| Microfluidic flow cells are advantageous in chemical analysis due to small sample volume and tunable flow dependencies. These devices are complex systems, where mass transfer, electrical effects, and electrochemical reaction kinetics collectively determine the output current. The current response is also dependent on cell geometry and electrode placement. This work sought to determine the impact that various geometry changes have on the amperometric response in microfluidic flow cells. This was accomplished by first investigating the current distribution of segmented microband electrode arrays to explore the potential and concentration shielding effects in the microchannel. Potential shielding is prevalent with large electrode separation and concentration shielding is observed for close electrode separation. By increasing the number of segments in the array, a resulting contribution of both potential and concentration shielding is evident by the coexistence of high and low activity segments. In addition, patterns were further explored using a three working electrode configuration with on oscillatory reaction in a branched channel configuration. Due to the inherent coupling imposed by the microchannel, synchronization patterns of the current oscillations during Ni dissolution were observed. It was revealed that the coupling strength can be tuned by changing the total resistance of the cell and the relative placements of the downstream electrodes in the branched channels. With increasing coupling strength, transition to full synchrony is observed. By changing the relative positions of the downstream electrodes the coupling topology can be varied between global (all-to-all) to localized between the upstream and the two downstream electrodes. Delineation of these coupling effects could improve accuracy of electroanalytical detection by proper cell design. |
