Effects of low oxygen annealing on the photoelectrochemical water splitting properties of α-Fe₂O₃

Abstract

Photoelectrochemical (PEC) water splitting is a promising method for conversing solar energy into chemical energy stored in the form of hydrogen. Nanostructured hematite (α-Fe2O3) is one of the most attractive materials for highly efficient charge carrier generation and collection due to its large specific surface area and shortening minority carrier diffusion length required to reach the surface. In the present work, PEC water splitting performance of α-Fe2O3 prepared by anodization of thin iron layers on an FTO glass and subsequent annealing in low O2-Ar ambient with only 0.03% O2 was investigated. The key finding is that annealing the anodic nanostructures with low oxygen concentration provides a strongly enhanced PEC performance compared with classic air annealing. The photocurrent of the former at 1.5 V vs. RHE results in 1.1 mA/cm 2 , being 11 times higher than that of the latter. The enhancement of the PEC performance for α-Fe2O3 annealed in low oxygen atmosphere can be attributed to controlled morphology, Sn doping, and introduction of oxygen vacancies, which contribute to the enhancement of the hole flux from the photogenerated site to the reactive surface and additionally lead to an enhanced hole transfer at the interface between the α-Fe2O3 and the electrolyte. From the obtained results, it is evident that low oxygen annealing is a surprisingly effective method of defect engineering and optimizing α-Fe2O3 electrodes for a maximized PEC water splitting performance.

Constructing Chemical Interaction between Hematite and Carbon Nanosheets with Single Active Sites for Efficient Photo‐Electrochemical Water Oxidation

“…The Fe 2p spectrum of pristine α‐Fe 2 O 3 ( Figure a) displays two distinct peaks of Fe 2p 3/2 at 710.8 eV and Fe 2p 1/2 at 724.5 eV with a satellite peak located at 718.8 eV, which is the typical feature of α‐Fe 2 O 3 . [ 37,38 ] After annealing at 300 °C, the intensity of the signal at ≈716.0 eV (corresponding to the satellite peak of Fe 2+ species) [ 36,39,40 ] slight increases in comparison to the bare α‐Fe 2 O 3 (Figure S17, Supporting Information).These results suggest the generation of oxygen vacancies in α‐Fe 2 O 3 structure, which is further confirmed by analyzing the O 1s spectra in Figure S18 (Supporting Information). [ 38 ] After the integration of α‐Fe 2 O 3 with Ni‐NC, the binding energy of Fe 2p in α‐Fe 2 O 3 ‐Ni‐NC keeps almost unchanged compared with the pure α‐Fe 2 O 3 (Figure 4a).…”

Synergies of co-doping in ultra-thin hematite photoanodes for solar water oxidation: In and Ti as representative case

“…The characteristics of In/Ti co-doped ultra-thin hematite photoanodes with high V O enable high PEC performance and introduce a useful strategy to design superstructure-based systems for efficient solar fuel production. 50…”

A Water‐Splitting System with a Cobalt (II,III) Oxide Co‐Catalyst‐Loaded Bismuth Vanadate Photoanode Along with an Organo‐Photocathode

“…Metal oxides responding to visible light are considered to be promising photocatalyst materials. However, they typically lose the ability to catalyze decomposition of water into O 2 and H 2 as a result of the downward shift of their conduction band edge, consisting of a d‐orbital, where the evolution of H 2 from H + is expected to occur [13–15] . Bismuth vanadium oxide (BiVO 4 ) is a type of metal oxide, which has been applied as a photoanode for the evolution of O 2 from water [16–20] .…”