利用外部作用增加水電解產氫效率之研究

The improvement of efficiency on the water electrolysis hydrogen production by exterior actions

林明源(Ming-Yuan Lin)

指導教授 ： 洪勵吾

國立中央大學/工學院/機械工程學系/博士(2013年)

摘要

水電解產氫是目前產生氫氣常用的方法，擁有高效能、產生氫氣純度高、使用便利等特色。本實驗利用鎳電極，在水電解產氫時加入脈衝與磁力和超音波場，探討磁流體動力學與脈衝作用和超音波場下，水電解產氫相關參數之影響。在實驗中觀察到，磁力會形成勞倫茲力，促使電解液之對流方向不同，影響水電解之氣泡流向，適當磁力有增強產氫效果；且鐵磁性電極容易受磁化作用，與磁力形成之勞侖茲力，對磁流體動力學彼此有相加乘之效果，能降低極化作用與電解時之過電壓，進而增加產氫效率。而脈衝會使瞬間電流值提升、促使氣泡加速脫離電極表面、加速電解液離子質傳擴散作用、降低氣泡擴散層、降低電化學極化作用，進而提高電解產氫效率。水電解會產生氫氣與氧氣之微小氣泡，此氣泡附著於電極表面，將會產生氣阻現象，因而導致電流下降、造成能量損失，在電解時提供超音波場，將可使此現象改善。利用電化學阻抗頻譜(EIS)，探討超音波水電解之極化阻抗現象，以EIS方法與曲線迴歸方式，探討水電解之電化學反應。
在常溫下、電極間距2 mm、電壓4 V，加入磁場狀態下：鐵磁材料鎳電極所提升之電流增加率為14.6%；順磁材料之白金電極提升之電流增加率為10%；逆磁材料之石墨電極增加較不明顯，可知加入磁力確實會提升水電解產氫效率，且在鐵磁性電極與電極距離越近提升效果最佳。加入脈衝時，當循環負載10%、Ton=10 ms時，整體電量可節省將近88%、電流密度增加值可增加680 mA/cm2、電流密度增加率約為38%；整體來說同時加入脈衝與磁場作用，在適當脈衝與基礎電壓作用下，會有相互增強之效果。超音波水電解實驗中發現，主要是改善活性與濃度阻抗現象，並影響水電解時上升之氣泡束，且超音波大小、電極間距、電解液濃度等，為影響水電解時的重要參數。在常溫下、當電極間距2 mm、電壓4 V、40 wt%、超音波強度225 W時，電流差值約為240 mA/cm2，扣除超音波場之能量消耗，省電能約為3.5 kW、節能增加率約15%左右。

關鍵字

電解水 ； 勞侖茲力 ； 脈衝 ； 超音波 ； 磁流體動力學 ； 電化學阻抗頻譜

並列摘要

Water electrolysis is one of the most common ways to produce hydrogen gas. It has several merits, such as: high efficiency, high purity, and easy use. This experiment uses nickel electrodes and adds pulses and magnetic force and ultrasonic wave field in the production of hydrogen via electrolysis of water, exploring how related parameters are affected by magnetohydrodynamics (MHD) and pulses and ultrasonic wave field.The experiment observed that the Lorentz force of the magnetic field causes the electrolyte’s convective flow to change direction, affecting the flow of bubbles during electrolysis; suitable magnetic force can enhance hydrogen production. Furthermore, ferromagnetism electrodes are more affected by magnetism, and multiply the Lorentz effect. It reduces the polarization and over-potential during electrolysis, and thus increases the effectiveness of hydrogen production. Pulse causes instantaneous current to increase, accelerating the speed bubbles leave the surface of the electrode, as well as the rate of mass transfer in the electrolyte, which lowers the diffusion layer and electrochemical polarization, and further increases hydrogen production efficiency. The water electrolysis generated minute hydrogen and oxygen bubbles, and the bubbles adhered to the electrode surface resulting in air lock phenomenon, so that the fall of current caused energy loss. This phenomenon can be improved by providing ultrasonic wave field in electrolysis. This study used Electrochemical Impedance Spectroscopy (EIS) to discuss the polarization impedance phenomenon of ultrasonic water electrolysis. The EIS method and curvilinear regression have never been used to discuss the electrochemical reaction of water electrolysis.
With the magnetic field at room temperature, electrode spacing of 2 mm and a voltage of 4 V, nickel electrodes (ferromagnetism material) can promote current density by 14.6%, and Platinum electrodes (paramagnetism material) can promote current density by 10%. The promotion of current density is not significant for graphite electrodes (diamagnetism material). It indicates the magnetic force does enhance the efficiency of water electrolysis, and ferromagnetism is the best choice for electrodes; when there is a 10% duty cycle and Ton=10 ms, almost 88% of overall power can be conserved, current density will increase by 680 mA/cm2, with an increase rate of roughly 38%. In general, pulse and magnetic field effects will enhance one another when added under suitable pulse and basic voltage.the ultrasonic wave field improved the activity and concentration impedance, and affected the rising air bubble plume in water electrolysis. The ultrasonic intensity, electrode gap and electrolyte concentration were important parameters influencing water electrolysis. At normal temperature, when the electrode gap was 2 mm, the potential was 4 V, 40 wt%, and the ultrasonic intensity was 225 W, the difference in current density was 240 mA/cm2. After deducting the energy consumption of ultrasonic wave field, 3.5 kW of energy was saved, and the economical power efficiency was 15%.

並列關鍵字

Electrolytic Water ； Lorentz Force ； Pulse ； ultrasonic ； Magnetohydrodynamics ； EIS

參考文獻

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