Method and device for measuring surface hole density of photoelectric catalyst

Abstract

The invention provides a method and device for measuring the surface hole density of a photoelectric catalyst, and the method comprises the steps: preparing a nano-porous gold film on the surface of a semiconductor photo-anode, forming a semiconductor-solution-metal three-phase interface, placing the photoelectric catalyst on the semiconductor-solution-metal three-phase interface, and measuring the hole density of the surface of the photoelectric catalyst. The semiconductor-solution-metal three-phase interface is used for carrying out a photoelectric catalytic reaction of the photoelectric catalyst; under a short-circuit reaction condition, measuring a quasi-Fermi level change value of a hole in the surface of the semiconductor photo-anode in real time through a differential amplifier; and obtaining the surface hole density of the photoelectric catalyst according to the quasi-Fermi level change value. According to the method, a complex spectrum testing device is eliminated, errors caused by artificial fitting are eliminated, charge signals related to surface reaction can be accurately distinguished, the measurement precision is improved, and accurate measurement of the surface hole density of the photoelectric catalyst can be achieved while the quasi Fermi level is used for monitoring the interface charge transfer process.

Description

Technical Field

[0001] The present invention relates to the field of photoelectrocatalysis technology, and in particular to a method and device for measuring the surface hole density of a photoelectrocatalyst. Background Art

[0002] Photoelectrocatalytic water splitting is an effective way to convert solar energy into clean fuels such as hydrogen. It involves the conversion of light energy into chemical energy in semiconductors. The efficiency of solar-to-hydrogen conversion is limited by the concentration of holes that ultimately reach the surface to participate in the reaction. Therefore, measuring the surface hole concentration is crucial. Photoinduced absorption spectroscopy (PIA) uses multiple averaging techniques to acquire signals. Combined with pump-probe technology, it measures the absorption value (optical density, ΔOD) of photogenerated charges under quasi-steady-state conditions, thereby determining the surface hole density. However, this test requires complex spectral measurement equipment, and the resulting charge absorption signal may contain a small amount of information that is not related to the surface reaction. Photoelectrochemical impedance spectroscopy (PEIS) uses quasi-steady-state illumination to obtain an impedance spectrum at a constant potential. Equivalent circuit fitting is used to determine the charge transfer resistance and capacitance during the surface reaction. Finally, the charge is determined using related formulas. However, the equivalent circuit fitting is subject to artificial selectivity, and the interpretation of the impedance data requires careful consideration of the kinetic model. Surface photovoltage microscopy (SPVM) can characterize the charge separation process and further determine the concentration of photogenerated holes, but it can only be performed under ex-situ conditions in air, which is far from the actual working conditions of photocatalysts. Summary of the Invention

[0003] The present invention provides a method and device for measuring the surface hole density of a photoelectrocatalyst, which is used to solve the defects of the traditional method for measuring the surface hole density of a photoelectrocatalyst, such as the error caused by artificial fitting, and the difficulty in measuring the surface photogenerated hole concentration in real time under actual reaction conditions.

[0004] The present invention provides a method for measuring the surface hole density of a photoelectrocatalyst, the method comprising: preparing a nanoporous gold film on the surface of a semiconductor photoanode to form a semiconductor-solution-metal three-phase interface, wherein a photoelectrocatalyst is placed at the semiconductor-solution-metal three-phase interface, and the semiconductor-solution-metal three-phase interface is used to carry out a photoelectrocatalytic reaction of the photoelectrocatalyst; under short-circuit reaction conditions, measuring the quasi-Fermi level change value of the holes on the surface of the semiconductor photoanode in real time by a differential amplifier; and obtaining the surface hole density of the photoelectrocatalyst based on the quasi-Fermi level change value.

[0005] According to the method for determining the surface hole density of a photoelectrocatalyst provided by the present invention, the short-circuit reaction conditions are achieved in the following manner: under light and without an external bias, the first working electrode and the counter electrode are short-circuited by a wire, the first working electrode, the counter electrode and the reference electrode are connected through an electrochemical workstation, and the second working electrode is connected to a differential amplifier to measure the quasi-Fermi level change value of the holes on the surface of the semiconductor photoanode, wherein the first working electrode is prepared according to the semiconductor photoanode; and the second working electrode is prepared according to the nanoporous gold film.

[0006] According to the method for measuring the surface hole density of a photoelectrocatalyst provided by the present invention, the first working electrode is prepared in the following manner: based on a double-throw-doped strontium niobate titanate single crystal, the semiconductor photoanode is prepared; and on the back of the semiconductor photoanode, an ohmic contact is constructed using indium gallium eutectic, silver glue and tin-copper wire to obtain the first working electrode.

