The hydrogen-assisted, reductive desorption of hydroquinone-derived adlayers (Q((ads))) is reported at nearly defect-free Pt(111) single crystal electrodes in 0.5 M H2SO4. Classical electroanalytical techniques are used to evaluate surface packing density of Q((ads)) under a variety of conditions. Charge density measurements suggest that two limiting conditions are observed. High surface packing densities of the adsorbate are detected in the presence of 2 mM H2Q((aq)), while lower surface packing densities are observed upon rinsing with 0 mM H(2)Q((aq)) supporting electrolyte. A strong dependence between the mode of adsorption/desorption of Q((ads)) and the presence of long-range order at the Pt(1 11) electrode surface is revealed. The reductive displacement of Q((ads)) with CO is also reported. The experiments show that the extent of CO displacement can be controlled potentiometrically and that the progress of the displacement can be observed quantitatively through amperometric detection. Some additional applications of these novel electrochemical observations are discussed. (c) 2006 Elsevier B.V. All rights reserved.