Method for in-situ determination of interfacial charge transfer kinetics

Abstract

The invention belongs to the technical field of photoelectrochemical interface kinetics, and discloses a method for in-situ determination of interface charge transfer kinetics, which comprises the following steps: (1) constructing a photoelectrochemical reaction solution, and forming a solid-liquid interface; (2) obtaining a current approximation curve of the current changing along with the position of the probe; (3) applying vertically incident light to the solid-liquid interface, and applying different potentials to the second working electrode to obtain at least five current feedback approximation curves of current changing along with the position of the probe under different second working electrode potential settings; and (4) obtaining a change relationship between different second working electrode potentials and heterogeneous effective charge transfer rate constants obtained by fitting, and thus obtaining a photon-generated carrier exchange rate constant at a solid-liquid interface. According to the invention, quantitative acquisition of solid / liquid interface reaction kinetics information can be conveniently realized, and interface charge transfer kinetics mechanism research in photoelectrocatalysis and optimization of process properties of related devices can be promoted.

Description

Technical Field

[0001] The present invention belongs to the technical field of photoelectrochemical interface dynamics, and more specifically, relates to a method for in-situ determination of interface charge transfer dynamics, which can determine the charge transfer dynamics behavior of the solid / liquid interface of photoelectric thin film materials. Background Art

[0002] As the world's dependence on fossil fuels continues to increase, the reality of the gradual depletion of fossil fuel resources in the future has made solar energy, an inexhaustible clean energy, attract more and more attention from researchers. This demand for renewable energy has prompted the extensive research of photoelectrochemical technology. Photoelectrocatalytic technology, by simulating photosynthesis in nature, uses sunlight and semiconductor materials to convert water and carbon dioxide into high-energy-density hydrogen, oxygen and various small-molecule chemicals, so it is called "artificial photosynthesis."

[0003] The advantage of photoelectrocatalysis is that it can efficiently capture and utilize solar energy, reduce reaction energy consumption, and achieve long-term energy storage. Because its products have high industrial added value and controllable reaction conditions, this technology is expected to achieve "zero emission, zero bias" clean energy and chemical production solutions when combined with intermittent and distributed energy systems. Although these application technologies have made a lot of progress, the scientific community still has many unknowns about the specific mechanisms of the reactions, especially the reaction kinetics of the photoelectrochemical interface. Therefore, it is crucial to explore and develop advanced technologies that capture detailed information on interfacial carrier dynamics in order to promote the design and optimization of more efficient photoelectrocatalytic materials and improve the overall reaction efficiency and the economic value of the products.

[0004] Traditionally, the analysis of photoelectrochemical carriers includes spectroscopic methods, such as fluorescence spectrometers and transient absorption spectrometers, and electrochemical measurement techniques. Although ordinary electrochemical methods help to reveal the characteristics of the photoelectrochemical reaction of materials, most of them provide an overall perspective on the macroscopic scale and are non-in situ. These methods have limited ability to deconstruct the microscopic dynamics of carriers at the interface between semiconductors and solutions, making it difficult to accurately describe the true charge transfer at the solid / liquid interface, which is the key to optimizing photoelectrochemical performance. Therefore, the development of more sophisticated and specific analytical techniques to understand the microscopic mechanism of the interface in detail has become a research focus.

[0005] Although transient absorption spectroscopy is capable of detecting the solid / liquid interface kinetic behavior of optoelectronic materials, it is very necessary to develop a low-cost, easy-to-operate in situ photoelectrochemical interface kinetic test method because the equipment is expensive and relies on imports.

[0006] Scanning Electrochemical Microscopy (SECM) is a new electrochemical method with high spatial resolution. When the probe is scanned very close to the substrate electrode surface, the electrochemical conditions of the electrode and the scanning probe are controlled by a bipotentiostat, and the redox current generated has different feedback characteristics and is directly related to the active components in the solution, the probe-substrate distance, and the surface characteristics of the substrate electrode.

[0007] The inventors of the present invention have previously studied a photoelectrochemical kinetics test system and method based on a scanning electrochemical microscope (see Chinese patent document CN104502388A), which focuses on the construction and application of the kinetics test system. Although this method can achieve the determination of the effective heterogeneous charge transfer rate constant k eff The final result is the photogenerated hole regeneration kinetic constant (k ox ), which is mainly used to qualitatively describe the amount of charge transfer between the photoanode material and the electrolyte. However, in the actual photoelectrocatalytic interface reaction process, the separation and transmission process of photogenerated carriers is very complicated. In addition to the direct participation of the photogenerated minority carrier interface in the reaction, it also involves multiple mechanisms such as the return transmission of majority carriers and carrier recombination processes at the bulk phase and semiconductor / solution interface. Therefore, only analyzing the behavior of photogenerated minority carriers and the amount of transferred charge is not enough to fully understand the interface dynamics process. It is necessary to further obtain the exchange rate constants of photogenerated electrons and holes at the interface to more effectively reveal the laws of semiconductor solution interface dynamics and provide more scientific guidance for the design and optimization of efficient photoelectrocatalytic materials. Summary of the invention

[0008] In view of the above defects or improvement needs of the prior art, the purpose of the present invention is to provide a method for in-situ determination of interfacial charge transfer kinetics, based on scanning electrochemical microscopy technology, by using a platinum (Pt) ultramicroelectrode probe, under illumination, using a photoelectrochemical cell composed of four electrodes to determine the photogenerated carrier exchange rate constant (the carrier exchange rate constant is an important kinetic constant). The present invention breaks through the limitations of traditional electrochemical methods, can easily achieve quantitative acquisition of solid / liquid interface reaction kinetics information, and provides important theoretical and practical guidance for the study of interfacial charge transfer kinetics mechanism in photoelectrocatalysis and the optimization of process performance of related devices.

