In-situ Ti and non-in-situ Ge co-doped hematite-based photoelectrode, preparation method and application thereof

Abstract

The application discloses an in-situ Ti and non-in-situ Ge co-doped hematite-based photoelectrode and a preparation method and application thereof, and belongs to the technical field of functional materials. The in-situ Ti and non-in-situ Ge co-doped hematite-based photoelectrode is obtained by taking NiFeOOH as a cocatalyst and simultaneously co-doping in-situ Ti and non-in-situ Ge. The carrier concentration can be remarkably improved, and the bulk phase separation of photo-generated carriers is promoted.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional materials, and in particular relates to an in-situ Ti and ex-situ Ge co-doped hematite-based photoelectrode and a preparation method and application thereof. Background Art

[0002] Since Fujishima and Honda first placed TiO2 under ultraviolet light to achieve water decomposition in 1972, photoelectrocatalytic (PEC) water splitting technology has been considered an ideal solution for achieving solar energy conversion and storage. PEC overcomes the shortcomings of traditional photocatalytic carriers such as low separation efficiency and difficulty in performing full water splitting. At the same time, unlike traditional electrocatalysis, the most ideal PEC reaction system can achieve photoelectrocatalytic water decomposition by self-driving through light without an external bias. Among them, the water oxidation reaction is the rate-controlling step because it involves a complex four-proton coupled multi-electron process (2H2O+4H + →O2+4H + , E = 1.23 V vs RHE). Therefore, the study of the water oxidation process is very necessary. Among the many photoanode materials, hematite has received widespread attention since it was first studied in 1976. The reason is that hematite has excellent properties such as a band gap suitable for absorbing visible light, excellent stability in electrolyte solutions (pH = 4-14), high natural abundance and non-toxicity. However, factors such as poor conductivity (about 10-14 S / cm), limited hole diffusion length (2-4 nm), limited charge carrier lifetime and slow oxidation reaction (OER) kinetics have hindered the application of hematite in PEC.

[0003] Doping, as an excellent modification technique, can improve PEC performance in three ways: increasing carrier concentration to improve conductivity, enhancing the separation efficiency of photogenerated carriers, and modulating the band structure to expand the absorption range. Titanium is an effective dopant that can increase carrier concentration and thus conductivity. However, the advantages of titanium doping are relatively limited due to the recombination of electrons and holes. Some believe that titanium doping reduces the number of active sites on the hematite surface, thereby affecting PEC performance. How to promote the separation of holes and electrons remains a challenge. Compared with single doping, recent research has focused more on the co-doping strategy of two foreign elements, which can further improve the photocurrent density. Summary of the Invention

[0004] To address the above technical issues, the present invention proposes a hematite (α-Fe2O3)-based photoelectrode co-doped with in-situ Ti and ex-situ Ge, as well as its preparation method and application. This method utilizes in-situ Ti doping and ex-situ Ge doping to significantly increase carrier concentration and promote bulk phase separation of photogenerated carriers. This method offers numerous advantages, including simple preparation, convenient operation, and easily controllable experimental conditions. These features make it widely applicable and feasible for scientific research and industrial applications.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] The invention discloses an in-situ Ti and non-in-situ Ge co-doped hematite-based photoelectrode. NiFeOOH is used as a co-catalyst. In-situ Ti and non-in-situ Ge co-doped hematite are used to obtain the in-situ Ti and non-in-situ Ge co-doped hematite-based photoelectrode.

[0007] The present invention also provides a method for preparing an in-situ Ti and ex-situ Ge co-doped hematite-based photoelectrode, comprising the following steps:

[0008] Dissolving an iron salt and a titanium salt in deionized water to obtain a precursor solution; subjecting the precursor solution to a hydrothermal reaction with a conductive glass to grow a precursor titanium-doped FeOOH on the conductive glass to obtain a precursor photoelectrode (denoted as Ti-FeOOH);

[0009] The precursor photoelectrode is immersed in a germanium precursor solution, and then taken out and dried. The obtained Ti-Ge co-doped hematite-based photoelectrode (denoted as Ti,Ge-FeOOH) is annealed and calcined to obtain a Ti,Ge-Fe2O3 photoelectrode;

[0010] NiFeOOH is deposited on the Ti, Ge-Fe2O3 photoelectrode by an electrodeposition method to obtain a NiFeOOH / Ti, Ge-Fe2O3 photoelectrode material.

