Charge transfer enhancement by substitutional N and NiFeOOH cocatalyst of N-TiO2/NiFeOOH nanorod photoanode for solar water splitting

The increasing demand for renewable and substantial energy has aroused the development of semiconductors for applications in photoelectrochemical (PEC) water splitting. Herein, we demonstrate the synthesis of the nitrogen-doping NiFeOOH modified TiO2 nanorods (N-TiO2/NiFeOOH) as photoanode. The N-TiO2/NiFeOOH photoanode has the core-shell structure. The “core” is nitrogen doping TiO2 nanorods with anatase and rutile phase while the “shell” is NiFeOOH layers. The XPS characterization presents the oxygen vacancy (Ov) increase with the substitutional N sites increase. The trends of applied bias photon-to-current efficiency are agreed with the substitutional N sites and Ov atomic content. That infers that the substitutional N sites affect the Ov content, which could function as the active sites for the enhanced PEC properties by increase the charge separation/injection efficiencies. After NiFeOOH modification, that leads to an enhanced photocurrent density of 3.61 mA cm−2 for the N-TiO2/NiFeOOH photoanode, which is 1.2 and 2.4 times larger than that of the N-TiO2 and original TiO2 photoanodes. The enhancement in the PEC performance and efficiency are attribute to the synergetic effect of the substitutional N doping for the defect modulation and NiFeOOH modification for the oxygen evolution reaction kinetics promotion, thus enhance the charge separation/injection efficiencies at the interface between the N-TiO2/NiFeOOH photoanode and the electrolyte.