A photochargeable homojunction electrode based on water-soluble carbon-rich carbon nitride polymer and its preparation method and application

Abstract

The present invention relates to a photochargeable homojunction electrode based on a water-soluble carbon-rich carbon nitride polymer, and a preparation method and application thereof, and belongs to the field of solar photovoltaic conversion and storage technology. The present invention provides a photochargeable homojunction electrode based on a water-soluble carbon-rich carbon nitride polymer, which is composed of a substrate layer, an electron transport layer, and a homojunction layer from bottom to top. The carbon-rich carbon nitride CNx and the carbon-rich carbon nitride CNy used to construct the homojunction layer are water-soluble, and the dispersibility is improved, which helps to form an effective interface; at the same time, the two are isomers, and have the dual functions of photoelectric conversion and charge storage. The structural matching helps to form a closely contacted homojunction, and the built-in electric field of the internal interface of the homojunction separates the photogenerated electron holes, which can realize the electronic cycle of the battery itself, without adding an electron sacrificial agent to the electrolyte. The battery prepared with the electrode can obtain a capacity of 200 to 500C / g under AM1.5 solar irradiation.

Description

Technical Field

[0001] The present invention belongs to the technical field of solar photovoltaic conversion and storage, and relates to a photochargeable homojunction electrode based on a water-soluble carbon-rich carbon nitride polymer, and a preparation method and application thereof. Background Art

[0002] Energy storage devices such as supercapacitors, lithium (sodium / potassium) ion batteries, zinc ion capacitors, and fuel cells have been widely studied as energy output terminals of photovoltaic technology. At present, the hybrid energy system of solar cells and energy storage devices can achieve the simplest structure by sharing the counter electrode. However, due to problems such as potential window matching, battery connection impedance, and circuit design, the system still faces severe challenges in terms of improving energy conversion efficiency, simplifying devices, circuit structure, and reducing production energy consumption. In other words, the complexity of the hybrid energy system seriously hinders the improvement of its performance. In order to solve this problem, the development of photorechargeable electrode materials with dual functions of photoelectric conversion and charge storage has become the forefront of research in this field.

[0003] In photochargeable electrode materials, photoelectric conversion and charge storage occur simultaneously, and different electrode reaction kinetics or reaction active sites / regions are coordinated with each other, which is the most direct solution to achieve solar photovoltaic storage, minimizing the electron loss caused by circuit connection, and there is no problem of matching the potential window of photovoltaic electrode and energy storage electrode. Since S. Kalasina et al. reported in 2016 that Co(OH)2 with a band gap value of 2.85eV can produce pseudocapacitive behavior under light, various electrode materials with photochargeable effect have been developed one after another. In recent years, carbon nitride photochargeable electrode materials have been studied the most, but they are still in the research and development stage, the preparation technology of electrodes is not yet mature, and their photocharging capacity is at a level below 100C / g.

[0004] Carbon nitride is an organic semiconductor polymer with heptazine ring as the structural unit, which forms a two-dimensional molecular network through polycondensation. Its photochargeable performance comes from the molecular skeleton formed by carbon-nitrogen conjugated double bonds (provided by heptazine rings). The conjugation effect of the π bond supports the delocalized movement of electrons in the entire skeleton and increases the life span, thereby realizing the charge accumulation in carbon nitride. The biggest problem facing carbon nitride in the field of optoelectronic technology is the significant recombination effect of photogenerated charges, which leads to low photogenerated charge yield, thus hindering the improvement of charging performance. In order to promote the separation of photogenerated charges and increase the storage capacity of carbon nitride photorechargeable batteries, there are currently two commonly used technical solutions: one is to construct a heterojunction formed by carbon nitride and other materials; the other is to add an electron sacrificial agent to the electrolyte solution. Since the formation of a heterojunction requires the two materials to form a close contact interface, the matching of the material structure is required to be high. However, the commonly used carbon nitride materials are not water-soluble, which makes it difficult to improve their dispersibility and increase the difficulty of forming an effective interface with other materials. In addition, the materials that can form an effective heterojunction with carbon nitride do not have the dual functions of photoelectric conversion and charge storage. Therefore, the constructed heterojunction has no obvious effect on improving the photocharging performance. Although adding an electron sacrificial agent to the electrolyte and transferring holes in time effectively improves the separation of photogenerated charges, it cannot meet the actual needs of rechargeable battery recycling. Therefore, in order to improve the deficiencies of the existing technology, it is necessary to develop a new type of carbon nitride photochargeable electrode material. Summary of the invention

