Preparation of a TNTs / NiO@CoPi array electrode for photoelectrocatalytic decomposition of water

Abstract

This invention discloses a method for preparing a TNTs / NiO@CoPi array electrode (TNCP) for photoelectrocatalytic water splitting, belonging to the field of photoelectrocatalytic new energy materials technology. The invention first prepares a highly ordered anatase TiO2 nanotube array (TNTs) using secondary anodic oxidation, then loads Ni nanoparticles onto the surface and inside the nanotubes via constant current electrodeposition, followed by high-temperature calcination to generate p-type NiO, constructing a TNTs / NiO p-n heterojunction (TN). Finally, it uses AM 1.5 simulated sunlight to selectively deposit an amorphous CoPi cocatalyst, where the CoPi only coats the NiO nanospheres without blocking the TiO2 mass transfer channels. This invention utilizes the p-n heterojunction to broaden the full-spectrum light absorption from 250 to 800 nm, and CoPi acts as a hole-trapping layer to suppress electron-hole recombination, significantly reducing interfacial charge transport impedance; the steady-state photocurrent of the TNCP deposition sample reaches 0.06 mA·cm⁻. 2 It is three times that of pure TNTs. This process involves no precious metals or highly toxic corrosive solvents, and the reaction conditions are mild. The electrodes produced can be used for photoelectric water splitting to produce hydrogen, photoelectric oxidation of organic pollutants, and ethylene glycol photoelectric fuel cells. They exhibit excellent cycle stability and have promising prospects for large-scale industrial applications.

Description

Technical Field

[0001] This invention relates to the fields of photoelectrocatalytic water splitting and photoelectro-fuel cell technology, specifically to a low-cost, full-spectrum-response TNTs / NiO@CoPi composite nanotube array photoanode preparation process, which can be used for photoelectrocatalytic water splitting to produce hydrogen. Background Technology

[0002] The scarcity of fossil fuels and water pollution are two major challenges that urgently need to be addressed in the environmental and energy sectors. Photoelectrocatalysis technology can simultaneously produce hydrogen from water and degrade organic pollutants in water, offering advantages such as low energy consumption, green and pollution-free operation, and mild reaction conditions. The core lies in developing photoanode materials with high visible light utilization, strong carrier separation efficiency, and low interfacial charge transport resistance. Titanium dioxide nanotube arrays (TNTs) are classic n-type semiconductor photoanodes with excellent chemical stability and mature preparation processes. However, they suffer from drawbacks such as a wide intrinsic band gap (responding only to ultraviolet light), a fast photogenerated electron-hole recombination rate, and low photoelectric conversion efficiency, which greatly limit their practical applications.

[0003] Existing research has introduced CoPi cobalt-based cocatalysts to modify heterojunction electrodes. Compared with CoO, CoPi... x Significant advantages: The amorphous structure can quickly capture photogenerated holes and reduce the water oxidation overpotential. It can also self-assemble and reconstruct during the reaction, resulting in stronger resistance to photocorrosion. However, existing processes are difficult to achieve selective deposition of CoPi, which tends to indiscriminately coat the TNTs tube walls, blocking the nanotube channels and blocking the light absorption sites, thus reducing photoelectric performance. Furthermore, there is a lack of a complete, controllable, and adaptable composite electrode fabrication process that can not simultaneously achieve the three major properties of light absorption, charge separation, and interfacial hole transport. Summary of the Invention

[0004] This invention provides a method for preparing a TNTs / NiO@CoPi array electrode for photoelectrocatalytic water splitting, overcoming the technical shortcomings of pure TNTs (only UV response, severe carrier recombination), TNTs / NiO heterojunction (low hole utilization, weak built-in electric field separation), and traditional cobalt-based cocatalysts (random coating and clogging of nanotubes, poor electrode stability). The method achieves selective CoPi deposition on the surface of NiO nanoparticles without obstructing TiO2 nanotube channels, simultaneously broadening full-spectrum light absorption, enhancing charge separation in the pn heterojunction, and reducing interfacial charge transport resistance. This significantly improves the performance of photoelectrocatalytic water splitting for hydrogen production and the oxidation and degradation of organic pollutants. The entire process involves no highly toxic reagents, has low equipment requirements, and is suitable for large-scale preparation.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] 1. A method for preparing a TNTs / NiO@CoPi array electrode for photoelectrocatalytic water splitting, characterized by comprising titanium substrate pretreatment, secondary anodic oxidation to prepare TNTs, constant current electrodeposition of TNTs / Ni precursor, and visible light selective photodeposition of CoPi to obtain the catalyst.