[0011] Furthermore, the molar ratio of the iron salt to the titanium salt is (1000-1500):1.

[0012] Furthermore, the iron salt is ferric chloride hexahydrate or ferric sulfate; and the titanium salt is titanium chloride with a mass concentration of 15-20 wt%.

[0013] Furthermore, the conditions of the hydrothermal reaction are: hydrothermal reaction at 90-120° C. for 3-5 hours.

[0014] Furthermore, the germanium precursor solution is a germanium dioxide solution with a concentration of 30-50 mmol / L; and the immersion time is 15-30 min.

[0015] Furthermore, the annealing and calcining conditions are: calcining at 400-600°C for 1-3h in the first stage, with a heating rate of 1-10°C / min; and calcining at 700-800°C for 10-30min in the second stage, with a heating rate of 1-10°C / min.

[0016] Furthermore, the electrolyte used in the deposition process is a mixed solution of ferric chloride, nickel chloride, sodium fluoride, potassium chloride and hydrogen peroxide.

[0017] The present invention also provides application of the in-situ Ti and ex-situ Ge co-doped hematite-based photoelectrode in photoelectrocatalytic water decomposition.

[0018] Compared with the prior art, the present invention has the following advantages and technical effects:

[0019] (1) The present invention provides a preparation method of hematite co-doped with Ti in situ and Ge non-in situ, wherein the in situ doping of Ti increases the carrier concentration, and the non-in situ doping of Ge increases the separation efficiency of bulk carriers, which can effectively improve the photoelectrochemical water oxidation capacity.

[0020] (2) The NiFeOOH / Ti,Ge-Fe2O3 photoelectrode provided by the present invention has a photoelectrocatalytic reaction activity under simulated sunlight that is about 9.5 times that of blank Fe2O3 and has good stability.

[0021] (3) The NiFeOOH / Ti,Ge-Fe2O3 photoelectrode provided by the present invention is simple and convenient to operate, provides a new photoelectrocatalytic anode material for water decomposition, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0023] Figure 1 XRD comparison diagrams of Fe2O3, Ti, Ge-Fe2O3 and NiFeOOH / Ti, Ge-Fe2O3 in Example 1, Ti-Fe2O3 in Comparative Example 1 and Ge-Fe2O3 in Comparative Example 2;

[0024] Figure 2 It is a partial enlarged view of the XRD comparison diagram of Fe2O3, Ti,Ge-Fe2O3 and NiFeOOH / Ti,Ge-Fe2O3 in Example 1, Ti-Fe2O3 in Comparative Example 1 and Ge-Fe2O3 in Comparative Example 2;

[0025] Figure 3SEM images of the morphology of Ti,Ge-Fe2O3 and NiFeOOH / Ti,Ge-Fe2O3 in Example 1,

[0026] Figure 4 HRTEM images of Ti,Ge-Fe2O3 and NiFeOOH / Ti,Ge-Fe2O3 in Example 1;

[0027] Figure 5 Photocurrent density plots of Fe2O3, Ti,Ge-Fe2O3 and NiFeOOH / Ti,Ge-Fe2O3 in Example 1 and Ti-Fe2O3 in Comparative Example 1 and Ge-Fe2O3 in Comparative Example 2;

[0028] Figure 6 Open circuit voltage (OPC) plots of Fe2O3, Ti,Ge-Fe2O3 and NiFeOOH / Ti,Ge-Fe2O3 in Example 1 and Ti-Fe2O3 in Comparative Example 1 and Ge-Fe2O3 in Comparative Example 2;

