Impedance study of electropolymerized films of polyNi(II)-macrocycles

Glassy carbon electrodes modified by electropolymerization of two water-soluble compounds, Ni(II)tetrasulphophthalocyanine (NiTSPc) and Ni(II)tetrasulphophenylporphyrin (NiTSPP), and of two water-insoluble compounds, Ni(II)tetraaminophthalocyanine (NiTAPc) and Ni(II)tetraaminophenylporphyrin (NiTAPP), have been studied by impedance measurements. While in the tetrasulpho films the Ni(II)/Ni(III) process was operative, the tetraamino films required activation by repetitive potential cycling before the peaks of this process appeared in the CV, and even then the charge was a fraction of that shown by the tetrasulpho films. The Nyquist plots of all these films shown in the potential range of the Ni(II)/Ni(III) process the semicircle typical of a charge transfer, the charge-transfer resistance decreasing very much with increasing potential. The uncompensated resistance of the GC electrode was barely affected by the films, showing that they were very porous. The impedance at low frequencies of the thick polyNiTSPP film, the thin polyNiTSPc film, and also the activated polyNiTAPc film fitted the Warburg model, the diffusing species being probably the hydroxyl ions involved in the process.