Solution combustion is an exciting phenomenon, which involves propagation of self-sustained exothermic reactions along an aqueous or sol–gel media. This process allows for the synthesis of a variety of nanoscale materials, including oxides, metals, alloys, and sulfides. This Review focuses on the analysis of new approaches and results in the field of solution combustion synthesis (SCS) obtained during recent years. Thermodynamics and kinetics of reactive solutions used in different chemical routes are considered, and the role of process parameters is discussed, emphasizing the chemical mechanisms that are responsible for rapid self-sustained combustion reactions. The basic principles for controlling the composition, structure, and nanostructure of SCS products, and routes to regulate the size and morphology of the nanoscale materials are also reviewed. Recently developed systems that lead to the formation of novel materials and unique structures (e.g., thin films and two-dimensional crystals) with unusual...

Solution Combustion Synthesis of Nanoscale Materials

The increasing world population and the need to improve quality of life for a large percentage of human beings are the driving forces for the search for sustainable energy production systems, alternative to fossil fuel combustion. Among the various types of alternative energy production technologies, solid oxide fuel cells (SOFCs) operating at intermediate temperatures (400–700 °C) show the advantage of possible use both for stationary and mobile energy production. To reach the goal of reducing the SOFC operating temperature, proton-conducting oxides are gaining wide interest as electrolyte materials. This critical review provides a broad overview of the most recent progresses obtained tailoring the properties of proton-conducting oxides for fuel cell applications, analyzing and comparing the different strategies proposed to match high-proton conductivity with good chemical stability (170 references).

Materials challenges toward proton-conducting oxide fuel cells: a critical review

This article provides a perspective on solid oxide fuel cells operating at low temperature, defined here to be the range from ∼400 °C to 650 °C. These low-temperature solid oxide fuel cells (LT-SOFCs) have seen considerable research and development and are widely viewed as the “next generation” technology, following the 650–850 °C SOFCs that are currently undergoing commercialization. LT-SOFCs have potential advantages for conventional SOFC applications such as stationary power generation, and may be viable for new portable and transportation power applications, along with electrolytic fuel production and energy storage. The characteristics of electrolyte and electrode materials are reviewed, with a focus on materials that have demonstrated good properties and cell performance at low temperature. Only oxygen-ion-conducting electrolytes are considered here. Anode materials are discussed, primarily the various Ni–cermet anode compositions that yield good low-temperature performance. Mixed ionically and electronically conducting cathode materials are described in detail, reflecting the extensive research activity that has aimed at providing useful oxygen reduction kinetics at low operating temperature. Cell design, materials compatibility, processing methods, and resulting microstructures are discussed, along with their role in determining cell performance. Results from state of the art LT-SOFCs are presented, and future prospects are discussed.

A perspective on low-temperature solid oxide fuel cells

Water is of fundamental importance for life on earth. The synthesis and structure of cell constituents and transport of nutrients into the cells as well as body metabolism depend on water. The contaminations present in water disturb the spontaneity of the mechanism and result in long/short-term diseases. The probable contaminations and their possible routes are discussed in the present review. Continued research efforts result in some processes/technologies to remove the contaminations from water. The review includes concepts and potentialities of the technologies in a comprehensible form. It also includes some meaningful hybrid technologies and promising awaited technologies in coming years.

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Drinking water contamination and treatment techniques

The need for reducing the solid oxide fuel cell (SOFC) operating temperature below 600 °C is imposed by cost reduction, which is essential for widespread SOFC use, but might also disclose new applications. To this aim, high-temperature proton-conducting (HTPC) oxides have gained widespread interest as electrolyte materials alternative to oxygen-ion conductors. This Progress Report describes recent developments in electrolyte, anode, and cathode materials for protonic SOFCs, addressing the issue of chemical stability, processability, and good power performance below 600 °C. Different fabrication methods are reported for anode-supported SOFCs, obtained using state-of-the-art, chemically stable proton-conducting electrolyte films. Recent findings show significant improvements in the power density output of cells based on doped barium zirconate electrolytes, pointing out towards the feasibility of the next generation of protonic SOFCs, including a good potential for the development of miniaturized SOFCs as portable power supplies.

Towards the next generation of solid oxide fuel cells operating below 600 °c with chemically stable proton-conducting electrolytes.

