Abstract
An air-breathing direct formic acid microfluidic fuel cell, which had a self-made anode electrode of 10 mg/cm2 Pd loading and 6 mg/cm2 Nafion content, was fabricated and tested. The microfluidic fuel cell was achieved by bonding a PDMS microchannel that was fabricated by a soft-lithography process and a PMMA sheet that was machined by a CO2 laser for obtaining 50 through holes of 0.5 mm in diameter. Formic acid of 0.3 M, 0.5 M, and 1.0 M, mixed with 0.5-M H2SO4, was supplied at a flow rate ranging from 0.1 to 0.7 mL/min as fuel. The maximum power density of the fuel cell fed with 0.5-M HCOOH was approximately 31, 32.16, and 31 mW/cm2 at 0.5, 0.6, and 0.7 mL/min, respectively. The simultaneous recording of the flow in the microchannel and the current density of the fuel cell at 0.2 V, within a 100-s duration, showed that the period and amplitude of each unsteady current oscillation were associated with the bubble resident time and bubble dimension, respectively. The effect of bubble dimension included the longitudinal and transverse bubble dimension, and the distance between two in-line bubbles as well.
Highlights
In the past few years, miniature fuel cells without a polymer electrolyte membrane, called membraneless fuel cells or microfluidic fuel cells, have been widely proposed and tested
Before assembling the fuel cell, a 35-mm-long, 1.5-mm-wide, and 0.05-mm-deep microchannel on a PDMS slab was fabricated by a soft-lithography process and a PMMA sheet was machined by CO2 laser for obtaining 50 through holes of 0.5 mm in diameter
Formic acid of 0.3 M, 0.5 M, and 1.0 M, mixed with 0.5-M H2SO4, was fed at a flow rate ranging from 0.1 mL/min to 0.7 mL/min as the fuel and air was inhaled as the oxidant for generating electricity
Summary
In the past few years, miniature fuel cells without a polymer electrolyte membrane, called membraneless fuel cells or microfluidic fuel cells, have been widely proposed and tested. Some of those microfluidic fuel cells operate a co-laminar flow in a microchannel to keep both the fuel and oxidant streams separated, such that both anode and cathode half-cell reactions are able to properly take place at relative catalyst-coated electrodes with slight mixing at the inter-diffusion zone. With a formic acid concentration and electrolyte concentration of 0.5 M and 1.0 M, respectively, their microfluidic fuel cell yielded a peak power density of 21.5 mW/cm at a flow rate of
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