[0005] In view of this, one of the objects of the present invention is to provide a photochargeable homojunction electrode based on a water-soluble carbon-rich carbon nitride polymer; a second object of the present invention is to provide a method for preparing a photochargeable homojunction electrode based on a water-soluble carbon-rich carbon nitride polymer; a third object of the present invention is to provide the application of a photochargeable homojunction electrode based on a water-soluble carbon-rich carbon nitride polymer in a photoelectrochemical cell.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] 1. A photochargeable homojunction electrode based on a water-soluble carbon-rich carbon nitride polymer, the electrode consisting of a substrate layer, an electron transport layer, and a homojunction layer from bottom to top;

[0008] The lower layer in the homogeneous junction layer is a carbon-rich carbon nitride CNx layer, and the upper layer is a carbon-rich carbon nitride CNy layer; x and y in the carbon-rich carbon nitride CNx layer and the carbon-rich carbon nitride CNy layer are both relative content ratios of C=C-C groups and C=N-C groups in the carbon-rich carbon nitride, 1.5≤x≤4, 1≤y≤1.4.

[0009] Preferably, the substrate layer is one of conductive glass FTO and conductive glass ITO; the material of the electron transport layer is titanium dioxide nanofilm.

[0010] Preferably, the carbon-rich carbon nitride is prepared according to the following method:

[0011] (1) Preparation of a reaction system: dinitrile diamine and urea are mixed in a mass ratio of 1:1 to 1:3 to form a mixture, and the mixture is dissolved in water to form a mixed solution;

[0012] (2) hydrothermal reaction: subjecting the mixed solution in step (1) to a hydrothermal reaction to obtain a hydrothermal reaction product;

[0013] (3) aging reaction: storing the hydrothermal product in step (2) at 4 to 30° C. for 2 to 12 months to obtain an aqueous solution of a carbonitride-rich carbon polymer;

[0014] (4) Freeze-drying: The aqueous solution of the carbon-rich carbon nitride polymer in step (3) is freeze-dried at -80°C and a vacuum degree of less than 30 Pa to obtain carbon-rich carbon nitride.

[0015] Preferably, the concentration of the mixture in the mixed solution in step (1) is 0.033 to 0.067 g / mL.

[0016] Preferably, the temperature of the hydrothermal reaction in step (2) is 200-250° C. and the time is 3-4 h.

[0017] 2. A method for preparing the photochargeable homojunction electrode, the method being as follows:

[0018] (1) sintering the electron transport layer material on the base layer to form an electron transport layer;

[0019] (2) mixing carbon-rich carbon nitride CNx and water in a mass ratio of 10000:1, and applying the mixture by scraping or spin coating on the electron transport layer to form a carbon-rich carbon nitride CNx layer on the electron transport layer;

[0020] (3) mixing carbon-rich carbon nitride CNy and water in a mass ratio of 10000:1, and applying the mixture by scraping or spin coating on the carbon-rich carbon nitride CNx layer to form a carbon-rich carbon nitride CNy layer on the carbon-rich carbon nitride CNx layer;

[0021] (4) The product of step (3) is placed in an environment at 25° C. and with a humidity below 30% for 8-24 hours to obtain a photochargeable homojunction electrode based on a water-soluble carbon-rich carbon nitride polymer.

