Unbiased Photoelectrochemical Water Splitting in Z-Scheme Device Using W/Mo-Doped BiVO4 and ZnxCd1-xSe

Photoelectrochemical water splitting to generate H-2 and O-2 using only photon energy (with no added electrical energy) has been demonstrated with dual n-type-semiconductor (or Z-scheme) systems. Here we investigated two different Z-scheme systems; one is comprised of two cells with the same metal-oxide semiconductor (W-and Mo-doped bismuth vanadate), that is, Pt-W/Mo-BiVO4, and the other is comprised of the metal oxide and a chalcogenide semiconductor, that is, Pt-W/Mo-BiVO4 and Zn0.2Cd0.8Se. The redox couples utilized in these Z-scheme configurations were I-/IO3- or S2-/S-n(2-), respectively. An electrochemical analysis of the system in terms of cell components is shown to illustrate the behavior of the complete photoelectrochemical Z-scheme water-splitting system. H-2 gas from the unbiased photolysis of water was detected using gas chromatography-mass spectroscopy and using a membrane-electrode assembly. The electrode configuration to achieve the maximum conversion efficiency from solar energy to chemical energy with the given materials and the Z-scheme is discussed. Here, the possibilities and challenges of Z-scheme unbiased photoelectrochemical water-splitting devices and the materials to achieve practical solar-fuel generation are discussed.