Title : Electrochemically derived Poly-porphyrin films with electrocatalytic properties
Abstract:
The fundamental and applied interest in natural porphyrins and their synthetic analogues is related to the possibility of obtaining porphyrin-based materials. They have various functional properties which can vary due to the molecular interacting and substitutes.
We present electrocatalytic films of ClFe(III)5,10,15,20-tetrakis(p-aminophenyl) porphyrin (FeClT(p-NH2Ph)P) formed by new electrochemical deposition method using oxygen saturated dimethyl sulfoxide solutions (DMSO) as a medium. Superoxide promotes the poly-porphyrin film formation on the working electrode surface due to it high affinity both to hydrogen atom and to proton. The most favorable pathway of the superoxide-assisted electrochemical polymerization is proposed. The resulting poly-FeClT(p-NH2Ph) P films are smooth, golden colored, well adhesed with substrate and quite insoluble in water, ethanol and dichloromethane. The film formation accompanied with broadening and red-shifting of the Soret band. Atomic force microscopy (AFM) investigation shows homogeneity, low roughness and nanoscale globular structure of the poly-FeClT(p-NH2Ph)P films.
The poly-FeClT(p-NH2Ph)P films obtained on glassy carbon were studied for electrocatalytic activity in the reaction of electrochemical reduction of oxygen in an alkaline medium. Current densities about 0.1 mA/cm2 are recorded near -0.2 V while the potential is cycled on the glassy carbon in the degassed 1 M solution of KOH (Fig., curves 1). It can be related to the incomplete removal of oxygen from the solution. An irreversible wave of electroreduction of oxygen with a current density of about 0.42 mA/cm2 is detected when the solution is saturated with oxygen. The oxygen electroreduction onset on glassy carbon is close to 0 V vs. Ag/AgCl electrode. The maximum of the electrochemical response of the oxygen electroreduction is localized in the potential region (-0.2?-0.3 V). For the electrodes modified by the poly-FeClT(p-NH2Ph)P film the potential of the oxygen electroreduction onset is shifted to the positive region by 0.14 V(Fig., curves 3). The intensity of the current density peak of the oxygen electroreduction increases. The films obtained from DMSO solutions have a sufficiently smooth surface and do not significantly change the capacitance of the working electrode. It is indicated by the same value of current densities at the initial and modified electrodes under polarization in the potential range 0.2?0.7 V. Consequently the set of changes in the response of the electrochemical reduction of oxygen indicates the electrocatalytic activity of the poly-FeClT(p-NH2Ph)P film.
Working ability of the electrode modified by polyporphyrin film was tested by repeated cycling under the conditions of the electrocatalytic process. It was found that for more than 20 cycles the electrochemical response of the oxygen electroreduction remains unchanged. After removal from the cell, the film retained its original form.
Polyporphyrin films are a new class of electrically conducting polymers with semiconductor properties. These materials can be used as elements of solar batteries, sensors, catalysts, etc. The electrochemical method of production allows controlling the properties of films by changing the electrolysis modes, the nature of the solvent and the nature of the porphyrin monomer.
