Ov

El Fl(G

Steady-state methanol oxidation studies were done in 2M MeOHfl).5M H2S04 solution. An initial step to -50mV was performed to reduce surface oxides and then each electrode was subjected to a series of potentiostatic steps; a 10 minute time period was used to reach the steady-state current of methanol oxidation at each potential.

Dispersed catalysts:

Pt, Pt-Ru(50:50) and Pt-Ru-Os(65:25:10) catalysts were prepared by reduction of aqueous H2PtCl6, RuC13, OsCI3. AH catalysts showed single phase FCC XRD patterns. Membrane electrode assemblies were fabricated with the catalysts and tested in liquid feed direct methanol fuel cells.

RESULTS:

Figure 5 shows the CV obtained on a Pt-Ru-Os(65:25:10) electrode as the potential was swept to 0 V and then to 1,2V after dosing CO at 0.3 V. On the first scan, the hydrogen oxidation charge (QhC°) is limited by the presence of adsorbed CO. On the second scan, the maximum hydrogen oxidation charge (Qh11) is obtained since the CO^ is oxidized during the first scan. In Figure 6 the value of Y^Qh -Qh^VQh1 (O^P^l) is used as a measure of CO poisoning for each electrode. Based on x¥, the ternary alloy Pt-Ru-Os(65:25:10) is the most resistant to CO

poisoning, with Pt-Ru(50:50) and Pt-0s(80:20) slightly worse. As shown in the Figure 7, Pt-Ru(5():50) and Pt-Ru-Os(65:25:l(l) exhibited tlie lowest potentials for methanol oxidation and the highest steady-state currents', below 0.6V. tlie steady-state activity was similar for Pt-Ru(50:50) and Pt-Ru-Os(65:25:H)) with tlie latter exhibiting better performance at overpotentials above 0.6V. Pt had tlie highest onset potential for methanol oxidation and lowest methanol oxidation currents.

0 0

Post a comment