α-Fe2O3 photoanode preparation method, α-Fe2O3 photoanode and doped α-Fe2O3 photoanode

Abstract

The present invention provides a method for preparing an α-Fe2O3 photoanode, an α-Fe2O3 photoanode, and a doped α-Fe2O3 photoanode. The α-Fe2O3 photoanode preparation method comprises the following steps: preparing oxyhydroxide or doped oxyhydroxide on a substrate using a hydrothermal method to obtain an oxyhydroxide / substrate sample or a doped oxyhydroxide / substrate sample; annealing the oxyhydroxide / substrate sample or the doped oxyhydroxide / substrate sample under a first annealing condition at a first vacuum degree, and then annealing the oxyhydroxide / substrate sample or the doped oxyhydroxide / substrate sample under a second annealing condition at a second vacuum degree, thereby obtaining an α-Fe2O3 photoanode intrinsically modified with oxygen vacancies and β-Fe2O3 or a doped α-Fe2O3 photoanode intrinsically modified with oxygen vacancies and β-Fe2O3, wherein the first vacuum degree is greater than the second vacuum degree, and the annealing temperature in the first annealing condition is lower than the annealing temperature in the second annealing condition. The scheme of the present invention achieves the simultaneous generation of β-Fe2O3 and oxygen vacancies in α-Fe2O3 by controlling the annealing pressure and temperature in stages. The obtained α-Fe2O3 exhibits high photoelectrochemical performance.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of α-Fe2O3 photoanodes, and in particular to a preparation method of an α-Fe2O3 photoanode, an α-Fe2O3 photoanode and a doped α-Fe2O3 photoanode. Background Art

[0002] The introduction of oxygen vacancies in hematite (α-Fe2O3), i.e., intrinsic doping, has been considered a good way to improve the photoelectrochemical (PEC) performance. It can significantly improve charge transfer with slightly changed structure, which is beneficial for further modification. In recent years, researchers have developed various methods to create oxygen vacancies in hematite. For example, by sintering FeOOH in an oxygen-deficient atmosphere, oxygen vacancy-modified hematite can reach 1.82 mA / cm at 1.23 V vs. RHE. 2 Although many hematite photoanodes with oxygen vacancies have been reported, the corresponding PEC performance is unfortunately still not met. Summary of the Invention

[0003] One object of the present invention is to improve the photoelectrochemical performance of α-Fe2O3 photoanode.

[0004] In particular, the present invention provides a method for preparing an α-Fe2O3 photoanode, comprising the following steps:

[0005] preparing iron oxyhydroxide or doped iron oxyhydroxide on a substrate by a hydrothermal method to obtain an iron oxyhydroxide / substrate sample or a doped iron oxyhydroxide / substrate sample;

[0006] The ferric oxyhydroxide / substrate sample or the doped ferric oxyhydroxide / substrate sample is annealed under a first annealing condition at a first vacuum degree, and then annealed under a second annealing condition at a second vacuum degree, thereby obtaining an α-Fe2O3 photoanode intrinsically modified with oxygen vacancies and β-Fe2O3 or a doped α-Fe2O3 photoanode intrinsically modified with oxygen vacancies and β-Fe2O3, wherein the first vacuum degree is greater than the second vacuum degree, and the annealing temperature in the first annealing condition is lower than the annealing temperature in the second annealing condition.

[0007] Optionally, the first vacuum degree is any value between 1-10 Pa, and the second vacuum degree is any value between 10 Pa-1 atm.

[0008] Optionally, the first annealing condition is sintering at 500-650° C. for 90-180 min;

[0009] The second annealing condition is sintering at 550-760° C. for 10-20 minutes.

[0010] Optionally, the doped iron oxyhydroxide in the doped iron oxyhydroxide / substrate sample is hafnium-doped iron oxyhydroxide.

[0011] In particular, the present invention also provides an α-Fe2O3 photoanode, which is prepared using the aforementioned α-Fe2O3 photoanode preparation method, wherein the α-Fe2O3 photoanode is intrinsically modified with oxygen vacancies and β-Fe2O3.

[0012] In particular, the present invention also provides a doped α-Fe2O3 photoanode, which is prepared using the aforementioned α-Fe2O3 photoanode preparation method, wherein the doped α-Fe2O3 photoanode is intrinsically modified with oxygen vacancies and β-Fe2O3.

[0013] Optionally, the doped α-Fe2O3 photoanode is a hafnium-doped α-Fe2O3 photoanode or a phosphorus-doped α-Fe2O3 photoanode.

