Mechanism and analytical aspects of the polarographic maximum wave of tellurium.

The polarogram of tellurium(IV) in weakly basic solution has a sharp maximum on the diffusion current plateau. The electrode process causing this maximum has been examined by means of various techniques such as semiconductor catalysis, "block" polarography and ultraviolet irradiation of the dropping mercury electrode. The maximum was found to be caused by the catalytic wave of hydrogen produced by the tellurium deposited on the mercury surface. Part of the tellurium is reduced to hydrogen telluride by nascent hydrogen formed catalytically. The brown mist which usually appears in the vicinity of the surface of the dropping mercury cathode consists of elemental tellurium produced by the decomposition of the hydrogen telluride near the electrode. The sudden decrease in the current maximum at a potential more negative than the peak potential of the maximum is due to desorption of tellurium, caused by movement of mercury.