Microwaves as a synthetic route for preparing electrochemically active TiO 2 nanoparticles
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Alexandre Ponrouch Institut de Ciència de Materials de Barcelona (ICMAB-CSIC) Campus UAB, E-08193 Bellaterra, Catalonia, Spain
Marc Estruga Departament de Química, Universitat Autònoma de Barcelona, Campus UAB, E-08193 Bellaterra, Catalonia, Spain
Maria Rosa Palacína) Institut de Ciència de Materials de Barcelona (ICMAB-CSIC) Campus UAB, E-08193 Bellaterra, Catalonia, Spain
José Antonio Ayllónb) Departament de Química, Universitat Autònoma de Barcelona, Campus UAB, E-08193 Bellaterra, Catalonia, Spain
Anna Roig Institut de Ciència de Materials de Barcelona (ICMAB-CSIC) Campus UAB, E-08193 Bellaterra, Catalonia, Spain (Received 5 May 2012; accepted 13 August 2012)
Nanocrystalline anatase was synthesized, using both domestic and laboratory microwave ovens, from different precursors. Nanoparticulate anatase was obtained after microwave irradiation of tetra-butyl orthotitanate solution in benzyl alcohol. As-synthesized samples have orange color due to the presence of organics that were eliminated after annealing at 500 °C, whereas the size of small anatase nanocrystals (around 8 nm) was preserved. Other nanocrystalline anatase samples were obtained from hexafluorotitanate-organic salt ionic liquid-like precursors. In this case, use of a domestic microwave oven and very short processing times (1–3 min irradiation time) were involved. Good specific capacity values and capacity retention at high C rates for insertion/deinsertion of Li1 were recorded when testing such nanoparticles as electrode material in lithium cells. The electrochemical performances were found be strongly dependent on the phase composition, which in turn could be tuned through the synthetic procedure.
I. INTRODUCTION
Titanium dioxide can be considered a key technological material as it is used in a large panel of applications; also, titanium is a plentiful element, being the 10th most abundant element on the earth. Titanium dioxide is widely used as a white pigment (i.e., in paints and cosmetic products)1 and plays a role in the biocompatibility of bone implants.2 Other prospective applications include photocatalysis,3,4 fuel cells,5 solar cells,6 sensors,7 corrosion-protective coatings,8,9 capacitors and thin films transistors.10,11 Energy storage is another most promising application for TiO2. Anatase was tested long ago in lithium secondary cells with nonaqueous electrolytes12 showing a flat discharge curve (;1.8 V) and quite a good cyclability but moderate reversible capacity. The feasibility of a rocking chair lithium ion battery using nanosized anatase as negative electrode was proved13 and the electrochemical Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2012.289 340
J. Mater. Res., Vol. 28, No. 3, Feb 14, 2013
testing of other TiO2 polymorphs in the form of nanoparticles further investigated.14,15 TiO2 has a theoretical specific capacity of 335 mAh/g [assuming full reduction to Ti(III) to yield lithium titanate (III) (LiTiO2)] and a higher operation voltag
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