An effective CdS/Ti-Fe2O3 heterojunction photoanode: Analyzing Z-scheme charge-transfer mechanism for enhanced photoelectrochemical water-oxidation activity

Z-scheme photocatalytic system has been regarded as a popular field of research in photoelectrochemical (PEC) water splitting. Among the many obstacles facing a Z-scheme photocatalytic system, the analysis methods of interfacial Z-scheme charge transfer still remain a significant challenge. Hence, in this study, CdS/Ti-Fe 2 O 3 heterojunction photoanodes are elaborately designed to explore the charge-transfer behavior in PEC water splitting. In this study, photophysical measurements, including the Kelvin probe measurement, surface photovoltage spectroscopy (SPV), and transient photovoltage spectroscopy (TPV), are used to monitor the migration behavior of photogenerated charges at the interface electric field of CdS/Ti-Fe 2 O 3 Z-scheme heterojunction photoanodes. The Kelvin probe and SPV measurements demonstrate that CdS/Ti-Fe 2 O 3 interfacial driving force favors the rapid transfer of photoexcited electrons to CdS. The double-beam strategy based on TPV indicates that more electrons of Ti-Fe 2 O 3 are combined with the holes of CdS owing to the intensive interface electric field. The results of these measurements successfully prove the Z-scheme migration mechanism of CdS/Ti-Fe 2 O 3 photoanodes. Benefiting from the desirable charge transfer at the interface electric field, CdS/Ti-Fe 2 O 3 photoanodes exhibit superior photocatalytic oxygen evolution reaction performance compared with that of pure Ti-Fe 2 O 3 . The photocurrent density of the 25CdS/Ti-Fe 2 O 3 photoanode reaches 1.94 mA/cm 2 at 1.23 V versus reversible hydrogen electrode without excess cocatalyst, and it is two times higher than that of pure Ti-Fe 2 O 3 photoanode. Therefore, an outstanding strategy is provided in this study to prove the Z-scheme charge-transfer mechanism of photocatalytic systems in PEC water splitting. As Ti-Fe 2 O 3 and CdS make contact to form the Z-scheme heterojunction, the electrons of Ti-Fe 2 O 3 recombine with the holes of CdS at the internal electric field, leading to more holes transferring to the Ti-Fe 2 O 3 surface.