One-dimensional mesoporous-nanocomposite structure titanium dioxide photoanode, preparation method and application thereof

Abstract

The application discloses a one-dimensional mesoporous-nanocomposite structure titanium dioxide photoanode and a preparation method and application thereof. The titanium dioxide nanorod photoanode photoanode comprises one-dimensional TiO2 nanorods and TiO2 mesoporous structures. The one-dimensional TiO2 nanorods serve as a substrate, and the TiO2 mesoporous structures are loaded on the one-dimensional TiO2 nanorods to form a mesoporous TiO2 film. The one-dimensional mesoporous-nanocomposite structure titanium dioxide photoanode takes one-dimensional nanostructures as a substrate to load mesoporous structures, combines the advantages of both, can promote electron transmission to inhibit the recombination of electron-hole pairs and improve mechanical strength and stability by using one-dimensional nanostructures, and can increase the specific surface area and active area of the photoanode by using mesoporous structures, increases the transmission distance of light in the mesoporous structures, thereby promoting the absorption of light and improving the catalytic performance.

Description

Technical Field

[0001] This invention relates to the field of photoelectrochemical cell technology, specifically to a one-dimensional mesoporous-nanocomposite titanium dioxide photoanode, its preparation method, and its application. Background Technology

[0002] Fossil fuel combustion contributes 73% of global carbon dioxide emissions, leading to problems such as climate change, acid rain, and smog. Ammonia (NH3), as an energy carrier, has advantages such as high energy density, ease of storage and transportation, zero carbon emissions during combustion, and the ability to be produced using renewable energy sources. These characteristics make ammonia a promising candidate for replacing fossil fuels and reducing greenhouse gas emissions. Currently, the commonly used method for large-scale ammonia synthesis is the industrial Haber-Bosch process. However, this method requires production at 300–550°C and 200–350 atm, and each ton of NH3 produced generates approximately 1.9 tons of CO2 greenhouse gas, resulting in harsh reaction conditions, high energy consumption, and severe pollution.

[0003] In recent years, photoelectrochemical cells that utilize solar energy to drive the reduction of nitrogen to synthesize ammonia have gradually attracted attention due to their ability to directly utilize and convert solar energy, effectively reducing energy consumption. Currently, photoelectrochemical cells used in the reduction of nitrogen to synthesize ammonia mainly take three forms: electrochemical cathode-photoanode, photocathode-electrochemical anode, or dual photoelectrode. Because the photocathode easily leads to the photo-oxidation of the generated ammonia into nitric acid, reducing the yield of synthesized ammonia, photoelectrochemical cells using electrocatalysis at the cathode and photoelectrocatalysis at the anode have a higher ammonia yield.

[0004] Photoanodes typically use semiconductor materials as catalysts. If the photoanode catalyst has low light energy utilization and severe electron-hole recombination, it will inhibit the photoelectrocatalytic reaction kinetics, increase the overpotential of the photoanode, and make it difficult to effectively reduce the applied bias voltage and system energy consumption. Since photoelectrochemical cells utilize solar energy to drive the reduction of nitrogen to synthesize ammonia, the design and fabrication of the photoanode have a significant impact on improving the ammonia production performance of the photoelectrochemical cell and reducing the energy consumption of nitrogen reduction. By changing the photoanode structural design, electron transport and light scattering can be enhanced, electron-hole recombination can be suppressed, and the light energy utilization and photoanode performance can be improved.

[0005] Among various photocatalysts, TiO2 has become a widely used photoanode catalyst due to its excellent chemical stability, high catalytic activity, suitable band structure, non-toxicity, and low cost. In the nitrogen reduction reaction, although one-dimensional titanium dioxide nanorod photoanodes have the advantage of high electron transport rates, their nanoscale porous structure limits the enhancement of mass transport within the pores, affecting photoelectrochemical performance and inhibiting its catalytic performance. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention proposes a one-dimensional mesoporous-nanocomposite titanium dioxide photoanode, its preparation method, and its application, which exhibits better photoelectrochemical performance compared to one-dimensional titanium dioxide nanorods.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution: a one-dimensional mesoporous-nanoporous composite titanium dioxide photoanode, comprising a one-dimensional TiO2 nanorod and a TiO2 mesoporous structure, wherein the one-dimensional TiO2 nanorod serves as a substrate, and the TiO2 mesoporous structure is loaded on the one-dimensional TiO2 nanorod to form a mesoporous TiO2 thin film.

[0008] Furthermore, the surface of the mesoporous TiO2 film has a regularly arranged and uniformly distributed mesoporous structure.

[0009] Furthermore, the mesoporous structure is loaded on the surface of the one-dimensional TiO2 nanorods and located in the inter-rod voids of the one-dimensional TiO2 nanorods, forming a continuous three-dimensional interconnected network on the surface of the one-dimensional TiO2 nanorods and in the inter-rod voids.

[0010] The beneficial effects of the aforementioned one-dimensional mesoporous-nanocomposite titanium dioxide photoanode are as follows: by using a one-dimensional nanostructure as a substrate to support a mesoporous structure, the advantages of both are combined. The one-dimensional nanostructure can be used to promote electron transport to suppress electron-hole recombination and improve mechanical strength and stability, while the mesoporous structure can be used to increase the specific surface area and active area of ​​the photoanode, thereby increasing the light transmission distance in the mesoporous structure, promoting light absorption, and improving catalytic performance.

[0011] A method for preparing a one-dimensional mesoporous-nanocomposite titanium dioxide photoanode, comprising the following steps: Preparation of one-dimensional TiO2 nanorods; Mesoporous TiO2 was loaded onto one-dimensional TiO2 nanorods to obtain a one-dimensional mesoporous-nanocomposite titanium dioxide photoanode.

[0012] Furthermore, the preparation of one-dimensional TiO2 nanorods includes the following steps: The conductive glass was placed in acetone, anhydrous ethanol and deionized water in sequence, and ultrasonically cleaned each time. Tetrabutyl titanate was added to concentrated hydrochloric acid and mixed thoroughly to obtain a mixed solution; The mixed solution and conductive glass were transferred to a high-pressure reactor for hydrothermal reaction. After the reaction was completed, the solution was taken out, rinsed with anhydrous ethanol and deionized water, dried, and then calcined in a tube furnace to obtain a TiO2 nanorod film loaded on the conductive glass.

