Internal resistance of cells

Figure 6. Comparison of internal resistance of cells with different /T-Al20, electrolyte geometries.

Figure 22-1 An electrolytic cell for determining (a) Current = 0.00 mA. (b) Schematic of cell in (a) with internal resistance of cell represented by a 15.0 n resistor and fiappued increased to give a current of 2.00 mA.

Fig. 10. Power and voltage characteristics of the nickel—iron cell where the internal resistance of the cell, R, is 0.70 mQ, at various states of discharge ( )...

Soluble corrosion products may increase corrosion rates in two ways. Firstly, they may increase the conductivity of the electrolyte solution and thereby decrease internal resistance of the corrosion cells. Secondly, they may act hygroscopically to form solutions at humidities at and above that in equilibrium with the saturated solution (Table 2.7). The fogging of nickel in SO2-containing atmospheres, due to the formation of hygroscopic nickel sulphate, exemplifies this type of behaviour. However, whether the corrosion products are soluble or insoluble, protective or non-protective, the... 

Figure 4. Qminbuuun.v to the internal resistance of a ZEBRA cell.

The reduction of the internal resistance of the cell can obviously be achieved by two measures ... 

Relaxation methods for the study of fast electrode processes are recent developments but their origin, except in the case of faradaic rectification, can be traced to older work. The other relaxation methods are subject to errors related directly or indirectly to the internal resistance of the cell and the double-layer capacity of the test electrode. These errors tend to increase as the reaction becomes more and more reversible. None of these methods is suitable for the accurate determination of rate constants larger than 1.0 cm/s. Such errors are eliminated with faradaic rectification, because this method takes advantage of complete linearity of cell resistance and the slight nonlinearity of double-layer capacity. The potentialities of the faradaic rectification method for measurement of rate constants of the order of 10 cm/s are well recognized, and it is hoped that by suitably developing the technique for measurement at frequencies above 20 MHz, it should be possible to measure rate constants even of the order of 100 cm/s. 

It was shown by our investigations that such cell can be cycled with self-charging at least during 10-15 cycles. After that, the internal resistance of such cell is incremented considerably due to the accumulation of... 

The proper mixing of the graphite with the Mn02 is critical for high rate performance. It is necessary to put work into the mix to uniformly coat the manganese dioxide particles with a thin layer of graphite. This provides a low resistance path from the manganese to the cell terminals to minimize the internal resistance of the cell. A similar effect can be expected if used in cathode formulations for Li-Ion cells. 

Operating temperature has a significant influence on PEFC performance. An increase in temperature lowers the internal resistance of the cell, mainly by decreasing the ohmic resistance of the electrolyte. In addition, mass transport limitations are reduced at higher temperatures. 

If the potential of the Daniell cell is to be determined accurately, we have already seen that the measurement has to be made at zero current. In order to ensure zero current, the internal resistance of the voltmeter shown in Figure 3.1 must be vast, as discussed in the previous chapter. The voltmeter operates in much the same way as a switch or circuit breaker does reaction (in this case, cell discharge) would occur but for the incorporation of the voltmeter in the circuit. 

The assumption of transfer by a purely turbulent mechanism in the Handlos-Baron model leads to the prediction that the internal resistance is independent of molecular diffusivity. However, such independence has not been found experimentally, even for transfer in well-stirred cells or submerged turbulent jets (D4). In view of this fact and the neglect of shape and area oscillations, models based upon the surface stretch or fresh surface mechanism appear more realistic. For rapid oscillations in systems with Sc 1, mass transfer rates are described by identical equations on either side of the drop surface, so that the mass transfer results embodied in Eqs. (7-54) and (7-55) are valid for the internal resistance if is replaced by p. Measurements of the internal resistance of oscillating drops show that the surface stretch model predicts the internal resistance with an average error of about 20% (B16, Yl). Agreement of the data for drops in liquids with Eq. (7-56) considerably improves if the constant is increased to 1.4, i.e.. 

The impregnation of porous nickel discs with CoPc was difficult because of the limited solubility of the chelate in the usual solvents. CoPc cathodes with carbon as substrate were therefore prepared for use in H2/O2 fuel cells. A mixture of 72 mg CoPc and 48 mg acetylene black, with PTFE as binder, was pressed into a nickel mesh of area 5 cm2. Electrodes of this type were tested in an H2/O2 fuel cell with 35% KOH electrolyte in an asbestos matrix at 80° C. Figure 5 compares the current/voltage characteristics of CoPc cathodes (14 mg/cm2) with those of other catalysts, including platinum (9 mg/cm2), silver (40 mg/cm2), and pure acetylene black (20 mg/cm2). An hydrogen electrode (9 mg Pt/cm2) was used as the anode in all tests. To facilitate comparison of the activity of different cathodes, the pure ohmic internal resistance of the cells (of the order of 0.02 ohm) was eliminated. 

Factor (a) can be minimized by making the internal resistance of the cell as small as possible, for example, by having a high concentration of an inert electrolyte in the cell. Factor (b) can be reduced by stirring the cell contents vigorously. Factor (c), since it originates in chemical reaction kinetics, can... 

Ohmic potential (= IR) is that voltage needed to overcome internal resistance of the cell. 

It is well known that the working voltage of a practical cell under load usually rises with an increase in temperature. However, this is almost entirely due to a reduction in the internal resistance of the cell caused by an increase in the conductivity of the electrolytic phase and in the diffusion rates of the eleclroactive species. 

The source of ohmic potential drop is the internal resistance of the bulk phases within the cell. If the current distribution is uniform, then for a phase with conductance a (S m" 1), the resistance is R = x/Across-sectional area. Thus for the passage of a current i through a cell with j sequential phases,... 

The thermal energy generated or absorbed by an electrochemical cell is determined first by the thermodynamic parameters of the cell reaction, and second by the overvoltages and efficiencies of the electrode processes and by the internal resistance of the cell system. While the former are generally relatively simple functions of the state of charge and temperature, the latter are dependent on many variables, including the cell history. 

With the larger cells, continuous discharge drains of 1 A and intermittent discharges of 2.5 A are possible. The internal resistance of such cells is low ( 0.1 Q). A typical discharge curve for a high current/high capacity cell is shown in Fig. 3.31. 

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