TY - JOUR
T1 - First principles analysis of H 2O adsorption on the (110) surfaces of SnO 2, TiO 2 and their solid solutions
AU - Hahn, Konstanze R.
AU - Tricoli, Antonio
AU - Santarossa, Gianluca
AU - Vargas, Angelo
AU - Baiker, Alfons
PY - 2012/1/17
Y1 - 2012/1/17
N2 - Both associative and dissociative H 2O adsorption on SnO 2(110), TiO 2(110), and Ti-enriched Sn 1-xTi xO 2(110) surfaces have been investigated at low ( 1/ 12 monolayer (ML)) and high coverage (1 ML) by density functional theory calculations using the Gaussian and plane waves formalism. The use of a large supercell allowed the simulation at low symmetry levels. On SnO 2(110), dissociative adsorption was favored at all coverages and was accompanied by stable associative H 2O configurations. Increasing the coverage from 1/ 12 to 1 ML stabilized the (associatively or dissociatively) adsorbed H 2O on SnO 2(110) because of the formation of intermolecular H bonds. In contrast, on TiO 2(110), the adsorption of isolated H 2O groups ( 1/ 12 ML) was more stable than at high coverage, and the favored adsorption changed from dissociative to associative with increasing coverage. For dissociative H 2O adsorption on Ti-enriched Sn 1-xTi xO 2(110) surfaces with Ti atoms preferably located on 6-fold-coordinated surface sites, the analysis of the Wannier centers showed a polarization of electrons surrounding bridging O atoms that were bound simultaneously to 6-fold-coordinated Sn and Ti surface atoms. This polarization suggested the formation of an additional bond between the 6-fold-coordinated Ti 6c and bridging O atoms that had to be broken upon H 2O adsorption. As a result, the H 2O adsorption energy initially decreased, with increasing surface Ti content reaching a minimum at 25% Ti for 1/ 12 ML. This behavior was even more accentuated at high H 2O coverage (1 ML) with the adsorption energy decreasing rapidly from 145.2 to 101.6 kJ/mol with the surface Ti content increasing from 0 to 33%. A global minimum of binding energies at both low and high coverage was found between 25 and 33% surface Ti content, which may explain the minimal cross-sensitivity to humidity previously reported for Sn 1-xTi xO 2 gas sensors. Above 12.5% surface Ti content, the binding energy decreased with increasing coverage, suggesting that the partial desorption of H 2O is facilitated at a high fractional coverage.
AB - Both associative and dissociative H 2O adsorption on SnO 2(110), TiO 2(110), and Ti-enriched Sn 1-xTi xO 2(110) surfaces have been investigated at low ( 1/ 12 monolayer (ML)) and high coverage (1 ML) by density functional theory calculations using the Gaussian and plane waves formalism. The use of a large supercell allowed the simulation at low symmetry levels. On SnO 2(110), dissociative adsorption was favored at all coverages and was accompanied by stable associative H 2O configurations. Increasing the coverage from 1/ 12 to 1 ML stabilized the (associatively or dissociatively) adsorbed H 2O on SnO 2(110) because of the formation of intermolecular H bonds. In contrast, on TiO 2(110), the adsorption of isolated H 2O groups ( 1/ 12 ML) was more stable than at high coverage, and the favored adsorption changed from dissociative to associative with increasing coverage. For dissociative H 2O adsorption on Ti-enriched Sn 1-xTi xO 2(110) surfaces with Ti atoms preferably located on 6-fold-coordinated surface sites, the analysis of the Wannier centers showed a polarization of electrons surrounding bridging O atoms that were bound simultaneously to 6-fold-coordinated Sn and Ti surface atoms. This polarization suggested the formation of an additional bond between the 6-fold-coordinated Ti 6c and bridging O atoms that had to be broken upon H 2O adsorption. As a result, the H 2O adsorption energy initially decreased, with increasing surface Ti content reaching a minimum at 25% Ti for 1/ 12 ML. This behavior was even more accentuated at high H 2O coverage (1 ML) with the adsorption energy decreasing rapidly from 145.2 to 101.6 kJ/mol with the surface Ti content increasing from 0 to 33%. A global minimum of binding energies at both low and high coverage was found between 25 and 33% surface Ti content, which may explain the minimal cross-sensitivity to humidity previously reported for Sn 1-xTi xO 2 gas sensors. Above 12.5% surface Ti content, the binding energy decreased with increasing coverage, suggesting that the partial desorption of H 2O is facilitated at a high fractional coverage.
UR - http://www.scopus.com/inward/record.url?scp=84855978050&partnerID=8YFLogxK
U2 - 10.1021/la204124p
DO - 10.1021/la204124p
M3 - Article
SN - 0743-7463
VL - 28
SP - 1646
EP - 1656
JO - Langmuir
JF - Langmuir
IS - 2
ER -