[0009] To achieve the above object, according to one aspect of the present invention, a method for in-situ determination of photogenerated carrier dynamics at a solid-liquid interface based on a scanning electrochemical microscope is provided, comprising the following steps:

[0010] (1) selecting an organic solvent or an inorganic solvent, and using an electrolyte and a redox mediator to prepare a redox electrolyte solution to obtain a photoelectrochemical reaction solution;

[0011] Prepare a photoelectrochemical reaction cell with a through hole in the center of the bottom, fix the photoelectric thin film material to be tested on the center of the bottom of the photoelectrochemical reaction cell from the outside, inject the photoelectrochemical reaction solution into the photoelectrochemical reaction cell, so that the photoelectrochemical thin film material to be tested contacts with the photoelectrochemical reaction solution through the through hole to form a solid-liquid interface;

[0012] A Pt ultramicroelectrode probe is used as the first working electrode, the photoelectric thin film material to be tested is used as the second working electrode, the silver / silver chloride electrode is used as the reference electrode, and the platinum electrode is used as the counter electrode, forming a four-electrode system in a scanning electrochemical microscope system; wherein the Pt ultramicroelectrode probe is fixed on a moving platform of the scanning electrochemical microscope, and the moving platform can drive the Pt ultramicroelectrode probe to move;

[0013] (2) applying a working voltage to the four-electrode system, taking the position of the Pt ultramicroelectrode probe directly above the through hole and not in contact with the photoelectrochemical reaction solution as the starting position, and using the mobile platform to continuously move the Pt ultramicroelectrode probe closer to the solid-liquid interface of the photoelectric thin film material to be measured, while recording the position of the Pt ultramicroelectrode probe and the corresponding current to obtain a current approximation curve of the current changing with the probe position; recording the position of the Pt ultramicroelectrode probe corresponding to the current mutation in the current approximation curve as position 0 of the photoelectrochemical reaction cell;

[0014] (3) applying vertically incident light to the solid-liquid interface of the photoelectric thin film material to be tested, and keeping the light intensity and wavelength unchanged; then, by applying a preset potential to the first working electrode and the second working electrode, driving the Pt ultramicroelectrode probe to start from a position above the 0 position of the photoelectrochemical reaction cell, and approaching the solid-liquid interface of the photoelectric thin film material to be tested at a constant speed, while recording the position of the Pt ultramicroelectrode probe and the corresponding current, to obtain a current feedback approximation curve of the current changing with the probe position at the potential;

[0015] The potential applied to the first working electrode is kept unchanged, while the potential applied to the second working electrode is adjusted, and the operation is repeated to obtain a current feedback approximation curve of the current changing with the probe position under the new potential setting;

[0016] Repeating this process, at least 5 current feedback approximation curves of the current changing with the probe position under different second working electrode potential settings are obtained;

[0017] (4) Fitting each current feedback approximation curve obtained in step (3) to obtain a heterogeneous effective charge transfer rate constant, thereby obtaining a relationship between different second working electrode potentials and the heterogeneous effective charge transfer rate constant obtained by fitting, and thereby obtaining a photogenerated carrier exchange rate constant at a solid-liquid interface formed by the contact between the photoelectric thin film material to be tested and the redox electrolyte solution; wherein the photogenerated carriers are photogenerated electrons or photogenerated holes.

[0018] As a further preferred embodiment of the present invention, in step (1), with the vacuum energy level as a reference, the redox potential of the redox medium is more negative than the minimum value of the conduction band energy of the photoelectric thin film;

[0019] In step (3), the second working electrode always applies a reduction potential, and the first working electrode applies an oxidation potential, serving as a reduction medium;

[0020] Correspondingly, the photogenerated carrier exchange rate constant obtained in step (4) is the photogenerated electron exchange rate constant.

[0021] As a further preferred embodiment of the present invention, in step (1), when the solvent is an inorganic solvent, the redox mediator is potassium ferrocyanide K4Fe(CN)6.

[0022] As a further preferred embodiment of the present invention, in step (1), the redox potential of the redox mediator is higher than the maximum value of the valence band energy of the photoelectric thin film, with reference to the vacuum energy level, and serves as an oxidizing mediator;

[0023] In step (3), the second working electrode always applies an oxidation potential, and the first working electrode applies a reduction potential;

[0024] Correspondingly, the photogenerated carrier exchange rate constant obtained in step (4) is the photogenerated hole exchange rate constant.

[0025] As a further preferred embodiment of the present invention, in step (1), when the solvent is an inorganic solvent, the redox mediator is potassium ferrocyanide K3Fe(CN)6.