[0014] Optionally, the doped α-Fe2O3 photoanode is a FeNiOOH-P-Hf-Fe2O3 photoanode.

[0015] In this field, in order to improve the PEC performance, researchers have tried various methods to generate oxygen vacancies in α-Fe2O3. A common method is to anneal the obtained iron oxyhydroxide / substrate sample or doped iron oxyhydroxide / substrate sample, and the annealing conditions are basically fixed, that is, continuously introducing a protective gas during vacuum high-temperature annealing. This has become a mainstream treatment method in this field and has formed a technical bias to a certain extent. In the present invention, the inventors broke this technical bias and achieved the simultaneous generation of β-Fe2O3 and oxygen vacancies in α-Fe2O3 by controlling the annealing pressure and temperature in stages, thereby enhancing charge extraction to generate more photogenerated electron-hole pairs, promoting charge transfer, and inhibiting electron-hole recombination. The resulting α-Fe2O3 exhibits very high photoelectrochemical performance. At 1.23V vs.RHE, the photocurrent is 2.72mA / cm 2 , achieving unexpected technical effects. In addition, one of the differences between the present invention and conventional hydrothermal methods is the staged pressure and temperature control, the preparation method is simple, and can be extended to various further modifications to achieve practical solar water splitting.

[0016] Furthermore, the obtained α-Fe2O3 has slight structural changes, which can be well combined with various further modifications, such as P treatment, Hf treatment and deposition of FeNiOOH co-catalyst, and accumulate positive effects. Due to the high initial photocurrent, the final photoanode can reach 5.24 mA / cm at 1.23 V vs. RHE. 2This is one of the highest photocurrent values ever reported for hematite-based photoanodes.

[0017] Based on the following detailed description of specific embodiments of the present invention in conjunction with the accompanying drawings, those skilled in the art will become more aware of the above and other objects, advantages and features of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Hereinafter, some specific embodiments of the present invention will be described in detail in an exemplary and non-limiting manner with reference to the accompanying drawings. The same reference numerals in the accompanying drawings indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the accompanying drawings:

[0019] Figure 1 A schematic flow chart of a method for preparing an α-Fe2O3 photoanode according to one embodiment of the present invention is shown;

[0020] Figure 2 shows a transmission electron microscope image of an α-Fe2O3 photoanode according to one embodiment of the present invention;

[0021] Figure 3 shows a high-resolution transmission electron microscopy image of an α-Fe2O3 photoanode according to one embodiment of the present invention;

[0022] Figure 4 Shows the XRD patterns of the α-Fe2O3 photoanode in the prior art and the α-Fe2O3 photoanode of an embodiment of the present invention;

[0023] Figure 5 Shown Figure 4 A partial schematic enlarged view of ;

[0024] Figure 6 Shown Figure 4 a schematic enlarged view of another part;

[0025] Figure 7 shows a current density and voltage characteristic curve of an α-Fe2O3 photoanode according to one embodiment of the present invention;

[0026] Figure 8 shows a graph of current density and voltage characteristics of a doped α-Fe2O3 photoanode according to one embodiment of the present invention;

[0027] Figure 9 A comparison diagram of current density and voltage characteristic curves of an α-Fe2O3 photoanode and a doped α-Fe2O3 photoanode according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0028] The following describes the embodiments of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, in the absence of conflict, the features in the following embodiments and embodiments can be combined with each other. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of this application.

[0029] It should also be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present application. The illustrations only show the structures related to the present application and are not drawn according to the number, shape and size of the structures in actual implementation. In actual implementation, the type, quantity and proportion of each structure may be changed at will, and its structural layout may also be more complicated.

[0030] Additionally, in the following description, specific details are provided to provide a thorough understanding of the examples. However, one skilled in the art will appreciate that the aspects described can be practiced without these specific details.

[0031] Figure 1 FIG1 shows a schematic flow chart of a method for preparing an α-Fe2O3 photoanode according to an embodiment of the present invention. Figure 1 As shown, the method for preparing the α-Fe2O3 photoanode includes:

[0032] Step S100, preparing iron oxyhydroxide or doped iron oxyhydroxide on a substrate by a hydrothermal method to obtain an iron oxyhydroxide / substrate sample or a doped iron oxyhydroxide / substrate sample;

[0033] Step S200, annealing the ferric oxyhydroxide / substrate sample or the doped ferric oxyhydroxide / substrate sample under a first annealing condition at a first vacuum degree, and then annealing it under a second annealing condition at a second vacuum degree, thereby obtaining an α-Fe2O3 photoanode intrinsically modified with oxygen vacancies and β-Fe2O3 or a doped α-Fe2O3 photoanode intrinsically modified with oxygen vacancies and β-Fe2O3, wherein the first vacuum degree is greater than the second vacuum degree, and the annealing temperature in the first annealing condition is lower than the annealing temperature in the second annealing condition.

