2003). This was achieved with a channel only 750W and 400H, and power output remained consistent despite tests using 2M, 4M, and 8M methanol solutions as fuels (Lu et al. 2003). This shows that temperature has a much higher influence on performance than fuel solution or rate.
A more recent and in many ways more innovative use of silicon materials, in combination with others, shows potential to further increase the efficacy and efficiency of micro direct methanol fuel cells. By utilizing high-aspect-ratio carbon nanotubes as fuel delivery and reaction area structures for either the cathode or anode end of a micro direct methanol fuel cell, the reaction area and thus the efficiency of the fuel cell can be greatly increased (Wu et al. 2008). Though this conclusion has yet to be borne out by direct observational evidence, initial experimentation has shown that these nanotubes can be controlled in their growth to produce consistent and effective fuel channels ranging from 100H 10 150H, 80W to 100W, and only 3L-5L. (Wu et al. 2008). This network of micro fuel channels would allow for far greater control of fuel flow and will also increase the exposure of the fuel to the fuel cell (and vice versa), increasing fuel efficiency and ultimately energy production, as the researchers predict with careful addendums (Wu et al. 2008).
None of the current research into these increasingly smaller and more productive micro direct methanol fuel cells would be possible, of course, were it not for foundational work that first developed and described this emerging technology. The essential quality of the micro direct methanol fuel cell design is that it is a pumpless and totally energy-independent system; as long as a fuel supply is maintained the cell will operate through gravitational forces, capillary action, and natural buoyancy and air movement (Mench et al. 2001). The fact that it requires no purposeful energy to operate is key to the continued interest in these fuel cells.
It is this feature that makes micro direct methanol fuel cells so attractive in very small applications, and that allows for the ever-decreasing size of the fuel cells themselves. The creation of micro direct methanol fuel cells on printed circuitry boards has even been achieved, with fairly encouraging results; though temperatures were at 80C, improving performance vastly over room temperature performance according to previous research, the fact that stacked eight cell system was able to produce 180mW/cm2 with channels only 200W and a fuel of 2M methanol shows a high efficiency and energy output per the amount of fuel consumed (Lim et al. 2006). Utilizing microtechnologies to further control the flow rate and exposure of fuel in micro direct methanol fuel cells has increasing benefits in fuel efficiency and in ultimate energy output, and it is expected that a similar system operating at room temperature, though undoubtedly reduced in its efficiency, would show greater energy output than many other devices with similar fuel consumption rates (Lim et al. 2006).
As the capabilities to produce smaller channels for fuel delivery increase, fuel efficiency in micro direct methanol fuel cells is also expected to rise. The ability to control fuel flow in these microstructures is essential to increasing efficiency, and it cannot be easily achieved through mechanical movement. The alteration of the fuel delivery system and the environment in which the micro direct methanol fuel cells operate through design will lead to greater levels of efficiency.
Kamitani, a. Morishita, S.; Kotaki, H.; Arscott, S. (2008). "Miniaturized microDMFC using silicon microsystems techniques: performances at low fuel flow rates." Journal of micromechanics and microengineering 18.
Lim, S.; Kim, S.; Kim, H.; Ahn, J; Han, H.; Shul, Y. (2006). "Effect of operation parameters on performance of micro direct methanol fuel cell fabricated on printed circuit board." Journal of power sources 161, pp. 27-33.
Lu, G.; Wang, C. Yen, T.: Zhnag, X. (2003). "Development and characterization of a silicon-based micro direct methanol fuel cell." Electrochimica Acta 49, pp. 821 -- 828.
Mench, M.; Wang, Z.; Bhatia, K.; Wnag, C. (2001). "Design of a micro direct methanol fuel cell." Proceedings of the IMECE'01 International Mechanical Engineering Congress and Exposition (IMECE) New York, New York USA November 11-16, 2001.