鋁的化學研究 (Ⅰ)鋁/水反應使用合成的催化劑製造氫氣 (II)在低溫下電沉積鋁

Study of the chemistry of aluminum (I). Hydrogen generation from the aluminum/water reaction using synthesized Al(OH)3 catalysts (II). Electrodeposition of aluminum at low temperature

蒲山明(Samikannu Prabu)

指導教授 ： 王宏文

中原大學/理學院/化學研究所/博士(2019年)

https://doi.org/10.6840/cycu201900428

摘要

本研究首先合成納米尺寸的 Al(OH)3 粉末，催化促進Al /水反應產生氫氣。在本研究中，使用鋁酸鈉 NaAlO2，蒸餾水和乙醇合成氫氧化鋁。溶液中乙醇/水的摩爾比和鋁酸鈉的濃度顯著影響 Al(OH)3 粉末的晶體結構，形態和尺寸。這些 Al(OH)3 粉末含有三水鋁石相(Gibbsite)和三羥鋁石相(Bayerite)，並且對 Al /水體系的氫生成具有不同的催化能力。本研究提出 Al(OH)3 粉末的兩個主要特徵主導著其催化能力。即，Al(OH)3 的表面積和高能位點。當乙醇/水的摩爾比在 0.3-0.6 之間並且 NaAlO2 的濃度高於 0.0167g/ml 時，合成的 Al(OH)3 粉末處於更多的三水鋁石取向和板狀結構。相反地，除了上述條件之外，將導致生成更多的三羥鋁石相和顆粒狀結構。由於板邊緣上存在高能位元點，板狀結構表現出強大的催化能力，即使其表面積不是很高。但當顆粒狀結構具有高表面積時，它也可具有強催化能力。通過利用放熱反應，使用 3g 合成的 Al(OH)3 在 30 秒內從 1g Al/10g 水系統產生約 100％ 的氫產率。
第二部份，氫氧化鋁粉末 (Al(OH)3)在室溫下使用不同溶劑（甲醇，乙醇和 HNO3）製備 (25 ℃)。使用乙醇和 HNO3 合成的材料顯示出三羥鋁石，混合相和甲醇作為溶劑顯示出三水鋁石相，通過X射線繞射，XPS 拉曼光譜和場發射光譜 (FESEM) 證實。由於較小的晶體尺寸，使用三羥鋁石相和混合相的氫生成顯示出比粗大的純三水鋁石相更高的催化效率。Bayerite在 2 小時內顯示出100％產率, 但是三水鋁石相在 15 小時顯示出約 60-70％ 的產率。但當板狀 (更多的三水鋁石相取向) 結構具有高表面積，小而薄的層時，也可具有強催化能力。
第三部份，本研究使用石墨改質的 Al(OH)3 納米顆粒 (NPs) 增加催化 Al和水產生氫的反應。 通過簡單的溶劑合成該石墨改質的 Al(OH)3 NPs。 使用粉末X射線繞射，場發射掃描電子顯微鏡 (FESEM) 和透射電子顯微鏡 (TEM, JEOL JEM 2010) 進行驗證。 發現加入 Al(OH)3 中的少量石墨可顯著提高Al 和 H2O反應。在恆溫產氫反應, 施加條件（Al:Al(OH)3:水為1:1:200）， 20 分鐘內釋放 1360 mL g-1 氫（100％理論氫產率）。 合成的石墨改質的 Al(OH)3 表現出良好的活性穩定性，可用於多個 Al /水反應。
第四部份，研究了在室溫下使用 AlCl3-尿素離子液體電解質電沉積鋁金屬。 AlCl3 /尿素的摩爾比，甲苯的加入量，攪拌速度，沉積時間和溫度是影響鋁沉積的主要因素。 電鍍在 20-60℃ 的溫度下以 0-80rpm 的攪拌速度進行，使用 1V 的偏壓施加 2 小時。 使用 20％ 稀釋的甲苯電解質，在高摩爾比的 AlCl3/尿素下增強鋁電沉積。 使用X射線衍射（XRD），能量色散譜（EDS）和掃描電子顯微鏡 (SEM) 檢查沉積的鋁層的微結構。 發現電流密度隨著持續時間和較低溫度而降低。 在這項研究中，在 60 oC 時可以獲得高達 ~89.98％ 的電流效率。
最後一部份，使用兩種電解質溶液研究鋁（Al）的電沉積，例如無水AlCl3-尿素和含水 AlCl3·6H2O-尿素。 使用 1.0~2.0V 的電池電壓進行系統檢查，溫度為 50~100±2℃。 針狀陰極用於鋁的沉積。 在針狀陰極上觀察到Al的枝晶和微粒結構。 從非水電解質的電流效率（產率）獲得 84-99％ 的純Al，與水合電解質的電流效率僅為 8.6~9.3％。 電解質的電導率在 50~100±2℃ 時仍然很大。 低溫電沉積的鋁粉用於與水反應，室溫下產生純 H2，產率為 100％。 電沉積的鋁金屬可用作優異的能量載體。

