The Preparation And Electrocatalytic Properties Of Platinum Electrode Modified With Polypyrrole

Due to the special structure and the excellent physical properties, conducting polymers have attracted great interest in many applied fields such as electrode materials, chemically modified electrodes, enzyme electrodes and sense organs. Compared with conventional acidic aqueous solutions and organic solvents, ionic liquids have many unique properties such as high conductivity, excellent stability, a wide electrochemical potential window and friendly environments, so they can be used as electrolytes to electrochemically synthesize conducting polymers.In this paper, a platinum sheet (Pt) electrode was electrochemically modified with polypyrrole (PPy) in an ionic liquid 1-ethylimidazolium trifluoroacetate (HEImTfa) to produce a modified electrode (PPy-HEImTfa/Pt). Its electrocatalytic performance toward the oxidation of formaldehyde and formic acid has been investigated by cyclic voltammetry. Compared with a bare Pt electrode and a PPy-H2SO4/Pt electrode, which was prepared in a solution of H2SO4/H2O, the electrocatalytic activity of PPy-HEImTfa/Pt for the oxidation of formaldehyde and formic acid was greatly improved. The electrochemical activity of PPy was improved when it was prepared in HEImTfa, which was used as electrolytes to take the place of H2SO4/H2O. So the electrochemical properties of Pt modified with PPy-HEImTfa films were enhanced. In situ FTIR spectroscopy results showed that the oxidation of formic acid and formaldehyde on PPy-HEImTfa/Pt was accordant with the double-ways mechanism, the modified PPy-HEImTfa films could inhibit the formation of poisonous intermediates such as CO and reduce the CO poisoning of Pt, thus the formic acid and formaldehyde were oxidized directly to the final product CO2 by active intermediates.At the same time, the electrocatalytic activity of PPy-HEImTfa/Pt for the oxidation of ascorbic acid has been also investigated by cyclic voltammetry and in situ FTIR spectroscopy. Compared with bare Pt and PPy-H2SO4/Pt, PPy-HEImTfa/Pt showed higher electrocatalytic activity for the oxidation of ascorbic acid. Results of in situ FTIR spectroscopy showed that the oxidation of ascorbic acid on PPy-HEImTfa/Pt was an inreversible electrochemical process. Ascorbic acid was firstly oxidized to dehydroascorbic acid and then underwent a fast hydration reaction to give hydrated dehydroascorbic acid in aqueous solution. The hydrated dehydroascorbic acid then underwent further hydrolysis to form 2,3-diketogulonic acid by a ring opening reaction. Finally, a part of ascorbic acid was oxidized to CO2 at high potentials.Platinum nanoparticles (nm-Pt) were firstly electrodeposited on a platinum sheet electrode by cyclic voltammetry in H2PtCl6 solutions, and then nm-Pt was electrochemically modified with PPy-HEImTfa films which were prepared in HEImTfa to produce a PPy-HEImTfa/nm-Pt electrode. Its electrocatalytic performance toward the oxidation of formaldehyde has been investigated by cyclic voltammetry. The results showed that PPy-HEImTfa/nm-Pt exhibited higher electrocatalytic activity and stability as compared with nm-Pt and PPy-HEImTfa modified with nm-Pt (nm-Pt/PPy-HEImTfa). In situ FTIR spectroscopic measurements confirmed that the modified PPy-HEImTfa films could suppress the formation of linear adsorbed CO and reduce the CO poisoning of nm-Pt. So the electrocatalytic performance of nm-Pt modified with PPy-HEImTfa was better than that of PPy-HEImTfa modified with nm-Pt.