Miniaturized microDMFC using silicon microsystems techniques: performances at low fuel flow rates

This paper reports the design, fabrication and characterization of high performance miniaturized micro direct methanol fuel cells (microDMFC) functioning at room temperature under a forced low input fuel flow rate (<10 µL min^-1) fabricated using silicon microsystems techniques. A room temperature maximum power output of 12.5 mW cm^-2 has been measured at a fuel flow rate of 5.52 µL min^-1 for a fuel cell surface area as small as 0.3 cm² (corresponding to a fuel use efficiency of 14.1% at 300 K). At a lower flow rate of 1.38 µL min^-1, the fuel use efficiency rises to 20.1% although the power density falls to 4.3 mW cm^-2. The study revealed that improved room temperature cell performances in terms of power density can be achieved at low flow rates (<10 µL min^-1) by (i) reducing the fuel cell area and (ii) reducing the microchannel cross-section. The study also revealed that higher fuel use efficiencies are obtained at lower fuel flow rates. Fuel (methanol) for the anode and an oxidant (air) for the cathode are supplied via a compact serpentine network of micron-size microfluidic and gas microchannels; by using silicon microsystems techniques we also render the fuel cell compatible with other silicon technologies such as microelectronics and micro- and nanoelectromechanical systems (MEMS/NEMS).