A key requirement for the large-scale commercialization of proton exchange membrane (PEM) fuel cells is to produce highly active, durable catalysts, while minimizing the use of precious noble metals, especially platinum (Pt). Higher utilization of Pt catalyst can be realized by understanding the effect of the carbon support microstructure on the distribution and formation of Pt nanoparticles (NPs) and by optimizing the synthesis method. In this work, Pt NPs were fabricated using a simple alcohol reduction method and then varying the carbon support pore structure and surface properties. The catalysts were then tested for their activity in 1 M C₂H₅OH + 0.5 M H₂SO₄ solutions.

For Pt NP preparation, either ethanol or butanol were used as the solvent and reductant. The ethanolic or butanolic solution containing H₂PtCl₆ was then added to the carbon support dispersed in the same solvent at room temperature, and the mixture was heated at the boiling point for 2 hrs. In the case of the ethanol solvent, an aqueous alkaline solution was added to ensure the completion of Pt reduction [1]. However, this step was not used during synthesis when using butanol, due to its higher reducing power. Three types of carbon supports were investigated, Vulcan carbon (VC), Ketjenblack (KB), and colloid-imprinted carbon powders (CICs). The structure and distribution of the Pt NPs were confirmed by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM).

Figure 1 shows the cyclic voltammograms of JM Pt/VC and Pt/CIC85 (i.e., 85 nm pore size), prepared by both the ethanol and butanol synthesis methods, in 0.5 M H₂SO₄. Even though the theoretical specific surface areas were 70-80 m²/g_Pt (particle size of 3-3.5 nm), the electrochemical active surface area (ECSA) was found to depend on the synthesis method and the carbon support. The ethanol oxidation activity of catalysts per Pt area for the three carbon supports is shown in Figure 2. A strong dependence on the carbon microstructure was observed, with Pt/CIC and Pt/KB, showing a higher activity than Pt/VC, likely due to their higher content of mesopores in the catalyst layer [2]. The correlation between catalyst activity and the carbon microstructure for each synthesis method will be discussed in detail.

References:

1. J. Xie, Q. Zhang, L. Gu, S. Xu, P. Wang, J. Liu, Y. Ding, Y.F. Yao, C. Nan, M. Zhao, Y. You, Z. Zou, Nano Energy (2016) 21, 247–257.

2. T. Soboleva, X. Zhao, K. Malek, Z. Xie, T. Navessin, S. Holdcroft, ACS applied materials and interfaces (2010) 2, 2, 375–384.