[0026] As a further preferred embodiment of the present invention, in step (4), each current feedback approximation curve obtained in step (3) is fitted to obtain the heterogeneous effective charge transfer rate constant, specifically:

[0027] First, each current feedback approximation curve obtained in step (3) is fitted to obtain the dimensionless heterogeneous apparent transfer rate constant κ, and then the heterogeneous effective charge transfer rate constant k is calculated according to the following formula (1): eff ,

[0028]

[0029] In formula (1), D diffusion is the diffusion coefficient of the redox electrolyte, r T is the radius of the Pt ultramicroelectrode probe.

[0030] As a further preferred embodiment of the present invention, in step (4), the photogenerated carrier exchange rate constant k 0 is the heterogeneous effective charge transfer rate constant k corresponding to different second working electrode potentials eff It is obtained by fitting the following formula (2):

[0031] ln(k eff )=lnk 0 -αnfη (2)

[0032] In formula (2),

[0033] α is the charge transfer coefficient in the SEM test,

[0034] n is the number of charges transferred during the redox reaction,

[0035] f = F / RT, where T is temperature, R is the ideal gas constant, and F is the Faraday constant;

[0036] η is the overpotential, which is equal to the difference between the potential applied by the second working electrode and the redox equilibrium potential of the redox mediator.

[0037] As a further preferred embodiment of the present invention, in step (3), the constant speed is 0.5 μm / s-2 μm / s.

[0038] As a further preferred embodiment of the present invention, in step (1), the concentration of the redox mediator in the redox electrolyte solution is 0.01 mM-5 mM.

[0039] As a further preferred embodiment of the present invention, the diameter of the Pt ultramicroelectrode probe is 10nm-100μm;

[0040] The through hole is preferably a round through hole;

[0041] The photoelectrochemical reaction cell is made of polytetrafluoroethylene.

[0042] Through the above technical scheme conceived by the present invention, compared with the prior art, the present invention provides a new method for in-situ determination of charge transfer dynamics at the solid / liquid interface, which is based on scanning electrochemical microscopy technology and can measure the difference in photoelectric properties of different carriers at the interface between the material and the solution under different potentials, and calculate the exchange rate constant of photogenerated carriers. This will break through the limitations of traditional electrochemical methods, provide quantitative determination in the study of solid / liquid interface carrier dynamics, and have important guiding significance for promoting the development of this field.

[0043] By using this method, the kinetic constants of different types of carriers in semiconductor materials can be effectively measured, and the photogenerated electrons or photogenerated holes can be selected as the research object in conjunction with the selection of the redox mediator and the oxidation and reduction potentials applied to the first working electrode and the second working electrode. When it is necessary to obtain the exchange rate constant of electrons, a reduction mediator should be selected, that is, with the vacuum energy level as a reference, the redox potential of the redox mediator is negative to the minimum value of the conduction band energy of the photoelectric film, and at the same time, the second working electrode applies a reduction potential and the first working electrode applies an oxidation potential; when it is necessary to measure the kinetics of hole reaction, a reduction mediator should be selected, that is, with the vacuum energy level as a reference, the redox potential of the redox mediator is positive to the maximum value of the valence band energy of the photoelectric film, and at the same time, the second working electrode applies an oxidation potential and the first working electrode applies a reduction potential.

[0044] Existing technologies can detect the kinetic behavior of the solid / liquid interface of optoelectronic materials, but most of them are limited to non-in-situ testing. The present invention introduces SECM technology to further expand its application in the determination of photoelectrocatalytic charge transfer kinetics and realizes the in-situ characterization of interface dynamics. How to quantitatively obtain the kinetic constants of photogenerated carriers under light excitation is a key issue in the study. Different from the previous study CN104502388A obtained the photogenerated minority carrier regeneration kinetic constant K of the transparent photoanode sample film in the redox electrolyte ox , which is used to qualitatively describe the amount of charge transferred between the photoanode material and the electrolyte. The present invention uses formula (2) and can select appropriate redox pairs and applied potentials for different types of carriers, and can quantitatively obtain different types of photogenerated carrier exchange rate constants. This method captures the charge reaction in situ under illumination conditions, realizes the accurate determination of different types of photogenerated carrier charge exchange constants, and provides a key quantitative tool and theoretical guidance for a deep understanding of the photoelectrocatalytic process.

[0045] In summary, the present invention provides a way to measure the carrier dynamics at the solid / liquid interface. The present invention is based on scanning electrochemical microscopy technology, which can measure the difference in the photoelectric properties of different photogenerated carriers at the interface between the material and the solution, and obtain the photogenerated carrier exchange rate constant. This will break through the limitations of traditional electrochemical methods, provide valuable insights in the study of solid / liquid interface carrier dynamics, and have important guiding significance for promoting the development of this field. The present invention provides a way to study the photoelectrochemical kinetic behavior of solid / liquid interface carriers, which can overcome the current defect of insufficient acquisition of photoelectrocatalytic interface chemical reaction kinetics information, quickly obtain accurate interface reaction kinetics information, and provide useful experimental parameters for further research on the mechanism of photoelectrocatalytic water decomposition and carbon dioxide reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a schematic diagram of a device for detecting carrier dynamics of photoelectrocatalytic materials using a Pt ultramicroelectrode in the present invention.

[0047] Figure 2 It is the current signal when the Pt ultramicroelectrode probe is close to the surface of the photoelectric thin film material to be tested.

