[en] The sorption and deposition of technetium species formed from TcO₄^- at gold and platinized surfaces was followed by a coupled in situ radiometric and electrochemical technique. It was found: (i) that a layer of TcO₂ species is formed preceding the massive deposition of technetium species, and (ii) that the deposition process is not connected with hydrogen evolution or reaction with adsorbed hydrogen as has been assumed in the literature. An important new finding, the electrocatalytic reduction of ClO₄^-ions at surfaces covered by technetium species, was demonstrated on the basis of a comparative study of the phenomena observed in H₂SO₄ and HClO₄ supporting electrolytes. (Author)