Self-assembled monolayer of 2,9,16,23-tetrahydroxythiophenylphthalocyanatocobalt(II) on gold electrode and its electrocatalytic activity towards dioxygen reduction

• 2,9,16,23-Tetrahyroxythiophenylphthalocyanato-cobalt(II) was synthesized and self-assembled on Au electrode.
• Two redox peaks were observed for the SAM due to both CoIII/CoII and CoIIIPc1−/CoIIIPc2.
• Raman spectrum shows a characteristic stretching band at 250 cm−1 corresponding to Au–S.
• The SAM modified electrode was used for the reduction of dioxygen.

This paper describes the synthesis of 2,9,16,23-tetrahyroxythiophenylphthalocyanato-cobalt(II) (4β-CoIITHTPhPc) and its self-assembly on Au surface. The self-assembled monolayer (SAM) was formed by immersing the Au electrode in dimethylformamide containing 4β-CoIITHTPhPc. The SAM of 4β-CoIITHTPhPc on Au electrode was characterized by cyclic voltammetry, Raman spectroscopy and electrochemical impedance spectroscopy (EIS). The cyclic voltammogram of 4β-CoIITHTPhPc SAM in HClO4 shows two pairs of redox peaks at 0.38 V and 0.53 V, corresponding to CoIII/CoII and CoIIIPc1−/CoIIIPc2−, respectively. Raman and electrochemical reductive desorption studies confirm that the SAM of 4β-CoIITHTPhPc was formed on Au electrode via Au–S linkage. Raman spectrum shows a characteristic stretching band at 250 cm−1 corresponding to Au–S. Further, the electrochemical reduction of dioxygen was carried out using the SAM modified Au electrode in HClO4. The SAM modified electrode not only decreased the oxygen reduction overpotential but also enhanced its current in contrast to bare Au electrode.