Oxygen free polarization curve

The oxygen-transport-free polarization curve in Equation 4.141 can be considered as the zero-order term in the expansion of the solution to the full system of equations (4.53) through (4.55) over the parameter 1 /(s D). The goal of this section will be to find the first-order correction in this series. 

The analytical CCL polarization curve Equation 4.189 is compared to the exact numerical solution of the system (4.53) and (4.54) in Eigure 4.21. A reference value ofDrt = 1.37 10 cm s is taken from measurements (Shen et al., 2011). The curves in Eigure 4.21 correspond to the indicated ratios D/Dre/- Clearly, as this ratio tends to infinity, the analytical and numerical results tend to the diffusion-free polarization curve Equation 4.141. Note that as b decreases, the overpotential due to oxygen transport increases, and the accuracy of the model drops. Nonetheless, in the region of currents Jo < 1, the model works well for D/Dref as small as 0.1 (Figure 4.21). 

The effect of ultrasonic field on the polarization curves of Cu-Pb, and some brasses has been studied in chloride and sulfate solutions in the presence and absence of the respective metal ions [108]. The main effect of the ultrasound at low current densities is the acceleration of diffusion. The passivation current density in solutions free of the respective metal ions is considerably increased when ultrasound is applied. Stable passivity cannot be attained because of the periodic destruction of the salt film. The hydrogen evolution reaction is accelerated because of the destruction of the solvation shell. The oxygen depolarization reaction is also enhanced due to the increased diffusion. The rate of metal deposition is likewise increased by ultrasound. The steady-state potentials of reactions with anodic control are shifted in the negative direction when ultrasound is applied. 

Figure 10. Polarization curves (IR-free) for oxygen reduction at LSM cathode without (O) and with ( ) loading Pt catalysts in O2 at 7 ceii = 800 °C. Pt(A) 0.5 ing/cnr A Pt(A) 0.1 mg/em Pt(C) 0.1 mg/cm. Reproduced from Ref. 30, Copyright (1996), by permission from The Electrochemical Society of Japan.

Figure 11. Polarization curves (IR-free, measured in O2) for oxygen reduction at LSC cathodes. A LSC1050/SDC400, O LSC1050/ SDCl 150.

Fig. 7 Polarization curve of cathodic oxygen reduction with superimposed cathodic water dissociation at 18-8-CrNi steel in air-saturated, stirred NaOH/0.5 M NaCi solution, pH 11,25°C ( ) as well as in practically 02-free solution (o) potential referred to saturated calomel electrode [2].

Figure 6.12 Polarization curves for iron in oxygen-free 4% NaCl solution, at various pH values (adapted from Kaesche [6.15]).

To the best of my knowledge, the hemoglobin oxygenation curve is historically the first example of a biologically essential positive cooperativity. Because of this, it becomes an important objective to explore the phenomenology of hemoglobin s positive cooperativity and compare it with that of the consilient mechanism due to an apolar-polar repulsive free energy of hydration (as is done in Chapter 7) and, in fact, to do so for a number of protein-based machines that exhibit positive cooperativity. 

---