Electronic absorption spectra for free hydrazyl radicals,their ionic forms and initial hydrazines

The results of the calculations of π–π^* transition energies of some free hydrazyl radicals, their ionic forms and initial hydrazines by the SCF –MO –LCAO method with restricted configuration interaction are presented. The comparison of the data obtained with the electronic spectra experimentally found, revealed that the absorption of radical solutions in the visible area was due to the electronic structure of radical molecules, the contribution of ionic forms to the absorption being negligible.     

Computer-Aided Simulation of Porous Electrodes of a Filled-up Type

In the paper, computer-aided simulation of porous electrodes of a filled-up type is done using two-dimensional lattices as an example. The attention is mainly focused on the simulation of porous electron-conducting substrates that are required to put the catalyst particles on. The principal parameter of the system is the share of the electron-conducting particles of the substrate. Calculated are the share of the electron-conducting particles of the substrate (a conducting cluster), the distribution of this quantity over the electrode thickness, and the number of exits made by a conducting cluster onto the rear surface of the electrode. The notion of transparency is introduced. The perimeter of a conducting cluster is determined. The number of active particles of a catalyst is found out. Two versions of the electrode functioning are investigated for catalysts-enzymes. In one version the electrochemical process proceeds no matter the position of the enzyme molecules. In the other, the electrochemical process takes place provided certain conditions of contact between enzyme molecules and a conducting cluster are ensured. Established is the region of optimum concentrations of components at which the electrochemical activity of the electrode is maximum.     

Cathode of a fuel cell with a solid polymer electrolyte: Calculating overall currents in the presence of a gas-diffusion layer

Mathematical apparatus, which makes it possible to perform calculations of the current-voltage characteristics of cathodes of fuel cells with a solid polymer electrolyte in conditions where there are present extraneous diffusion restrictions is proposed. In so doing, the partial pressure of oxygen and the absolute pressure of gas in the gas chamber may assume any values. First of all presented are the results of calculations of the current-voltage characteristics intrinsic to active layers of the air and oxygen cathodes, which are performed under the assumption that the extraneous diffusion restrictions are absent altogether. Thereafter, in the same conditions (at the same parameters that characterize the active layer of a cathode), obtained are results of a calculation of the current-voltage characteristics inherent in the air and oxygen cathodes in the presence of extraneous diffusion restrictions. Afterward there is performed an analysis of the way a gas-diffusion layer restricts the process of generation of current in a cathode and of what measures should be taken in order for the extraneous diffusion restrictions to become less significant.     

Effect of the conditions of activated carbon synthesis from wood on its porous structure and the specific characteristics of double layer supercapacitors with a sulfuric acid-based electrolyte

For supercapacitors with sulfuric acid electrolyte, a promising carbon material was suggested, namely, activated carbon from waste wood. It was shown how the synthesis conditions of activated carbon affect its porous structure and electrochemical characteristics of supercapacitors on its basis. The changes in the porous material under different synthesis conditions were controlled using the highly informative limited evaporation method, which allows us to obtain complete information about the porous structure of the micro- and mesopores of the material within a relatively short period of time. The negative effect of the excess volume of macropores in the electrode on the capacity and energy based on the dry mass of electrodes was shown experimentally and analyzed. The properties of the synthesized material were compared with those of other carbon materials. The best samples of the developed material possess a specific electric capacity of over 390 F/g.     

Computer simulation of active layer of fuel cell electrode with polymer electrolyte: Complete combined carbon support grains, calculation of overall characteristics

Full computer simulation of the active layer of a fuel cell cathode with polymer electrolyte and complete combined carbon support grains is carried out. The active layer structure included two types of equal-size cubic grains (combined support grains and voids) together forming a cubic lattice. Also, the structure of combined grains was modeled; a carbon cluster was formed in them, with the oxygen reduction process occurring on its surface; the rest of the grain volume was filled by polymer electrolyte. The completeness of the grains consisted in the fact that they were characterized by 3D electron conductivity, ability to take part in the transport of protons in the active layer and the carbon cluster in the grains had the maximum possible surface area. Calculation of overall currents of oxygen cathodes with full combined carbon support grains, Nafion, and platinum yielded the following result. At t = 80°C, pressure p* = 101 kPa, cathode potential E ₀ = 0.8 V, and optimum active layer thickness Δ* = 20 μm, maximum overall current I _max = 0.38 A/cm², maximum power density W _max = 0.31 W/cm². At potential E ₀ = 0.7 V, Δ* = 9.8 μm, I _max = 1.13 A/cm², W _max = 0.79 W/cm². At potential E ₀ = 0.6 V, Δ* = 3.8 μm, I _max = 2.95 A/cm², W _max = 1.76 W/cm². At potential E ₀ = 0.5 V, Δ* = 1.4 μm, I _max = 7.71 A/cm², W _max = 3.86 W/cm². The overall current values are higher than those observed experimentally at the given cathode potentials. The discrepancy is explained by the fact that calculations of active cathode layers with a practically regular structure were carried out. All combined support grains in them are full and identical, while in fact the active layer structure is not characterized by the properties of fullness and equivalence. The second circumstance is that experimental active layers rarely have a strictly optimum thickness. Meanwhile deviation from this optimum results in losses in current. Transition to cathodes with combined grains has additional advantages. (1) In such grains, all platinum participates in current generation, the catalyst utilization degree reaches 100%. (2) Oxygen can enter the active layer not through small Knudsen pores, but through large (with the diameter of hundreds and more nm) gas pores, in which usual molecular gas diffusion occurs, so that diffusion limitations in the active layer become less significant. 3. In the active layer, the danger of gas pore flooding by evolving water decreases. Now, water vapor is much more easily removed from large gas pores directing then into the gas-diffusion layer pores.     

Active layer of fuel cell electrode with polymer electrolyte: Modeling of support grains, calculation of overall cathode characteristics

The active layer of the cathode of a fuel cell with polymer electrolyte (Nafion) is considered. The optimum carbon support structure is constructed using computer simulation: its carbon “skeleton” possesses the maximum outer surface area and provides electronic conductivity of the grains, support cubes, along the three coordinate axes. Nafion is absent in the support grain, so that the grain is capable of participating only in the transport of oxygen molecules, it possesses no proton conductivity. An estimate of all parameters of an optimum support grain is provided; in particular, the value of the effective Knudsen diffusion coefficient of oxygen is established. After this, effective proton conductivity and effective Knudsen diffusion coefficient are calculated already on the whole active layer scale, according to the model of equally sized cube grains of three types. In conclusion, the overall current in the active layer of a cathode with a polymer electrolyte was calculated for the percolation cluster consisting only of Nafion grains and the Knudsen diffusion of oxygen created only by a combined gas percolation cluster consisting of void grains and all support grains. The overall current value for t = 80°C and pressure of p* = 101 kPa proved to be low, hundreds of mA/cm². The current value can apparently be increased to several A/cm² if the support grains are developed that would simultaneously possess both proton conductivity and ability to sustain oxygen diffusion.     

Focusing of a high-energy particle beam at an extremely short distance

It has recently been realized that the focusing of high-energy particle beams at a distance of about 1 cm is promising. A new idea is proposed in this work to focus the beam at a short distance by using a bent plane–parallel silicon plate whose side edges are rotated at a small angle with respect to crystallographic planes. At the U-70 accelerator (IHEP, Protvino), a 50-GeV proton beam has been focused to a narrow line with a width of no more than 30 μm at a distance of 17 cm.