IN-SITU VOLT-RESISTOMETRIC STUDY OF ADSORPTION AND PREMONOLAYER OXIDATION OF COPPER IN ALKALINE-SOLUTIONS IN CONNECTION WITH SOME ASPECTS OF ELECTROCATALYSIS

Contact electroresistance (CER) measurements have been performed in or der to study in situ the electrochemical behaviour of copper in alkali ne solutions (pH 11-13.6) at potentials negative of voltammetric (VAM) peak A(1) (0.6 V, rhe). An adsorption of oxyspecies was shown to comm ence at potential -0.4 V (the) resulting in the negative charge of the interface. In the potential region of VAM peak A(0) (0.35-0.45 V, rhe ) the coverage of oxyspecies decreases about two times owing to dissol ution of Cu(OH)(2)(-) species. A formation of the first monolayer of c uprous oxide at potential 0.47+/-0.02 V (the) results in the CER incre ase of the interface from 5 x 10(-5) up to 100 Omega. S-shaped kinetic curves corresponding to the formation and growth of the cuprous oxide monolayer are presented. A consumption of the adsorbed oxyspecies in the course of an electrocatalytic formaldehyde oxidation has been prov ed experimentally. Inhibition of the formaldehyde oxidation reaction i n the potential region negative of peak A(1) was shown to be linked to the growth of the cuprous oxide film insulating the electrode surface rather then to a loss of mediating oxyspecies. In connection with the nature of active electrocatalytic centres at the interface, two metho ds have been used to enhance the coverage of adatoms in the course of formaldehyde oxidation at copper, nickel, cobalt and gold electrodes. It was found, that native adatoms (eg, Cu-ad on copper or Ni-ad at nic kel surface) cannot be considered as being the only (or the main) acti ve electrocatalytic centres at the electrode surface. The coverage (th eta greater than or equal to 0.001) of foreign adatoms (eg, Cu-ad on n ickel, cobalt or gold surface) did create the new more effective elect rocatalytic centres on the substrate meals. Copyright (C) 1996 Elsevie r Science Ltd.