[0022] 3. Application of the photorechargeable homojunction electrode based on water-soluble carbon-rich carbon nitride polymer in photoelectrochemical cells.

[0023] 4. A photoelectrochemical cell, wherein the working electrode of the photoelectrochemical cell is the photochargeable homojunction electrode, the counter electrode is a platinum-loaded conductive glass, and the electrolyte is an acetonitrile solution containing LiI.

[0024] Preferably, the concentration of LiI in the electrolyte is 0.14 g / mL.

[0025] The beneficial effects of the present invention are:

[0026] 1. The present invention discloses a photochargeable homojunction electrode based on a water-soluble carbon-rich carbon nitride polymer. The electrode is composed of a substrate layer, an electron transport layer, and a homojunction layer from bottom to top, and has the following advantages: (1) The carbon-rich carbon nitride CNx and the carbon-rich carbon nitride CNy used to construct the electrode homojunction layer are water-soluble and can be mixed with water to form a uniform slurry. They have high film-forming properties and good dispersibility, which helps to form an effective interface; (2) The molecular skeletons of the carbon-rich carbon nitride CNx and the carbon-rich carbon nitride CNy both contain heptazine rings and carbon rings, which are isomers and have dual functions of photoelectric conversion and charge storage; (3) The matching of the material structure in the homojunction layer is conducive to the formation of a close bond. The contacting homojunction, due to the effectiveness of the homojunction in separating the photogenerated charges, can realize the electronic circulation of the battery itself by separating the photogenerated electron holes through the built-in electric field of the internal interface of the homojunction, so there is no need to add an electron sacrificial agent in the electrolyte, meeting the actual needs of the photochargeable technology; (4) in the material synthesis process in the homojunction layer, by adjusting the mass ratio of dinitrile diamine and urea in the material synthesis process to control the ratio of C=CC and C=NC in the carbon-rich carbon nitride molecular structure, thereby realizing the controllable adjustment of the product energy band structure, and by matching carbon-rich carbon nitride materials with different band gaps, HOMO energy values ​​and LUMO energy values, the photocharge capacity can be adjusted within the range of 200 to 500C / g. The photochargeable homojunction electrode based on the water-soluble carbon-rich carbon nitride polymer of the present invention has good application prospects in photoelectrochemical cells.

[0027] 2. The present invention also discloses a method for preparing a photochargeable homojunction electrode based on a water-soluble carbon-rich carbon nitride polymer. The preparation method is simple and easy to operate and can achieve scale-up production.

[0028] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0030] Figure 1 The flowchart of the preparation of the photochargeable homojunction electrode based on the water-soluble carbon-rich carbon nitride polymer in Examples 1-3;

[0031] Figure 2 is a morphology diagram of the photochargeable homojunction electrode in Example 1;

[0032] Figure 3 A diagram showing the structure of a battery composed of the photochargeable homojunction electrode in Example 1;

[0033] Figure 4 The cyclic voltammetric characteristic curve and charge-discharge curve of the battery constructed by the photochargeable CN1.62 / CN1.30 homojunction electrode in Example 1 under light and dark conditions, a is the cyclic voltammetric characteristic curve, and b is the charge-discharge curve;

[0034] Figure 5 The energy band relationship diagram of TiO2 and four carbon-rich carbon nitrides CN1.62, CN1.52, CN1.40 and CN1.30 in Examples 1-3;

[0035] Figure 6 This is a diagram of type II homojunction formed by four carbon-rich carbon nitrides CN1.62, CN1.52, CN1.40 and CN1.30;

[0036] Figure 7 This is a comparison chart of the photocharging capacity of four types of carbon-rich carbon nitrides, CN1.62, CN1.52, CN1.40 and CN1.30, and their combination before and after forming a homojunction electrode. DETAILED DESCRIPTION

[0037] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention 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 invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0038] Example 1

