Electronically-Coupled Phase Boundaries in α-Fe₂O₃/Fe₃O₄ Nanocomposite Photoanodes for Enhanced Water Oxidation

Abstract

Photoelectrochemical (PEC) water splitting reactions are promising for sustainable hydrogen production from renewable sources. We report here, the preparation of α-Fe 2 O 3 /Fe 3 O 4 composite films via a single-step chemical vapor deposition of [Fe(O t Bu) 3 ] 2 and their use as efficient photoanode materials in PEC setups. Film thickness and phase segregation was controlled by varying the deposition time and corroborated through cross-section Raman spectroscopy and scanning electron microscopy. The highest water oxidation activity (0.48 mA/cm 2 at 1.23 V vs RHE) using intermittent AM 1.5 G (100 mW/cm 2 ) standard illumination was found for hybrid films with a thickness of 11 μm. This phenomenon is attributed to an improved electron transport resulting from a higher magnetite content toward the substrate interface and an increased light absorption due to the hematite layer mainly located at the top surface of the film. The observed high efficiency of α-Fe 2 O 3 /Fe 3 O 4 nanocomposite photoanodes is attributed to the close proximity and establishment of 3D interfaces between the weakly ferro-(Fe 2 O 3 ) and ferrimagnetic (Fe 3 O 4 ) oxides, which in view of their differential chemical constitution and valence states of Fe ions (Fe 2+ /Fe 3+ ) can enhance the charge separation and thus the overall electrical conductivity of the layer.

High Photothermally Active Fe2O3 Film for CO2 Photoreduction with H2O Driven by Solar Light

“…According to previous reports, the peak position of Fe 2p 3/2 is between 710.6 and 711.2 eV, and the area of the Fe 2p 3/2 peak is greater than that of Fe 2p 1/2 . The Fe 2p 3/2 peak has also been associated with a satellite peak located approximately 8 eV higher than the main Fe 2p 3/2 peak for α-Fe 2 O 3 , and Fe 2p 3/2 of Fe 3 O 4 does not have a satellite peak. , Therefore, the presence of the satellite peak at 718.8 eV in Figure A confirms the existence of α-Fe 2 O 3 ; and after reaction, the weakening of the satellite peak implies the reduction of α-Fe 2 O 3 Furthermore, the peak position of Fe 2p 3/2 moves downward after reaction, which can be attributed to the formation of Fe 2+ 2p 3/2 of Fe 3 O 4 . The XPS spectra thus indicate the reduction of α-Fe 2 O 3 to Fe 3 O 4 during the reaction.…”

“…19,20 Therefore, the presence of the satellite peak at 718.8 eV in Figure 3A confirms the existence of α-Fe 2 O 3 ; and after reaction, the weakening of the satellite peak implies the reduction of α-Fe 2 O 3 Furthermore, the peak position of Fe 2p 3/2 moves downward after reaction, which can be attributed to the formation of Fe 2+ 2p 3/2 of Fe 3 O 4 . 21 The XPS spectra thus indicate the reduction of α-Fe 2 O 3 to Fe 3 O 4 during the reaction.…”

Nanoscale ZnO/α‐Fe2O3 Heterostructures: Toward Efficient and Low‐Cost Photoanodes for Water Splitting

“…These factors lead to an enhancement of the photocurrent density up to 0.48 mA cm −2 at 1.23 V (vs RHE), despite a film thickness of 11 μm. [ 123 ]…”

Comparative Study on Electronic Structure and Optical Properties of α-Fe2O3, Ag/α-Fe2O3 and S/α-Fe2O3

“…After a long period of research, Al-Kuhaili et al [7] found that hematite α-Fe 2 O 3 had a 2.18 eV direct band gap, which theoretically allows the utilization of approximately 40% of the solar spectrum. However, the actual conversion efficiency of solar energy is not ideal due to poor performance, such as a very short excited-state lifetime [8][9][10], relatively poor absorptivity [11,12] and poor oxygen evolution reaction kinetics [13]. Therefore, improving the properties of α-Fe 2 O 3 becomes hard work.…”