| AVS 55th International Symposium & Exhibition | |
| Energy Science and Technology Focus Topic | Tuesday Sessions |
| Session EN+BI+SS+SE-TuM |
| Session: | Catalysis for Energy Sustainability |
| Presenter: | D.E. Ramaker, George Washington University |
| Authors: | D.E. Ramaker, George Washington University F.J. Scott, George Washington University S. Mukerjee, Northeastern University |
| Correspondent: | Click to Email |
Metal-ligand effects on Pt are commonly utilized to decrease the CO poisoning of the anode in methanol as well as to increase the activity for oxygen reduction at the cathode. However, these effects are not clearly understood because of the general lack of information on the particle morphology (M island size, homogeneity, etc.) and CO or OH adsorbate coverages. In this work, in situ X-Ray Absorption Spectroscopy (XAS) measurements, in the near edge and extended regions (XANES and EXAFS) at the Pt L3 edge, were carried out on three different carbon-supported electrocatalysts (Pt3Mo, Pt4Mo, and PtSn) in an electrochemical cell in 1 M HClO4 along with 0.3 M methanol. The CO, OH, O, and Hupd relative adsorbate coverages on Pt are determined as a function of the applied potential via the ΔXANES technique and compared with comparable data reported for three different PtRu electrocatalysts (PtRu Etek, PtRu Watanabe, and Pt3Ru) reported previously1. The average particle morphology of each catalysts is determined from EXAFS coordination numbers and a modeling technique.1 The onset of the n-fold O atom coverage between 0.5 and 0.9 V (RHE) tracks essentially with the particle size. The more reactive Sn and Mo atoms interact more strongly with Pt, and hence the ligand effect for the M and MOn islands are comparable, in contrast to that for Ru vs. RuOn. Our results are correlated with the extensive electrochemical results found in the literature on similar PtnM catalysts. The results suggest that the strength of the ligand effect increases in the order Ru < Mo, MoOn < Sn, SnOn ≤ RuOn, where the relative Pt-CO bond strength is found to decrease and the Pt-OH bond strength increases with ligand effect. In the Sn and Mo bimetallics, the ligand effect is found to be sufficiently strong to allow CO replacement by H2 at low currents.
1F. J. Scott, S. Mukerjee, and D. E. Ramaker, J. Electrochem. Soc. 154, A396-A406 (2007).