Citrate–nitrate auto-combustion synthesis is used to prepare an iron, a cobalt and a cerium-perovskite. The influence of different synthesis conditions on the combustion process, phase composition, textural and morphological properties is studied in detail by X-ray diffraction, nitrogen adsorption and scanning electron microscopy. Results show that the combustion intensity increases from iron, to cerium, to cobalt-perovskite. Conversely, the combustion intensity decreases and thus the safety and the gain of the combustion process increase by using high fuel/oxidant ratios, low pH values or combustion reactors with high heat dispersion capacity. High fuel/oxidant ratios increase particle size and may enhance dopant segregation. Low citric acid/metal nitrates ratios may cause precipitation of the most insoluble compounds or segregation of the dopant. High citric acid/metal nitrates ratios increase the formation temperature of the perovskite-type structure. Low pH values are deleterious for the phase composition and/or for the morphology of the final product, although at high pH values dopant segregation may occur.

Citrate-nitrate auto-combustion synthesis of perovskite-type nanopowders: A systematic approach

Solution combustion synthesis, energy and environment: Best parameters for better materials

Two series of pumice-supported palladium and palladium–copper catalysts, prepared by impregnation with different palladium and copper precursors, were tested for the hydrogenation of aqueous nitrate and nitrite solutions. Measurements were performed in a stirred tank reactor, operating in batch conditions, in buffered water solution at atmospheric pressure and at 293 K. The activities of the catalysts were calculated in terms of nitrate and/or nitrite removal. With the monometallic Pd/pumice, the reduction of nitrite is highly selective; only 0.2% of the initial nitrite content is converted to ammonium ions. The activity in terms of turn over frequency (TOF) is higher as compared to a catalyst of Pd on silica. Addition of copper to the palladium catalyst is essential for the reduction of nitrates, although it decreases the nitrite reduction activity and increases the production of ammonium ions. Nitrate reduction appears to be structure-insensitive and a volcano-type dependence of the activity versus the overall Cu atomic weight percentage is observed for the two series of catalysts.

Catalytic reduction of nitrates and nitrites in water solution on pumice-supported Pd–Cu catalysts

Catalytic partial oxidation of methane (CPO) to synthesis gas was performed over differently prepared CeO 2 supported nickel catalysts with 6 wt% Ni content. The samples were synthesized by microwave assisted procedures and by hydrothermal deposition procedure. Differences in the catalyst structural properties of the prepared catalysts were detected by XRD, TPR and XPS measurement. When tested at atmospheric pressure with feed gas mixture containing methane and oxygen in molecular ratio CH 4 /O 2  = 2, all the samples reached 98% conversion with CO selectivity values >95% in the 700–800 °C temperature range. The samples exhibited different behavior towards carbon formation during the tests. Moreover, according to XRD, XPS and TGA results, when the carbon was formed it did not cause catalyst deactivation. TPR profiles confirmed different degree of chemical interaction between NiO and CeO 2 support, depending on the preparation method. The building up or the easy removal of carbon during the CH 4 temperature programmed surface reaction (TPSR), substantiate the role of the CeO 2 lattice oxygen mobility, enhanced by metal-support interaction, in the removal of the deposited carbon through CO evolution. Structure-activity relationship established a close dependence of the CPO performance on the combination of NiO and CeO 2 crystallite sizes and the interaction between the two.

Ni/CeO2 catalysts for methane partial oxidation: Synthesis driven structural and catalytic effects

Spinel-type CoMn(2)O(4)nano-powders are prepared using sol-gel auto combustion (SGC) and co-precipitation (CP) methods and their catalytic activities are evaluated in combustion of 2-propanol and toluene The chemical-physical properties of the oxides are characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N(2)-adsorption-desorption, temperature programmed reduction (TPR) and scanning electron microscopy (SEM) After calcination at 700°C, CoMn(2)O(4)-SGC shows higher amounts of the normal-type spinel phase and is more crystalline than CoMn(2)O(4)-CP Higher calcination temperatures (850°C) do not affect very much the weight percentage of the normal-type spinel phase; although the crystal size slightly increased The TPR analysis evidences a large number of Mn(3+) cations in CoMn(2)O(4)-SGC compared to CoMn(2)O(4)-CP This difference, together with the higher surface area, could justify the higher activity of CoMn(2)O(4)-SGC in both the investigated reactions

Chemical-physical properties of spinel CoMn2O4 nano-powders and catalytic activity in the 2-propanol and toluene combustion: Effect of the preparation method

Francesca Deganello

Papers

Citrate-nitrate auto-combustion synthesis of perovskite-type nanopowders: A systematic approach

Solution combustion synthesis, energy and environment: Best parameters for better materials

Catalytic reduction of nitrates and nitrites in water solution on pumice-supported Pd–Cu catalysts

Ni/CeO2 catalysts for methane partial oxidation: Synthesis driven structural and catalytic effects

Chemical-physical properties of spinel CoMn2O4 nano-powders and catalytic activity in the 2-propanol and toluene combustion: Effect of the preparation method