CN112481634A - Ternary composite TiO2Preparation method and application of-STO-CdS NRs photoelectrode - Google Patents

Ternary composite TiO2Preparation method and application of-STO-CdS NRs photoelectrode Download PDF

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CN112481634A
CN112481634A CN202011070791.7A CN202011070791A CN112481634A CN 112481634 A CN112481634 A CN 112481634A CN 202011070791 A CN202011070791 A CN 202011070791A CN 112481634 A CN112481634 A CN 112481634A
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CN112481634B (en
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何艳芳
曹大威
刘圆
陈明明
朱建飞
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Jiangsu University
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Abstract

The invention belongs to the technical field of photoelectrochemical water decomposition, and relates to ternary composite TiO2Preparation of-STO-CdS NRs photoelectrode: contains 0.2 to 0.5M hydroxylamine hydrochloride and 0.1 to 0.25M Na2S·9H2Transferring the mixed solution of O into a high-pressure reaction kettle, and immersing into TiO2Performing hydrothermal reaction on the NR array electrode for 2-10 h, and reacting the TiO containing the surface amorphous nano layer2Putting the NR array electrode into a high-pressure reaction kettle, and pouring 0.01-0.03M of Sr (OH)2·8H2Immersing in water solution of O, hydrothermal reaction to obtain TiO2(ii)/STO NRs; CdS quantum dots which are uniformly distributed are deposited on the surface of the STO nano-layer by a chemical bath deposition method, so that the coupling of a 1D/0D heterojunction and a dipole layer induced by interface ferroelectric polarization is realized. Ternary composite TiO constructed by the invention2the/STO/CdS NRs photoelectrode is applied to high-efficiency PEC water decomposition. Ferroelectric STO nanolayers produce strong and persistent spontaneous polarization that causes the orientation of TiO from the STO/CdS interface2The polar charge at the/STO interface induces an electric field. The ternary heterojunction and the STO polar charge induction electric field are coupled, and the ternary heterojunction and the STO polar charge induction electric field are cooperated to endow durable and rapid photo-generated charge separation capability, and inhibit possible body or interface charge recombination.

Description

Ternary composite TiO2Preparation method and application of-STO-CdS NRs photoelectrode
Technical Field
The invention belongs to the technical field of photoelectrochemical water decomposition, relates to a composite photoelectric catalyst, and particularly relates to a ternary composite TiO2 -STO-CdS NRs（TiO2A preparation method and application of a/STO/CdS NRs) photoelectrode.
Background
Photoelectrochemical water splitting provides an efficient way to produce chemical fuels by converting solar energy. Essentially, a photoelectrochemical reaction is a process of photoelectric conversion that involves photoexcitation, separation, and transfer of charge carriers. Based on this, TiO2Nanorod (NR) arrays have been considered as a very promising photoelectrochemical photoelectrode for water splitting due to their specific one-dimensional structure with high aspect ratio, strong light trapping ability and directional electron transporting and transferring ability. Despite the advantageous properties mentioned above, there are some inevitable disadvantages that limit TiO2Photoelectrochemical activity of NR including underutilization of sunlight and TiO2In NR, the severe recombination of photo-generated charge carriers on the bulk or surface results from: (1) the absorption range of the solar spectrum is narrow (ultraviolet light only accounts for 5 percent of sunlight) due to wide band gaps (3.0-3.2 eV); (2) TiO22The charge separation efficiency is low due to the short diffusion path of the photogenerated carriers.
In recent years, TiO of narrow band gap semiconductor composite2The NR array photoanode shows outstanding advantages in photoelectrochemical water splitting application, and on one hand, the structure takes a semiconductor with narrow band gap width as a composite light absorption layer, so that TiO is greatly increased2The visible light response photoelectrochemical activity of the NR array photoanode; on the other hand, the two semiconductor materials form a heterojunction structure, and a built-in electric field is formed at the interface due to the Fermi level difference to drive the photo-generated charges to be separated efficiently. However, in the light ofIn internal transport of the charge generating material, TiO2The electrons in (b) still tend to undergo in vivo recombination. At the same time, TiO2The charge transfer at the interface of the nanomaterial composite photoelectrode is hindered by the inevitable charge traps on the NR surface. Furthermore, the rapid accumulation of charge carriers during the photoreaction will severely neutralize the built-in electric field between the heterojunctions, resulting in a gradual decrease of the driving force for separating electron-hole pairs. These inherent defects severely restrict TiO2The charge separation efficiency of the NR-based heterojunction photoelectrode limits the photoelectrochemical water splitting performance of the photoelectrode. Therefore, there is an urgent need to develop an integrated design that can solve the above problems at the same time to maximize TiO enhancement2Photoelectrochemical activity of NR-based heterojunction photoelectrodes.
