Electrochemical Switching of Photoelectrochemical Processes at CdS QDs and Photosystem I‑Modified Electrodes

Abstract

Photoactive inorganic CdS quantum dots (QDs) or the native photosystem I (PSI) is immobilized onto a pyrroloquinoline quinone (PQQ) monolayer linked to Au electrodes to yield hybrid relay/QDs (or photosystem) assemblies. By the electrochemical biasing of the electrode potential, the relay units are retained in their oxidized PQQ or reduced PQQH₂ states. The oxidized or reduced states of the relay units dictate the direction of the photocurrent (anodic or cathodic). By the cyclic biasing of the electrode potential between the values <i>E </i>≥ −0.05 V and <i>E</i> ≤ −0.3 V <i>vs</i> Ag quasi-reference electrode (Ag QRE), retaining the relay units in the oxidized PQQ or reduced PQQH₂ states, the photocurrents are respectively switched between anodic and cathodic values. Different configurations of electrically switchable photoelectrochemical systems are described: (i) the PQQ/CdS QDs/(triethanolamine, TEOA) or PQQ/PSI/(ascorbic acid/dichlorophenolindophenol, DCPIP) systems, leading to anodic photocurrents; (ii) the PQQ/CdS QDs (or PSI)/(flavin adenine dinucleotide) systems, leading to cathodic photocurrents; (iii) the PQQ/CdS QDs (or PSI)/(O₂) switchable systems, leading to cyclic anodic/cathodic switching of the photocurrents