[0029] Figure 7 Charge separation efficiency and charge injection efficiency plots of Fe2O3, Ti,Ge-Fe2O3 and NiFeOOH / Ti,Ge-Fe2O3 in Example 1 and Ti-Fe2O3 in Comparative Example 1 and Ge-Fe2O3 in Comparative Example 2;

[0030] Figure 8 Hydrogen and oxygen evolution and corresponding Faradaic efficiency of Fe2O3, Ti,Ge-Fe2O3 and NiFeOOH / Ti,Ge-Fe2O3 in Example 1 and Ti-Fe2O3 in Comparative Example 1 and Ge-Fe2O3 in Comparative Example 2. DETAILED DESCRIPTION

[0031] Various illustrative embodiments of the present application are now described in detail below. The following description includes specific details for the purpose of providing a thorough understanding of the present application. However, it will be apparent to those skilled in the art that the present application can be practiced without these specific details. In other instances, well-known structures and functions have not been described in detail in order to avoid obscuring the understanding of the present application.

[0032] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. Additionally, for a range of values of a parameter, unless otherwise indicated, each intervening value by each intervening value, as well as any other stated or intervening value in that stated range is encompassed. In addition, any combination of the above values, as well as any other stated or intervening value in that stated range is encompassed. Unless otherwise stated, the above-mentioned ranges are inclusive of the recited endpoints. The above-mentioned ranges are also inclusive of any values 'that fail within the stated ranges.

[0033] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0034] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0035] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0036] The present invention provides a hematite (α-Fe2O3)-based photoelectrode with NiFeOOH as a co-catalyst and in-situ Ti and non-in-situ Ge co-doping, as well as a preparation method and application thereof. Among them, the in-situ doping of Ti increases the carrier concentration and improves the conductivity of the electrode. The non-in-situ doping of Ge increases the separation efficiency of bulk carriers. The dopant in the non-in-situ doping method is concentrated on the surface and dispersed in a gradient form, generating a built-in electric field, which promotes the effective separation of electrons and holes. Especially under low voltage. At the same time, the loading of NiFeOOH improves the kinetics of the reaction. The present invention uses NiFeOOH as a co-catalyst and Ti-Ge co-doped hematite photoelectrode to greatly improve the photoelectrocatalytic water decomposition performance.

[0037] The method for preparing the in-situ Ti and ex-situ Ge co-doped hematite-based photoelectrode comprises the following steps:

[0038] 1) dissolving an iron salt and a titanium salt in deionized water and stirring to obtain a precursor solution; placing the precursor solution and conductive glass FTO in a hydrothermal reactor, and growing a precursor Ti-doped FeOOH on the conductive glass FTO through a hydrothermal reaction to obtain a precursor photoelectrode (denoted as Ti-FeOOH);

[0039] 2) immersing the precursor photoelectrode in a germanium precursor solution, and then taking it out and drying it to obtain a Ti-Ge co-doped hematite-based photoelectrode (denoted as Ti,Ge-FeOOH);

[0040] 3) annealing and calcining the Ti-Ge co-doped hematite-based photoelectrode at a certain temperature in a tube furnace to obtain a Ti, Ge-Fe2O3 photoelectrode;

[0041] 4) depositing NiFeOOH on the Ti, Ge-Fe2O3 photoelectrode by electrodeposition to obtain a NiFeOOH / Ti, Ge-Fe2O3 photoelectrode material.

[0042] In step 1) of the following preferred embodiment of the present invention, the molar ratio of the iron salt to the titanium salt is (1000-1500):1 (because the concentration of the purchased titanium trichloride standard itself is 15-20wt%, so it can only be a range). The iron salt is ferric chloride hexahydrate or ferric sulfate, preferably ferric chloride hexahydrate; the titanium salt is titanium trichloride with a mass concentration of 15-20wt% (purchased from Anaiji). The conditions of the hydrothermal reaction are: hydrothermal reaction at 90-120°C for 3-5h, preferably hydrothermal reaction at 100°C for 3h.

