實用化的進程。本文在全面綜述國內外LiBH4儲氫材料的研究進展的基礎上,研究了六方型氮化硼(h-BN)摻雜、h-BN分別負載NbCl5和NbH摻雜對LiBH4的儲氫性能的影響規(guī)律,并探索揭示了其改性機理。將h-BN作為添加劑摻雜至LiBH4體系以改善其吸放氫性能,詳細研究了h-BN添加量為5mol%、15mol%、30mol%和50 mol%的h-BN摻雜LiBH4體系的放氫動力學性能。結果表明：當h-BN添加量為30 mol%時,h-BN摻雜LiBH4體系具有最佳綜合儲氫性能,其起始放氫溫度和放氫反應活化能分別由未摻雜LiBH4樣品的280℃和198.31 kJ/mol降低至180℃和155.80 kJ/mol;樣品在400℃下完成放氫反應所需時間由未摻雜LiBH4樣品的6000分鐘減少至120分鐘。經過30 mol% h-BN摻雜改性后,LiBH4能夠在400℃和10 MPa氫壓條件下實現(xiàn)再吸氫,且循環(huán)放氫性能相對穩(wěn)定,第三次放氫容量可達到6 wt%。進一步分析認為：h-BN表面N原子上“孤電子對”對LiBH4起到一定的反應失穩(wěn)作用,因此h-BN表面的LiBH4率先分解,其分解產物則成為后續(xù)LiBH4分解反應的形核中心,降低了LiBH4的分解溫度。為了進一步改善LiBH4的儲氫性能,采用NbCl5/h-BN復合摻雜LiBH4,并對比分析NbCl5/h-BN復合摻雜LiBH4體系、NbCl5與h-BN單獨摻雜LiBH4體系的儲氫性能。研究發(fā)現(xiàn)：NbCl5/h-BN復合摻雜LiBH4儲氫性能比NbCl5或h-BN單獨摻雜LiBH4體系具有更好的放氫動力學性能。其中,1 mol% NbCl5+30 mol% h-BN復合摻雜改性的LiBH4樣品在20分鐘內能夠釋放出12.19 wt%,為同樣條件下1 mol% NbCl5和30 mol% h-BN單獨摻雜LiBH4樣品所能釋放氫氣量的17.41和2.61倍。經1 mol% NbCl5+30 mol% h-BN復合摻雜后,LiBH4放氫峰值溫度降低了100℃,放氫反應活化能降低122.75 kJ/mol,循環(huán)放氫性能得到明顯改善。進一步分析認為：NbCl5/h-BN復合摻雜LiBH4時,在h-BN表面NbCl5與LiBH4發(fā)生反應原位生成的納米NbH,起到進一步催化改性LiBH4儲氫性能的作用。本文進一步采用機械球磨化學法研究制備出h-BN負載5-20 nm的NbH復合型催化劑,并將其用于催化改性LiBH4儲氫性能。通過添加1 mol% 3NbH@h-BN催化劑,LiBH4的放氫峰值降低到380℃,并且LiBH4能夠在30分鐘完成放氫反應,其反應速率是未摻雜的LiBH4的200倍,LiBH4的循環(huán)放氫性能也得到了進一步改善,第三次循環(huán)放氫容量可達8 wt%�；谖⒂^結構分析和放氫動力學模型計算結果,我們認為其催化改性機理：NbH@h-BN催化劑在LiBH4放氫反應過程起到了異相形核的作用,使LiBH4放氫反應避免了臨界晶核形核功,一定程度上降低LiBH4的放氫溫度；納米NbH負載在h-BN表面,形成穩(wěn)定納米結構,能夠為LiBH4放氫反應形核提供足夠多的形核中心,從而加快LiBH4放氫反應速率。
[Abstract]:Hydrogen energy is widely concerned as an ideal clean energy source with great potential. Safety, high efficiency and low cost hydrogen storage technology is an urgent bottleneck in the development and application of hydrogen energy. Lithium borohydride (LiBH4) has become the current high capacity hydrogen storage material because of the mass hydrogen storage density of 18.5 wt% and the storage hydrogen density of the body of 121 kg H2/m3 However, the thermodynamic stability of LiBH4 is high, the kinetic properties of hydrogen absorption and desorption are poor, the conditions for reversible hydrogen absorption are too harsh, which seriously impede the process of application. On the basis of a comprehensive review of the research progress of LiBH4 hydrogen storage materials at home and abroad, this paper studies the six square boron nitride (h-BN) doping, h-BN load NbCl5 and Nb respectively. The effect of H doping on the hydrogen storage properties of LiBH4 was investigated and its modification mechanism was explored. H-BN was doped into the LiBH4 system to improve the performance of hydrogen absorption and desorption. The hydrokinetics of h-BN addition of 5mol%, 15mol%, 30mol% and 50 mol% h-BN doped LiBH4 system was studied in detail. The results showed that the addition of h-BN was 30. At%, the h-BN doped LiBH4 system has the best comprehensive hydrogen storage performance. The initial hydrogen storage temperature and the activation energy of the hydrogen release reaction are reduced to 180 and 155.80 kJ/mol, respectively, from the 280 and 198.31 kJ/mol of the undoped LiBH4 samples. The time required for the completion of the hydrogen