Covalent Immobilization of Oriented Photosystem II
on a Nanostructured Electrode for Solar Water Oxidation
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Abstract
Photosystem
II (PSII) offers a biological and sustainable route
of photochemical water oxidation to O<sub>2</sub> and can provide
protons and electrons for the generation of solar fuels, such as H<sub>2</sub>. We present a rational strategy to electrostatically improve
the orientation of PSII from a thermophilic cyanobacterium, Thermosynechococcus elongatus, on a nanostructured
indium tin oxide (ITO) electrode and to covalently immobilize PSII
on the electrode. The ITO electrode was modified with a self-assembled
monolayer (SAM) of phosphonic acid ITO linkers with a dangling carboxylate
moiety. The negatively charged carboxylate attracts the positive dipole
on the electron acceptor side of PSII via Coulomb interactions. Covalent
attachment of PSII in its electrostatically improved orientation to
the SAM-modified ITO electrode was accomplished via an amide bond
to further enhance red-light-driven, direct electron transfer and
stability of the PSII hybrid photoelectrode