Towards a detailed in situ characterization of non-stationary electrocatalytic systems

Abstract

A complementary combination of cyclic voltammetry, impedance spectroscopy and quartz crystal microbalance techniques was used to: (i) control the assembly of a model electrocatalytic system consisting of monolayer and sub-monolayer amounts of Ag and Pb on a Au electrode, (ii) evaluate the system performance for the reduction of NO₃⁻ and (iii) study the disassembly of the electrocatalytic system to explore any changes which occurred during the assembly and/or catalytic stages. Physical models of the electrochemical interface (described in terms of equivalent electric circuits) at all stages are found to be considerably different but consistent with each other. Deposition of the Ag atomic layer on Au is accompanied by spontaneous surface alloying and specific adsorption of anions. In the following, deposition of the Pb atomic layer triggers further alloying in the Ag_ad/Au layer while perchlorate-ions leave the surface. Approximately 1/3 of the Pb atomic layer on Ag_ad/Au was found to demonstrate the best activity towards nitrate reduction. The developed experimental approach shows promise for the in situ characterization and control of all the non-stationary stages which are usually of particular importance in electrocatalytic research.