*3.3. Microfluidic Fuel Cell Performance*

A microfluidic fuel cell was used for testing samples to verify their activity under real operating conditions, using 0.5 M formic acid with 0.5 M H2SO4 as the electrolyte for the anodic reaction. Three materials have been tested, namely, PdA-MMT, PdA-CON, and the commercial Pd/C catalysts used as reference materials. Linear sweep voltammetry is a specific electrochemical protocol to discriminate the catalytic activity of the anode materials. The microcell works by pumping 200 μL min−<sup>1</sup> of the electrolyte fuel (0.5 M HCOOH in 0.5 M H2SO4) into the anode, and 200 μL min−<sup>1</sup> of only 0.5 M H2SO4 into the Pt/C cathode. Both electrodes were normalized to a mass charge of 0.1 mg of each material over an area of 0.019 cm2. The polarization curves were obtained for stable open circuit voltage (OCV) and values registered for the PdA-MMT, Pd/C, and PdA-CON samples were 0.88, 0.9, and 0.84 V, respectively. The power density obtained in Figure 7f shows favorable results for the aerogel obtained by MW heating. Small bubbles could be detected on the anode during the experiment, corresponding to the generation of hydrogen. The mass current of the PdA-MMT aerogel is almost three times higher than the commercial Pd/C catalyst (i.e., Figure 7e), corroborating, again, the superior performance of the aerogels obtained by using microwave heating during the synthesis. The superior catalytic activity of PdA-MMT may be attributed to the most active Pd surface. The use of microwave heating during the

synthesis of the aerogels leads not only to a better morphology of the aerogels but also to a higher content of metallic Pd0. Previous studies reveal that Pd2+ species are catalytically inactive for FAO [41]. Therefore, the use of microwave heating has a determinant influence on the production of effective Pd aerogel catalysts.

Table 3 shows the performance of other microfluidic devices from the bibliography in comparison with the one used in this work with the Pd catalyst obtained by the innovative method presented. It may be observed that the configuration used in this work using PdA-MMT as anodic material allows to obtain extremely higher yield per mass of catalyst in terms of density power.

**Table 3.** Anodic catalyst comparison.

