| Hydrogen energy is widely used in petroleum,chemical and metallurgical industries,and is known as the core of the world’s energy architecture in the future.Water electrolysis can produce high purity hydrogen product,which is relatively simple and environmentally.Nowadays,it is commonly used in renewable energy storage technology.Studies have proved that the external magnetic field can effectually manage the gas evolution process on the electrode surface,and reduce the additional energy consumption caused by the bubble effect.However,the mechanism of the magnetic field on the bubble growth and detachment process on the electrode surface remains unclear.The dynamic evolution process of bubble interface under magnetic field still to be explored.In order to investigate the influence of current density and magnetic field intensity on the growth and detachment process of single bubble on the electrode surface,both the horizontal and vertical microelectrode electrolysis experimental systems have been designed.The evolution process of a single bubble on the microelectrode surface under different electrolysis conditions has been recorded using high-speed cameras.The characteristic parameters of the bubble are extracted and analyzed through the specially developed Open CV-python program.The bubble growth diameter,growth time,contact diameter,departure diameter,contact point position and working electrode potential under different magnetic field intensity and current density conditions have been investigated.The dynamic growth process of a single bubble on the horizontal microelectrode under the vertical magnetic field has been stimulated through the VOF method.The main conclusions are as following:(1)Through the accurate measurement of the bubble diameter,both the dynamic evolutions of a single bubble on the horizontal and vertical microelectrode surface under electrode-normal magnetic fields are described.The bubble growth rates for the horizontal and vertical microelectrodes approximately satisfied the growth law D(t)=βt~13,which is consistent with the literature conclusions.The bubble growth rate is mainly determined by the current density on the microelectrode surface,and it increases with the increase of the current density.Moreover,the external magnetic field has little effect on the bubble growth rate.(2)The bubble detachment process was accurately judged based on the image-processing program and statistics method,and the influence of magnetic field intensity on the bubble detachment process has been investigated.For horizontal microelectrode,the external magnetic field can effectively enhance the bubble detachment behavior under lower current density.When the current density is relatively high,the weak magnetic field will inhibit the bubble detachment behavior,while the stronger magnetic field will promote the bubble detachment behavior.For vertical microelectrode,the external magnetic field has little effect on the bubble detachment behavior under lower current density,and only a few conditions will inhibit the bubble detachment process.The external magnetic fields obvious promote the bubble detachment behavior under higher current density and the effects of magnetic field depend on the specific current density.(3)The dynamic evolutions of the bubble contact point and contact diameter have been captured using the corner detection algorithm.The left and right contact bubble points on the horizontal microelectrode surface are approximately symmetrical and the bubble can completely fill the electrode surface in a short time.The bubble on the vertical microelectrode surface has a tendency to cover the upper surface of the microelectrode.The electrode area around the bubble presents an obvious asymmetrical distribution.The obvious coalescence phenomena between large and small bubbles can be seen beside the lower bubble contact point.(4)The bubble periodic growth and detachment process on the microelectrode surface cause the periodic change of the working electrode potential.With the increase of the current density,the absolute value of the working electrode potential rises significantly.The magnetic field can significantly affects the working electrode potential range.However,the actual effect is closely associated with the specific current density.(5)Base on the VOF interface capture method,combined with the bubble contact diameter prediction model,the growth evolution of a single bubble on the horizontal microelectrode surface has been simulated.The stimulated bubble diameter evolution curve agrees well with the experiment result.Higher hydrogen superstition is concentrated in the wedge-shape area between the bubble foot and the microelectrode,in which the gas-liquid mass transfer rate is very large.Affected by the current distribution around the microelectrode surface,the current density and Lorenz force near the bubble foot area are significantly larger,and gradually increase with the increase of the bubble size.The rotational electrolyte velocity around a single bubble increases and then decreases during one bubble growth cycle. |
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