Disclosure of Invention
In order to solve the above problems, an object of the present invention is to disclose a ternary composite TiO2A preparation method of a/STO/CdS NRs photoelectrode.
Technical scheme
By simple in situ hydrothermal conversion at TiO2A layer of tightly coated ferroelectric SrTiO is constructed on the surface of NR3And (STO) a nano layer, and depositing uniformly distributed CdS quantum dots on the surface of the STO nano layer by a chemical bath deposition method, so that the coupling of a 1D/0D heterojunction and an interface ferroelectric polarization induced dipole layer is realized, and the photo-generated charge separation efficiency of a photoelectrode is well regulated and controlled.
Ternary composite TiO2The preparation method of the/STO/CdS NRs photoelectrode comprises the following steps:
(1) in TiO2Construction of ferroelectric SrTiO on NR surface3Nanolayer (TiO)2 /STO）：
Containing 0.2 to 0.5M hydroxylamine hydrochloride and 0.1 to 0.25M Na2S·9H2Transferring the mixed solution of O into a stainless steel high-pressure reaction kettle with a polytetrafluoroethylene lining, and immersing the stainless steel high-pressure reaction kettle into TiO2The NR array electrode continuously reacts for 2-10 h at 120-180 ℃, preferably for 4h at 180 ℃, so as to achieve the purpose of corroding the surface and constructing an amorphous nano layer on the surface; cooling to room temperature, thoroughly washing with deionized water, and making the surface amorphousNano-layered TiO2Putting the NR array electrode into a polytetrafluoroethylene lining stainless steel high-pressure reaction kettle, and pouring 0.01-0.03M of Sr (OH)2·8H2Immersing the O aqueous solution, continuously reacting for 2-6 h at 120-180 ℃, preferably reacting for 4h at 180 ℃, and reacting on TiO2In-situ construction of ferroelectric STO nanolayers (TiO) on NR surface2/STO NRs）；
(2) Constructing CdS quantum dot modified ternary composite TiO2the/STO/CdS NRs photoelectrode:
adding TiO into the mixture2the/STO NRs are immersed in an open container containing 10 mL of deionized water, and stirred at 45 ℃ to be heated uniformly; 5mL of 40mM C was added4H6CdO4·2H2Continuously stirring the O aqueous solution for 30min, adding 5mL of 40mM thiourea aqueous solution, then injecting 100 mu L of concentrated ammonium hydroxide, and continuously stirring for 20min to realize the chemical bath deposition growth of CdS QD; the resulting TiO2the/STO/CdS NRs were washed thoroughly with ethanol and washed in N2Drying; the above process is repeated for 1-3 times (repeated from the step of immersing in deionized water); annealing at 350 deg.C for 30min in Ar atmosphere to obtain TiO2/STO/CdS NRs。
The TiO of the invention2NR array electrodes, a common preparation method for the prior art: adding 0.45g of NaCl and 0.4mL of tetrabutyl titanate into 24mL of 4-8M HCl aqueous solution at an ambient temperature, and stirring for 10-30 min; transferring the mixture into a polytetrafluoroethylene-lined stainless steel high-pressure reaction kettle, placing the FTO conductive glass electrode in the mixed solution in a downward inclined manner, and carrying out hydrothermal reaction at 120-200 ℃ for 4-10 h, preferably at 150 ℃ for 7 h; TiO cooled to room temperature2The NRs array is annealed for 1h at 450 ℃ in the air after being washed by deionized water to obtain TiO2And NR array electrodes.
The ternary composite TiO prepared by the method of the invention2the/STO/CdS NRs photoelectrode is in a multilayer coaxial nanorod array structure: TiO22Is a nano-rod core, the tightly coated ferroelectric STO nano-layer is a nano-rod shell, and discontinuous CdS quantum dots are used as a nano-rod surface modification layer.
It is a further object of the present invention to provide a ternary composite TiO material2the/STO/CdS NRs photoelectrode is applied to high-efficiency PEC water decomposition.
The prepared photoelectric electrode is taken as a working electrode, a platinum sheet is taken as a counter electrode, Ag/AgCl is taken as a reference electrode, and the electrolyte is 0.35M Na2SO3 + 0.25 M Na2S (pH value of 12.5), atmosphere lamp with AM1.5G filter, and light intensity of 100 mW/cm2And performing photoelectrochemical test.