[0048] Figure 3 Normalized SECM feedback curves of ZnTe films in 0.5M KHCO3 supported electrolyte and 2mM K4Fe(CN)6 electrolyte under blue light (450nm) irradiation.

[0049] Figure 4 The ZnTe photocathode was exposed to blue light (450 nm) in 0.5 M KHCO3 supporting electrolyte and 2 mM K4Fe(CN)6 electrolyte. eff )vs.η curve analysis.

[0050] Figure 5 Normalized SECM feedback curves of ZnTe films in 0.5M KHCO3 supported electrolyte and 2mM K3Fe(CN)6 electrolyte under blue light (450nm) irradiation.

[0051] Figure 6 The ZnTe photocathode was exposed to blue light (450 nm) in 0.5 M KHCO3 supporting electrolyte and 2 mM K3Fe(CN)6 electrolyte. eff )vs.η curve analysis.

[0052] Figure 7 The BiVO4 photoanode was exposed to blue light (450 nm) in 0.1 M PBS supporting electrolyte and 2 mM K4Fe(CN)6 electrolyte. eff )vs.η curve analysis.

[0053] Figure 8 The BiVO4 photoanode was exposed to blue light (450 nm) in 0.1 M PBS supporting electrolyte and 2 mM K3Fe(CN)6 electrolyte. eff )vs.η curve analysis.

[0054] Fig. 9 This is the current approximation mutation curve obtained in Example 1.

[0055] Fig.10 This is the negative feedback type feedback curve obtained in Example 2.

[0056] Figure 1 The meanings of the figures are as follows: 1-scanning electrochemical microscope control system, 2-counter electrode, 3-second working electrode, 4-photoelectric thin film material, 5-photoelectrochemical cell, 6-electrolyte solution, 7-light source, 8-reference electrode, 9-Pt ultramicroelectrode (first working electrode). DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0058] The schematic diagram of the device used in the following examples is as follows. Figure 1 As shown, it includes a scanning electrochemical microscope device, a Pt ultramicroelectrode, and a light source device; the photoelectrochemical reaction cell 5 used in the embodiments below is a photoelectrochemical reaction cell with a round through hole in the center of the bottom of the cell (the photoelectrochemical reaction cell is made of polytetrafluoroethylene), the scanning electrochemical microscope device is a CHI920 scanning electrochemical microscope, and the Pt ultramicroelectrode probe is a Pt ultramicroelectrode probe with a diameter of 25 μm.

[0059] Embodiment 1:

[0060] 0.5M KHCO3 is selected to prepare a supporting electrolyte (the solvent is water, the same as in the subsequent embodiments), 2mM K4Fe(CN)6 is used as a medium, and in the photoelectrochemical reaction solution 6 containing the medium as described above, the photoelectric thin film material 4 to be tested is fixed at the bottom of the photoelectrochemical reaction cell 5, a Pt ultramicroelectrode 9 is used as the first working electrode, the photoelectric thin film material is connected with a copper wire as the second working electrode 3, a silver / silver chloride electrode is used as the reference electrode 8, and a Pt wire is used as the counter electrode 2. The Pt ultramicroelectrode 9 is connected to the scanning electrochemical microscope control system 1 to form a precisely controlled scanning mobile platform, and the scanning electrochemical microscope is precisely controlled to move the Pt ultramicroelectrode 9 close to the surface of the photoelectric thin film area 4 to be tested, and the current approximates the mutation curve (such as Figure 2 As shown in the example, the curve can be measured in the dark state or under light), and the position of the Pt ultramicroelectrode probe corresponding to the current mutation in the current approach mutation curve is recorded as position 0 of the photoelectrochemical reaction cell, thereby ensuring the accurate positioning of the Pt ultramicroelectrode ( Figure 2 The medium current mutation position is defined as the Pt ultramicroelectrode position corresponding to the current reaching 125%*initial current value. At this time, the Pt ultramicroelectrode probe position is that of the photoelectrochemical reaction cell 0; of course, in addition to 125%*initial current value, other threshold settings can also be used, such as 150%*initial current value); turn on the blue light source 7, and adjust the light source to ensure that a light spot of a certain intensity and wavelength is vertically irradiated onto the surface of the photoelectric thin film material 4 to be tested. In a medium of a given concentration, drive the Pt ultramicroelectrode 9 to rise a certain distance from the distance 0 to the photoelectrochemical reaction cell 5, and then under the irradiation of the light source, apply an oxidation potential to the Pt ultramicroelectrode 9 as the first working electrode, and apply a reduction potential to the photoelectric thin film material 4 to be tested as the second working electrode (this is because the sample detected in this embodiment is a p-type ZnTe thin film material synthesized by hydrothermal synthesis, and electrons are minority carriers. This embodiment is to obtain the exchange rate constant of photogenerated electrons. At this time, an oxidation potential is applied to the first working electrode, and a reduction potential is applied to the second working electrode). The Pt ultramicroelectrode 9 is controlled to approach the substrate electrode at a constant speed of 1 μm / s, and the current of the first working electrode is collected at the same time. A series of overpotentials η (the difference between the actual potential and the redox equilibrium potential of the mediator) are obtained by changing the potential of the second working electrode. Figure 3 The current feedback approximation curve is shown. The horizontal and vertical axes are the normalized distance parameter and the feedback current (i T,inf is the current at infinity). The current feedback approximation curve is fitted to obtain the heterogeneous apparent transfer rate constant κ, and then the heterogeneous effective charge transfer rate constant k is obtained using formula (1) eff Finally, the solution is Figure 4 Different overpotentials η and k are shown eff The change relationship curve of , and then use formula (2) to Figure 4 The photogenerated electron exchange rate constant was obtained by curve fitting Here we calculated the hydrothermally synthesized p-type ZnTe thin film material in 0.5M KHCO3 solution. 9.52×10 -4 cm s -1 In order to make the fitting result based on formula (2) accurate, the fitting needs to use at least 5 current feedback approximation curves of the current changing with the probe position under different second working electrode potential settings (the fitting process of this embodiment, such as Figure 4 As shown, 7 current feedback approximation curves corresponding to the change of current with probe position under different second working electrode potential settings were used).

