Transient photocurrent behavior of (e) Si-doped Fe2O3 and (f) Si- and Ti-doped Fe2O3 at 1.23 VRHE. a) EIS circuit of hematite photoanodes under dark conditions. a) PEIS circuit of hematite photoanodes in light. The BET surface area of each sample is about 10 m2/g. f) ECSA values of each photoanode.
Introduction: hydrogen energy
Hydrogen: grey, blue and green hydrogen
Therefore, catalysts made of cheap materials are being developed to reduce the production costs of green hydrogen. In addition, work is being done on the development of systems that can handle the energy consumption required for water electrolysis more efficiently. In this thesis, we will focus on the principle of a solar powered water splitting system and the challenges that need to be solved.
Understanding the photoelectrochemical water splitting
However, hematite is currently showing about 1-2% STH performance due to characteristics such as poor electrical property and short length for hole movement, which are applied as fatal disadvantages in the PEC system. Therefore, solving the low electrical conductivity and short hole diffusion length of hematite is the most challenging task in the hematite-based PEC system.
In the case of the substrate, it was used as the electron transport layer (ETL) with junction, which improves the conductivity of the substrate and uses up- or down-conversion to maximize the wavelength at which hematite is most effective. In the case of the overcoat, it is more widely applied than the undercoat.
Nanotubular/porous anodic hematite photoanode for solar water splitting: Crucial effect of iron substrate purity. Porous synthesis of hematite with Ti-doped FeOOH OER co-catalyst for efficient photoelectrochemical water splitting system.
Porous hematite synthesis with Ti doped FeOOH OER co-catalyst for efficient
Introduction
Schematic images of different approaches for hematite electrode fabrication and comparison of productivity and fabrication cost of different technologies.
Experimental section
- Fabrication of Ti-H photoanode
- Fabrication of Ti-PH photoanode
- Fabrication of FeOOH decorated Ti-PH or Ti-FeOOH decorated Ti-PH photoanode
- PEC measurements
Results and Discussion
It was confirmed that the pores of Ti-FeOOH/Ti-PH were maintained differently from those of FeOOH/Ti-PH. Several TEM images to confirm the selective deposition of FeOOH and Ti-FeOOH co-catalyst on the outer and inner surfaces of Ti-PH. FeOOH or Ti-FeOOH cocatalyst loaded on Ti-PH were observed by XPS measurements, as shown in Figure 2.11.
Interestingly, Ti-PH loaded with Ti-FeOOH showed worse OER performance than FeOOH/Ti-PH. Our Ti-FeOOH decorated Ti-PH showed little decrease in photocurrent density over 36 hours (Figure 2.16). This means that the SiOx coating and the Ti-FeOOH cocatalyst can be used in the base electrolyte for a long time.
Faradic efficiency of Ti-FeOOH/Ti-PH at 1.23 V vs RHE under AM 1.5 illumination in a 1 M NaOH electrolyte.
Conclusion
Insight into the role of titanium oxide as a water oxidation promoter in hematite-based photoanodes. Gradient Tantalum-Doped Hematite Homojunction Photoanode Improves Both Photocurrents and Turn-On Voltage for Solar Water Splitting. Highly conformal deposition of an ultrathin FeOOH layer on a hematite nanostructure for efficient solar water splitting.
Nanostructured iron oxyhydroxide decorated hematite films as photoanodes for efficient and stable photoelectrochemical water splitting. Rapid synthesis of cobalt nitride nanowires: Highly efficient and low-cost catalysts for oxygen evolution. A selectively decorated Ti-FeOOH co-catalyst for a highly efficient porous hematite-based water splitting system.
Insight into the dopability of hematite photoanode for an efficient water splitting
Introduction
Experimental section
- Fabrication of Si-Fe 2 O 3 or Si:Ti-Fe 2 O 3 electrodes
- Fabrication of NiFeO x coated Si:Ti-Fe 2 O 3 electrodes
- PEC measurements
- DFT calculation details
All ion positions were relaxed using the conjugate gradient method until an atomic force convergence of 0.01 eV A−1 was achieved. In the case of transition metal oxide systems, the 3d electronic states are strongly coupled, so keeping the same in mind, we used the spin polarized GGA + U formalism due to the incorrect behavior of the d-electrons with standard DFT.12 The GGA + U calculations depend on the U-J values and were set to 4.2 eV, which is in agreement with the experimental band gap value of hematite (2.2 eV).
Results and Discussion
Therefore, this allows us to reveal the correlation between the Si doping method and the formation energy reported so far. So far, Si doping has been successfully achieved through nonequilibrium processes such as APCVD and UPS. The best we have found is that so far there is no report that Si can be doped in equilibrium. Obviously, several attempts have been made, but it is expected that the Si doping was not successful through the equilibrium process due to the high formation energy of Si doping. Sn is also diffused, as shown in Figure 3.6. However, since Sn doping is not completely blocked, we also checked the effect of Sn on Si doping via the formation energy, as shown in Figure 3.7. The results show that Sn can also play a role in lowering the formation energy for Si doping. As shown in Figure 3.8a, it can be seen that the Si element is only intensively distributed on the surface before the annealing process.
