Abstract
Photoelectrochemical (PEC) water splitting is a promising method for the conversion of solar energy into chemical energy stored in the form of hydrogen. Nanostructured hematite (α‐Fe2O3) is one of the most attractive materials for a highly efficient charge carrier generation and collection due to its large specific surface area and the short minority carrier diffusion length. In the present work, the PEC water splitting performance of nanostructured α‐Fe2O3 is investigated which was prepared by anodization followed by annealing in a low oxygen ambient (0.03 % O2 in Ar). It was found that low oxygen annealing can activate a significant PEC response of α‐Fe2O3 even at a low temperature of 400 °C and provide an excellent PEC performance compared with classic air annealing. The photocurrent of the α‐Fe2O3 annealed in the low oxygen at 1.5 V vs. RHE results as 0.5 mA cm−2, being 20 times higher than that of annealing in air. The obtained results show that the α‐Fe2O3 annealed in low oxygen contains beneficial defects and promotes the transport of holes; it can be attributed to the improvement of conductivity due to the introduction of suitable oxygen vacancies in the α‐Fe2O3. Additionally, we demonstrate the photocurrent of α‐Fe2O3 annealed in low oxygen ambient can be further enhanced by Zn‐Co LDH, which is a co‐catalyst of oxygen evolution reaction. This indicates low oxygen annealing generates a promising method to obtain an excellent PEC water splitting performance from α‐Fe2O3 photoanodes.
Highlights
With an increasing global demand for clean and sustainable energy systems, hydrogen as a renewable energy source is a candidate to replace fossil fuels
We investigated the photoelectrochemical behavior of a-Fe2O3 prepared by anodization of iron foils and the effect of annealing the electrode in a low oxygen content environment that is a 0.03 % O2-Ar ambient
The a-Fe2O3 layer annealed at 400 8C in low oxygen ambient provides a significantly enhanced PEC performance compared with conventional air annealing
Summary
With an increasing global demand for clean and sustainable energy systems, hydrogen as a renewable energy source is a candidate to replace fossil fuels. Nanostructuring of a-Fe2O3 provides a highly improved efficiency in charge carrier generation and collection due to the enhancement of the specific surface area and the drastic shortening of the minority carrier diffusion length.[14] Nanostructured a-Fe2O3 has been synthesized using a variety of techniques including sol-gel processing,[21] electrodeposition,[22] spray pyrolysis,[23] hydrothermal synthesis,[20,24] magnetron sputtering,[25,26] and electrochemical anodization.[27,28] Among them, anodization is considered as a promising method for the fabrication of nanostructured a-Fe2O3 from the viewpoint of low cost and large scale production.[28] it is well established that various precursor iron oxides are formed by anodizing and a suitable annealing procedure is needed to obtain a-Fe2O3 Annealing conditions such as temperature and atmosphere affect the PEC performance of a-Fe2O3 layers.[15,28,29,30,31,32] Ling et al.[29] reported that photoresponse of aFe2O3 nanowires fabricated on an FTO (fluorine doped tin oxide) glass by hydrothermal synthesis was activated by annealing in an oxygen deficient atmosphere achieved in an evacuated furnace refilled by pure N2. The light intensity was modulated by 10 % between 10 kHz and 0.1 Hz
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