Thierry Djenizian

Three‐Dimensional Self‐Supported Metal Oxides for Advanced Energy Storage

The miniaturization of power sources aimed at integration into micro- and nano-electronic devices is a big challenge. To ensure the future development of fully autonomous on-board systems, electrodes based on self-supported 3D nanostructured metal oxides have become increasingly important, and their impact is particularly significant when considering the miniaturization of energy storage systems. This review describes recent advances in the development of self-supported 3D nanostructured metal oxides as electrodes for innovative power sources, particularly Li-ion batteries and electrochemical supercapacitors. Current strategies for the design and morphology control of self-supported electrodes fabricated using template, lithography, anodization and self-organized solution techniques are outlined along with different efforts to improve the storage capacity, rate capability, and cyclability.

Nanostructured negative electrodes based on titania for Li-ion microbatteries

This work reviews recent developments on Li-ion microbatteries. After a short literature overview, use of TiO2 as an alternative anode for Li-ion batteries and enhanced electrochemical performances of nanostructured titania electrodes is introduced. Principle and formation mechanism of self-organized TiO2 nanotubes by electrochemical anodization and electrochemical fabrication of metallic nanowires are discussed in detail. Electrochemical performance of negative electrodes for Li-ion microbatteries composed of self-organized TiO2 nanotubes and composite TiO2 nanotubes–oxide nanowires is presented.

A novel architectured negative electrode based on titania nanotube and iron oxide nanowire composites for Li-ion microbatteries

We report a novel procedure for the fabrication of vertical iron oxide nanowires with quite regular form and diameters ranging between 20 and 150 nm grown from a matrix of self-organized TiO2 nanotubes. The 3 μm thick nanocomposite electrode presented here shows relatively high areal capacities of 468 μAh cm−2 (1st reversible discharge) and 200 μA h cm−2 over 45 cycles at a rate of 25 μA cm−2 (specific capacities of 1190 and 510 mAh g−1, respectively). Additionally, studies performed at kinetics of 6, 12.5, and 50 μA cm−2 suggest that this architectured nanocomposite material reveals excellent electrochemical performance with promising potential applications as nano-architectured negative electrodes for Li-ion microbatteries.

Nanocomposite Electrode for Li-Ion Microbatteries Based on SnO on Nanotubular Titania Matrix

A nanocomposite electrode made by electrochemical deposition of Sn on TiO 2 nanotube (ntTiO 2 ) layers and subsequent thermal oxidization to SnO is proposed. X-ray diffraction patterns confirmed the presence of SnO. The spongelike structure of SnO combined with the presence of titania nanotubes is beneficial to buffer large volume changes during reaction with lithium. Galvanostatic discharge/charge tests have been carried out to characterize the electrochemical properties. The electrochemical performance shows that nanocomposite SnO-ntTiO 2 is a promising alternative negative electrode for Li-ion microbatteries.

Electrochemical fabrication of Sn nanowires on titania nanotube guide layers

We describe a novel approach for the fabrication of tailored nanowires using a two-step electrochemical process. It is demonstrated that self-organized TiO(2) nanotubes can be used to activate and guide the electrochemical growth of Sn crystallites, leading to the formation of vertical features with a high aspect ratio. We show that the dimensions and the density of Sn crystallites depend on the electrodeposition parameters.

Porous Silicon Nanotube Arrays as Anode Material for Li-Ion Batteries

We report the electrochemical performance of Si nanotube vertical arrays possessing thin porous sidewalls for Li-ion batteries. Porous Si nanotubes were fabricated on stainless steel substrates using a sacrificial ZnO nanowire template method. These porous Si nanotubes are stable at multiple C-rates. A second discharge capacity of 3095 mAh g(-1) with a Coulombic efficiency of 63% is attained at a rate of C/20 and a stable gravimetric capacity of 1670 mAh g(-1) obtained after 30 cycles. The high capacity values are attributed to the large surface area offered by the porosity of the 3D nanostructures, thereby promoting lithium-ion storage according to a pseudocapacitive mechanism.

