| dc.description.abstract | 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%. | en_US |