C / Co3O4 / TiO2 composite electrode material and preparation method thereof

Abstract

The present invention relates to the field of electrochemical energy storage technology, and specifically to a C / Co3O4 / TiO2 composite electrode material and a preparation method thereof. The present invention utilizes atomic layer deposition technology to first deposit Co3O4 on the surface of activated carbon cloth, and then deposits n-type semiconductor TiO2 on the surface of Co3O4 to form a p-n junction, thereby obtaining a C / Co3O4 / TiO2 composite electrode material having a p-n junction. The p-n junction can not only increase the light absorption of TiO2, promote the separation of photogenerated charges, and allow light energy to participate in the charge and discharge process of the electrode, thereby increasing the specific capacity of the electrode, but the p-n junction can also form a built-in electric field, accelerate the redox reaction process, and promote the charge transfer reaction, thereby making the C / Co3O4 / TiO2 composite electrode material with a p-n junction have a higher specific capacity and rate performance, thereby solving the technical problem of poor specific capacity and rate performance of existing Co3O4.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical energy storage, and in particular to a C / Co3O4 / TiO2 composite electrode material with a pn junction and a preparation method thereof. Background Art

[0002] Co3O4 is a typical pseudocapacitive material. Due to its easy preparation, low cost, stable performance and high theoretical specific capacity of 890 F / g, Co3O4 is an ideal supercapacitor electrode material. 2+ / Co 3+ Reversible redox occurs in the state, forming a layered CoOOH intermediate with a large interlayer spacing in Co(OH)2, which is beneficial to the embedding of ions during the charge storage process and has battery-like Faraday behavior.

[0003] However, in practical applications, the actual specific capacity of Co3O4 is far lower than the theoretical value, leaving much room for improvement. Furthermore, as a semiconductor, Co3O4 has poor conductivity and is not suitable for rapid ion adsorption and desorption processes, which significantly reduces the rate performance of the electrode material and limits its practical application. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a Co3O4 composite electrode material with a pn junction and a preparation method thereof, thereby solving the technical problems of poor specific capacity and rate performance of the existing Co3O4.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] See Figure 1 The present invention provides a method for preparing a C / Co3O4 / TiO2 composite electrode material having a pn junction, comprising the following steps:

[0007] The carbon cloth is immersed in an acidic liquid, and oxygen-containing functional groups are grafted onto the surface of the carbon cloth to obtain an activated carbon cloth; a cobalt source and a first oxygen source are used as deposition precursors, and a first deposition treatment is performed by atomic layer deposition to deposit Co3O4 on the surface of the activated carbon cloth to obtain a C / Co3O4 composite electrode material; a titanium source and a second oxygen source are used as deposition precursors, and a second deposition treatment is performed by atomic layer deposition to deposit TiO2 on the surface of the C / Co3O4 composite electrode material, and the p-type semiconductor Co3O4 and the n-type semiconductor TiO2 form a pn junction to obtain a C / Co3O4 / TiO2 composite electrode material with a pn junction.

[0008] The specific working principle of the present invention is as follows: the present invention uses atomic layer deposition technology to deposit n-type semiconductor TiO2 on the surface of Co3O4 to form a pn junction. This pn junction can not only increase the light absorption of TiO2 and promote the separation of photogenerated charges, so that light energy can participate in the charging and discharging process of the electrode, thereby improving the specific capacity of the electrode; but it can also form a built-in electric field, accelerate the redox reaction process, and promote the charge transfer reaction.

[0009] The possible mechanism of action of the C / Co3O4 / TiO2 electrode is as follows:

[0010] TiO2 + nhv → nh + + ne - .

[0011] Photocatalytic assisted charging process:

[0012] TiO2+ Co3O4+ 4OH - + nhv → TiO2+ 3CoO2+ 2H2O+ (n + 4) e - + nh + .

[0013] Photocatalytic assisted discharge process:

[0014] TiO2+ 3CoO2+ 2H2O + nhv → TiO2+ Co3O4+ 4OH - + (n-4) e - + nh + .

