Tomokazu Fukutsuka

Synthesis of polyaniline-intercalated layered materials via exchange reaction

Polyaniline (PANI)-intercalated graphite oxides (GOs) or FeOCl were synthesized via exchange reaction of n-hexadecylamine-intercalated graphite oxides or FeOCl by PANI in an organic solvent. PANI-intercalated GOs with interlayer spacings (Ic values) of 1.14–1.68 nm and compositions of (PANI)1.1–5.0GO were obtained, depending on the amine contents in the starting materials. On the other hand, only one type of intercalation compound was successfully obtained for FeOCl with the composition (PANI)0.42FeOCl without excess PANI particles deposited on the surface. A structure model for the intercalated PANI chains in (PANI)5.0GO with Ic = 1.68 nm has been proposed: a double layer of PANI chains with their benzene rings parallel to the GO layer.

Characterization of n-hexadecylalkylamine-intercalated graphite oxides as sorbents

Abstract Adsorption properties of graphite oxides hydrophobized by n-hexadecylamine, (C16)xGO, were investigated using pyrene molecules as a model of nonionic organic contaminants. A large quantity of pyrene (28.5 mg/g) was adsorbed from a water–ethanol mixture (1:2) containing 2 mM of pyrene when (C16)0.6GO was used. The isotherm of pyrene adsorption was better described by Freundlich equation rather than Langmuir equation, which indicated a single adsorption mechanism was involved. The change in the amount of adsorbed pyrene as a function of amine content in GO was very similar to that which occurs upon introduction of pyrene into (C16)xGO films from chloroform solution, as determined by X-ray measurements. This suggests that pyrene molecules were adsorbed not only on the outer surface but also within the interlayer space of the intercalation compound. Swelling of the intercalation compound by ethanol can render the interlayers more organophilic and make access to hexadecylamine molecules bonded to the graphite oxide layer easier for pyrene molecules, especially in (C16)xGOs with lower amine contents.

Single-step synthesis of nano-sized perovskite-type oxide/carbon nanotube composites and their electrocatalytic oxygen-reduction activities

Composites of nano-sized perovskite-type oxides of La1−xSrxMnO3 (LSMO) and carbon nanotubes (CNTs) were synthesized in a single step by the electrospray pyrolysis method, and their electrocatalytic activities for oxygen reduction were evaluated in an alkaline solution. The resulting LSMO nanoparticles with a diameter of less than 20 nm were well dispersed and deposited on the surface of CNTs. Elemental analysis showed that the metal-composition of LSMO/CNT composites was controlled by altering the concentrations of a precursor solution. Rotating-disk-electrode measurements revealed that the electrocatalytic activities of LSMO/CNT composites increased with an increase in a molar ratio of Sr element. Composites of LSMO nanoparticles and CNTs showed greater catalytic activities than conventional LSMO particles (1 µm) supported on carbon black for oxygen reduction. Moreover the LSMO/CNT catalyst showed larger oxygen-reduction currents even in the presence of ethylene glycol while a Pt disk electrode was affected by the oxidation currents of ethylene glycol. These results indicate that LSMO/CNT composites are a promising candidate as a cathode catalyst with a higher catalytic selectivity for oxygen reduction and a higher crossover-tolerance for use in anion-exchange membrane fuel cells.

Depth-resolved X-ray absorption spectroscopic study on nanoscale observation of the electrode–solid electrolyte interface for all solid state lithium ion batteries

Depth-resolved X-ray absorption spectroscopy (DR-XAS) measurements were performed for the direct observation of the chemical state and local structure at the LiCoO2 electrode–solid electrolyte model interface, which can contribute towards the enhancement of the power density in all solid-state lithium batteries. The charge transfer resistance, measured by AC impedance spectroscopy, of the LiCoO2 electrode–solid electrolyte interface decreased with the introduction of a NbO2 interlayer at the interface, while the resistance increased with ZrO2 and MoO2 interlayers. Using DR-XAS with a depth resolution of about 7 nm, the changes in electronic structure and local structure of the LiCoO2 electrode were clarified. The extended X-ray absorption fine structure of DR-XAS revealed that the introduction of the NbO2 layer is effective for restricting the large Co–O bond change at the interface during delithiation. This interlayer relieved the stress at the interface due to the volume change of LiCoO2 during delithiation and then decreased the activation energy for the charge transfer process.

Electronic and local structural changes with lithium-ion insertion in TiO2-B: X-ray absorption spectroscopy study

X-Ray absorption fine structure (XAFS) spectroscopy was carried out on submicron sized TiO2-B, which is one of the promising candidates for negative electrode materials, in order to clarify the electronic and local structural changes during its lithium-ion insertion process. From the extended X-ray absorption fine structure (EXAFS) results of lithiated LixTiO2-B, we propose the changes in lithium-ion insertion sites during electrochemical discharging. The lithium ions are inserted into the five-fold coordinated sites and/or distorted octahedral sites distributed at the vicinity of O layers parallel to the ab plane for x ≤ 0.5, while the lithium ions are accommodated into the five-fold coordinated site distributed at the vicinity of TiO2 layers parallel to the ab plane for x > 0.5. The interaction between the inserted lithium ion and TiO6 octahedra affects the lattice distortion of LixTiO2-B for x > 0.5, as well as the titanium reduction during discharging. It is suggested through the X-ray absorption near edge structure (XANES) spectroscopy of Ti K-, Ti L- and O K-edges that the distortion of TiO6 octahedra makes the hybridized state of O 2p and Ti 3d broad, and has a significant effect on the lithium-ion insertion properties of TiO2-B.

