when I made the cole -cole plot for conductor thin film, the imagenary impedance values was negative.
Negative real impedances
are sometimes associated with persistent current reductions
as potential increases; this might be characteristic of unstable
electrochemical systems e.g. when some of the following processes
might take place: a) potential-dependent adsorption/desorption of a
catalyst, b) electrostatic effects at low ionic strengths, as in the
reduction of anions at a negatively charged surface, or c) when the
active surface available for electron-transfer decreases as polarization
raises (for example, when the interface shows activity peaks
followed by passivity stabilization); in these cases, a part of the
polarization curve (or voltammogram if it is the case) has a negative
slope—the value of the impedance at zero frequency is related
to the slope of the steady-state polarization curve—then the impedance
measured in the potential range where this occurs is found
with a negative real part.
Reference: Xochitl D. Benetton, Navarro-Avila S., Carrera-Figueiras C. (2010) Electrochemical evaluation of Ti/TiO2-polyaniline anodes for microbial fuel cells using hypersaline microbial consortia for synthetic-wastewater treatment, Journal of New Materials for Electrochemical Systems, Vol.13., No. 1, p. 1-6.
Hopefully this point will help to solve your doubts
Negative real impedances
are sometimes associated with persistent current reductions
as potential increases; this might be characteristic of unstable
electrochemical systems e.g. when some of the following processes
might take place: a) potential-dependent adsorption/desorption of a
catalyst, b) electrostatic effects at low ionic strengths, as in the
reduction of anions at a negatively charged surface, or c) when the
active surface available for electron-transfer decreases as polarization
raises (for example, when the interface shows activity peaks
followed by passivity stabilization); in these cases, a part of the
polarization curve (or voltammogram if it is the case) has a negative
slope—the value of the impedance at zero frequency is related
to the slope of the steady-state polarization curve—then the impedance
measured in the potential range where this occurs is found
with a negative real part.
Reference: Xochitl D. Benetton, Navarro-Avila S., Carrera-Figueiras C. (2010) Electrochemical evaluation of Ti/TiO2-polyaniline anodes for microbial fuel cells using hypersaline microbial consortia for synthetic-wastewater treatment, Journal of New Materials for Electrochemical Systems, Vol.13., No. 1, p. 1-6.
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