Utilization, of active materials

When a battery produces current, the sites of current production are not uniformly distributed on the electrodes (45). The nonuniform current distribution lowers the expected performance from a battery system, and causes excessive heat evolution and low utilization of active materials. Two types of current distribution, primary and secondary, can be distinguished. The primary distribution is related to the current production based on the geometric surface area of the battery constmction. Secondary current distribution is related to current production sites inside the porous electrode itself. Most practical battery constmctions have nonuniform current distribution across the surface of the electrodes. This primary current distribution is governed by geometric factors such as height (or length) of the electrodes, the distance between the electrodes, the resistance of the anode and cathode stmctures by the resistance of the electrolyte and by the polarization resistance or hinderance of the electrode reaction processes. 

Efforts to improve the ratio of effective to theoretical specific energy involve, in general (1) replacement, where possible, of inert grid, container, connector, and current collector materials by lightweight substances (2) increase of utilization of active materials by improved cell design and/or use of special additives (3) careful modeling and optimization of current collection and (4) use of bipolar electrodes. 

The development of a vertical concentration gradient of acid can give rise to non-uniform utilization of active material and, consequently, shortened service life through the irreversible formation of PbS04 [8]. 

Uneven use of battery electrodes, resulting in poor utilization of active material, and reduced energy efficiency,... 

Increased specific energy. By raising specific energy from 56 to 80 Wh/kg through increased utilization of active materials, the battery cost in S/kWh has decreased significantly (>S1000/kWh to [Pg.889]

Moreover, the Janus separator, besides modifying electrode materials and electrolyte formulations, essentially opens new opportunities for facilitating the utilization of active materials that are... 

The primary determinant of catalyst surface area is the support surface area, except in the case of certain catalysts where extremely fine dispersions of active material are obtained. As a rule, catalysts intended for catalytic conversions utilizing hydrogen, eg, hydrogenation, hydrodesulfurization, and hydrodenitrogenation, can utilize high surface area supports, whereas those intended for selective oxidation, eg, olefin epoxidation, require low surface area supports to avoid troublesome side reactions. 

Semiconductor electrodes seem to be attractive and promising materials for carbon dioxide reduction to highly reduced products such as methanol and methane, in contrast to many metal electrodes at which formic acid or CO is the major reduction product. This potential utility of semiconductor materials is due to their band structure (especially the conduction band level, where multielectron transfer may be achieved)76 and chemical properties (e.g., C02 is well known to adsorb onto metal oxides and/ or noble metal-doped metal oxides to become more active states77-81). Recently, several reports dealing with C02 reduction at n-type semiconductors in the dark have appeared, as described below. 

It is apparent that optimum utilization of raw materials, capital, and energy resources will influence the choice of catalyst. Catalytic activity alone is not a sufficient criterion. A hypothetical catalyst might be wonderfully active and selective at 25°C and one atmosphere, but it would be difficult to build an economical process around it. 

Therefore the utilization of porous materials with high surface areas serving as electrodes enables capacitors to be made with high capacitance. For example, the use of an activated carbon (10 pF cm ) with the specific surface area of 1000 m g gives a capacitance as high as 100 F g . It should be noted that the capacitance measured in a unit cell corresponds to a quarter of the capacitance per unit weight or volume of the single electrode (F g or F cm ), because the... 

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