REDUCTION OF GOLD IN CONCENTRATED LICL

Reduction of gold from concentrated solutions of LiCl containing low g old concentration was investigated using electrochemical and microscop ic techniques. Cyclic voltammetric measurements id solutions containin g 0.5 mM Au in 6 M LiCl show two reduction peaks on both platinum and HOPG electrodes, indicating that the reduction of gold occurs in two s teps. Chronocoulometric measurements on platinum electrodes give evide nce of a two-electron reaction in the region of the first reduction pe ak, whereas in the region of second peak a three-electron reaction is approached. The morphology of deposited gold on highly oriented pyroly tic graphite (HOPG) substrates from solutions containing 5.10(-4) M Au Cl4- in 6 M LiCl was characterized using in situ-scanning tunneling mi croscopy (STM). In situ STM images in the potential range of the first reduction peak show the formation of gold clusters weakly bound to th e HOPG substrate. In the region of the second reduction peak an increa se in the z-range of the STM images was observed due to the formation of the three-dimensional gold bulk phase. However no stable gold clust ers could be imaged in situ in this potential range due to reproportio nation of freshly deposited gold and Au(III) from the electrolyte to f orm Au(I).