The physics of bubble evolution

Avoiding bubble troubles.

Bubbles are known to influence energy and mass transfer in gas-evolving electrodes. However, there is a lack of understanding of the intricate dependencies between bubble evolution processes and electrochemical phenomena.

Numerous electrochemical reactions produce gas that can prompt bubbles forming at the reaction site. Those bubbles can lessen the proficiency of response, which leads to energy losses.

In a new study by the University of Twente in collaboration with New York University, scientists explored different strategies to mitigate losses or even exploit bubbles.

David Fernandez Rivas from the University of Twente said, “Increasing our knowledge of the relationship between bubbles and electrochemistry will lead to design guidelines for high-performing electrochemical reactors, which are highly desirable in the chemical industry because bubbles decrease the performance of electrodes.”

“Increasing our knowledge of the relationship between bubbles and electrochemistry will lead to design guidelines for high-performing electrochemical reactors, which are highly desirable in the chemical industry.”

“Bubbles typically form on cracks and crevices or other microscopic bumps in the electrode surface. An example of such a surface suitable for bubble formation is the edge of a glass. When the glass is filled with cola – or any other carbonated liquid – you can find a nice ‘train’ of bubbles being formed from the dissolved carbon dioxide.”

 The formation of bubbles on the surface of an electrode
The formation of bubbles on the surface of an electrode

“The bubbles on electrodes, however, can prevent the desired reaction from happening, which means the efficiency of the reaction is reduced. A better understanding of the formation of bubbles can help us control their formation and thus increase the efficiency of reactions.”

There are various methodologies available to remove or reduce bubbles are available. One of which has been created in Twente in the last decade utilizes microscopic engineered defects or pits on the surface of the electrode. The hydrophobic pit is where bubbles like to form. This strategy makes it conceivable to form bubbles away from the electrode active surfaces.

Bubble evolution at a hydrophobic pit
Bubble evolution at a hydrophobic pit

The formation away from the active electrode surfaces lets three things happen. First, each new bubble in a series takes longer to grow. Then a continuous gas production increases the local gas supersaturation, which in turn increases the growth rate of bubbles. At last, the growth rate levels off to a steady growth rate. The formation of bubbles away from the electrodes may be used to minimize bubble-induced energy losses in electrochemical devices, like fuel cells.

The Netherlands Centre supported Their work for Multiscale Catalytic Energy Conversion (MCEC), an NWO Gravitation program funded by the Ministry of Education, Culture and Science of the government of the Netherlands, and by the Swiss National Science Foundation. The results were published today in the journal Joule.

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