【作者】 盖卫卓；

【导师】 邓振炎；

【作者基本信息】 上海大学 ， 凝聚态物理， 2013， 博士

【摘要】 Al与水反应产氢的技术具有常温常压下产氢、产氢量高（1kg Al产生0.11kg氢）、反应的副产物（AlOOH或Al（OH）₃）为化学中性、对环境无污染等特点。Al与水反应的副产物可以通过拜耳过程（Hall-Heroult process）还原成金属Al作循环使用或直接用于生产耐火材料和高铝水泥等。Al的价格相对低廉、在地壳中储量丰富（8.1%）。这些优点使得Al-水反应成为一种很有潜力的原位制氢技术，可以为便携式或千瓦级燃料电池提供氢源。近年来，Al-水反应产氢技术已取得了很大进展，各种Al的活化方法相继出现。同时，Al的产氢性能受到很多因素的影响，如反应温度、Al的形貌及颗粒大小、活化方法、水型及水质、搅拌速率、Al与水的质量比等。本文主要研究了纯Al粉体与水反应产氢的规律及其影响因素，具体研究内容如下：1、纯Al粉体在常压下与水反应产氢规律的研究研究了纯Al粉体在常压下与去离子水反应产氢的特性。结果表明，纳米及微米级纯Al粉体可以在常压下温水中与去离子水反应并产生氢气，纯Al粉体与水反应产氢的动力学规律可以用收缩核模型进行分析：在反应的初始阶段，Al与水反应产氢的速率由表面反应控制；随着反应的进行，表面的副产物越来越多，阻碍了水分子向内输运，这时Al与水反应产氢的速率由水分子在产物层中的扩散来控制。Al与水反应的活化能计算表明，活化能随着Al粉体粒径的增加而增加；当Al粉体的粒径从98.38nm增加到24.94μm时，反应的活化能从64.2kJ/mol增加到88.7kJ/mol。X-射线衍射（XRD）分析表明，Al与水反应产氢的副产物为AlOOH、Al（OH）₃或两者的混合物，主要由反应的温度决定。2、纯Al粉体和表面改性Al粉体与水反应产氢动力学差异的研究应用陶瓷材料的制备方法（混合、干燥、压片、高温真空热处理、粉碎和过筛等）制备得到γ-Al2O3表面改性的活化Al粉体，研究了纯Al粉体和改性Al粉体在相同条件下的反应动力学差异。结果表明，纯Al粉体和改性Al粉体与水反应产氢性能的差异主要体现在反应的初始阶段；改性Al粉体与水反应的诱导时间比纯Al粉与水反应的诱导时间短得多。这是因为改性Al颗粒表面的钝化膜为松散的γ-Al₂O₃相，具有较低的拉伸强度，从而使得Al颗粒表面层的Al:Al₂O₃界面上的H₂气泡具有较低的临界破裂气压。3、氧化物催化作用下Al与水反应产氢的研究研究了纯Al粉体在含有Al（OH）₃、γ-Al₂O₃、α-Al₂O₃或TiO₂粉体的悬浮液中的产氢特性。结果表明，上述氧化物或氢氧化铝悬浮颗粒的存在极大地促进了Al与水的反应产氢，缩短了反应的诱导时间。XRD分析结果显示，氧化物或氢氧化物在反应前后并没有发生变化，说明这些氧化物或氢氧化物只是充当Al-水反应的催化剂。机理分析表明，水分子在氧化物和氢氧化物表面会加速解离，从而有效促进了Al颗粒表面钝化层的水合过程，加速了Al-水反应。4、水中微量物质对Al与水反应产氢性能影响的研究研究了纯Al粉体在去离子水、蒸馏水、自来水及海水中的产氢特性，分析了以上水中的主要阴离子、阳离子和有机物。结果表明，水型对Al-水反应产氢有很大的影响。自来水和海水中的微量F-离子和微量有机酸离子对Al-水反应有明显的抑制作用，而其它阳离子和阴离子对Al-水反应的影响可以忽略不计。机理分析显示，F-离子和有机酸离子会与Al颗粒表面的铝醇基形成稳定的络合物，从而延缓了Al颗粒表面钝化膜的水合过程，抑制了Al-水反应。5、初始气压对Al与水反应产氢性能影响的研究研究了初始气压对Al与水反应产氢性能的影响。结果表明，Al与水反应的动力学与初始气压密切相关：反应的诱导时间随着初始气压从大气压开始降低而降低，然后达到一个最低值，最后随着初始气压的进一步降低而增加。机理分析表明，当初始气压接近水的饱和蒸气压时，诱导时间最短；当初始气压低于饱和蒸气压时，水沸腾，一些水蒸气泡经过或吸附在Al颗粒表面，阻碍了Al表面氧化膜的水合过程，从而增加了Al与水反应的诱导时间。更多还原