[0034] In this field, in order to improve the PEC performance, researchers have tried various methods to generate oxygen vacancies in α-Fe2O3, and a common method is to anneal the obtained iron oxyhydroxide / substrate sample or doped iron oxyhydroxide / substrate sample, and the annealing conditions are basically fixed, that is, annealing at about 550°C at one time. This has reached a consensus in this field and has formed a technical bias to a certain extent. In the present invention, the inventors broke this technical bias and achieved the simultaneous generation of β-Fe2O3 and oxygen vacancies in α-Fe2O3 by controlling the annealing pressure and temperature in stages, thereby enhancing charge extraction to generate more photogenerated electron-hole pairs, promoting charge transfer, and suppressing electron-hole recombination. The resulting α-Fe2O3 exhibits high photoelectrochemical performance, with a photocurrent of 2.72 mA / cm at 1.23 V vs. RHE. 2 , achieving unexpected technical effects. In addition, one of the differences between the present invention and conventional hydrothermal methods is the staged pressure and temperature control, the preparation method is simple, and can be extended to various further modifications to achieve practical solar water splitting.

[0035] In step S100, it is common knowledge in the art to prepare ferric oxyhydroxide or doped ferric oxyhydroxide on a substrate by a hydrothermal method. For example, FeCl3-6H2O can be used as a precursor, and a hydrothermal reaction can be carried out at 95°C for 4 hours to grow FeOOH on the surface of the FTO substrate. Other existing technologies can also be used, which will not be repeated here.

[0036] In step S200, annealing can be performed in a tube furnace, for example. The first vacuum degree is any value in the range of 1-10 Pa, for example, 1 Pa, 2 Pa, 4 Pa, 6 Pa, 8 Pa, or 10 Pa. The annealing temperature in the first annealing condition is any value in the range of 500-650° C., for example, 500° C., 550° C., 600° C., or 650° C. The sintering time in the first annealing condition is 90-180 minutes, for example, 500° C., 550° C., 600° C., or 650° C.

[0037] The second vacuum degree is any value between 10 Pa and 1 atm, for example, 1 Pa, 10 Pa, 50 Pa, 100 Pa, 500 Pa, 800 Pa, 1000 Pa, 5000 Pa, 8000 Pa, or 1 atm. The second annealing condition is an annealing temperature between 550° C. and 760° C., for example, 550° C., 600° C., 650° C., 700° C., or 760° C. The second annealing condition is a sintering time between 10 and 20 minutes, for example, 10 minutes, 15 minutes, or 20 minutes. Finally, the temperature is naturally lowered to room temperature to obtain an α-Fe2O3 photoanode or a doped α-Fe2O3 photoanode.

[0038] In the embodiment of the present invention, by carefully controlling the sintering pressure and temperature, β-Fe2O3 can be successfully generated in hematite, while simultaneously forming oxygen vacancies. Both enhance charge extraction, promote charge transfer, and then inhibit electron-hole recombination, synergistically improving charge utilization. As a result, the photoanode can achieve 2.72 mA / cm at 1.23 V vs. RHE. 2 The excellent photocurrent density is 3.3 times that of the original hematite. Due to its good intrinsic modification and adaptability, the obtained hematite can be used as a good starting material for various further processing.

[0039] In one embodiment, in step S100, the iron oxyhydroxide doped in the iron oxyhydroxide / substrate sample is hafnium-modified FeNiOOH, which is labeled as Hf-FeNiOOH. The product prepared after step S200 is labeled as Hf-Fe2O3. There are many methods for preparing Hf-FeOOH / FTO. For example, in one embodiment, a colorless and transparent hafnium chloride ethanol solution can be added to a mixed solution of FeCl3-6H2O and NaNO3 to mix them evenly. Then, 100 μl of concentrated nitric acid is added to adjust the pH value of the solution. After that, the solution is heated to 95°C by a hydrothermal method and naturally cooled to room temperature after 4 hours to obtain Hf-FeOOH / FTO. Of course, the present invention only illustrates one possible embodiment and is not limited to this embodiment. As long as Hf-FeOOH / FTO can be finally prepared, it will be sufficient. The final step S200 produces a hafnium-doped α-Fe2O3 photoanode.

