Nanoporous hexagonal TiO2 superstructure as a multifunctional material for energy conversion and storage

Abstract

Tremendous efforts have been devoted for the development of rationally designed titanium dioxide (TiO₂) nanostructures, because structural characteristics such as morphology, porosity, size, and crystal phase significantly affect the physical properties of TiO₂. Despite the significant advances made in synthesis strategies over the past few decades, designing an innovative TiO₂ nanostructure that overcomes the limitations that TiO₂ encounters in various applications remains a great challenge. In this study, we demonstrate the synthesis of a hierarchically nanostructured TiO₂ having a higher symmetry (hexagonal structure) than its own constituent tectons. Anatase TiO₂ possesses only a primitive tetragonal unit cell, and there is no hexagonal symmetry axis. Thus, a hexagonal TiO₂ superstructure is hardly obtainable without the multiple twinning of primitive units, which rarely occurs under conventional reaction conditions. Our exotic TiO₂ nanostructure is synthesized by the calcination of a novel TiO₂ precursor that is formed by a simple precipitation reaction and is utilized as an electrode material in energy conversion and storage devices. Due to the unique physical properties offered by this morphology, nanoporous hexagonal TiO₂ is superior to conventionally used TiO₂ in these applications, highlighting the benefits as an advanced, multifunctional electrode material.