Photoelectrochemical activity of electrospun WO₃/NiWO₄ nanofibers under visible light irradiation

Electrospun tungsten oxide/nickel tungstate (WO₃/NiWO₄) composite nanofibers were tested for photoelectrochemical (PEC) performance under visible light irradiation under three voltages, 1.6, 1.8 and 2.0 V with reference to Ag/AgCl electrode in 0.5 M H₂SO₄. It was found that the photocurrent density of this novel nanostructure fiber is about 70% higher than the pristine electrospun WO₃ fibers under similar conditions. WO₃/NiWO₄ heterojunction was identified within the fiber through high-resolution transmission electron microscopy imaging. The fibrous form is expected to provide greater exposure to the WO₃/NiWO₄ heterojunctions for the photocatalytic reaction. This heterojunction within the fibrous form is expected to provide a higher photoanode performance due to a lower charge-transfer resistance than the pristine WO₃ fibers as also confirmed through the electrochemical impedance spectra. Interestingly, calcination of these composite fibers at 800 °C instead at 550 °C increased the percentage of NiWO₄ phase, yet with a contemporaneous increase in larger crystallites of metal tungstate. The latter was responsible for giving lower photocurrents which helped in understanding the PEC performance with respect to material structure for the composite fiber under the current study.