[0015] Optionally, the acidic liquid is sulfuric acid with a mass concentration of 30% to 70% or concentrated nitric acid with a mass concentration of 20% to 50%.

[0016] Optionally, the soaking time of the soaking treatment is 1 day to 4 days.

[0017] Optionally, the deposition temperature of the first deposition process is 150° C. to 200° C., and the number of deposition cycles is 100 to 200 times.

[0018] Optionally, the deposition temperature of the second deposition process is 60° C. to 200° C., and the number of deposition cycles is 5 to 20 times.

[0019] Optionally, the cobalt source is cobaltocene or cobalt acetylacetonate, and the first oxygen source is ozone or water.

[0020] Optionally, the titanium source is titanium isopropoxide or titanium tetrachloride, and the second oxygen source is water.

[0021] Optionally, the oxygen-containing functional group is at least one of a hydroxyl group, a carboxyl group, a carbonyl group, and an ester group. Specifically, the oxygen-containing functional group and the carbon cloth are connected mainly by covalent bonds or surface redox reactions.

[0022] Optionally, in the first deposition process, the pulse time of the cobalt source is 0.5s, the exposure time is 10s, and the purge time is 25s; in the second deposition process, the pulse time of the titanium source is 0.5s, the exposure time is 10s, and the purge time is 25s; in the first deposition process and the second deposition process, the pulse time of the first oxygen source and the second oxygen source is 1s, the exposure time is 10s, and the purge time is 25s.

[0023] The present invention provides a C / Co3O4 / TiO2 composite electrode material with a pn junction, which is prepared by adopting the above-mentioned method for preparing the C / Co3O4 / TiO2 composite electrode material with a pn junction.

[0024] The present invention has the beneficial effect of first depositing Co₃O₄ on an activated carbon cloth surface using atomic layer deposition technology, and then depositing n-type semiconductor TiO₂ on the Co₃O₄ surface to form a pn junction, thereby producing a C / Co₃O₄ / TiO₂ composite electrode material having a pn junction. This pn junction not only increases the light absorption of TiO₂, promoting the separation of photogenerated charges, allowing light energy to participate in the charge and discharge process of the electrode, thereby improving the specific capacity of the electrode, but also forms a built-in electric field, accelerating the redox reaction process and promoting the charge transfer reaction. As a result, the C / Co₃O₄ / TiO₂ composite electrode material having a pn junction has higher specific capacity and rate performance, thereby resolving the technical problem of poor specific capacity and rate performance of the existing Co₃O₄. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the preparation process of a C / Co3O4 / TiO2 composite electrode material with a pn junction provided by the present invention.

[0026] Figure 2 These are scanning electron microscope images of the C / Co3O4 / TiO2 composite electrode material with a pn junction prepared in Example 1 of the present invention at different magnifications. Image a is a 20 μm SEM image, image b is a 10 μm SEM image, image c is a 4 μm SEM image, and image d is a 2 μm SEM image.

[0027] Figure 3X-ray diffraction patterns of the C / Co3O4 composite electrode material and the C / Co3O4 / TiO2 composite electrode material with pn junction prepared in Example 1 provided by the present invention.

[0028] Figure 4 This is an XPS characterization of the C / Co3O4 / TiO2 composite electrode material with a pn junction prepared in Example 1 of the present invention. (a) is the full XPS spectrum, (b) is the high-resolution spectrum of Co2p, (c) is the high-resolution spectrum of O1s, and (d) is the high-resolution spectrum of Ti 2p.

[0029] Figure 5 Statistical graphs of the CV curves of different composite electrode materials provided by the present invention within a scan rate range of 5 mV / s to 100 mV / s. Figure a is a statistical graph of the CV curve of the C / Co3O4 composite electrode material prepared in Example 1 within this scan rate range, and figure b is a statistical graph of the CV curve of the C / Co3O4 / TiO2 composite electrode material with a pn junction prepared in Example 1 within this scan rate range.