[0061]

[0062] where κ is the heterogeneous apparent charge transfer rate constant (dimensionless), expressed by Figure 3 Fitting, D diffusion is the diffusion coefficient of the redox electrolyte, and it is known in the prior art r T is the radius of the Pt ultramicroelectrode.

[0063] ln(k eff )=lnk 0 -αnfη (2)

[0064] where α is the charge transfer coefficient in the SEM test, f = F / RT, T is the temperature, n is the number of transferred charges, η is the overpotential, R is the ideal gas constant, F is the Faraday constant, k 0 is the photogenerated carrier exchange rate constant, specifically, is the photogenerated electron exchange rate constant, is the photogenerated hole exchange rate constant.

[0065] Embodiment 2:

[0066] 0.5M KHCO3 is selected as the supporting electrolyte, 2mM K3Fe(CN)6 is used as the medium, and the photoelectric thin film material 4 to be tested is fixed on the bottom of the photoelectrochemical reaction cell 5 in the photoelectrochemical reaction solution 6 containing the medium as described above, a Pt ultramicroelectrode 9 is used as the first working electrode, the photoelectric thin film material is connected with a copper wire as the second working electrode 3, a silver / silver chloride electrode is used as the reference electrode 8, and a Pt wire is used as the counter electrode 2. The Pt ultramicroelectrode 9 is connected to the scanning electrochemical microscope control system 1 to form a precisely controlled scanning mobile platform, and the scanning electrochemical microscope is used to precisely control the movement of the Pt ultramicroelectrode 9 so that it is close to the surface of the photoelectric thin film area 4 to be tested, and the accurate positioning of the Pt ultramicroelectrode is ensured by the current approximation curve; the blue light source 7 is turned on, and the light source is adjusted to ensure that a light spot of a certain intensity and wavelength is just vertically irradiated onto the surface of the photoelectric thin film material 4 to be tested, and in a medium of a given concentration, the Pt ultramicroelectrode 9 is driven to rise a certain distance from a distance of 0 from the photoelectrochemical reaction cell 5, and then under the irradiation of the light source, a reduction potential is applied to the Pt ultramicroelectrode 9 as the first working electrode, and an oxidation potential is applied to the photoelectric thin film material 4 to be tested as the second working electrode (this is because the sample detected in this embodiment is a p-type ZnTe thin film material synthesized by hydrothermal synthesis, and the holes are majority carriers. This embodiment is to obtain the exchange rate constant of photogenerated holes. At this time, a reduction potential is applied to the first working electrode, and an oxidation potential is applied to the second working electrode). The Pt ultramicroelectrode 9 is controlled to approach the substrate electrode at a constant speed of 1 μm / s, and the current of the first working electrode is collected at the same time. A series of overpotentials η (the difference between the actual potential and the redox equilibrium potential of the mediator) are obtained by changing the potential of the second working electrode. Figure 5 A series of current feedback approximation curves are shown. The horizontal and vertical axes are the normalized distance parameter and feedback current, respectively. The current feedback approximation curve is fitted to obtain the heterogeneous apparent transfer rate constant κ, and then the heterogeneous effective charge transfer rate constant k is obtained using formula (1) eff Finally, the solution is Figure 6 The different potentials and k eff The change relationship curve of , and then use formula (2) to Figure 6 The hole exchange rate constant was obtained by curve fitting. Here we calculated the hydrothermally synthesized p-type ZnTe thin film material in 0.5M KHCO3 solution. is 3.83×10 -4 cm s -1 .

[0067] Embodiment three:

