Effect of thiourea and substituted thioureas on copper underpotential deposition on gold

The formation of metal monolayers through underpotential deposition (UPD) d epends on the interactions between the electrode surface and the depositing species. Other adsorbable species, if present in the solution, will influe nce the formation of UPD metal films through their adsorption on the electr ode surface, taking place simultaneously. Copper UPD formation on polycryst alline gold surfaces has been investigated in the presence of small amounts of urea, thiourea (TU) and N substituted thioureas using cyclic voltammetr y. The results show that the UPD of copper on gold is significantly influen ced by the presence of thiourea in solution. The charge corresponding to th e stripping peak obtained in the presence of both Cu2+ and TU in solution i s always larger than the sum of the charges resulting when either of them i s present alone. Again, the charge observed during stripping in the presenc e of both Cu2+ and TU is believed to arise from (i) stripping of the UPD Cu , (ii) adsorption-desorption of TU and (iii) oxidation of Cu(TU)(n)(+) comp lexes. The addition of N-substituted TUs is found to influence the UPD of C u to different extents. This is tentatively explained in terms of the struc ture of the organic molecules. (C) 2000 Elsevier Science S.A. All rights re served.