A versatile planar membraneless microchannel fuel cell (PMMFC) device platform will be presented. The design eliminates the need for a polyelectrolyte membrane (PEM) and takes advantage of laminar flow of fuel and oxidant streams. Diffusion at the interface is the only mode of mass transport between the two solutions. In addition, ion conduction occurs readily, and fuel crossover is virtually eliminated. The planar design also gives rise to large contact areas between the electrodes and fuel/oxidant streams. Platinum evaporated onto polyamide films (KaptonŽ) was employed as large area electrodes. Silicon microchannels of varying dimensions were fabricated and tested. Using the PMMFC described above, an asymmetric dual electrolyte H2/O2 fuel system was investigated and compared to single electrolyte H2/O2 systems under analogous conditions. The fuel was H2 dissolved in 0.1M KOH, and oxidant was O2 dissolved in 0.1M H2SO4, comprising a system with a calculated thermodynamic potential > 1.9V. This value surpasses the calculated thermodynamic maximum of 1.23V for an acid, or alkaline, single electrolyte H2/O2 system. Experimentally, open-circuit potentials greater than 1.4V have been achieved with the dual electrolyte system. Power generation of 0.6 mW/cm2 from a single device was measured, which is nearly 0.25mW/cm2 greater than values obtained for single electrolyte H2/O2 systems studied. Preliminary studies of the use of sodium borohydride as a fuel and hydrogen peroxide as an oxidant in a dual electrolyte configuration will also be presented.