Real-time determination of CO2 production and estimation of adsorbate coverage on a proton exchange membrane fuel cell under oscillatory operation

The oscillatory electro-oxidation of 2-propanol on platinum: the effect of temperature and addition of methanol

The oscillatory electro-oxidation of 2-propanol on platinum and platinum-based catalysts has attracted growing attention in recent years due to its importance in the interconversion between chemical and electrical energies. This reaction might proceed with a very high selectivity to acetone, nearly without the formation of carbon dioxide, and the reversibility of the 2-propanol/acetone pair is very appropriate for hydrogen transfer. An important aspect of this system is the ubiquitous emergence of potential oscillations under current control, and it has been pointed out as a problem to be avoided and a primary cause of limitations to the use of 2-propanol in practical devices. Herein, we present an experimental study of the electrochemical instabilities in the electro-oxidation of 2-propanol on platinum. The system was studied using polycrystalline platinum, in acidic media and at different temperatures. Besides the extensive characterization of the potential oscillations, we have also discussed possible venues for engineering the dynamics to benefit from the potential oscillations. In this sense, we have also characterized the instabilities in the system containing a mixture of 2-propanol and methanol. The efficiency of a hypothetical fuel cell operated under different conditions is also presented.

Voltage Oscillations in a Polymer Electrolyte Membrane Fuel Cell with Pd-Pt/C and Pd/C Anodes

Polymer electrolyte membrane fuel cells (PEMFC) fed with H₂ contaminated with CO may exhibit oscillatory behavior when operated galvanostatically. The self-organization of the anodic overpotential is interesting because it can be accompanied by an increase in the average performance. Herein we report experimental studies of voltage oscillations that emerge in a PEMFC equipped with a Pd/C or PdPt/C anode and fed with H₂ contaminated with CO (100 ppm). We used on-line mass spectrometry to investigate how the mass fragments associated with CO₂ and CO (m/z 44 and 28, respectively) varied with the voltage oscillations. Overall, we observed that oscillations in the anodic overpotential are in phase with that of the CO and CO₂ signals. This fact is consistent with an autonomous adsorption-oxidation cyclic process. For both anodes, it has been observed that, in general, an increase in current density implies an increase in oscillatory frequency. By using CO stripping, we also discuss how the onset of CO oxidation is related to the maximum overpotential reached during a cycle, whereas the minimum overpotential can be associated with the catalytic activity of the electrode for H₂ oxidation.