Contact electroresistance method for in situ studies of metal surfaces in electrolytes: Adsorption of hydroxyl ions and submonolayer electrooxidationof gold

The contact electroresistance (CER) of gold is studied as a function of pot ential E in acidic, neutral, and alkaline solutions. It is shown that CER s tarts to increase in all solutions at E greater than or equal to 0.1 V (wit h respect to reversible hydrogen electrode). In alkaline solutions, the gro wth of CER increases at higher KOH concentrations at the expense of adsorpt ion of hydroxyl ions on gold. In acid solutions, the growth of CER decrease s with increasing concentration of H2SO4. At E = 1.28 V, CER dramatically i ncreases in all solutions. The increase in this case is caused by the forma tion of primary oxides of gold. Upon reaching E = 1.47 V, the oxides transf orm into Au2O3. The CER growth in alkaline and acidic solutions is found to correlate with the electrocatalytic activity of gold in oxidizing hydrazin e and reducing bichromate ions. Coverages of gold by adsorbed hydroxyl ions are determined in alkaline solutions, and isotherms of their adsorption ar e plotted for different potentials.