Design of a Passive and Portable DMFC Operating in All Orientations

A microfluidic layout concept for passive and portable direct methanol fuel cells (DMFCs) is presented. We proofed this concept by developing a DMFC that continuously runs for 40 hours in all orientations without the need for any active components such as pumps or valves. In contrast to our previous work [1], the system now is truly portable. In any orientation of the DMFC, a bubble driven self regulating supply mechanism safely removes carbon dioxide and transports at least 3.5 times more methanol to the anode than critically needed to sustain DMFC operation. On the cathode, diffusive oxygen supply and the transport of the reaction product water along a capillary gradient out of the DMFC ensures a stable performance. Compared to our previous work [1], the power output was increased by a factor of 2.5 and reached p = 5.5 mW cm^-2. A stable power output for 40 hours of p = 4 mW cm^-2 was achieved for the preferred vertical position with bubbles moving against buoyancy forces. In the most challenging horizontal position with the anode facing downwards, a power output of at least p = 3.1 mW cm^-2 was reached for the same period of time.