[0013] Furthermore, the conductive glass is FTO conductive glass, and the ultrasonic cleaning time is not less than 10 minutes; The volume ratio of concentrated hydrochloric acid to tetrabutyl titanate is 30:0.3~1. Tetrabutyl titanate is added dropwise to concentrated hydrochloric acid under magnetic stirring for a stirring time of not less than 30 minutes. The hydrothermal reaction temperature of the mixed solution and FTO conductive glass is 130~150℃, the hydrothermal heating time is 4~15 hours, the calcination atmosphere is air, and the temperature is increased from room temperature over 48 minutes at a rate of 10℃·min. -1 The final temperature was 500 ℃, and the calcination time was 1 h.

[0014] Furthermore, loading mesoporous TiO2 onto one-dimensional TiO2 nanorods includes the following steps: Triblock polymer F127, concentrated hydrochloric acid and anhydrous ethanol were mixed evenly to obtain mixed solution A; Tetrabutyl titanate, acetylacetone and anhydrous ethanol were mixed evenly to obtain mixed solution B; Adding mixed solution A to mixed solution B yields a mesoporous solution; Mesoporous solution was dropped onto one-dimensional TiO2 nanorods and then subjected to evaporation self-assembly. One-dimensional TiO2 nanorods were calcined in a tube furnace to obtain a one-dimensional mesoporous-nanoparticle composite titanium dioxide photoanode.

[0015] Further, the mass ratio of the triblock polymer F127, concentrated hydrochloric acid, and anhydrous ethanol is 0.36:1.44:9~200, and the mixture is magnetically stirred for 30 minutes to obtain mixed solution A; The mass ratio of tetrabutyl titanate, acetylacetone and anhydrous ethanol is 0.9:0.54:9~200, and the mixture is magnetically stirred for 20 minutes to obtain mixed solution B; Mixed solution A was added dropwise to mixed solution B, and the mixture was magnetically stirred for 24 hours to obtain a mesoporous solution. The undiluted concentration was the one with the lowest ratio of anhydrous ethanol in the mesoporous solution. The concentration of the mesoporous solution gradually decreased as the ratio of anhydrous ethanol increased. Mesoporous solution was dropped onto the surface of one-dimensional TiO2 nanorods and then placed in a constant temperature and humidity chamber for evaporative self-assembly. The temperature for the evaporative self-assembly method was 28 °C, the humidity was 45%, and the duration was 24 h. One-dimensional TiO2 nanorods were placed in a tube furnace for calcination in an air atmosphere. The calcination was started from room temperature and the temperature was increased over a period of 480 min at a rate of 1 °C / min for a total calcination time of 150 min.

[0016] Furthermore, the steps of adding mesoporous solution and performing evaporation self-assembly can be repeated multiple times. After the one-dimensional TiO2 nanorods have completed evaporation self-assembly for 24 hours, they can be heated on a heating plate at 300°C for 15 minutes, cooled to room temperature, and then the mesoporous solution can be added again and the evaporation self-assembly method can be performed to obtain a one-dimensional mesoporous-nanocomposite titanium dioxide photoanode with a multilayer mesoporous-nanocomposite structure.

[0017] The beneficial effects of the above-mentioned method for preparing a one-dimensional mesoporous-nanocomposite titanium dioxide photoanode are: using a one-dimensional nanostructure as a substrate to support a mesoporous structure to prepare the photoanode can both increase the specific surface area of ​​the photoanode through the mesoporous structure and reduce the influence of thermal stress during the preparation process by utilizing the one-dimensional structure.

[0018] An application of a one-dimensional mesoporous-nanocomposite titanium dioxide photoanode: The aforementioned one-dimensional mesoporous-nanocomposite titanium dioxide photoanode is used for nitrogen reduction synthesis of ammonia in a photoelectrochemical cell.

[0019] The beneficial effects of the above-mentioned one-dimensional mesoporous-nanocomposite titanium dioxide photoanode are: because the nanorod photoanode has a good improvement on light absorption, electron-hole pair separation and transport, and photocatalytic activity, it can significantly improve the ammonia production performance of photoelectrochemical cells and reduce nitrogen reduction energy consumption. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the specific embodiments will be briefly described below. In all the drawings, the elements or parts are not necessarily drawn to scale.

[0021] Figure 1 This is a schematic diagram of a one-dimensional mesoporous-nanocomposite titanium dioxide photoanode provided in an embodiment of the present invention; Figure 2 SEM images of one-dimensional mesoporous-nanocomposite titanium dioxide photoanodes prepared from mesoporous solutions with different dilution ratios according to an embodiment of the present invention; Figure 3 for Figure 2 Photoluminescence spectra of one-dimensional mesoporous-nanocomposite titanium dioxide photoanodes prepared from mesoporous solutions with different dilution ratios are shown. Figure 4 for Figure 2 Time-resolved fluorescence lifetime of one-dimensional mesoporous-nanocomposite titanium dioxide photoanodes prepared from mesoporous solutions with different dilution ratios is shown. Figure 5 for Figure 2 The surface photovoltage diagrams of one-dimensional mesoporous-nanocomposite titanium dioxide photoanodes prepared from mesoporous solutions with different dilution ratios are shown. Figure 6 SEM image of a one-dimensional mesoporous-nanocomposite titanium dioxide photoanode prepared by loading mesopores with different numbers of layers, provided in an embodiment of the present invention; Figure 7 for Figure 6 The photoluminescence spectra of one-dimensional mesoporous-nanocomposite titanium dioxide photoanodes prepared by loading mesoporous layers with different numbers of layers are shown. Figure 8 Photoluminescence spectra of TiO2 nanorods, TiO2 mesoporous powder, and a one-dimensional mesoporous-nanocomposite titanium dioxide photoanode provided in an embodiment of the present invention; Figure 9 XRD patterns of TiO2 nanorods, TiO2 mesoporous powder, and a one-dimensional mesoporous-nano composite titanium dioxide photoanode provided in an embodiment of the present invention; Figure 10 The adsorption-desorption curves of TiO2 nanorods and one-dimensional mesoporous-nanocomposite titanium dioxide photoanodes provided in an embodiment of the present invention are shown. Figure 11 Time-current response curves of one-dimensional mesoporous-nanocomposite titanium dioxide photoanodes prepared from mesoporous solutions with different dilution ratios according to an embodiment of the present invention; Figure 12 LSV curves of one-dimensional mesoporous-nanocomposite titanium dioxide photoanodes prepared from mesoporous solutions with different dilution ratios according to an embodiment of the present invention; Figure 13 Electrochemical impedance spectroscopy curves of one-dimensional mesoporous-nanocomposite titanium dioxide photoanodes prepared from mesoporous solutions with different dilution ratios according to an embodiment of the present invention; Figure 14 The current density diagram of a one-dimensional mesoporous-nanocomposite titanium dioxide photoanode prepared from mesoporous solutions with different dilution ratios according to an embodiment of the present invention is shown. Figure 15 This is a time-current response curve of a one-dimensional mesoporous-nano composite titanium dioxide photoanode with different numbers of mesoporous load layers provided in an embodiment of the present invention; Figure 16 LSV curves of one-dimensional mesoporous-nano composite titanium dioxide photoanodes with different numbers of mesoporous loading layers provided in an embodiment of the present invention; Figure 17 Electrochemical impedance spectroscopy curves of one-dimensional mesoporous-nanocomposite titanium dioxide photoanodes with different numbers of mesoporous loading layers provided in an embodiment of the present invention; Figure 18 The current density diagram of a one-dimensional mesoporous-nanocomposite titanium dioxide photoanode with different numbers of mesoporous load layers is provided in an embodiment of the present invention. Detailed Implementation

