Ten different nanotextured TiO2 films were prepared from six commercial and four laboratory synthesized precursors. Krypton adsorption isotherms on the films and parent powders indicate the effect of sintering and agglomeration. Electrochemical characterization of the films was aimed at double‐layer charging and Li+ insertion. The relations between the film's morphology, adsorption properties, and electrochemical behavior in the accumulation regime are discussed.

Ultrasmall, crystalline, and dispersible NiO nanoparticles are prepared for the first time, and it is shown that they are promising candidates as catalysts for electrochemical water oxidation. Using a solvothermal reaction in tert‐butanol, very small nickel oxide nanocrystals can be made with sizes tunable from 2.5 to 5 nm and a narrow particle size distribution. The crystals are perfectly dispersible in ethanol even after drying, giving stable transparent colloidal dispersions. The structure of the nanocrystals corresponds to phase‐pure stoichiometric nickel(ii) oxide with a partially oxidized surface exhibiting Ni(iii) states. The 3.3 nm nanoparticles demonstrate a remarkably high turn‐over frequency of 0.29 s–1 at an overpotential of g = 300 mV for electrochemical water oxidation, outperforming even expensive rare earth iridium oxide catalysts. The unique features of these NiO nanocrystals provide great potential for the preparation of novel composite materials with applications in the field of (photo)electrochemical water splitting. The dispersed colloidal solutions may also find other applications, such as the preparation of uniform hole‐conducting layers for organic solar cells.

Thin layer electrodes (0.2−0.5 μm) of highly organized nanotextured anatase were prepared by hydrolysis of TiCl4 in the presence of poly(alkylene oxide) block copolymer, Pluronic P-123, acting as the structure-directing agent. Electrochemical properties of these layers were studied in KCF3SO3 + propylene carbonate and in LiN(CF3SO2)2 + ethylene carbonate + dimethoxyethane. The electrodes showed unusually fast capacitive and Li-insertion charging. A most striking effect was the occurrence of two new pairs of peaks in cyclic voltammograms in Li+ containing electrolyte solutions. These, so-called S-peaks, appear in addition to the “ordinary” peaks of Li insertion into anatase. The S-peaks can act as indicators of mesoscopic ordering of the skeleton as they diminish after mechanical or thermal destruction of the organized nanotexture. We suggest that the occurrence of S-peaks is connected to the presence of amorphous TiO2 in the organized skeleton.

A study of electrochemical Li insertion combined with structural and textural analysis enabled the identification and quantification of individual crystalline and amorphous phases in mesoporous TiO2 films prepared by the evaporation‐induced self‐assembly procedure. It was found that the properties of the amphiphilic block copolymers used as templates, namely those of a novel poly(ethylene‐co‐butylene)‐b‐poly(ethylene oxide) polymer (KLE) and commercial Pluronic P123 (HO(CH2CH2O)20(CH2CH(CH3)O)70(CH2CH2O)20H), decisively influence the physicochemical properties of the resulting films. The KLE‐templated films possess a 3D cubic mesoporous structure and are practically amorphous when calcined at temperatures below 450 °C, but treatment at 550–700 °C provides a pure‐phase (anatase), fully crystalline material with intact mesoporous architecture. The electrochemically determined fraction of crystalline anatase increases from 85 to 100 % for films calcined at 550 and 700 °C, respectively. In contrast, the films prepared using Pluronic P123, which also show a 3D cubic pore arrangement, exhibit almost 50 % crystallinity even at a calcination temperature of 400 °C, and their transformation into a fully crystalline material is accompanied by collapse of the mesoporous texture. Therefore, our study revealed the significance of using suitable block‐copolymer templates for the generation of mesoporous metal oxide films. Coupling of both electrochemical and X‐ray diffraction methods has shown to be highly advisable for the correct interpretation of structure properties, in particular the crystallinity, of such sol–gel derived films.

Crystalline niobium-doped titania nanoparticles were synthesized via solvothermal procedures using tert-butyl alcohol as a novel reaction medium, and their assembly into mesoporous films was investigated. The solvothermal procedure enables the preparation of crystalline doped and undoped nonagglomerated titania nanoparticles, whose size can be controlled from 4 to 15 nm by changing the reaction temperature and time. The anatase lattice of these particles can incorporate more than 20 mol % of Nb ions. The nanoparticles can be easily dispersed at high concentrations in THF to form stable colloidal suspensions and can be assembled into uniform porous mesostructures directed by the commercial Pluronic block copolymer F127. The resulting mesoporous films show a regular mesostructure with a d spacing of about 17 nm, a uniform pore size of about 10 nm with crystalline walls, a high porosity of 43%, and a large surface area of 190 m(2) cm(-3). Substitutional doping with niobium ions drastically increases the electrical conductivity of the titania particles. The electrical conductivity of as-prepared nanoparticles containing 20 mol % of Nb is 2 x 10(-5) S cm(-1); it increases to 0.25 S cm(-1) after treatment at 600 °C in nitrogen.

Ultrasmall and highly soluble anatase nanoparticles were synthesized from TiCl(4) using tert-butyl alcohol as a new reaction medium. This synthetic protocol widens the scope of nonaqueous sol-gel methods to TiO(2) nanoparticles of around 3 nm with excellent dispersibility in ethanol and tert-butanol. Microwave heating was found to enhance the crystallinity of the nanoparticles and to drastically shorten the reaction time to less than 1 h at temperatures as low as 50 degrees C. The extremely small size of the nanoparticles and their dispersibility make it possible to use commercial Pluronic surfactants for evaporation-induced self-assembly of the nanoparticulate building blocks into periodic mesoporous structures. A solution of particles after synthesis can be directly used for preparation of mesoporous films without the need for particle separation. The mesoporous titania coatings fabricated using this one-pot procedure are crystalline and exhibit high surface areas of up to 300 m(2)/g. The advantages of the retention of the mesoporous order with extremely thin nanocrystalline walls were shown by electrochemical lithium insertion. The films made using microwave-treated nanoparticles showed supercapacitive behavior with high maximum capacitance due to quantitative lithiation with a 10-fold increase of charging rates compared to a standard reference electrode made from 20 nm anatase particles.

Conducting antimony-doped tin oxide (ATO) nanoparticles are prepared by a nonaqueous solution route, using benzyl alcohol as both the oxygen source and the solvent, and tin tetrachloride and various Sb(III) and Sb(V) compounds as tin and antimony sources, respectively. This reaction produces nonagglomerated crystalline particles 3−4 nm in size, which can be easily redispersed in high concentrations in a variety of solvents to form stable transparent colloidal solutions without any stabilizing agents. The synthesis temperature is the most important processing parameter largely governing the reaction course and the particle properties, while the nature of the antimony source has only a marginal influence. The cassiterite SnO2 lattice can accommodate up to 30 mol % antimony without significant changes in the structure. The incorporation of an increasing percentage of antimony causes a continuous decrease in particle size and a slight asymmetric lattice distortion. The introduction of an antimony dopant dramatically increases the particle conductivity, which reaches a maximum for 4% antimony, being more than 2 orders of magnitude higher than that of the pristine SnO2 nanoparticles. The obtained conductivity of 1 × 10−4 S/cm is the highest ever reported for the nonannealed nanosized ATO particles. Annealing in air at 500 °C further improves the conductivity to 2 × 102 S/cm, because of the particle sintering. Exceptionally high conductivity, small size, narrow size distribution, and dispersibility in various organic solvents make the ATO nanoparticles excellent primary building units for assembling nanostructured transparent conducting oxide materials with defined porous architectures.

No abstract