Investigation Oxygen Redution Reaction in the Presence of Methanol Using Electrochemical Quartz Crystal Microbalance

초록

Oxygen reduction has been one of the most important electrocatalytic reactions in electrochemical energy conversion, industrial processes, and corrosion.[1] In direct methanol fuel cell operation, methanol crossover through membrane causes the decrease of overall fuel efficiency as well as the deactivation in the performance of cathode.[2,3] In this work, the effect of methanol on oxygen reduction reaction was investigated by measuring the in-situ mass changes on platinized Pt electrode. Polycrystalline Pt was electrodeposited on 9MHz At-cut Pt quartz crystal and used as cathode. In the presence of oxygen, cyclic voltammogram(CV) in 1.0M H2SO4 indicates that strongly adsorbed oxygen on Pt surface occupies the hydrogen adsorption sites at lower potential and cannot be reduced even in oxygen reduction potential range. Figure 1 shows the cyclic voltammogram performed at hydrogen adsorption/ desorption region with different concentration of methanol. Hydrogen adsorption/desorption currents are substantially decreased with the increase of methanol concentration. Adsorbed methanol and/or intermediate species, CO, formed in the dehydrogenation of methanol are responsible for the current decrease and the suppression of oxygen adsorption take place simultaneously. Accompanying mass changes are shown in Figure 2 and the adsorption of reaction intermediate becomes more evident above 1M CH3OH. Simultaneous measurement of current and mass variations at different cathodic potentials suggests that adsorbed reaction intermediate occupies more sites than adsorbed OH.