[0007] Furthermore, the titanium sheet was mechanically polished using 1000-grit sandpaper, and then ultrasonically cleaned with ethanol and ultrapure water for 10-20 minutes respectively to remove the oxide film and oil stains on the surface of the nickel sheet, and then dried at room temperature.

[0008] Furthermore, the secondary anodic oxidation electrolyte was an ethylene glycol solution containing 0.3~0.5 wt% NH4F and 2 Vol% ultrapure water; the oxidation voltage was 30 V; the primary oxidation time was 3 h, followed by a secondary oxidation under the same conditions for 3 h after ultrasonic stripping of the oxide film; the annealing heating rate was 2 ℃ / min, and the temperature was maintained at 500 ℃ for 2 h.

[0009] Furthermore, the oxidation products were washed and dried, and then subjected to a process at 2 °C·min. -1 The TNT substrate was obtained by calcining at 500 ℃ for 2 h.

[0010] Furthermore, the TNTs / NiO electrode employs a three-electrode constant current electrodeposition process, with the pH of the nickel salt mixed electrolyte adjusted to 4.5, a deposition current of 5 mA, and an effective deposition area of ​​1 × 2 cm⁻². -2 The deposition time is controlled to be 2~10 min.

[0011] Furthermore, the obtained electrodeposited product was calcined at 400 °C for 240 min to convert metallic nickel into NiO nanoparticles.

[0012] Preferably, the CoPi film is deposited using AM1.5 simulated sunlight-assisted photodeposition with a light intensity of 100 mW·cm. -2 Before deposition, the TNTs / NiO electrode was immersed in the cobalt precursor solution for 5-10 min.

[0013] Furthermore, the CoPi deposition electrolyte was a 0.5 mM Co(NO3)2 solution prepared with 0.05 M PBS, and the photodeposition time range was 30~300 s, thereby controlling the CoPi film loading.

[0014] Furthermore, the product obtained after photodeposition is placed in a vacuum drying oven and dried at 40-60℃ to obtain the TNTs / NiO@CoPi composite photoanode (TNCP).

[0015] This invention employs four core processes to prepare a TNTs / NiO@CoPi array electrode for photoelectrocatalytic water splitting: titanium substrate pretreatment, secondary anodic oxidation to prepare TNTs, constant current electrodeposition of TNTs / Ni precursor, and visible light selective photodeposition of CoPi. The titanium dioxide nanotube (TNTs) substrate electrode is prepared using secondary anodic oxidation. A three-electrode constant current electrodeposition process is then used, employing a nickel salt mixed solution as the electrodeposition liquid. The NiO loading can be precisely controlled by simply changing the electrodeposition time (2-10 min), without changing core parameters such as electrolyte or voltage. This single variable facilitates comparative experiments to screen for the optimal loading ratio. Driven by the photogenerated electrons of TNTs / NiO, CoPi selectively grows only on the surface of NiO nanoparticles, without extensively coating the TNTs substrate, thus maximizing the light-harvesting ability of TiO2. Unlike traditional immersion and hydrothermal methods, this allows for the controllable preparation of ultrathin co-catalytic films, avoiding the masking of active sites. The entire preparation process requires no precious metals or highly toxic corrosive reagents such as HF and DMF. The anodic oxidation, electrodeposition, and photodeposition processes are mild and easily scalable. The pn heterojunction constructed based on TNTs / NiO achieves full-spectrum absorption of 250~800 nm UV-Vis light. Amorphous CoPi can selectively coat Ni nanospheres without blocking the mass transfer channels of TiO2 nanotubes. It can efficiently capture photogenerated holes, passivate surface charge traps, and significantly suppress electron-hole recombination. It can also increase the carrier concentration difference on both sides of the heterojunction to enhance the charge separation effect of the built-in electric field. It can be efficiently adapted to photoelectric water splitting for hydrogen production.

