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

Abstract

Photoelectrochemical cells (PECs) with a structure of F-doped SnO2 (FTO)/graphene oxide (GO)/ hematite (alpha-Fe2O3) photoanode were fabricated, in which GO serves as a sacrificial underlayer. In contrast to low-temperature sintering carried out under a normal atmosphere, hightemperature sintering was carried out for the GO underlayerbased 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/cm(2). The higher performance of the GO/alpha-Fe2O3 photoanodes was attributed to the improved FTO/alpha-Fe2O3 interface. When sintered at 800 degrees C for activation of the hematite (FTO/GO/alpha-Fe2O3) photoanodes, the GO layers before being decomposed act as localized hot zones at the FTO/alpha-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 alpha-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/alpha-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 alpha-Fe2O3 in the short range. The effects of the GO sacrificial layers are restricted to the FTO/alpha-Fe2O3 interface, and they do not affect the bulk properties of alpha-Fe2O3.