[0039] A photochargeable homojunction electrode based on a water-soluble carbon-rich carbon nitride polymer, the electrode is composed of a FTO conductive glass substrate layer, a titanium dioxide nanofilm layer, a carbon-rich carbon nitride CN1.62 and a carbon-rich carbon nitride CN1.30 homojunction layer from bottom to top. The preparation method of the electrode is as follows:

[0040] (1) Preparation of a reaction system: dinitrile diamine and urea were mixed at a mass ratio of 1:1.9 and 1:3 to form a mixture, and dissolved in water to form a mixed solution with a mixture concentration of 0.048 g / mL and a mixed solution with a mixture concentration of 0.067 g / mL, respectively;

[0041] (2) hydrothermal reaction: the mixed solutions of the two concentrations in step (1) were subjected to hydrothermal reaction at 200° C. for 3 h to obtain hydrothermal reaction product A (the mass ratio of dinitrile diamine to urea was 1:1.9) and hydrothermal reaction product B (the mass ratio of dinitrile diamine to urea was 1:3);

[0042] (3) aging reaction: storing the hydrothermal reaction product A and the hydrothermal reaction product B in step (2) at 20° C. for 4 months to obtain an aqueous solution of the carbon-rich carbon nitride polymer A and an aqueous solution of the carbon-rich carbon nitride polymer B;

[0043] (4) freeze-drying: freeze-drying the aqueous solution of carbon-rich carbon nitride polymer A and the aqueous solution of carbon-rich carbon nitride polymer B in step (3) at -80°C and a vacuum degree of less than 30 Pa to obtain carbon-rich carbon nitride CN1.62 and carbon-rich carbon nitride CN1.30;

[0044] (5) Preparation of electrode: First, the carbon-rich carbon nitride CN1.62 in step (4) and water are mixed in a mass ratio of 10000:1, and the mixture is scraped on a FTO conductive glass substrate layer on the surface of which a layer of titanium dioxide nanofilm is sintered to form a carbon-rich carbon nitride CN1.62 layer; then, the carbon-rich carbon nitride CN1.30 in step (4) and water are mixed in a mass ratio of 10000:1, and the mixture is scraped on the carbon-rich carbon nitride CN1.62 layer to form a carbon-rich carbon nitride CN1.30 layer; finally, the prepared electrode is placed in an environment at 25°C and with a humidity below 30% for 8 hours to obtain a photochargeable CN1.62 / CN1.30 homojunction electrode based on a water-soluble carbon-rich carbon nitride polymer.

[0045] Example 2

[0046] A photochargeable homojunction electrode based on a water-soluble carbon-rich carbon nitride polymer, the electrode is composed of an ITO conductive glass substrate layer, a titanium dioxide nanofilm layer, a carbon-rich carbon nitride CN1.52 layer and a carbon-rich carbon nitride CN1.30 layer from bottom to top. The preparation method of the electrode is as follows:

[0047] (1) Preparation of a reaction system: dinitrile diamine and urea were mixed at a mass ratio of 1:1.5 and 1:3 to form a mixture, and dissolved in water to form a mixed solution with a mixture concentration of 0.042 g / mL and a mixed solution with a mixture concentration of 0.067 g / mL, respectively;

[0048] (2) hydrothermal reaction: the mixed solutions of the two concentrations in step (1) were subjected to hydrothermal reaction at 200° C. for 3 h to obtain hydrothermal reaction product A (the mass ratio of dinitrile diamine to urea was 1:1.5) and hydrothermal reaction product B (the mass ratio of dinitrile diamine to urea was 1:3);

[0049] (3) aging reaction: storing the hydrothermal reaction product A and the hydrothermal reaction product B in step (2) at 20° C. for 5 months to obtain an aqueous solution of the carbon-rich carbon nitride polymer A and an aqueous solution of the carbon-rich carbon nitride polymer B;