[0007] According to the method for measuring the surface hole density of a photoelectrocatalyst provided by the present invention, the second working electrode is prepared by using silver glue to connect the wire to the nanoporous gold film formed on the surface of the epoxy resin coated on the semiconductor photoanode to obtain the second working electrode, wherein the nanoporous gold film is obtained by the following method: vacuum sputtering treatment is performed on the surface of the semiconductor photoanode partially coated with epoxy resin to form a nanoporous gold film on the exposed part of the semiconductor photoanode and the surface of the epoxy resin coated on the semiconductor photoanode.

[0008] According to the method for determining the surface hole density of a photoelectrocatalyst provided by the present invention, the surface hole density of the photoelectrocatalyst is obtained according to the change value of the quasi-Fermi level, specifically including: obtaining the surface hole density, Boltzmann constant, elementary charge amount, and preset temperature of the photoelectrocatalyst under dark equilibrium conditions; and obtaining the surface hole density of the photoelectrocatalyst based on the change value of the quasi-Fermi level, the surface hole density, Boltzmann constant, elementary charge amount, and preset temperature of the photoelectrocatalyst under dark equilibrium conditions.

[0009] According to the method for determining the surface hole density of a photoelectrocatalyst provided by the present invention, the surface hole density of the photoelectrocatalyst under dark equilibrium conditions is obtained in the following manner: obtaining the valence band state density of the semiconductor photoanode, the valence band energy of the semiconductor photoanode, the formal electrochemical potential of the redox species, and the reorganization energy of the solution, the Boltzmann constant, and a preset temperature; based on the valence band state density of the semiconductor photoanode, the valence band energy of the semiconductor photoanode, the formal electrochemical potential of the redox species, and the reorganization energy of the solution, the Boltzmann constant, and the preset temperature, the surface hole density of the photoelectrocatalyst under dark equilibrium conditions is obtained, wherein the redox species is a component of the solution in the semiconductor-solution-metal three-phase interface.

[0010] According to the method for determining the surface hole density of a photoelectrocatalyst provided by the present invention, after obtaining the surface hole density of the photoelectrocatalyst, the method further includes: based on the surface hole density of the photoelectrocatalyst, determining the reaction order and reaction rate constant of the photoelectrocatalyst in the photoelectrocatalytic reaction through photocurrent-hole density kinetic analysis.

[0011] According to the method for determining the surface hole density of a photoelectrocatalyst provided by the present invention, the reaction order and reaction rate constant of the photoelectrocatalyst in a photoelectrocatalytic reaction are determined based on the surface hole density of the photoelectrocatalyst through photocurrent-hole density kinetic analysis, specifically comprising: measuring the photocurrent density of the photoelectrocatalyst in a photoelectrocatalytic reaction under different light intensities; performing double logarithmic coordinate fitting on the photocurrent density of the photoelectrocatalyst in a photoelectrocatalytic reaction under the different light intensities and the surface hole density of the photoelectrocatalyst, and obtaining the reaction order and reaction rate constant of the photoelectrocatalytic reaction of the photoelectrocatalyst respectively according to linear regression of the rate equation.

[0012] The present invention also provides a device for measuring the surface hole density of a photoelectrocatalyst, the device comprising: a semiconductor photoanode, wherein a nanoporous gold film is provided on the surface of the semiconductor photoanode; an electrochemical workstation for controlling the short-circuit reaction state between the semiconductor photoanode and the counter electrode; a differential amplifier connected to the nanoporous gold film for real-time monitoring of the quasi-Fermi level change value of the holes on the surface of the semiconductor photoanode; a reference electrode placed in a solution at the semiconductor-solution-metal three-phase interface to provide a stable potential reference; a light source module for providing excitation light with adjustable intensity for exciting the semiconductor photoanode to generate holes, so that the holes participate in the reaction to form the quasi-Fermi level change value of the holes on the surface of the semiconductor photoanode; and a data processing unit for calculating the surface hole density of the photoelectrocatalyst based on the measured quasi-Fermi level change value.

[0013] According to the device for measuring the surface hole density of a photoelectrocatalyst provided by the present invention, the semiconductor photoanode includes an n-type semiconductor material and / or a p-type semiconductor material.

