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. 64.70.Nd, 81.16.Be Au, Ag, Pt and Pd doped TiO 2 nanocrystals were prepared using sol-gel routes. X-ray Near Edge Structure (XANES) was used to study the location of these precious metal dopants in nanocrystalline TiO 2 . The effects of these dopants on the phase transformation and grain growth were investigated using X-ray diffraction (XRD). Two dopant concentrations i.e. 1 and 5% were studied and similar results were found. Silver and Palladium initially form oxides but annealing at high temperatures converts them to metals. Gold and and silver do not affect the anatase -rutile transformation temperature whereas palladium and platinum do. 1 Introduction Titanium dioxide, TiO 2 , is a very important technological material which is currently being investigated for advanced functional and environmental applications, such as photocatalysis, photovoltaic cells and solid state gas sensing [1,2]. TiO 2 has a large band gap energy and due to this, it absorbs only the ultraviolet (UV) part of solar radiation leading to low conversion efficiency. Various approaches have been employed to extend the absorption edge of TiO2 from the UV into the visible region. In photovoltaic cells, TiO2 is sensitized with dyes to extend its photosensitivity to longer wavelengths. Alternatively, the light sensitivity of TiO 2 can be shifted into the visible region by narrowing the band gap [3,4]. This is generally done by doping TiO 2 with certain elements [5].In the nanocrystalline state, TiO 2 , like other oxides, can dissolve higher concentrations of impurities than its bulk counterparts as they have an increased density of grain boundaries where considerable amounts of dopants can segregate. This dopant segregation has been found in some cases to improve the catalytic activity and electrical properties. In previous computational work [6] we have studied the influence of the dopants (i.e. Pt, Pd, Ag, and Au) on the optical and structural properties of single crystalline anatase TiO 2 using the local spin density approximation (LSDA) within the density functional theory. The results show that doping TiO 2 with these precious metals enhances absorption in the visible range (i.e. above 400 nm) with Ag showing the most enhanced absorption. This offers the possibility of considerable improvement in photovotaic cells.Experimental information is essential for the verification and ultimate improvement of the simulations and EXAFS experiments are unique in providing this kind of information . For example, the EXAFS can determine the oxidation state of the dopant, the detailed local environment of the dopant (nature of the neighbours, bond distances to neighbours, degree of disorder, etc.) and segregation of the dopant.In this contribution we report the XANES and XRD studies of precious metal doped nano-TiO 2.

Power output is central to the viability of a Liion battery and is, in part, dependent upon the activation energy barrier associated with Li intercalation/deintercalation into the host lattice (electrode). The lower the energy barrier, the faster the intercalation reaction rate and greater the power. The activation energy is governed by the atomistic structure(s) of the entrance sites for Li intercalation. Accordingly, a first step in optimizing battery power via structural manipulation of entrance sites is to understand the structure of these entrance sites. However, HRTEM is (presently) unable to characterize the structures of entrance sites with atomistic resolution. Accordingly, we generate models of the entrance sites using molecular dynamics. In particular, we simulate the synthetic protocol used to fabricate nanostructured TiO 2 experimentally. The resulting atomistic models reveal a highly complex and diverse structural distribution of entrance sites, which emanate from the surface curvature of the nanostructured material. In particular, we show how nanostructuring can be used to change profoundly the nature and concentration of such entrance sites. ■ INTRODUCTIONNanostructured materials have shown great promise recently as potential electrodes for Li-ion batteries. 1,2 In particular, Ren et al. showed that mesoporous TiO 2 , with a 3D pore structure, can be used as an anode-replacing graphite. 3 Similarly, mesoporous MnO 2 can act as a cathode. 4 Nanostructuring of the electrodes was shown, in both cases, to confer electrochemical activity upon the materials; 5 the parent bulk materials are electrochemically inactive. A recent simulation study revealed that mesoporous materials are able to expand and contract elastically (during charge cycling) as pseudo "breathingcrystals"enabling retention of the structure and crucially the 1 × 1 tunnels in which the Li ions enter and reside. 6 Conversely, the bulk parent material deforms plastically during intercalation, pulverizing the tunnels. 4,6 Central to the power output and charge time of batteries is the activation energy barriers associated with Li intercalation/ deintercalation from the host electrodes. The lower the energy barriers, the faster the reactions facilitating higher power and lower charge times. The activation energy is governed by the atomistic structure(s) of the entrance sites for Li intercalation. Accordingly, a first step in tuning battery power, via structural manipulation of entrance sites, is to understand their structure.Inspection of HRTEM images of mesoporous TiO 2 ( Figure 1) reveals that the entrance sites are not structurally uniform; 3 rather the figure reveals a diverse structural complexity, which emanates from the three-dimensional curvature of the pore. Accordingly, if one were to use a model of the perfect surface to calculate energy barriers associated with Li intercalation, the results would prove erroneous because the model would not capture the structural perturbations emanating from the curvature of the surface. Indeed,...