[0030] Figure 6 Statistical graphs of the CV curves of different composite electrode materials provided by the present invention within a scan rate range of 300mV / s to 1000mV / s. Figure a is a statistical graph of the CV curve of the C / Co3O4 composite electrode material prepared in Example 1 within this scan rate range, and figure b is a statistical graph of the CV curve of the C / Co3O4 / TiO2 composite electrode material with a pn junction prepared in Example 1 within this scan rate range.

[0031] Figure 7 CV curve statistics of different composite electrode materials provided by the present invention at scan rates of 20mV / s, 50mV / s, 100mV / s, and 300mV / s. Figure a is a CV curve statistical graph at a scan rate of 20mV / s, b is a CV curve statistical graph at a scan rate of 50mV / s, c is a CV curve statistical graph at a scan rate of 100mV / s, and d is a CV curve statistical graph at a scan rate of 300mV / s.

[0032] Figure 8 This is a relationship diagram between the specific capacitance and scanning speed of different composite electrode materials provided by the present invention.

[0033] Figure 9 Characterization diagrams of electrochemical performance of different composite electrode materials provided by the present invention. Among them, a is the CP curve of the C / Co3O4 composite electrode material prepared in Example 1, b is the CP curve of the C / Co3O4 / TiO2 composite electrode material with pn junction prepared in Example 1, and c is the CP curve of different composite electrode materials at a current density of 0.2 mA / cm2 d is the CP curve diagram of different composite electrode materials at open circuit voltage, and d1 is a local enlarged schematic diagram in figure d. DETAILED DESCRIPTION

[0034] In order to solve the above technical problems, the present invention provides a C / Co3O4 / TiO2 composite electrode material and a preparation method thereof. The technical solutions and embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0035] The technical solutions adopted in the present invention are as follows:

[0036] The present invention is described in detail below through specific examples. The examples are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0037] Example 1

[0038] This embodiment provides a method for preparing a C / Co3O4 / TiO2 composite electrode material having a pn junction, comprising the following steps:

[0039] The carbon cloth was immersed in an acidic liquid to graft oxygen-containing functional groups onto its surface. The carbon cloth was then removed and washed three times with alcohol and deionized water to produce an activated carbon cloth. The acidic liquid was 50% concentrated nitric acid and the immersion time was four days.

[0040] A cobalt source and a first oxygen source were used as deposition precursors, and a first deposition process was performed by atomic layer deposition to deposit Co₃O₄ on the surface of the activated carbon cloth to produce a C / Co₃O₄ composite electrode material. The cobalt source was cobaltocene, and the first oxygen source was ozone. The deposition temperature of the first deposition process was 200°C, and the number of deposition cycles was 200.

[0041] A titanium source and a second oxygen source were used as deposition precursors, and a second deposition process was performed using atomic layer deposition. TiO2 was deposited on the surface of the C / Co3O4 composite electrode material. The p-type semiconductor Co3O4 and the n-type semiconductor TiO2 formed a pn junction, producing a C / Co3O4 / TiO2 composite electrode material with a pn junction. The titanium source was titanium isopropoxide, and the second oxygen source was water. The deposition temperature of the second deposition process was 60°C, and the number of deposition cycles was 10.

[0042] Example 2

[0043] This embodiment provides a method for preparing a C / Co3O4 / TiO2 composite electrode material with a pn junction, which differs from Example 1 in that the cobalt source is acetylacetone and the first oxygen source is water.

[0044] Example 3

[0045] This embodiment provides a method for preparing a C / Co3O4 / TiO2 composite electrode material with a pn junction, which differs from Example 1 in that the titanium source is titanium tetrachloride.

[0046] Example 4

[0047] This embodiment provides a method for preparing a C / Co3O4 / TiO2 composite electrode material with a pn junction, which differs from Example 1 in that the cobalt source is acetylacetone and the first oxygen source is water.

[0048] Example 5

[0049] This embodiment provides a method for preparing a C / Co 3 O 4 / TiO 2 composite electrode material with a pn junction. The difference from Example 1 is that the deposition temperature of the first deposition process is 150° C.