[0014] The present invention provides a method and device for measuring the surface hole density of a photoelectrocatalyst. A nanoporous gold film is prepared on the surface of a semiconductor photoanode to form a semiconductor-solution-metal three-phase interface. A photoelectrocatalyst is placed at the semiconductor-solution-metal three-phase interface, and the semiconductor-solution-metal three-phase interface is used to carry out the photoelectrocatalytic reaction of the photoelectrocatalyst. Under short-circuit reaction conditions, the quasi-Fermi level change value of the surface holes of the semiconductor photoanode is measured in real time by a differential amplifier. Based on the quasi-Fermi level change value, the surface hole density of the photoelectrocatalyst is obtained. The test conditions of the present invention do not require the construction of a complex spectral test device. Unlike impedance technology, a complex kinetic model is not required to determine the equivalent circuit, thereby eliminating the error caused by artificial fitting. The present invention can accurately distinguish charge signals related to surface reactions, improve the sensitivity of measuring the surface hole density of the photoelectrocatalyst, and achieve a more sensitive measurement of the surface hole density of the photoelectrocatalyst while using the quasi-Fermi level to monitor the interfacial charge transfer process. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the present invention or the prior art, a brief introduction is given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 1 is a flow chart of a method for measuring the surface hole density of a photoelectrocatalyst provided in an embodiment of the present invention; Figure 2 1 is a schematic diagram of a quasi-Fermi level test using a gold film and a differential amplifier according to an embodiment of the present invention; Figure 3 Schematic diagram of a device for testing quasi-Fermi level under short-circuit working conditions provided by an embodiment of the present invention; Figure 4 This is a schematic diagram of the charge transfer process between conduction band electrons and valence band holes at the semiconductor-solution interface provided by an embodiment of the present invention; Figure 5 This is a schematic diagram of the photoelectrochemical reaction principle provided by an embodiment of the present invention; Figure 6 1 is a flow chart of obtaining the surface hole density of the photoelectrocatalyst according to the quasi-Fermi level change value provided by an embodiment of the present invention; Figure 71 is a schematic diagram of a process for determining the surface hole density of the photoelectrocatalyst under dark equilibrium conditions provided by an embodiment of the present invention; Figure 8 is the surface quasi-Fermi level E provided by the embodiment of the present invention h Graph of changes with light intensity; Figure 9 This is a Mott-Schottky test curve diagram under dark and light conditions provided by an embodiment of the present invention; Figure 10 The embodiment of the present invention provides the use operando Variation of surface hole density at different light intensities measured by quasi-Fermi level; Figure 11 is a time-resolved photoinduced absorption spectrum provided by an embodiment of the present invention; Figure 12 Graph showing changes in PIA optical density versus light intensity, provided by an embodiment of the present invention; Figure 13 The embodiment of the present invention provides a method and method for using PIA operando Comparison of surface hole density measured by QFL method; Figure 14 Schematic diagram of a device for testing the photocurrent of a photochemical cell using a 2450 source meter under short-circuit working conditions provided by an embodiment of the present invention; Figure 15 This is a graph showing the variation of photocurrent with light intensity in a photochemical cell using a 2450 source meter, provided in an embodiment of the present invention; Figure 16 1 is a diagram showing the relationship between the photocurrent and the surface hole density in double logarithmic coordinates and the principle diagram of the kinetic parameters obtained by linear fitting using the origin software, provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0017] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0018] The method for measuring the hole density on the surface of the photoelectrocatalyst provided by the present invention is to operando Precise monitoring of the hole quasi-Fermi level (corresponding to the change in the quasi-Fermi level of holes on the surface of the semiconductor photoanode) can accurately determine the surface hole density of the photoelectrocatalyst.

[0019] Figure 1This is a flow chart of a method for measuring the hole density on the surface of a photoelectrocatalyst provided by an embodiment of the present invention. Figure 1 The process of the method for measuring the surface hole density of the photoelectrocatalyst provided by the present invention is described.

[0020] In an exemplary embodiment of the present invention, Figure 1 It can be seen that the method for measuring the hole density on the surface of the photoelectrocatalyst may include steps 110 to 130, and each step will be introduced below.

[0021] In step 110, a nanoporous gold film is prepared on the surface of a semiconductor photoanode to form a semiconductor-solution-metal three-phase interface, wherein a photoelectrocatalyst is placed at the semiconductor-solution-metal three-phase interface, and the semiconductor-solution-metal three-phase interface is used to perform a photoelectrocatalytic reaction of the photoelectrocatalyst; In step 120, under short-circuit reaction conditions, the quasi-Fermi level change of the holes on the surface of the semiconductor photoanode is measured in real time by a differential amplifier; In step 130, the surface hole density of the photoelectrocatalyst is obtained according to the quasi-Fermi level change value.

[0022] In an embodiment of the present invention, the quasi-Fermi level is measured by constructing a nanoporous gold film on the surface of a semiconductor photoanode. Specifically, a nanoporous gold film is prepared on the surface of the semiconductor photoanode, forming a semiconductor-solution-metal three-phase interface. The gold film is used for several reasons: gold has a high work function (second only to platinum, which has the highest metal work function), and its contact with the semiconductor creates a high potential barrier to form a minority carrier device. Due to the strong mutual coupling between gold and the semiconductor, the minority carrier injection efficiency is close to 100%, so the gold Fermi level is always in equilibrium with the quasi-Fermi level of the minority carriers. The nanoporous Au film forms an equilibrium at the semiconductor-solution-metal three-phase interface. Due to the slow kinetics of the oxygen evolution reaction (OER) and redox reaction (ORR) of Au, the Au film only serves to monitor the potential and does not cause significant current flow.