【Abstract】 Metal Al is a new hydrogen-generation material, which can continuously reactwith water and generate hydrogen under ambient condition. Al is the most abundantmetal in the earth’s crust, and has a relative low cost. Meanwhile, the reactionbyproduct of Al with water is bayerite or boehmite, which is environmentally benignand can be reduced to metal Al for recycle by a Hall-Heroult process or used to makerefractory and calcium aluminate cement.1kg Al reacts with water to generate asmuch as0.11kg H₂, making it a very promising in-situ hydrogen-generation materialfor portable and kW-grade fuel cells. The research on Al-water reaction to generatehydrogen has been an active area in the past few years, and various activationmethods for pure Al were developed. The hydrogen-generation performance ofAl-water reaction depends on many factors such as the reaction temperature, Alparticle size and morphology, activation method, water quality and type, stirring rate,Al to water weight ratio, etc. In this thesis, the hydrogen-generation performance bythe reaction of pure Al powder with water was investigated systematically, and therelated influencing factors were analyzed as well, which includes1. Hydrogen generation by pure Al powder with water under ambient conditionDifferent size Al powders were used to react with deionized water, and theirhydrogen generation performance was investigated systematically. The results showedthat both nano-and micro-sized Al powders could react with water and generatehydrogen under atmospheric pressure at mild temperature. A shrinking core modelwas used to analyze the reaction progress, indicating that the Al-water reaction iscontrolled by the surface chemical reaction at the initial stage, and then by the H₂Omolecule diffusion in the byproduct layer afterwards. Because the byproduct layerbecomes thick with the reaction progress, impeding the transport of water moleculestowards inner Al. The activation energy of Al-water reaction increased from64.2kJ/mol to88.7kJ/mol with increasing the Al particle size from98.38nm to24.94μm. X-ray analyses revealed that the reaction byproducts are bayerite, boehmite or amixture of them, depending on the reaction temperature.2. Dynamics difference between pure Al and modified Al powders with water-Al₂O₃modified Al powder was prepared by a ceramic processing procedure.The dynamics difference between the reaction of pure Al and γ-Al₂O₃modified Alpowders with water under the same condition was investigated. The results showedthat the reaction difference between two types of Al powders is just at the initial stage.The reaction induction time of modified Al powder with water is obviously shorterthan that of pure Al powder. This difference probably originates from a lower tensilestrength of the Al surface passive oxide films on modified Al particles, leading to alower critical breakage gas pressure in H₂bubbles at Al:Al₂O₃interface.3. Catalysis of oxides in hydrogen generation by the reaction of Al with waterHydrogen generation by the reaction of pure Al powder in Al（OH）₃,-Al₂O₃,α-Al₂O₃, or TiO₂suspensions was investigated. The results showed that the reactionof Al powder with water is promoted and the reaction induction time decreasesgreatly by the above hydroxide and oxides. X-ray diffraction analyses revealed thatthe hydroxide and oxide phases have no any change during the Al-water reaction,indicating that they are just as catalysts to assist the reaction of Al with water. Amechanism analysis revealed that hydroxide and oxides could dissociate watermolecules and promote the hydration of the passive oxide film on Al particlesurfaces, leading to the decrease in the induction time.4. Effect of trace species in water on the reaction of Al with waterHydrogen generation by the reaction of pure Al powder with deionized water,distilled water, tap water and sea water was investigated systematically. The anions,cations and organic substance in the above water were analyzed in detail. The resultsshowed that the water type has a significant impact on Al-water reaction. The traceorganic acids and trace F-ions, rather than other cations and anions, play a key role in the reaction dynamics of Al with water. The mechanism analyses revealed that theorganic acids and F-ions form stable complexes with aluminol groups on Al particlesurfaces, impeding the hydration process of Al surface oxide film and retarding thereaction of Al with water.5. Effect of initial pressure on the reaction of Al with waterThe effect of initial gas pressure on Al-water reaction dynamics wasinvestigated systematically. It was found that there is a non-monotonic correlationbetween the initial pressure and the induction time for the beginning of Al-waterreaction. The induction time decreases with decreasing the initial pressure at the firststage, then reaches a minimum, and finally increases with further decreasing theinitial pressure. The mechanism analyses revealed that the special vacuum pressurecorresponding to the minimum induction time is close to the saturated vapor pressure,below which there are some vapor bubbles passing or adsorbing on Al particlesurfaces due to boiling, retarding the hydration process of Al surface oxide film andincreasing the reaction induction time.更多还原