[0050] Example 6

[0051] This embodiment provides a method for preparing a C / Co 3 O 4 / TiO 2 composite electrode material with a pn junction. The difference from Example 1 is that the number of deposition cycles in the first deposition process is 100.

[0052] Example 7

[0053] This embodiment provides a method for preparing a C / Co 3 O 4 / TiO 2 composite electrode material with a pn junction. The difference from Example 1 is that the deposition temperature of the second deposition process is 200° C.

[0054] Example 8

[0055] This embodiment provides a method for preparing a C / Co 3 O 4 / TiO 2 composite electrode material with a pn junction. The difference from Example 1 is that the number of deposition cycles in the second deposition process is 5.

[0056] Example 9

[0057] This embodiment provides a method for preparing a C / Co 3 O 4 / TiO 2 composite electrode material with a pn junction. The difference from Example 1 is that the number of deposition cycles in the second deposition process is 20.

[0058] Example 10

[0059] This embodiment provides a method for preparing a C / Co3O4 / TiO2 composite electrode material with a pn junction. The difference from Example 1 is that the acidic liquid is concentrated nitric acid with a mass concentration of 20%.

[0060] Example 11

[0061] This embodiment provides a method for preparing a C / Co3O4 / TiO2 composite electrode material with a pn junction. The difference from Example 1 is that the acidic liquid is sulfuric acid with a mass concentration of 30%.

[0062] Example 12

[0063] This embodiment provides a method for preparing a C / Co3O4 / TiO2 composite electrode material with a pn junction. The difference from Example 1 is that the acidic liquid is sulfuric acid with a mass concentration of 70%.

[0064] Example 13

[0065] This embodiment provides a method for preparing a C / Co3O4 / TiO2 composite electrode material with a pn junction, which differs from Example 1 in that the immersion time of the immersion treatment is 1 day.

[0066] It should be noted that, compared with Example 1, there is no significant difference in the performance of the C / Co3O4 / TiO2 composite electrode materials with pn junction prepared in Examples 2 to 13.

[0067] This electrode was used as the working electrode, saturated calomel as the reference electrode, and platinum as the counter electrode. The three electrodes were assembled to perform cyclic voltammetry test, constant current charge-discharge test, and AC impedance test.

[0068] Material surface morphology characterization test and results

[0069] The C / Co3O4 composite electrode material and the C / Co3O4 / TiO2 composite electrode material with a pn junction prepared in Example 1 were subjected to scanning electron microscopy, X-ray diffraction, and XPS spectroscopy tests, respectively, to characterize the surface morphology of the materials.

[0070] The test results are as follows:

[0071] Figure 2 Scanning electron microscope images of the C / Co3O4 / TiO2 composite electrode material with a pn junction, provided by the present invention, at different magnifications. As can be seen in Figures a through d, a large amount of granular material, approximately 2µm to 5µm in size, is evenly dispersed within the gaps between the carbon cloth fibers. This granular material is a pn junction composite material formed by the deposition of Co3O4 and TiO2.

[0072] Figure 3The X-ray diffraction patterns of the C / Co3O4 composite electrode material and the C / Co3O4 / TiO2 composite electrode material with a pn junction provided by the present invention show that the diffraction peaks of both samples at 2θ are around 24.8°, which is mainly the characteristic peak of carbon cloth, indicating that the C / Co3O4 composite electrode material and the C / Co3O4 / TiO2 composite electrode material with a pn junction mainly exist in an amorphous form.

[0073] The chemical composition and state of the C / Co3O4 / TiO2 composite electrode material with pn junction prepared in Example 1 were studied by XPS spectroscopy. Figure 4 shown.

[0074] Among them, the full XPS spectrum of the C / Co3O4 / TiO2 composite electrode material is shown in Figure a. It can be seen from the figure that the sample has a main peak at the binding energy of 287.94eV, 531.88eV, 781.85eV and 454.1eV, respectively corresponding to the XPS spectra of C1s, O1s, Co2p and Ti2p, indicating that Co3O4 / TiO2 was successfully prepared and there are no other impurities in the prepared sample.