[0023] In one embodiment, a nanoporous gold film can be formed on the surface of a semiconductor photoanode to form a semiconductor-solution-metal triple-phase interface. A photoelectrocatalyst can be placed at this semiconductor-solution-metal triple-phase interface, where it can be used to perform a photoelectrocatalytic reaction.

[0024] Furthermore, the quasi-Fermi level change value of the holes on the surface of the semiconductor photoanode can be measured in real time by a differential amplifier under short-circuit reaction conditions. For example, operandoThe quasi-Fermi level change value is calculated, and the surface hole density of the photoelectrocatalyst is obtained based on the quasi-Fermi level change value.

[0025] In one embodiment, the semiconductor photoanode may include an n-type semiconductor material and / or a p-type semiconductor material. For ease of description, in this embodiment, the semiconductor photoanode is described as an n-type semiconductor.

[0026] During the application process, after the semiconductor photoanode (taking n-type semiconductor as an example) and the electrolyte solution (corresponding to the solution in the semiconductor-solution-metal three-phase interface) come into contact, a solid-liquid interface similar to a Schottky junction will be formed, and the Fermi level of the semiconductor will be balanced with the electrochemical potential of the solution. After the semiconductor is excited by light, the balance is broken, and the quasi-Fermi level (Quansi-Fermi Level, also known as QFL) is used to describe the distribution of electrons and holes in the non-equilibrium state. The electron-hole pairs are separated and transferred, and finally participate in the surface catalytic reaction. The change of the quasi-Fermi level (corresponding to the change in the quasi-Fermi level of the holes on the surface of the semiconductor photoanode) can accurately describe the charge transfer process occurring at the semiconductor-liquid interface. The difference between the minority carrier quasi-Fermi level and the electrochemical potential of the solution is the driving force of the photoelectrocatalytic reaction. By accurately monitoring under actual working conditions operando Minority carrier quasi-Fermi level ( operando The change of QFL) (corresponding to the change of the quasi-Fermi level of the holes on the surface of the semiconductor photoanode) can effectively measure the surface hole density of the photoelectrocatalyst.

[0027] The method for measuring the surface hole density of a photoelectrocatalyst provided by an embodiment of the present invention comprises preparing a nanoporous gold film on the surface of a semiconductor photoanode to form a semiconductor-solution-metal three-phase interface, wherein a photoelectrocatalyst is placed at the semiconductor-solution-metal three-phase interface, and the semiconductor-solution-metal three-phase interface is used to carry out the photoelectrocatalytic reaction of the photoelectrocatalyst; under short-circuit reaction conditions, the quasi-Fermi level change value of the surface holes of the semiconductor photoanode is measured in real time by a differential amplifier; and based on the quasi-Fermi level change value, the surface hole density of the photoelectrocatalyst is obtained. The present invention gets rid of complex spectral testing equipment, eliminates errors caused by human fitting, can accurately distinguish charge signals related to surface reactions, improves measurement accuracy, and can achieve the measurement of the surface hole density of the photoelectrocatalyst by monitoring the interfacial charge transfer process using the quasi-Fermi level.

[0028] Based on any of the above embodiments, the nanoporous gold film is prepared by vacuum sputtering, and the nanoporous gold film forms a Schottky contact with the surface of the semiconductor photoanode. In one example, the nanoporous gold film has a thickness of 5-50 nm and a porosity of 10%-60%.

[0029] In another exemplary embodiment of the present invention, the short-circuit reaction condition can be achieved in the following manner: Under illumination and without external bias, the first working electrode and the counter electrode are short-circuited by a wire, the first working electrode, the counter electrode and the reference electrode are connected through an electrochemical workstation, and the second working electrode is connected to a differential amplifier to measure the change in the quasi-Fermi energy level of holes on the surface of the semiconductor photoanode, wherein the first working electrode is prepared according to the semiconductor photoanode; and the second working electrode is prepared according to the nanoporous gold film.

[0030] In one embodiment, under illumination and without an external bias, the first working electrode and the counter electrode can be short-circuited by a wire, the first working electrode, the counter electrode and the reference electrode can be connected through an electrochemical workstation, and the second working electrode can be connected to a differential amplifier to measure the quasi-Fermi energy level change of the holes on the surface of the semiconductor photoanode, thereby achieving rapid and efficient measurement of the quasi-Fermi energy level change of the holes on the surface of the semiconductor photoanode.

[0031] In an exemplary embodiment of the present invention, the first working electrode can be prepared in the following manner: A semiconductor photoanode was prepared based on a double-thaw doped strontium niobate titanate single crystal. An ohmic contact is constructed on the back of the semiconductor photoanode using indium gallium eutectic, silver glue and tin-copper wire to obtain the first working electrode.