[0050] (4) freeze-drying: freeze-drying the aqueous solution of carbon-rich carbon nitride polymer A and the aqueous solution of carbon-rich carbon nitride polymer B in step (3) at -80°C and a vacuum degree of less than 30 Pa to obtain carbon-rich carbon nitride CN1.52 and carbon-rich carbon nitride CN1.30;

[0051] (5) Preparation of electrode: First, the carbon-rich carbon nitride CN1.52 in step (4) and water are mixed in a mass ratio of 10000:1, and the mixture is scraped on an ITO conductive glass substrate layer on the surface of which a layer of titanium dioxide nanofilm is sintered to form a carbon-rich carbon nitride CN1.62 layer; then, the carbon-rich carbon nitride CN1.30 in step (4) and water are mixed in a mass ratio of 10000:1, and the mixture is scraped on the carbon-rich carbon nitride CN1.52 layer to form a carbon-rich carbon nitride CN1.30 layer; finally, the prepared electrode is placed in an environment at 25°C and with a humidity below 30% for 8 hours to obtain a photochargeable CN1.52 / CN1.30 homojunction electrode based on a water-soluble carbon-rich carbon nitride polymer.

[0052] Example 3

[0053] A photochargeable homojunction electrode based on a water-soluble carbon-rich carbon nitride polymer, the electrode is composed of an ITO conductive glass substrate layer, a titanium dioxide nanofilm layer, a carbon-rich carbon nitride CN1.40 layer and a carbon-rich carbon nitride CN1.30 layer from bottom to top. The preparation method of the electrode is as follows:

[0054] (1) Preparation of a reaction system: dinitrile diamine and urea were mixed in a mass ratio of 1:2 and 1:3 to form a mixture, and dissolved in water to form a mixed solution with a mixture concentration of 0.05 g / mL and a mixed solution with a mixture concentration of 0.067 g / mL, respectively;

[0055] (2) hydrothermal reaction: the mixed solutions of the two concentrations in step (1) were subjected to hydrothermal reaction at 200° C. for 3 h to obtain hydrothermal reaction product A (the mass ratio of dinitrile diamine to urea was 1:2) and hydrothermal reaction product B (the mass ratio of dinitrile diamine to urea was 1:3);

[0056] (3) aging reaction: storing the hydrothermal reaction product A and the hydrothermal reaction product B in step (2) at 20° C. for 6 months to obtain an aqueous solution of the carbon-rich carbon nitride polymer A and an aqueous solution of the carbon-rich carbon nitride polymer B;

[0057] (4) freeze-drying: freeze-drying the aqueous solution of carbon-rich carbon nitride polymer A and the aqueous solution of carbon-rich carbon nitride polymer B in step (3) at -80°C and a vacuum degree of less than 30 Pa to obtain carbon-rich carbon nitride CN1.40 and carbon-rich carbon nitride CN1.30;

[0058] (5) Preparation of electrode: First, the carbon-rich carbon nitride CN1.40 in step (4) and water are mixed in a mass ratio of 10000:1, and the mixture is spin-coated on an ITO conductive glass substrate layer on the surface of which a layer of titanium dioxide nanofilm is sintered to form a carbon-rich carbon nitride CN1.40 layer; then, the carbon-rich carbon nitride CN1.30 in step (4) and water are mixed in a mass ratio of 10000:1, and the mixture is spin-coated on the carbon-rich carbon nitride CN1.40 layer to form a carbon-rich carbon nitride CN1.30 layer; finally, the prepared electrode is placed in an environment at 25°C and with a humidity below 30% for 8 hours to obtain a photochargeable CN1.40 / CN1.30 homojunction electrode based on a water-soluble carbon-rich carbon nitride polymer.