[0040] In one embodiment, there are multiple methods for preparing the FeNiOOH-P-Hf-Fe2O3 photoanode. The present invention provides a method, first soaking the Hf-Fe2O3 photoanode prepared above in a phosphoric acid solution, and then drying it in an oven at 40-60°C for 30-90 minutes to obtain P-Hf-Fe2O3. The degree of phosphating is controlled by adjusting the soaking time and the concentration of the phosphoric acid solution. The surface modification of FeNiOOH is to deposit P-Hf-Fe2O3 using an existing electrodeposition method to finally obtain FeNiOOH-P-Hf-Fe2O3. Of course, the present invention only illustrates one possible embodiment and is not limited to this embodiment, as long as FeNiOOH-P-Hf-Fe2O3 can be finally prepared.

[0041] In particular, the present invention also provides an α-Fe2O3 photoanode, which is prepared using the aforementioned α-Fe2O3 photoanode preparation method, and the α-Fe2O3 photoanode is intrinsically modified with oxygen vacancies and β-Fe2O3.

[0042] In particular, the present invention also provides a doped α-Fe2O3 photoanode, which is prepared using the aforementioned α-Fe2O3 photoanode preparation method, and the doped α-Fe2O3 photoanode is intrinsically modified with oxygen vacancies and β-Fe2O3.

[0043] In one embodiment, the doped α-Fe 2 O 3 photoanode is a hafnium-doped α-Fe 2 O 3 photoanode, a phosphorus-doped α-Fe 2 O 3 photoanode, or a FeNiOOH-P-Hf-Fe 2 O 3 photoanode.

[0044] According to the scheme of the embodiment of the present invention, the photoanode obtained in the scheme of the present invention has good intrinsic modification and good adaptability. The sample can be well combined with various modifications, such as P treatment to promote surface charge transfer, Hf treatment to improve light absorption efficiency, and deposition of surface FeNiOOH co-catalyst to accelerate OER kinetics. Therefore, all the above treatments can be actively accumulated to obtain an efficient hematite photoanode with a baseline photocurrent of 5.24 mA / cm at 1.23 V vs. RHE. 2 , which could potentially be used for practical solar water splitting in the future.

[0045] Figure 2 A transmission electron microscope image of an α-Fe2O3 photoanode according to one embodiment of the present invention is shown. Figure 3 FIG1 shows a high-resolution transmission electron micrograph of an α-Fe2O3 photoanode according to an embodiment of the present invention. Figure 2 and Figure 3 As shown in the figure, the solution of the present invention has indeed successfully doped β-Fe2O3 into α-Fe2O3. Figure 4 The XRD patterns of the α-Fe2O3 photoanode in the prior art and the α-Fe2O3 photoanode in an embodiment of the present invention are shown, wherein the only difference between the two is that the α-Fe2O3 photoanode in the prior art is not doped with β-Fe2O3. Figure 5 Shown Figure 4 A partially enlarged schematic diagram of . Figure 6 Shown Figure 4 Another part of the schematic enlarged diagram. Figures 4 to 6 It can be seen that the α-Fe2O3 photoanode in the embodiment of the present invention is doped with β-Fe2O3, while the α-Fe2O3 photoanode in the prior art is not doped with β-Fe2O3. It can be understood that in the present invention, the α-Fe2O3 photoanode is not doped with β-Fe2O3, and the main component of the photoanode is still α-Fe2O3, with β-Fe2O3 accounting for a small amount.

[0046] Figure 7The current density and voltage characteristic curve of the α-Fe2O3 photoanode according to one embodiment of the present invention is shown, wherein the one labeled as Fe2O3 represents the α-Fe2O3 photoanode in the prior art, the one labeled as Fe2O3(LV) represents the α-Fe2O3 photoanode intrinsically modified with oxygen vacancies and β-Fe2O3 according to the embodiment of the present invention, and Dark represents the dark current. Figure 7 It can be seen that Fe2O3(LV) exhibits high photoelectrochemical performance. At 1.23V vs.RHE, the photocurrent is 2.72mA / cm 2 .

