(Keynote) Benefits and Limitations of Metal-Oxide Supports in Proton-Exchange Membrane Fuel Cells and Water Electrolyzers
Authors: Cognard Gwenn , Claudel Fabien , Dubau Laetitia , Chatenet Marian , Sola-Hernandez Lluis , Ozouf Guillaume , Beauger Christian , Maillard Frederic 
Published: February 2020

Decreasing the size of metallic materials to nanometre-size dimensions has always proven beneficial to increase their mass activity for electrocatalytic reactions in proton-exchange membrane fuel cells (PEMFC) and proton-exchange membrane water electrolyzers (PEMWE). However, such strategy requires adequate supports which are (i) electron-conducting, (ii) corrosion-resistant, and (iii) exhibiting opened and interconnected architecture compatible with facile gas–transport and ionomer insertion. Due to a standard potential close to 0.2 V vs. the normal hydrogen electrode, carbon corrosion of classical carbon supports slowly proceeds at a PEMFC cathode, the kinetics of this reaction being even faster at the anode of a PEMWE; this calls for alternative support materials. It is possible to meet the first and second requirements by doping tin oxide (SnO2, TO), a metal oxide that is stable at pH close to 0, and 0 < E < 1.5 V vs. RHE and T = 80°C, with Sb [1-6] or Nb [2]. The third requirement can also be met by structuring the metal oxide in an aerogel form.

However, benefits and limitations of this strategy under simulated or real-life operating conditions remain poorly explored and will be the focus of this presentation. Here, we synthesized Pt or Ir nanoparticles and supported them onto antimony-doped (ATO) or niobium-doped (NTO) tin oxide aerogels featuring tailored porosity and tested their initial and long-term performance in simulated PEMFC or PEMWE operating conditions. By combining chemical, physical and electrochemical techniques, we show that Sb and Sn atoms are dissolved from ATO and poison the Pt catalytic sites in a PEMFC cathode. This process is accelerated during potential excursions at low electrode potential, e.g. during electrochemical characterizations or kinetic measurements. Sb dissolution also takes place in the potential range where a PEMWE anode operates. This leads to a Sb-poor surface covering a core featuring a Sb content close to the nominal on the long-term and restricts the capacity of the metal nanoparticles to exchange electrons. Despite such observations, better long-term stability under accelerated stress tests was evidenced compared to conventional carbon based supports, both in simulated PEMFC or PEMWE operating conditions.

This work was supported by the French National Research Agency in the frame of the SURICAT (grant number ANR-12-PRGE-007) and MOISE projects (grant number ANR-17-CE05-0033).

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