Carbon corrosion hydrogen current density

Initially, the electrolysis of aqueous brine was carried out in amalgam cells [4,10, 11]. Typical conditions employed were an electrolyte feed of 25% NaCl at pH 4, a temperature of 343 K, and a current density in the range of 0.7 -1.4 A cm . The desired anode reaction, the evolution of chlorine, was accompanied by corrosion of the carbon at a rather rapid rate. Sodium amalgam was formed at the mercury cathode, which was then reacted with water to give 50% sodium hydroxide and hydrogen gas in a catalytic reactor known as a denuder. 

Under normal fuel cell operating conditions, the highest oxidative potentials in the cathode range between 0.6 V (vs. RHE) at high-current density and 0.95 V (vs. RHE) at open circuit (the anode potential remains always near 0 V vs. RHE), so that carbon-support corrosion is negligible. However, under start/stop conditions or in the case of localized hydrogen starvation, the cathode potential significantly exceeds 1 V versus RHE and the associated rapid carbon-support corrosion leads to... 

FIGURE 5.32 (a) Normalized hydrogen and oxygen concentrations, and the shape of the membrane phase potential along the channel, (b) The ORR and carbon corrosion (COR) cnr-rent densities on the cathode side of the cell, (c) The HOR and ORR cnrrent densities on the anode side of the cell, (d) The differences between HOR -ORR" and ORR -COR are coincidental and equal to the z-component of proton current density in the membrane. The shaded region indicates the domain where the approximation of e = 0 fails. For aU the cnrves, s = 0.04 and = 0.63329 V. 

The negative effect of cell reversal under local hydrogen starvation can be mitigated by using a thicker membrane. The equivalent current density of oxygen crossover, through the membrane, is inversely proportional to the membrane thickness. Thus, larger Ipem lowers the carbon corrosion current density and increases the cell lifetime. 

The right-hand side of Equation 5.237 is the proton current density f, produced in the ACL, minus the proton current density f consumed in the CCL. In this section, our goal is to demonstrate the effect due to the dead spot, and all transport losses on either side of the cell will be ignored. If necessary, transport losses in the GDL can be taken into account, as described in the section Carbon Corrosion in PEFCs from Hydrogen Depletion, while the transport losses in the CLs can be accounted for, using equations of Chapter 4. 

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