[0068] The selected 0.1M PBS buffer is prepared as the supporting electrolyte, and 2mM K4Fe(CN)6 is used as the medium. In the photoelectrochemical reaction solution 6 containing the medium as described above, the photoelectric thin film material 4 to be tested is fixed at the bottom of the photoelectrochemical reaction cell 5, and a Pt ultramicroelectrode 9 is used as the first working electrode, and the photoelectric thin film material is connected with a copper wire as the second working electrode 3, a silver / silver chloride electrode is used as the reference electrode 8, and a Pt wire is used as the counter electrode 2. The Pt ultramicroelectrode 9 is connected to the scanning electrochemical microscope control system 1 to form a precise control scanning mobile platform, and the scanning electrochemical microscope is used to precisely control the movement so that the Pt ultramicroelectrode 9 is close to the surface of the photoelectric thin film area 4 to be tested, and the current approximation curve is used to ensure the accurate positioning of the Pt ultramicroelectrode; turn on the blue light source 7, and adjust the light source to ensure that the light spot of a certain intensity and wavelength is just vertically irradiated on the surface of the photoelectric thin film material 4 to be tested. In a medium of a given concentration, the Pt ultramicroelectrode 9 is driven to rise a certain distance from a distance of 0 from the photoelectrochemical reaction cell 5, and then, under the irradiation of a light source, an oxidation potential is applied to the Pt ultramicroelectrode 9 as the first working electrode, and a reduction potential is applied to the photoelectric thin film material 4 to be tested as the second working electrode (this is because the sample tested in this embodiment is an n-type BiVO4 thin film material synthesized by electrodeposition, and the electrons are majority carriers. This embodiment is to obtain the exchange rate constant of photogenerated electrons. At this time, the first working electrode is applied with an oxidation potential, and the second working electrode is applied with a reduction potential). The Pt ultramicroelectrode 9 is controlled to approach the substrate electrode at a uniform speed of 1 μm / s, and the current of the first working electrode is collected at the same time. By changing the potential of the second working electrode, a series of overpotentials η (the difference between the actual potential and the redox equilibrium potential of the medium) are obtained, and a series of current feedback approximation curves are obtained. The current feedback approximation curve is fitted to obtain the heterogeneous apparent transfer rate constant κ, and then the formula (2) is used to convert Figure 7 The photogenerated electron exchange rate constant was obtained by curve fitting Here we calculate the electron exchange rate of n-type BiVO4 thin film material synthesized by electrodeposition in 0.1M PBS buffer. 2.91×10 -4 cm s -1 .

[0069] Embodiment 4:

[0070] The selected 0.1M PBS buffer is prepared as the supporting electrolyte, and 2mM K3Fe(CN)6 is used as the medium. In the photoelectrochemical reaction solution 6 containing the medium as described above, the photoelectric thin film material 4 to be tested is fixed at the bottom of the photoelectrochemical reaction cell 5, and a Pt ultramicroelectrode 9 is used as the first working electrode, and the photoelectric thin film material is connected with a copper wire as the second working electrode 3, a silver / silver chloride electrode is used as the reference electrode 8, and a Pt wire is used as the counter electrode 2. The Pt ultramicroelectrode 9 is connected to the scanning electrochemical microscope control system 1 to form a precise control scanning mobile platform, and the scanning electrochemical microscope is used to precisely control the movement so that the Pt ultramicroelectrode 9 is close to the surface of the photoelectric thin film area 4 to be tested, and the current approximation curve is used to ensure the accurate positioning of the Pt ultramicroelectrode; turn on the blue light source 7, and adjust the light source to ensure that the light spot of a certain intensity and wavelength is just vertically irradiated on the surface of the photoelectric thin film material 4 to be tested. In a medium of a given concentration, the Pt ultramicroelectrode 9 is driven to rise a certain distance from a distance of 0 from the photoelectrochemical reaction cell 5, and then, under the irradiation of a light source, a reduction potential is applied to the Pt ultramicroelectrode 9 as the first working electrode, and an oxidation potential is applied to the photoelectric thin film material 4 to be tested as the second working electrode (this is because the sample tested in this embodiment is an n-type BiVO4 thin film material synthesized by electrodeposition, and holes are minority carriers. This embodiment is to obtain the exchange rate constant of photogenerated holes. At this time, the first working electrode applies a reduction potential, and the second working electrode applies an oxidation potential). The Pt ultramicroelectrode 9 is controlled to approach the substrate electrode at a uniform speed of 1 μm / s, and the current of the first working electrode is collected at the same time. A series of overpotentials η (the difference between the actual potential and the redox equilibrium potential of the medium) are obtained by changing the potential of the second working electrode, and a series of current feedback approximation curves are obtained. The current feedback approximation curve is fitted to obtain the heterogeneous apparent transfer rate constant, and then the formula (2) is used to convert Figure 8 The photogenerated hole exchange rate constant was obtained by curve fitting. Here we calculate the photogenerated hole exchange rate of the n-type BiVO4 thin film material synthesized by electrodeposition in 0.1M PBS buffer. 5.91×10 -4 cm s -1 .

[0071] Comparative Example 1

[0072] 0.5M KHCO3 is selected as the supporting electrolyte, 2mM K4Fe(CN)6 is used as the medium, and in the photoelectrochemical reaction solution 6 containing the medium as described above, glass is used as the sample to be tested (glass is a non-conductive sample, different from the photoelectric thin film material), the glass is fixed at the bottom of the photoelectrochemical reaction cell 5, a Pt ultramicroelectrode 9 is used as the first working electrode, the photoelectric thin film material is connected with a copper wire as the second working electrode 3, a silver / silver chloride electrode is used as the reference electrode 8, and a Pt wire is used as the counter electrode 2. The Pt ultramicroelectrode 9 is connected to the scanning electrochemical microscope control system 1 to form a precisely controlled scanning moving platform, and the scanning electrochemical microscope is used to precisely control the movement so that the Pt ultramicroelectrode 9 is close to the surface of the glass, and by Fig. 9 The current approximation mutation curve shown in the figure is used to mark the position of the Pt ultramicroelectrode probe corresponding to the current mutation in the current approximation mutation curve as position 0 of the photoelectrochemical reaction cell. However, since the interface is a non-conductive medium, at this time Fig. 9 The feedback curve shown is of negative feedback type. Then, the Pt ultramicroelectrode 9 is controlled to approach the substrate electrode at a uniform speed of lμm / s, and the current of the first working electrode is collected at the same time. A series of overpotentials η (the difference between the actual potential and the redox equilibrium potential of the mediator) are obtained by changing the potential of the second working electrode. The data of a series of current feedback approximation curves are meaningless.

