| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2014) | |
| Energy Harvesting & Storage | Wednesday Sessions |
| Session EH-WeM |
| Session: | Characterization of Materials for Energy Applications I |
| Presenter: | Xueqiang Zhang, University of Notre Dame |
| Authors: | XQ. Zhang, University of Notre Dame S. Ptasinska, University of Notre Dame |
| Correspondent: | Click to Email |
A photoelectrochemical (PEC) solar cell for water splitting can convert solar energy into chemical energy and store it in the form of hydrogen, a molecule regarded as a promising candidate for sustainable and clean fuels [1]. PEC solar cells using phosphide-based III-V semiconductors are known to have higher efficiency than other materials. They are, however, usually limited by issues such as photocorrosion or decreased electron extraction efficiency due to formation of interfacial oxide species, which becomes especially critical when operating electrodes (typically, semiconductors) are exposed to aqueous electrolytes [2]. Therefore, It is desirable to understand the process of water interactions with semiconductors and possible oxidation and reduction mechanisms at the H2O/semiconductor interface, especially under near realistic conditions.
In the present study, water dissociative adsorption on a GaP (111) surface was investigated using near ambient pressure X-ray photoelectron spectroscopy (NAP XPS) at various pressures and temperatures. The interfacial chemistry was tracked by recording high resolution photoemission spectra of Ga 2p3/2, O 1s and P 2p. In the pressure-dependent study (room temperature, ~300 K), enhanced surface Ga hydroxylation and oxidation were observed with an increase of water vapor pressure, which was also mirrored by the photoemission spectra of O 1s. In the temperature-dependent study, surface Ga hydroxylation and oxidation were further enhanced at temperatures below 673 K. While a large-scale conversion of surface O-Ga-OH species into Ga hydroxide, along with surface P oxidation, was observed at a temperature of 773 K. The formation of Ga and P oxide/hydroxide networks with a schematic formula of GaaPbOc(OH)d (a, b, c and d represent a ratio of different elements and groups) is suggested. Our results can be compared with recent theoretical findings [3, 4] and lead to a better understanding of water splitting mechanisms and photo-corrosion on semiconductor surfaces.
Reference
1. H.-J., L.; Peter, L. Photoelectrochemical Water Splitting: Materials, Processes and Architectures; Royal Society of Chemistry: Cambridge, GBR, 2013.
2. Lewerenz, H. J. et al. Photoelectrocatalysis: Principles, Nanoemitter Applications and Routes to Bio-Inspired Systems. Energ. Environ. Sci. 2010, 3, 748-760.
3. Wood, B. C. et al. Hydrogen-Bond Dynamics of Water at the Interface with InP/GaP(001) and the Implications for Photoelectrochemistry. J. Am. Chem. Soc. 2013, 135, 15774-15783.
4. Munoz-Garcia, A. B. et al. Non-innocent Dissociation of H2O on GaP(110): Implications for Electrochemical Reduction of CO2. J. Am. Chem. Soc. 2012, 134, 13600-13603.