Effect of camphor on Cu(II) reduction kinetics in acid solutions

Linear potential sweep (LPS) voltammetry and electrochemical impedance spectroscopy (EIS) was used for investigation of camphor effect on the stepwise Cu(II) reduction kinetics in 0.01 M Cu(II) solutions containing 0.6 M H2SO4 as supporting electrolyte. Polycrystalline Cu coatings deposited in acid CuSO4 solution do not display the properties that were established for clean (oxygen-free) copper surfaces. Their surface activity seems to be suppressed by chemisorption of oxygen, which prevents the formation of two-dimensional condensed adsorption layers that are typical of other metals.Addition of camphor (up to 6 mM) results in slight changes in impedance spectra and LPS voltammograms. Rather weak adsorption of camphor is enhanced by bromide anions, especially in the presence of Cu(II). Significant fall in double layer capacitance (down to ∼5.4 μF cm−2) and exchange current density (down to ∼8 μA cm−2) is accompanied by increase in cathodic charge transfer coefficient from 0.4 to 0.6. The model is suggested for synergistic adsorption of bromide and camphor, according to which specifically adsorbed halides act as species bridging the copper substrate with Cu(I)-camphor surface complexes.