Micro-fluidic flow cells for studies of electrochemical reactions

Abstract

Micro fluidic flow cells (MFFCs) are a relatively new technique for characterization of electrochemical reactions. This work includes both techniques for manufacturing the cells and electrochemical characterization of them.Improvements to a previously established procedure for the manufacturing MFFCs included change of template for PDMS-masters from glass slides to silicon wafers and the change from electrodes consisting of titanium gold and platinum to only titanium and platinum. The changes to the PDMS-masters improved the channel parameters and durability. The changes to the electrodes removed the problem with exposed gold surfaces interfering with at the platinum electrode, and increased the life time of the electrodes significantly. A method for removing oxygen from the MFFCs was also established. Experiments using ferrocyandie redox couple did not show reversible behavior using both platinum and iodine-coated platinum electrodes. Experiments using ruthenium redox couple achieved near reversible behavior using both platinum and iodine-coated platinum electrodes. The iodine-coating showed higher stability and was implemented as a part of the standard procedure. The effect of the placement of the internal reference electrode was investigated. The results indicate that the reference should be place upstream for the working electrode and the counter electrode should be placed downstream for the working electrode. The distance between the working and counter should exceed the distance between the working and reference electrode to minimize interference. Results from potentiostatic and downstream glavnostatic electrochemical impedance both showed trends compatible with theoretical predictions. Due to fluctuations in the open-circuit potential the results showed low reproducibility.