[0022] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0023] Please see Figure 1 This invention provides a one-dimensional mesoporous-nanoparticle composite titanium dioxide photoanode, its preparation method, and its application. The titanium dioxide nanorod photoanode includes a one-dimensional TiO2 nanorod and a TiO2 mesoporous structure. The one-dimensional TiO2 nanorod is used as a substrate, and the TiO2 mesoporous structure is loaded on the one-dimensional TiO2 nanorod to form a mesoporous TiO2 film.

[0024] Specifically, the surface of the mesoporous TiO2 film has a regularly arranged and uniformly distributed mesoporous structure with a pore size of approximately 5.3 nm. The mesoporous structure is loaded on the surface of the one-dimensional TiO2 nanorods and located in the inter-rod voids of the one-dimensional TiO2 nanorods, forming a continuous three-dimensional interconnected network on the surface of the one-dimensional TiO2 nanorods and in the inter-rod voids.

[0025] The aforementioned titanium dioxide nanorod photoanodes possess advantages in both their large specific surface area (enhancing electron transport rate and suppressing electron-hole recombination) and high aspect ratio (promoting light absorption and scattering). Mesoporous structures, on the other hand, offer advantages such as large specific surface area and ordered pore structure, along with a larger pore volume than one-dimensional nanostructures, which facilitates light scattering and mass transport. Therefore, both one-dimensional nanostructures and mesoporous structures can effectively improve the performance of photoanodes.

[0026] Therefore, using one-dimensional nanostructures as a substrate to support mesoporous structures, forming micro / nano structures, combines the advantages of both. Because one-dimensional nanostructures lack sufficient pore structure, their ability to enhance material transport within the pores is limited. Mesoporous structures, on the other hand, possess abundant pore structure and a large specific surface area, increasing the light transmission distance. Furthermore, mesoporous structures are susceptible to cracking due to thermal stress during fabrication, which reduces the mechanical strength of the motor. One-dimensional nanostructures, acting as a substrate, provide support, reducing the impact of thermal stress during fabrication and improving mechanical strength and stability.

[0027] The preparation method of the above-mentioned one-dimensional mesoporous-nanocomposite titanium dioxide photoanode includes the following steps: Preparation of one-dimensional TiO2 nanorods; Mesoporous TiO2 was loaded onto one-dimensional TiO2 nanorods to obtain a one-dimensional mesoporous-nanocomposite titanium dioxide photoanode.

[0028] The preparation of one-dimensional TiO2 nanorods includes the following steps: The conductive glass was placed in acetone, anhydrous ethanol and deionized water in sequence, and ultrasonically cleaned each time. Tetrabutyl titanate was added to concentrated hydrochloric acid and mixed thoroughly to obtain a mixed solution; The mixed solution was transferred to a stainless steel high-pressure reactor lined with polytetrafluoroethylene (PTFE). Half of the conductive side of the conductive glass was covered with Teflon fluoropolymer tape and vertically inserted into a PTFE support. The glass was then placed at the bottom of the high-pressure reactor for hydrothermal reaction. After the reaction was complete, the glass was removed and the tape was peeled off. The surface of the conductive glass was rinsed with anhydrous ethanol and deionized water to remove any remaining adhesive residue and dried. The glass was then calcined in a tube furnace to obtain a TiO2 nanorod film loaded on the conductive glass.

[0029] Specifically, FTO conductive glass is selected for the conductive glass, and each ultrasonic cleaning session lasts for at least 10 minutes. The volume ratio of concentrated hydrochloric acid to tetrabutyl titanate is 30:0.3~1. Tetrabutyl titanate is added dropwise to the concentrated hydrochloric acid under magnetic stirring for at least 30 minutes. The hydrothermal reaction temperature of the mixed solution and the FTO conductive glass is 130~150℃, the hydrothermal heating time is 4~15 hours, the calcination atmosphere is air, and the temperature is increased from room temperature over 48 minutes at a rate of 10℃·min. -1 The final temperature was 500 ℃, and the calcination time was 1 h.

[0030] Loading mesoporous TiO2 on one-dimensional TiO2 nanorods includes the following steps: Triblock polymer F127, concentrated hydrochloric acid and anhydrous ethanol were mixed evenly to obtain mixed solution A; Tetrabutyl titanate, acetylacetone and anhydrous ethanol were mixed evenly to obtain mixed solution B; Mixed solution A was added dropwise to mixed solution B, and the mixture was magnetically stirred for 24 hours to obtain a mesoporous solution. The undiluted concentration was the one with the lowest ratio of anhydrous ethanol in the mesoporous solution. The concentration of the mesoporous solution gradually decreased as the ratio of anhydrous ethanol increased. Mesoporous solution was dropped onto one-dimensional TiO2 nanorods and then subjected to evaporation self-assembly. One-dimensional TiO2 nanorods were calcined in a tube furnace to obtain a one-dimensional mesoporous-nanoparticle composite titanium dioxide photoanode.

