Synthesis, Stabilization and Activation of Pt Nanoparticles for PEMFC Applications

Abstract

Amongst the main challenges of catalyst materials for Proton Exchange Membrane Fuel Cells (PEMFCs) are activity and durability. Here we report on the synthesis of monodisperse nanoparticles and stabilization with traces of the surfactant, here Na‐AOT (bis‐(2‐ethylhexyl) sulfosuccinate sodium salt), used in the synthesis procedure. The surfactants prevent agglomeration and reduce Ostwald ripening. We compare the performance of Pt catalyst nanoparticles synthesized in dense microemulsions, Na‐AOT/heptane/water and Triton X‐100/toluene/water, with a commercial state‐of‐the‐art catalyst for the Oxygen Reduction Reaction (ORR). The produced catalyst nanoparticles were extracted onto a carbon support, Vulcan XC‐72R, washed and activated by heat‐treatment, which led to heavy agglomeration, or by electrochemical treatment, which led to an enhanced activity for ORR. Additionally, in comparison to the other two catalysts an increased durability of the platinum nanoparticles synthesized in the microemulsion of Na‐AOT/heptane/water was observed.

Mesoporous Platinum Prepared by Electrodeposition for Ultralow Loading Proton Exchange Membrane Fuel Cells

“…Platinum (Pt) is a commonly used catalyst for proton exchange membrane fuel cells (PEMFCs) due to its relatively high catalytic activity, selectivity for the oxygen reduction reaction (ORR), and resistivity to chemical and electrochemical degradation under fuel cell operating conditions 1 , 2 . To increase the competitiveness of PEMFCs in contrast to internal combustion engines (ICEs) for automotive applications, the mass of Pt used in PEMFCs must be reduced to lower the cost of these systems 3 , 4 . Researchers have proposed and demonstrated the use of electrodeposition as a superior method for creating catalysts with a higher Pt utilization than the Pt nanoparticle-based powdered catalysts that are widely adopted by current PEMFC manufacturing techniques 5 – 7 .…”

“…Advances have been made to lower these costs by preparing catalysts using Pt alloys that incorporate more abundant metals, but Pt is still the optimal material for the cathode catalyst in PEMFCs after taking into account both the catalytic selectivity for the ORR and the electrochemical stability of the material 14 – 18 . Current manufacturing practices aim to increase Pt mass activity and reduce system costs by utilizing Pt nanoparticles (NPs) that maximize the surface area to volume ratios of these catalysts 3 , 19 , 20 . During catalyst preparation, these Pt NPs are mixed with support materials that consist of conductive carbon NPs and a non-electrically conductive perfluorosulfonate containing polymer (i.e., a proton conductive ionomer) 12 .…”

“…The carbon particles and ionomer conduct electrons and protons, respectively, to the Pt surfaces for the catalysis of the ORR. The processing of these catalyst and catalyst support materials can, however, result in agglomeration of the carbon particles that can impede the infiltration of oxygen gas, and the ionomer can coat the conductive particles and insulate them from the conductive pathways within the catalyst layers (CLs) 3 , 21 . A large amount (ranging from 30 to 80%) of the Pt NPs incorporated into the powder processed, particle-based CLs can be inactive due to the formation of these agglomerates 22 – 24 .…”

Template assisted preparation of high surface area macroporous supports with uniform and tunable nanocrystal loadings

“…Platinum remains one of the optimal catalysts for PEMFC cathodes for its catalytic activity and stability. 21 It is, however, also one of the most expensive precious metals in the world. 73 The use of ordered macroporous supports for these and related nanocrystals could further optimize their utilization and reduce the overall costs for preparing catalyst materials.…”

“…These techniques may, however, result in the formation of nanocrystal agglomerates due to the of processing conditions. 18,21 This agglomeration can reduce the overall mass efficiency of the nanocrystals by reducing their surface area to volume ratio. 14,18 Macroporous materials can be created to replace powder based catalyst supports to reduce the possible aggregation of the nanocrystals.…”