Electrolysis of Ammonium Carbamate: A Voltammetric and Xray Photoelectron Spectroscopic Investigation into theModification of Carbon Electrodes

Abstract

Uchiyama et al. (J. Electrochem. Soc., 154, F31 (2007)) report that a glassy carbon (GC) electrodemodified with surface amino groups via the electrochemical oxidation of ammonium carbamate canreact with catechol in a 1,4-Michael addition through the surface amino groups. This was deducedfrom XPS data and the observation of a new reversible couple at less positive potentials than thecatechol redox couple, which was attributed to a quinone-imine-like adduct.In this paper wedemonstrate that identical voltammetry is observed at an unmodified GC electrode that has beenoxidatively pre-treated in an identical fashion to that reported by Uchiyama et al. but in the absence ofammonium carbamate and any other sources of nitrogen. XPS characterisation of a graphite electrodebefore and after electrolysis in ammonium carbamate solution suggests that the nitrogen species on thecarbon surface may not be in the form of amino groups, but may due to adsorbed ammonium ions orthe formation of amides. This indicates that it is not the surface amino groups that are reacting withcatechol, and alternative explanations are discussed.