Motoki Osada1 Kazunori Nishio2 3 Kyuho Lee4 Harold Hwang2 3 Yasuyuki Hikita3

1, Stanford University, Stanford, California, United States
2, Stanford University, Stanford, California, United States
3, SLAC National Accelerator Laboratory, Menlo Park, California, United States
4, Stanford University, Stanford, California, United States

Development of scalable semiconductor photoanodes with a suitable bandgap (1.8 - 2.4 eV), low resistivity, and long-term chemical stability is a primary challenge in photocatalyst and photoelectrochemical (PEC) research. The complex oxide semiconductor, pseudobrookite Fe2TiO5, is a prospective candidate consisting of earth-abundant elements Ti and Fe with an ideal optical bandgap of 2.18 eV [1]. Despite a few studies focusing on the application of Fe2TiO5 as photoanodes in polycrystalline thin films and in heterojunctions [2], the intrinsic PEC properties of Fe2TiO5 have not been clarified, fundamentally limiting further evaluation and development of this materials system.
Recently, we successfully fabricated epitaxial Fe2TiO5 thin films on single crystalline LaAlO3 (001) substrates using pulsed laser deposition, and thoroughly characterized their optical and transport properties, finding that the intrinsic resistivity (10 - 100 Ωcm) at room temperature is substantially lower than that of un-doped α-Fe2O3, despite similar optical gaps [3]. Based on these results, here we present our investigation of the intrinsic PEC properties of epitaxial Fe2TiO5 thin film photoanodes for solar-water splitting. A photocurrent density of 0.08 mA/cm2 was achieved at 2 V vs. RHE under 1 Sun, and a flatband potential of 0.40 vs. RHE was obtained in pH = 13. These results indicate that Fe2TiO5 has high potential as an ideal photoanode in solar-fuel conversion. Details of the photocurrent measurement, Mott-Schottky analysis, and long-term stability in solution will be discussed in the presentation.

[1] D. S. Ginley and M. A. Butler, J. Appl. Phys. 48, 2019 (1977).
[2] Q. Liu et al., Nat. Commun. 5, 5122 (2014).
[3] M. Osada, et al., 2017 MRS Spring Meeting & Exhibit ES7.18.03.