關鍵字

使用Al(OH)3催化剂合成有效的Al(OH)3催化剂 ； 铝和水 ； 石墨改性的Al(OH)3催化剂的合成 ； 室温下离子液体中Al的电沉积

並列摘要

Firstly, a synthesized and nano-sized Al(OH)3 powder that promotes the generation of hydrogen from a Al/water reaction is demonstrated. In this study, aluminum hydroxides are synthesized using sodium aluminate NaAlO2, distilled water and ethanol. The mole ratio of ethanol/water and the concentration of sodium aluminate in solution affect the crystal structure, morphology and sizes of the Al(OH)3 powders significantly. These Al(OH)3 powders contain both gibbsite and bayerite phases and exhibit excellent catalytic power on the hydrogen generation of Al/water system. It is proposed that two major characteristics of Al(OH)3 powders dominate the catalytic power. That is, the surface area and the high-energy sites of Al(OH)3. When mole ratio of ethanol/water is between 0.3–0.6 and the concentration of NaAlO2 is higher than 0.0167 g/ml, the synthesized Al(OH)3 powders are in a more gibbsite-oriented and plate-like structure. Other than above conditions result in a more bayerite-oriented and particulate-like structure. The plate-like structure exhibits strong catalytic power due to the existence of high-energy sites on the edge of plates even its surface area is not so high. The particulate-like structure may also have strong catalytic power when it has a high surface area. By taking advantage of the exothermic reaction, ~ 100% yield of hydrogen can be produced from 1 g Al/10 g water system within 30 s using 3 g synthesized Al(OH)3.
Secondly, aluminum hydroxide powders, (Al(OH)3), have also been prepared both distinctly using solvothermal reactions in different solvents (methanol, ethanol, and HNO3) at room temperature (25 oC). Interestingly, the materials synthesized by using ethanol and HNO3 showed bayerite, and methanol as solvent showed a gibbsite phase, which was confirmed by X-ray diffraction, XPS, Raman spectroscopy, and field emission spectroscopy (FESEM). The hydrogen generation using small sized bayerite phase and mixed phase show higher catalytic efficiency than the pure and large gibbsite phase powders. The bayerite catalyst displayed the highest yield (100 %) within 2 hours, but the gibbsite phase shows around 60-70 % yield for a long time of 15 h. The plate-like (more gibbsite phase orientation) structure may also have strong catalytic power when it has a high surface area, small and thin layer.
In the third section, the high catalytic effect for the hydrogen generation from Al and water reaction using a graphite-mixed Al(OH)3 nanoparticles (NPs) was reported. This graphite-mixed Al(OH)3 NPs were synthesized through a simple solvothermal procedure. Characterization using powder X-ray diffraction, field emission scanning electron microscopy (FESEM) and transmission electron microscope (TEM, JEOL JEM 2010) were carried out. The results show that small amounts of graphite added into Al(OH)3 could significantly enhance the hydrolysis reaction of Al and H2O reaction, releases 1360 mL g-1 hydrogen in 20 mins (about 100% of the theoretical hydrogen generation yield) when isothermal condition (1:1:200 for Al:Al(OH)3:water) was applied. The synthesized graphite-mixed Al(OH)3 exhibits good activity-stability, which can be used for multiple Al/water reactions.
In the 4th section, electrodeposition of aluminum metal using an AlCl3–urea ionic liquid electrolyte at room temperature is studied. The molar ratio of AlCl3/urea, addition of toluene, stirring speed, deposition duration, and temperature are the major factors that affect the deposition of aluminum. The electroplating is carried out at temperatures in the range 20–60 oC at a stirring speed 0–80 rpm using bias of 1 V applied for 2 h. The aluminum electrodeposition is enhanced at a high molar ratio of AlCl3/urea using 20% diluted toluene electrolyte. The microstructure of the deposited aluminum layer is examined using X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and scanning electron microscopy (SEM). The current density is found to decrease with the duration and at lower temperatures. In this study, a current efficiency as high as ~89.98% could be obtained at 60 oC.
Finally, the electrodeposition of aluminum (Al) was studied using two electrolyte solutions, such as anhydrous AlCl3-urea and hydrated AlCl36H2O-urea. A systematic examination using cell voltages 1.0~2.0 V was carried out at temperatures 50~100±2 oC. A needle-shape cathode was employed for the deposition of aluminum. A dendrite and particulate microstructure of Al were observed on the needle-shaped cathode. Pure Al with a current efficiency (yield) of 84-99% was obtained from those of non-aqueous electrolytes and only of 8.6~9.3% from those of hydrated electrolytes. The electrical conductivities of electrolytes remained considerable at 50~100±2 oC. The electrodeposited aluminum powders were used for the reaction with water. The aluminum reacts with water at room temperature, producing pure H2 with 100% yield. The electrodeposited aluminum metal can be used as an excellent energy carrier.

並列關鍵字

Synthesis of effective Al(OH)3 catalysts ； Aluminum and water using Al(OH)3 catalysts ； Synthesis of graphite-modified Al(OH)3 catalysts ； elEctrodeposition of Al in ionic liquids at room temperature

參考文獻

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