CuO metallic aerogels with a tailored nodular morphology.

This work reports, for the first time, an efficient and fast microwave-based method for the preparation of CuO aerogels. For that, CuCl2, glyoxylic acid and sodium carbonate are employed as reagents. Different experimental conditions such as synthesis temperature, synthesis time and concentration of the precursor solution are investigated to design CuO aerogels with customizable nodular morphologies. The resulting aerogels exhibit well-defined three-dimensional structures and nodular sizes, and therefore, textural properties vary according to the experimental parameters applied in their synthesis.

Ultralight-Weight Graphene Aerogels with Extremely High Electrical Conductivity.

The integration of 2D graphene sheets into a porous and macroscopic structure is extremely attractive for application in several electrochemical fields. In this regard, for the first time, the synthesis of 3D graphene aerogels is reported by using a rapid, easy, cost-effective, and scalable at industrial level methodology. These aerogels integrate the intrinsic properties of graphene with a high pore volume. To achieve this ultraporous graphene network, resorcinol/formaldehyde polymer with controllable porosity is employed as a binder and a cross-linker material, and a graphene oxide solution provides the graphene building blocks. Two series of materials with and without catalyst for resorcinol/formaldehyde reaction and with different synthesis conditions and graphene contents are studied. The resulting graphene aerogels present low density, large macroporosity, and electrical conductivity values as high as 852 S m-1 , with 97.58% of porosity, which is the highest value of electrical conductivity reported so far in the literature for ultralight-weight graphene aerogels.

Structural and proton conductivity studies of fibrous π-Ti2O(PO4)2·2H2O: application in chitosan-based composite membranes.

Although the fibrous polymorphic modification of titanium phosphate, π-Ti2O(PO4)2·2H2O (π-TiP) has been known for decades, its crystal structure has remained unsolved. Herewith, we report the crystal structure of π-TiP at room temperature, as determined from synchrotron radiation powder X-ray diffraction, and corroborated by 31P solid state NMR and accurate density functional theory calculations. In contrast to the previously reported ρ-TiP polymorph, the as-synthesized hydrated phase crystallizes in the monoclinic system (P21/c, a = 5.1121(2) Å, b = 14.4921(9) Å, c = 12.0450(11), ß = 115.31(1)°, Z = 4), and is composed of corner-sharing titanium octahedra and phosphate units arranged in a pattern that is unique to the ρ-TiP polymorph. The unit cell was confirmed by electron diffraction, while the formation of planar packing imperfections and stacking faults along the [101] plane was revealed by HRTEM analysis. An in situ dehydration study of π-TiP, monitored by high-temperature powder X-ray diffraction, led to a new anhydrous monoclinic (P21/c, a = 5.1187(13) Å, b = 11.0600(21) Å, c = 14.4556(26), ß = 107.65(2)°, Z = 4) phase that crystallizes at 500 °C. The latter resembles the packing fashion of the parental π-TiP, albeit titanium atoms are present in both distorted tetrahedral and octahedral coordination environments. Anhydrous π-TiP was found to partially rehydrate at room temperature, reversibly adopting the structure of the initial phase. The studies carried out under different conditions of leaching and impregnation with H3PO4 showed that π-TiP exhibits an extrinsic proton conductivity (1.3 × 10-3 S cm-1 at 90 °C and 95% RH) due to the presence of the protonated phosphate species bound on the particles surface, as revealed by 31P MAS-NMR spectroscopy data. The composite membranes of Chitosan (CS) matrices filled with H3PO4-impregnated π-TiP solid show an increment of proton conductivity up to 4.5 × 10-3 S cm-1, at 80 °C and 95% RH, which is 1.8-fold higher than those of the bare CS membranes.

Sol-Gel Processing of Water-Soluble Carbon Nitride Enables High-Performance Photoanodes*.

In spite of the enormous promise that polymeric carbon nitride (PCN) materials hold for various applications, the fabrication of high-quality, binder-free PCN films and electrodes has been a largely elusive goal to date. Here, we tackle this challenge by devising, for the first time, a water-based sol-gel approach that enables facile preparation of thin films based on poly(heptazine imide) (PHI), a polymer belonging to the PCN family. The sol-gel process capitalizes on the use of a water-soluble PHI precursor that allows formation of a non-covalent hydrogel. The hydrogel can be deposited on conductive substrates, resulting in formation of mechanically stable polymeric thin layers. The resulting photoanodes exhibit unprecedented photoelectrochemical (PEC) performance in alcohol reforming and highly selective (∼100 %) conversions with very high photocurrents (>0.25 mA cm-2 under 2 sun) down to <0 V vs. RHE. This enables even effective PEC operation under zero-bias conditions and represents the very first example of a 'soft matter'-based PEC system capable of bias-free photoreforming. The robust binder-free films derived from sol-gel processing of water-soluble PCN thus constitute a new paradigm for high-performance 'soft matter' photoelectrocatalytic systems and pave the way for further applications in which high-quality PCN films are required.