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Studies on TiO2 nanosheets for energy storage and conversion, including anode in lithium ion batteries (LIB) and electrodes in dye solar cells respectively, are not as abundant as those of nanoparticle and nanoporous structures [1]. Such nanosheets are ideal owing to exposure of highly reactive surfaces, such as the anatase {001}facets, which can now be stabilised [2]. Electrochemical investigations reveal that the exposed (001) high-energy facets of the nanosheet result in enhanced rate capability which originates from both the shortened diffusion path and lowered insertion energy barriers on the active surface for Li+ ions [3]. Furthermore, the electrolyte/electrode contact is enhanced via hollow structures; and such features collectively allow for more efficient lithium diffusion in anodes of LIB. In addition to the anatase polymorph [4], TiO2–B [5] nanosheets have also been observed. Generally, studies of nanostructures with the brookite structure are scarce since this polymorph is difficult to grow. Aggregations of nanoparticles with the brookite structure have been reported [6]. However, TiO2 nanosheets with the brookite and rutile components have been recently observed [7]. In order to understand such nano-architecture better, we present results of TiO2 simulated nanosheets, which were generated by amorphisation recrystallisation method [8]. Simulated X-ray diffractions of such structures allude to the presence of the brookite and rutile polymorphs. In addition analysis of their microstructures clearly show zigzag patterns associated with the brookite and straight tunnels related to twinned rutile polymorphs. The lithiated nanosheets of TiO2 were also investigated, and lithium ions were located well within the observed tunnels. The suitability of this TiO2polymorph and nano-architecture for lithium ion batteries electrodes, as compared to the bulk form, will be discussed. References [1] Su X., Wu Q-L., Zhan X., Wu J., Wei S. and Guo Z. (2012) J. Mater Sci. 47,2519. [2] Yang H. G., Sun C. H., Qiao S. Z., Liu J. Z. Smith S. C. Cheng H. M. and Lu G. Q. (2008) Nature 453, 638. [3] Knauth P. and Tuller H. L. (1999) J. Appl. Phys. 85, 897. [4] Wei X., Liu J., Chua Y. Song J. and Liu X. (2011) Energy Environ. Sci. 4,2054. [5] Liu S.,Jia H., Han L., Wang J., Gao P., Yang J. and Che S. (2012) Adv. Mater. 24,3201. [6] Reddy M. A., Pralong V., Varadaraju U. V. and Raveau B. (2008), Electrochem. Solid-State Lett. 11, A132 – A134. [7] Sussman M., Clouteau, Yasin A., Guo F., and Demopoulos G.P. (2013) Abstract #881, 224th ECS Meeting, © 2013 The Electrochemical Society. [8] P.E.Ngoepe, R.R. Maphanga and D.C. Sayle, (2013), “Towards the Nanoscale”, Chapter 9 in Computational Approaches to Energy Materials, pp 261-290, edited by C.R.A. Catlow, A. Sokol and A. Welsch, John Wiley and Sons Ltd.