Niobium-based oxides possess varieties of composition and structure, such as NbO, Nb₂O₃, Nb₂O₅ and Nb₃O₇X (X=OH, F) with different nanostructure forms of nanoparticles, nanorods and nanobelts. Owing to their unique composite and structural properties, these niobium-based oxides draw intensive attention in energy storage and conversion fields. However, their relatively low surface area generally results in low performance of materials when applied to energy technology.

To tackle the issues mentioned above, a research group in Centre of Environmental and Energy Nanomaterials (CEEN), Institute of Solid State Physics, Hefei Institutes of Physical Science, made progress in controllable synthesis and applications of highly ordered Nb₃O₇ (OH) nanowire array assembled three-dimensional (3D) structures in dye-sensitized solar cells (DSSCs) and lithium-ion batteries (LiBs). The related work was published in ACS Nano entitled Highly Ordered Single Crystalline Nanowire Array Assembled Three-Dimensional Nb₃O₇(OH) and Nb₂O₅Superstructures for Energy Storage and Conversion Applications. 

The research group fabricated highly ordered single crystal Nb₃O₇ (OH) nanowire array assembled 3D structure material by a facile hydrothermal method (figure A-L). The obtained 3D Nb₃O₇ (OH) nanowire array structure possesses high surface area of 121.5 m²g^-1 and microporous/mesoporous structure, which can be directly hydrothermally grown onto FTO conducting glass substrate to form stable 3D Nb₃O₇(OH) nanowire array structure film. With no need for further high-temperature thermal treatment, the fabricated 3D Nb₃O₇ (OH) nanowire array structure film onto FTO can be directly used as photoanode for dye-sensitized solar cells, exhibiting superior light-to-electricity conversion efficiency (figure M).

Additionally, this obtained 3D Nb₃O₇ (OH) nanowire array structures after high-temperature thermal treatment can readily transform into Nb₂O₅ nanowire array structure with well-preserved 3D framework structure and a surface area of 81.8 m²g^-1. As anode material, the obtained 3D Nb₂O₅ nanowire array structure is potentially applicable to lithium-ion batteries (LiBs) (figure N). The superior performance in DSSCs and LiBs can be ascribed to the 3D Nb₃O₇ (OH) and Nb₂O₅ materials with high surface area, porous structure and high crystallinity of nanowires, which help to improve dye molecule adsorption, mass transport and electron transfer.

This study was sponsored by the CAS Pioneer Hundred Talents Program and the Natural Science Foundation of China, the Strategic Priority Research Program of the Chinese Academy of Sciences and the CAS/SAFEA International Partnership Program for Creative Research Teams of Chinese Academy of Sciences, China.

(A-L) XRD patterns, SEM and TEM images of 3D Nb3O7(OH) nanowire array structure; (M) DSSCs performance; (N) LiBs performance. (Image by ZHANG Haimin)