Facile synthesis of α -Fe 2 O 3 nanoparticle: layer-sequence engineering of α -Fe 2 O 3 /TiO 2 photoanodes for enhanced photoelectrochemical water splitting

Abstract We report the influence of the deposition sequence of α -Fe 2 O 3 and TiO 2 layers on the photoelectrochemical (PEC) water-splitting performance of α -Fe 2 O 3 /TiO 2 heterostructured photoanodes. Hematite nanoparticles (NPs), synthesized via a co-precipitation method followed by calcination, together with commercial TiO 2 NPs, were employed to fabricate α -Fe 2 O 3 /TiO 2 photoanodes using a spin-coating approach. Linear sweep voltammetry (LSV) measurements reveal that heterostructured photoanodes deliver significantly higher photocurrent densities than the corresponding single-layer electrodes, with a strong dependence on the layer-deposition sequence. Specifically, at applied potentials below 1.65 V (versus RHE ), the FTO/TiO 2 / α -Fe 2 O 3 photoanode exhibits the highest photocurrent density. In contrast, at potentials above 1.65 V versus RHE, the FTO/ α -Fe 2 O 3 /TiO 2 configuration becomes dominant, achieving a photocurrent density of up to 1.16 mA cm −2 at 1.8 V (versus RHE ), which is approximately 2.47, 5.04, and 12.89 times higher than those of the FTO/TiO 2 / α -Fe 2 O 3 heterostructured electrode and the single-layer FTO/ α -Fe 2 O 3 and FTO/TiO 2 electrodes, respectively. Combined optical characterization and electrochemical impedance spectroscopy analyses indicate that the distinct PEC behaviors of the heterostructured photoanodes can be rationalized by their band alignment, applied-bias effects, and the role of interfacial trap states in charge separation and recombination processes.