First Insight into Fluorinated Pt/Carbon Aerogels as More Corrosion-Resistant Electrocatalysts for Proton Exchange Membrane Fuel Cell Cathodes

Abstract

International audienceThis study evaluates the fluorination of a carbon aerogel and gives first insights into its durability when used as platinum electrocatalyst substrate for proton exchange membrane fuel cell (PEMFC) cathodes. Fluorine has been introduced before or after platinum deposition. The different electrocatalysts are physico-chemically and electrochemically characterized, and the results discussed by comparison with commercial Pt/XC72 from E-Tek. The results demonstrate that the level of fluorination of the carbon aerogel can be controlled. The fluorination modifies the texture of the carbons by increasing the pore size and decreasing the specific surface area, but the textures remain appropriate for PEMFC applications. Two fluorination sites are observed, leading to both high covalent C-F bonds and weakened ones, the quantity of which depends on whether the treatment is done before or after platinum deposition. The order of the different treatments is very important. Indeed, the presence of platinum contributes to the fluorination mechanism, but leads to amorphous platinum, which is demonstrated rather inactive towards the oxygen reduction reaction. On the contrary, a better durability was demonstrated for the fluorinated and then platinized catalyst compared both to the same but not fluorinated catalyst and to the reference commercial material (based on the loss of the electrochemical real surface area after accelerated stress tests)

Activity and Durability of Platinum-Based Electrocatalysts Supported on Bare or Fluorinated Nanostructured Carbon Substrates

“…89 The synthesis protocol has been thoroughly described in earlier contributions of the authors. 77,90 Briefly, the two precursors, resorcinol (R, 99% C 6 H 6 O 2 , Alfa Aesar) and formaldehyde (F, 37 wt% CH 2 O in aqueous solution stabilized with 10-15 wt% methanol) were mixed with the sodium carbonate (C, 99.9999% Na 2 CO 3 , Sigma Aldrich) catalyst in deionized water with molar ratios F/R = 2, R/C = 200 and 5 wt% solid in solution. The resulting solution was then heated at T = 358 K under confined atmosphere for one week for gelation and mechanical handling.…”

“…76 Recently, fluorination of carbon supports has also been proposed to prepare Pt-based electrocatalysts for oxygen reduction in PEMFC. 77 However, it has been shown that fluorination must be conducted prior to Pt deposition at the carbon substrate, as post-fluorination of a Pt/C electrocatalyst leads to deactivation of the Pt nanoparticles. Fluorination of the carbon support enables to bind fluorine atoms to their dangling groups, the latter likely being the ones that are oxidized first during PEMFC operation.…”

Non-PGM Electrocatalysts for PEM Fuel Cells: A DFT Study on the Effects of Fluorination of FeNx-Doped and N-Doped Carbon Catalysts

“…There are indications that the fluorination of materials in acidic media improves their oxidative stability. Examples of such systems include Nafion ionomer, Pt/C, and platinum group metal-free catalysts for PEM fuel cells [ 30 , 31 , 32 ]. Recently, we also fluorinated a highly active FeN x -doped carbon catalyst in the hopes that fluorine would increase its stability in PEM fuel cells [ 33 ].…”

Advances in tailoring the water content in porous carbon aerogels using RT-pulsed fluorination

“…This issue can be mitigated by "protecting" the carbon surface via appropriate surface treatments, e.g. metaloxides deposition [22] or fluorination [23]. Fluorination may have other advantageous effects regarding the physicochemical properties of the CA support, though.…”