With unmodified TiO2Compared with the nanorod array photoelectrode, the charge separation efficiency of the photoelectrode is improved by 148% under the regulation and control of the method. Due to effective visible light absorption and the extremely small size of the 0D nano material, the charge carrier density is greatly improved by the 0D CdS quantum dots on the surfaces of the nanorods; in addition, the greatly enhanced hole extraction rate of CdS quantum dots further promotes TiO2Charge separation of the/STO/CdS ternary heterojunction. The regulation and control of the invention ensures that the photoelectrode shows excellent photoelectrochemical activity, and the photocurrent density of the photoelectrode reaches 1.85 mA/cm2(1.23V vs RHE), pure TiO under the same test conditions2Nanorod array photoelectrode (0.25 mA/cm)2) 7.4 times of the total weight of the powder.
In this specification, the term "STO" is SrTiO3The two are used interchangeably.
In the present specification, the term "NR" is an abbreviated name of "nanorod", which are used interchangeably.
In the present specification, the term "NRs" is an abbreviated name of "nanorod array", which are used interchangeably.
In this specification, the term "TiO"2by/STO "is meant that the STO shell coats the TiO2A core heterojunction structure complex, the two being used interchangeably.
In this specification, the term "TiO"2The term/STO/CdS refers to TiO with CdS quantum dots modified on the surface2the/STO complex, both of which are used interchangeably.
Advantageous effects
The preparation method has simple operation steps, and the constructed ternary composite TiO2The ferroelectric STO nano-layer of the/STO/CdS NRs photoelectrodeProlonged spontaneous polarization, resulting in TiO pointing from the STO/CdS interface2The polar charge at the/STO interface induces an electric field. TiO with cascade energy band arrangement2the/STO/CdS ternary heterojunction and the STO polar charge induction electric field are coupled, and the composite photoelectrode is endowed with lasting and quick photo-generated charge separation capability cooperatively, so that possible bulk or interface charge recombination of the composite photoelectrode is inhibited.
Drawings
FIG. 1 (A and D) TiO2NR, (B and E) TiO2STONR and (C and F) TiO2A scanning electron micrograph of/STO/CdS NR, wherein FIG. A, B, C is a surface topography of the nanoarray and FIG. D, E, F is a cross-sectional view of the nanoarray;
FIG. 2.TiO2Transmission electron micrographs of/STO/CdS NR, where FIG. A, B, C is a low power transmission electron micrograph (A) and a high power transmission electron micrograph (B, C), respectively, and FIG. D is a TiO2Schematic diagram of crystal plane structure at the/STO interface;
FIG. 3 (A) is a linear sweep voltammogram for each photoelectrode, and (B) is a plot of charge separation efficiency for each photoelectrode as a function of applied bias voltage;
FIG. 4 (A) TiO2STO and (B) TiO2Linear sweep voltammograms of/STO/CdS before and after polarization.
Detailed Description
The following detailed description of the embodiments of the present invention is provided with reference to the drawings, which are implemented on the premise of the technical solution of the present invention, and the detailed implementation and the specific operation process are provided, but the protection scope of the present invention is not limited to the following embodiments.
Example 1
(1) Preparation of TiO2NR array electrode:
0.45g NaCl and 0.4mL tetrabutyltitanate are added to 24mL aqueous HCl (4M) at ambient temperature and stirred for 10 min. Then, the mixed solution is transferred into a polytetrafluoroethylene-lined stainless steel high-pressure reaction kettle, and the FTO conductive glass electrode is placed in the mixed solution with the conductive surface facing downwards and reacts for 4 hours at 120 ℃ to carry out hydrothermal synthesis. However, the device is not suitable for use in a kitchenThen, the TiO cooled to room temperature2NRs arrays were rinsed with deionized water and TiO2Annealing NR in air at 450 ℃ for 1h to obtain TiO2And NR array electrodes.
(2) In TiO2Construction of ferroelectric SrTiO on NR surface3Nanolayer (TiO)2 /STO）：
Will contain 0.2M hydroxylamine hydrochloride and 0.1M Na2S·9H2Transferring the mixed solution of O into a polytetrafluoroethylene-lined stainless steel high-pressure reaction kettle, and putting the TiO obtained in the step (1)2Performing continuous reaction for 2h at 120 ℃ on the NR array electrode to achieve the purpose of constructing an amorphous nano-layer on the surface by surface corrosion; when the temperature is cooled to room temperature, the mixture is thoroughly washed by deionized water; then adding the TiO containing the surface amorphous nano-layer2The NR array electrode was placed in a stainless steel autoclave lined with Teflon, and 0.01M Sr (OH) was poured into the autoclave2·8H2Continuously reacting O aqueous solution for 2 hours at the temperature of 120 ℃ to obtain the product2The NR surface builds the ferroelectric STO nanolayers in situ.
