Nanosized fuels

Both batteries and fuei cells utilize controlled chemical reactions in which the desired process occurs electrochemically and all other reactions including corrosion are hopefully absent or severely kinetically suppressed. This desired selectivity demands careful selection of the chemical components including their morphology and structure. Nanosize is not necessarily good, and in present commercial lithium batteries, particle sizes are intentionally large. All batteries and fuel cells contain an electropositive electrode (the anode or fuel) and an electronegative electrode (the cathode or oxidant) between which resides the electrolyte. To ensure that the anode and cathode do not contact each other and short out the cell, a separator is placed between the two electrodes. Most of these critical components are discussed in this thematic issue. 

Pyrotechnics will take an important step forward by making use of several nanosized fuels and oxidizers for pyrotechnic formulations in the near future. As a result, the performance of such pyrotechnic formulations will become considerably better and thus the problem of availability of space for pyrotechnic devices will not remain as critical as it is now, because several metal powders and oxidizers are commercially available at the nanoscale these days. Before we discuss nanosized fuels, oxidizers and their formulations, it is considered essential to describe in brief nanomaterials (NMs)including carbon nanotubes (CNTs), their methods of preparation, their properties in general, and some important applications. 

Sometimes nanosized powders are also referred as ultrafine (UF) powders with an equivalent size of 10 to a few hundred nanometers. The commonly employed fuels for explosives, propellants and pyrotechnics are aluminum (Al), magnesium (Mg) and boron (B). However, the share in terms of quantity consumed is maximum for aluminum. 

Pt superfine clusters on conductive supports are effective catalysts of redox reactions proceeding in fuel cells. High specific surface, support conductivity, high dispersity (nanosizes of Pt clusters) and their strong fixation on a surface are necessary criterions of preparation of the effective catalyst. From these points of view CNM for example single- (SWNT) and multi-walled (MWNT) nanotubes, nanofibers (CNF) and x-ray amorphous carbon (AC) can be a successful supports of Pt clusters. 

Palladium nanoparticles vfith a size of a few nanometers supported on carbon are widely used as catalysts, for instance in three-way automotive exhaust catalysts and fuel cells, and can easily be prepared by impregnation of a porous support body with a precursor solution, followed by drying, decomposition of the precursor and, if necessary, reduction. It is well-known that the activity and selectivity of these catalysts for hydrogenation reactions depend on the palladium dispersion for particles sizes in the range 1-10 nm. It is, hence, not surprising that the interaction of Pd with hydrogen, and the infiuence of nanosizing, have been widely studied. 

Flame processes have been widely used to synthesize nanosize powders of oxide materials. Chemical precursors are vaporized and then oxidized in a combustion process using a fuel/oxidant mixture such as propane/oxygen or methane/air [190]. They combine the rapid thermal decomposition of a precursor/carrier gas stream in a reduced pressure environment with thermophoretically driven deposi-... 

Lanthanum strontium manganate, known also as LSM, is known for its magnetoresistance properties, and is also used in solid oxide fuel cells (SOFC). Sonochemistry was used for its preparation [121]. Electron magnetic resonance (EMR) spectra of nanosized sonochemically sintered powders of Lao.7Sro.3Mn03 (annealed, Tc = 340 K) were studied. 

A third technique used to prepare both Gd-doped CeOi and NiO/YSZ powders is that of aerosol flame deposition [134, 135]. In the case of NiO/YSZ powders used for the anodes (see Chapter 12), nanosized spherical particles were obtained and the particle size distribution could be limited by controlling the processing parameters [135]. Subsequently, the electrical conductivity of 70% NiO/YSZ was found to be lO Scm at 700°C, with the material exhibiting typically metallic behavior. However, the use of such materials in fuel cells was not reported. 

The use of RF-GC methodologies has been successfully extended to the study of selective CO oxidation over various fuel processing candidate catalysts, such as monometallic Rh/Si02, bimetalhc Pt-Rh/Si02, and nanosized AU/7-AI2O3, under different conditions, compatible with the operation of fuel cell units. These studies concern 1) activity/selectivity measurements 2) the determination of kinetic rate constants and 3) investigation of the surface topography. 

Rh/Si02, bimetallic Pt-Rh/Si02, and nanosized An/ 7-AI2O3, under different conditions, compatible with the operation of fuel cells units. 

Carbon has been used in various areas of nanosize research, such as electronics, sensors, super capacitors, batteries, fuel cells, and biosensors, because of its remarkable mechanical, optical, thermal, magnetic, nucleating, and electronic properties. ... 

Lan et al. [27] used alkaline membrane fuel cells for electricity production from urea. Power densities of up to 0.10 mW cm were achieved with a urine feed and a Ni/C anode. The performance was substantially increased by using nanosized nickel particles instead of nickel powder [28]. Again, no long-term experiments were conducted to prove the resilience and steadiness of the process. 

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