(509aa) Understanding the Interactions between Bubble Dynamics and Electrochemical Energy Losses in Flow Electrolyzers

Potential losses in water electrolyzers are affected by bubble evolution due to the negligible conductivity of gases, blocking available pathways for ion conduction, reducing the available electrocatalytic area and disrupting concentration gradients that arise due to mass transport limitations near the electrode-electrolyte interface. Bubble evolution is of special concern in membrane-less flow reactors where convection is used to avoid product cross-over. In this presentation, I will provide insights into the interplay of convective forces and gas evolution and their effects on activation, ohmic and concentration overpotentials in flow-based water electrolyzers .

For this purpose, we use microfluidic membrane-less flow electrochemical reactors with a single set of electrodes where single bubble evolution can be carefully controlled and monitored. First, we study the overall effect of convective flow in bubble evolution dynamics on the total overpotential of electrolyzers at a set current density, or on the current density at set potential. We find that high Re number flows (i.e., Re > 20) mitigate large fluctuations on the overpotential, while at smaller Re periodic bubble evolution leads to overpotential fluctuations in the order of ~100 mV. Next, to better understand concentration overpotentials, we use fluorescence microscopy and pH sensitive dyes to capture the spatio-temporal dynamics of proton concentration gradients and correlate the strength and shape of these gradients to the applied potential and convective forces. Understanding the effects of fluid dynamic forces in concentration overpotentials of electrochemical reactors will serve as a stepstone to create a set of design rules for this type of reactors and develop optimal electrolytic hydrogen production, which can then be applied to other types of electrochemical reactions.