Work function change study of oxygen adsorption on Pt(111) and Pt(100)

Journal Article · Fri Mar 15 04:00:00 EST 1985 · J. Chem. Phys.; (United States)

DOI:https://doi.org/10.1063/1.448274· OSTI ID:6011090

Derry, G N; Ross, P N

Oxygen adsorption on Pt(111) and Pt(100) was investigated using a Kelvin probe to measure adsorbate induced work function changes. The variation of ..delta..phi with theta was linear (p = 0.103 D/atom) on Pt(111) even up to theta/sub max/approx.7 x 10/sup 14/ atoms cm/sup -2/. On Pt(100), there was an abrupt increase in ..delta..phi at low coverage (<1 x 10/sup 14/ atom cm/sup -2/) which was presumed to be adsorption at defect sites (p = 0.62 D/atom). Sticking coefficients were calculated from the rate of change of the work function with time. For room temperature adsorption on Pt(111), the sticking coefficient followed the functional form S/sub 0/(1-theta)/sup 2/, theta = theta/theta/sub max/, and S/sub 0/ = 0.038. On Pt(100) the functional dependence was more complex with an initial increase in S (from S/sub 0/ = 0.042) to a theta of approx.0.1, then an approximately quadratic decrease as the coverage increased to saturation. The maximum coverage observed in room temperatue dosing of either surface was approx.3 x 10/sup 14/. However, dosing at 200--300 /sup 0/C at 10/sup -5/--10/sup -4/ Torr induced coverages as high as (7--9) x 10/sup 14/ on both surfaces. The isosteric heat of adsorption was measured from equilibrium isotherms and found to be 232 +- 36 kJ mol/sup -1/ with a coverage dependence less than the experimental precision. For Pt(111), it is postulated that population of the high coverage state proceeds via the activated process of direct dissociation, whereas the unactivated room temperature process is via a molecularly adsorbed precursor. For Pt(100), population of the high coverage state involves activated transitions in the Pt surface structure which require further study.

• Research Organization: Materials and Molecular Research Division, Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720
• OSTI ID: 6011090
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 82:6; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical &amp; Physicochemical Properties
ADSORPTION
ELEMENTS
FUNCTIONS
METALS
NONMETALS
OXYGEN
PLATINUM
PLATINUM METALS
POTENTIALS
SORPTION
SORPTIVE PROPERTIES
SURFACE POTENTIAL
SURFACE PROPERTIES
TRANSITION ELEMENTS
WORK FUNCTIONS