ABSTRACT
The design of electrocatalysts for polymer electrolyte membrane fuel cells must satsify two equally important fundamental principles: optimization of electrocatalytic activity and long-term stability in acid media (pH <1) at high potential (0.8 V). We report here a solution-based approach to the preparation of Pt-based alloy with early transition metals and realistic parameters for the stability and activity of Pt(3)M (M = Y, Zr, Ti, Ni, and Co) nanocatalysts for oxygen reduction reaction (ORR). The enhanced stability and activity of Pt-based alloy nanocatalysts in ORR and the relationship between electronic structure modification and stability were studied by experiment and DFT calculations. Stability correlates with the d-band fillings and the heat of alloy formation of Pt(3)M alloys, which in turn depends on the degree of the electronic perturbation due to alloying. This concept provides realistic parameters for rational catalyst design in Pt-based alloy systems.
Subject(s)
Alloys/chemistry , Electronics , Oxygen/chemistry , Platinum/chemistry , Catalysis , Drug Stability , Electrochemistry , Nanotechnology , Oxidation-ReductionABSTRACT
Density functional theory calculations were performed on the energetics of an adatom and adlayer of Cu on a Ru(0001) slab and on the interdiffusion of Cu or Ru at the interface of Cu/Ru(0001) slab. The total energy calculations showed the equal possibilities of both pseudomorphic hcp- and fcc-adlayers of Cu on the Ru(0001) slab. The formation energies of mono-vacancy at the Cu/Ru(0001) interface and the barrier energies of the vacancy-mediated interdiffusion were calculated. The formation energies of mono-vacancy at the Cu/Ru(0001) interface were determined to be 1.31 eV for Cu atom and 1.83 eV for Ru atom, respectively. The diffusion of Ru atom into the vacancy of Cu across the Cu/Ru(0001) interface required energy increase of 0.98 eV, and the barrier energy was substantially high, 1.80 eV. On the other hand, the diffusion of Cu atom into the vacancy of Ru across the Ru/Cu(0001) interface was favored with the energy reduction of 0.35 eV. However, under this most favorable situation, the barrier energy is 0.52 eV. The calculation results imply that, as far as energetics is concerned, the diffusion of both Cu and Ru atoms via the vacancy-mediated diffusion mechanism at the Cu/Ru(0001) interface seems rather restricted unless considerable thermal activation is provided.
ABSTRACT
We report Pt-based alloys with early transition metals. Significant electrocatalysis occurs during oxygen reduction reaction (ORR) at the Pt-Y alloy electrodes, and the extent depends on the alloy composition. The Pt-Y alloy electrode activity is related to the d-band center position, and the lattice strain and stability for oxygen reduction reaction.
