Light‐induced Electron Transport Across Semiconductor Electrode/Reaction‐center Film/Electrolyte Interfaces

Abstract

Abstract— Reaction center (RC) complexes isolated from the photosynthetic bacterium Rhodopseudomonas sphaeroides R‐26 were dried as a film onto platinum and semiconductor (SnO2) electrodes. The light‐induced primary charge separation which occurs across the biological complex couples electrically with the SnO2 but not with the metal electrode on the time scale of observation. As the working electrode in a two‐electrode photoelectrochemical cell, RC‐coated SnO2 generated photovoltages as high as 80 mV and photocurrents as high as 0.5µA·cm2 when exposed to light of λ >600nm. The number of quinone molecules per RC strongly influences the photovoltage and photocurrent observed. Photo‐effects generated by RC electrodes persist after several days of storage; however, the kinetics and polarity of the effects are subject to change. The potential use of RC electrodes lies more as a new probe of photosynthetic electron transport rather than as a solar energy conversion device because modification to the RCs and their environment affect the electrical properties of the cell. An energy‐level model is proposed to explain how the photoelectrochemical cell functions.

Progress and perspectives in exploiting photosynthetic biomolecules for solar energy harnessing

“…87 Thus, the mediocre performance of the orientation with H subunit 70 bound to electrode is attributed to the higher electron tunnelling distance between the electron acceptors and the electrode, owing to the presence of the relatively thick H subunit. 81 A similar account on the importance of the protein orientation to minimize the distance of electron transfer pathway is elucidated by Kondo 75 et al 39 with the study of photoelectrodes modified by RC-LH1 isolated from Rhodopseudomonas palustris, where the orientation of RC complex with the H-chain facing the electrode was found to be more favourable than the opposite orientation. 39 The effect of the dependence of electron transfer kinetics on 80 the distance between the electron acceptor and the electrode has been systematically studied using a series of MHisRCs modified Ni-NTA SAM coated gold electrodes having SAMs of different thicknesses with the number (n) of methylene units in the linker molecule (n= 3,6,10 and 15) being the measure of SAM thickness 85 ( Fig.…”

“…28 The photophysical properties of the pigments are 75 fine-tuned by nature by an elegantly engineered biopolymer material called protein that offers the biological systems the required degree of specificity, efficiency and control to accomplish a biological function. 33 Thus the antenna systems exist as an assemblage of pigment and protein where the 80 photosynthetic pigments are bound to the proteins in highly specific associations to ensue in an effective light absorption.…”

“…The RCs are some of the most widely studied photosynthetic components for employment in solar cells. While some studies only use the core RCs for the purpose, there are also a few studies using the RCs with the surrounding light harvesting complexes, in view of obtaining 75 improved performance. 22,27,39,[40][41][42][43][44][45] Photosystems I and II are also studied for photoelectrochemical applications.…”

“…The addition of secondary quinone was found to change the kinetics of electron transfer and stabilize the primary charge separation in a longer time duration thus facilitating enough time for the tunnelling of 85 electrons through SnO 2 /RC interface. 75 Although no attempt was made to orient the RCs in these pioneering works, it had been predicted that a better photoresponse could be possible with controlled orientation. 74 90 A number of perspectives then engendered to control RC orientation, one being the widely used method of making SAMs.…”

A Photovoltaic Device Using an Electrolyte Containing Photosynthetic Reaction Centers

“…However, the external power conversion efficiency is low when the surface of an electrode is coated with a monolayer of an RC in an electrochemical-based photovoltaic device [3]. The low efficiency is partly due to weak absorption of light in a thin film of RC, and charge transfer between the RC and the electrode is not efficient.…”