[0043] In step 2) of the following preferred embodiment of the present invention, the germanium precursor solution is a germanium dioxide solution with a concentration of 30-50 mmol / L, preferably 40 mmol / L; the immersion time is 15-30 min, preferably 30 min.

[0044] In step 3) of the following preferred embodiment of the present invention, the annealing and calcination conditions are: in the first stage, calcination at 400-600°C (preferably 550°C) for 1-3h (preferably 2h) with a heating rate of 1-10°C / min (preferably 10°C / min); in the second stage, calcination at 700-800°C (preferably 730°C) for 10-30min (preferably 15min) with a heating rate of 1-10°C / min (preferably 10°C / min).

[0045] In step 4) of the following preferred embodiment of the present invention, the electrolyte used in the deposition process includes ferric chloride hexahydrate solution, nickel chloride hexahydrate solution, sodium fluoride solution, potassium chloride solution, and 30 wt% hydrogen peroxide solution in a molar ratio of 5:3:5:100:100. The applied voltage is -0.49 to 0.41 V vs. Ag / AgCl, and the number of cycles is 3. Cyclic voltammetry is used for electrodeposition, with 3 deposition cycles.

[0046] The in-situ Ti and ex-situ Ge co-doped hematite-based photoelectrode can be applied to photoelectrocatalytic water splitting.

[0047] The raw materials used in the present invention are all purchased from the market.

[0048] The technical solution of the present invention is further illustrated by the following examples.

[0049] Example 1

[0050] Preparation of in-situ Ti and non-in-situ Ge co-doped hematite-based photoelectrode:

[0051] 1) Preparation of Ti-FeOOH photoelectrode

[0052] 0.8109 g of iron trichloride hexahydrate was weighed into 20 mL of deionized water, then 2 uL of 15-20 wt% TiCl3 solution was added, and the mixture was stirred and dissolved to make it uniform (the molar ratio of iron salt to titanium salt was (1000-1500): 1); the obtained mixed solution was added to a 50 mL polytetrafluoroethylene-lined reaction kettle together with conductive glass FTO, and hydrothermal reaction was carried out at 100°C for 3 h; after cooling, it was taken out, the FeOOH adsorbed on the non-conductive surface was scraped off, and then it was dried in a drying box at 60°C for 60 min to obtain a precursor photoelectrode, which was recorded as Ti-FeOOH photoelectrode;

[0053] 2) Preparation of Ti,Ge-FeOOH photoelectrode

[0054] The Ti-FeOOH photoelectrode was soaked in a 40 mmol / L germanium dioxide solution for 30 min, naturally air-dried, and then placed in a tube furnace for annealing and calcination; the specific process was as follows: the temperature was raised to 550°C at a rate of 10°C / min, calcined for 2 h, then raised to 730°C at the same rate of 10°C / min, calcined for 15 min, and then naturally cooled to obtain a Ti,Ge-Fe2O3 photoelectrode;

[0055] 3) Preparation of covalently bridged NiFeOOH / Ti,Ge-Fe2O3 photoelectrode

[0056] In order to prepare the FeNiOOH modified electrode, a cathodic electrodeposition method was used, and the deposition electrolyte solution contained 5 mM of FeCl3, 3 mM of NiCl2, 5 mM of NaF, 0.1 M of NaCl and 0.1 M of H2O2. Specifically, the Ti,Ge-Fe2O3 photoelectrode was placed in the electrodeposition solution (i.e. the deposition electrolyte solution), and was gently stirred during the synthesis process. The potential was cycled between -0.49 and 0.41 V at a scan rate of 200 mV s -1 , and cyclic scanning was performed 3 times to obtain a NiFeOOH / Ti,Ge-Fe2O3 photoelectrode material.

