Hematite (α-Fe2O3) is currently considered to be a promising candidate for solar hydrogen production. However, poor conductivity, short hole diffusion length (2-4 nm), and sluggish oxygen evolution kinetics are severe limitations of hematite for effective solar water splitting. Various strategies have been proposed to address these obstacles, including element doping, nanoconstructuring and surface modifications. Tailoring Fe2O3 with a desired one-dimensional (1-D) arrayed heterojunction nanostructure offers essential advantages to address its limitations.
In our study, we design and fabricate a highly-oriented Fe2O3/ZnFe2O4 in 1-D nanocolumnar arrays to construct nanoscale heterojunctions employing the reactive ballistic deposition (RBD) of a hematite backbone and atomic layer deposition (ALD) of ZnO combined with annealing to form ZnFe2O4. This Fe2O3/ZnFe2O4 heterojunction photoanode can effectively facilitate the charge separation as the interface, generating a photocurrent of about 0.8 mA cm-2 at 1.23 V vs. RHE under simulated sunlight illumination. The I-V characteristics with H2O2 as the hole scavenger, as well as the photoluminescence and transient photocurrent study reveal that the enhanced PEC performance is due to the charge separation effect of the Fe2O3/ZnFe2O4 heterojunction.
Our work demonstrates that constructing a highly-oriented heterojunction with a well-organized nanostructure is an effective approach to improve the charge separation for enhanced PEC water oxidation performance. Further improvement of this Fe2O3/ZnFe2O4 photoanode could be attained by doping the Fe2O3 with increased electrical conductivity or by passivating the surface states, as well as by loading water oxidation cocatalysts to achieve low onset potential and higher water oxidation efficiency. |