[0073] Comparative Example 2

[0074] 0.5M KHCO3 is selected as the supporting electrolyte, 2mM K3Fe(CN)6 is used as the medium, and the photoelectric thin film material 4 to be tested is fixed on the bottom of the photoelectrochemical reaction cell 5 in the photoelectrochemical reaction solution 6 containing the medium as described above, a Pt ultramicroelectrode 9 is used as the first working electrode, the photoelectric thin film material is connected with a copper wire as the second working electrode 3, a silver / silver chloride electrode is used as the reference electrode 8, and a Pt wire is used as the counter electrode 2. The Pt ultramicroelectrode 9 is connected to the scanning electrochemical microscope control system 1 to form a precisely controlled scanning mobile platform, and the scanning electrochemical microscope is used to precisely control the movement of the Pt ultramicroelectrode 9 so that it is close to the surface of the photoelectric thin film area 4 to be tested, and the accurate positioning of the Pt ultramicroelectrode is ensured by the current approximation curve; the blue light source 7 is turned on, and the light source is adjusted to ensure that a light spot of a certain intensity and wavelength is just vertically irradiated onto the surface of the photoelectric thin film material 4 to be tested, and in a medium of a given concentration, the Pt ultramicroelectrode 9 is driven to rise a certain distance from a distance of 0 from the photoelectrochemical reaction cell 5, and then under the irradiation of the light source, an oxidation potential is applied to the Pt ultramicroelectrode 9 as the first working electrode, and a reduction potential is applied to the photoelectric thin film material 4 to be tested as the second working electrode (this is because the sample detected in this embodiment is a p-type ZnTe thin film material synthesized by hydrothermal synthesis, and holes are majority carriers. This embodiment is to obtain the exchange rate constant of photogenerated electrons. At this time, an oxidation potential is applied to the first working electrode, and a reduction potential is applied to the second working electrode). The Pt ultramicroelectrode 9 is controlled to approach the substrate electrode at a constant speed of 1 μm / s, and the current of the first working electrode is collected at the same time. Although the first working electrode applies an oxidation potential and the second working electrode applies a reduction potential to meet the potential setting requirements for measuring the electron exchange rate constant, the K3Fe(CN)6 used in this comparative example is an oxidizing medium for p-type ZnTe thin film materials and is not suitable for measuring the electron exchange rate constant of p-type ZnTe thin film materials and is an inappropriate electrolyte. Fig.10 The feedback curve shown is of negative feedback type and cannot be fitted.

[0075] The above embodiments are only examples. For example, the light source can be selected from yellow, blue, white and other LED light sources, and the light source direction can be irradiated from directly above or directly below the sample to ensure that the light spot is vertically irradiated onto the photoelectric thin film material to be tested. If the irradiation is performed from directly below the sample, it is necessary to ensure that the photoelectric catalyst thin film sample is a transparent material. For another example, the actual needs of electrons or holes as the research object are to flexibly adjust the oxidation mediator (that is, when it is necessary to measure the electron reaction kinetics, the reduction mediator should be selected, that is, with the vacuum energy level as a reference, the redox potential of the redox mediator is negative to the minimum value of the conduction band energy of the photoelectric thin film; when it is necessary to measure the hole reaction kinetics, the oxidation mediator should be selected, that is, with the vacuum energy level as a reference, the redox potential of the redox mediator is positive to the maximum value of the valence band energy of the photoelectric thin film), as well as the potentials of the first working electrode and the second working electrode (when it is necessary to measure the electron reaction kinetics, the second working electrode applies a reduction potential, and the first working electrode applies an oxidation potential; when it is necessary to measure the hole reaction kinetics, the second working electrode applies an oxidation potential, and the first working electrode applies a reduction potential). In addition, the construction of the four-electrode system in the scanning electrochemical microscope system, for parts not described in detail (such as the connection of each lead, etc.), can be carried out by referring to the relevant existing technology (such as CN104502388A).

