Revealing the Multiple Function of Nitrogen-Doped Carbon Layer in Hematite-Based Photoanode for Photoelectrochemical Water Oxidation

Incorporating the charge transfer medium between semiconductor and cocatalyst accelerates the separation of photogenerated charges, enhancing the photoelectrochemical water oxidation performance. However, the structure regulation of cocatalyst in situ generated by the transfer medium is usually neglected, which would alter the injection efficiency of photogenerated holes. Besides, more relevant technologies are necessary to investigate the intrinsic action of each part on water oxidation. Herein, a novel triadic photoanode is designed rationally, involving Ti-doped hematite (Ti-Fe₂O₃) core, nitrogen-doped carbon (CN) interlayer, and Ce-doped NiFe-LDH (NFC) shell. The results like single-molecule fluorescence and short-pulse transient photocurrent experiments reveal CN not only employs as a hole transfer layer to facilitate bulk charge transfer and suppress back recombination, but also polishes up the OH⁻ absorption in conjunction action with NFC. Furthermore, CN exhibits an additional functionality by inducing oxygen vacancies and more Ce⁴⁺ in NFC to further raise the injection efficiency, expediting the generation of O₂ from absorbed OH⁻. Consequently, NFC/CN/Ti-Fe₂O₃ presents a significantly higher photocurrent density than NFC/Ti-Fe₂O₃, accomplishing a photocurrent density of 2.87 mA cm⁻² at 1.23 V versus RHE. The design of the multiple-functional CN exhibits a strategic approach for regulating the reactant absorption and photogenerated hole transfer, thereby enhancing the water oxidation performance.