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Title: Site-Specific vs Specific Adsorption of Anions on Pt and Pt-Based Alloys

Abstract

X-ray absorption spectroscopy (XAS) is utilized in situ to gain new insights into the electronic and chemical interactions of anions specifically adsorbed on Pt/C. A novel difference methodology was utilized, along with full-multiple scattering calculations using the FEFF8 code, to interpret the X-ray absorption near edge structure (XANES). Significant direct contact ('specific') anion adsorption occurs in 1 M H{sub 2}SO{sub 4} and 6 M TFMSA, while it does not in 1 M HClO{sub 4} and 1 M TFMSA. This specific anion adsorption significantly hinders O(H) chemisorption, particularly formation of subsurface O, causes the Pt nanoparticle to become more round, and weakens the Pt-Pt bonding at the surface. The specific anion adsorption becomes site-specific only after lateral interactions from other chemisorbed species such as OH on the surface force the anions to adsorb into specific sites. Alloying has a profound effect on the strength of the anion adsorption and whether site-specific or just specific adsorption occurs.

Authors:
; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
929998
Report Number(s):
BNL-80608-2008-JA
TRN: US200822%%956
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Chemistry C; Journal Volume: 111
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ABSORPTION; ADSORPTION; PLATINUM; PLATINUM ALLOYS; ANIONS; CHEMICAL BONDS; SURFACE PROPERTIES; INTERACTIONS; POSITIONING; national synchrotron light source

Citation Formats

Teliska,M., Murthi, V., Mukerjee, S., and Ramaker, D.. Site-Specific vs Specific Adsorption of Anions on Pt and Pt-Based Alloys. United States: N. p., 2007. Web. doi:10.1021/jp071106k.
Teliska,M., Murthi, V., Mukerjee, S., & Ramaker, D.. Site-Specific vs Specific Adsorption of Anions on Pt and Pt-Based Alloys. United States. doi:10.1021/jp071106k.
Teliska,M., Murthi, V., Mukerjee, S., and Ramaker, D.. Mon . "Site-Specific vs Specific Adsorption of Anions on Pt and Pt-Based Alloys". United States. doi:10.1021/jp071106k.
@article{osti_929998,
title = {Site-Specific vs Specific Adsorption of Anions on Pt and Pt-Based Alloys},
author = {Teliska,M. and Murthi, V. and Mukerjee, S. and Ramaker, D.},
abstractNote = {X-ray absorption spectroscopy (XAS) is utilized in situ to gain new insights into the electronic and chemical interactions of anions specifically adsorbed on Pt/C. A novel difference methodology was utilized, along with full-multiple scattering calculations using the FEFF8 code, to interpret the X-ray absorption near edge structure (XANES). Significant direct contact ('specific') anion adsorption occurs in 1 M H{sub 2}SO{sub 4} and 6 M TFMSA, while it does not in 1 M HClO{sub 4} and 1 M TFMSA. This specific anion adsorption significantly hinders O(H) chemisorption, particularly formation of subsurface O, causes the Pt nanoparticle to become more round, and weakens the Pt-Pt bonding at the surface. The specific anion adsorption becomes site-specific only after lateral interactions from other chemisorbed species such as OH on the surface force the anions to adsorb into specific sites. Alloying has a profound effect on the strength of the anion adsorption and whether site-specific or just specific adsorption occurs.},
doi = {10.1021/jp071106k},
journal = {Journal of Physical Chemistry C},
number = ,
volume = 111,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • In situ X-ray absorption spectroscopy along with electrochemical measurements (CV and RDE) and previously published EQCN data provide further understanding of the nature of chloride poisoning on different faces/sites of carbon supported platinum clusters (1?2 nm) in acidic medium (HClO{sub 4}). Chloride is shown to adsorb in 3-fold sites on the Pt(111) faces at the investigated Cl{sup -} concentrations (10{sup -3} and 10{sup -2} M). Atop chloride was found to be present within a narrow potential range (0.4-0.7 V RHE) when compressed adlayers of Cl{sup -} are formed on the Pt(111) faces forcing some Cl{sup -} to exist in atop/bridgedmore » sites. The interplay of anionic (Cl{sup -}, Br{sup -}, OH{sup -}, and HSO{sub 4}{sup -}) adsorption on the different surfaces of Pt are also considered. For example O/OH can easily displace atop chloride on the edges/corners but not the Cl{sup -} at the Pt(111) sites, and therefore Cl{sup -} dramatically raises the overpotential for water activation at the Pt(111) sites. Chloride also drastically alters the ORR causing an increase of the overpotential by 85 mV for every 10-fold increase in chloride concentration with a total 150?200 mV increase in the overpotential at large concentrations at the Pt(111) sites. Finally Cl{sup -} ions cannot displace the bisulfate overlayer on the Pt(111) faces after it is formed at lower potentials; however, once the bisulfate adsorption is disturbed at higher potentials, the bisulfate cannot displace the Cl{sup -} adsorption. These relative anion adsorption preferences can help to explain the different dependencies of the important ORR on anion adsorption, and suggests that the effect of Cl{sup -} poisoning might be quite dependent on the Pt particle size.« less
  • In this paper we present x-ray scattering results of iodide, bromide, and chloride adsorption onto the Pt(111) surface in solution. Iodide forms two commensurate adlayer structures, a ({radical}(7){times}{radical}(7))R19.1{degree} phase and a hexagonal (3{times}3) phase, which coexist on the Pt surface. Formation of the (3{times}3) phase appears to be kinetically limited, whereas the {radical}(7) phase shows a hysteretic effect as a function of the electrode potential, associated with an order-disorder transition. Bromide forms a series of high-order commensurate structures on Pt(111) that are poorly ordered unless the size of the unit cell is small. No ordered structures for chloride adsorption aremore » observed and specular x-ray reflectivity results suggest that the chloride coverage at low potential is too small to form a close-packed monolayer on the surface. The differences between the structures formed by the adsorbed anions, and the differences between results for Pt(111) and Au(111), are discussed in terms of the strength of the metal-halide interaction. {copyright} {ital 1997} {ital The American Physical Society}« less
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