Improvement of the Pt/Graphene Interface Adhesion by Metallic Adatoms for Fuel Cell Applications
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1213-T07-02
Improvement of the Pt/graphene interface adhesion by metallic adatoms for fuel cell applications Fatih G. Sen1, Yue Qi2 and Ahmet T. Alpas1 1 Department of Mechanical, Automotive and Materials Engineering, University of Windsor, 401 Sunset Ave, Windsor, Ontario N9B 3P4 Canada 2 Materials and Processes Laboratory, General Motors R&D Center 30500 Mound Rd, Warren, Michigan 48090-9055 U.S.A. ABSTRACT The degradation of carbon supported Pt catalyst limits the lifetime of polymer electrolyte membrane fuel cells. The bond between Pt and carbon must be significantly strengthened in order to prevent detachment of Pt particles from carbon support. In this work, first principles calculations were carried out in an attempt to understand the role that metallic adatoms play in the enhancement of the Pt/carbon interface adhesion. Metallic adatoms including all first row transition metals as well as Li, Al, Zr, Nb, and Au were inserted into a Pt(111)/graphene interface. The work of separation required to break the interface between Pt-adatom or carbonadatom bond was then calculated for each configuration, revealing that the carbon-adatom bond was weaker than the Pt-adatom bond, making it easier to break the interface from the carbonadatom bond side. Among all the investigated metal adatoms, Co, Ni and V were the most promising elements for bridging Pt onto graphene surface. These metals donated charges that were distributed more evenly between carbon and Pt and formed covalent bonds with carbon and metallic bonds with Pt. The strength of the Pt-adatom bond was proportional to the amount of charge transferred from the adatom to the Pt particle. The strength of graphene-adatom bond correlated with the ratio of the charge transfer to graphite and Pt, depending on the bridging nature of the adatoms. INTRODUCTION The operation lifetime of proton exchange membrane fuel cells (PEMFCs) still requires an improvement, while the degradation of the carbon supported Pt catalyst system causes a substantial performance decrease due to a decrease in the electrochemically active surface area (ECSA) [1]. This loss of ECSA is caused by both the dissolution of Pt particles from carbon support [2], and the agglomeration of Pt particles during electrochemical cycling. The agglomeration of Pt particles occurs via two distinct mechanisms: The Ostwald ripening process and migration of Pt particles on the carbon support [3]. In order to mitigate the Pt particle agglomeration on the carbon surface, either this surface or the Pt catalyst surface--or both-should be modified [4-6]. The agglomeration of Pt particles on the carbon support was found to be mitigated either by the alloying of Pt with non-noble metals or modifying the carbon found in PEMFCs, which was believed to be due to the enhancement in the anchoring of Pt to carbon [6]. Functionalizing the carbon support with sulphur, nitrogen and phosphorus yielded a decrease in Pt particle size and increased its bond strength to carbon, while nitrogen doping additionally improved the catalytic a
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