[0032] In one embodiment, the The backside of a 5 mm double-polished strontium niobate titanate single crystal wafer uses an indium gallium eutectic, silver paste, and tin-copper wire to form an ohmic contact, serving as the first working electrode. The backside of the double-polished strontium niobate titanate wafer is opposite the surface of the semiconductor photoanode, which participates in the photoelectrocatalytic reaction.

[0033] In another exemplary embodiment of the present invention, the second working electrode can be prepared in the following manner: The wire is connected to the nanoporous gold film on the surface of the epoxy resin coated with the semiconductor photoanode using silver glue to obtain the second working electrode, wherein the nanoporous gold film is obtained by the following method: A vacuum sputtering process is performed on the surface of a semiconductor photoanode partially coated with epoxy resin to form a nanoporous gold film on the exposed portion of the semiconductor photoanode and the surface of the epoxy resin coated on the semiconductor photoanode.

[0034] In one embodiment, a 10 nm thick gold film can be vacuum sputtered on the surface of the semiconductor photoanode and on the epoxy resin surrounding the semiconductor photoanode, and then a second wire can be connected to the gold film on the epoxy resin surface using silver glue as a second working electrode. Finally, the contact point is coated with epoxy resin to ensure that no silver or tin copper wire is exposed to the electrolyte.

[0035] It should be noted that the semiconductor photoanode is partially coated with epoxy resin. In addition, the semiconductor photoanode also includes an exposed portion, i.e., a portion not coated with epoxy resin. By vacuum sputtering Au, a nanoporous gold film can be formed on the surface of the epoxy resin coated on the semiconductor photoanode portion, and a nanoporous gold film can also be formed on the exposed portion of the semiconductor photoanode. Since the formation of the nanoporous gold film on the exposed portion of the semiconductor photoanode and the formation of the nanoporous gold film on the surface of the epoxy resin coated on the semiconductor photoanode portion are balanced, the measurement results are the quasi-Fermi level changes on the surface of the semiconductor photoanode.

[0036] Figure 2 : is a schematic diagram of a quasi-Fermi level test using a gold film and a differential amplifier according to an embodiment of the present invention. Figure 3 This is a schematic diagram of a device for testing quasi-Fermi level under short-circuit working conditions provided by an embodiment of the present invention. Figure 2 and Figure 3 Provide explanation.

[0037] Under short-circuit reaction conditions, the first working electrode (corresponding to Figure 2 The leftmost vertical line in the figure is connected to the bipotentiostat) and the working electrode line of the workstation, with Ag / AgCl as the reference electrode, platinum mesh as the counter electrode, and potassium phosphate buffer solution as the electrolyte solution. The second working electrode (corresponding to Figure 2 The serrated part in the figure represents gold) is connected to the differential amplifier (corresponding to Figure 2 As shown in the voltmeter icon, the other end of the differential amplifier is connected to the reference electrode through a dotted line) to measure the surface quasi-Fermi level E h In the application process, a 365 nm LED lamp can be used as the light source, and the surface quasi-Fermi level E can be obtained by adjusting the light intensity. h The curve of light intensity change, such as Figure 8 As shown. Among them, Figure 2 E in e The bipotentiostat is an electrochemical experimental device that can simultaneously control the potential of two electrodes (reference electrode and counter electrode).

[0038] Figure 6The present invention provides a schematic flow chart of obtaining the surface hole density of the photoelectrocatalyst according to the quasi-Fermi level change value. Figure 6 The process of obtaining the surface hole density of the photoelectrocatalyst according to the quasi-Fermi level change value provided by the present invention is described.

[0039] In another exemplary embodiment of the present invention, Figure 6 It can be seen that obtaining the surface hole density of the photoelectrocatalyst according to the change value of the quasi-Fermi level may include steps 610 and 620, and each step will be described below.

[0040] In step 610, the surface hole density, Boltzmann constant, elementary charge, and preset temperature of the photoelectrocatalyst under dark equilibrium conditions are obtained; In step 620, the surface hole density of the photoelectrocatalyst is obtained based on the quasi-Fermi level change value, the surface hole density of the photoelectrocatalyst under dark equilibrium conditions, the Boltzmann constant, the elementary charge, and the preset temperature.

[0041] In one embodiment, the surface hole density p of the photoelectrocatalyst under dark equilibrium conditions can be obtained. s0 , Boltzmann constant k B , the elementary charge q, and the preset temperature T. Further, based on the quasi-Fermi level change value , the surface hole density p of the photoelectrocatalyst under dark equilibrium conditions s0 , Boltzmann constant k B , elementary charge q, and preset temperature T to obtain the surface hole density of the photoelectrocatalyst.

