Adsorption of camphor and 2,2′-bipyridine on Bi(111) electrode surface

Impedance spectroscopy and in situ STM methods have been used for investigation of the camphor and 2,2'-bipyridine (2,2'-BP) adsorption at the electrochemically polished Bi(111) electrode from weakly acidified Na2SO4 supporting electrolyte solution. The influence of electrode potential on the adsorption kinetics of camphor and 2,2'-BP on Bi(111) has been demonstrated. In the region of maximal adsorption, i.e. capacitance pit in the differential capacitance versus electrode potential curve, the heterogeneous adsorption and diffusion steps are the rate determining stages for camphor and 2,2'-BP adsorption at the Bi(111) electrode. It was found that for camphor | Bi(111) interface the stable adsorbate adlayer detectable by using the in situ STM method has been observed only at the positively charged electrode surface, where the weak co-adsorption of SO42- anions and camphor molecules is possible. At the weakly negatively charged Bi(111) electrode surface there are only physically adsorbed camphor molecules forming the compact adsorption layer. The in situ STM data in a good agreement with impedance data indicate that a very well detectable 2,2'-BP adsorption layer is formed at Bi(111) electrode in the wide region of charge densities around the zero charge potential. (C) 2007 Elsevier Ltd. All rights reserved.