Characterization of Ligand Effects on Water Activation in Triaryl Phospine Stabilized Pt Nanoparticle Catalysts by X-ray Absorption Spectroscopy
The synthesis, preparation, and electrochemical characterization of triphenylphosphine triphosphonate (TPPTP) stabilized Pt particles have been reported previously with the observation that the TPPTP ligands increase the specific activity of Pt for the oxygen reduction reaction (ORR). In this work the ORR activity of the Pt/TPPTP electrocatalyst is probed by analyzing water activation with Pt L{sub 3}-edge X-ray absorption spectroscopy and the EXAFS and Delta XANES analysis techniques. The results are compared with that for similarly prepared Pt/C and Pt stabilized by an oxidized TPPTP ligand (Pt/ox-TPPTP). The Pt particles in the Pt/TPPTP catalyst at 0.54 V (RHE) are complexed via the P (i.e., Pt-P<tp) with about 0.3 ML of TPPTP. Approximately one-half of this converts to a Pt-O-P<tp linkage at 1.0 V; these species exist on the surface along with a dramatically reduced OH coverage. The reduction in OH coverage enhances the surface-specific (ORR) rate relative to the same-sized Pt particles on carbon. The Pt/ox-TPPTP catalysts are linked via a 3-fold coordinated Pt{triple_bond}O-P<tp, which severely blocks sites and makes the electrocatalysts almost inactive to water activation and the ORR. The relative importance of site blocking, hydrophobic effects, and electronic effects are discussed with hydrophobic effects believed to dominate in the Pt/TPPTP catalyst and site blocking in the Pt/ox-TPPTP catalyst.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States). National Synchrotron Light Source
- Sponsoring Organization:
- DOE - OFFICE OF SCIENCE
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 1019931
- Report Number(s):
- BNL-95777-2011-JA; TRN: US201115%%567
- Journal Information:
- Journal of Physical Chemistry C, Vol. 112, Issue 13; ISSN 1932-7447
- Country of Publication:
- United States
- Language:
- English
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