[0031] Specifically, a mixed solution A was obtained by magnetically stirring triblock polymer F127, concentrated hydrochloric acid, and anhydrous ethanol at a mass ratio of 0.36:1.44:9~200 for 30 minutes. A mixed solution B was obtained by magnetically stirring tetrabutyl titanate, acetylacetone, and anhydrous ethanol at a mass ratio of 0.9:0.54:9~200 for 20 minutes. Mixed solution A was added dropwise to mixed solution B, and the mixture was magnetically stirred for 24 hours to obtain a mesoporous solution. The mesoporous solution was then added dropwise to the surface of one-dimensional TiO2 nanorods, which were then placed in a constant temperature and humidity chamber for evaporative self-assembly. The evaporative self-assembly method was performed at a temperature of 28 °C and a humidity of 45% for 24 hours. The one-dimensional TiO2 nanorods were then calcined in a tube furnace under an air atmosphere. The calcination started at room temperature, with a heating time of 480 min, a heating rate of 1 °C / min, and a calcination time of 150 min.

[0032] The above steps of adding mesoporous solution and performing evaporation self-assembly can be repeated multiple times. After the one-dimensional TiO2 nanorods have completed evaporation self-assembly for 24 hours, they can be heated on a heating plate at 300°C for 15 minutes, cooled to room temperature, and then the mesoporous solution can be added again and the evaporation self-assembly method can be performed to obtain a one-dimensional mesoporous-nanocomposite titanium dioxide photoanode with a multilayer mesoporous-nanocomposite structure.

[0033] Mesoporous TiO2 was loaded onto one-dimensional TiO2 nanorods using an evaporation self-assembly method. The mesoporous solution was dropped onto the one-dimensional TiO2 nanorods of conductive glass and then subjected to evaporation self-assembly, which successfully formed a continuous mesoporous TiO2 film on the surface of the conductive glass. The film uniformly covered the surface of the conductive glass, forming a thin layer with a complete structure and no obvious cracks, exhibiting good continuity. Observation revealed that the film surface had a regularly arranged mesoporous structure. The mesoporous structure was loaded on the surface of the TiO2 nanorods, and a continuous TiO2 mesoporous film network covered the surface of the TiO2 nanorods and the gaps between the rods, forming a three-dimensional interconnected network.

[0034] The application of the aforementioned one-dimensional mesoporous-nanocomposite titanium dioxide photoanode, used as a photoanode in photoelectrochemical cells for nitrogen reduction to synthesize ammonia, significantly improves light absorption, electron-hole pair separation and transport, and photoelectrocatalytic activity, exhibiting good photoelectrochemical performance. It can significantly enhance the ammonia production performance of photoelectrochemical cells and reduce nitrogen reduction energy consumption.

[0035] The following is an analysis and description of a one-dimensional mesoporous-nanocomposite titanium dioxide photoanode prepared using the above method: By adding mesoporous solutions of different concentrations (by increasing the amount of anhydrous ethanol to dilute the concentration to different ratios) onto TiO2 nanorod arrays and performing evaporation self-assembly, the morphological changes of the mesoporous film on the nanorod surface were observed. Figure 2SEM images of mesoporous films formed by evaporation and self-assembly after adding mesoporous solutions of different concentrations. Figure 2 In Figure (a), the nanorods are loaded with an undiluted mesoporous solution, with the top of the nanorods completely covered by a dense mesoporous anatase film with a thickness of approximately 1.8 μm. This thick film almost completely obscures the array structure of the underlying nanorods. This blockage prevents the solution from smoothly entering the gaps between the nanorods, resulting in only a small amount of mesoporous titanium dioxide forming in the pores, which affects the uniformity and pore connectivity of the film. Figure 2 In (b), the loading condition is shown when the mesoporous solution concentration is diluted to 4 times. The thickness of the mesoporous layer is significantly reduced to about 0.6 μm, forming a continuous thin film covering the top of the nanorods. The outline of the nanorods begins to be faintly visible. At this concentration, although fewer mesoporous structures are formed in the pores, the overall film is still not continuous enough and fails to form an ideal pore network. Figure 2 Image (c) shows the loading condition when the mesoporous solution is diluted 8 times. No continuous capping film forms at the tips of the nanorods, and the mesoporous anatase forms a three-dimensional interconnected network structure between the nanorods, while retaining abundant pores and channels. The mesoporous structure formed at this concentration effectively improves the diffusion efficiency of reactants and facilitates the rapid transport of photogenerated carriers, thereby enhancing catalytic performance. When the mesoporous solution is further diluted 16 times, i.e. Figure 2 As shown in (d), it can be seen that the mesoporous content is too low at this time, and a continuous structure cannot be formed. Instead, it is randomly attached to the surface and gaps of the nanorods in the form of isolated aggregates. The formation of this structure greatly reduces the connectivity and stability of the channels, thus affecting the performance improvement.

[0036] Figure 3 The images show the photoluminescence spectra of one-dimensional mesoporous-nanoplasmic titanium dioxide photoanodes formed by evaporation and self-assembly after adding mesoporous solutions of different concentrations. It can be seen that the photoluminescence (PL) signal of the undiluted mesoporous solution structure is the strongest, indicating that recombination of photogenerated carriers dominates in this structure. This is because the thicker mesoporous layer itself has poor crystallinity, introducing numerous bulk defects that become effective recombination centers. Furthermore, the thick film completely covers the nanorods, making it difficult for electrons in the rutile nanorods to be effectively utilized; instead, recombination occurs with holes at the interface between the nanorods and the mesoporous film. The thick film also hinders electrolyte wetting, preventing timely hole capture and further exacerbating recombination.