Electrochemical Properties of Carbonaceous Thin Films Prepared by Plasma Chemical Vapor Deposition

Carbonaceous thin films were prepared from acetylene and argon by plasma-assisted chemical vapor deposition (plasma CVD). The carbonaceous thin films were characterized mainly by scanning electron microscope (SEM) and Raman spectroscopy Then their electrochemical properties were studied by cyclic voltammetry, charge-discharge measurements, and linear sweep voltammetry. From the SEM image carbonaceous thin films appeared flat and pinhole free. Crystallinity of carbonaceous thin films are affected by the applied rf power from Raman spectra. The difference of the applied rf power also affected the results of cyclic voltammetry and charge-discharge measurements. The lithium ion storage mechanism of carbonaceous thin film is discussed from the results of electrochemical measurements.

Ionic and Electronic Conductivities and Fuel Cell Performance of Oxygen Excess-Type Lanthanum Silicates

Highly dense pellets of an oxygen excess-type lanthanum silicate (La 9.333+x Si 6 O 26+1.5x , x > ca. 0.3, OE-LSO) were successfully fabricated, and their electrical conducting properties were studied. The replacement of Si by Al enhanced its conductivity, and the slightly Al-doped OE-LSO specimen [La 9.62 (Si 5.79 Al 0.21 )O 26.33 ] had excellent features as a solid electrolyte; that is, it had high ionic conductivity and was highly stable under reducing as well as oxidizing conditions at 873-1073 K. In addition, the ionic transference number was higher than 0.99. In the fuel cell utilizing this electrolyte (0.72 mm thick), (La 0.6 Sr 0.4 )(Co 0.2 Fe 0.8 )O 3―δ cathode, and Ni―Ce 0.9 Gd 0.1 O 1.95―δ anode, good performance with the maximum power density of ca. 0.25 W cm ―2 was obtained at 1073 K. In addition, this electrolyte also had high compatibility with these conventional mixed conducting electrodes, according to an analysis near the electrode/electrolyte interfaces after the fuel cell test.

Synthesis of highly graphitized carbonaceous thin films by plasma assisted chemical vapor deposition and their electrochemical properties in propylene carbonate solution

Abstract Carbonaceous thin film electrode was prepared by plasma assisted chemical vapor deposition. The films were very flat and pin-hole free with c -axis orientation. X-ray diffraction and Raman spectroscopy revealed that the bulk of the film was highly graphitized but the surface of the film was less crystallized, indicating that the surface modified graphitized thin film electrode was obtained by a single process. Electrochemical properties of this film were studied in electrolyte of propylene carbonate (PC) containing 1 mol dm −3 LiClO 4 by cyclic voltammetry. The first cycle of voltammogram showed reduction current observed at 1.0–0.5 V (vs. Li/Li + ), but the reduction current at those potentials completely disappeared over the second cycle. Large reduction and oxidation currents were observed near 0 V (vs. Li/Li + ), and in addition, the peak splitting was observed for oxidation peaks near 0 V. These electrochemical properties are quite similar to that of graphite electrode used in Li-ion batteries.

Photochemical dimerization of acenaphthylene in hydrophobized graphite oxide

Photochemical dimerization of acenaphthylene was performed in various hydrophobized graphite oxide films. A large quantity of acenaphthyelene was intercalated into hydrophobized graphite oxide. The conversion of acenaphthyelene increased with the increase of acenaphthyelene contents in the intercalation compounds. Syn/anti ratio of acenaphthylene dimers increased with the increase of acenaphthylene contents and became larger in intercalation compounds containing alkyl amine with shorter alkyl chain probably because of the difference in diffusion rate of exited molecules.

Electrochemical Properties of Graphitized Carbonaceous Thin Films Prepared by PACVD

Graphitized carbonaceous thin-film electrodes were prepared by plasma-assisted chemical vapor deposition (PACVD). X-ray diffraction and Raman spectroscopy showed that while the bulk of the film was highly crystallized, its surface was less crystallized, indicating that this surface-modified graphitized thin-film electrode was obtained by a single process. The structures of the surface and bulk of the thin film are influenced by applied radio frequency (rf) powers: the crystallinity of the surface increased with increasing applied rf power, while the crystallinity of the interior bulk decreased with increasing applied rf power. The electrochemical properties of the obtained films were studied in electrolyte consisting of propylene carbonate or ethylene carbonate and diethyl carbonate (1:1 by volume) containing 1 mol dm -3 LiClO 4 by cyclic voltammetry and ac impedance spectroscopy. Because the crystallinity of the surface is low, nearly identical electrochemical properties were seen regardless of the electrolytes used, although the bulk structure is highly graphitized. AC impedance spectroscopy showed that charge transfer resistance decreased with decreasing applied rf power, which suggests that highly graphitized carbonaceous thin films with a less-crystallized surface should be ideal electrodes for the fabrication of thin-film batteries.