*2.4. Photoelectrochemical Properties*

In order to evaluate the photocatalytic performance of the pure titania (PT), pure hematite (PF) and the prepared hematite incorporated titania nanocomposites, we conducted photoelectrochemical measurements as indicated in Figure 8. Cyclic voltammetry, chronoamperometry and EIS were performed in a three-electrode cell configuration where dissolved air free 0.1 M Na2SO4 electrolyte was employed. The working electrode was prepared from the powder materials via a drop-casting technique using isopropanol solvent and fluorine-doped tin oxide (FTO) substrate without any post-treatment of the

electrodes. The oxidation and reduction current values displayed in the cyclic voltammetry measurement can be used to judge the catalytic activity of the prepared materials. All samples exhibited only reduction current, except the PT sample exhibited both oxidation and reduction current. The reduction current density of the electrodes was 2.8, 1.65, 1.5 and 0.9 mA for PT, 0.1F, 0.5F and PF samples, respectively, while the oxidation current of PT samples was 1.5 mA. Therefore, the pure titania sample has the highest catalytic activity, while incorporating it with hematite its catalytic activity decreases. Moreover, to investigate the effective separation of the photogenerated charge carriers, we examined the photocurrent response under fixed potential (0.6 V versus Ag/AgCl) using the chronoamperometry technique. The photoresponse under light illumination demonstrates the rate of electrons transport as the majority charge carriers of n-type semiconductor from the sample to FTO as the collecting electrode. It was found that the PT sample shows the highest photocurrent magnitude reached ca. 800 μA/cm2 while 0.1F sample reached almost half this value and, 0.5F and PF samples give negligible photocurrent response. This could be explained based on the low bandgap value of the hematite, which increases the recombination rate of the photogenerated electron/hole pair and the existence of a high density of surface electron traps. Furthermore, an EIS test was performed to assess the charge transfer resistance under dark conditions of the prepared samples. Since the semicircle radius shown in the Nyquist plots of the EIS data indicates the conductivity at the interface between the electrode/electrolyte and electrode/FTO substrate. Thus, the smaller semicircle radius suggests improvement of the charge transfer of the prepared composite. Accordingly, the conductivity of the prepared samples was found to be in the following order: 0.1F > 0.5F > PT > PF.

**Figure 8.** (**a**) Cyclic voltammetry profiles; (**b**) Transient photocurrent response (*I-t*) curves and (**c**) Nyquist plots of Electrochemical Impedance Spectroscopy (EIS) data for PT, 0.1F, 0.5F, and PF samples.
