Micro direct methanol fuel cells and their stacks using a polymer electrolyte sandwiched by multi-window microcolumn electrodes

In this paper, we present a micro-DMFC (Direct Methanol Fuel Cell), whose uniform contacts at electrode–electrolyte interface is achieved by supporting structures on the back-side of the microcolumn electrodes (multi-window electrode), and an integrated serial stack structure using pair-electrodes and skew-symmetrical configuration for minimal voltage drop in cell interconnections. We fabricate a set of single DMFC with three different types of the multi-window electrodes, having an identical projected electrode area of 10 mm × 10 mm: the 4-window microcolumn electrode (ME4), the 16-window microcolumn electrode (ME16) and the 16-window planar electrode (PE16). The 2- and 4-cell stacks have been fabricated in the integrated stack structure, where the common polymer electrolyte is sandwiched by the ME16 electrode pairs. In the experimental study, the single cells with ME16 and PE16 electrodes show the maximum power densities of 31.04 ± 0.29 μW/cm2 and 9.75 ± 0.29 μW/cm2, respectively; thus indicating the microcolumn electrode (ME16) generates the power density 3.2 times higher than the planar electrode (PE16) does. The single cell tests of ME16 and ME4 electrodes show the maximum power of 31.04 ± 0.29 μW/cm2, and 25.23 ± 2.7 μW/cm2, respectively; thus demonstrating the increased multi-window frame reduces the normalized standard power deviation (standard deviation over the average power). The normalized deviation of 0.11 in ME4 cell has been reduced to 0.01 in ME16 cell due to the increased window frames. The 2-cell and 4-cell stacks show the maximum power density of 92.6 ± 0.31 μW/cm2, and 329.8 ± 0.47 μW/cm2, respectively. The maximum power density of 4-cell stack is 15.7 times higher than that of the single cell, indicating that the present integrated serial stack structure is effective for accumulating cell power.