(3) Constructing CdS quantum dot modified ternary composite TiO2the/STO/CdS NRs photoelectrode:
adding TiO into the mixture2the/STO NRs were immersed in a beaker containing 10 mL of deionized water and heated to homogeneity with stirring at 45 ℃. Then 5mL of C was added4H6CdO42H2O in water (40 mM). After stirring for 30min, 5mL of an aqueous thiourea solution (40 mM) was added to the beaker. And then, 100 mu L of concentrated ammonium hydroxide is injected into the solution and is kept for 20min, so that the chemical bath deposition growth of the CdS QD is realized. The resulting TiO2the/STO/CdS NRs were washed thoroughly with ethanol and washed in N2And (4) drying. Finally, annealing at 350 ℃ for 30min under Ar atmosphere to obtain TiO2the/STO/CdS NR samples.
(4) And performing photoelectrochemical test on the prepared photoelectrode by utilizing a three-electrode system:
the prepared photoelectric electrode is taken as a working electrode, a platinum sheet is taken as a counter electrode, Ag/AgCl is taken as a reference electrode, and the electrolyte is 0.35M Na2SO3 + 0.25 M Na2S (pH 12.5) aqueous solution. Atmosphere lamp with AM1.5G optical filterThe light intensity is adjusted to be 100 mW/cm2。
Example 2
(1) Preparation of TiO2NR array electrode:
0.45g NaCl and 0.4mL tetrabutyltitanate are added to 24mL aqueous HCl (8M) at ambient temperature and stirred for 15 min. Then, the mixed solution is transferred into a polytetrafluoroethylene-lined stainless steel high-pressure reaction kettle, and the FTO conductive glass electrode is placed in the mixed solution with the conductive surface facing downwards and reacts for 7 hours at 150 ℃ to carry out hydrothermal synthesis. Then, the TiO cooled to room temperature2NRs arrays were rinsed with deionized water and TiO2Annealing NR in air at 450 ℃ for 1h to obtain TiO2And NR array electrodes.
(2) In TiO2Construction of ferroelectric SrTiO on NR surface3Nanolayer (TiO)2 /STO）：
Will contain 0.35M hydroxylamine hydrochloride and 0.17M Na2S·9H2Transferring the mixed solution of O into a polytetrafluoroethylene-lined stainless steel high-pressure reaction kettle, and putting the TiO obtained in the step (1)2The NR array electrode continuously reacts for 4 hours at 150 ℃ to achieve the purpose of constructing an amorphous nano-layer on the surface by surface corrosion; when the temperature is cooled to room temperature, the mixture is thoroughly washed by deionized water; then adding the TiO containing the surface amorphous nano-layer2The NR array electrode was placed in a stainless steel autoclave lined with Teflon, and 0.02M Sr (OH) was poured into the autoclave2·8H2O aqueous solution is continuously reacted for 4 hours at 150 ℃ to realize the reaction on TiO2The NR surface builds the ferroelectric STO nanolayers in situ.
(3) Constructing CdS quantum dot modified ternary composite TiO2the/STO/CdS NRs photoelectrode:
adding TiO into the mixture2the/STO NRs were immersed in a beaker containing 10 mL of deionized water and heated to homogeneity with stirring at 45 ℃. Then 5mL of C was added4H6CdO42H2O in water (40 mM). After stirring for 30min, 5mL of an aqueous thiourea solution (40 mM) was added to the beaker. And then, 100 mu L of concentrated ammonium hydroxide is injected into the solution and is kept for 20min, so that the chemical bath deposition growth of the CdS QD is realized. The resulting TiO2the/STO/CdS NRs were washed thoroughly with ethanol and washed in N2And (4) drying. The above process was repeated 2 times. Finally, TiO2/STO/CdS NR samples were obtained after annealing at 350 ℃ for 30min under Ar atmosphere.
