Probing the effect of atomic and morphological arrangements in the pseudocapacitive properties of TT-Nb2O5 nanostructures

In this study, we determine the role of oxygen vacancies and preferred surface orientation on the charge storage properties of the lithium intercalation host, pseudohexagonal TT-Nb₂O₅. Two different morphologies were synthesized, namely nanosheets and nanowires. We employed a set of advanced characterization techniques including entropic potential measurements, high-resolution synchrotron X-ray diffraction and synchrotron X-ray absorption spectroscopy together with electrochemical measurements and density functional theory calculations. Our results indicate that the two morphologies exhibit different oxygen vacancy characteristics as nanosheets have oxygen vacancies limited to the surface while nanowires possess vacancies which tend to be located in the bulk solid. Oxygen vacancies in the bulk of TT-Nb₂O₅ lead to an appreciable increase in specific capacity compared to nanosheets where oxygen vacancies confined to specific crystallographic surfaces do not make a significant contribution to the electrochemical response of the TT-Nb₂O₅ anodes. These results show how the distribution and concentration of oxygen vacancies play a major role in the lithiation mechanisms of TT-Nb₂O₅.