Stability Enhancement of the Interaction Between Pt Nanoparticles and Carbon Supports through Carbon Surface Functionalization

Proton exchange membrane fuel cells (PEMFCs) that use hydrogen and oxygen in air as fuels to produce electricity have attracted extensive interests over the past decades.¹ The high efficiency and zero emission make PEMFCs promising candidates for viable propulsive systems in electric automobiles.² One of the major challenges that hinder the commercialization of PEMFCs vehicles is the poor stability of Pt nanoparticles on carbon supports, which mainly due to the dissolution and re-deposition of Pt and migration of Pt over carbon supports.^{3 4}Both of them will cause the agglomeration of Pt nanoparticles, resulting in loss of Pt electrochemical surface area (ECSA) and the increasing of activation overpotentials.  

Aiming to minimize the growth of Pt nanoparticles due to the Pt migration on carbon supports, fundamental understanding of their interaction is required, so as to modify the carbon supports to enhance the binding energy between Pt and carbons. In our recent work, Pt of 3% to 5% loading was deposited on XC-72 carbon black, graphene, functionalized XC-72 carbon black and functionalized graphene, where the Pt clusters or islands of about 3-6 atoms thickness on different supports can be achieved by a general two step method. The dispersion and morphology of Pt on pristine graphene, SO₃H-graphene and NH₂-graphene were then characterized by high resolution transmission electron microscopy (HRTEM). It is clearly shown that spherical Pt nanoparticles of very small size were uniformed dispersed on functionalized graphene, whereas on pristine graphene, some rod-like Pt crystals were observed. It indicates that the presence of functional groups prevents the migration of Pt nuclei on the two-dimentional graphene sheet during the synthetic process. X-ray absorption near edge structure (XANES) of Pt L-edge and C K-edge were performed to further characterize the interaction between Pt and different supports. The increasing of the intensity of the Pt L-edge adsorption peak compared with unsupported Pt suggests electron withdrawn from Pt to carbon supports might exists between Pt and carbon supports and the interaction strength follows the order of Pt/SO₃H-Graphene > Pt/SO₃H-XC72 carbon black > Pt/Graphene > Pt/XC72 carbon black. On the other hand, the shift of Pt L-edge adsorption peak to higher photon energy also indicates the possible increase of oxidation state of Pt due to the Pt-C interaction. This study will shed light on the strategy to improve not only the durability but also activity of Pt based catalysts in fuel cells.

(1)          Gasteiger, H. A.; Markovic, N. M. Science 2009, 324, 48.

(2)          Debe, M. K. Nature 2012, 486, 43.

(3)          Xie, J.; Wood, D. L.; More, K. L.; Atanassov, P.; Borup, R. L. Journal of The Electrochemical Society 2005, 152, A1011.

(4)          Shao-Horn, Y.; Sheng, W. C.; Chen, S.; Ferreira, P. J.; Holby, E. F.; Morgan, D. Topics in Catalysis 2007, 46, 285.