Ex Situ Methanol Oxidation

Methanol oxidation is a self-poisoning process, in which the intermediate adsorbate CO, formed from the dissociation of methanol, poisons the catalytic sites of Pt. The mechanism of methanol oxidation is as follows  

In the circuit, Rs is the electrolyte resistance, CPE indicates the double-layer capacitance, Rc, is the methanol oxidation charge-transfer resistance, while R1 and Cl are the mass transfer related resistance and capacitance (mainly due to methanol adsorption or CO coverage). The physical expression of these parameters can be deduced from the reaction kinetics. In the methanol oxidation reaction, the overall charge transfer rate is the sum of each charge-transfer step (rct). The Faradaic resistance (Rj) equals the inverse of the DC polarization curve slope  

The dependence of the charge-transfer rate on the intermediate coverage and electrode potential gives 

The first term in Equation 6.27 corresponds to the inverse of the charge-transfer resistance, and the second term represents the inverse of the intermediate coverage resistance (Rc)  

According to the equivalent circuit, at zero frequency the Faradaic resistance equals the sum of the charge-transfer resistance and the mass transfer resistance  

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This chapter has examined a variety of EIS applications in PEMFCs, including optimization of MEA structure, ionic conductivity studies of the catalyst layer, fuel cell contamination, fuel cell stacks, localized impedance, and EIS at high temperatures, and in DMFCs, including ex situ methanol oxidation, and in situ anode and cathode reactions. These materials therefore cover most aspects of PEMFCs and DMFCs. It is hoped that this chapter will provide a fundamental understanding of EIS applications in PEMFC and DMFC research, and will help fuel cell researchers to further understand PEMFC and DMFC processes. 

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