[0057] Comparative Example 1

[0058] Preparation of Ti-Fe2O3 photoelectrode:

[0059] 1) Preparation of Ti-FeOOH photoelectrode was the same as in Example 1;

[0060] 2) Preparation of Ti-Fe2O3 photoelectrode: The Ti-FeOOH photoelectrode was put into a tube furnace for annealing calcination, and the specific process was as follows: the temperature was raised to 550℃ at a rate of 10℃ / min, calcined for 2h, then raised to 730℃ at the same rate of 10℃ / min, calcined for 15min, and then naturally cooled to obtain the Ti-Fe2O3 photoelectrode.

[0061] Comparative Example 2

[0062] Preparation of Ge-Fe2O3 photoelectrode: 1*1cm 2 FeOOH was soaked in a 40mmol / L germanium dioxide solution for 30min, naturally dried, and then put into a tube furnace for annealing calcination, and the specific process was as follows: the temperature was raised to 550℃ at a rate of 10℃ / min, calcined for 2h, then raised to 730℃ at the same rate of 10℃ / min, calcined for 15min, and then naturally cooled to obtain the Ge-Fe2O3 photoelectrode.

[0063] Figure 1 XRD comparison chart of Fe2O3, Ti, Ge-Fe2O3 and NiFeOOH / Ti, Ge-Fe2O3 in Example 1 and Ti-Fe2O3 in Comparative Example 1 and Ge-Fe2O3 in Comparative Example 2. Figure 2 Figure 1 Figure 1 As can be seen from Figure 2 , whether Ge-doped, Ti-doped or Ge-Ti co-doped, the same hematite (JCPDS No. 33-0664) and FTO (F-SnO2) crystal structures are exhibited, and no new phase appears. This indicates that the doping does not significantly disturb the original crystal orientation of hematite, thereby maintaining the transfer of electrons along the (110) direction. In addition, the XRD enlarged image

[0064] Figure 3 Morphology SEM image of Ti, Ge-Fe2O3 and NiFeOOH / Ti, Ge-Fe2O3 in Example 1, from which it can be observed that the hematite photoanode presents a nanorod structure at the position marked with a yellow dashed line.

[0065] Figure 4 HRTEM image of Ti, Ge-Fe2O3 and NiFeOOH / Ti, Ge-Fe2O3 in Example 1. From the HRTEM image, the nanorod structure can also be seen. The flakes and a thin layer of material on the nanorod are clearly visible, which indicates that the electrodeposition of NiFeOOH is successful.

[0066] ​​Application Example 1

[0067] The Fe2O3, Ti,Ge-Fe2O3 and NiFeOOH / Ti,Ge-Fe2O3 in Example 1, the Ti-Fe2O3 in Comparative Example 1 and the Ge-Fe2O3 in Comparative Example 2 were subjected to linear sweep voltammetry (LSV), open circuit voltage (OCP), electrochemical impedance spectroscopy and water decomposition performance tests.

[0068] All electrochemical experimental tests were conducted in a three-electrode electrochemical workstation (Shanghai Chenhua CHI760E). The hematite-based photoanode was used as the working electrode, the platinum sheet was used as the counter electrode, the Ag / AgCl was used as the reference electrode, the electrolyte was 1 M potassium hydroxide solution, and the sample illumination area was 1 cm 2 The water decomposition test uses gas chromatography (GC-9A) to detect the content of hydrogen and oxygen at regular intervals.

[0069] The light source in the photocurrent density test is a 300W xenon lamp, under the conditions of simulated sunlight, simulated sunlight AM1.5G, 100mW / cm 2 , the external bias voltage is 1.23Vvs RHE, the potential fluctuates from 0.6Vvs RHE to 1.6Vvs RHE, the test results are shown in Figure 5 .from Figure 5 It can be seen that the photocurrent densities of Fe2O3, Ge-Fe2O3, Ti-Fe2O3, Ti,Ge-Fe2O3 and NiFeOOH / Ti,Ge-Fe2O3 photoanodes at 1.23 V vs RHE are 0.31, 1.21, 1.26, 2.19 and 2.94 mA cm, respectively. -2 Notably, the photocurrents of the Ge-Fe2O3, Ti-Fe2O3, Ti, Ge-Fe2O3, and NiFeOOH / Ti, Ge-Fe2O3 photoanodes are 3.9, 4.1, 7.1, and 9.5 times that of the Fe2O3 photoanode, respectively. Furthermore, it is worth noting that Ge-Fe2O3 exhibits superior performance at low voltages compared to Fe2O3 and Ti-Fe2O3. Specifically, at the same potential, the photocurrent of Ge-Fe2O3 at 1.0 V vs RHE is approximately 4.3 times that of Fe2O3.

