Surface analysis and photoelectrochemical studies of mixed polycrystals of p-WSe{sub 2}/WS{sub 2}
- Univ. of Puerto Rico, San Juan (Puerto Rico)
Mixed polycrystals of p-WSe{sub 2}/WS{sub 2} with varied composition have been grown by the physical vapor transport technique by using the original compounds as starting materials. Three atomic ratios of WSe{sub 2}/WS{sub 2}, I(1:2), II(1:1), and III(2:1), were used. The mixed polycrystals were studied by scanning electron microscopy, X-ray fluorescence, and Auger electron spectroscopy. For the three syntheses, two types of polycrystals, rough (r) and smooth (s), were observed. The rough side had axial planes at the surface, while the smooth side had basal planes. The average size of the hexagonal single-crystal flakes, which form the polycrystal array, increased with a decrease in the sulfur content; Ir(118 {micro}m) < IIr (256 {micro}m) < IIIr (295 {micro}m). Direct energy bandgaps of 1.78, 1.71, and 1.66 eV were calculated for compounds I, II, and III, respectively. These p-type semiconductors have been characterized as electrode materials in nonaqueous systems by using cyclic voltammetry and photovoltammetry. Without illumination compound Ir showed a diffusion control cyclic voltammogram with the highest dark current. This is due to the high density of axial to basal plane ratio. The flatband potential in acetonitrile in the dark decreased with a decrease in the sulfur content, from 1.12 for compound Ir to 0.78 V vs. SSCE for compound IIIr. The compound with the highest sulfur concentration (Ir) presented the highest underpotential in all the redox systems, while the compound with the lowest sulfur concentration showed the highest photocurrent. Compound IIr combines a large crystal size with an adequate sulfur concentration to present the highest conversion efficiency (0.36%) in a chloranil{sup 0/+1} (0.010M/0.001M) and TBAP 0.25M solution.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 110134
- Journal Information:
- Journal of the Electrochemical Society, Vol. 142, Issue 8; Other Information: PBD: Aug 1995
- Country of Publication:
- United States
- Language:
- English
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