[0076] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for in-situ determination of photogenerated carrier dynamics at a solid-liquid interface based on a scanning electrochemical microscope, characterized in that: The steps include: (1) selecting an organic solvent or an inorganic solvent, and using an electrolyte and a redox mediator to prepare a redox electrolyte solution to obtain a photoelectrochemical reaction solution; Prepare a photoelectrochemical reaction cell with a through hole in the center of the bottom, fix the photoelectric thin film material to be tested on the center of the bottom of the photoelectrochemical reaction cell from the outside, inject the photoelectrochemical reaction solution into the photoelectrochemical reaction cell, so that the photoelectrochemical thin film material to be tested contacts with the photoelectrochemical reaction solution through the through hole to form a solid-liquid interface; A Pt ultramicroelectrode probe is used as the first working electrode, the photoelectric thin film material to be tested is used as the second working electrode, the silver / silver chloride electrode is used as the reference electrode, and the platinum electrode is used as the counter electrode, forming a four-electrode system in a scanning electrochemical microscope system; wherein the Pt ultramicroelectrode probe is fixed on a moving platform of the scanning electrochemical microscope, and the moving platform can drive the Pt ultramicroelectrode probe to move; (2) applying a working voltage to the four-electrode system, taking the position of the Pt ultramicroelectrode probe directly above the through hole and not in contact with the photoelectrochemical reaction solution as the starting position, and using the mobile platform to continuously move the Pt ultramicroelectrode probe closer to the solid-liquid interface of the photoelectric thin film material to be measured, while recording the position of the Pt ultramicroelectrode probe and the corresponding current to obtain a current approximation curve of the current changing with the probe position; recording the position of the Pt ultramicroelectrode probe corresponding to the current mutation in the current approximation curve as position 0 of the photoelectrochemical reaction cell; (3) applying vertically incident light to the solid-liquid interface of the photoelectric thin film material to be tested, and keeping the light intensity and wavelength unchanged; then, by applying a preset potential to the first working electrode and the second working electrode, driving the Pt ultramicroelectrode probe to start from a position above the 0 position of the photoelectrochemical reaction cell, and approaching the solid-liquid interface of the photoelectric thin film material to be tested at a constant speed, while recording the position of the Pt ultramicroelectrode probe and the corresponding current, to obtain a current feedback approximation curve of the current changing with the probe position at the potential; The potential applied to the first working electrode is kept unchanged, while the potential applied to the second working electrode is adjusted, and the operation is repeated to obtain a current feedback approximation curve of the current changing with the probe position under the new potential setting; Repeating this process, at least 5 current feedback approximation curves of the current changing with the probe position under different second working electrode potential settings are obtained; (4) Fitting each current feedback approximation curve obtained in step (3) to obtain a heterogeneous effective charge transfer rate constant, thereby obtaining a relationship between different second working electrode potentials and the heterogeneous effective charge transfer rate constant obtained by fitting, and thereby obtaining a photogenerated carrier exchange rate constant at a solid-liquid interface formed by the contact between the photoelectric thin film material to be tested and the redox electrolyte solution; wherein the photogenerated carriers are photogenerated electrons or photogenerated holes.

2. The method according to claim 1, characterized in that: In step (1), the redox potential of the redox mediator is more negative than the minimum conduction band energy value of the photoelectric thin film with reference to the vacuum energy level, and the redox mediator serves as a reduction mediator; In step (3), the second working electrode always applies a reduction potential, and the first working electrode applies an oxidation potential; Correspondingly, the photogenerated carrier exchange rate constant obtained in step (4) is the photogenerated electron exchange rate constant.

3. The method according to claim 2, characterized in that: In step (1), when the solvent is an inorganic solvent, the redox mediator is potassium ferrocyanide K4Fe(CN)6.

4. The method according to claim 1, characterized in that: In step (1), the redox potential of the redox mediator is higher than the maximum value of the valence band energy of the photoelectric thin film, taking the vacuum energy level as a reference, and the redox mediator serves as an oxidizing mediator; In step (3), the second working electrode always applies an oxidation potential, and the first working electrode applies a reduction potential; Correspondingly, the photogenerated carrier exchange rate constant obtained in step (4) is the photogenerated hole exchange rate constant.

5. The method according to claim 4, characterized in that: In step (1), when the solvent is an inorganic solvent, the redox mediator is potassium ferrocyanide K3Fe(CN)6.

6. The method according to claim 1, characterized in that: In step (4), each current feedback approximation curve obtained in step (3) is fitted to obtain the heterogeneous effective charge transfer rate constant, specifically: First, each current feedback approximation curve obtained in step (3) is fitted to obtain the dimensionless heterogeneous apparent transfer rate constant κ, and then the heterogeneous effective charge transfer rate constant k is calculated according to the following formula (1): eff , In formula (1), D diffusion is the diffusion coefficient of the redox electrolyte, r T is the radius of the Pt ultramicroelectrode probe.

7. The method according to claim 1, characterized in that: In step (4), the photogenerated carrier exchange rate constant k 0 is the heterogeneous effective charge transfer rate constant k corresponding to different second working electrode potentials eff It is obtained by fitting the following formula (2): ln(k eff )=link 0 -anf (2) In formula (2), α is the charge transfer coefficient in the SEM test, n is the number of charges transferred during the redox reaction, f = F / RT, where T is temperature, R is the ideal gas constant, and F is the Faraday constant; η is the overpotential, which is equal to the difference between the potential applied by the second working electrode and the redox equilibrium potential of the redox mediator.

8. The method according to claim 1, characterized in that: In step (3), the constant speed is 0.5 μm / s-2 μm / s.

9. The method according to claim 1, characterized in that: In step (1), the concentration of the redox mediator in the redox electrolyte solution is 0.01 mM-5 mM.

10. The method according to claim 1, characterized in that: The diameter of the Pt ultramicroelectrode probe is 10nm-100μm; The through hole is preferably a round through hole; The photoelectrochemical reaction cell is made of polytetrafluoroethylene.

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