Theoretical and Experimental Study on the Optoelectronic Properties of Nb₃O₇(OH) and Nb₂O₅ Photoelectrodes

Nb₃O₇(OH) and Nb₂O₅ nanostructures are promising alternative materials to conventionally used oxides, e.g. TiO₂, in the field of photoelectrodes in dye-sensitized solar cells and photoelectrochemical cells. Despite this important future application, some of their central electronic properties such as the density of states, band gap, and dielectric function are not well understood. In this work, we present combined theoretical and experimental studies on Nb₃O₇(OH) and H–Nb₂O₅ to elucidate their spectroscopic, electronic, and transport properties. The theoretical results were obtained within the framework of density functional theory based on the full potential linearized augmented plane wave method. In particular, we show that the position of the H atom in Nb₃O₇(OH) has an important effect on its electronic properties. To verify theoretical predictions, we measured electron energy-loss spectra (EELS) in the low loss region, as well as, the O–K and Nb–M₃ element-specific edges. These results are compared with corresponding theoretical EELS calculations and are discussed in detail. In addition, our calculations of thermoelectric conductivity show that Nb₃O₇(OH) has more suitable optoelectronic and transport properties for photochemical application than the calcined H–Nb₂O₅ phase