Time-Resolved DRIFTS, MS, and Resistance Study of SnO2 Materials: The Role of Surface Hydroxyl Groups in Formation of Donor States

• Published in: Journal of physical chemistry. C Vol. 117; no. 8; pp. 4158 - 4167
• Main Authors: Pavelko, Roman G, Daly, Helen, Hübner, Michael, Hardacre, Christopher, Llobet, Eduard
• Format: Journal Article
• Language: English
• Published: Columbus, OH American Chemical Society 28.02.2013
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Exact sciences and technology; Impurity and defect levels; energy states of adsorbed species; Physics; Surface and interface electron states; Defect states; Chemisorption; Diffuse reflection; Doping; Time resolved spectra; Gas solid adsorption; Surface conductivity; Tin oxide; Hydroxyl group; Chemical bonds; Donor center; Kinetics; Fourier-transformed infrared spectrometry; Recovery (properties)
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp312532u

Time-resolved DRIFTS, MS, and resistance measurements were used to study the interaction of undoped and Pd-doped SnO2 with H2 in air and argon at 300 °C. Using first-order kinetics, we compare the time constants for the resistance drop and its partial recovery with those of the surface hydroxyl evolution and water formation in the gas phase upon exposure to hydrogen. In the case of the undoped oxide, resistance and bridging hydroxyls (BOHs) evolve similarly, manifesting a fast main drop followed by recovery at a similar rate. The rate of water formation for this material was found to be much slower than that of the main drop in both the resistance and BOHs. In contrast, the resistance change for SnO2–Pd appeared to be similar to that of water formation, and no correlation was found between the evolution of resistance and surface OHs. Isotopic exchange on both materials revealed that water formation occurs via fast and slow hydrogen transfer to surface oxygen species. While the former originates from just-adsorbed hydrogen, the latter appears to proceed from the preadsorbed OHs. Both surfaces exhibit close interaction between chemisorbed oxygen and existing bridging OH groups, indicating that the latter is an intermediate in the hydrogen oxidation and generation of donor states on the surface.