Artificial Photosynthesis of Alcohols by Multi-Functionalized Semiconductor Photocathodes.

Novel artificial photosynthesis systems are devised as cells of dye/Pd/NR-MOx (M=Ti, Zn)∥CoPi/W:BiVO4 that convert efficiently CO2 to alcohols. The photocathodes are aminofunctionalized, palladium-deposited, and in situ sensitized nano-TiO2 or ZnO/FTO (FTO: fluorine-doped tin oxide) electrodes that are characterized by X-ray photoelectron spectroscopy (XPS), TEM, XRD, UV/Vis spectra, and evaluated by electrochemical techniques. The cell of dye/Pd/S-TiO2 ∥CoPi/W:BiVO4 uniquely generates ethanol under irradiation of 200 mW cm-2 , reaching 0.56 % quantum efficiency (QE) at -0.56 V and 0.13 % QE without external electron supply. The cell of dye/Pd/ N-ZnO∥CoPi/W:BiVO4 produces solely methanol at a rate of 42.8 μm h-1  cm-2 at -0.56 V of a Si solar cell, which is far less than the electrochemical voltage of water splitting (1.23 V). Its QE reaches to 0.38 %, which is equal to plants. The isotopic labeling experiments confirm the carbon source and oxygen releasing. The selectivity for alcohols of multi-functionalized semiconductors is discussed.