Electrochemistry of Co(TPTZ)2 Complex on a Carbon Paste Electrode Modified with TiO2 Nanoparticles

Abstract

Nowadays, the cobalt based complexes have attracted considerable interest in dye sensitized solar cells (DSSC). They have been widely used as a redox electrolyte [1], sensitizing agent [2] and the component of counter electrode (CE) material [3]. Therefore, their electron-proton transfer behavior should be taken into account to achieve success in efficient DSSC [4]. In the present study, electrochemical behavior of cobalt (II) complex with the N-donor ligand 2,2’-bipyridyl-1,3,5-tripyridyl-s-triazine (TPTZ) on the TiO2 modified carbon paste (T/CPE) was compared with the bare carbon paste electrode (CPE). The electrochemical response of the complex was studied by means of square-wave voltammetry (SWV) technique in a conventional one compartment cell using a saturated Ag/AgCl and a platinum wire as the reference and counter electrode, respectively. The effect of TiO2/graphite ratio of T/CPE on the voltammetric response of the Co(TPTZ)2 complex was examined and the best result was obtained for 60 % (w/w). The ligand/metal ratio and stability constant of the complex as well as the mechanisms of the electrode processes were elucidated by examining the effects of pH, ligand concentration and frequency on the voltammograms. The optimum pH was selected as 7.5 for comparison of the T/CPE and CPE electrodes. The electrochemical impedance spectroscopy (EIS) results obtained in the phosphate buffer indicated that T/CPE had higher charge transfer resistance and electroactivity than those of the bare electrode. It was concluded from the Bode-phase diagrams that nano-TiO2 structure increases the conductivity between electrode and electrolyte interface due to the good penetration of the Co(TPTZ)2 complex into the electrode surface trough the nano-TiO2 pores. All the electrochemical results were found to be consistent with the surface morphology of the working electrodes obtained using atomic force microscopy (AFM).