[0059] Figure 1 The flowchart of the preparation of photochargeable CN1.62 / CN1.30 homojunction, CN1.52 / CN1.30 homojunction and CN1.40 / CN1.30 homojunction electrodes based on water-soluble carbon-rich carbon nitride polymer in Examples 1-3. Figure 1 It can be seen that different homojunction electrodes are stacked successively from bottom to top according to the base layer, electron transport layer, and homojunction layer (where the carbon-rich carbon nitride CNx in the homojunction layer is the lower layer, the carbon-rich carbon nitride CNy is the upper layer, and x>y).

[0060] Figure 2 This is a morphology image of the photochargeable CN1.62 / CN1.30 homojunction electrode in Example 1; Figure 3 FIG. 1 is a diagram of a battery structure composed of the photochargeable homojunction electrode in Example 1. Figure 2 It can be observed that the electrode is a dark green colloid. Using the photochargeable homojunction electrode as the working electrode and the platinum-loaded conductive glass as the counter electrode, the acetonitrile solution of LiI is injected between the two electrodes to form a battery with a sandwich structure. The battery has a simple structure and can be charged by light when placed under light. The battery is placed under light and dark states for cyclic voltammetry and charge-discharge performance tests. The experimental results are shown in the figure. Figure 4As shown, a is the cyclic voltammetric characteristic curve of the battery under light and dark conditions, and b is the charge and discharge curve of the battery under light and dark conditions. Figure 4 From the graph a in the figure, we can see that the cyclic voltammetry curve of the battery tested under light is a closed curve, indicating that it has charge and discharge behavior, and from the curve we can see that the battery has significant positive and negative current peaks during the charge and discharge process; the cyclic voltammetry curve tested in the dark state is also a closed curve, indicating that it also has charge and discharge behavior, but only has significant negative current peaks, but no significant positive current peaks, indicating that the electrode reactions of the battery under light and dark states are different. Figure 4 It can be seen from Figure b that the battery can be charged to 1V both under light and in the dark, and the charge and discharge capacity under light is significantly higher than that in the dark.

[0061] Figure 5 The energy band relationship diagram of TiO2 and the four carbon-rich carbon nitrides CN1.62, CN1.52, CN1.40 and CN1.30 in Examples 1-3. The four carbon-rich carbon nitride materials CN1.62, CN1.52, CN1.40 and CN1.30 are obtained by hydrothermal treatment, aging and freeze-drying of dinitrile diamine and urea at a mass ratio of 1:1.9, 1:1.5, 1:2 and 1:3 respectively. The ratios of C=C–C and C=N–C in the molecular structures of CN1.62, CN1.52, CN1.40 and CN1.30 are 1.62, 1.52, 1.40 and 1.30 respectively. Figure 5 It can be seen that the LUMO orbital energy values, HOMO orbital energy values ​​and band gap values ​​of TiO2 and the four carbon-rich carbon nitrides are significantly different. Based on this band structure relationship, they can be combined in pairs to construct Figure 6 The homojunction shown.

[0062] Figure 7 The photocharging capacity comparison of four carbon-rich carbon nitrides, CN1.62, CN1.52, CN1.40 and CN1.30, and their combinations before and after forming homojunction electrodes. The photocharging capacity is expressed as mass specific capacitance, and its unit is C / g. Each group of homojunction electrodes is exposed to simulated sunlight, and the illumination condition is AM1.5 (irradiance 100mW cm 2 ) conditions. Figure 7 It can be seen that by matching the four carbon-rich carbon nitride materials differently, the homojunction electrode formed can achieve the adjustment of the photocharging capacity from 200 to 500 C / g.