[0042] In another example, the surface hole density of the photoelectrocatalyst can be realized using the following formula (1): (1) in, It represents the surface hole density of the photoelectrocatalyst. The physical meanings of other parameters have been noted in the previous text and will not be repeated here.

[0043] Figure 7 3 is a flow chart of determining the surface hole density of the photoelectrocatalyst under dark equilibrium conditions provided by an embodiment of the present invention.

[0044] The following will be combined Figure 7 The process of determining the surface hole density of the photoelectrocatalyst under dark equilibrium conditions is described.

[0045] In an exemplary embodiment of the present invention, Figure 7It can be seen that the surface hole density of the photoelectrocatalyst under dark equilibrium conditions may include steps 710 and 720, and each step will be described below.

[0046] In step 710, the valence band state density of the semiconductor photoanode, the valence band energy of the semiconductor photoanode, the formal electrochemical potential of the redox species, the reorganization energy of the solution, the Boltzmann constant, and the preset temperature are obtained; In step 720, the surface hole density of the photoelectrocatalyst under dark equilibrium conditions is obtained based on the valence band state density of the semiconductor photoanode, the valence band energy of the semiconductor photoanode, the formal electrochemical potential of the redox species, the reorganization energy of the solution, the Boltzmann constant, and the preset temperature, wherein the redox species are components of the solution in the semiconductor-solution-metal three-phase interface.

[0047] In one embodiment, the valence band state density N of the semiconductor photoanode can be obtained. V , valence band energy E of semiconductor photoanode V , the formal electrochemical potential of redox species , and the reorganization energy of the solution , the Boltzmann constant k B , and the preset temperature T. Further, based on the valence band state density N of the semiconductor photoanode V , valence band energy E of semiconductor photoanode V , the formal electrochemical potential of redox species , and the reorganization energy of the solution , the Boltzmann constant k B , and the preset temperature T, the surface hole density p of the photoelectrocatalyst under dark equilibrium conditions is obtained s0。

[0048] Figure 4 This is a schematic diagram of the charge transfer process between conduction band electrons and valence band holes at the semiconductor-solution interface provided by an embodiment of the present invention; Figure 5 This is a schematic diagram of the photoelectrochemical reaction principle provided by an embodiment of the present invention. Figure 4 and Figure 5 The derivation process of the formula (corresponding to Formula 1) for obtaining the surface hole density of the photoelectrocatalyst based on the change value of the quasi-Fermi level, the surface hole density of the photoelectrocatalyst under dark equilibrium conditions, the Boltzmann constant, the elementary charge, and the preset temperature is explained.

[0049] In one embodiment, according to the Macus-Gerischer theory, under dark conditions, the charge transfer processes of conduction band electrons and valence band holes at the semiconductor-solution interface follow the following formulas: in and represent the electron transfer from the conduction band edge to the acceptor species A and from the donor species A, respectively. − The forward and reverse rate constants for transfer to the conduction band energy level, and represent the hole transfer from the valence band edge to the donor species A − and the forward and reverse rate constants for transfer from acceptor A to the valence band energy level. and They represent the surface equilibrium concentrations of conduction band electrons and valence band holes, respectively. Their expressions can be written as: in, , are the effective state densities of the conduction band and valence band, respectively, where Corresponding to the valence band state density of the semiconductor photoanode mentioned above, the exponential term in the formula is called the nuclear factor (or Franck-Condon factor), which is a measure of the overlap between the occupied / vacant states of the redox species and the valence band / conduction band state density of the solid, and includes the electrochemical potential of the redox species. , taking into account the fluctuations of the solvent shell around the redox species and thus including the reorganization energy .

[0050] Consider the simplest photoelectrochemical reaction: The reaction rate can be expressed as: in is the surface hole concentration under illumination, using the definition of photoelectrochemical affinity: in is the difference in the quasi-Fermi energy level of the surface holes before and after illumination, which corresponds to the change in the quasi-Fermi energy level mentioned above and can be obtained experimentally. From this, we can deduce the above formula (1). The surface hole density of the photoelectrocatalyst can then be calculated based on formula (1).

[0051] Continue to the previous article Figure 8The above embodiment is used as an example to illustrate that in order to determine the surface hole density of the photoelectrocatalyst, it is necessary to calculate the width of the space charge region. For this purpose, a Mott-Schottky test can be performed. The test conditions are selected as the potential of −0.4 – 1.4 V (vs. RHE), while applying a 10 mV perturbation at a frequency of 1 kHz, and testing in the dark state and under different light intensities. Figure 9 The slope and intercept of the sample (semiconductor photoanode) can be deduced to have a flat band potential of − 0.3 V (vs. RHE) and a doping concentration of 4.2×10 19 carriers cm -3 , from which the width of the space charge region is calculated to be 25 nm. Substituting it into the surface hole density formula, the surface hole density is calculated, and the result is as follows Figure 10 shown.

