Poisoning the catalytic reduction of peroxide on Pb underpotential deposition modified Au surfaces with iodine

The electrocatalysis of peroxide reduction by Pb underpotential deposition on Au(1 1 1) was studied through poisoning of the active surface by I−. The addition of I− decreases the catalytic peroxide reduction activity; this decrease was fit with a Langmuir-type isotherm yielding a Gibbs free energy of adsorption of −43 kJ/mol. Analysis of STM images suggests that the active site for peroxide reduction is at the edge of the circular Pb islands as the reduction in island circumference scales with the reduction in catalytic activity as I− is added. At high-I− concentrations, oblong PbI2 islands are observed throughout potentials where a smooth Pb monolayer was present in the system absent I−.