Hybrid Wiring of the Rhodobacter sphaeroides Reaction Center for Applications in Bio-photoelectrochemical Solar Cells

Abstract

The growing demand for nonfossil fuel-based energy production has drawn attention to the utilization of natural proteins such as photosynthetic reaction center (RC) protein complexes to harvest solar energy. The current study reports on an immobilization method to bind the wild type Rhodobacter sphaeroides RC from the primary donor side onto a Au electrode using an immobilized cytochrome c (cyt c) protein via a docking mechanism. The new structure has been assembled on a Au electrode by layer-by-layer deposition of a carboxylic acid-terminated alkanethiol (HOOC (CH2)5S) self-assembled monolayer (SAM), and layers of cyt c and RC. The Au|SAM|cyt c|RC working electrode was applied in a three-probe electrochemical cell where a peak cathodic photocurrent density of 0.5 μA cm–2 was achieved. Further electrochemical study of the Au|SAM|cyt c|RC structure demonstrated ∼70% RC surface coverage. To understand the limitations in the electron transfer through the linker structure, a detailed energy study of the SAM and cyt c was performed using photochronoamperometry, ellipsometry, photoemission spectroscopy, and cyclic voltammetry (CV). Using a simple rectangle energy barrier model, it was found that the electrode work function and the large barrier of the SAM are accountable for the low conductance in the devised linker structure.