Characterization of bubble formation in microfluidic fuel cells employing hydrogen peroxide

In order to examine bubble evolution and discuss the effects of bubbles effect on the performance of microfluidic fuel cells, two 1.2-mm-depth microfluidic fuel cells employing 0.1-M H₂O₂ dissolved in 0.1-M NaOH solution and 0.05-M H₂SO₄ solution as fuel and oxidant, respectively, with transparent lids having width of 1.0 mm and 0.5 mm, are fabricated in the present study for both cell performance measurement and flow visualization. The results show that the present cells operating at either a higher volumetric flow or a smaller microchannel width yield both better performance and more violent bubble growth. The bubble growth rate, Q_g, in a given microfluidic fuel cell is almost the same at different regions of that cell at a given volumetric flow rate, i.e. 10⁻⁵ cm³ s⁻¹ and 5 × 10⁻⁵ cm³ s⁻¹, respectively, for cells having widths of 0.5 mm and 1.0 mm at Q_l = 0.05 mL min⁻¹, and slightly increases at higher volumetric flow rates. Furthermore, the present study reports approximately constant values of Q_g/C_dA at various volumetric flow rates, which are 2 × 10⁻² and 5 × 10⁻² cm³ s⁻¹ A⁻¹, respectively, for cells having channel widths of 0.5 mm and 1.0 mm. In addition, the 0.5-mm-wide cell has higher cell output and performs more tortuous polarization curve.