[0052] In the embodiment of the present invention, the Mott-Schottky test is performed in a dark state and under different light intensities, with a test potential range of -0.4 V to 1.4 V, a frequency of 1 kHz, and a perturbation voltage of 10 mV.

[0053] In this embodiment of the present invention, a dual working electrode is prepared by vacuum sputtering an Au film on the surface of the photoelectrocatalyst to be tested. The sample, counter electrode, and reference electrode are placed in a solution. The second working electrode is connected to a differential amplifier, and the counter and reference electrodes are connected to an electrochemical workstation. Testing is performed under short-circuit conditions by modulating light intensity. Mott-Schottky tests are also performed on the same samples to determine the width of the space charge region.

[0054] In order to further verify the correctness of the method, PIA test was carried out on the same sample in short-circuit working state, the pump light was 365 nm LED light, the wavelength of the probe light was 550 nm, and the light intensity was modulated to obtain a series of optical densities, such as Figure 11 As shown. By dividing the optical density by the absorption coefficient, the surface hole density change curve corresponding to different light intensities is obtained, as shown Figure 12 shown. Figure 13 The figure is a comparison of the two methods. It can be seen that the values measured by the two methods are of the same order of magnitude and correspond well in the entire light intensity range, further verifying the correctness of the method.

[0055] In another exemplary embodiment of the present invention, after obtaining the surface hole density of the photoelectrocatalyst, the method for determining the surface hole density of the photoelectrocatalyst may further include the following steps: Based on the surface hole density of the photoelectrocatalyst, the reaction order and reaction rate constant of the photoelectrocatalytic reaction of the photoelectrocatalyst are determined by photocurrent-hole density kinetic analysis.

[0056] In another exemplary embodiment of the present invention, based on the surface hole density of the photoelectrocatalyst, the reaction order and reaction rate constant of the photoelectrocatalyst in the photoelectrocatalytic reaction are determined by photocurrent-hole density kinetic analysis, which can be achieved in the following manner: Measuring the photocurrent density of the photoelectrocatalyst during the photoelectrocatalytic reaction under different light intensities; The photocurrent density of the photoelectrocatalyst under different light intensities during the photoelectrocatalytic reaction was fitted with the surface hole density of the photoelectrocatalyst by double logarithmic coordinates, and linear regression was performed based on the rate equation to obtain the reaction order and reaction rate constant of the photoelectrocatalytic reaction of the photoelectrocatalyst.

[0057] In one embodiment, Figure 14 The device is used to test the photocurrent of the photochemical cell using the 2450 source meter under short-circuit working conditions. At the same time, the device is used to test the photocurrent of the photochemical cell using the 2450 source meter under short-circuit working conditions. Figure 15 The photoelectrocatalytic reaction rate is correlated with the surface hole density as shown in the figure, and the reaction order and reaction rate constant of the water oxidation reaction are determined. Then, the photocurrent of the photochemical cell under no bias conditions is measured using a 2450 source meter, and the photocurrent density and surface hole density are double-logarithmized, as shown in the figure below. Figure 16 As shown, a rate equation analysis is then performed to determine the reaction order and reaction rate constant of the water oxidation reaction.

[0058] The method for measuring the hole density on the surface of the photoelectrocatalyst provided by the embodiment of the present invention is to operando The quasi-Fermi level of holes is precisely monitored to determine the photogenerated hole density, eliminating complex spectral devices, eliminating errors caused by human fitting, and accurately distinguishing charge signals related to surface reactions. Combining in-situ measurements with advanced characterization techniques, this method provides a simple method for real-time determination of surface photogenerated charge concentration under actual working conditions. Compared with the PIAS test method of multiple averaging, the outstanding advantage of the present invention is its high test sensitivity, which can measure lower concentrations of charge. At the same time, the present invention has the advantages of simple operation, applicability to the characterization of various semiconductor materials, and good stability and repeatability.

[0059] The device for measuring the surface hole density of a photoelectrocatalyst provided by the present invention is described below. The device for measuring the surface hole density of a photoelectrocatalyst described below and the method for measuring the surface hole density of a photoelectrocatalyst described above can be referred to each other.

[0060] The device for measuring the hole density on the surface of a photoelectrocatalyst provided in an embodiment of the present invention may include the following components: A semiconductor photoanode, wherein a nanoporous gold film is provided on the surface of the semiconductor photoanode; an electrochemical workstation for controlling the short-circuit reaction state between the semiconductor photoanode and the counter electrode; A differential amplifier connected to the nanoporous gold film for real-time monitoring of the quasi-Fermi level change of holes on the surface of the semiconductor photoanode; The reference electrode is placed in the solution at the semiconductor-solution-metal triple-phase interface to provide a stable potential reference; A light source module, configured to provide excitation light of adjustable intensity, configured to excite the semiconductor photoanode to generate holes, so that the holes participate in a reaction to form a quasi-Fermi level change value of holes on the surface of the semiconductor photoanode; A data processing unit is used to calculate the surface hole density of the photoelectrocatalyst based on the measured quasi-Fermi level change value.

