Influence of Bubbly Flow on the Ohmic Overpotential of Electrochemical Reactions in a Microchannel Reactor

Microchannel reactors intensify electrochemical reactions by limiting ionic transport distances and controlling laminar flow conditions within small reaction spaces. However, these reactors are also strongly affected by the electrolytic bubbles flowing inside, contributing to both promoting and inhibiting electrochemical reactions. This study aims to understand the effect of bubbly flow on the resistance of ionic transport and determine key parameters for governing gas–liquid flow control in microchannels. Visualization experiments were conducted using a glass microchannel chip integrated with microelectrodes to investigate the relationship between the cell voltage and bubble geometries during the benzyl alcohol oxidation and hydrogen evolution reactions. The effects of the flow rate, applied current, and support electrolyte concentration on the overpotential were investigated individually. The bubbles significantly contributed to the ohmic overpotential of the reaction solution, with the additional resistance showing two linear relationships as the ionic transport distance increased. The microchannel width and electrode distance were identified as key dimensions for bubble size control in the microchannel reactor, which determined the turning points of the bubble-induced electric resistance.