NASICON Membrane with High Ionic Conductivity Synthesized by High-Temperature Solid-State Reaction.

In the present work, we studied the impact of excess Na addition on the structure of the standard NASICON ion conductor along with Na ion transport mechanisms. In this sense, NASICON ceramic membranes (NZSP) were prepared by a simple chemical synthesis method, the solid state reaction (SSR), using an excess of 5% Na (Na3.15Zr2Si2PO12) and an excess of 10% Na (Na3.3Zr2Si2PO12), in order to improve the conduction properties of the ceramic membrane. The characterization of the NZSP nanoparticles was performed by measuring the particle size by dynamic light scattering (DLS), the morphology of the NASICON samples pre-sintered at 1100 °C was analyzed by the SEM method (scanning electron microscope), and X-ray diffraction (XRD) analysis was used to investigate the crystal structure of samples, while the surface area was measured using the BET technique. The electrical properties (i.e., ionic conductivity) were evaluated by impedance spectroscopic methods at room temperature (RT). Following the experiments for NASICON membranes without Na excess, with 5% Na excess, and with 10% Na excess synthesized at different pressing forces and sintering temperatures, it was found that membranes with a 10% Na excess, sintered at 1175 °C for 10 h, presented a good ionic conductivity (4.72 × 10-4 S/cm).

Preparation of Copper-Based Catalysts for Obtaining Methanol by the Chemical Impregnation Method.

This paper presents the preparation of heterogeneous catalysts for the direct hydrogenation process of CO2 to methanol. The development of the modern chemical industry is inextricably linked to the use of catalytic processes. As a result, currently over 80% of new technologies introduced in the chemical industry incorporate catalytic processes. Since the basic factor of catalytic processes is the catalysts, the studies for the deepening of the knowledge regarding the nature of the action of the catalysts, for the development of new catalysts and catalytic systems, as well as for their improvement, represent a research priority of a fundamental or applied nature. The Cu/ZnO/Al2O3 catalyst for the synthesis of green methanol, using precursors of an inorganic (copper nitrate, denoted by Cu/ZnO/Al2O3-1) and organic (copper acetate, denoted by Cu/ZnO/Al2O3-2) nature, are obtained by chemical impregnation that includes two stages: preparation and one of calcination. The preparation methods and conditions, as well as the physico-chemical properties of the catalyst precursor, play a major role in the behavior of the catalysts. The prepared catalysts were characterized using atomic adsorption analysis, scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis, specific surface area and pore size analyses, adsorption, and the chemisorption of vapor (BET).

Nitrogen-Doped Graphene Oxide as Efficient Metal-Free Electrocatalyst in PEM Fuel Cells.

Nitrogen-doped graphene is currently recognized as one of the most promising catalysts for the oxygen reduction reaction (ORR). It has been demonstrated to act as a metal-free electrode with good electrocatalytic activity and long-term operation stability, excellent for the ORR in proton exchange membrane fuel cells (PEMFCs). As a consequence, intensive research has been dedicated to the investigation of this catalyst through varying the methodologies for the synthesis, characterization, and technologies improvement. A simple, scalable, single-step synthesis method for nitrogen-doped graphene oxide preparation was adopted in this paper. The physical and chemical properties of various materials obtained from different precursors have been evaluated and compared, leading to the conclusion that ammonia allows for a higher resulting nitrogen concentration, due to its high vapor pressure, which facilitates the functionalization reaction of graphene oxide. Electrochemical measurements indicated that the presence of nitrogen-doped oxide can effectively enhance the electrocatalytic activity and stability for ORR, making it a viable candidate for practical application as a PEMFC cathode electrode.

Noble Metals Functionalized on Graphene Oxide Obtained by Different Methods-New Catalytic Materials.

