The Impact of Surfactants on the Inertial Separation of Bubbles in Microfluidic Electrolyzers

Improving the throughput of electrochemical reactions such as water electrolysis is an ongoing effort. In a membrane-less electrolyzer, product separation can be achieved via controlled two-phase flows within the electrochemical flow cells. In this case, it is important to keep the diameter of the bubbles small while ensuring that they follow an off-center trajectory in the channel. This can be accomplished by either increasing the flow, which in turn increases the power loss due to the fluidic resistance, and/or decreasing the electrical current which means a lower production rate. To avoid these drawbacks, here we show that by adding surfactants to the electrolyte, bubbles are kept smaller due to the bubble coalescence inhibition and faster bubble detachment from the electrodes. We find out that by using surfactants, the required flow rate for efficient product separation and the corresponding pumping power decrease. Moreover, we show that higher throughputs can be achieved at a given flow rate by using surfactants. The surfactant used in this study introduces an undesirable increase in the overpotential. This is compensated at high production rates where the surface coverage of the electrodes by the generated gas bubbles is smaller in the presence of the surfactant.