[0075] Specifically, the XPS spectrum of Co2p is shown in Figure b. It can be seen from the figure that there are two main peaks at 780.3eV and 795.1eV, corresponding to Co2p3 / 2 and Co2p1 / 2, respectively, and two satellites at 789.8eV and 803.5eV, which are characteristics of the Co3O4 phase. The Co2p3 / 2 peak with a binding energy of 780.3eV can be decomposed into two fitting peaks at 780.3eV and 784.7eV, while the Co2p3 / 2 peak with a binding energy of 795.1eV can be decomposed into two fitting peaks at 794.8eV and 798.8eV.

[0076] The high-resolution O1s spectrum in Figure c shows three fitted peaks at 531.1 eV corresponding to Co-O-Co / Ti-O-Ti, 531.7 eV corresponding to Co-OH / Ti-OH, and 532.9 eV corresponding to CO / C=O, confirming the presence of lattice oxygen, hydroxyl oxygen, and surface oxygen on the surface. The characteristic peaks at 531.1 eV and 531.7 eV are attributed to lattice oxygen and hydroxyl oxygen in TiO2 and Co3O4, while the peak at 532.9 eV corresponds to oxygen adsorbed on the surface of the composite electrode material. The adsorbed oxygen primarily originates from the absorption of hydroxyl groups, water, or oxygen by oxygen vacancies on the sample surface, demonstrating that the immersion treatment of the carbon cloth can indeed graft oxygen-containing functional groups onto the carbon cloth surface. These oxygen vacancies can suppress carrier recombination, thereby enhancing the semiconductor's photoelectric activity.

[0077] Figure d shows the XPS spectrum of Ti2p. It can be seen from the figure that the peaks at 458.7eV and 464.4eV correspond to the binding energies of Ti2p3 / 2 and Ti2p1 / 2, respectively, which indicates that the main state of Ti element in this sample is Ti 4+ .

[0078] Electrochemical performance characterization test and results

[0079] The C / Co3O4 composite electrode material prepared in Example 1 and the C / Co3O4 / TiO2 composite electrode material with a pn junction were used as working electrodes, saturated calomel was used as the reference electrode, and a platinum sheet was used as the counter electrode. A three-electrode system was assembled to perform cyclic voltammetry tests, constant current charge-discharge tests, and AC impedance tests.

[0080] The test results are as follows:

[0081] Figure 5 The CV curve statistics of different composite electrode materials provided by the present invention at a scan rate range of 5mV / s to 100mV / s are shown. Figure 6 The CV curves of different composite electrode materials provided by the present invention are statistically plotted over a scan rate range of 300mV / s to 1000mV / s. As can be seen, the CV curve distortion of the C / Co3O4 composite electrode material and the C / Co3O4 / TiO2 composite electrode material remains essentially unchanged with increasing scan rate, and even at very high scan rates, they maintain a well-defined rectangular shape. This means that when the voltage changes direction, the current quickly reaches its maximum value, indicating that both materials have relatively fast charge and discharge rates and excellent capacitive performance.

[0082] Figure 7 CV curve statistics of different composite electrode materials provided by the present invention at scan rates of 20mV / s, 50mV / s, 100mV / s, and 300mV / s. As can be seen from the figure, when the scan rate is 20mV / s, the CV curves of the C / Co3O4 composite electrode material and the C / Co3O4 / TiO2 composite electrode material both have a pair of redox peaks, and their possible surface oxidation reactions are:

[0083] Co3O4+ OH - + H2O → 3CoOOH + e - ;

[0084] CoOOH + OH - → CoO2 + H2O + e - .

[0085] The possible reduction reactions are:

[0086] CoO2+ H2O + e- → CoOOH + OH - ;

[0087] 3CoOOH + e - → Co3O4+ OH - + H2O.