[0037] When the mesoporous solution was diluted four times, its plasma density (PL) intensity decreased significantly compared to the original concentration of the mesoporous photoanode, but remained at a high level. This demonstrates that reducing the mesoporous layer thickness effectively shortens the hole migration path and reduces the number of bulk defects, allowing some holes to participate in surface reactions and thus inhibiting recombination to some extent. However, the continuous thin film structure at the top still restricts the free diffusion of the electrolyte and the rapid consumption of holes to some extent, resulting in a still high recombination rate.

[0038] When the mesoporous solution was diluted 8 times, the photoanode exhibited the lowest PL intensity, indicating that under this optimal morphology, the radiative recombination process of photogenerated carriers was suppressed to the greatest extent. The mesoporous network structure connecting the pores of the nanorods not only increased the specific surface area of ​​the photoanode, allowing the electrolyte to fully wet the photoanode, but also provided a mesh-like, lateral collection and transport interface for holes, enabling efficient transport. This allowed the separated electrons and holes to be rapidly and efficiently consumed before they met and recombinated, thus significantly reducing the probability of recombination.

[0039] When the mesoporous solution was diluted 16 times, the PL intensity of the photoanode increased compared to the 8-fold dilution. This is because the mesoporous loading was too low to form a continuous mesoporous network and transport channels, resulting in the charge carriers still recombinating inside the rutile nanorods.

[0040] Figure 4 Fluorescence lifetimes of one-dimensional mesoporous-nanocomposite titanium dioxide photoanodes loaded with mesoporous solutions at different dilution ratios are shown. The photoanode loaded with undiluted mesoporous solution exhibits the longest fluorescence lifetime, indicating that photogenerated electron-hole pairs exist for the longest time in this structure. The excessively thick mesoporous layer leads to severe bulk recombination and transport blockage. The separated charge carriers are trapped by a large number of defects before reaching the surface, and then undergo a relatively slow annihilation process dominated by radiative recombination. Therefore, the long fluorescence lifetime reflects the unfavorable state of blocked charge carrier transport paths and enrichment of recombination centers. For the photoanode with a 4-fold dilution of the mesoporous solution, the shortened lifetime is mainly due to partially effective charge separation. The thinner mesoporous layer improves hole transport to some extent, thereby shortening the charge carrier lifetime, but its continuous thin film structure still limits the completeness of charge separation to some extent. The photoanode diluted 8 times in mesoporous solution exhibited the shortest fluorescence lifetime, consistent with its weakest PL signal, demonstrating the rapid transport of photogenerated carriers. The rapid longitudinal transport of electrons along the one-dimensional rutile nanorods and the rapid lateral transport of holes through the three-dimensional anatase network prevented the recombination of most electron-hole pairs.

[0041] Figure 5Surface photovoltage (SPV) plots of one-dimensional mesoporous-nanocomposite titanium dioxide photoanodes loaded with mesoporous solutions at different dilution ratios are presented. The SPV signal trends of the four photoanodes show a negative correlation with the photopotential (PL) intensity, further confirming the above analysis. The SPV signal of the photoanode with undiluted mesoporous solution is the weakest, indicating that the excessively thick mesoporous layer not only consumes most of the charge carriers as recombination centers, but its excessively long transport path also causes a large number of holes to recombine before reaching the surface, failing to contribute effectively to the surface potential and making it difficult to establish a photovoltage. The SPV signal of the photoanode with a 4-fold dilution of the mesoporous solution is enhanced, but the amplitude is limited. This indicates that thinning the capping layer does improve charge separation and transport, allowing more charge carriers to contribute to the generation of photovoltage. However, insufficient electrolyte wetting and the still tortuous transport path limit further performance improvement.

[0042] The photoanode diluted 8 times with mesoporous solution exhibited the strongest SPV response, indicating that this structure achieved the most efficient charge separation and the most effective carrier utilization. Photogenerated carriers were rapidly transported under illumination and bias. The separated electrons and holes were transported by one-dimensional nanorods and a three-dimensional mesoporous network, respectively, avoiding recombination and jointly maintaining a strong and stable space charge layer, resulting in the highest surface photovoltage. The SPV signal of the photoanode diluted 16 times with mesoporous solution declined. This is because the mesopores were insufficient to form a continuous hole transport path, preventing the separated holes from being effectively extracted and consumed, ultimately leading to poor overall SPV performance.

[0043] It can be seen that the most ideal composite structure was obtained when the mesoporous solution was diluted to 8 times its original concentration.

[0044] One-dimensional mesoporous-nanocomposite titanium dioxide photoanodes loaded with 2, 3, 4, and 5 layers of mesoporous films were prepared by diluting the solution 8 times to achieve the desired mesoporous solution concentration. The morphological changes of the mesoporous films on the nanorod surface were then observed. Figure 6 SEM images of mesoporous loads with different numbers of layers on the surface of nanorod arrays show significant differences, which directly affect the optoelectronic properties. Figure 6 (a) shows a photoanode with two layers of mesoporous structure. It can be seen that the photoanode with two layers of mesoporous structure shows that only a thin mesoporous film is attached to the surface of the nanorod. The mesoporous structure is uniformly distributed, but the film is relatively thin and fails to fully cover the surface of the nanorod. Figure 6 (b) With 3 layers of mesoporous structure, multiple small agglomerations can be seen on the surface of the nanorod. The mesoporous structure aggregates on the surface to form small blocky aggregates. This aggregation effect may form an uneven coating layer on the surface of the nanorod, and some areas may be blocked by pores. Figure 6(c) The nanorods are loaded with 4 layers of mesoporous material. A connected mesoporous network appears between the nanorods, forming a good pore structure. The mesoporous film is relatively uniform and has good connectivity. The mesoporous film forms a stable three-dimensional network structure between the nanorods, and the connectivity between the pores is significantly improved. Figure 6 (d) shows a load of 5 layers of mesoporous material. It can be seen that the pores of the nanorod are blocked, and an extremely thin mesoporous film appears at the top of the nanorod. This indicates that the excessive mesoporous structure not only covers the surface of the nanorod, but may also block the internal pores of the nanorod, which may affect the light transmittance.