[0070] The open circuit potential test condition is that under light illumination, the open circuit potential is negative. However, when the light is turned off, the potential quickly shifts to the positive direction due to the photoinduced potential generated by the charge carriers. The larger voltage difference (OCP) observed when the light source is turned off means that there are fewer defect states and larger energy band bending. This in turn is conducive to promoting charge separation. Specifically, the order of OCP size of several materials is as follows: blank Fe2O3<Ti-Fe2O3<Ti,Ge-Fe2O3<Ge-Fe2O3<NiFeOOH / Ti,Ge-Fe2O3 (see Figure 6 ).

[0071] In order to further investigate the effects of uniform and gradient doping on charge carrier separation and transfer characteristics, 0.1 M Na2SO3 was added to 1 M KOH solution as a hole scavenger, and the charge separation efficiency (η separation ) and charge injection efficiency (η injection ), η separation represents the proportion of holes that reach the photoelectrode / electrolyte interface without undergoing recombination in the bulk material. injection It represents the ratio of holes successfully injected into water oxidation at the interface. The separation efficiency of photogenerated carriers and the charge injection efficiency are shown in Figure 7 . It can be seen that the charge separation efficiency and hole injection efficiency of the doped photoelectrode material are improved under the condition of 1.23VvsRHE. Among them, the charge separation efficiency and charge injection efficiency of Ti-Ge co-doped hematite are the highest compared with single doping. This shows that Ti-Ge co-doping can synergistically improve the charge separation efficiency and charge injection efficiency. Interestingly, the performance of Ge-Fe2O3 is significantly improved in the lower potential range, especially compared with 0.7-1.1VvsRHE. This phenomenon may be due to the fact that the gradient doping of Ge generates an intrinsic electric field in hematite, which provides an additional driving force for charge carrier separation.

[0072] The light source for the water decomposition hydrogen production test was a 300W xenon lamp with a bias voltage of 1.23V vs RHE. The measured results are as follows: Figure 8 As shown, in the 150-min test of NiFeOOH / Ti,Ge-Fe2O3 prepared in Example 1, the production of hydrogen and oxygen was basically in a ratio of 2:1, and the Faraday efficiency reached more than 98%.

[0073] Table 1 shows the carrier concentrations of Fe2O3, Ge-Fe2O3, Ti-Fe2O3, Ti,Ge-Fe2O3 and NiFeOOH / Ti,Ge-Fe2O3 prepared in Example 1, Comparative Example 1 and Comparative Example 2.

[0074] Table 1

[0075]

[0076] As can be seen from Table 1, the doping of Ti significantly improves the carrier concentration, and the Ti-Ge co-doping further improves the carrier concentration.

[0077] Comparative Example 3

[0078] The same as Example 1, except that the germania solution is replaced with an equal volume of MgCl2solution.

[0079] The photo-current density of the product Ti,Mg-Fe2O3 prepared in this comparative example at 1.23 V vs RHE is reduced by 0.78 mA cm-2compared with Example 1. -2 .

[0080] Comparative Example 4

[0081] The same as Example 1, except that the germania solution is replaced with an equal volume of ruthenium acetylacetonate solution.

[0082] The photo-current density of the product Ti,Ru-Fe2O3 prepared in this comparative example at 1.23 V vs RHE is reduced by 0.50 mA cm-2compared with Example 1. -2 .

