(Invited) Controllable Deposition of Platinum Layers on Oxide Surfaces for the Synthesis of Fuel Cell Catalysts
Authors: Vukmirovic Miomir B , Kuttiyiel Kurian A , Adzic Radoslav R. , Meng Hui 
Published: February 2020

Proton exchange membrane fuel cell (PEMFC) is a promising power source for automobiles since they address many issues arising from using fossil fuels as a source of energy. Although already on the market, fuel cell electric vehicles have to decrease their cost in order to be economically competitive to the internal combustion engine.
The high cost of PEMFC is due to low reaction rate towards oxygen reduction reaction (ORR) [1] on the cathode, even on Pt - the best ORR catalyst, thus requiring high loading of very expensive Pt. Consequently, cost of Pt constitutes significant portion of the total cost of the fuel cell stack [2]. Therefore, the pursuit of reducing Pt loading and improving catalyst performance is intensifying.
Platinum monolayer (PtML) ORR catalysts present promising way of reducing the Pt content without scarifying fuel cell performance [3, 4, 5]. They have a core-shell structure where core is made of less expensive but corrosion stable noble metals or alloys while the shell is made of Pt monolayer. In addition, the catalytic properties of the Pt monolayer catalysts can be tuned through its interaction with the substrate core [3, 4, 5]. However, noble metals from which cores are made although cheaper than Pt still represent a considerable expense. Additionally, due to the incomplete Pt shell, noble metal core shows some instability under the prolonged highly oxidizing conditions that can occur during fuel cell operation [6]. Also, PtML catalysts are relevant to anodic electrocatalytic fuel cell reactions, for example, hydrogen oxidation reaction (HOR) and oxidation of small organic molecules [4, 7].
Metal oxides, such as NbO2 [8] or Ebonex (TinO2n-1, 4 ≤ n ≤ 10, Magneli phase) [9, 10] are excellent candidates as core materials for PtML ORR electrocatalysts, as they possess high electrical conductivity and good corrosion resistance under the acidic and oxidizing operating conditions on the cathode side of PEMFCs. In addition, they might have a beneficial influence on the catalytic properties of PtML through electronic (ligand) interactions and geometric effects. On the fuel cell anode, the conditions are not especially harsh. However, a reduction in Pt group metal loading by using metal oxide cores and enhancing the activity of PtML anode catalysts by PtML-metal-oxide interactions is desirable. Therefore, there is a great potential for metal-metal-oxide nanoparticle systems to be catalysts of important reactions.
Here, we present a versatile method for controllable deposition of metal sub-monolayers to multilayers on oxides. Controlled deposition of Pt was achieved by utilizing the ability of the metal oxide to adsorb various cations. The method involves the following steps: 1) Pb cation adsorption, 2) electrochemical reduction of Pb cations, and 3) galvanic displacement of Pb with Pt. This method can be also applied to oxidized carbon materials. We demonstrate this approach using RuO2(110), SnO2 nanoparticles, and reduced graphene oxide as supports for metal catalysts. Their activities for the ORR, the HOR, and ethanol oxidation were investigated.
Acknowledgements
This manuscript has been authored by employees of Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy. The publisher by accepting the manuscript for publication acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes.
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