Redox couples passivation

Most electrodes are metallic. Sometimes the metal of an electrode can also be one component part of a redox couple. Good examples include metallic iron, copper, zinc, lead or tin. A tin electrode forms a couple when in contact with tin(IV) ions, etc. Such electrodes are called redox electrodes (or non-passive). In effect, a redox electrode has two roles first, it acts as a reagent and, secondly, it measures the energy of the redox couple of which it forms one part when connected to a voltmeter. 

In principle, interfacial recombination processes can be inhibited by modifying the interface. The use of t-butylpyridine in the DSSC electrolyte solution to increase its photovoltage is one example [2,97]. We wished to explore general methods for passivating interfacial recombination sites in DSSCs that might allow the use of a variety of redox couples and therefore facilitate making a viable solid-state DSSC. 

Figure 10 Dark and photocurrents with FeCp 70 redox couple before and after interfacial passivation, (a) Effect of blocking recombination at the Sn02 surface, reaction (5) (Fig. 9a), by electropolymerization of PPO. (b) Effect of blocking recombination at both the Sn02 and Ti02 surfaces, reactions (4) and (5) (Fig. 9b), by vapor-phase silane treatment without PPO. (Data from Ref. 49.)...

E4.8. An active-passive alloy corrodes in the active state in an acidic solution in the presence of the redox couple Fe Fe. The corrosion potential and corrosion current are Ecorr= 0.35 V vs. SHE and Jcorr=10 iA/cm. If the reduction occurs under activation control with bc = — 0.1 V/decade, concentration of Fe of 10 M, and the exchange current density of the redox couple p 2+ = 0.01 pA/cw , calculate the concentration of Fe " oxidizer necessary to passivate the alloy. Recalculate the oxidizer concentration for an exchange current density of 0.1 and 1 ihJcrr for the redox couple. 

Figure 3-8. Schematic representation of the principle of photoelectrochemical measurements for an n-type semiconducting passive film under anodic polarization. The photon illumination forms electron and hole pairs whose charge can be consumed in the oxidation of redox couples at the surface of the film, giving rise to a photocurrent.

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