Gas Bubbles in Electrochemical Gas Evolution Reactions

Abstract

Electrochemical gas evolution reactions are of vital importance in numerous electrochemical processes including water splitting, chloralkaline process, and fuel cells. During gas evolution reactions, gas bubbles are vigorously and constantly forming and influencing these processes. In the past few decades, extensive studies have been performed to understand the evolution of gas bubbles, elucidate the mechanisms of how gas bubbles impact gas evolution reactions, and exploit new bubble-based strategies to improve the efficiency of gas evolution reactions. In this feature article, we summarize the classical theories as well as recent advancements in this field and provide an outlook on future research topics.

Ultrasound-enhanced mass transfer during single-bubble diffusive growth

“…Streaming is held mostly responsible for the mass-transfer enhancement: Gas-rich liquid advected from the bulk disrupts the concentration boundary layer surrounding the bubble, greatly strengthening the concentration gradients therein. Our findings have direct impact on diverse applications concerning ultrasonic-driven spherical or quasispherical bubbles attached to a solid surface; namely, in microfluidic devices [7], sonochemical reactors [8], gas-evolving electrodes [51] or catalysts [52], or even during heterogeneous cavitation [53] and pool nucleation boiling [54] of gas-containing vapor bubbles.…”

Enhancing carbon dioxide gas-diffusion electrolysis by creating a hydrophobic catalyst microenvironment

“…How is gaseous CO 2 formed in the MPL? It can be formed directly by trapping the purged CO 2 gas bubbles 34 , or indirectly from the dissolved CO 2 molecules in the electrolyte 43 . If it is the former case, the gas bubbling rate will affect the trapping of gaseous CO 2 and the CO 2 RR rate 34 ; otherwise the CO 2 RR rate should not depend on the gas bubbling rate in the latter case, as long as the electrolyte remains saturated with CO 2 .…”

Oscillating Hydrogen Bubbles at Pt Microelectrodes

“…Impressive examples are related to sonoluminescence [2,3] or cavitation phenomena [4][5][6] or even the evolution of CO 2 bubbles in champagne [7]. The growth of hydrogen bubbles in light-driven water splitting [8][9][10] or water electrolyzers is a particularly interesting problem of high practical relevance due to the prominent role of hydrogen in energy storage via power-togas processes [11][12][13][14]. Alkaline water electrolysis is still the most mature and least platinum-consuming technology, albeit one suffering from inadequate efficiency.…”