[0016] Most specifically, a method for preparing a TNTs / NiO@CoPi array electrode (TNCP) for photoelectrocatalytic water splitting is characterized by the following steps:

[0017] First, titanium dioxide nanotubes (TNTs) substrate electrodes were prepared using a two-stage anodic oxidation method. A titanium sheet was used as the working electrode, and a platinum sheet as the counter electrode. An ethylene glycol-ammonium fluoride mixture (0.3-0.4 wt% NH4F, 2.0 vol% ultrapure water) was used as the electrolyte. Two anodic oxidation processes were performed at 30-50 V for 3-5 h each. After the first oxide film was stripped, a second oxidation was performed. Following cleaning, the electrodes were annealed and crystallized at 450-500 °C to obtain well-defined, large-diameter TNTs electrodes. Subsequently, a three-electrode constant-current electrodeposition process was employed, using a nickel salt mixture as the electrodeposition solution. The three-electrode system underwent constant-current deposition, and after deposition, the temperature remained constant at 300-400 °C. Ni was calcined in air at ℃ to convert Ni into NiO, obtaining a TNTs / NiO composite substrate (abbreviated as TN). Finally, the TN electrode substrate was immersed in cobalt nitrate phosphate (PBS) precursor solution and photodeposited under AM1.5 standard sunlight. CoPi was selectively grown on the surface of NiO nanoparticles. After rinsing with pure water and drying at low temperature, a TNTs / NiO@CoPi (TNCP) array composite electrode that can be used for photoelectrocatalytic water splitting was finally obtained.

[0018] The present invention has the following technical effects:

[0019] The method developed in this invention for preparing TNTs / NiO@CoPi array electrodes for photoelectrocatalytic water splitting possesses multiple advantages, including a green and low-cost preparation process, excellent optical and photoelectric properties, wide application scenarios, and strong cycling stability. The entire preparation process requires no precious metals or highly toxic corrosive reagents such as HF and DMF. The anodic oxidation, electrodeposition, and photodeposition processes are mild and easily scalable. The pn heterojunction constructed using TNTs / NiO achieves full-spectrum absorption of 250–800 nm UV-Vis light. Amorphous CoPi can selectively coat Ni nanospheres without blocking the mass transfer channels of TiO2 nanotubes, efficiently capturing photogenerated holes, passivating surface charge traps, and significantly suppressing electron-hole recombination. It also expands the carrier concentration difference across the heterojunction, enhancing the charge separation effect of the built-in electric field. The steady-state photocurrent of TNCP reaches 2–3 times that of pure TNTs, and the interfacial charge transfer impedance is significantly reduced. Furthermore, CoPi can self-assemble and reconstruct during the catalytic process, exhibiting stronger resistance to photocorrosion. After multiple cycles, the decline in crystal structure and catalytic activity is minimal, making it highly suitable for photoelectrocatalytic water splitting to produce hydrogen. Attached Figure Description

[0020] Figure 1 SEM images of TNTs, TN, and TNCP, and average particle size of surface NiO particles.

[0021] Figure 2 MS diagrams of TNTs, TN, and TNCP.

[0022] Figure 3Photocurrent density diagrams for TNTs, TN, and TNCP.

[0023] Figure 4 EIS diagrams of TNTs, TN, and TNCP Detailed Implementation

[0024] Example 1

[0025] A method for preparing a TNTs / NiO@CoPi array electrode for photoelectrocatalytic water splitting comprises the following steps:

[0026] Titanium dioxide nanotube (TNT) substrate electrodes were prepared using a two-stage anodic oxidation method. A titanium sheet was used as the working electrode, a platinum sheet as the counter electrode, and an ethylene glycol-ammonium fluoride mixture as the electrolyte. Two anodic oxidation processes were performed at 30 V for 3 h each time. After the first oxide film was peeled off, a second oxidation was performed. After cleaning, the electrodes were annealed and crystallized at 400 °C to obtain regular, large-diameter TNT electrodes. Subsequently, a three-electrode constant-current electrodeposition process was used, with a nickel salt mixture as the electrodeposition solution. The three-electrode system underwent constant-current deposition. After deposition, the electrodes were calcined in air at 300 °C to convert Ni to NiO, obtaining a TNTs / NiO composite substrate (abbreviated as TN). Finally, the TN electrode substrate was immersed in cobalt nitrate phosphate (PBS) precursor solution and photodeposited under AM1.5 standard sunlight. CoPi selectively grew on the surface of NiO nanoparticles. After rinsing with pure water and low-temperature drying, a TNTs / NiO@CoPi (TNCP) array composite electrode suitable for photoelectrocatalytic water splitting was obtained.