[0045] Figure 7 The figures show the surface photovoltage (SPV) diagrams of one-dimensional mesoporous-nanocomposite titanium dioxide photoanodes loaded with 2, 3, 4, and 5 mesoporous layers, respectively. With a mesoporous loading of 2 layers, only a very thin mesoporous film forms on the nanorod surface, resulting in limited interfacial contact area and difficulty in effectively constructing cross-interfacial charge transport channels. Since charge carriers mainly recombine within the nanorods, the SPV signal of the photoanode with a mesoporous loading of 2 layers is the weakest. As the number of mesoporous layers increases, multiple small agglomeration regions appear on the nanorod surface, increasing the interfacial area and generating some charge carriers, thus increasing the SPV signal. However, due to localized light blocking and electron retention caused by agglomeration, the overall SPV does not reach the optimal level. With a 4-layer loading, the mesoporous layers form a well-connected three-dimensional network structure, maintaining unobstructed pores between nanorods, while achieving an optimal balance between interfacial area and electron transport channels. Under this structure, the separation driving force and cross-interfacial transport capacity of photogenerated charge carriers are significantly improved, resulting in the highest SPV signal intensity, reflecting the most effective interfacial charge separation behavior. When a 5-layer mesoporous structure is loaded, the pores between the nanorods are largely blocked, and a dense mesoporous film is formed on top. The excessively thick mesoporous layer weakens light transmittance and reduces the light absorption of the nanorod body. At the same time, the dense film forms a carrier retention region, which reduces the electron transport rate. Therefore, the SPV drops, which is significantly lower than that of a 4-layer mesoporous photoanode.

[0046] It can be seen that the most ideal composite structure was obtained when the four-layer mesoporous structure was loaded.

[0047] Figure 8The photoluminescence spectra of TiO2 nanorods, TiO2 mesoporous powder, and a one-dimensional mesoporous-nanocomposite titanium dioxide photoanode (supported with a 4-layer mesoporous structure) are shown. It can be observed that TiO2 nanorods (TNR) exhibit the highest photoluminescence (PL) signal intensity, mesoporous TiO2 (Mesopore) shows the weakest PL signal, while the PL signal intensity of the one-dimensional mesoporous-nanocomposite titanium dioxide photoanode falls between the two. TNR exhibits the strongest band-edge and deep-level emission in the 350-600 nm range, indicating that its photogenerated carriers mainly undergo radiative recombination. In contrast, the PL signal of mesoporous TiO2 is significantly weakened because of its high specific surface area. Once photogenerated electrons and holes are generated, they only need to diffuse a very short distance to reach the surface and react, greatly reducing their recombination probability in the bulk phase. The porous structure can reflect and scatter incident light multiple times, improving the efficiency of light energy utilization and indirectly generating more charge carriers. The PL signal intensity of the one-dimensional mesoporous-nanoporous composite titanium dioxide photoanode is between the two, indicating that photogenerated carriers are accelerated through the mesoporous network, thereby reducing the probability of radiative recombination inside the nanorod.

[0048] Figure 9 To analyze the crystal phase characteristics of TiO2 nanorods, TiO2 mesoporous powder, and one-dimensional mesoporous-nanoparticle composite titanium dioxide photoanode (supported with 4 layers of mesoporous structure) by XRD, the prepared TiO2 mesoporous powder showed characteristic diffraction peaks at 25.3°, 37.8°, 53.8°, and 55.1°, which correspond to (101), (001), (105), and (211) of anatase phase TiO2 (JCPDS No. 21-1272), respectively. TiO2 nanorods (TNR) and one-dimensional mesoporous-nanocomposite titanium dioxide photoanodes exhibit characteristic diffraction peaks at 27.4°, 36.1°, 41.1°, 62.8°, and 37.8°, respectively, corresponding to the (110), (101), (111), and (002) crystal planes of rutile TiO2 (JCPDS No. 21-1276) and the (004) crystal plane of anatase.

[0049] Figure 10 The N2 adsorption-desorption isotherms are shown for a TiO2 nanorod and one-dimensional mesoporous-nanoporous composite titanium dioxide photoanode (supported with a 4-layer mesoporous structure). The inset shows the specific surface area. The corresponding BET specific surface area values ​​are 0.3741 m² / m³. 2 / g and 0.4516m 2 / g, indicating that by loading a mesoporous film onto the nanorods, the external surface area of ​​the photoanode and the number of accessible catalytic sites are increased, providing more active sites and a larger electrolyte / surface contact interface for the photoelectrochemical reaction. The two N2 adsorption-desorption curves show type IV isotherms accompanied by a type H3 hysteresis loop, indicating that the sample contains a mesoporous structure. The adsorption volume of the one-dimensional mesoporous-nanocomposite titanium dioxide photoanode in the medium-pressure region is significantly larger than that of the TiO2 nanorods, showing a larger volume of mesopores available for condensation.

[0050] One-dimensional mesoporous-nanocomposite titanium dioxide photoanodes were prepared with different dilution factors of mesoporous solutions, and their photoelectric performance was tested. Figure 11 The time-current response curves of one-dimensional mesoporous-nanoplasmic titanium dioxide photoanodes with different mesoporous solution dilution factors are shown. It can be seen that the photoanodes under different dilution factors of mesoporous solutions exhibit significantly different photoelectric responses, indicating that the thickness and morphology of the mesoporous layer directly affect the generation and transport behavior of photogenerated carriers. Among them, the photoanode with a mesoporous solution diluted 8 times has the highest photocurrent density, indicating that the mesoporous network formed at this dilution factor can provide additional surface sites without significantly hindering light penetration into the TiO2 nanorods. Furthermore, the good connectivity of the mesoporous network does not significantly increase electron diffusion resistance, thus effectively reducing carrier loss during transport. The photoanode with a mesoporous solution diluted 16 times shows a slight increase in photocurrent compared to pure nanorods, indicating that the moderate introduction of a small amount of mesopores can still improve interfacial properties and specific surface area. In contrast, the photocurrent of the undiluted mesoporous solution photoanode and the photoanode with the mesoporous solution diluted 4 times was significantly lower. The main reason is that the high-concentration mesoporous membrane forms a thick accumulation layer on the surface of the nanorod. Agglomeration makes it difficult for light to penetrate into the nanorod body. At the same time, the diffusion path of electrons in the thick mesoporous layer becomes longer, and the recombination probability increases, resulting in a significant decrease in photocurrent.

