Peculiarities of silver reduction from acid thiourea solutions

Sulfur-containing decomposition products of thiourea, which are present in thiourea solutions, exert a considerable effect on silver electroreduction rate in these solutions. The technique involving electrode surface renewal by cutting off a thin metal layer directly in the solution at a fixed electrode potential makes it possible to minimize the influence of adsorbed impurities on the rate of the process under study. The values of exchange current and transfer coefficient of the electrode reaction of silver reduction from thiourea solutions have been determined using this technique. It has been shown that impurities in acid thiourea solution substantially increase reduction rate in the region of potentials more positive than about -0.5 V vs Ag/AgCl.