In recent years, research has focused on developing materials exhibiting outstanding mechanical, electrical, thermal, catalytic, magnetic and optical properties such as graphene/polymer, graphene/metal nanoparticles and graphene/ceramic nanocomposites. Two-dimensional sp2 hybridized graphene has become a material of choice in research due to the excellent properties it displays electrically, thermally, optically and mechanically. Noble nanomaterials also present special physical and chemical properties and, therefore, they provide model building blocks in modifying nanoscale structures for various applications, ranging from nanomedicine to catalysis and optics. The introduction of noble metal nanoparticles (NPs) (Au, Ag and Pd) into chemically derived graphene is important in opening new avenues for both materials in different fields where they can provide hybrid materials with exceptional performance due to the synergistical result of the specific properties of each of the materials. This review presents the different synthetic procedures for preparing Pt, Ag, Pd and Au NP/graphene oxide (GO) and reduced graphene oxide (rGO) composites.

Platinum-Functionalized Graphene Oxide: One-Pot Synthesis and Application as an Electrocatalyst.

This paper presents the preparation of platinum on a reduced graphene oxide matrix (PtrGO) using the microwave-assisted method with three different pH solutions. The platinum concentration determined by energy-dispersive X-ray analysis (EDX) was 4.32 (weight%), 2.16 (weight %) and 5.70 (weight%), corresponding to pH 3.3, 11.7 and 7.2, respectively. Pt functionalization of reduced graphene oxide (rGO) decreased the rGO specific surface, as shown by Brunauer, Emmett and Teller (BET) analysis. An XRD spectrum of platinum-decorated reduced graphene oxide (rGO) showed the presence of the associated phases of rGO and centered cubic platinum peaks. An oxygen reduction reaction (ORR) electrochemical characterization performed using the rotating disk electrode (RDE) method showed that in PtGO1 synthetized in an acidic environment, with 4.32 Pt (weight%) determined by EDX, platinum is much more dispersed, which explains its better electrochemical oxygen reduction reaction performance. Koutecky-Levich (K-L) plots calculated at different potentials prove a good linear relationship. Electron transfer numbers (n) determined from the K-L plots are between 3.1 and 3.8, which confirms that the ORR for all the samples can be regarded as first-order reaction kinetics of O2 concentration formed on the Pt surface during ORR.

Iodine-Doped Graphene Oxide: Fast Single-Stage Synthesis and Application as Electrocatalyst.

Iodine-doped graphene oxide is attracting great attention as fuel cell (FC) electrocatalysts with a high activity for the oxygen reduction reaction (ORR). However, most of the reported preparation techniques for iodine-doped graphene (I/rGO) could be transposed into practice as multiple step procedures, a significant disadvantage for scale-up applications. Herein, we describe an effective, eco-friendly, and fast technique for synthesis by a microwave-tuned one-stage technique. Structural and morphological characterizations evidenced the obtaining of nanocomposite sheets, with iodine bonded in the graphene matrix. The ORR performance of I/rGO was electrochemically investigated and the enhancement of the cathodic peak was noted. Based on the noteworthy electrochemical properties for ORR activity, the prepared I/rGO can be considered an encouraging alternative for a more economical electrode for fuel cell fabrication and commercialization. In this perspective, the iodine-based catalysts synthesis can be considered a step forward for the metal-free electrocatalysts development for the oxygen reduction reaction in fuel cells.

Chitosan-Sulfated Titania Composite Membranes with Potential Applications in Fuel Cell: Influence of Cross-Linker Nature.

Chitosan-sulfated titania composite membranes were prepared, characterized, and evaluated for potential application as polymer electrolyte membranes. To improve the chemical stability, the membranes were cross-linked using sulfuric acid, pentasodium triphosphate, and epoxy-terminated polydimethylsiloxane. Differences in membranes' structure, thickness, morphology, mechanical, and thermal properties prior and after cross-linking reactions were evaluated. Membranes' water uptake capacities and their chemical stability in Fenton reagent were also studied. As proved by dielectric spectroscopy, the conductivity strongly depends on cross-linker nature and on hydration state of membranes. The most encouraging results were obtained for the chitosan-sulfated titania membrane cross-linked with sulfuric acid. This hydrated membrane attained values of proton conductivity of 1.1 × 10-3 S/cm and 6.2 × 10-3 S/cm, as determined at 60 °C by dielectric spectroscopy and the four-probes method, respectively.