[0051] Figure 12The LSV curves of one-dimensional mesoporous-nanocomposite titanium dioxide photoanodes with different mesoporous solution dilution factors are shown. It can be seen that the one-dimensional mesoporous-nanocomposite titanium dioxide photoanodes with different mesoporous solution dilution factors exhibit significant differences in current density under illumination, which is closely related to their carrier utilization efficiency. The curve of the photoanode with an 8-fold dilution of the mesoporous solution rises the fastest overall and exhibits the highest current density under high bias voltage, indicating that this structure can provide the most active carriers to participate in the surface reaction under an applied electric field. Its excellent performance is closely related to the reasonable thickness and high connectivity of the mesoporous network, as well as the interfacial gain brought by the synergy between the mesoporous and nanorods. The curve of the photoanode with a 16-fold dilution of the mesoporous solution is the second best, reflecting that a small number of mesopores can also provide a moderate interfacial enhancement effect for the reaction. Both the undiluted mesoporous solution photoanode and the photoanode diluted 4 times in the mesoporous solution exhibited significantly lower photocurrents in the range of 0.8-1.5 V. This resulted in decreased light transmittance and increased electron transport resistance due to the thicker mesoporous layer. The excessively thick mesoporous cover not only made it difficult for light to reach the interior of the nanorod, but also increased the path length for electrons to migrate in the porous disordered structure, making it difficult for them to participate in surface reactions before being composited.

[0052] Figure 13 Electrochemical impedance spectroscopy (EIS) curves of one-dimensional mesoporous-nanoplasmic titanium dioxide photoanodes with different mesoporous solution dilution factors are shown. In the Nyquist plot, the semicircle diameter of each sample represents the magnitude of interfacial charge transport resistance. It can be seen that the photoanode diluted 8 times with the mesoporous solution has the smallest semicircle, indicating that this sample has the lowest interfacial transport resistance. Photogenerated electrons are more easily transported and reacted at the electrode / electrolyte interface because the resulting mesoporous network is more interconnected, enhancing electrolyte wettability and the contact area of ​​the active interface, thereby reducing the overall charge transport resistance. The photoanode diluted 16 times with the mesoporous solution has a higher impedance than the photoanode diluted 8 times, but is better than the pure nanorod (TNR), indicating that the thin mesoporous layer still promotes interfacial properties. Conversely, the impedances of the undiluted mesoporous solution photoanode and the photoanode diluted 4 times with the mesoporous solution are significantly increased, indicating that the excessively thick mesoporous layer hinders the effective transport of electrons. This is because the electron diffusion is impeded due to the lack of interconnection of channels or local aggregation within the mesoporous layer, resulting in a decrease in the carrier transport efficiency at the interface.

[0053] Figure 14 The current density graphs for one-dimensional mesoporous-nanocomposite titanium dioxide photoanodes with different dilution factors of mesoporous solutions are shown. It can be seen that the current density first decreases and then increases with increasing dilution of the mesoporous solution; the photoanode with an 8-fold dilution of the mesoporous solution exhibits a higher current density than the pure nanorod photoanode.

[0054] One-dimensional mesoporous-nanocomposite titanium dioxide photoanodes with different numbers of mesoporous layers were prepared, and their photoelectric properties were tested. Figure 15 The time-current response curves of one-dimensional mesoporous-nanoplasmic titanium dioxide photoanodes with different numbers of mesoporous loading layers are shown. It can be seen that with only two loading layers, a thin mesoporous film forms on the nanorod surface, slightly increasing the specific surface area, but not significantly improving interfacial contact and transport conditions, resulting in a low photocurrent. Three-layer mesoporous structures produce an inhomogeneous pore structure due to local aggregation; although the number of sites increases, local shading and diffusion obstruction limit the overall improvement. Four-layer mesoporous structures form a continuous and interconnected mesoporous network between nanorods, maintaining good light transmittance while significantly improving electrolyte wetting and carrier transport to the interface, thus exhibiting the highest and most stable photocurrent. In contrast, five-layer mesoporous structures lead to significant pore blockage and the formation of a dense film at the top, restricting both light transmittance and electrolyte diffusion, ultimately resulting in the lowest photocurrent.

[0055] Figure 16 The LSV curves for one-dimensional mesoporous-nanoparticle composite titanium dioxide photoanodes with different numbers of mesoporous loading layers are shown. It can be seen that the photoanode with two mesoporous layers has a low overall effective interface area due to limited mesoporous coverage, and the curve is located in the lower current region. Although the photoanode with three mesoporous layers shows some site increases, the local channel obstruction caused by agglomeration limits its growth. The photoanode with four mesoporous layers exhibits the highest current density across the entire potential region, especially showing a faster growth rate in the high potential region, indicating that its utilization rate of photogenerated carriers and interfacial reaction kinetics are significantly better than other layer numbers. In contrast, the photoanode with five mesoporous layers suffers from reduced light absorption and limited mass transfer due to pore blockage and dense film, resulting in a lower current density even under higher applied driving forces.

[0056] Figure 17 Electrochemical impedance spectroscopy (EIS) curves of one-dimensional mesoporous-nanoporous composite titanium dioxide photoanodes with the same number of mesoporous loading layers are shown. The results reveal significant differences with the number of mesoporous layers. The photoanode with two mesoporous layers exhibits a higher charge transport impedance, indicating that its thin mesoporous layer provides limited improvement to interfacial contact and electrolyte wetting. The photoanode with three mesoporous layers shows a relatively lower charge transport impedance, but due to localized blockage caused by agglomeration, its overall transport resistance remains high. The photoanode with four mesoporous layers exhibits the lowest impedance, indicating the smoothest interfacial charge transport. This advantage stems from the interconnected mesoporous network formed between the nanorods, which increases the interfacial contact area, reduces ion diffusion distance, and promotes the directional migration of photogenerated carriers. Conversely, the photoanode with five mesoporous layers shows a significantly increased charge transport impedance due to pore blockage and a dense top film, which lengthens the migration path of carriers and ions within the porous layers.

