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New electrodes for low temperature water electrolysis (PEMWE) based on doped tin dioxide aerogels (SnO2˸ Sb or Ta) as catalyst support

  • Sola Hernandez, Lluis
Publication Date
Jan 26, 2021
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Sb-doped tin dioxide aerogels (ATO aerogels) showed promising results as corrosion resistive Pt catalyst supports for proton exchange membrane fuel cells (PEMFC). Mimicking this strategy to reduce the iridium loading in proton exchange membrane water electrolysis (PEM-WE) cells, Ir nanoparticles (NPs) were deposited on tin dioxide-based aerogels synthesized as catalysts supports. The mesoporous morphology and high specific surface area of aerogels is indeed particularly well adapted for an optimal dispersion of catalyst nanoparticles. The synthesis route of SnO2-based aerogels was thus further studied in order to improve the sought-after properties. On top of antimony, tantalum was also evaluated as another doping agent to increase the tin dioxide (TO) electronic conductivity as well as the catalyst stability. The sol-gel method parameters of the aerogel synthesis route were modified so as to optimize the sol-gel catalyst, the calcination time or the dopant concentration. Using sodium hydroxide (NaOH) instead of nitric acid (HNO3) as the sol-gel catalyst allowed to increase the specific surface area (up to 90 m2·g-1) of Sb-doped tin dioxide aerogels (ATO). A beneficial impact was also observed on limiting the Sb segregation. A better Sb repartition in the material is expected to result in lower dissolution and a better stability during oxygen evolution (OER).Tantalum-doped tin dioxide aerogels (TaTO) showed a much lower electronic conductivity than ATO. The value is depending on the Ta concentration as is the specific surface area. The best compromise between both properties was obtained for 2 at. % (40 m²·g-1 and 4.6 mS·cm-1). Iridium nanoparticles where then deposited in-situ by chemical reduction of an iridium salt on the selected tin-dioxide aerogels. Their performance were assessed on rotating disk electrode (RDE) and compared to those of non-supported Ir NPs, prepared following the same protocol but without any support. The developed electrocatalysts reached similar mass activity values than those reported in the literature for different tin dioxide morphologies. Supported iridium NPs presented much higher activities (x5) and stabilities (x16) than non-supported Ir NPs. They also featured similar mass and specific activity whatever the catalyst support (TO, ATO or TaTO aerogels), despite their very different electronic conductivity. The deactivation of the catalysts observed with time under OER working conditions, was caused by an Ir detachment, or dissolution, from the electrode. Countermeasures are now under investigation in order to limit this phenomenon.

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