Article pubs.acs.org/JPCC
Thermodynamic Control of Metal Loading and Composition of Carbon Aerogel Supported Pt−Cu Alloy Nanoparticles by Supercritical Deposition S. E. Bozbag,† U. Unal,‡,⊥ M. A. Kurykin,§ C. J. Ayala,∥ M. Aindow,∥ and C. Erkey†,#,* †
Department of Chemical and Biological Engineering, Koç University, 34450, Sariyer, Istanbul, Turkey Department of Chemistry, Koç University, 34450, Sariyer, Istanbul, Turkey § A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 19991, V-334, Moscow, Russia ∥ Department of Materials Science and Engineering, Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269, United States ⊥ Koç University Surface Science and Technology Center (KUYTAM), Koç University, 34450, Sariyer, Istanbul, Turkey # Koç University TÜ PRAŞ Energy Center (KUTEM), Koç University, 34450, Sariyer, Istanbul, Turkey ‡
S Supporting Information *
ABSTRACT: Carbon aerogel (CA) supported Pt−Cu bimetallic nanoparticles were synthesized via simultaneous adsorption of bis(1,1,1,3,5,5,6,6,6-nonafluorohexane-2,4-diiminate)copper (CuDI6) and dimethyl(1,5-cyclooctadiene)platinum(II) (Pt(cod)me2) onto CAs in the presence of supercritical carbon dioxide (scCO2) and subsequent thermal conversion at ambient pressure. Binary adsorption isotherms of metal precursors on CAs in scCO2 were measured at 35 °C and 10.6 MPa by analyzing the fluid phase concentrations in a batch system and could be predicted from pure component adsorption isotherms using ideal adsorbed solution theory (IAST). Homogeneously dispersed Pt−Cu nanoparticles were formed on the surface of the CAs via the thermal conversion of the precursors at 400 °C. As the Pt/Cu ratio decreased from 97:3 to 21:79, both the mean and the standard deviation of the particle size increased from 2.9 to 7.2 nm and from 1.3 to 3.7 nm, respectively. The alloying of Pt and Cu within the nanoparticles was confirmed via XRD peak shifts, and XPS data indicated that the surfaces of these Pt−Cu alloy nanoparticles were enriched in Pt.
1. INTRODUCTION Carbon supported Pt−Cu bimetallic nanoparticles have been investigated as electrocatalysts for oxygen reduction in fuel cells. These studies have shown promise for reducing the amount of Pt currently used in fuel cells.1,2 These electrocatalysts usually consists of Pt and Cu loadings ranging between 20 and 30 wt % and 1.5−5.5 wt %, respectively.3−5 The catalytic activities of these bimetallic electrocatalysts depend significantly on the physical configuration (alloy, core−shell, segregation, etc.), phase behavior (ordered, disordered, etc.), metal concentration, surface crystal orientation, particle size, and distribution of the nanoparticles.6−8 For Pt−Cu alloy nanoparticles, studies have showed that at the Cu 3Pt stoichiometry the system exhibits some characteristics that are consistent with those expected on the basis of the bulk equilibrium Pt−Cu binary phase diagram. For example, a phase transformation from a disordered FCC alloy at temperatures >650 °C to the ordered L12 Cu3Pt phase was observed at temperatures
