Proton Exchange Membrane Fuel Cell (PEMFC) Catalysts with Transition Metal Oxides Supports
Proton Exchange Membrane Fuel Cells or Polymer Electrolyte Membrane Fuel Cells (PEMFCs) is one of the most promising and advancing technology, because of its various advantages such as low temperature operations, quick start-up times and high current and power densities. It has wide range of applications from portable to transportation to stationary applications. But commercialization of this technology is still hindered by several challenges such as cathode catalytic activity and durability.
Homogeneously dispersed platinum nanoparticles over carbon-based supports is the commercial benchmark catalyst at the cathode. However, carbon supports are highly susceptible to corrosion when subjected to high potentials leading to cause major performance losses. Hence corrosion-resistant highly stable support materials are needed. In this study we are exploring highly stable transition metal oxide supports for Pt and Pt-Ni alloy catalysts in PEMFC.
Density functional theory calculations were used to understand the structural, electronic, and stability properties of doped transition metal oxides and to guide the material synthesis. Four different metal oxide (Sb-SnO2, Ru-TiO2, Ta-TiO2, Nb-TiO2) supports were obtained using Sol-Gel and Aerogel-Xerogel methods. Platinum nanoparticles and platinum-nickel alloy nanoparticles were deposited onto a commercial carbon (XC 72R), and metal oxide supports using a microwave-assisted modified polyol method to attain uniform and homogenous Pt nanoparticles dispersion.
All the catalysts were subjected to several physico- chemical and electrochemical characterizations to understand their structural, morphological and electrocatalytic properties towards oxygen reduction reaction at cathode. The surface morphology of these catalysts observed through scanning-transmission electron microscopy (STEM) showed epitaxial growth of Pt nanoparticles onto the support oxides, unlike carbon support.
The oxygen reduction reaction specific activity, investigated in 0.1M HClO4 electrolyte, using rotating disk electrode set-up showed a 5-fold and 2-fold enhancement in the case of Pt/Ru-SnO2, and Pt-Ni/Ru-SnO2 respectively, and a similar performance in case of Pt/Sb-SnO2 compared to Pt/XC 72R because of the strong metal support interactions. The in-situ performance of these catalysts is also investigated in PEMFC.
This dissertation provides an exploration of transition metal oxide supports for Pt and Pt-alloy catalysts, and possible applications of these materials in different fuel cells and electrolyzers.