Paper EN2+TF-WeA8
Photoelectrochemical Water Splitting by Hematite Nanostructures Prepared by Chemical Bath Deposition

Wednesday, November 2, 2011, 4:20 pm, Room 106

Hematite (a-Fe₂O₃) is a promising material for sustainable generation of H₂ due to its low cost, widespread availability, chemical stability, and ability to absorb a significant fraction of visible light. However numerous challenges remain in order for this material to approach its theoretical potential of 15% solar to hydrogen efficiency. Nanorod geometries are an ideal configuration for this material, decoupling the different length scales required for photon absorption and efficient carrier transport. Unfortunately such structures have historically yielded poor photoelectrochemical performance (<5 mA/cm²).¹ We recently demonstrated that nanorods synthesized by chemical bath deposition (CBD) could be activated through the use of appropriate annealing treatments.² Photocurrents >500 mA/cm² were achieved at 1.23 V versus RHE, and the photoanodes displayed low onset potentials. These changes were correlated with significant amount of tin diffusion from the underlying FTO substrate into the Fe₂O₃ matrix occurs during high temperature annealing process. The benefits of this process may include enhanced conductivity as well as improvement of the FTO/ Fe₂O₃ interface. Despite these advancements, significant room remains for further improvement. In this paper we describe a number of strategies to reach this goal. First, the nanostructure of the hematite can be further improved. This is explored by varying the CBD chemistry, optimizing the post-deposition annealing conditions, and through subtractive processing. A second issue is electron transport at the hematite/FTO interface, and this is explored through the use of novel treatments of the FTO prior to deposition. Finally, the addition of an electrocatalyst can further reduce the onset potential. Each of these three strategies has demonstrated enhanced photocurrent over our previous results. We plan to integrate these advancements in order to maximize performance. Detailed characterization of the structure, composition, and electrochemical changes observed with these processes will be used to provide fundamental insight into the mechanisms underlying the improvements.

References

[1] N. Beermann, L. Vayssieres, S.-E. Lindquist & A. Hagfeldt, "Photoelectrochemical Studies of Oriented Nanorod Thin Films of Hematite", 2456-2461, (2000).

[2] R. Morrish, M. Rahman, J. M. D. MacElroy & C. A. Wolden, "Activation of hematite nanorod arrays for photoelectrochemical water splitting", 474-479, (2011).