[0088] When the scan rate increases to 50, 100, and 300 mV / s, the redox peaks on the CV curve of the C / Co3O4 composite electrode material significantly weaken or even disappear, but they still exist on the CV curve of the C / Co3O4 / TiO2 composite electrode material. This is because when the scan rate increases, the reaction speed accelerates, and the ions do not have enough time to undergo redox reactions. Therefore, as the scan rate increases, the oxidation and reduction reaction peaks on the CV curve of the C / Co3O4 composite electrode material gradually disappear. However, when TiO2 is added, since Co3O4 is a p-type semiconductor and TiO2 is an n-type semiconductor, a pn junction is formed between them. The pn junction creates a built-in electric field that promotes charge transfer and accelerates the charge and discharge rate. Therefore, the redox peaks on the CV curve of the C / Co3O4 / TiO2 composite electrode material with a pn junction do not disappear.

[0089] Depend on Figure 8 It can be seen that with the increase of scan rate, the specific capacitance of C / Co3O4 composite electrode material and C / Co3O4 / TiO2 composite electrode material both show a downward trend. Under the same scan rate conditions, the specific capacitance of C / Co3O4 / TiO2 composite electrode material is larger than that of C / Co3O4 composite electrode material. For example, when the scan rate is 5mV / s, the specific capacitance of C / Co3O4 / TiO2 composite electrode material increases from 13.4mF / cm 2 Increased to 16.3 mF / cm 2 This is because semiconductor TiO2 generates a pair of electrons and holes under the action of light. The generated holes oxidize Co3O4 in Co3O4 / TiO2 into CoO2, promoting the separation of photogenerated charges. Light energy participates in the electrode charging and discharging process, thereby increasing the electrode specific capacity.

[0090] Figure 9Characterization diagrams of the electrochemical performance of different composite electrode materials provided by the present invention. As can be seen from Figures a and b, the CP curves of the C / Co3O4 composite electrode material and the C / Co3O4 / TiO2 composite electrode material at different scanning speeds both exhibit an isosceles triangle shape, indicating that the charge and discharge processes of the two materials are reversible and both have excellent electrochemical energy storage characteristics. At the same current density, the discharge time of the C / Co3O4 / TiO2 composite electrode material is longer than that of the C / Co3O4 composite electrode material. According to the electrode calculation formula, the longer the discharge time, the greater the electrode specific capacity, which means that the C / Co3O4 / TiO2 composite electrode material has a larger specific capacity.

[0091] Figure c shows the different composite electrode materials at a current density of 0.2 mA / cm 2 The CP curve at the time of the experiment shows that compared with the C / Co3O4 composite electrode material, the charging and discharging time of the C / Co3O4 / TiO2 composite electrode material formed after TiO2 modification are both increased, indicating that TiO2 has an impact on the entire electrode charging and discharging process. TiO2 has excellent catalytic activity. It can absorb visible light and generate holes and electrons under the action of the electric field. The holes and electrons participate in the charging and discharging process of the electrode, thereby increasing its capacity. The possible mechanism of action of the C / Co3O4 / TiO2 electrode is as follows:

[0092] TiO2 + nhv → nh + + ne - .

[0093] Photocatalytic assisted charging process:

[0094] TiO2+ Co3O4+ 4OH - + nhv → TiO2+ 3CoO2+ 2H2O+ (n + 4) e - + nh + .

[0095] Photocatalytic assisted discharge process:

[0096] TiO2+ 3CoO2+ 2H2O + nhv → TiO2+ Co3O4+ 4OH - + (n-4) e - + nh + .

[0097] where h + represents photogenerated holes, e -represents the photogenerated electrons or free electrons in the oxidation / reduction reaction, and n is the number of photogenerated carriers. As light irradiation increases the number of photogenerated carriers from 0 to n, more electrons are stored as charge and separated from holes by the built-in electric field formed by the pn junction, thereby increasing the specific capacity.

