ZnCdSe-Sensitized WO3 and TiO2 based Photoelectrodes: A Comparative Study

After about four decades since Honda and Fujishima’s electrochemical photolysis report using TiO₂(1), intensive research is still ongoing to identify efficient and cost effective semiconductor materials to be integrated in a photoelectrochemicalsystem. The ultimate goal is to have such a design that can simultaneously drive, both the hydrogen evolution and water oxidation reactions. Among all candidate materials, inexpensive metal oxides have been the primary choice due to their stability and excellent corrosion resistance.(2) However, the major drawback is their poor optical absorption that restrains solar-to-hydrogen efficiency to only few percent (3).

The best research strategy is to focus on a thermodynamically stable system with appropriate absorption properties and then attempt to improve its absorption, transport and catalytic properties. A stable tungsten based material with appropriate band edge alignment was chosen and the change in its band gap in the presence of a transition metal dopant was theoretically calculated. Based on the preliminary calculations, an optimal concentration of dopant was chosen and the material was synthesized via spray deposition. Surface morphology of the films (before and after sensitization) was examined using scanning electron microscope.Composition of substrate and oxidation state of elements was analyzed using X-ray diffraction and X-ray photoelectron spectroscopy. Absorption characteristics were determined using UV-Visible spectroscopy. Photoelectrochemical measurements (photocurrent/ photovoltage versus time and I-V characteristics) were undertaken to depict the photoconversion efficiency of designed photoanodes. The correlation of morphological changes with photoelectrochemical response of doped-oxide nanostructures will be discussed. Stability studies of the oxide films, conducted using ICP-OES, will also be presented.

Our results show that the bandgap can be altered significantly by using different dopants.  Furthermore, for a given dopant, the synthesis parameters such as composition, film thickness, temperature, and dopant concentration play a significant role in determining the final characteristics.  

 

Acknowledgements: This work was funded by Department of Energy under contract DE-FC36-06-GO86066. Dr. David Peterson and Dr. Eric Miller act as the program manager and the technical manager, respectively.

 

References

1.             A. Fujishima and K. Honda, Nature, 238, 37 (1972).

2.             N. M. Gaillard, in Meeting Abstracts, p. 1741 (2012).

3.             N. Gaillard, Y. Chang, J. Kaneshiro, A. Deangelis and E. Miller, in SPIE Solar Energy+ Technology, p. 77700V (2010).