Bulk embedding of Ti-defected TiO₂ nano-heterointerfaces in hematite photoanode for boosted photoelectrochemical water splitting

The practical application of the most promising α-Fe₂O₃ photoanode in solar hydrogen generation is facing an awkward challenge arising from its poor bulk carrier transport. Present work demonstrates the acceleration of the carrier transport via embedding the p-type Ti-defected TiO₂ (TiO₂-V_Ti) nanocrystals in the n-type Fe₂O₃ photoanode matrix, which results in significantly improved photoelectrochemical performance. By embedding sub-5 nm TiO₂-V_Ti nanocrystals in the bulk of α-Fe₂O₃ photoanode, numerous p-n nano-heterointerfaces were constructed for the first time in Fe₂O₃ photoanode matrix. The formed p-n nano-heterointerfaces lead to 10 times enhancement of charge transfer rate constant (k_tran), and 1.5 times reduction of the charge recombination rate constant (k_rec), which is due to the formation of the built-in electric fields and effective carrier transport and separation at the p-n nano-heterointerfaces of TiO₂-V_Ti/Fe₂O₃. Such strategy leads to the Fe₂O₃ photoanode with a reduction of photogenerated carrier transport time by 3 times, resulting in an excellent photocurrent density as high as 1.45 mA cm⁻² at 1.23 V_RHE, 5 times higher than that of pristine hematite (0.27 mA cm⁻²). We thus believe that our study opens up a route to regulate hematite or even metal-oxide semiconductor chemical/physical features via p-n nano-heterostructure embedding.