O Programa de Pós-Graduação em Física convida para o Seminário:
Hydrogen from Sunlight – Photoelectrochemical Water Splitting with Li-doped TiO2 Nanotubes
Giovanni Zangari
Department of Materials Science and Engineering, University of Virginia
Charlottesville, VA, USA
Resumo:
While solar energy is one of the few energy sources capable of meeting the world’s energy demands,1 the transient nature of sunlight necessitates the development of technologies to store that energy for on-demand use to supplement photovoltaics.2 Photoelectrochemical solar cells use sunlight to electrolyze water to produce hydrogen as a storable fuel, which can then be converted to electricity by a fuel cell. TiO2 nanotubes formed by the anodization of titanium foils in electrolytes containing fluoride ions produce aligned arrays of tube-like structures 70-100 nm in width and tunable length on the order of microns as shown in Figure 1(a, b). These structures are a promising architecture for photoelectrochemical applications3 because of their high stability in solution and under irradiation, high surface area, and 1-dimensional charge transport for efficient movement of photogenerated charges. While hundreds of microns long nanotubes in principle may be grown, one major limitation on the performance of TiO2 nanotubes is the presence of defects in the crystal structure which facilitate the recombination of photogenerated electron-hole pairs;4 the best photoelectrochemical performance of TiO2 nanotubes for water splitting has been observed in Nb-doped TiO2 with a length of 7 mm and an associated photocurrent of 1.0 mA/cm2.5 Electrochemical Li doping was demonstrated to passivate the trap states in TiO2 nanotubes, suppressing recombination. This process resulted in up to a 2 fold increase in the photoelectrochemical performance of 1 mm long TiO2 nanotubes compared to the undoped samples.6 For long TiO2 nanotubes, a new optimum length of 15 mm was achieved, resulting in 1.5 mA/cm2 of photocurrent at 1.0 VSCE under simulated sunlight as seen in Figure 1(c). These results demonstrate the ability to produce high performance TiO2 nanotubes for photoelectrochemical solar energy devices using simple electrochemical techniques.
Figure 1. (a) Cross section and (b) surface view of TiO2 nanotubes grown by anodization. (c) Lithium intercalation enhances the photocurrent by trap state passivation, resulting in up to 1.5 mA/cm2 of photocurrent at 15 m.
References
(1) Lewis, N. S.; Nocera, D. G. Proc. Natl. Acad. Sci. U. S. Amer. 2006, 103, 15729.
(2) Cook, T. R.; Dogutan, D. K.; Reece, S. Y.; Surendranath, Y.; Teets, T. S.; Nocera, D. G. Chem. Rev. 2010, 110, 6474.
(3) Tsui, L. -k.; Zangari, G. J. Electrochem. Soc. 2014, 161, D3066
(4) Tsui, L.; Zangari, G. Electrochim. Acta 2014, 121, 203.
(5) Das, C.; Roy, P.; Yang, M.; Jha, H.; Schmuki, P. Nanoscale 2011, 3, 3094.
(6) Tsui, L.; Saito, M.; Homma, T.; Zangari, G. J. Mater. Chem. A 2015, 3, 360.
Data: 27 de março de 2015 – (sexta-feira) – Local: Sala 212 – Auditório do Departamento de Física- Horário: 10h15min
