Flow cell porous silicon

Another way to use silicon wafers as DLs was presented by Meyers and Maynard [77]. They developed a micro-PEMFC based on a bilayer design in which both the anode and the cathode current collectors were made out of conductive silicon wafers. Each of fhese componenfs had a series of microchannels formed on one of their surfaces, allowing fhe hydrogen and oxygen to flow through them. Before the charmels were machined, a layer of porous silicon was formed on top of the Si wafers and fhen fhe silicon material beneath the porous layer was electropolished away to form fhe channels. After the wafers were machined, the CEs were added to the surfaces. In this cell, the actual diffusion layers were the porous silicon layers located on top of the channels because they let the gases diffuse fhrough fhem toward the active sites near the membrane. 

The small dimensions in microreactors imply the presence of laminar flow. This type of flow makes it easier to extract chemical kinetic parameters and fully characterize phenomena. The correct incorporation of the active catalyst onto the surface of the membrane is one of the important aspects of catalytic microreactors. Drott et al. (1997) investigated the use of porous silicon as a carrier matrix in microstructured enzyme reactors. The matrix was created by anodization and the fabrication of the microreactor used flow-through silicon cell comprising 32 channels of 50 pm wide, 250 pm deep and separated by 50 pm. The aim was to increase the surface area on which the enzymes (glucose oxidase) could be coupled. Comparisons were made with the classical non-porous reference device and the glucose turnover rates. The results showed that when compared with the reference reactor the enzyme activity increased 100-fold. 

Miniaturization of fuel cells (FC) can offer a possibility in the field of small energy sources. Many silicon-based technologies can be used to perform micro-fuel cells and, in particular, porous silicon. In this chapter, after general consideration on fuel cells, we describe the state of the art of porous silicon integration in micro-fuel cells. In particular, we show how porous silicon has arisen as a promising material to perform many functions necessary to the core fuel cell such as proton exchange membrane, gas diffusion layer and catalyst support or flow fields. The performances of the several final devices reported in the literature are discussed. 

Wei X, Mares JW, Gao Y, Li D, Weiss SM (2012) Biomolecule kinetics measurements in flow cell integrated porous silicon waveguides. Biomed Opt Express 3(9) 1993-2003... 

Microstructured Hydrogen Fuel Cells, Figure 2 Examples of microstructures for hydrogen fuel cells (a) microchannel flow field (b) silicon microma-chined diffusion media with porous coating for water management (c) silicon pillars as electrode stnjctures (d) porous silicon as a membrane support... 

This DMFC provides a closed-system operation-. Fuel cell designers believe that the porous silicon electrodes can be easily assembled into cells and stacks with minimum separation. The CFfjOFI fuel and the oxidant react at the catalyst locations in the porous silicon structure to generate electrical energy. After completion of the electrochemical reaction, leftover or residual fuel can be removed from the cells using a continuous flow of liquid tlirough the electrodes. 

Bottom-up strategies, which employ silicate precursors, such as tetraethoxysi-lane (TEOS), produce porous silicon dioxide. Silicon dioxide is a much more chemically stable interface than silicon, and precludes some forms of surface functionalization, such as carbonization, which is used to tune particle properties. Additionally, bottom-up approaches are hmited to the production of either spherical or ellipsoid particles, unless used in conjunction with top-down lithography. Shape has been shown fundamentally to determine several properties of the particle that are relevant for drug deUvery, such as flow dynamics, margination, degradation rate and cell uptake [21, 22]. For these reasons, top-down approaches to the production of pSi for biomedical applications have been historically favored. 

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