Catalytic effect of cis-diammineplatinum α-pyrrolidone tan adsorbed on a platinum electrode in electrochemical oxidation of water into molecular oxygen

Abstract

Cyclic voltammograms of cis-diammineplatinum α-pyrrolidone-blue and -tan, [Pt 4(NH 3) 8(C 4H 6NO) 4] n+ ( n = 5 and 6, respectively) show for either complex only one redox peak at 0.53 V (average potential of the anodic and cathodic peak potentials). Coulometry and UVVis spectra of bulk- electrolyzed solution indicated that the redox peak corresponds to the reaction [Pt 4(NH 3) 8(C 4H 6NO) 4] 8+ + 4e ⇄ 2[Pt 2(NH 3) 4(C 4H 6NO) 2] 2+. When cyclic voltammetry is carried out in a solution of [Pt 4(NH 3) 8(C 4H 6NO) 4] 6+ or a platinum electrode adsorbed with [Pt 4(NH 3) 8(C 4H 6NO) 4] 6+ is used in the presence of oxidizing agent in the solution, O 2 gas generates from the electrode surface with large catalytic cathodic current at potentials below ca. 0.8 V. The O 2 gas was confirmed to generate from water by GC-MS analysis. This abnormal O 2 generation phenomenon is explained with cyclic reactions of chemical surface oxide formation on the electrode by the oxidizing agent and electrochemical reduction of the surface oxide. Oxygen gas generates from the reaction of [Pt 4(NH 3) 8(C 4H 6NO) 4] 8+ or [Pt 4(NH 3) 8(C 4H 6NO) 4] 6+ with OH − produced in the course of the electrochemical reduction of the electrode surface oxide. The ability of [Pt 4(NH 3) 8(C 4H 6NO) 4] 8+ and [Pt 4(NH 3) 8(C 4H 6NO) 4] 6+ to oxidize OH − into O 2 has been reported previously.