Role of Graphene Oxide as a Sacrificial Interlayer for Enhanced Photoelectrochemical Water Oxidation of Hematite Nanorods

Photoelectrochemical cells (PECs) with a structure of F-doped SnO₂ (FTO)/graphene oxide (GO)/hematite (α-Fe₂O₃) photoanode were fabricated, in which GO serves as a sacrificial underlayer. In contrast to low-temperature sintering carried out under a normal atmosphere, high-temperature sintering was carried out for the GO underlayer-based hematite photoanodes. The photocurrent density of the PECs with GO underlayers gradually increased as the spin speed of the FTO substrate increased. In particular, GO at a spin speed of 5000 rpm showed the highest photocurrent of 1.3 mA/cm². The higher performance of the GO/α-Fe₂O₃ photoanodes was attributed to the improved FTO/α-Fe₂O₃ interface. When sintered at 800°C for activation of the hematite (FTO/GO/α-Fe₂O₃) photoanodes, the GO layers before being decomposed act as localized hot zones at the FTO/α-Fe₂O₃ interface. These localized hot zones play a very crucial role in reducing the microstrain (increased crystallinity) which was confirmed from the synchrotron X-ray diffraction studies. The sacrificial GO underlayer may contribute to relaxing the inhomogeneous internal strain of the α-Fe₂O₃ nanorods and reducing the deformation of FTO to an extent. In other words, the reduction of the microstrain minimizes the lattice imperfections and defects at the FTO/α-Fe₂O₃ interface, which may enhance the charge collection efficiency, as demonstrated by the impedance measurements. From the EXAFS analysis, it is clearly evident that the sacrificial GO underlayer does not affect the structure of α-Fe₂O₃ in the short range. The effects of the GO sacrificial layers are restricted to the FTO/α-Fe₂O₃ interface, and they do not affect the bulk properties of α-Fe₂O₃.