[0027] Example 2

[0028] A method for preparing a TNTs / NiO@CoPi array electrode for photoelectrocatalytic water splitting comprises the following steps:

[0029] First, titanium dioxide nanotubes (TNTs) substrate electrodes were prepared using a two-stage anodic oxidation method. A titanium sheet was used as the working electrode, and a platinum sheet as the counter electrode. An ethylene glycol-ammonium fluoride mixture (0.4 wt% NH4F, 2.0 vol% ultrapure water) was used as the electrolyte. Two anodic oxidation processes were performed at 40 V for 4 h each. After the first oxide film was stripped, a second oxidation was performed. Following cleaning, the electrodes were annealed and crystallized at 450 °C to obtain well-formed, large-diameter TNTs electrodes. Subsequently, a three-electrode constant-current electrodeposition process was employed, using a nickel salt mixture as the electrodeposition solution. The three-electrode system underwent constant-current deposition, and after deposition, the electrode was deposited at 350 °C. Ni was calcined in air at ℃ to convert Ni into NiO, obtaining a TNTs / NiO composite substrate (abbreviated as TN). Finally, the TN electrode substrate was immersed in cobalt nitrate phosphate (PBS) precursor solution and photodeposited under AM1.5 standard sunlight. CoPi was selectively grown on the surface of NiO nanoparticles. After rinsing with pure water and drying at low temperature, a TNTs / NiO@CoPi (TNCP) array composite electrode that can be used for photoelectrocatalytic water splitting was finally obtained.

[0030] Example 3

[0031] A method for preparing a TNTs / NiO@CoPi array electrode for photoelectrocatalytic water splitting comprises the following steps:

[0032] Titanium dioxide nanotube (TNT) substrate electrodes were prepared using a two-stage anodic oxidation method. A titanium sheet was used as the working electrode, and a platinum sheet as the counter electrode. An ethylene glycol-ammonium fluoride mixture (0.5 wt% NH4F, 2.0 vol% ultrapure water) was used as the electrolyte. Two anodic oxidation processes were performed at 40 V for 5 h each. After the first oxide film was peeled off, a second oxidation was performed. Following cleaning, the electrodes were annealed and crystallized at 500 °C to obtain well-formed, large-diameter TNT electrodes. Subsequently, a three-electrode constant-current electrodeposition process was used, with a nickel salt mixture as the electrodeposition solution. The three-electrode system underwent constant-current deposition. After deposition, the electrodes were calcined in air at 400 °C to convert Ni to NiO, obtaining a TNTs / NiO composite substrate (abbreviated as TN). Finally, the TN electrode substrate was immersed in cobalt nitrate phosphate (PBS) precursor solution and photodeposited under AM1.5 standard sunlight. CoPi selectively grew on the surface of NiO nanoparticles. After rinsing with pure water and low-temperature drying, a TNTs / NiO@CoPi (TNCP) array composite electrode suitable for photoelectrocatalytic water splitting was obtained.

[0033] From the appendix Figure 1It can be seen that the pure TNT nanotubes are densely arranged and have smooth walls; NiO nanospheres are uniformly distributed on the surface of the electrodeposited TN sample; after photodeposition of CoPi, only the particle size of Ni particles increases, and the TiO2 nanotube channels are unobstructed throughout, confirming that CoPi grows selectively only on the NiO surface; particle size statistics show that the NiO loading size of the TNCP-90 sample is moderate and the catalytic activity is optimal.

[0034] From the appendix Figure 2 It can be seen that the Mott-Schottky curve of pure TNTs is a positive slope n-type semiconductor; the TN electrode shows an inverted U-shaped curve, confirming that TNTs / NiO successfully constructed a pn heterojunction; the second half of the TNCP sample curve shows a slight red shift, with only the NiO band changing, further confirming that the selective modification of NiO by CoPi does not affect the TNTs substrate.

[0035] Comparison Appendix Figure 3 The transient spectral changes show that the steady-state photocurrent of pure TNTs is only 0.02 mA·cm⁻¹ within 120 minutes. -2 The TN electrode exhibits a high transient peak value but rapid charge recombination, with a steady-state peak value of only 0.05 mA·cm⁻¹. -2 The steady-state photocurrent of TNCP reaches 0.06 mA·cm. -2 It is significantly superior to pure TNTs.

