A sensitized Nb2O5 photoanode for hydrogen production in a dye-sensitized photoelectrosynthesis cell
Orthorhombic Nb2O5 nanocrystalline films functionalized with [Ru(bpy)2(4,4?-(PO3H2)2bpy)]2+ were used as the photoanode in dye-sensitized photoelectrosynthesis cells (DSPEC) for hydrogen generation. A set of experiments to establish key properties—conduction band, trap state distribution, interfacial electron transfer dynamics, and DSPEC efficiency—were undertaken to develop a general protocol for future semiconductor evaluation and for comparison with other wide-band-gap semiconductors. We have found that, for a T-phase orthorhombic Nb2O5 nanocrystalline film, the conduction band potential is slightly positive (<0.1 eV), relative to that for anatase TiO2. Anatase TiO2 has a wide distribution of trap states including deep trap and band-tail trap states. Orthorhombic Nb2O5 is dominated by shallow band-tail trap states. Trap state distributions, conduction band energies, and interfacial barriers appear to contribute to a slower back electron transfer rate, lower injection yield on the nanosecond time scale, and a lower open-circuit voltage (Voc) for orthorhombic Nb2O5, compared to anatase TiO2. In an operating DSPEC, with the ethylenediaminetetraacetic tetra-anion (EDTA4–) added as a reductive scavenger, H2 quantum yield and photostability measurements show that Nb2O5 is comparable, but not superior, to TiO2.
Luo, H., Song, W., Hoertz, P., Hanson, K., Ghosh, R., Rangan, S., ... Meyer, T. J. (2013). A sensitized Nb2O5 photoanode for hydrogen production in a dye-sensitized photoelectrosynthesis cell. Chemistry of Materials, 25(2), 122-131. DOI: 10.1021/cm3027972