Direct Z-scheme Cs2O-Bi2O3-ZnO heterostructures for photocatalytic overall water splittingElectronic supplementary information (ESI) available: PXRD spectra, electrochemical impedance measurements, photostability of the prepared samples, dependence of the rate of H2 evolved on the wavelength of incident light and summary of recent Z-scheme photocatalysts for overall water splitting. See DOI: 10.1039/c8ta08033j

In this work, a direct Z-scheme Cs 2 O-Bi 2 O 3 -ZnO heterostructure without any electron mediator is fabricated by a simple solution combustion route. Cs 2 O is chosen as a sensitizer to expand the light absorption range, and in addition, its conduction band minimum (CBM) and valence band maximum (VBM) positions are suitable to construct a direct Z-scheme system with ZnO and Bi 2 O 3 . Structural and elemental analyses show clear evidence for heterostructure formation. The Z-scheme charge carrier migration pathway in Cs 2 O-Bi 2 O 3 -ZnO is confirmed by high resolution XPS and ESR studies. The fabricated heterostructure exhibits a good ability to split water to H 2 and O 2 under simulated sunlight irradiation without any sacrificial agents or co-catalysts and has excellent photostability. The apparent quantum efficiency of the optimized Cs 2 O-Bi 2 O 3 -ZnO heterostructure reaches up to 0.92% at 420 nm. The excellent efficiency of this fabricated heterostructure is attributed to the efficient charge carrier separation, the high redox potential of the CBM and VBM benefiting from a direct Z-scheme charge carrier migration pathway and the extended light absorption range. In this work, a direct Z-scheme Cs 2 O-Bi 2 O 3 -ZnO heterostructure without any electron mediator is fabricated by a simple solution combustion route.