(4) And performing photoelectrochemical test on the prepared photoelectrode by utilizing a three-electrode system:
the prepared photoelectric electrode is taken as a working electrode, a platinum sheet is taken as a counter electrode, Ag/AgCl is taken as a reference electrode, and the electrolyte is 0.35M Na2SO3 + 0.25 M Na2S (pH 12.5) aqueous solution. Atmosphere lamp with AM1.5G optical filter, light intensity is adjusted to 100 mW/cm2。
Example 3
(1) Preparation of TiO2NR array electrode:
0.45g NaCl and 0.4mL tetrabutyltitanate are added to 24mL aqueous HCl (6M) at ambient temperature and stirred for 30 min. Then, the mixed solution is transferred into a polytetrafluoroethylene-lined stainless steel high-pressure reaction kettle, and the FTO conductive glass electrode is placed in the mixed solution with the conductive surface facing downwards and reacts for 10 hours at 200 ℃ to carry out hydrothermal synthesis. Then, the TiO cooled to room temperature2NRs arrays were rinsed with deionized water and TiO2Annealing NR in air at 450 ℃ for 1h to obtain TiO2An NR array electrode;
(2) in TiO2Construction of ferroelectric SrTiO on NR surface3Nanolayer (TiO)2 /STO）：
Will contain 0.5M hydroxylamine hydrochloride and 0.25M Na2S·9H2Transferring the mixed solution of O into a polytetrafluoroethylene-lined stainless steel high-pressure reaction kettle, and putting the TiO obtained in the step (1)2Performing continuous reaction for 10 hours at 180 ℃ on the NR array electrode to achieve the purpose of constructing an amorphous nano-layer on the surface by surface corrosion; when the temperature is cooled to room temperature, the mixture is thoroughly washed by deionized water; then adding the TiO containing the surface amorphous nano-layer2The NR array electrode was placed in a stainless steel autoclave lined with Teflon, and 0.03M Sr (OH) was poured into the autoclave2·8H2O aqueous solution is continuously reacted for 6 hours at 180 ℃ to realize the reaction on TiO2The NR surface builds the ferroelectric STO nanolayers in situ.
(3) Constructing CdS quantum dot modified ternary composite TiO2the/STO/CdS NRs photoelectrode:
adding TiO into the mixture2the/STO NRs were immersed in a beaker containing 10 mL of deionized water and heated to homogeneity with stirring at 45 ℃. Then 5mL of C was added4H6CdO4·2H2O aqueous solution (40 mM). After stirring for 30min, 5mL of an aqueous thiourea solution (40 mM) was added to the beaker. And then, 100 mu L of concentrated ammonium hydroxide is injected into the solution and is kept for 20min, so that the chemical bath deposition growth of the CdS QD is realized. The resulting TiO2the/STO/CdS NRs were washed thoroughly with ethanol and washed in N2And (4) drying. The above process was repeated 3 times. Finally, annealing at 350 ℃ for 30min under Ar atmosphere to obtain TiO2the/STO/CdS NR samples.
(4) And performing photoelectrochemical test on the prepared photoelectrode by utilizing a three-electrode system:
the prepared photoelectric electrode is taken as a working electrode, a platinum sheet is taken as a counter electrode, Ag/AgCl is taken as a reference electrode, and the electrolyte is 0.35M Na2SO3 + 0.25 M Na2S (pH 12.5) aqueous solution. Atmosphere lamp with AM1.5G optical filter, light intensity is adjusted to 100 mW/cm2。
Comparison of the results of the photoelectrochemical measurements obtained in the above three examples (linear sweep voltammogram therein) shows the TiO prepared in example 22the/STO/CdS NRs array photoelectrode has the maximum photocurrent density.
Example 4
(1) Preparation of TiO2NR array electrode:
0.45g NaCl and 0.4mL tetrabutyltitanate are added to 24mL aqueous HCl (6M) at ambient temperature and stirred for 30 min. Then, the mixed solution is transferred into a polytetrafluoroethylene-lined stainless steel high-pressure reaction kettle, and the FTO conductive glass electrode is placed in the mixed solution with the conductive surface facing downwards and reacts for 7 hours at 150 ℃ to carry out hydrothermal synthesis. Then, the TiO cooled to room temperature2NRs arrays were rinsed with deionized water and TiO2Annealing NR in air at 450 ℃ for 1h to obtain TiO2An NR array electrode;
(2) in TiO2Construction of ferroelectric SrTiO on NR surface3Nanolayer (TiO)2 /STO）：
Will contain 0.5M hydroxylamine hydrochloride and 0.25M Na2S·9H2Transferring the mixed solution of O into a polytetrafluoroethylene-lined stainless steel high-pressure reaction kettle, and putting the TiO obtained in the step (1)2Performing continuous reaction for 10 hours at 180 ℃ on the NR array electrode to achieve the purpose of constructing an amorphous nano-layer on the surface by surface corrosion; when the temperature is cooled to room temperature, the mixture is thoroughly washed by deionized water; then adding the TiO containing the surface amorphous nano-layer2The NR array electrode was placed in a stainless steel autoclave lined with Teflon, and 0.03M Sr (OH) was poured into the autoclave2·8H2O aqueous solution is continuously reacted for 6 hours at 180 ℃ to realize the reaction on TiO2The NR surface builds the ferroelectric STO nanolayers in situ.
