鎂鋁合金電極研製及其產氫效益之研究;Study on the preparation of Mg-Al alloy electrodes and their applications in efficiency improvement of hydrogen production

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Title:	鎂鋁合金電極研製及其產氫效益之研究;Study on the preparation of Mg-Al alloy electrodes and their applications in efficiency improvement of hydrogen production
Authors:	許,文濃;Hsu,Wen-Nong
Contributors:	機械工程學系
Keywords:	超音波震盪;鑄造鎂合金;電極;水解;極化阻抗;勞倫茲力;Ultrasonic vibration;Cast magnesium alloys;Electrode;Water electrolysis;Polarization impedance;Lorentz Force
Date:	2016-06-30
Issue Date:	2016-10-13 14:49:31 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究之第一部分是探討鎂鋁合金晶粒細緻化及電極材料之研製，研究結果顯示熔煉時，導入超音波於純鎂及鋁鎂合金熔湯中，由於除氣及介在物的分散作用，可以使所形成之鎂金屬及鎂鋁合金晶粒細緻化，進而改善其鑄造之品質，晶粒精細化之主要原因是空泡阻礙晶體成長及氧化物和鋁錳化合物之分散。然而純鎂及鎂合金的機械性質反而下降，主要原因是鎂元素及鋅元素本身在熔煉時蒸氣壓較高之故。另外以鑄造方式製作鎂鋁合金電極是不適當的，因為無法控制電極材料的品質。本研究第二部份係以粉末冶金的方法，燒結不同成分的鋁鎂合金電極，作為電解水電極用。實驗結果顯示鎂鋁電極的電流密度大小依序如下：Mg < Mg-10wt%Al < Mg-25wt%Al < Mg-50wt%Al < Mg-75wt%Al < Mg-90wt%Al < Al 。純Al電極具有最佳的電解效果；但如果同時考慮電解效果及抗腐蝕之能力，則應選用Mg-Al(75 wt%)當電極材料為最佳。另外在電解的過程中,若加入超音波場可有效的提昇電解之效率，在30wt%KOH的電解液中，電流增加率大約為23.1％，使用FRA模組量測電化學阻抗頻譜(EIS)及曲線回歸，顯示超音波震盪均有效地改善電極間的極化阻抗，其中以降低電解時的濃度阻抗值約44-51％Ω最為顯著。最後,採用三組並聯電極組方式做實驗，研究相關水電解實驗參數。結果顯示三電極組的產氫量會比單電極組產氫量增加2.2~2.9倍數。最後本研究並探討外加磁場對電解水之影響，加入磁場會使得電解反應變快，若外加勞倫茲力往上之磁場，電極距離為5mm，電解液濃度為10wt%的條件下，可以得到最佳的電流密度差值約370 mA/cm2 。 ;The first part of this study is aimed to investigate the grain size refinement for magnesium and magnesium-aluminum (Mg-Al) alloys. Under the ultrasonic treatment, the cavitation bubbles were generated in the melt. Both degassing action and dispersion of inclusion imped the growth of crystal grains and result in the refinement of crystal grains of magnesium and magnesium- aluminum alloys. Therefore, the casting property of the metal and alloys was improved. Nevertheless, the mechanical properties of both magnesium and its alloys were decreased. The reason is due to lower vapor pressure of magnesium and zinc in the melt. We also found that casting method is not suitable for the preparation of Mg-Al alloy electrodes because their properties were difficult to control by this method. In the second part of this study, power metallurgy was used to sinter the Mg-Al alloy electrodes with different compositions. The obtained electrodes were used for water electrolysis. The results demonstrate that the current density decreases as the following tendency: Mg < Mg-10wt%Al < Mg-25wt%Al < Mg-50wt%Al < Mg-75wt%Al < Mg-90wt%Al < Al 。 The Al electrode possesses the best electrolysis efficiency. However if both the anti -corrosion ability and electrolysis are considered, the Mg-Al (75 wt %) should be the best electrode material. During the electrolysis process, if the ultrasonic field was applied to the electrolysis cell, the electrolysis efficiency was greatly enhanced. The current increased about 23.1% in the 30 wt% KOH aqueous solution. The Electrochemical Impedance Spectroscopy (EIS) curves measured by Frequency Response Analysis (FRA) module and the regression curves showed that the polarization impedances between electrodes were effectively improved. The concentration polarization in the 30wt% KOH aqueous solution was reduced to 44-51% during the electrolysis process. Furthermore, three groups of parallel electrodes were used for the water electrolysis experiments. The results demonstrate that the hydrogen electrolysis cell using a multi-electrode(6 sheets) group is 2.2-2.9 time higher than that using a single electrode group. Finally, the magnetic field was also used to enhance the electrolysis reaction. The results show that the optimal current density is 370 mA/cm2 at electrode distance of 5mm and a 10 wt% electrolyte concentration with the Lorentz force up.
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