[0036] Appendix Figure 4 The charge transport capability of the TNTs / NiO@CoPi (TNCP) composite photoelectrode was investigated. The TN electrode interface transfer impedance was 1086.0 Ω, while that of the TNCP electrode was reduced to 394.9 Ω, resulting in a 2.5-fold reduction in charge transport resistance. The dark recombination rate constant decreased significantly when the lamp was off, the half-life of photogenerated electrons was prolonged, and the hole utilization rate was greatly improved.

[0037] Obviously, the above description is merely an embodiment of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the present invention or the practicality of the patent.

Claims

1. A method for preparing a TNTs / NiO@CoPi array electrode for photoelectrocatalytic water splitting, characterized in that: Titanium dioxide nanotube (TNT) substrate electrodes were prepared by a two-stage anodic oxidation method. A titanium sheet was used as the working electrode and a platinum sheet as the counter electrode. An ethylene glycol-ammonium fluoride mixture was used as the electrolyte. The electrodes were anodicly oxidized twice for 3-5 hours at a voltage of 30-50 V. After the oxide film was peeled off, the electrodes were oxidized again. After cleaning, the electrodes were annealed and crystallized at 400-500 °C to obtain regular, large-diameter TNT electrodes. Subsequently, a three-electrode constant current electrodeposition process was adopted, using a nickel salt mixed solution as the electrodeposition solution. The three-electrode system was subjected to constant current deposition. After deposition, the substrate was calcined in air at 300~400 °C to convert Ni into NiO, obtaining a TNTs / NiO composite substrate (abbreviated as TN). Finally, the TN electrode substrate was immersed in cobalt nitrate phosphate (PBS) precursor solution and photodeposited under AM1.5 standard sunlight. CoPi selectively grew only on the surface of NiO nanoparticles. After rinsing with pure water and drying at low temperature, a TNTs / NiO@CoPi (TNCP) array composite electrode that can be used for photoelectrocatalytic water splitting was finally obtained, named TNCP.

2. The method for preparing a TNTs / NiO@CoPi composite photoanode for photoelectrocatalytic water splitting as described in claim 1, characterized in that: The TNT electrodes were prepared using a two-stage anodic oxidation process with a two-electrode system. The electrolyte was an ethylene glycol solution containing 0.3–0.5 wt% NH4F and 2.0 vol% ultrapure water. Anodizing was performed in two stages for 3 hours at room temperature and 30 V. After the initial oxidation, the surface oxide film was removed by ultrasonication at 100% power for 10 minutes. The oxidation product was then rinsed, dried, and subjected to an anodic oxidation process at 2 °C for 1 minute. -1 The TNT substrate was obtained by calcining at 500 ℃ for 2 h.

3. The method for preparing a TNTs / NiO@CoPi composite photoanode for photoelectrocatalytic water splitting as described in claim 1 or 2, characterized in that: The TNTs / NiO electrode employs a three-electrode constant current electrodeposition process. The pH of the nickel salt mixed electrolyte is adjusted to 4.5, the deposition current is 5 mA, and the effective deposition area is 1 × 2 cm⁻². -2 The deposition time is controlled to be 2~10 min.

4. The method for preparing a TNTs / NiO@CoPi composite photoanode for photoelectrocatalytic water splitting as described in any one of claims 1-3, characterized in that: The obtained electrodeposited product was calcined at 400 °C for 240 min to convert metallic nickel into NiO nanoparticles.

5. A TNTs / NiO@CoPi array electrode for photoelectrocatalytic water splitting as described in claim 4, characterized in that: CoPi thin films were deposited using AM1.5 simulated sunlight-assisted photodeposition with a light intensity of 100 mW·cm⁻¹. -2 Before deposition, the TNTs / NiO electrode was immersed in the cobalt precursor solution for 5-10 min.

6. A TNTs / NiO@CoPi array electrode for photoelectrocatalytic water splitting as described in claim 5, characterized in that: The CoPi deposition electrolyte was a 0.5 mM Co(NO3)2 solution prepared with 0.05 M PBS, and the photodeposition time range was 30~300s to control the CoPi film loading.

7. A TNTs / NiO@CoPi array electrode for photoelectrocatalytic water splitting as described in claim 5 or 6, characterized in that: After photodeposition, the product is placed in a vacuum drying oven and dried at 40-60℃ to obtain the TNTs / NiO@CoPi composite photoanode (TNCP).

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