[0047] Figure 8 The current density and voltage characteristic curve of the doped α-Fe2O3 photoanode according to one embodiment of the present invention is shown, wherein the one labeled as Fe2O3 represents the α-Fe2O3 photoanode in the prior art, the one labeled as Hf-Fe2O3 represents the α-Fe2O3 photoanode doped with hafnium in the prior art, the one labeled as Hf-Fe2O3(LV) represents the α-Fe2O3 photoanode doped with hafnium in the present invention, and Dark represents the dark current. Figure 8 It can be seen that Hf-Fe2O3(LV) exhibits high photoelectrochemical performance. At 1.23V vs.RHE, the photocurrent is 3.69mA / cm 2 , which is much higher than the photoelectrochemical performance of Hf-Fe2O3 in the existing technology.

[0048] Figure 9 A comparison of the current density and voltage characteristic curves of the α-Fe2O3 photoanode and the doped α-Fe2O3 photoanode according to an embodiment of the present invention is shown, wherein the one labeled as Fe2O3 represents the α-Fe2O3 photoanode in the prior art, the one labeled as Fe2O3(LV) represents the intrinsically modified α-Fe2O3 photoanode with oxygen vacancies and β-Fe2O3 according to an embodiment of the present invention, the one labeled as Hf-Fe2O3(LV) represents the α-Fe2O3 photoanode doped with hafnium according to the present invention, the one labeled as P-Hf-Fe2O3(LV) represents the α-Fe2O3 photoanode doped with phosphorus and hafnium according to the present invention, the one labeled as FeNiOOH-P-Hf-Fe2O3(LV) represents the α-Fe2O3 photoanode doped with FeNiOOH, phosphorus and hafnium according to the present invention, and Dark represents the dark current. Figure 9 It can be seen that FeNiOOH-P-Hf-Fe2O3(LV) exhibits the highest photoelectrochemical performance, with a photocurrent of 5.24 mA / cm at 1.23 V vs. RHE. 2 .

[0049] At this point, it should be recognized by those skilled in the art that although a number of exemplary embodiments of the present invention have been shown and described in detail herein, many other variations or modifications that conform to the general principles of the present invention may be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the present invention. Therefore, the scope of the present invention should be understood and deemed to cover all such other variations or modifications.

Claims

1. A method for preparing an α-Fe2O3 photoanode, characterized in that: The steps include: preparing iron oxyhydroxide or doped iron oxyhydroxide on a substrate by a hydrothermal method to obtain an iron oxyhydroxide / substrate sample or a doped iron oxyhydroxide / substrate sample; The ferric oxyhydroxide / substrate sample or the doped ferric oxyhydroxide / substrate sample is annealed under a first annealing condition at a first vacuum degree, and then annealed under a second annealing condition at a second vacuum degree, thereby obtaining an α-Fe2O3 photoanode intrinsically modified with oxygen vacancies and β-Fe2O3 or a doped α-Fe2O3 photoanode intrinsically modified with oxygen vacancies and β-Fe2O3, wherein the first vacuum degree is greater than the second vacuum degree, and the annealing temperature in the first annealing condition is lower than the annealing temperature in the second annealing condition.

2. The method for preparing an α-Fe2O3 photoanode according to claim 1, wherein: The first vacuum degree is any value between 1-10 Pa, and the second vacuum degree is any value between 10 Pa-1 atm.

3. The method for preparing an α-Fe2O3 photoanode according to claim 2, wherein: The first annealing condition is sintering at 500-650°C for 90-180 minutes; The second annealing condition is sintering at 550-760° C. for 10-20 minutes.

4. The method for preparing an α-Fe2O3 photoanode according to any one of claims 1 to 3, characterized in that: The doped iron oxyhydroxide in the doped iron oxyhydroxide / substrate sample is hafnium-doped iron oxyhydroxide.

5. An α-Fe2O3 photoanode, characterized in that The α-Fe2O3 photoanode is prepared using the α-Fe2O3 photoanode preparation method according to any one of claims 1 to 4, wherein the α-Fe2O3 photoanode is intrinsically modified with oxygen vacancies and β-Fe2O3.

6. A doped α-Fe2O3 photoanode, characterized in that The photoanode is prepared using the α-Fe2O3 photoanode preparation method according to any one of claims 1 to 4, wherein the doped α-Fe2O3 photoanode is intrinsically modified with oxygen vacancies and β-Fe2O3.

7. The doped α-Fe2O3 photoanode according to claim 6, characterized in that The doped α-Fe2O3 photoanode is a hafnium-doped α-Fe2O3 photoanode or a phosphorus-doped α-Fe2O3 photoanode.

8. The doped α-Fe2O3 photoanode according to claim 6, characterized in that The doped α-Fe2O3 photoanode is a FeNiOOH-P-Hf-Fe2O3 photoanode.

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