rate. This type of cell is not a two stream laminar flow fuel cell. Since the formation of bubbles can disrupt two separate laminar flows, a combined stream of fuel and oxidant was used. In laminar conditions, mixing will still not occur. It was found that using selective catalysts (i.e. Not platinum) or extremely low flow rates can prevent crossover. Scaling Issues Membraneless fuel cells are currently being manufactured on the micro scale using fabrication processes found in the MEMS/NEMS area. These cell sizes are suited for the small scale due to the limit of their operating principles. The scale-up of these cells to the 2–10 Watt range has proven difficult since, at large scales, the cells cannot maintain the correct operating conditions. For example, laminar flow is a necessary condition for these cells. Without laminar flow, crossover would occur and a physical electrolytic membrane would be needed. Maintaining laminar flow is achievable on the macro scale but maintaining a steady Reynolds number is difficult due to variations in pumping. This variation causes fluctuations at the reactant interfaces which can disrupt laminar flow and affect diffusion and crossover. However, self-pumping mechanisms can be difficult and expensive to produce on the macro-scale. In order to take advantage of hydrophobic effects, the surfaces need to be smooth to control the contact angle of water. To produce these surfaces on a large scale, the cost will significantly increase due to the close tolerances which are needed. Also, it is not evident whether using a carbon-dioxide based pumping system on the large scale is viable. Membraneless fuel cells can utilize self-pumping mechanisms but requires the use of fuel which release GHG's (greenhouse gases) and other unwanted products. To use an environmentally friendly fuel configuration (such as H2-O2), self pumping can be difficult. Thus, external pumps are required. However, for a rectangular channel, the pressure required increases proportional to the L−3, where L is a length unit of the cell. Thus, by decreasing the size of a cell from 10 cm to 1 cm, the required pressure will increase by 1000. For micro fuel cells, this pumping requirement requires high voltages. Although in some cases, Electroosmotic flow can be induced. However, for liquid mediums, high voltages are also required. Further, with decreasing size, surface tension effects also become significantly more important. For the fuel cell configuration with a carbon dioxide generating mechanism, the surface tension