A Biological-Based Photovoltaic Electrochemical Cell: Modelling the Impedance Spectra

Abstract

The impedance response of an electrochemical cell able to convert sunlight into electrical power is analyzed and discussed. Light conversion is due to a photosynthetic system known as reaction center, which is the core of photosynthesis in several living beings. Under illumination, an abrupt transformation drives the cell electrical response from insulator to conductor and a photocurrent is observed. The impedance spectrum shows a peculiar shape which significantly modifies after the protein activation. It has been analyzed by means of a graphical/analytical/numerical procedure. Some impedance graphical representations are indicated as the most appropriate to suggest the design of an equivalent electrical circuit. Then, the analytical expression of this circuit is formulated and used to set-up a custom Phyton code useful for fitting experimental data. Finally, an appropriate normalization procedure is proposed, which validates data in dark and light and can be useful as a fast screening of measurements.

Reaction Center of Rhodobacter Sphaeroides, a Photoactive Protein for pH Sensing: A Theoretical Investigation of Charge Transport Properties

“…In this range, experiments detect the solution effects, mainly at the highest frequencies, and the electrode resistance, at the lowest frequencies. Otherwise, all the cell elements contribute to the global impedance response in the full frequency range [20,21]. The impedance model may be more or less complex to account several effects that could be detected by experiments.…”

“…The impedance model may be more or less complex to account several effects that could be detected by experiments. Anyway, the main contribution is given by Equation ( 1) and accounts for both the polarization and some leakage currents which are usually present in real dielectrics [9,21]. In an electrochemical cell conduction has both an electronic and ionic origin, i.e.…”

“…charge may travel through both organic/inorganic matter and also the electrolytic solution. Furthermore, charge may accumulate between different solid/liquid or solid/solid interfaces [21]. Equation ( 1) describes an elemental circuit consisting of a resistance (R) and a capacitor (C) in parallel, R//C, and its graphical representations in terms of frequency are called Bode plots.…”

“…Results account for both the sample and solution response and it is in general not easy to discriminate the contributes to the total impedance. Electronic models are continuously updated to give a macroscopic interpretation of the very complex chemical processes [20,21] . As a matter of fact, many devices, for example sensors, are characterized by the EIS technique, therefore the modelling of results is relevant for both the speculative and applicative aspect [22].…”

“…As a matter of fact, many devices, for example sensors, are characterized by the EIS technique, therefore the modelling of results is relevant for both the speculative and applicative aspect [22]. Experiments performed with the EIS technique detect a sensitive enhancement of the cell conductance in light [17,21]. Specifically, it was observed that the charge transfer involves the protein, the quinones in solution and also depends on the electrode.…”