12Energy storage technologies provide an alternative solution to the problem of balancing power generation and power consumption. Redox flow cells are designed to convert and store electrical energy into chemical energy and release it in a controlled fashion when required. Many redox couples and cell designs have being evaluated. In this paper, redox flow systems are compared in the light of characteristics such as open circuit potential, power density, energy efficiency and charge-discharge behaviour. The key advantages and disadvantages of redox flow cells are considered while areas for further research are highlighted.

No abstract

The aim of this paper is the characterization of a carbon felt (Le Carbone Lorraine, RVC 4002) to be used as three-dimensional electrode. A wide group of very different techniques were used in the physical and structural characterization of this material. Both, structural (porosity, mean pore radius, specific surface area, tortuosity) and physical properties (permeability, electrical resistance) were determined by using mercury porosimetry, adsorption isotherm analysis, a filamentary analog procedure and liquid permeametry (pressure drop method). The results obtained from the modelling of the hydrodynamic behaviour, from previous work, were also applied here. The carbon felt studied was found to have a porosity around 0.98, a specific surface area of 22100-22700 m -1 , 2.7 10 -3 Ω m electrical resistivity and a tortuosity between 5 and 6. The comparison of these results with those found in the literature for other similar materials, used as three-dimensional electrodes, highlights the attractions of this

No abstract

The intensity distribution of the ultrasonic energy is, after the frequency, the most significant parameter to characterize ultrasonic fields in any sonochemical experiment.Whereas in the case of low intensity ultrasound the measurement of intensity and its distribution is well solved, in the case of high intensity (when cavitation takes place) the measurement is much more complicated. That is why the predicting the acoustic pressure distribution within the cell is desirable.A numerical solution of the wave equation gave the distribution of intensity within the cell. The calculations together with experimental verification have shown that the whole reactor behaves like a resonator and the energy distribution depends strongly on its shape.The agreement between computational simulations and experiments allowed optimisation of the shape of the sonochemical reactor. The optimal geometry resulted in a 2 strong increase in intensity along a large part of the cell. The advantages of such optimised geometry are (i) the ultrasonic power necessary for obtaining cavitation is low, (ii) low power delivered to the system results in only weak heating; consequently no cooling is necessary and (iii) the "active volume" is large, i.e. the fraction of the reactor volume with high intensity is large and is not limited to a vicinity close to the horn tip.

As one of several types of pollutants in water, chlorinated compounds have been routinely subjected to sonochemical analysis to check the environmental applications of this technology. In this review, an extensive study of the influence of the initial concentration, ultrasonic intensity and frequency on the kinetics, degradation efficiency and mechanism has been analyzed. The sonochemical degradation follows a radical mechanism which yields a very wide range of chlorinated compounds in very low concentrations. Special attention has been paid to the mass balance comparing the results from several analytical techniques. As a conclusion, sonochemical degradation alone is not an efficient treatment to reduce the organic pollutant level in waste water.

The use of phenolic resins for manufacturing different textile products in a company, our case example, generates wastewater with high phenol concentration (30-400 ppm) and chemical oxygen demand (COD) between 3,000 and 15,000 ppm. Moreover, the effluent also contains high chloride concentrations ranging between 4000 and 7000 ppm, Ca2+ ions with a concentration of ca. 2000 ppm, and suspended solids. A study at the laboratory scale of the anodic electrochemical treatment of this industrial effluent has been carried out. The influence of variables such as current density, pH, and charge passed on phenol degradation and COD reduction was studied. As anodes, PbO2/normalTi or normalBi­PbO2/normalPt/normalTi or Pt/Ti were used. As the separator, a 117 Nafion cation exchange membrane was employed. The results showed that the final COD value was lower than 1000 ppm. After electrochemical treatment the final concentration of phenol was lower than 1 ppm, and the COD decrease was 70-80%. Unidentified aliphatic carboxylic acids and alcohols were the main products of oxidation. For electrolyses carried out at alkaline pH, the only halocompound detected in the anolyte, gas, and aqueous phases, was chloroform regardless the electric charge passed, the current density employed, and the anode used. © 2002 The Electrochemical Society. All rights reserved.

No abstract