Chinese Journal of Catalysis ›› 2021, Vol. 42 ›› Issue (6): 904-919.DOI: 10.1016/S1872-2067(20)63712-3
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Received:
2020-08-08
Accepted:
2020-09-21
Online:
2021-06-18
Published:
2021-01-30
Contact:
Ke Fan
About author:
*E-mail: kefan@kth.seSupported by:
Dinghua Zhou, Ke Fan. Recent strategies to enhance the efficiency of hematite photoanodes in photoelectrochemical water splitting[J]. Chinese Journal of Catalysis, 2021, 42(6): 904-919.
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URL: https://www.cjcatal.com/EN/10.1016/S1872-2067(20)63712-3
Fig. 3. (a-c) SEM images of some 3D ordered nanophotonic structures of hematite: (a), (b), and (c) adapted with permission from Refs. [10,11], and [13]. Copyright (2016) and (2014) Royal Society of, Chemistry, and (2014) American Chemical Society, respectively. UV-vis optical absorption spectra of the NSP substrate-based device with: (d) different pitches and (e) different heights in a 1000 nm pitch. (f) J-V curves of the Ti-doped hematite photoelectrodes based on the three different NSP arrays. Adapted with permission from Ref. [13]. Copyright (2014) American Chemical Society.
Fig. 4. (a) Schematic of hematite/Ag/CoPi; UV-Vis spectra (b), and IPCE (c) for hematite photoelectrodes. Adapted with permission from Ref. [21]. Copyright (2016) Wiley.
Sample | Electrolyte | Photocurrent density (mA cm-2, at 1.23 V vs. RHE) | Ref. |
---|---|---|---|
3D branched Fe2O3 nanorod | 1 M NaOH | 0.61 | [ |
3D nanocone Ti-Fe2O3 array | 1 M NaOH | 2.24 | [ |
3D Ti-Fe2O3 nanospikes | 1 M NaOH | 2.42 | [ |
Au-Fe2O3 | 1 M NaOH | ~1.00 | [ |
Ag-Fe2O3 | 1 M NaOH | 3.20 | [ |
Pd-Fe2O3 | 0.1 M Na2S and 0.1 M Na2SO3 | N/A | [ |
BiVO4-Fe2O3 | 1 M NaOH | ~0.50 | [ |
WO3-Fe2O3 | 0.1 M NaOH | 0.70 | [ |
WO3-Fe2O3 | 0.5 M NaSO4 | 1.66 | [ |
Si-Fe2O3 F-doped Fe2O3 | 1 M NaOH 1 M KOH | ~0.90 2.52 | [ [ |
Table 1 Reports on photon absorption efficiency enhancement.
Sample | Electrolyte | Photocurrent density (mA cm-2, at 1.23 V vs. RHE) | Ref. |
---|---|---|---|
3D branched Fe2O3 nanorod | 1 M NaOH | 0.61 | [ |
3D nanocone Ti-Fe2O3 array | 1 M NaOH | 2.24 | [ |
3D Ti-Fe2O3 nanospikes | 1 M NaOH | 2.42 | [ |
Au-Fe2O3 | 1 M NaOH | ~1.00 | [ |
Ag-Fe2O3 | 1 M NaOH | 3.20 | [ |
Pd-Fe2O3 | 0.1 M Na2S and 0.1 M Na2SO3 | N/A | [ |
BiVO4-Fe2O3 | 1 M NaOH | ~0.50 | [ |
WO3-Fe2O3 | 0.1 M NaOH | 0.70 | [ |
WO3-Fe2O3 | 0.5 M NaSO4 | 1.66 | [ |
Si-Fe2O3 F-doped Fe2O3 | 1 M NaOH 1 M KOH | ~0.90 2.52 | [ [ |
Fig. 6. Morphological images (a-c) and PEC performance curves (d-f) of some special nanostructure hematite electrodes. Adapted with permission from Ref. [44,45,50]. Copyright (2018) American Chemical Society, (2017) and (2020) Wiley.
