  Hybridisation is a powerful strategy towards the next generation of
multifunctional materials for environmental and sustainable energy
applications. Here, we report a new inorganic nanocarbon hybrid material
prepared with atomically controlled deposition of a monocrystalline TiO2 layer
that conformally coats a macroscopic carbon nanotube (CNT) fiber. Through X-ray
diffraction, Raman spectroscopy and photoemission spectroscopy we detect the
formation of a covalent Ti-O-C bond at the TiO2/CNT interface and a residual
strain of approximately 0.7-2 \%, which is tensile in TiO2 and compressive in
the CNT. It arises after deposition of the amorphous oxide onto the CNT surface
previously functionalized by the oxygen plasma used in ALD. These features are
observed in samples of different TiO2 thickness, in the range from 10 to 80 nm.
Ultraviolet photoemission spectroscopy on a 20 nm-thick TiO2 coated sample
gives a work function of 4.27 eV, between that of TiO2 (4.23 eV) and the CNT
fiber (4.41 eV), and the presence of new interband gap states that shift the
valence band maximum to 1.05 eV below the Fermi level. Photoelectrochemical
measurements demonstrate electron transfer from TiO2 to the CNT fiber network
under UV irradiation. Electrochemical impedance spectroscopy measurements
reveal a low resistance for charge transfer and transport, as well as a large
capacitance. Our results point to the fact that these hybrids, in which each
phase has nanometric thickness and the current collector is integrated into the
material, are very different from conventional electrodes and can provide a
number of superior properties.
