| 摘要: | 氫能為潔淨且能量密度高的燃料，被看好未來能取代石化燃料。電解水製氫是目前較為成熟且產氣純度較高的技術，只是在電解過程會消耗大量的電能。為了節省電力，提升電解效率是當今相當重要的課題。在電解過程中，電極表面會累積大量的氫氣與氧氣氣泡，阻礙離子於電極上之反應。要改善此現象，最常用的方法為攪拌電解液，而超音波產生的空蝕效應也有類似的作用。因此本文將探討不同頻率與強度的超音波對氣阻現象之影響。 本文實驗所設定之參數為電解液濃度(1M、4M、8M、11M)、電解電位(3V、5V) 、超音波頻率(25kHz、40kHz、68kHz、100kHz)、超音波強度(90W、180W、270W、540W)，每次電解時間為600秒，並利用恆電位儀記錄實驗數據，以探討在不同的反應電量在各超音波場下之提升效率。 結果顯示，在高反應電流下，空蝕效應所引發的微小噴射液滴與高壓滯流環可有效帶走電極表面氣泡，改善氣阻現象。而當空蝕氣泡密度夠高時，其爆破產生的高溫可加速電化學反應速率，並增進其效率。 在常溫下，電極間距4mm，濃度8M、電位5V，超音波場25kHz、540W有最佳電流提升效率為27%。 As an energy carrier, hydrogen will play an important role in the future because of its high energy content per unit mass and it is cleaner than the chemical fuels. Today, water electrolysis is a developed technology that generates the purest hydrogen gas. However, it may cause high energy cost. Therefore, energy conservation becomes more and more important and is a major object in many researches. During the process of electrolysis, the electrode plate would be covered by bubbles resulting in the drag of the reactions and high overpotentials at the surface of electrodes. To abate this phenomenon, agitation would be added, and ultrasonic field would offer comparable effect. In this study, we will discover the influence of ultrasonic on electrolysis by 4 parameters such as concentration, voltage, frequency, and power. Each electrolysis treatment takes 600 seconds, data recorded by a potentiostat / galvanostat. The results of experiment show that in the condition of high current density, micro jet and stagnation flow circular produced by cavitation would remove bubbles on the electrode plate, and lower ohmic polarization effectively. The bulk of explosion of cavitation bubbles close to electrode plate will produce high temperature to accelerate reactive rate, and increase efficiency of chemical reaction. Finally, the maximum current density enhancement of the system is about 27%, for concentration 8M, voltage 5V, while an ultrasonic field (25kHz, 540W) is applied. |