Fig. 7. (a) J-V curves of different photoanodes based on hematite. (b) Charge separation efficient in bulk; (c-e) the band bending schemes in hematite with different P concentrations. (f) Gradient P concentration; EF is the Fermi level. Adapted with permission from Ref. [51]. Copyright (2017) Royal Society of Chemistry.
Fig. 9. Mott-Schottky plots (a) and UPS spectra for hematite (b) and Fe2O3@FeNbO4 nanorods (c), and (d) corresponding band alignment (d). Adapted with permission from Ref. [66]. Copyright (2018) American Chemical Society.
Samples | Electrolyte | Photocurrent density (mA cm-2, at 1.23 V vs RHE) | Ref. |
---|---|---|---|
Ultrafine Ti-Fe2O3 nanowire array | 1 M NaOH | 0.90 | [ |
TiO2/Ti: Fe2O3 BNR | 1 M KOH | 2.50 | [ |
Ti-modified mesoporous Fe2O3 | 1 M NaOH | 4.30 | [ |
Sn-doped Fe2O3 P-doped Fe2O3 | 1 M NaOH 1 M NaOH | 1.83 2.70 | [ [ |
Grad P-doped Fe2O3 | 1 M KOH | 1.48 | [ |
Ti, Mg co-doped Fe2O3 | 1 M NaOH | 1.08 | [ |
Ti/Au/Fe2O3 | 1 M NaOH | 0.51 | [ |
Mg-doped Fe2O3/ P-doped Fe2O3 | 1 M KOH | 2.40 | [ |
U3O8/Fe2O3 | 1 M NaOH | 2.43 | [ |
Fe2O3@FeNbO4 Fe2O3/TiO2 | 1 M NaOH 1 M KOH | 2.24 2.90 | [ [ |
Table 2 Summary of studies on enhancing the separation efficiency of bulk semiconductors.
Samples | Electrolyte | Photocurrent density (mA cm-2, at 1.23 V vs RHE) | Ref. |
---|---|---|---|
Ultrafine Ti-Fe2O3 nanowire array | 1 M NaOH | 0.90 | [ |
TiO2/Ti: Fe2O3 BNR | 1 M KOH | 2.50 | [ |
Ti-modified mesoporous Fe2O3 | 1 M NaOH | 4.30 | [ |
Sn-doped Fe2O3 P-doped Fe2O3 | 1 M NaOH 1 M NaOH | 1.83 2.70 | [ [ |
Grad P-doped Fe2O3 | 1 M KOH | 1.48 | [ |
Ti, Mg co-doped Fe2O3 | 1 M NaOH | 1.08 | [ |
Ti/Au/Fe2O3 | 1 M NaOH | 0.51 | [ |
Mg-doped Fe2O3/ P-doped Fe2O3 | 1 M KOH | 2.40 | [ |
U3O8/Fe2O3 | 1 M NaOH | 2.43 | [ |
Fe2O3@FeNbO4 Fe2O3/TiO2 | 1 M NaOH 1 M KOH | 2.24 2.90 | [ [ |
Fig. 10. Processes that may exist at the semiconductor-solution interface. G represents the generation of electron-hole pairs; Et is trap energy level in the bulk semiconductor; and Ess is the surface state energy level.
Fig. 11. Band edge pinning diagrams (a) and Fermi level pinning (b) for a photoanode system. Adapted with permission from Ref. [73]. Copyright (2015) American Chemical Society.
Fig. 12. (a) J-V curves for PEC water oxidation based on different hematite electrodes under illumination (1 Sun, AM 1.5) from 1.0 M NaOH solution; (b) OCP in the dark and under illumination for hematite electrodes. Adapted with permission from Ref. [74]. Copyright (2015) American Chemical Society.
