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Magnetic field induced motion behavior of gas bubbles in liquid.

ABSTRACT: The oxygen evolution reaction generally exists in electrochemical reactions. It is a ubiquitous problem about how to control the motion of oxygen bubbles released by the reaction. Here we show that oxygen bubbles during oxygen evolution reaction exhibit a variety of movement patterns in the magnetic field, including directional migration and rotational motion of oxygen bubbles when the magnet in parallel with the electrode, and exclusion movement of oxygen bubbles when the magnet perpendicular to the electrode. The results demonstrate that the direction of oxygen bubbles movement is dependent upon the magnet pole near the electrode, and the kinetics of oxygen bubbles is mainly proportional to intensity of the electromagnetic field. The magnetic-field induced rotational motion of oxygen bubbles in a square electrolyzer can increase liquid hydrodynamics, thus solve the problems of oxygen bubbles coalescence, and uneven distribution of electrolyte composition and temperature. These types of oxygen bubbles movement will not only improve energy saving and metal deposition for energy storage and metal refinery, but also propel object motion in application to medical and martial fields.

SUBMITTER: Wang K

PROVIDER: S-EPMC4751573 | biostudies-other | 2016

REPOSITORIES: biostudies-other

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Project description:In electrochemical processes, gas bubbles on the electrode can cause an increase in both overpotential and ohmic voltage drop which leads to higher energy consumption. Applying power ultrasound during water electrolysis can help to reduce the overpotential, enhance mass transfer, and save energy. In this study, we investigated the effect of ultrasound (20 kHz) on the hydrogen evolution reaction (HER) on a stainless steel plate with varying concentrations of NaOH solutions at 298 K, using linear sweep voltammetry (LSV). We especially focused on understanding the bubble behavior on the stainless steel plate during HER using high-speed imaging in ultrasonic field. When ultrasound was applied to solutions with NaOH concentrations of 0.1, 0.5, 1 M, the current density increased by about 9.0, 5.9, 2.8 %, respectively. As the ultrasound irradiation began, the bubbles tended to hover around on the electrode surface, coalescing with other bubbles, rather than rising. When the size of the coalesced bubbles became too large to stay on the surface of the electrode, they were expelled from the ultrasonic field. The repeated collapse and coalescence of these bubbles was observed while they were rising. The velocity increased about 2 times when ultrasound irradiation began, and increased by more than 6 times in the ultrasonic field. More nucleation of bubbles was observed on the electrode in the ultrasonic field. Using ultrasound reduced the critical diameter of bubbles which detached from the electrode, from 58.0 to 15.9 μm, and the residence time of the bubbles, from 533 to 118 ms. Further, when the ultrasound was applied, the mean diameter of bubbles decreased from 71.8 to 17 μm. Hence, bubble coverage on the electrode surface decreased from 8.3 to 1 % despite an increase in the total number of bubbles. As a result, ultrasound was found to be effective for hydrogen production during water electrolysis, increasing current by the faster removal of gas from the stainless steel plate.

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Magnetic field induced motion behavior of gas bubbles in liquid.

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