Debora Marani

Accelerated ceria–zirconia solubilization by cationic diffusion inversion at low oxygen activity

Fast elemental diffusion at the Gd-doped ceria/Y-stabilized zirconia interface occurs under reducing conditions at low oxygen activity (pO2 < 10−12 atm) and high temperature (1400 °C). This effect leads to formation of thick ceria–zirconia solid solution reaction layers in the micro-range vs. thin layers of few tens of nanometers under oxidative conditions (i.e. in synthetic air at pO2 = 0.21 atm). The fast dissolution occurs by an inversion of the dominating limiting mechanism from the expected Zr4+ diffusion into the CGO lattice at high pO2 to an unexpected Ce3+ diffusion into the YSZ component under reducing conditions. The diffusion coefficient of 8-fold coordinated Ce3+ in YSZ at 1400 °C and pO2 = 10−13 atm is estimated to be around 10−11 cm2 s−1. This value is around 3 orders of magnitude higher than Zr4+ interdiffusion in CGO under oxidative conditions and about 8 orders of magnitude higher than Ce4+ self-diffusion in CGO in air at the same temperature.

NOx selective catalytic reduction (SCR) on self-supported V–W-doped TiO2 nanofibers

Electrospun V–W–TiO2 catalysts, resulting in a solid solution of V and W in the anatase phase, are prepared as nonwoven nanofibers for NOx selective catalytic reduction (SCR). Preliminary catalytic characterization indicates their superior NOx conversion efficiency to the-state-of-the-art material. A novel concept of a self-supported, ultra-compact, and lightweight nanofibrous SCR-reactor is defined.

Aqueous metal–organic solutions for YSZ thin film inkjet deposition

Inkjet printing of 8% Y2O3-stabilized ZrO2 (YSZ) thin films is achieved by designing a novel water-based reactive ink for Drop-on-Demand (DoD) inkjet printing. The ink formulation is based on a novel chemical strategy that consists of a combination of metal oxide precursors (zirconium alkoxide and yttrium salt), water and a nucleophilic agent, i.e. n-methyldiethanolamine (MDEA). This chemistry leads to metal–organic complexes with long term ink stability and high precision printability. Ink rheology and chemical reactivity are analyzed and controlled in terms of metal–organic interactions in the solutions. Thin dense nanocrystalline YSZ films below 150 nm are obtained by low temperature calcination treatments (400–500 °C), making the deposition suitable for a large variety of substrates, including silicon, glass and metals. Thin films and printed patterns achieve full densification with no lateral shrinkage and high ionic conductivity.

Effect of chemical redox on Gd-doped ceria mass diffusion

The valence and size of cations influence mass diffusion and oxygen defects in ceria. Here we show that reduction of Ce4+ to Ce3+, at high temperatures and low oxygen activity, activates fast diffusion mechanisms which depend on the aliovalent cation concentration. As a result, polycrystalline solid solutions with enhanced electrochemical properties are formed.

3D-printed barium titanate/poly-(vinylidene fluoride) nano-hybrids with anisotropic dielectric properties

Electrospun BaTiO3 nanofibers (BTNFs) are synthesized and blended in a poly(vinylidene fluoride) (PVDF) matrix to obtain a flexible nano-hybrid composite with high dielectric constant (flexible high-k). The blending is performed with different BTNF contents (0.6, 4.5, 20 vol%). The rheological properties of the starting materials are optimized to shape the hybrid by the precision-extrusion-based fuse deposition modeling technique. The 3D-printed BTNFs allow complex shapes with different degrees of fiber alignment as the result of printing shear stress and the chemical composition of the starting material. The dielectric properties of the nano-hybrid are controlled by anisotropy with an enhancement in the nanofiber cross direction (⊥), where the dielectric constant k⊥ at 1 kHz is increased to ca. 200 from 13 of the PVDF matrix.

Amorphous saturated cerium–tungsten–titanium oxide nanofiber catalysts for NOx selective catalytic reaction

Herein for the first time, Ce0.184W0.07Ti0.748O2−δ nanofibers are prepared by electrospinning to serve as a catalyst in the selective catalytic reduction (SCR) process. The addition of cerium is proven to inhibit crystallization of TiO2, yielding an amorphous TiOx-based solid solution stable up to 500 °C in air, with supersaturated substitutional Ce. At higher temperatures, anatase phase (titanium oxide) is then observed along with fluorite (cerium oxide). Tungsten is instead demonstrated to promote the reduction of the Ce4+ to Ce3+ with the formation of oxygen vacancies (δ). Catalytic experiments under the best working conditions (dry and in the absence of SO2) are performed to characterize the intrinsic catalytic behavior of the new catalysts. At a temperature lower than 300 °C, superior NOx conversion properties of the amorphous TiOx nanofibers over the crystallized TiO2 (anatase) nanofibers are observed and attributed to higher specific surface area (SSA), larger amount of oxygen vacancies, and higher amount of Ce3+ over Ce4+. Comparison with literature data for ceria–tungsten-based nanoparticles also points out higher catalytic performances for the developed nanofibers at the lowest temperatures (<300 °C). This is mainly attributed to the unique nanofibrous morphology and to the doping approach. The stability of the amorphous Ce–W–TiOx nanofibers over time (120 h) and over a number of cycles (5) is demonstrated. Yet, superior catalytic performances of the developed catalysts in a wide range of temperatures (200–500 °C) over state-of-the-art material V–W–titania nanoparticles and nanofibers are also proven.

Synthesis, spectroscopic and electrochemical characterization of hybrid membranes for Polymer Electrolyte Membrane Fuel Cells.

Commercial polyether-etherketone was sulfonated and reacted with SiCl 4 to obtain a hybrid polymer. Polymers having different inorganic content were characterized by 29 Si NMR, ATR/FTIR spectroscopies and mass spectrometry (FAB-MS) demonstrating the formation of covalent bonds between the organic and inorganic components and the absence of dispersed inorganic silicon. The physicochemical properties of the hybrids were suitable for the preparation of membranes which showed sufficiently high conductivity values to make them promising candidates for application in PEMFCs.