The conversion of sunlight in electricity by means of bio-hybrid devices has been widely explored in  in the last years due to the almost unitary quantum efficiency of natural photo-enzymes, which proved to be still an unattainable model for current artificial systems. In this contribution, a photo-responsive electrochemical cell will be described, based on a screen printed electrochemical cell where the platinum working electrode is modified with a thin layer of photosynthetic reaction center (RC) proteins entrapped in a polyvinyl alcohol matrix. Ferrocene-methanol and decylubiquinone were dissolved in the electrolytic medium, acting as RC electron donor and electron acceptor respectively. Under light, faradaic processes responsible for the photocurrent generation are triggered due to the RC photocycle activation, with the mediators acting as electron shuttles from/to the electrode surface. The cell has been comprehensively characterized by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy, gaining valuable information on the mechanisms responsible for the electrical photo-response of the device.

The anodic and cathodic current peaks in the cyclic voltammetry recorded in dark conditions featured a linear dependence on the square root of the scan rate, indicating a diffusion-controlled process, regardless the presence of the RC-PVA layer. Moreover, the ferrocenemethanol diffusion coefficient was found to be independent on the presence of the RC-PVA layer, pointing out its excellent permeability. Under light, the anodic and cathodic current peaks showed a linear dependence of the scan rate, this time indicating a surface-controlled process, likely due to the massive concentration of oxidized ferrocenemethanol produced in the proximity of the electrode. Moreover, the electrochemical reaction sustaining the faradaic process proved to be kinetically highly asymmetric, with a higher energy barrier in the anodic side.

Chronoamperometry experiments carried out at applied potentials that favor the reduction of the photo-oxidized ferrocenemethanol, feature a peculiar sudden photoinduced current increment, followed by a decay, resulting in the appearing of a characteristic current peak, whose value surprisingly decreases at higher cathodic potentials. A light-induced capacitive contribution, suggested by impedentiometric data, is proposed to explain this peculiar phenomenon. Interestingly, the equivalent electrical circuit proposed to model the bio-hybrid electrochemical cell proved to describe the impedance response with sufficient confidence in a quite wide range of applied potential both in dark and in light and accounts for the main dynamics introduced by the protein activation.