TiO2-Based Nanomaterials for the Production of Hydrogen and the Development of Lithium-Ion Batteries

The photocatalytic activity of different titanium oxide nanowires containing gold (Au@TiO2NWs), and gold-graphene (Au@TiO2NWs-graphene), was evaluated by studying the reaction of hydrogen production by water splitting under UV–vis light. The composites showed high surface areas, with values above 300 m2per gram, even after the incorporation of gold and graphene on the surface of titanium oxide nanowires. The highest hydrogen production of Au@TiO2NWs was 1436 μmol h–1g–1, under irradiation at 400 nm, and with a gold loading of 10 wt %. This photocatalytic activity was 11.5 times greater than that shown by the unmodified TiO2NWs. For the Au@TiO2NWs-graphene composites, the highest hydrogen amount obtained was 1689 μmol h–1g–1, at loadings of 10 and 1 wt % of gold and graphene, respectively. The photocatalytic activity of the gold-graphene compounds was 1.2 times greater than that shown by the titanium oxide catalysts and 13.5 times higher than the bare TiO2NWs. Even at wavelengths greater than 500 nm, the compounds exhibited yields of hydrogen above 1000 μmol h–1g–1, demonstrating the high catalytic activity of the compounds. In addition, TiO2-based materials are of great interest for energy storage and conversion devices, in particular for rechargeable lithium ion batteries. TiO2has a significant advantage due to its low volume change (<4%) during the Li ion insertion/desertion process, short paths for fast lithium ion diffusion, and large exposed surface, offering more lithium insertion channels. However, the relatively low theoretical capacity and electrical conductivity of TiO2greatly hamper its practical application. In this work, free-standing electrodes composed by TiO2NWs and carbon nanotubes, CNT@TiO2NWs, were used as anode materials for Li-ion batteries. As a result, the electronic conductivity and mechanical properties of the composite were greatly improved and a good cycling performance was obtained in these batteries. This research shows the potential of TiO2-based materials for the development of new catalysts for hydrogen production and energy storage systems.