A universal strategy boosting photoelectrochemical water oxidation by utilizing MXene nanosheets as hole transfer mediators

As the rapid development of oxygen evolution catalysts (OECs) for photoanodes, the issue of charge transfer at the interface of OEC and semiconductor, which becomes the key challenge for the photoelectrochemical (PEC) efficiency, has been rarely addressed and should be taken seriously. Herein, a novel charge transfer system for PEC water oxidation is designed by inserting MXene nanosheets (MNs) between alpha-Fe2O3 and OEC. In this system, MNs act as the hole transfer mediators to efficiently suppress the interfacial charge recombination owing to the high hole mobility of MNs and the formation of built-in electric field at the MNs/alpha-Fe2O3 junction. Meanwhile, the OEC layers, in turn, can protect the MNs from oxidation to achieve prominent stability. The optimized photoanode of Co-Pi/MNs/alpha-Fe2O3 can achieve a remarkable photocurrent density, up to 3.20 mA cm(-2) at 1.23 V vs. reversible hydrogen electrode (RHE) under AM 1.5 G illumination. An impressive cathodic onset potential shift of similar to 250 mV is obtained on Co-Pi/MNs/alpha-Fe2O3 compared with the pristine alpha-Fe2O3. Furthermore, this strategy is also applicable to other photoanode materials, such as BiVO4, WO3 and ZnO, verifying the versatility by utilizing the MNs as hole transfer mediators for efficient photogenerated charge separation to enhance the PEC water oxidation.

Automated summary

A novel charge transfer system for PEC water oxidation was developed by inserting MXene nanosheets between alpha-Fe2O3 and OEC, demonstrating efficient suppression of interfacial charge recombination and enhanced photoanode performance. The system showed remarkable photocurrent density and cathodic onset potential shift compared to pristine alpha-Fe2O3, and was proven versatile in enhancing PEC water oxidation for various photoanode materials.