The TOF-SIMS depth profile also showed that the Si element exhibited a more uniform distribution after heat treatment, as shown in Figure 3.8b. To directly compare the differences in crystallinity, XRD analysis was performed as shown in Figure 3.8g. You can see that Si-Fe2O3 has the widest and largest LO signal as shown in Figure 3.8h.25 Therefore, Si-Fe2O3 has the lowest crystallinity via TEM, to perform single doping correctly. in the equilibrium process. The role of Ti can be confirmed by the XPS measurement of Ti 2p. It was shown that the Ti 2p bond energy of Si:Ti-Fe2O3 is slightly higher than that of Ti-Fe2O3.
For a more direct comparison, we measured the conductivity of the electrode through the FET as shown in Figure 3.17. Si:Ti-Fe2O3 showed the highest electrical conductivity and Si-Fe2O3 showed the lowest electrical conductivity. RHE, it was confirmed that the charge transfer efficiency of Si:Ti-Fe2O3 (about 90%) and Si-Fe2O3 (about 2%) differed significantly by about 45 times as shown in Figure 3.13c. The charge separation efficiency was also calculated with or without a hole cleaner, as shown in Figure 3.13d and Figure 3.18. The load sharing efficiency showed the same result trend as the transfer efficiency trend. Transient photocurrent behavior with (e) Si-doped Fe2O3 and (f) Si-Ti co-doped Fe2O3 at 1.23 VRHE. a) EIS circuit of hematite photoanodes under dark conditions.
Conclusion
Synergistic effects of dopant (Ti or Sn) and oxygen vacancy on the electronic properties of hematite: a DFT investigation. Ultrathin insulating underlayer with a hematite thin film for enhanced photoelectrochemical (PEC) water splitting activity. Revealing the role of the Ti dopant and viable Si doping of hematite for practically efficient solar water splitting.
NiFeO x decorated Ge-hematite/perovskite for an efficient tandem water splitting
Introduction
Experimental section
- Fabrication of Fe 2 O 3 and Ge doped hematite (Ge-H) photoanode
- Fabrication of Ge doped porous hematite (Ge-PH) photoanode
- Fabrication of NiFeO x decorated Ge-PH photoanode
- PEC measurements
- Synthesis of methylammonium iodide (MAI)
- Synthesis of FAPbI 3 and MAPbBr 3 powders
- Photovoltaic device fabrication
- DFT calculation details
The solvent was removed under vacuum and the products were dissolved in ethanol and recrystallized in diethyl ether. The recrystallized products were collected by filtration and the collected products were dried at 60 oC under vacuum. FAPbI3 powders were synthesized by dissolving FAI and PbI2 in 2-methoxyethanol with vigorous stirring at 120 oC for 30 minutes, and MAPbBr3 powders were synthesized by dissolving MAI and PbBr2 in 2-methoxyethanol with vigorous stirring at 100 oC for 30 minutes. After annealing at 500 oC for 1 hour in air, the prepared FaPbI3 and MAPbBr3 powders were dissolved in the mixed solution.
The mixed solution is prepared in a 4:1 volume ratio of N-N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) at 60 oC for 1 hour with stirring. The prepared perovskite solution is loaded onto the mp-TiO2/bl-TiO2/FTO substrate using different spincoating conditions at 1000–5000 rpm for 15–20s. After synthesizing the hole-filling material, the hole-filling material was filled onto perovskite/mpTiO2/bl-TiO2/FTO by spin coating at 3000 rpm for 30 s.
In the case of transition metal oxide systems, 3d electronic states are strongly correlated, therefore we used the spin polarized GGA + U formalism due to improper action of d-electrons with standard DFT.26 The GGA + U calculations depend on the values of U-J and was set to 4.2 eV which is consistent with the experimental band gap value of hematite (2.2 eV).
Results and Discussion
In the Raman spectra, the LO signal of Ge-H was much sharper than that of Fe2O3 and Ge-PH as shown in Figure 4.4c. Ge-PH showed higher doping level than that of Ge-H and when the peaks were decomposed, it was also confirmed that more Ge4+ existed in Ge-PH as shown in Figure 4.6. However, the Ge/Sn ratio of Ge-PH was very small, less than 1% over the entire range as shown in Figure 4.4g.
Finally, the charge separation efficiency was calculated using a hole scavenger, Na2SO3 as shown in Figure 4.12d. The tandem system of hematite and PSC has been reported as a system capable of producing hydrogen without an applied external voltage as shown in Figure 4.13a. As for the operating point of the tandem device, it can be observed from the figure that the LSV of PSC and the LSV of NiFeOx@Ge-PH formed a photocurrent density of 3.9 mA cm-2, which was the overlapped part as shown in Figure 4.13c.
The tandem device was also confirmed to operate stably for about 5 hours as shown in Figure 4.13d.
Conclusion
Thickness and silicon doping on the performance of nanostructured hematite photoanodes for solar water splitting. Thin-film translucent Fe2O3 photoanodes for efficient water splitting by sunlight: nanostructure-directing effect of Si-doping. A highly transparent thin-film hematite with multi-element capability for an efficient, self-contained water splitting system.
Surface Treatment with Al3+ on a Ti-Doped α-Fe2O3 Nanorod Array Photoanode for Efficient Photoelectrochemical Water Splitting. Nanorod@Nanobowl Array photoanode with an adjustable light-trapping cutoff and bottom-selective field enhancement for efficient solar water splitting. Perovskite solar cell for photocatalytic water splitting with a TiO2/Co-doped hematite electron transport bilayer.
A highly transparent thin film hematite with multi-element dippability for an efficient, unsupported water splitting system.
