Oscilações de Potencial em Células a Combustível a Ácido Fórmico Direto

The understanding of how the electro-oxidation of formic acid occurs is of great importance for its application as fuel in Direct Formic Acid Fuel Cell (DFAFC). Some peculiarities of this reaction are the presence of kinetic instabilities under specific conditions and, for a given temperature range, negative apparent activation energy is observed under oscillatory condition.1,2Here we report an experimental study of the oscillatory electro-oxidation of formic acid at a DFAFC. It is worth noting that the cathode in this case acts as a reference for the characterization of the anode process only. Fig.1 shows the polarization curves andthe expected improvement in the performance of the DFAFC with increasing temperature. When the system is controlled galvanostaticallysustainedpotentialoscillations emerge for all temperatures studied. Fig. 2 presents an example of potential time-seriesobtainedat 50oC. In the window of evaluated temperatures only the typical Arrhenius behavior shown in Fig. 3 was verified, that is, with the increase of the temperature there is an increase in the oscillatory frequency. By means of the Arrhenius graph, it was also possible to estimate the apparent activation energy (Eapp) for the electro-oxidation of formic acid over Pt/C under regular and under oscillatory regime, ≈ 50 kJ mol-1and ≈ 120 kJ mol-1respectively.