Fabrication And Performance Investigation Of Platinum Monolayer Skin Electrocatalysts For Oxygen Reduction Reaction In Low Temperature Fuel Cells

Proton exchange membrane fuel cell (PEMFC) are typical fuel cells working at relatively low temperatures (<100 ℃). They are suitable for requirements of power sources from portable devices, electric vehicle and distributed power station with the advantages of low working temperature, rapid start-up and zero emission. State of the art anode and cathode electrocatalysts used in these fuel cells are commonly Pt-based noble metal catalysts. The improvement of activity and lifetime of the electrocatalyst (especially at the cathode side for oxygen reduction reaction, ORR) and reduction of the loading of noble metals such as Pt, are the key factors for large scale commercialization of such fuel cell. Herein, we focused on facricating Pt-monolayer skin electrocatalysts with different method, further investigated their structural characteristic and explored their application for the electrochemical catalysis. The results are as follows:1) In this work, core-shell structured Pd@Ptmonolayer nanoplates are generated by a defect-mediated thin film growth method which provides a unique operational strategy for the synthesis of atomically smooth Pt skin on ultrathin Pd nanoplates. With an average thickness blow 5 nm and an extended Pt surface, Pd@Ptmonolayer exhibits outstanding oxygen reduction reaction (ORR) activity in acidic electrolyte. Compared with the commercial Pt/C catalyst, it reaches a Pt mass activity～0.717 A mgPt-1 at 0.9 V vs. RHE, which points to a seven-fold enhancement. With nearly one atomic layer Pt coverage on the surface, this material also demonstrates surprisingly good durability, and after 5000 potential cycling, only 18 mV negative shift in half-wave potential was observed, with only 3% surface area loss. Defect-mediated thin film growth is thereby an interesting approach, holding potential for the fabrication of high quality core-shell nanostructures with ultra-thin surface layers.2) Under-potential deposition method was a common method to deposit a small amount of precious metals on the surface of nano-metallic materials. In this dissertation, we combined the advantages from 1) Nanoporous gold:high index facet on the surface and 2) Pd and Pt:best candidate for high activity electrocatalyst. And succeed generate controlled thickness of Pt and Pd layers on dealloyed nanoporous gold membrane (Nanoporous Gold-Pdx-Ptmonolayer) using under-potential deposition-in situ replacement method and investigated the oxygen reduction reaction activities. Nanoporous Gold-Pd1-Ptmonolayer material has been proved with high capability towards oxygen reduction reaction for fuel cell cathodic reaction with a half-wave potential upper shift of 33 mV (versus RHE), mass activity enhancement about 1.22 A mgPt-1 and area-specific activity about 0.79 mA cmPt-2. This achieves the United States Department of Energy’s 2017 target for area-specific and 2015 target for mass activity.