Oxygen Reduction Reaction Activity of Platinum Thin Films with Different Densities

Wednesday, 4 October 2017: 15:00
National Harbor 2 (Gaylord National Resort and Convention Center)
B. Ergul (University of Arkansas at Little Rock), M. Begum (University of Arkansas - Little Rock), N. Kariuki, D. J. Myers (Argonne National Laboratory), and T. Karabacak (University of Arkansas - Little Rock)
Polymer electrolyte membrane fuel cells (PEMFCs) have gained significant attention as alternative power sources, especially for automotive applications due to their high energy conversion efficiency, low operating temperature and being environmentally friendly compared to the other types of fuel cells. However, sluggish kinetics of oxygen reduction reaction (ORR) on the cathode requires a high loading of platinum (Pt), which increases the cost of the fuel cell. In addition, dissolution and agglomeration of Pt nanoparticles and oxidation of the carbon support are among the major factors that cause electrode degradation and performance loss. Therefore, extensive efforts are focused on developing high performance, durable, and low-cost electrocatalysts. Extended surfaces such as nanostructured thin films are good candidate for non-conventional catalysts due to their high surface area and having no need for a support material.

In this work, a new density-modulated platinum thin film (Pt-TF) design was fabricated by high pressure sputtering deposition (HIPS) and was investigated as potential electrocatalysts for the ORR in PEMFCs using cyclic voltammetry and rotating disk electrode techniques in aqueous perchloric acid electrolyte. Scanning electron microscopy and X-ray diffraction methods were used to study morphological and crystallographic properties of the density-modulated Pt-TF electrocatalysts. The Pt-TF catalyst was produced by changing working gas pressure from low to high values during film growth, which results in denser film bottoms and more porous tops. Low-density film top provides effective transportation of oxygen, which could enhance catalyst utilization and result in reduced Pt-loading and enhanced activity. Porous yet interconnected network of Pt atoms in the low-density Pt-TF surface can also eliminate the agglomeration and dissolution problems. In addition, high-density film bottom provides a strong adhesion to the substrate leading to enhanced physical and electrochemical stability of the Pt-TF. Stronger bonds along with self-protection against the acidic environment due to the dense-packing of Pt atoms at the interface with the substrate can hinder leaching of Pt and avoid the detachment of large regions of Pt-TF from the substrate as a whole. In addition, high-density layer can reduce contact resistance and enhance the electronic conductivity. This presentation will focus on electrochemically active surface area, area specific activity, and mass activity of density-modulated Pt-TFs during accelerated stability tests and compare them to conventional high-density Pt-TF and Pt/C electrocatalysts.