【摘要】：具有良好吸放氫動力學性能的儲氫材料一直是廣大研究者探索的熱點。鎂基合金因其豐富的資源,較高的吸放氫容量而備受關注。但純鎂仍存在一系列問題,比如動力學性能較差、活化困難、放氫溫度高等缺點,限制了其實際應用。稀土-鎂系儲氫合金具有儲放氫條件溫和、平臺壓適中、原料儲量豐富等優(yōu)點,在能源儲存和利用方面顯示出良好的應用前景。本文針對合金吸放氫過程中的擴散控速與界面控速兩種控制機制提出了一系列易于應用的動力學模型公式,包括反應時間與反應分數(shù)、最優(yōu)氫化溫度與對應的最小特征時間等關系式。采用粉末燒結法與氫化燃燒合成法兩種工藝制備鎂基儲氫合金,并用推導模型系統(tǒng)研究了合金的吸放氫動力學性能。另外,本文還歸納了部分文獻中的動力學實驗數(shù)據(jù),利用推導的模型研究了文獻中鎂系合金的吸放氫動力學,并進一步驗證了模型的正確性。通過對富鎂儲氫合金的相關動力學數(shù)據(jù)進行模型分析,發(fā)現(xiàn)Nd的添加對改善鎂基儲氫合金吸氫動力學性能較為顯著,在提升吸氫量的同時,能將活化能降低至79.29 k J/mol H_2,最優(yōu)反應溫度(696 K)、4 MPaH_2條件下吸氫完成所需的特征反應時間(83 s)最少。Mg_(95)Ni_5與少量Zr_(0.7)Ti_(0.3)Mn_2形成的富鎂儲氫合金吸氫活化能為109.85 k J/mol H_2,所需特征時間僅為49 s,比純鎂有大幅度降低,主要受界面控速為主,模型擬合相關系數(shù)平方值R~2高達0.99045。經(jīng)過對Mg_2Ni基三種儲氫合金吸放氫動力學實驗數(shù)據(jù)的擬合分析可得出:三種合金均受擴散控速。其中,采用球磨制備的Mg_2Ni合金擬合度R~2最高(0.98186),活化能為110.326 kJ/mol H_2,在4MPaH_2下最優(yōu)溫度707 K所需特征時間僅為109 s,整體效果最佳。放氫動力學結果顯示:在不同磁場下制備的三種合金中,4MPaH_2下的合金放氫速率最快,623 K時僅需約160 s就能夠將氫全部釋放出來,遠遠快于前兩者。三種合金的模型擬合度較高,R~2均大于0.95,2MPaH_2下得到的合金活化能最低,為161.371 kJ/mol H_2。La-Mg系復合儲氫材料動力學擬合結果顯示:Ni的加入對La-Mg系復合儲氫材料的吸氫動力學改善效果最佳,在573 K及2 MPa H_2條件下,達到3.87 wt.%的最大吸氫量所需時間僅為250 s,并且在80s內就能達到最大吸氫量的90%。模型擬合分析后發(fā)現(xiàn):不同壓力條件下的動力學數(shù)據(jù)都可用擴散控速模型進行擬合,R~2均大于0.98,La_2Mg_(17)-Ni的吸氫活化能為39.492 kJ/mol H_2,最優(yōu)氫化溫度下的特征反應時間可達到222 s,綜合性能最優(yōu)。通過對實驗制備的儲氫合金以及文獻中的吸放氫動力學數(shù)據(jù)進行模型擬合分析,得到了不同體系合金的吸放氫動力學機理和表觀活化能等信息,驗證了推導模型的正確性。對于吸氫過程,還可求出體系的最優(yōu)反應溫度和最少特征反應時間,模型的建立為儲氫合金的吸放氫以及類似氣固反應的理論研究提供了新的思路和方法。
[Abstract]:Hydrogen storage materials with good kinetic properties of hydrogen absorption and desorption have always been the focus of exploration by researchers. Magnesium-based alloys have attracted much attention because of their rich resources and high hydrogen absorption and desorption capacity. However, there are still a series of problems in pure magnesium, such as poor kinetic performance, difficult activation, high hydrogen release temperature and so on, which limit its practical application. Rare earth-magnesium hydrogen storage alloys have the advantages of mild hydrogen storage and desorption conditions, moderate platform pressure and rich raw material reserves, so they have a good application prospect in energy storage and utilization. In this paper, a series of kinetic model formulas, including reaction time and reaction fraction, are proposed for the control mechanism of diffusion control rate and interface speed control in the process of hydrogen absorption and desorption of alloys. The relationship between the optimal hydrogenation temperature and the corresponding minimum characteristic time. Magnesium-based hydrogen storage alloys were prepared by powder sintering process and hydrogenation combustion synthesis process, and the kinetic properties of hydrogen absorption and desorption of the alloys were studied systematically by using the derived model. In addition, the kinetic experimental data in some literatures are summarized, and the hydrogen absorption and desorption kinetics of magnesium alloys in the literature is studied by using the derived model, and the correctness of the model is further verified. Through the model analysis of the related kinetic data of magnesium-rich hydrogen storage alloy, it is found that the addition of Nd can improve the hydrogen absorption kinetics of magnesium-based hydrogen storage alloy significantly, and at the same time, it can increase the hydrogen absorption capacity of magnesium-based hydrogen storage alloy. The activation energy can be reduced to 79.29 k J/mol H 鈮，

本文編號：2480338