Unraveling the role of single layer graphene as overlayer on hematite photoanodes

In this work, the role of the single layer graphene as overlayer on hematite photoanodes surface was investigated for water oxidation reaction via photoelectrochemical process. Single layer graphene (SLG) was synthesized by chemical vapour deposition (CVD) and transferred from the copper foil to the alpha-Fe2O3 photoanode surface. To ensure the purity and quality of SLG, elemental composition of the samples was investigated in all steps and no metal (Cu) trace was found after the transference onto the photoanode surface. The photocurrent density of alpha-Fe2O3/graphene photoanode was increased from 1.25 to 1.64 mA cm(-2) at 1.23 V-RHE in comparison to bare alpha-Fe2O3 photoanode. The role of SLG added on alpha-Fe2O3 and the charge carrier dynamics were investigated combining transient absorption spectroscopy (TAS) and surface photovoltage spectroscopy (SPS). These combined techniques revealed that the photogenerated holes had their lifetime increased as a function of applied bias and after the SLG deposition onto the alpha-Fe2O3 photoanode surface. As consequence, the photochemical separation and transfer of the photogenerated charge carriers became more efficient in the presence of SLG. The incorporation of SLG on alpha-Fe2O3 photoanode is believed to suppress the surface traps, enabling holes to diffuse into the solid-liquid interface and promoting water oxidation reaction driven by sunlight irradiation. (C) 2019 Elsevier Inc. All rights reserved.