Inhibition of Hydrogen Adsorption by Submonolayer Deposition of Metals on Platinum

Submonolayer deposition of copper, silver, lead, and gold inhibit the adsorption of hydrogen at a platinum electrode. At low surface coverage, copper and silver preferentially inhibit the sites occupied by weakly adsorbed hydrogen. Lead and gold inhibit both weakly and strongly adsorbed hydrogen equally at all surface coverages. Copper(II) and silver(II) react quantitatively with adsorbed hydrogen at open circuit to produce deposits of copper(0) and silver(0) which are not distinguishable from the underpotential deposited metals. Copper deposited at underpotential forms a discrete monolayer before the second layer deposits. On the other hand, silver deposited at underpotential forms films 1.4 monolayers thick before complete surface coverage is achieved.