Covalent Immobilization of Oriented Photosystem Ⅱ on a Nanostructured Electrode for Solar Water Oxidation

摘要

Photosystem Ⅱ (PSII) offers a biological and sustainable route of photochemical water oxidation to O_2 and can provide protons and electrons for the generation of solar fuels, such as H_2. 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.