Graphene-intercalated Fe₂O₃/TiO₂ heterojunctions for efficient photoelectrolysis of water

Abstract

<p>Interfacial modification of α-Fe<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> multilayer photoanodes by intercalating few-layer graphene (FLG) was found to improve water splitting efficiency due to superior transport properties, when compared to individual iron and titanium oxides and heterojunctions thereof. Both metal oxides and graphene sheets were grown by plasma-enhanced chemical vapor deposition. Compared to the onset potential achieved for α-Fe<sub>2</sub>O<sub>3</sub> films (1 V vs. RHE), the α-Fe<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> bilayer structure yielded a better onset potential (0.3 V vs. RHE). Heterojunctioned bilayers exhibited a higher photocurrent density (0.32 mA cm<sup>-2</sup> at 1.23 V vs. RHE) than the single α-Fe<sub>2</sub>O<sub>3</sub> layer (0.22 mA cm<sup>-2</sup> at 1.23 V vs. RHE), indicating more efficient light harvesting and higher concentration of photogenerated charge carriers. For more efficient charge transport at the interface, a few layer graphene sheet was intercalated into the α-Fe<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> interface, which substantially increased the photocurrent density to 0.85 mA cm<sup>-2</sup> (1.23 V vs. RHE) and shifted the onset potential (0.25 V vs. RHE). Ultrafast transient absorption spectroscopy studies indicated that the incorporation of FLG between the α-Fe<sub>2</sub>O<sub>3</sub> and TiO<sub>2</sub> layers resulted in reduced recombination in the α-Fe<sub>2</sub>O<sub>3</sub> layer. The results showed that graphene intercalation improved the charge separation and the photocurrent density of the FTO/α-Fe<sub>2</sub>O<sub>3</sub>/FLG/TiO<sub>2</sub> system.</p>