Effect of Sr, Ni and Ti Co-doping on the Performance of [KNbO₃]_1−x-[Sr(Ni_1/2Ti_1/2)O₃]_x Nanofibers and Ceramics for Photocatalytic Hydrogen Production

[KNbO₃]_1−x-[Sr(Ni_1/2Ti_1/2)O₃]_x(KN-SNT) nanofibers and ceramics were synthesized by electrostatic spinning and solid-state reaction. A series of analyses were carried out, including X-ray diffraction (XRD), Raman spectroscopy, UV–visible spectroscopy, scanning electron microscopy (SEM), electrochemical impedance, transient photocurrent, and photocatalytic hydrogen evolution experiments. The results demonstrated that the co-doping of Sr, Ni, and Ti can narrow the bandgap of KNbO₃. Furthermore, under visible-light irradiation, the co-doped nanofibers exhibited the best hydrogen evolution performance at x = 0.03, with a hydrogen evolution rate of 5571.65 µmol g⁻¹ h⁻¹, while the hydrogen evolution rate of the KN-SNT ceramic at x = 0.03 was only 422 µmol g⁻¹ h⁻¹. The results show that the photocatalytic rate of nanofibers is much higher than that of conventional ceramic discs. These differences are caused by the fiber structure, which promotes the transfer and separation of photogenerated electrons, and the effect of increased surface area.