CQDs modified TiO2/Sn-Fe2O3-x heterojunction photoanode with abundant oxygen vacancies for enhanced photoelectrochemical water oxidation

An efficient CQDs/TiO 2 /Sn-Fe 2 O 3-x heterojunction photoanode was designed and fabricated to enhance the photoelectrochemical (PEC) performance of hematite for water oxidation. The key innovation of this work lies in the construction of an oxygen-vacancy-rich TiO 2 /Sn-Fe 2 O 3-x heterojunction photoanode by using Ti 3 C 2 MXene as the precursor of TiO 2 through a one-pot calcination process. The two main advantages of the present synthetic strategy are introducing abundant oxygen vacancies into the photoanode and preserving the nanostructure of the photoanode at high temperatures. During the synthesis, Ti 3 C 2 MXene was oxidized to form TiO 2 , while Sn-FeOOH was simultaneously converted into Sn-Fe 2 O 3-x nanorods. The high reducibility of Ti 3 C 2 MXene and the doping of Sn 4 + played a critical role in introducing abundant oxygen vacancies into Sn-Fe 2 O 3-x . The concurrent formation of TiO 2 and Sn-Fe 2 O 3-x effectively prevented the aggregation of α-Fe 2 O 3 nanorods at the high calcination temperature of 800°C and promoted close contact between the TiO 2 and Sn-Fe 2 O 3-x , reducing the interfacial transfer resistance. Lastly, the incorporation of CQDs further increased the light absorption ability and PEC performance of the heterojunction photoanode. The CQDs/TiO 2 /Sn-Fe 2 O 3-x photoanode achieved a photocurrent density of 1.47 mA/cm² at 1.23 V vs. RHE, which was 3.34 times higher than the α-Fe 2 O 3 . The enhanced PEC performance can be attributed to the introduction of abundant oxygen vacancies and the maintenance of its nanostructure at high temperatures, which can improve the donor density, charge transfer efficiency and light harvesting ability of the resultant photoanode.