Diffusion layer future direction

Another important parameter that has to be taken into account when choosing the appropriate diffusion layer is the overall cost of the material. In the last few years, a number of cost analysis studies have been performed in order to determine fuel cell system costs now and in the future, depending on the power output, size of the system, and number of xmits. Carlson et al. [1] reported that in 2005 the manufacturing costs of diffusion layers (for both anode and cathode sides) corresponded to 5% of the total cost for an 80 kW direct hydrogen fuel cell stack (assuming 500,000 units) used in the automotive sector. The total value for the DLs was US 18.40 m-, which included two carbon cloths (E-TEK GDL LT 1200-W) with 27 wt% P ILE, an MPL with PTFE, and Cabot carbon black. Capital, manufacturing, tooling, and labor costs were included in the total. 

Another important future area for diffusion layers is the use of three-dimensional catalyzed diffusion layers for liquid-based fuel cells. This allows the three-phase active zone to be extended into the diffusion layer to increase performance and utilization and reduce crossover [276,277]. Recent work by Lam, Wilkinson, and Zhang [278] has shown the scaleable use of this concept to create a membraneless direct methanol fuel cell. In other work by Fatih et al. [279], the... 

In a future, ideal enzyme biosensor, the enzymes would be immobilised in such a way that aU the enzyme molecules react with enzyme substrate diffusing easily from solution into the enzyme layer and the products of the enzyme reaction reach the sensor transducer surface without any diffusion limitations, which leads to efficiencies approaching 100 %. Ideally, there should be no redox mediator and direct electron transfer occurs. Two recent examples are a biosensor platform based on lactate oxidase where characterisation was done by AFM and SECM [65] and glucose oxidase using functionalised nanotubes within a dihexadecylphos-phate film (DHP) [66]— in this latter case, SEM shows clearly CNTs distributed homogeneously in the DCP film. Fig. 6.8. 

The ability of nanopores to deliver multiple analytes to pattern a surface is demonstrated in Figure 11.15. In this study, small-scale reproductions of famous pictures were recreated with the localized delivery of fluorescently labeled DNA strands from a double-barrel nanopipette. The two individually addressable barrels of a theta pipette allow independent delivery of different analytes from each barrel directly to a surface. This study was accomplished in air, and this environment leads to smaller feature sizes from the lack of lateral diffusion found in bath solutions. The control of deposition necessary to reproduce such detailed images comes from the potential-controlled delivery described previously. In the future, nanopipettes with more than two barrels may be used to deliver an even greater number of different analytes from each pore to produce surface patterns that are more complicated and layered. 

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