Sébastien Sallard

Photocatalytic performances of mesoporous TiO2 films doped with gold clusters

We report on the single-pot fabrication of ordered mesoporous crystallized titania films doped with gold. Au is incorporated in TiO2 films by adding to the coating solution precursors such as AuCl3 or monodisperse Au113+ nanoclusters, and Au nanoparticles are formed by calcination. A systematic study is performed to correlate structure, Au doping and photocatalytic activity of such films. Two-dimensional small angle X-ray scattering (2D-SAXS), transmission electronic microscopy (TEM), scanning electronic microscopy (SEM) and porosimetry–ellipsometry show that the films retain their mesoporous order even for doping levels as high as 1% Au : Ti atomic ratio. Wide angle X-ray scattering (WAXS), and cyclovoltammetry (CV) show that Au113+ nanoclusters promote the formation of the TiO2 (B) phase in competition with the anatase phase. AuCl3 stabilizes instead only the anatase phase. The highest photocatalytic activity is exhibited by films where Au113+ is employed as a precursor, which we attribute to the combination of the mixed anatase/TiO2 (B) phase, of Au nanoparticle doping and of a well-ordered mesoporous TiO2 matrix.

An All Low‐Temperature Fabrication of Macroporous, Electrochemically Addressable Anatase Thin Films

Macroporous TiO₂ (anatase) thin films are fabricated by an all low-temperature process in which substrates are dip-coated in suspensions of mixed anatase nanoparticles and polystyrene beads, and the templating agents are removed by ultraviolet (UV) irradiation at a temperature below 50 °C. Scanning electron microscopy (SEM) and Raman spectroscopy show that the templating polymer beads are removed by UV irradiation combined with the photocatalytic activity of TiO₂. X-Ray diffraction reveals that nanoparticle growth is negligible in UV irradiated films, while nanoparticle size increases by almost 10 times in calcined films that are prepared for comparison. The macroporous films are prepared on FTO-(fluorine-doped tin oxide) coated glass and ITO (indium tin oxide) coated flexible plastics and thereby used as working electrodes. In both cases, the films are electrochemically addressable, and cyclic voltammetry is consistent with the response of bulk TiO₂ for calcined films and of nanoscale-TiO₂ for UV-irradiated films.

Lithium chromium pyrophosphate as an insertion material for Li-ion batteries

Lithium chromium pyrophosphate (LiCrP2O7) and carbon-coated LiCrP2O7 (LiCrP2O7/C) were synthesized by solid-state and sol-gel routes, respectively. The materials were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and conductivity measurements. LiCrP2O7 powder has a conductivity of ~ 10(-8) S cm(-1), ~ 10(4) times smaller than LiCrP2O7/C (~ 10(-4) S cm(-1)). LiCrP2O7/C is electrochemically active, mainly between 1.8 and 2.2 V versus Li(+)/Li (Cr(3+)/Cr(2+) redox couple), whereas LiCrP2O7 has limited electrochemical activity. LiCrP2O7/C delivers a reversible specific charge up to ~ 105 mAh g(-1) after 100 cycles, close to the theoretical limit of 115 mAh g(-1). Operando XRD experiments show slight peak shifts between 2.2 and 4.8 V versus Li(+)/Li, and a reversible amorphization between 1.8 and 2.2 V versus Li(+)/Li, suggesting an insertion reaction mechanism.

A Cylindrical Cell for Operando Neutron Diffraction of Li-Ion Battery Electrode Materials

Neutron diffraction is a powerful technique to localize and quantity lithium in battery electrode materials. However, obtaining high-quality Operando neutron diffraction data is challenging because it requires achieving good electrochemical performance while cycling a large amount of active material to ensure optimal signal-to-noise ratios. We have developed a cylindrical cell specifically suited for operando neutron studies, and used it to investigate the structural changes in the Ni-rich LiNi0.6Co0.2Mn0.2O2 cathode material during cycling between 2.5 and 4.3 V vs Li+/Li. The cell demonstrates reliable electrochemical performance, even after long-term cycling, and the important crystal structure parameters of the active material, including Li occupancy, could be successfully refined with the Rietveld method using neutron diffraction data collected in operando after appropriate background subtraction.