Estimation of continuity of electroactive inorganic films based on apparent anti-Ohmic trend in their charge transfer resistance

- Anti-Ohmic trend is a decrease in charge transfer resistance with an increase in film amount.
- SEM confirms the “anti-Ohmic” region corresponds to the partially covered surface.
- In some cases, for instance for recessed electrodes, microscopy is hardly applicable.

We report on the microscopy-free, pure electrochemical approach for estimation of the continuity of electroactive inorganic films. Impedance spectra of the transition metal hexacyanoferrate films, electrochemically deposited under the optimized conditions, have been fitted to the Randles-type equivalent circuit, complicated by diffusion impedance with reflective boundary conditions, connected in series to the charge transfer resistance. An apparent anti-Ohmic trend is revealed in the sharp decrease of the latter with an increase in amount of the deposited inorganic film commonly presuming its thickness. Assigning charge transfer resistance to the resistance of the electrode|film interface, its observed decrease with subsequent saturation is explained in terms of an increase of the interface area until the entire electrode is covered with the inorganic film completely. Scanning electron microscopy (SEM) confirms the “anti-Ohmic” and saturation regions correspond to the partially covered and fully covered electrode surfaces, respectively. The dependence of charge transfer resistance on the amount of the deposited film thus provides an estimation of the continuity of inorganic films, which is highly important in a view of their practical applications. Except for cost efficiency, microscopy-free tools are attractive because in some cases, for instance for recessed electrodes, microscopy is hardly applicable.

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