Micro-Fabrication of a Compact Air-Breathing Microfluidic Fuel Cell and Its Electrochemical Evaluation for Formic Acid and Glucose

Microfluidic fuel cells (μFFC) are emerging as a promising solution for small-scale power demands. Some fuels frequently used in microfluidic fuel cells are formic acid [9–13], methanol [14,15] and glucose [16–18]. This work reports the air-breathing μFFC evaluation using 1.5 M formic acid in 0.5 M H₂SO₄ or 5 mM Glucose in KOH as fuels and the integration of an air-exposed electrode as cathode enabling oxygen delivery directly from air.

The formic acid μFFC  employed Pd/XC-72 and Pt/XC-72 as electrocatalyst for anode and cathode respectively. Moreover, Au/C and Pt/XC-72 were employed as anode and cathode respectively for the glucose μFFC.

Both μFFCs were assembled using a polymethylmethacrylate (PMMA) plate where the microfluidic channel was engraved as shown in figure 1. Polarization curves were obtained from an Epsilon/Bas potentiostate 1.40.67 (Bioanalytical Systems).

Fig. 1. Schematic diagram of the air-breathing  μFFC. All elements were assembled and tightened homogeneously by screws. The μFFC microchannel is 900 µm wide, 2 cm long and 50 µm depth; the electrode active area is 0.09 cm².

The maximum power densities achieved were 27 mW cm^-2 for the formic acid μFFC and 1.63 mW cm^-2 in the case of glucose μFFC. These results have shown that the oxygen reduction reaction have been enhanced by the air-breathing adaptation in comparison with similar acid formic or glucose-μFFCs which operate with an oxygen-saturated aqueous stream.