Nanostructured BaCo0.4Fe0.4Zr0.1Y0.1O3-δ Cathodes with Different Microstructural Architectures.

Lowering the operating temperature of solid oxide fuel cells (SOFCs) is crucial to make this technology commercially viable. In this context, the electrode efficiency at low temperatures could be greatly enhanced by microstructural design at the nanoscale. This work describes alternative microstructural approaches to improve the electrochemical efficiency of the BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY) cathode. Different electrodes architectures are prepared in a single step by a cost-effective and scalable spray-pyrolysis deposition method. The microstructure and electrochemical efficiency are compared with those fabricated from ceramic powders and screen-printing technique. A complete structural, morphological and electrochemical characterization of the electrodes is carried out. Reduced values of area specific resistance are achieved for the nanostructured cathodes, i.e., 0.067 Ω·cm2 at 600 °C, compared to 0.520 Ω·cm2 for the same cathode obtained by screen-printing. An anode supported cell with nanostructured BCFZY cathode generates a peak power density of 1 W·cm-2 at 600 °C.

Enhanced Intermediate-Temperature Electrochemical Performance of Air Electrodes for Solid Oxide Cells with Spray-Pyrolyzed Active Layers.

The potential of interactive layers of mixed-conducting oxides for improving the performance of air electrodes of solid oxide cells in the intermediate-temperature range is demonstrated. Active layers of Ce0.9Gd0.1O2-δ (CGO), Ce0.8Pr0.2O2-δ (CPO), and SrFe0.9Mo0.1O3-δ (SFM) with thickness in the range 200-400 nm are deposited on CGO-based electrolyte by spray pyrolysis, followed by deposition of a SFM/CGO composite air electrode by painting. The morphologies and phase composition of the active layers are examined by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy microanalysis. The electrochemical performance of the electrolyte-electrode assemblies is determined by impedance spectroscopy in the range 600-800 °C. Significant improvements in the performance of the electrode process and the geometrically normalized ohmic conductance are observed for the assembly with a CPO active layer with mixed-oxide-ionic-electronic conductivity, especially in the low-temperature range, attributable to extension of the surface path of the electrochemical reactions. The CGO intermediate layer also improves performance but to a lesser degree, most likely due to better ionic-current collection in comparison to the assemblies with either SFM as the active layer or no active layer.

Electrochemical stability of (La,Sr)CoO3-δ in (La,Sr)CoO3-δ/(Ce, Gd)O2-δ heterostructures.

A modulated coherent (La,Sr)CoO3-δ/(Ce,Gd)O2-δ heterostructure is characterized for the first time for its electronic and chemical properties. 2D-multilayer architectures are deposited on NdGaO3 (110) single crystal substrate by pulsed laser deposition, resulting in epitaxial structures with in-plane lattice rotation that, via the metal oxides' interfaces, induces mutual structural rearrangements. Our results show that (La,Sr)CoO3-d thin films of 10-100 nm are chemically unstable when exposed to air at 600 °C during electrical cyclic stress-tests. Conversely, improved stability is achieved confining LSC in the nanometric heterostructure. Remarkably, the chemical stabilization occurs without compromising substantially the electrical properties of the LSC component: the heterostructures show unexpected electrical behaviour with dominant electronic contributions, fast conductivity and mixed ionic-electronic properties, depending on the number of interfaces and the nano-scaled layers.

Near interface ionic transport in oxygen vacancy stabilized cubic zirconium oxide thin films.

The cubic phase of pure zirconia (ZrO2) is stabilized in dense thin films through a controlled introduction of oxygen vacancies (O defects) by cold-plasma-based sputtering deposition. Here, we show that the cubic crystals present at the film/substrate interface near-region exhibit fast ionic transport, which is superior to what is obtained with similar yttrium-stabilized cubic zirconia thin films.