[0083] The above, only for the preferred specific embodiments of the present application, but the scope of protection of the present application is not limited to this, any skilled in the art of the technical personnel in the technical range disclosed in the present application, can easily think of changes or replacement, should be covered in the scope of protection of the present application. Therefore, the scope of protection of the present application should be subject to the scope of protection of the claims.

Claims

1. An in-situ Ti and ex-situ Ge co-doped hematite-based photoelectrode, characterized in that: Using NiFeOOH as a co-catalyst, in situ Ti and ex situ Ge co-doped hematite simultaneously to obtain in situ Ti and ex situ Ge co-doped hematite-based photoelectrode; The method for preparing the in-situ Ti and ex-situ Ge co-doped hematite-based photoelectrode comprises the following steps: Dissolving an iron salt and a titanium salt in deionized water to obtain a precursor solution; subjecting the precursor solution to a hydrothermal reaction with a conductive glass to grow a precursor titanium-doped FeOOH on the conductive glass to obtain a precursor photoelectrode; Immersing the precursor photoelectrode in a germanium precursor solution, then taking it out, drying it, and annealing and calcining it to obtain a Ti,Ge-Fe2O3 photoelectrode; NiFeOOH is deposited on the Ti, Ge-Fe2O3 photoelectrode by an electrodeposition method to obtain a NiFeOOH / Ti, Ge-Fe2O3 photoelectrode material.

2. A method for preparing an in-situ Ti and ex-situ Ge co-doped hematite-based photoelectrode according to claim 1, characterized in that: The following steps are involved: Dissolving an iron salt and a titanium salt in deionized water to obtain a precursor solution; subjecting the precursor solution to a hydrothermal reaction with a conductive glass to grow a precursor titanium-doped FeOOH on the conductive glass to obtain a precursor photoelectrode; Immersing the precursor photoelectrode in a germanium precursor solution, then taking it out, drying it, and annealing and calcining it to obtain a Ti,Ge-Fe2O3 photoelectrode; NiFeOOH is deposited on the Ti, Ge-Fe2O3 photoelectrode by an electrodeposition method to obtain a NiFeOOH / Ti, Ge-Fe2O3 photoelectrode material.

3. The method for preparing an in-situ Ti and ex-situ Ge co-doped hematite-based photoelectrode according to claim 2, characterized in that: The molar ratio of the iron salt to the titanium salt is (1000-1500):

1.

4. The method for preparing an in-situ Ti and ex-situ Ge co-doped hematite-based photoelectrode according to claim 3, characterized in that: The iron salt is ferric chloride hexahydrate or ferric sulfate; the titanium salt is titanium chloride with a mass concentration of 15-20wt%.

5. The method for preparing an in-situ Ti and ex-situ Ge co-doped hematite-based photoelectrode according to claim 2, characterized in that: The conditions of the hydrothermal reaction are: hydrothermal reaction at 90-120° C. for 3-5 hours.

6. The method for preparing an in-situ Ti and ex-situ Ge co-doped hematite-based photoelectrode according to claim 2, characterized in that: The germanium precursor solution is a germanium dioxide solution with a concentration of 30-50 mmol / L; the immersion time is 15-30 minutes.

7. The method for preparing an in-situ Ti and ex-situ Ge co-doped hematite-based photoelectrode according to claim 2, characterized in that: The annealing and calcining conditions are as follows: the first stage is calcining at 400-600°C for 1-3h with a heating rate of 1-10°C / min; the second stage is calcining at 700-800°C for 10-30min with a heating rate of 1-10°C / min.

8. The method for preparing an in-situ Ti and ex-situ Ge co-doped hematite-based photoelectrode according to claim 2, characterized in that: The electrolyte used in the electrodeposition process is a mixed solution of ferric chloride, nickel chloride, sodium fluoride, potassium chloride and hydrogen peroxide.

9. Use of the in-situ Ti and ex-situ Ge co-doped hematite-based photoelectrode as claimed in claim 1 in photoelectrocatalytic water splitting.

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