Dear Researchers
I am studying the fundamental knowledge of fuel cell system recently and I would like to understand the role and the function of Nafion used in the fuel cell. I already know that Nafion can be added inside or on the surface of the catalyst layer. But I have some doubts as follows:
1. Why using Nafion can effectively reduce the amount of catalysts such as Pt?
2. What are the functions of adding Nafion inside the catalyst layer or on the surface of the catalyst layer?
3. What's the situation of real industrial applications in terms of Nation usage and optimal contents?
Can anyone provide answers, discussions, or relevant research materials in accordance with the above questions? I would be thankful for your help.
Best regards
Yun
Dear Yun Liu , Nafion has different roles or functions when used in fuel cells, it acts as electrolyte or the mean where ions move and also acts as a barrier membrane that keeps the gases supplied to anode and cathode semicells separated, in fact Nafion is a Polymer Electrolyte Membrane (PEM). Its PTFE backbone gives to Nafion its high chemical, mechanical and thermal resistance, so that it can withstand the harsh conditions of operation of fuel cells. The hydrophilic nature of the sulfonate groups favours the increase of ionic conductivity with the presence of water.
Probably this last point is the reason you could get the same current with less catalyst, the Nafion membrane makes the H+ ions (or other cations) move faster, and leaving the catalyst ready for a new cycle. You can see it as a way to avoid (protons or cations) "traffic jams".
About the real use of Nafion you could have a look to the folloing links:
https://www.factmr.com/media-release/1631/global-nafion-market
https://marketresearch.biz/report/nafion-market/
Hope it helps.
I add this to above answer that Nafion can also act as a stabilizer for nanomaterial that prevent aggregation hence narrow size distribution could achieve and smaller size distribution means higher surface for lower amount of catalyst. That is why it could reduce the amount of catalyst.
Dear all, nice details are summerized by Dr. Manuel Gómez. The attached chapter is an additional support. My Regards
1) Ionic conductance of protons to active sites is necessary for electrochemical reaction (the so-called three-phase interface), and Nafion provides this. The membrane provides the protons but it would essentially be a 2D electrode without the ionomer.
2) In addition to providing ionic conductivity, Nafion also provides flexibility & cohesion of the catalyst layer to maintain electronic conductivity long-term. Its content and the coating method and/or composition especially the dielectric of the coating ink impacts the mesoporosity of the catalyst layer, which impacts oxygen and water transport, critical for high performance catalyst layers, especially when reducing loading (i.e. making 'more active' active sites requiring improved oxygen influx and water efflux).
3) 30 wt% of solids is the answer across a large range of temperatures, catalysts, humidities and use-cases. There's some argument for +5% going to hot and/or dry conditions and -5% for cool and/or wet conditions but 30 wt% is definitely the initial go-to. If you're looking at Nafion/PFSA alternatives, do a density correction and reduce wt% to maintain a charge/volume ratio (they're all ~2 g/mL, whereas hydrocarbons e.g. are 1-1.2 g/mL and partially fluorinated materials somewhere in between). I have a pet methodology for IEC equivalents in my thesis appendix replacing F for H and re-calculating that I like even more to correlate properties but density correction gets you most of the way there.
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