Improving Photoelectrochemical Hydrogen Production: Analysis of Thin Film Bismuth Vanadate Using Raman Spectroscopy
Hydrogen produces no pollution when it is used as a fuel source and for this reason; it is desirable to develop an efficient, environmentally friendly, and economic method of obtaining it. The use of solar energy to directly separate hydrogen from oxygen is one of the best candidates for achieving this goal. A catalyst material is required to facilitate this photoelectrochemical process and finding ways to increase the effectiveness of the catalyst is paramount. Bismuth vanadate, BiV04 is known to be a photocatalyst. Bulk BiVO4 is known to exist in several crystalline forms (polymorphs). When its structure is monoclinic, it is expected to have increased efficiency over other polymorphs. A sample of thin film epitaxial BiV04 -grown by our collaborators on yittria-stabilized cubic zirconia substrate and expected to be of monoclinic structure- was provided for analysis. The sample was analyzed using Raman spectroscopy, a technique capable of distinguishing different crystalline structures. The spectra were measured with several excitation laser lines in the range from 325 to 514.5 nm. The 441.6 nm line was found to produce the strongest Raman signal from BiVO4, because it is close to resonance with the bandgap of BiVO4. Spectra were measured at both 10K and 300K sample temperatures. The analysis of the spectra indicated that the sample was most likely of monoclinic structure. Supported in part by the National Science Foundation through the Grant DMR-1006136.