(3) Constructing CdS quantum dot modified ternary composite TiO2the/STO/CdS NRs photoelectrode:
adding TiO into the mixture2the/STO NRs were immersed in a beaker containing 10 mL of deionized water and heated to homogeneity with stirring at 45 ℃. Then 5mL of C was added4H6CdO4·2H2O aqueous solution (40 mM). After stirring for 30min, 5mL of an aqueous thiourea solution (40 mM) was added to the beaker. And then, 100 mu L of concentrated ammonium hydroxide is injected into the solution and is kept for 20min, so that the chemical bath deposition growth of the CdS QD is realized. The resulting TiO2the/STO/CdS NRs were washed thoroughly with ethanol and washed in N2And (4) drying. The above process was repeated 2 times. Finally, annealing at 350 ℃ for 30min under Ar atmosphere to obtain TiO2the/STO/CdS NR samples.
(4) And performing photoelectrochemical test on the prepared photoelectrode by utilizing a three-electrode system:
the prepared photoelectric electrode is taken as a working electrode, a platinum sheet is taken as a counter electrode, Ag/AgCl is taken as a reference electrode, and the electrolyte is 0.35M Na2SO3 + 0.25 M Na2S (pH 12.5) aqueous solution. Atmosphere lamp with AM1.5G optical filter, light intensity is adjusted to 100 mW/cm2。
The practical effect of the invention is proved by experiments.
FIG. 1 is TiO2 NRs（A、D）、TiO2 /STO NRs（B、E）、TiO2SEM images of/STO/CdS NRs (C, F). As shown in FIG. 1B, E, in TiO2After the STO nano-layer is constructed on the surface of NRs, the top end of the nano-rod is compared with that of TiO2NRs (A, D) apparently have particle aggregation, probably due to the faster STO conversion at the top of the nanorods (Sr (OH))2·8H2The distribution of the O aqueous solution along the depth of the nano-rod is from more to less), which confirms the successful construction of the STO nano-layer; after CdS quantum dots are deposited by chemical bath, TiO2the/STO/CdS NRs (shown in FIG. 1C, F) surface presents a uniformly distributed quantum dot shape, confirming the successful deposition of surface CdS quantum dots.
FIG. 2 is TiO2Transmission electron microscopy of the/STO/CdS NR heterostructure. FIG. 2A shows TiO2Low power transmission electron microscopy images of/STO/CdS NRs, TiO2The diameter of the/STO/CdS NR is about 95 nm, CdS quantum dots are uniformly distributed, the particle size of the CdS quantum dots is 2-9 nm, and the result is consistent with the measurement of a scanning electron microscope. The high power transmission electron microscope images shown in FIGS. 2B and 2C show three sets of lattice fringes, corresponding to TiO, respectively2 NR core, STO shell and surface CdS quantum dots. These lattice fringes with distinct interfaces may correspond to rutile TiO2(001) (NR core, interplanar spacing 0.29 nm), cubic STO (220) (NR shell, interplanar spacing 0.14 nm), wurtzite CdS (002) and (102) (interplanar spacing on NR surface 0.336 nm and 0.245 nm, respectively, as shown in fig. 3). Measured, an approximately 8 nm thick STO shell uniformly covered the entire TiO2Nucleus (fig. 2C). As can be seen from FIG. 2C, the (220) plane of cubic phase STO and TiO2The (001) planes of the core are parallel, indicating that the (001) plane (c-axis) of the cubic STO is perpendicular to the rutile TiO2(110) crystal face of (c rutile type TiO)2Axis) (as shown in fig. 2D). Therefore, the STO spontaneous ferroelectric polarization direction caused by the lattice distortion of the STO (001) crystal plane coincides with the direction of interface charge separation (separation at the NR core-shell interface). Indicating that the ferroelectric STO shell induced polar charge induced electric field is advantageousThe photo-generated charges are separated.
FIG. 3 is TiO2 NRs、TiO2 /STO NRs、TiO2CdS and TiO2And testing the photoelectrochemical activity of the/STO/CdS NRs photoelectrode. Fig. 3A is a linear sweep voltammogram for each photoelectrode. Prepared TiO2NR showed a photocurrent density of only 0.25 mA/cm 2 at 1.23V vs. RHE due to severe recombination of electron-hole pairs and limited sunlight absorption. TiO22The photocurrent density of the/STO photoelectrode is 0.35 mA/cm2With TiO2Compared with NR, the NR is improved by 40 percent. TiO22The increase in photocurrent density of the/STO photoanode may be due to TiO induced ferroelectric polarization of the STO shell2The charge separation efficiency is effectively improved. In TiO2After CdS quantum dots are deposited on the surface of/STO NRs, TiO is obtained due to effective carrier separation and enlarged light absorption range2the/STO/CdS NR photo-anode reaches 1.85 mA/cm under the bias voltage of 1.23V vs. RHE2Photocurrent density of (2) to TiO2 NR，TiO2STO NR and TiO2CdS NR (about 1.65 mA/cm at 1.23V vs RHE2) The photocurrent density of (a) was 7.4, 5.2 and 1.12 times higher. Accordingly, the charge separation yield shown in FIG. 3B indicates that TiO2STO (16.5%) and TiO2CdS (27%) vs. original TiO2(12.5%) has a significant enhancement in charge separation efficiency due to TiO induced by ferroelectric polarization of STO2Electron band bending and TiO2And forming a/CdS heterojunction. Notably, with pure TiO2TiO, CdS heterojunction NRs comparison2The charge separation efficiency (31%) of/STO/CdS NRs shows a further improvement thanks to TiO with a cascade band arrangement2The coupling effect of the/STO/CdS ternary heterojunction and the STO polar charge induction electric field is cooperated to endow the composite photoelectrode with durable and quick photo-generated charge separation capability, so that possible bulk or interface charge recombination of the composite photoelectrode is inhibited.
