Use of electropolymerized films of macrocyclic compounds in direct methanol fuel cell components

Electropolymerized Co(III) and Ru(II)(CO)(2-aminophenyl)porphyrins (poly[Co(III)] and poly[Ru(II)]) were used as catalysts in a direct methanol fuel cell for the reduction of oxygen at the cathode and the oxidation of methanol at the anode, respectively. Although the half-wave potentials for oxygen reduction are +0.3 and +0.55V when using poly[Co(III)]/C and Pt/C, respectively, as catalysts, higher limiting currents can be obtained with the non-noble metal catalyst. Moreover, the macrocyclic catalyst is 10-fold less prone to methanol poisoning than the one based on Pt. The H₂O ₂ yields obtained during oxygen reduction, as measured by the RRDE technique, were 1.9, 4.1 and 2.3% for poly[Co(III)]/C, Pt/C and for a commercial heat-treated Co(III)porphyrin. Methanol oxidation with a catalyst consisting of Pt and poly[Ru(II)] was characterized by a higher limiting current (i _L=13mA/cm², E_1/2=+0.6V) than that obtained with a commercial Pt-Ru catalyst (i_L=4mA/cm², E _1/2=+0.5V) although the same Pt content was used in the two cases (1mg/cm²). Experiments conducted in a fuel cell configuration confirmed the half-cell results and indicated that better distribution of the catalysts in the porous structure of the electrodes and reduction of methanol crossover through the membrane are necessary in order to improve the performance of the cell.