Oriented epitaxial TiO₂nanowires for water splitting

Abstract

Highly oriented epitaxial rutile titanium dioxide (TiO) nanowire arrays have been hydrothermally grown on polycrystalline TiO templates with their orientation dependent on the underlying TiO grain. Both the diameter and areal density of the nanowires were tuned by controlling the precursor concentration, and the template surface energy and roughness. Nanowire tip sharpness was influenced by precursor solubility and diffusivity. A new secondary ion mass spectrometer technique has been developed to install additional nucleation sites in single crystal TiO templates and the effect on nanowire growth was probed. Using the acquired TiO nanowire synthesis knowhow, an assortment of nanowire arrays were installed upon the surface of undoped TiO photo-electrodes and assessed for their photo-electrochemical water splitting performance. The key result obtained was that the presence of short and dispersed nanowire arrays significantly improved the photocurrent when the illumination intensity was increased from 100 to 200 mW cm. This is attributed to the alignment of the homoepitaxially grown nanowires to the [001] direction, which provides the fastest charge transport in TiO and an improved pathway for photo-holes to find water molecules and undertake oxidation. This result lays a foundation for achieving efficient water splitting under conditions of concentrated solar illumination.

Synergistic Cooperation of Rutile TiO2 {002}, {101}, and {110} Facets for Hydrogen Sensing

“…Because of the advantages of low cost, stable physical and chemical properties, and abundant material availability, wide-band-gap metal oxide semiconductors (SnO 2 , NiO, TiO 2 , CuO, ZnO, etc.) have been extensively applied in various fields, such as solar cells, lithium ion batteries, electro- or photo-catalysis, and gas sensors. − The functionality of these semiconductor oxides is strongly dependent on the crystal structure especially the exposure of high energy surfaces, on which chemical reactions such as water splitting and gas dissociation can be easily realized. − The exposed facets introduce more atom steps, edges, kinks, and dangling bonds, which usually have high chemical activity. , Hierarchical SnO 2 nanoflowers with high-index {113} and {102} facets exposed have shown high NO 2 gas sensing sensitivity and selectivity . Fe 3 O 4 with exposed {110} facets has shown a significant potential in lithium storage with good cycle performance and specific capability .…”

Comparing Scanning Electron Microscope and Transmission Electron Microscope Grain Mapping Techniques Applied to Well-Defined and Highly Irregular Nanoparticles

“…The underlying grain structure of nanomaterials strongly affects their functional properties. Studies of well-defined semiconducting nanowires have identified specific effects of grain orientations, phase boundaries, and defect densities on electronic, optical, thermoelectric, and (photo)­electrochemical properties. − A broader understanding of these phenomena across diverse semiconductor materials is crucial for the design of next-generation optical/electronic devices. Recent studies have also probed the effects of the grain structure on the catalytic properties of nanomaterials.…”