Oxygen reduction semiconducting properties

Lead Telluride. Lead teUuride [1314-91 -6] PbTe, forms white cubic crystals, mol wt 334.79, sp gr 8.16, and has a hardness of 3 on the Mohs scale. It is very slightly soluble in water, melts at 917°C, and is prepared by melting lead and tellurium together. Lead teUuride has semiconductive and photoconductive properties. It is used in pyrometry, in heat-sensing instmments such as bolometers and infrared spectroscopes (see Infrared technology AND RAMAN SPECTROSCOPY), and in thermoelectric elements to convert heat directly to electricity (33,34,83). Lead teUuride is also used in catalysts for oxygen reduction in fuel ceUs (qv) (84), as cathodes in primary batteries with lithium anodes (85), in electrical contacts for vacuum switches (86), in lead-ion selective electrodes (87), in tunable lasers (qv) (88), and in thermistors (89). 

A key property of a passive film that may be manipulated in the future is its semiconductive nature in the context of the cathodic reaction that necessarily occurs on top of the film. It is not always appreciated that chromium oxide is a very good electrical insulator, so that in theory one could enrich chromium to such an extent that the reduction of oxygen on top of the passive film on stainless steel would cease, thus eliminating localized corrosion in salt water. In practice, not much iron content is required to make the film rather conductive, but still, manipulation of cathodic reaction kinetics on passive films has to be considered an important challenge for the future. Many tools and theoretical underpinnings are available for further progress in this area, including a variety of in situ probes, surface-science tools, and classical electrochemistry methods. 

---