Hydrothermal synthesis of nanostructured Cr-doped hematite with enhanced photoelectrochemical activity

Using the easily applicable hydrothermal method Cr-doped hematite thin films have been deposited polycrystalline on conductive glass substrates. The hydrothermal bath consisted of an aqueous solution containing a mixture of FeCl3·6H2O and NaNO3 at pH = 1.5. The samples were introduced in an autoclave and heated for a fixed time at a fixed temperature and then annealed in air at 550 °C. The concentration of the incorporated Cr atoms (Cr4+ ions) was controlled by varying the concentration of the Cr(ClO4)3 precursor solution, varied from 0% to 20%. All samples followed morphological and structural studies using field-emission scanning electron microscopy, high-resolution transmission electron microscopy and X-ray diffraction. Chronoamperometry measurements showed that Cr-doped hematite films exhibited higher photoelectrochemical activity than the undoped films. The maximum photocurrent density and incident photon conversion efficiencies (IPCE) were obtained for 16 at.% Cr-doped films. This high photoactivity can be attributed to both the large active surface area and increased donor density caused by Cr-doping in the α-Fe2O3 films. All samples reached their best IPCE at 400 nm. IPCE values for 16 at.% Cr-doped hematite films were thirty times higher than that of undoped samples. This high photoelectrochemical performance of Cr-doped hematite films is mainly attributed to an improvement in charge carrier properties.