Highly conformal electrodeposition of copolymer electrolytes into titania nanotubes for 3D Li-ion batteries

The highly conformal electrodeposition of a copolymer electrolyte (PMMA-PEO) into self-organized titania nanotubes (TiO2nt) is reported. The morphological analysis carried out by scanning electron microscopy and transmission electron microscopy evidenced the formation of a 3D nanostructure consisting of a copolymer-embedded TiO2nt. The thickness of the copolymer layer can be accurately controlled by monitoring the electropolymerization parameters. X-ray photoelectron spectroscopy measurements confirmed that bis(trifluoromethanesulfone)imide salt was successfully incorporated into the copolymer electrolyte during the deposition process. These results are crucial to fabricate a 3D Li-ion power source at the micrometer scale using TiO2nt as the negative electrode.

Electrochemical Fabrication and Properties of Highly Ordered Fe-Doped TiO2 Nanotubes

Highly-ordered Fe-doped TiO(2) nanotubes (TiO(2)nts) were fabricated by anodization of co-sputtered Ti-Fe thin films in a glycerol electrolyte containing NH(4)F. The as-sputtered Ti-Fe thin films correspond to a solid solution of Ti and Fe according to X-ray diffraction. The Fe-doped TiO(2)nts were studied in terms of composition, morphology and structure. The characterization included scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, UV/Vis spectroscopy, X-ray photoelectron spectroscopy and Mott-Schottky analysis. As a result of the Fe doping, an indirect bandgap of 3.0 eV was estimated using Taucs plot, and this substantial red-shift extends its photoresponse to visible light. From the Mott-Schottky analysis, the flat-band potential (E(fb)) and the charge carrier concentration (N(D)) were determined to be -0.95 V vs Ag/AgCl and 5.0×10(19) cm(-3) respectively for the Fe-doped TiO(2)nts, whilst for the undoped TiO(2)nts, E(fb) of -0.85 V vs Ag/AgCl and N(D) of 6.5×10(19) cm(-3) were obtained.

Direct immobilization of DNA on diamond-like carbon nanodots

We report an alternative technique for the immobilization of biological species in the sub-100 nm range. The feasibility of attaching DNA to electron-beam-deposited diamond-like carbon nanodots has been demonstrated. The key point of this approach is that direct patterning of a glass substrate is combined with a resist-free technique. Compared with conventional writing approaches, the high-resolution method presented here is simple, flexible, and compatible with the manipulation of a wide range of biological species.

Novel fabrication technologies of 1D TiO2 nanotubes, vertical tin and iron–based nanowires for Li–ion microbatteries

We present the combination of anodisation, sputtering and electrodeposition processes as a novel technology to fabricate nanoarchitectured materials. Titania nanotubes are successfully fabricated using Ti foils and Ti film on Si wafers; by simply varying the anodisation parameters a 600–900 nm range of tube length and a 50–150 nm range of tube diameter can be obtained. Iron and tin oxides nanowires, microballs, microcubes or with sponge–like morphology are obtained showing that the crystallinity can be tuned by optional heat treatment, but the initial morphology is preserved. We investigate all these materials as alternative electrodes for lithium–ion batteries and microbatteries. It should be highlighted the fabrication of vertical nanowires using a template–free approach exhibits some advantages because the electroactive species are fabricated directly onto the current collector, ensuring good electrical contact between titania nanotube layers and the current collector, and tackle the use of additives such as binder and conductive agents. Thus, Sn on an amorphous titania matrix and SnO nanowires on a crystalline titania matrix with a particular geometry (2 µm of tin/tin oxide length) have a remarkable reversible capacity of about 140 µA h cm−2 (675 mA h g−1 and 70 µA h cm−2 µm−1) which is kept about 85% over 50 cycles. The matrix presented here can allow the volume expansion of lithium–tin alloys and thus enhances the electrochemical performances as compared with usual tin–based electrodes. In the text is also described the electrochemistry of a series of samples such as a 3 µm thick nanocomposite made of vertical iron oxide nanowires with quite regular form and diameters ranging between 20 nm and 150 nm grown on a matrix of self–organised TiO2 nanotubes. The obtained capacities compare very favourably with the best literature data for Li–ion microbatteries.