[0063] In summary, the present invention provides a photochargeable homojunction electrode based on a water-soluble carbon-rich carbon nitride polymer, and a preparation method and application thereof. The electrode is composed of a conductive glass substrate layer, a titanium dioxide nanofilm layer, a carbon-rich carbon nitride CNx layer, and a carbon-rich carbon nitride CNy layer from bottom to top. The carbon-rich carbon nitride CNx and carbon-rich carbon nitride CNy used to construct the electrode are water-soluble, and the dispersibility is improved, which helps to form an effective interface; at the same time, the two are isomers, and have the dual functions of photoelectric conversion and charge storage. The structural matching helps to form a close contact homojunction, and the built-in electric field of the internal interface of the homojunction can separate the photogenerated electron holes to realize the electronic cycle of the battery itself, without adding an electron sacrificial agent to the electrolyte. The battery prepared with this electrode can obtain a capacity of 200 to 500C / g.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A photochargeable homojunction electrode based on a water-soluble carbon-rich carbon nitride polymer, characterized in that: The electrode is composed of a substrate layer, an electron transport layer, and a homojunction layer from bottom to top; The lower layer in the homogeneous junction layer is a carbon-rich carbon nitride CNx layer, and the upper layer is a carbon-rich carbon nitride CNy layer; x and y in the carbon-rich carbon nitride CNx layer and the carbon-rich carbon nitride CNy layer are both relative content ratios of C=C-C groups and C=N-C groups in the carbon-rich carbon nitride, 1.5≤x≤4, 1≤y≤1.

4.

2. The photochargeable homojunction electrode according to claim 1, characterized in that: The substrate layer is one of conductive glass FTO and conductive glass ITO; the material of the electron transport layer is titanium dioxide nano film.

3. The photochargeable homojunction electrode according to claim 1, characterized in that: The carbon-rich carbon nitride is prepared according to the following method: (1) Preparation of a reaction system: dinitrile diamine and urea are mixed in a mass ratio of 1:1 to 1:3 to form a mixture, and dissolved in water to form a mixed solution; (2) hydrothermal reaction: subjecting the mixed solution in step (1) to a hydrothermal reaction to obtain a hydrothermal reaction product; (3) aging reaction: storing the hydrothermal product in step (2) at 4 to 30° C. for 2 to 12 months to obtain an aqueous solution of a carbonitride-rich carbon polymer; (4) Freeze-drying: The aqueous solution of the carbon-rich carbon nitride polymer in step (3) is freeze-dried at -80°C and a vacuum degree of less than 30 Pa to obtain carbon-rich carbon nitride.

4. The photochargeable homojunction electrode according to claim 3, characterized in that: The concentration of the mixture in the mixed solution in step (1) is 0.033-0.067 g / mL.

5. The photochargeable homojunction electrode according to claim 3, characterized in that: The temperature of the hydrothermal reaction in step (2) is 200-250° C. and the time is 3-4 hours.

6. The method for preparing the photochargeable homojunction electrode according to claims 1 to 5, characterized in that: The method is as follows: (1) sintering the electron transport layer material on the base layer to form an electron transport layer; (2) mixing carbon-rich carbon nitride CNx and water in a mass ratio of 10000:1, and applying the mixture by scraping or spin coating on the electron transport layer to form a carbon-rich carbon nitride CNx layer on the electron transport layer; (3) mixing carbon-rich carbon nitride CNy and water in a mass ratio of 10000:1, and applying the mixture by scraping or spin coating on the carbon-rich carbon nitride CNx layer to form a carbon-rich carbon nitride CNy layer on the carbon-rich carbon nitride CNx layer; (4) The product of step (3) is placed in an environment at 25° C. and with a humidity below 30% for 8-24 hours to obtain a photochargeable homojunction electrode based on a water-soluble carbon-rich carbon nitride polymer.

7. Use of the photochargeable homojunction electrode based on the water-soluble carbon-rich carbon nitride polymer as claimed in claim 1 in a photoelectrochemical cell.

8. A photoelectrochemical cell, characterized in that: The working electrode in the photoelectrochemical cell is the photochargeable homojunction electrode according to claims 1 to 5, the counter electrode is a conductive glass loaded with platinum, and the electrolyte is an acetonitrile solution containing LiI.

9. A photoelectrochemical cell according to claim 8, characterized in that: The concentration of LiI in the electrolyte is 0.14 g / mL.

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