Microfluidic electrochemical cell

Miniaturisation of various devices and systems has become a popular trend in many areas of modern nanotechnology such as microelectronics, optics, etc. In particular, this is very important in creating chemical or electrochemical sensors where the amount of sample required for the analysis is a critical parameter and must be minimized. In this work we will focus on a micrometric channel flow system. We will call such miniaturised flow cells microfluidic systems , i.e. cells with one or more dimensions being of the order of a few microns. Such microfluidic channels have kinetic and analytical properties which can be finely tuned as a function of the hydrodynamic flow. However, presently, there is no simple and direct method to monitor the corresponding flows in. situ. 

Immuchip a disposable cartridge with polymer microfluidic electrochemical cells... 

The reasons to perform electrochemistry, in particular, electrosynthesis, in a microfluidic system are the following (Rode et al., 2009) (1) reduction of ohmic resistance in the electrochemical cell, by decreasing the distance between anode and cathode, (2) enhancement of mass transport by increase of electrode surface to cell volume ratio, also realized by small interelectrode gaps, (3) performing flow chemistry to establish single-pass conversion, and (4) coupling of cathode and anode processes, permitting simultaneous formation of products at both electrodes. The latter... 

Microfluidic electrochemical cells, as shown in Fig. 1.1, employ one laminar stream that contains the fuel (or first reactant) and a second laminar stream that contains the oxidant (or second reactant). As the fuel and oxidant streams flow in a... 

Fig. 3.1 Conceptual schematic of the main parts (microchannel layer, electrodes, and substrate) and assembly (top view) of a microfluidic electrochemical cell...

Fig. 3.4 Sample photograph of an assembled microfluidic electrochemical cell ready for testing and experimentation...

The co-laminar flow principles of microfluidic electrochemical cells enable mixed media operation, in contrast to traditional types of fuel cells aud redox flow batteries operating under all-acidic or all-alkaline conditions imposed by the membranes. The unique mixed media capability allows independent tuning of half-cell conditions for optimization of reaction kinetics and cell potential. In nuxed media conditions, the open-circuit cell voltage can be increased by shifting the reversible... 

Liquid phase reactant chemistries originally developed for redox flow batteries can be exploited to great effect in microfluidic electrochemical cells. Most commonly, vanadium redox flow battery technology utilizes soluble vanadium redox couples in both half-cells for regenerative electrochemical energy storage units [53]. The combination of aqueous redox pairs in vanadium redox cells, and VO V... 

The overall performance of microfluidic electrochentical cells is generally dictated by reactant mass transport limitations. It is also the unique mass transport characteristics of microfluidic cells that distinguish than from the conventional MEA-based cell designs. Therefore, mass transport in nuCTofluidic electrochemical cells is both an interesting and useful subject for research and has spearheaded the contributions towards enhanced cell performance over the past several years. 

Fig. 6.2 Number of journal publications on co-laminar flow-based microfluidic electrochemical cells (including both fuel cells and batteries). Reproduced and adapted with permission from Goulet and Kjeang [37]...

Fundamentally, both MEA-based and membraneless cells require two electrodes with an ionically conductive electrolyte between them. It is therefore proposed that a volumetric power density normalized by the essential volume of the electrochani-cal chamber, including both electrodes and the separating electrolyte, would be the most universally applicable metric for these devices. This metric captures any variations in electrolyte channel separation and electrode thickness with the only assumption being that the inlet/outlet flow field manifolds and other structural support elements are comparable between cells. With this new convention, the key microfluidic electrochemical cell technologies with the highest power densities reported to date were converted where possible and presented in Table 6.1. For comparative purposes, estimates for a typical MEA-based vanadium redox battery (VRB) [17, 18] and a DMFC [19] are also included. 

Table 6.1 Performance data on key microfluidic electrochemical cell technologies... 

The emerging use of microfluidic fuel cells and batteries for analytical applications and educational purposes is also encouraging. The low cost, fabrication flexibility, and unique visualization capabilities inherent to microfluidic cells make them well suited as instructional tools to engage students in the classroom, potentially for a wide variety of courses in the areas of energy conversion and storage, applied chemistry, and microsystems. For analytical applications, standardized units could be produced as a convenient, low-cost platform for in situ lab-scale testing and characterization of electrochemical cell components such as novel electrocatalysts, catalyst supports, and bioelectrodes. Overall, microfluidic electrochemical cells may come to serve equally important functions as analytical and educational tools in addition to commercial utility. 

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