Effect of adsorbed anions on the outer-sphere electron-transfer reactions of cobalt complexes at platinum single-crystal electrodes

• Published in: Journal of electroanalytical chemistry (Lausanne, Switzerland) Switzerland), 2001-02, Vol.499 (1), p.161-168
• Main Authors: Wakabayashi, Noriaki, Kitamura, Fusao, Ohsaka, Takeo, Tokuda, Koichi
• Format: Article
• Language: English
• Subjects: Chemistry; Electrochemistry; Exact sciences and technology; General and physical chemistry; Heterogeneous electron-transfer rate; Kinetics and mechanism of reactions; Platinum single-crystal electrodes; Tris(1,10-phenanthlorine)cobalt complex; Tris(2,2′-bipyridine)cobalt complex
• ISSN: 1572-6657; 1873-2569
• DOI: 10.1016/S0022-0728(00)00508-8

The redox-electrode reaction of [Co(phen) 3] 2+/3+ (phen=1,10-phenanthroline) in 0.1 M potassium halide solutions was studied kinetically at a platinum (111) single-crystal electrode (M=mol dm −3). The formal rate constants were found to be dependent on the electrolyte anions and to decrease in the order F −>Cl −>Br −. Furthermore, formal rate constants for this reaction in 0.1 M KF solution were obtained at platinum (111), (100), and (110) single-crystal electrodes and those modified with I −, SCN −, and CN − adlayers. It was found that Miller indices had little effect on the heterogeneous electron-transfer rate. The iodide monolayer retarded the electron-transfer reaction, whereas the reaction was accelerated by the modification with cyanide and thiocyanate. Similar results were obtained for the redox-electrode reaction of [Co(bpy) 3] 2+/3+ (bpy=2,2′-bipyridine) at the Pt(111) electrode and that modified with iodide and thiocyanate. These findings are discussed based on the electrical double layer effect and the theory of heterogeneous outer-sphere electron-transfer reactions reviewed by Weaver [M.J. Weaver, in: R.G. Compton, Comprehensive Chemical Kinetics, vol. 27, Elsevier, Amsterdam, 1987, Ch. 1].