Example 5
(1) Preparation of TiO2NR array electrode:
0.45g NaCl and 0.4mL tetrabutyltitanate are added to 24mL aqueous HCl (6M) at ambient temperature and stirred for 30 min. Then, the mixed solution is transferred into a polytetrafluoroethylene-lined stainless steel high-pressure reaction kettle, and the FTO conductive glass electrode is placed in the mixed solution with the conductive surface facing downwards and reacts for 7 hours at 150 ℃ to carry out hydrothermal synthesis. Then, the TiO cooled to room temperature2NRs arrays were rinsed with deionized water and TiO2Annealing NR in air at 450 ℃ for 1h to obtain TiO2An NR array electrode;
(2) in TiO2Construction of ferroelectric SrTiO on NR surface3Nanolayer (TiO)2 /STO）：
Will contain 0.5M hydroxylamine hydrochloride and 0.25M Na2S·9H2Transferring the mixed solution of O into a polytetrafluoroethylene-lined stainless steel high-pressure reaction kettle, and putting the TiO obtained in the step (1)2Performing continuous reaction for 10 hours at 180 ℃ on the NR array electrode to achieve the purpose of constructing an amorphous nano-layer on the surface by surface corrosion; when the temperature is cooled to room temperature, the mixture is thoroughly washed by deionized water; then adding the TiO containing the surface amorphous nano-layer2The NR array electrode was placed in a stainless steel autoclave lined with Teflon, and 0.03M Sr (OH) was poured into the autoclave2·8H2O aqueous solution is continuously reacted for 6 hours at 180 ℃ to realize the reaction on TiO2The NR surface builds the ferroelectric STO nanolayers in situ.
(3) Constructing CdS quantum dot modified ternary composite TiO2the/STO/CdS NRs photoelectrode:
adding TiO into the mixture2the/STO NRs were immersed in a beaker containing 10 mL of deionized water and heated to homogeneity with stirring at 45 ℃. Then 5mL of C was added4H6CdO4·2H2O aqueous solution (40 mM). After stirring for 30min, 5mL of an aqueous thiourea solution (40 mM) was added to the beaker. And then, 100 mu L of concentrated ammonium hydroxide is injected into the solution and is kept for 20min, so that the chemical bath deposition growth of the CdS QD is realized. The resulting TiO2the/STO/CdS NRs were washed thoroughly with ethanol and washed in N2And (4) drying. The above process was repeated 2 times. Finally, annealing at 350 ℃ for 30min under Ar atmosphere to obtain TiO2 / STO / CdS NR samples.
(4) And performing photoelectrochemical test on the prepared photoelectrode by utilizing a three-electrode system:
the prepared photoelectric electrode is taken as a working electrode, a platinum sheet is taken as a counter electrode, Ag/AgCl is taken as a reference electrode, and the electrolyte is 0.35M Na2SO3 + 0.25 M Na2S (pH 12.5) aqueous solution. Atmosphere lamp with AM1.5G optical filter, light intensity is adjusted to 100 mW/cm2. In order to verify the controllability of the polar charge induced electric field, the optical electrode is polarized, specifically as follows:
before the photoelectrode test, the positive and negative polarization was carried out for 5 seconds by applying bias voltages of 2V and-2V (vs Ag/AgCl) respectively in a current-time mode.
FIG. 4 shows (A) TiO2STO and (B) TiO2Linear sweep voltammograms of/STO/CdS before and after polarization. As shown in FIG. 4A, compared to TiO before polarization2STO, TiO after forward polarization2the/STO showed an increase in photocurrent density of 4.8%; conversely, negatively polarized TiO2the/STO showed a photocurrent density decreased by 22.5%. Similarly, as shown in FIG. 4B for TiO2/STO/CdS, TiO after positive and negative polarization respectively2the/STO/CdS showed photocurrent densities increased by 2.2% and decreased by 43.1%, respectively. The method shows that the polarity induced charges induced by the ferroelectric STO nano layer can be regulated and controlled through polarization treatment, so that the photoelectrochemical property of the photoelectrode is further effectively regulated and controlled.
