Abstract
There have been several reports concerning the performance improving properties of additives, such as polyvinylidene difluoride (PVDF), to the membrane or electrocatalyst layer of proton exchange membrane fuel cells (PEMFC). However, it is not clear if the observed performance enhancement is due to kinetic, mass transport, or anion blocking effects of the PVDF. In a previous investigation using a thin-film rotating disk electrode (RDE) approach (of decreased complexity as compared to membrane electrode assembly (MEA) tests), a performance increase for the oxygen reduction reaction (ORR) could be confirmed. However, even in RDE measurements, reactant mass transport in the catalyst layer cannot be neglected. Therefore, in the present study, the influence of PVDF is re-examined by coating polycrystalline bulk Pt electrodes by PVDF and measuring ORR activity. The results on polycrystalline bulk Pt indicate that the effects of PVDF on the reaction kinetics and anion adsorption are limited, and that the observed performance increase on high surface area Pt/C most likely is due to an erroneous estimation of the electrochemical active surface area (ECSA) from CO stripping and Hupd.
Highlights
Efficient energy converters, such as the proton exchange membrane fuel cell (PEMFC), are integral parts in an environmentally friendly hydrogen economy
The effect of polyvinylidene difluoride (PVDF) can be scrutinized by comparing the different cyclic voltammograms (CVs) in the respective potential regions
We have examined oxygen reduction reaction (ORR) on polycrystalline Pt with different amounts of PVDF deposited
Summary
Efficient energy converters, such as the proton exchange membrane fuel cell (PEMFC), are integral parts in an environmentally friendly hydrogen economy. A performance enhancement of PEMFCs by including additives such as polyvinylidene difluoride (PVDF) into the membrane has been reported [7]. If such studies are performed in single cell membrane electrode assembly (MEA) tests, it is very difficult to analyze the origin of observed performance increases. This is due to the complexity of the MEA system and the influence of multiple structural aspects on its performance. The specific oxygen reduction reaction (ORR) activity established by RDE in phosphoric acid electrolytes was found to improve when the catalyst layer contained PVDF. This system excludes any influence of catalyst film properties, and focusses on the interface between catalyst and electrolyte
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