Fig. 13. J-V curves under H2O and H2O2 oxidation conditions for hematite electrodes annealed at 500 °C (a) and 800 °C (b); CV curves scanned at 1 V s-1 under dark conditions for the electrodes annealed at 500 °C (c) and 800 °C (d). Adapted with permission from Ref. [78]. Copyright (2014) American Chemical Society.
Fig. 14. J-V curves of Fe2O3 electrodes under illumination in different pH electrolytes (1 Sun, AM 1.5): at pH 13.6 (a) and pH 7 (b) for the bare Fe2O3 (c) and Pi-Fe2O3 (d) electrodes. Adapted with permission from Ref. [86]. Copyright (2014) Wiley.
Fig. 15. Proposed RDS for water oxidation on hematite. (a) Stepwise electron/proton transfer pathway; (b) CPET transfer pathway. Adapted with permission from Ref. [90]. Copyright (2016) Royal Society of Chemistry.
Fig. 16. (a) J-V scans under illumination in a 0.5 M NaClO4 solution at different pH levels; (b) KIE values calculated from the steady photocurrent ratio in H2O and D2O at various electrolyte pH levels. Adapted with permission from Ref. [91]. Copyright (2016) American Chemical Society.
Fig. 18. Summary of IMPS data for three different photoelectrodes; (a) ktr; (b) kre. Adapted with permission from Ref. [93]. Copyright (2016) Royal Society of Chemistry.
Fig. 19. Back reaction in the FTO-solution interface. (a) without a blocking layer; (b) with a blocking layer. R represents the reactant (OH- or H2O).
Fig. 20. (a) J-V curves of the Ti4+ doped Fe2O3 before and after surface corrosion in 1 M NaOH; (b) Reduction dark current before and after surface corrosion in 1 M NaOH, FTO substrate as a reference, and different gas bubbling (N2 or O2) processes. Adapted with permission from Ref. [106]. Copyright (2014) Royal Society of Chemistry.
Samples | Electrolyte | Photocurrent density (mA cm-2, at 1.23 V vs RHE) | Ref. |
---|---|---|---|
TiO2-modified Fe2O3 | 1 M NaOH | 1.20 | [ |
Annealing at 800 °C Fe2O3 | 1 M KOH | ~0.78 | [ |
Acid treatment Fe2O3 | 1 M NaOH | ~1.30 | [ |
Pi-Fe2O3 | 1 M NaOH | 1.31 | [ |
0.1 M KPi | 1.26 | ||
F-doped Fe2O3 | 1 M KOH | 2.52 | [ |
Alkali treatment Fe2O3 | 1 M NaOH | 0.63 | [ |
Fe2O3/FeOOH | 1 M NaOH | 1.21 | [ |
Fe2O3/RuOEC | 1 M KOH | ~2.20 | [ |
Nb2O5 underlayer of hematite | 1 M NaOH | ~0.1 | [ |
Acid corrosion Ti-Fe2O3 | 1 M NaOH | ~1.7 | [ |
Table 3 Reports on surface injection efficiency enhancement.
Samples | Electrolyte | Photocurrent density (mA cm-2, at 1.23 V vs RHE) | Ref. |
---|---|---|---|
TiO2-modified Fe2O3 | 1 M NaOH | 1.20 | [ |
Annealing at 800 °C Fe2O3 | 1 M KOH | ~0.78 | [ |
Acid treatment Fe2O3 | 1 M NaOH | ~1.30 | [ |
Pi-Fe2O3 | 1 M NaOH | 1.31 | [ |
0.1 M KPi | 1.26 | ||
F-doped Fe2O3 | 1 M KOH | 2.52 | [ |
Alkali treatment Fe2O3 | 1 M NaOH | 0.63 | [ |
Fe2O3/FeOOH | 1 M NaOH | 1.21 | [ |
Fe2O3/RuOEC | 1 M KOH | ~2.20 | [ |
Nb2O5 underlayer of hematite | 1 M NaOH | ~0.1 | [ |
Acid corrosion Ti-Fe2O3 | 1 M NaOH | ~1.7 | [ |
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