[0098] Figure d shows the AC impedance curves of the C / Co3O4 composite electrode material and the C / Co3O4 / TiO2 composite electrode material at open circuit voltage. It can be seen that the charge transfer resistance Rct and equivalent resistance Rs of the C / Co3O4 / TiO2 composite electrode material are both smaller than those of the C / Co3O4 composite electrode material. This is likely due to the built-in electric field formed by the pn junction, which accelerates the redox reaction process and reduces the equivalent internal resistance of the electrode material.

[0099] The above description is merely a preferred embodiment of the present invention, and the above specific embodiment is not intended to limit the present invention. Various variations and modifications are possible within the technical scope of the present invention. Any modifications, alterations, or equivalent substitutions made by a person skilled in the art based on the above description are within the scope of protection of the present invention.

Claims

1. A method for preparing a C / Co3O4 / TiO2 composite electrode material with a pn junction, characterized in that: The following steps are involved: The carbon cloth is immersed in an acidic liquid to graft oxygen-containing functional groups onto the surface of the carbon cloth to obtain an activated carbon cloth; A cobalt source and a first oxygen source are used as deposition precursors, and a first deposition process is performed by atomic layer deposition to deposit Co3O4 on the surface of the activated carbon cloth to prepare a C / Co3O4 composite electrode material; A titanium source and a second oxygen source are used as deposition precursors, and a second deposition process is performed by atomic layer deposition to deposit TiO2 on the surface of the C / Co3O4 composite electrode material. The p-type semiconductor Co3O4 and the n-type semiconductor TiO2 form a pn junction to obtain a C / Co3O4 / TiO2 composite electrode material with a pn junction.

2. The method for preparing a C / Co3O4 / TiO2 composite electrode material having a pn junction according to claim 1, characterized in that: The acidic liquid is sulfuric acid with a mass concentration of 30% to 70% or concentrated nitric acid with a mass concentration of 20% to 50%.

3. The method for preparing a C / Co3O4 / TiO2 composite electrode material having a pn junction according to claim 2, characterized in that: The soaking time of the soaking treatment is 1 day to 4 days.

4. The method for preparing a C / Co3O4 / TiO2 composite electrode material having a pn junction according to claim 1, characterized in that: The deposition temperature of the first deposition process is 150° C. to 200° C., and the number of deposition cycles is 100 to 200 times.

5. The method for preparing a C / Co3O4 / TiO2 composite electrode material having a pn junction according to claim 1, characterized in that: The deposition temperature of the second deposition process is 60° C. to 200° C., and the number of deposition cycles is 5 to 20 times.

6. The method for preparing a C / Co3O4 / TiO2 composite electrode material having a pn junction according to claim 1, characterized in that: The cobalt source is cobaltocene or cobalt acetylacetonate, and the first oxygen source is ozone or water.

7. The method for preparing a C / Co3O4 / TiO2 composite electrode material having a pn junction according to claim 1, characterized in that: The titanium source is titanium isopropoxide or titanium tetrachloride, and the second oxygen source is water.

8. The method for preparing a C / Co3O4 / TiO2 composite electrode material having a pn junction according to claim 1, characterized in that: The oxygen-containing functional group is at least one of a hydroxyl group, a carboxyl group, a carbonyl group and an ester group.

9. The method for preparing a C / Co3O4 / TiO2 composite electrode material having a pn junction according to claim 1, characterized in that: In the first deposition process, the pulse time of the cobalt source is 0.5 s, the exposure time is 10 s, and the purge time is 25 s; In the second deposition process, the pulse time of the titanium source is 0.5 s, the exposure time is 10 s, and the purge time is 25 s; In the first deposition process and the second deposition process, the pulse time of the first oxygen source and the second oxygen source is 1 s, the exposure time is 10 s, and the purge time is 25 s.

10. A C / Co3O4 / TiO2 composite electrode material with a pn junction, characterized in that: The material is prepared by the method for preparing a C / Co3O4 / TiO2 composite electrode material with a pn junction as claimed in any one of claims 1 to 9.

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