Microfluidic fuel types

Miniaturized fuel cells are an attractive candidate for next-generation portable power sources. A microfluidic fuel cell is defined as a fuel cell with smaU-scale channels, typically submiUimeter in height, in which reactant delivery/removal and electrochemical energy conversion take place. This type of fuel cell can be incorporated with both metalhc and biological catalysts and normally operates without a physical barrier between anode and cathode compartments. Micromachined fuel cells employing ion-conducting membranes are not covered in this entry. 

Microfluidics is a relatively new branch of contemporary physics. It deals with fluid flow and transport phenomena in microstructures with at least one characteristic dimension in the range 1 to 1000 J,m. A microfluidic fuel cell (pFl-FC) (also called a membraneless fuel cell or laminar flow fuel cell) is a type of fuel cell in which all essential functions (i.e., reactant delivery, current-producing electrochemical reaction, and product removal) are conflned to a microfluidic channel. 

This relationship is valid for fully developed flow in a straight channel and does not include the contributions from inlet and outlet feed tubes and minor losses due to ports, bends, expansions/contractions, steps, comers, etc. In most microfluidic fuel cell designs, however, relatively long thin channels are applied where friction losses of the type described by Eq. (2.6) are known to dominate. 

Because of the higher energy density and better safety of liquid fuels compared with gaseous hydrogen, the types of fuel cell under active development usually includes direct methanol fuel cells (DMFCs) [4], direct formic acid fuel cells (DFAFCs) [5], proton exchange fuel cells (PEMFCs) run by hydrogen generated from metal hydride [6], and membraneless microfluidic fuel cells [7]. 

Research in laser micromachining wiU continue to new methods for the fabrication of microfluidic devices, particularly from polymers and glass. The development of 3D channel networks is important for numerous fluidic applications which wiU fuel the future demand for more research in this area. As these methods are refined, the processes wiU be tailored to processing of many different types of polymers. Future work will continue to seek methods to decrease the roughness of microchannels. 

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... 

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