Ohmic region

Prasarma et al. [185] were also able to observe an optimum thickness of DLs for fuel cells experimentally. They demonstrated that the thicker DLs experience severe flooding at intermediate current densities (i.e., ohmic region) due to low gas permeation and to possible condensation of water in the pores as the thickness of the DL increases. On the other hand, as the thickness of the DL decreases, the mass transport losses, contact resistance, and mechanical weakness increase significantly [113,185]. Through the use of mathematical modeling, different research groups have reported similar conclusions regarding the effect of DL thickness on fuel cell performance [186-189]. 

This result is important since it shows that for finite (non-zero) Schottky barrier, i.e. P 0) < oo, and for large value of C, the current changes from the space charge limited current to the ohmic current. This result is similar to that given by Mott [36] for a trap-free insulator. Just before the ohmic region there is a transition region between the conventional power law and the ohmic region. 

Fig. 3.17. J-V characteristics of the ITO/PEDOT PSS/MEH-PPV/Au diode at 240 K. The thickness of the active layer is 120 nm. The symbols represent die experimental data. The dash-dot line represents the ohmic region due to thermally generated and background carriers. The dashed line represents die calculated values using the conventional equation (3.42) with a zero Schottky barrier, while die dotted curve represents the calculated values using Eq. (3.46) with a Schottky barrier = 0.1 eV. At lower voltages below die point D, the plot of Eqs. (3.46) and (3.42) are practically identical. The values of die parameters used in this representation are N0 = 1019 cm-3, Tc = 400 K, e = 3, e0 = 8.85x 1(T14 F/cm, fi = 7x 1(T5 cm2/Vs, iVv = 2x 1019 cm-3 and Hh = 4.5 x 1018 cm-3 [44],...

Figure 22-4 Current-potential curve for electrolysis showing the linear or ohmic region, the onset of polarization, and the limiting cuirent plateau. In the limiting current region, the electrode is said to be completely polarized, since its potential can be changed widely without affecting the current.

Ohmic region AB (typically from 2 to 10—12 V) The mean current I increases nearly linearly with the terminal voltage U. 

This is the ohmic region. For higher currents, 6s will grow and significantly affect the inter-electrode resistance. The current will saturate at its maximal... 

In order to estimate P0, one has to first estimate the heat power PE of the electrochemical discharges. Therefore, Equation (5.1) can be used. The interelectrode resistance R can be evaluated by inspecting the slope of the mean I - U characteristics in the ohmic region (the linear part from 5-15 V of the mean I- Ucharacteristics). Typical values for PE are around a few watts (for machining voltages in the range of 30-40 V). 

In the three following sections S.4.3.2-8.4.3.4, we treat the contacts, charge-carrier injection, and the Ohmic region of the / —V characteristic and in Sect. 8.4.4, we return to the space-charge-limited current. 

Internal Resistance and Areal Resistivity By linearly fitting the ohmic region in the polarization curve, we can get... 

For simplicity, assume the height of both chambers are 100 pm and the conductivity for both anolyte and catholyte are 0.017 S cm the calculated is 1.2 O cm. According to prior art, r , resistivity of the ion exchange membrane (Nafion 117, for instance) is approximately 10 Q cm in phosphate buffer medium, r, resistivity of cathode is also low when the current density is low enough that the concentration loss is not a dominating factor, which is the case in the ohmic region. As a result, anode resistivity dominates over the total resistivity in microscale MFCs. 

Experimental Results on Electronic Current (0 Low-Field Ohmic Region... 

Figure 15. Typical voltage-ampere characteristic of Ta-TajOj-Au diode. Contact area about 10" cm. Note Ohmic region at low voltages and exp(K ) region at high voltages. Mead compared the transition voltage (0.46 V) with the difference in the work functions of the metals (110 A oxide thickness) [from Mead, Phys. Rev.

Three regions can be observed, region 1 is the Ohmic region where the electrical current or current density is related to the electrical potential difference by Ohm s law. In region 2 the current reaches a plateau value which implies that the Ohmic resistance has been increased. This is the region of the limiting current density The limiting current density (often expressed in mA/cm ) is the current necessary to transfer all the available ions. When the... 

By linearly fitting the ohmic region in the polarization curve, the slope is approximately equal to the internal resistance of ohmic region, / /. As shown in Equation (8.6), minimizing internal resistance yields a high power density MFC. 

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