release reaction at 400 centigrade is reduced from 6000 minutes of the undoped LiBH4 sample to 120 minutes. After the doping of mol% h-BN, LiBH4 can re absorb hydrogen at 400 and 10 MPa hydrogen pressure, and the performance of the cyclic hydrogen release is relatively stable, and the capacity of the third discharge can reach 6 wt%.. Further analysis shows that the "solitary electron pair" on the N atom on the h-BN surface has a certain reaction instability to LiBH4, so the LiBH4 of the h-BN surface is the first to decompose. The decomposition product becomes the nucleation center of the subsequent LiBH4 decomposition reaction and reduces the decomposition temperature of LiBH4. In order to further improve the hydrogen storage performance of LiBH4, the NbCl5/h-BN compound doping LiBH4 is adopted and the hydrogen storage properties of NbCl5/h-BN complex doping LiBH4 system are compared and analyzed. The hydrogen storage performance of NbCl5 and h-BN alone doped LiBH4 system is studied. The hydrogen storage performance of Co doped LiBH4 is better than that of NbCl5 or h-BN doped LiBH4 system. Among them, 1 mol% NbCl5+30 mol% h-BN doped LiBH4 samples can release 12.19 wt% in 20 minutes, which is 17. of the amount of hydrogen that can be released by the same condition under the same condition. 41 and 2.61 times. After 1 mol% NbCl5+30 mol% h-BN complex doping, the peak temperature of the LiBH4 dehydrogenation is reduced by 100, and the activation energy of the reaction is reduced by 122.75 kJ/mol, and the performance of the cyclic hydrogen release is obviously improved. Further analysis shows that when NbCl5/h-BN is mixed with LiBH4, the nano NbH, which occurs in the h-BN surface NbCl5 and LiBH4, begins. Further catalyze the hydrogen storage performance of modified LiBH4. This paper further uses mechanical ball milling chemical method to prepare a NbH composite catalyst with h-BN load 5-20 nm, and uses it to catalyze the hydrogen storage performance of the modified LiBH4. By adding 1 mol% 3NbH@h-BN catalyst, the peak dehydrogenation peak of LiBH4 is reduced to 380 C, and LiBH4 can finish in 30 minutes. The reaction rate is 200 times as high as that of the undoped LiBH4, and the performance of the cyclic hydrogen release of LiBH4 has been further improved. The third cycle discharge capacity is up to 8 wt%. based on the microstructure analysis and the calculation of the kinetic model of the hydrogen release. We think that the catalytic modification of the catalyst is that the NbH@h-BN catalyst is in the process of the LiBH4 dehydrogenation process. By the effect of the heterogeneous nucleation, the LiBH4 dehydrogenation reaction avoids the critical nucleation work and reduces the hydrogen release temperature of LiBH4 to a certain extent. The nano NbH load on the surface of h-BN forms a stable nanostructure, which can provide enough nucleation Center for the nucleation of the LiBH4 reactor and accelerate the reaction rate of the LiBH4.
【學位授予單位】：浙江大學
【學位級別】：博士
【學位授予年份】：2015
【分類號】：TB34

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