Electrochemical Flow Reactors: Mass Transport, iR Drop, and Membrane-Free Performance with In-Line Analysis

Continuous flow reactors are promising for electrochemical conversions, in large part due to the potentially rapid refreshment of reagents over the electrode surface. Microfluidic reactors enable a high degree of control over the fluid flow. Diffusion to and from the electrode and electrode area determine the efficiency of electrochemical conversion. The effective electrode area is limited by the loss in electrode potential due to iR drop, and further electrode length (and hence area) is limited due to ineffective mass transport to and from the electrode. Here, we report on a microfluidic electrochemical device with large (long) area electrodes running in parallel, which both minimizes the iR drop and ensures a constant electrode potential along the whole length of the electrodes. The electrodes are separated by laminar flow in the channels, instead of by a membrane, thereby reducing cell resistance. Herringbone grooves are used to increase mass transport rates by inducing transverse flow. We confirm fluid flow behavior in the devices using computational fluid dynamics (CFD) and verify the results experimentally using in-line and off-line UV/vis absorption and resonance Raman spectroscopy. We anticipate that this approach will aid future development of electrochemical flow reactors, enabling larger area-electrodes and realizing greater efficiencies.