The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes performed by the present invention or directly or indirectly applied to other related technical fields are included in the scope of the present invention.

Claims (7)

1. Ternary composite TiO2The preparation method of the/STO/CdS NRs photoelectrode is characterized by comprising the following steps of:
(1) in TiO2Construction of ferroelectric SrTiO on NR surface3Nanolayer (TiO)2 /STO）：
Containing 0.2 to 0.5M hydroxylamine hydrochloride and 0.1 to 0.25M Na2S·9H2Transferring the mixed solution of O into a stainless steel high-pressure reaction kettle with a polytetrafluoroethylene lining, and immersing the stainless steel high-pressure reaction kettle into TiO2Performing continuous reaction for 2-10 h at 120-180 ℃ on the NR array electrode; cooling to room temperature, thoroughly washing with deionized water, and removing the surface amorphous nano-layer-containing TiO2Putting the NR array electrode into a polytetrafluoroethylene lining stainless steel high-pressure reaction kettle, and pouring 0.01-0.03M of Sr (OH)2·8H2Immersing the O aqueous solution, continuously reacting for 2-6 h at 120-180 ℃, and reacting on TiO2In-situ construction of ferroelectric STO nanolayer TiO on NR surface2/STO NRs；
(2) Constructing CdS quantum dot modified ternary composite TiO2the/STO/CdS NRs photoelectrode:
adding TiO into the mixture2the/STO NRs are immersed in an open container containing 10 mL of deionized water, and stirred at 45 ℃ to be heated uniformly; 5mL of 40mM C was added4H6CdO4·2H2O aqueous solution, continuously stirring for 30min, adding 5mL of 40mM thiourea aqueous solution, injecting 100 mu L of concentrated ammonium hydroxide, and continuously stirring for 20 min; the resulting TiO2the/STO/CdS NRs were washed thoroughly with ethanol and washed in N2Drying; repeating the process for 1-3 times; annealing at 350 deg.C for 30min in Ar atmosphere to obtain TiO2/STO/CdS NRs。
2. The ternary complex TiO of claim 12The preparation method of the/STO/CdS NRs photoelectrode is characterized by comprising the following steps of: in the step (1), the solution contains 0.2-0.5M of hydroxylamine hydrochloride and 0.1-0.25M of Na2S·9H2Transferring the mixed solution of O into a stainless steel high-pressure reaction kettle with a polytetrafluoroethylene lining, and immersing the stainless steel high-pressure reaction kettle into TiO2NR array electrode, 180 degrees C reaction for 4 h.
3. The ternary complex TiO of claim 12The preparation method of the/STO/CdS NRs photoelectrode is characterized by comprising the following steps of: in the step (1), 0.01-0.03M of Sr (OH) is poured2·8H2Immersing in water solution of O, reacting at 180 deg.C for 4 hr, and reacting on TiO2NR surfaceIn-situ construction of ferroelectric STO nanolayer TiO2/STO NRs。
4. The ternary complex TiO of claim 12The preparation method of the/STO/CdS NRs photoelectrode is characterized by comprising the following steps of: the TiO in the step (1)2The preparation method of the NR array electrode comprises the steps of adding 0.45g of NaCl and 0.4mL of tetrabutyl titanate into 24mL of 4-8M HCl aqueous solution at ambient temperature, and stirring for 10-30 min; transferring the mixture into a polytetrafluoroethylene-lined stainless steel high-pressure reaction kettle, placing the FTO conductive glass electrode in the mixed solution in a downward inclined manner, and carrying out hydrothermal reaction at 120-200 ℃ for 4-10 h; TiO cooled to room temperature2And (4) washing the NRs array by deionized water, and annealing for 1h at 450 ℃ in the air to obtain the NRs array.
5. Ternary complex TiO obtainable by a process according to any one of claims 1 to 42the/STO/CdS NRs photoelectrode.
6. The ternary complex TiO of claim 52the/STO/CdS NRs photoelectrode is characterized in that: the appearance of the nano-rod is a multi-layer coaxial nano-rod array structure, TiO2Is a nano-rod core, the tightly coated ferroelectric STO nano-layer is a nano-rod shell, and discontinuous CdS quantum dots are used as a nano-rod surface modification layer.
7. The ternary composite TiO of claim 52The application of the/STO/CdS NRs photoelectrode is characterized in that: it was applied to high efficiency PEC water splitting.
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