[0057] Figure 18The graph shows the current density of one-dimensional mesoporous-nanocomposite titanium dioxide photoanodes with different numbers of mesoporous loading layers. It can be seen that the current density first increases and then decreases with the increase of the number of mesoporous layers, and the photoanode with 4 mesoporous layers has the highest current density.

[0058] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A one-dimensional mesoporous-nanoporous composite titanium dioxide photoanode, characterized in that, It includes one-dimensional TiO2 nanorods and TiO2 mesoporous structures, wherein the one-dimensional TiO2 nanorods serve as a substrate and the TiO2 mesoporous structures are loaded on the one-dimensional TiO2 nanorods to form a mesoporous TiO2 film.

2. The one-dimensional mesoporous-nanoporous composite titanium dioxide photoanode according to claim 1, characterized in that, The surface of the mesoporous TiO2 film has a regularly arranged and uniformly distributed mesoporous structure.

3. The one-dimensional mesoporous-nanoporous composite titanium dioxide photoanode according to claim 1, characterized in that, The mesoporous structure is loaded on the surface of the one-dimensional TiO2 nanorods and located in the inter-rod voids of the one-dimensional TiO2 nanorods. The mesoporous structure forms a continuous three-dimensional interconnected network on the surface of the one-dimensional TiO2 nanorods and in the inter-rod voids.

4. A method for preparing a one-dimensional mesoporous-nanocomposite titanium dioxide photoanode, used to prepare the one-dimensional mesoporous-nanocomposite titanium dioxide photoanode according to any one of claims 1-3, characterized in that, Includes the following steps: Preparation of one-dimensional TiO2 nanorods; Mesoporous TiO2 was loaded onto one-dimensional TiO2 nanorods to obtain a one-dimensional mesoporous-nanocomposite titanium dioxide photoanode.

5. The method for preparing a one-dimensional mesoporous-nanocomposite titanium dioxide photoanode according to claim 4, characterized in that, The preparation of one-dimensional TiO2 nanorods includes the following steps: The conductive glass was placed in acetone, anhydrous ethanol and deionized water in sequence, and ultrasonically cleaned each time. Tetrabutyl titanate was added to concentrated hydrochloric acid and mixed thoroughly to obtain a mixed solution; The mixed solution and conductive glass were transferred to a high-pressure reactor for hydrothermal reaction. After the reaction was completed, the solution was taken out, rinsed with anhydrous ethanol and deionized water, dried, and then calcined in a tube furnace to obtain a TiO2 nanorod film loaded on the conductive glass.

6. The method for preparing a one-dimensional mesoporous-nanocomposite titanium dioxide photoanode according to claim 5, characterized in that, The conductive glass is FTO conductive glass, and the ultrasonic cleaning time is not less than 10 minutes; The volume ratio of concentrated hydrochloric acid to tetrabutyl titanate is 30:0.3~1. Tetrabutyl titanate is added dropwise to concentrated hydrochloric acid under magnetic stirring for a stirring time of not less than 30 minutes. The hydrothermal reaction temperature of the mixed solution and FTO conductive glass is 130~150℃, the hydrothermal heating time is 4~15 hours, the calcination atmosphere is air, and the temperature is increased from room temperature over 48 minutes at a rate of 10℃·min. -1 The final temperature was 500 ℃, and the calcination time was 1 h.

7. The method for preparing a one-dimensional mesoporous-nanocomposite titanium dioxide photoanode according to claim 4, characterized in that, Loading mesoporous TiO2 on one-dimensional TiO2 nanorods includes the following steps: Triblock polymer F127, concentrated hydrochloric acid and anhydrous ethanol were mixed evenly to obtain mixed solution A; Tetrabutyl titanate, acetylacetone and anhydrous ethanol were mixed evenly to obtain mixed solution B; Adding mixed solution A to mixed solution B yields a mesoporous solution; Mesoporous solution was dropped onto one-dimensional TiO2 nanorods and then subjected to evaporation self-assembly. One-dimensional TiO2 nanorods were calcined in a tube furnace to obtain a one-dimensional mesoporous-nanoparticle composite titanium dioxide photoanode.

8. The method for preparing a one-dimensional mesoporous-nanocomposite titanium dioxide photoanode according to claim 7, characterized in that, The mass ratio of the triblock polymer F127, concentrated hydrochloric acid, and anhydrous ethanol is 0.36:1.44:9~200. The mixture is magnetically stirred for 30 minutes to obtain mixed solution A. The mass ratio of tetrabutyl titanate, acetylacetone and anhydrous ethanol is 0.9:0.54:9~200, and the mixture is magnetically stirred for 20 minutes to obtain mixed solution B; Mixed solution A was added dropwise to mixed solution B, and the mixture was magnetically stirred for 24 hours to obtain a mesoporous solution. The undiluted concentration was the one with the lowest ratio of anhydrous ethanol in the mesoporous solution. The concentration of the mesoporous solution gradually decreased as the ratio of anhydrous ethanol increased. Mesoporous solution was dropped onto the surface of one-dimensional TiO2 nanorods and then placed in a constant temperature and humidity chamber for evaporative self-assembly. The temperature for the evaporative self-assembly method was 28 °C, the humidity was 45%, and the duration was 24 h. One-dimensional TiO2 nanorods were placed in a tube furnace for calcination in an air atmosphere. The calcination was started from room temperature and the temperature was increased over a period of 480 min at a rate of 1 °C / min for a total calcination time of 150 min.

9. The method for preparing a one-dimensional mesoporous-nanocomposite titanium dioxide photoanode according to claim 7, characterized in that, The steps of adding mesoporous solution and performing evaporation self-assembly can be repeated multiple times. After the one-dimensional TiO2 nanorods have completed evaporation self-assembly for 24 hours, they can be heated on a heating plate at 300℃ for 15 minutes, cooled to room temperature, and then the mesoporous solution is added again and the evaporation self-assembly method is performed to obtain a one-dimensional mesoporous-nanocomposite titanium dioxide photoanode with a multilayer mesoporous-nanocomposite structure.

10. An application of a one-dimensional mesoporous-nanocomposite titanium dioxide photoanode, employing the one-dimensional mesoporous-nanocomposite titanium dioxide photoanode as described in any one of claims 1-3, characterized in that, Used in photoelectrochemical cells for nitrogen reduction synthesis of ammonia.

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