[0061] It should be noted that the light source module is used to excite holes generated by the semiconductor photoanode, which may be photogenerated holes. In one embodiment, the electrochemical workstation, reference electrode, and light source module may also constitute a short-circuit construction unit for creating short-circuit reaction conditions.

[0062] In yet another exemplary embodiment of the present invention, the semiconductor photoanode includes an n-type semiconductor material and / or a p-type semiconductor material.

[0063] The device for measuring the surface hole density of a photoelectrocatalyst provided by an embodiment of the present invention comprises a nanoporous gold film prepared on the surface of a semiconductor photoanode to form a semiconductor-solution-metal three-phase interface, wherein a photoelectrocatalyst is placed at the semiconductor-solution-metal three-phase interface, and the semiconductor-solution-metal three-phase interface is used to carry out the photoelectrocatalytic reaction of the photoelectrocatalyst; under short-circuit reaction conditions, the quasi-Fermi level change value of the surface holes of the semiconductor photoanode is measured in real time by a differential amplifier; and the surface hole density of the photoelectrocatalyst is obtained based on the quasi-Fermi level change value. The present invention gets rid of complex spectral testing equipment, eliminates errors caused by human fitting, can accurately distinguish charge signals related to surface reactions, improves measurement accuracy, and can simultaneously measure the surface hole density of the photoelectrocatalyst while monitoring the interfacial charge transfer process using the quasi-Fermi level.

[0064] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, i.e., they may be located in one location or distributed across multiple network units. Some or all of the modules may be selected based on actual needs to achieve the objectives of the present embodiment. Persons of ordinary skill in the art will be able to understand and implement the present invention without inventive effort.

[0065] Through the description of the above embodiments, those skilled in the art will clearly understand that each embodiment can be implemented using software plus a necessary general-purpose hardware platform, or of course, hardware. Based on this understanding, the essence of the above technical solution, or the portion that contributes to the relevant technology, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a magnetic disk, or an optical disk, and includes a number of instructions for causing a computer device (such as a personal computer, server, or network device) to execute the methods described in each embodiment or certain portions of the embodiments.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for measuring the surface hole density of a photoelectrocatalyst, characterized in that: The method comprises: A nanoporous gold film is prepared on the surface of a semiconductor photoanode to form a semiconductor-solution-metal three-phase interface, wherein a photoelectrocatalyst is placed at the semiconductor-solution-metal three-phase interface, and the semiconductor-solution-metal three-phase interface is used to carry out a photoelectrocatalytic reaction of the photoelectrocatalyst; Under short-circuit reaction conditions, a differential amplifier is used to measure in real time the change in the quasi-Fermi energy level of holes on the surface of the semiconductor photoanode; The surface hole density of the photoelectrocatalyst is obtained according to the quasi-Fermi level change value.

2. The method for measuring the surface hole density of a photoelectrocatalyst according to claim 1, wherein: The short-circuit reaction conditions are achieved in the following manner: Under illumination and without external bias, the first working electrode and the counter electrode are short-circuited by a wire, the first working electrode, the counter electrode and the reference electrode are connected through an electrochemical workstation, and the second working electrode is connected to a differential amplifier to measure the change in the quasi-Fermi energy level of the holes on the surface of the semiconductor photoanode, wherein the first working electrode is prepared according to the semiconductor photoanode; and the second working electrode is prepared according to the nanoporous gold film.

3. The method for measuring the surface hole density of a photoelectrocatalyst according to claim 2, wherein: The first working electrode is prepared in the following manner: The semiconductor photoanode is prepared based on a double-blanketed strontium niobate titanate single crystal; An ohmic contact is constructed on the back of the semiconductor photoanode using indium gallium eutectic, silver paste and tin-copper wire to obtain the first working electrode.

4. The method for measuring the surface hole density of a photoelectrocatalyst according to claim 2, wherein: The second working electrode is prepared in the following manner: The wire is connected to the nanoporous gold film on the surface of the epoxy resin coated with the semiconductor photoanode using silver glue to obtain the second working electrode, wherein the nanoporous gold film is obtained by the following method: A vacuum sputtering process is performed on the surface of a semiconductor photoanode partially coated with epoxy resin to form a nanoporous gold film on the exposed portion of the semiconductor photoanode and the surface of the epoxy resin coated on the semiconductor photoanode.

5. The method for measuring the surface hole density of a photoelectrocatalyst according to claim 1, wherein: Obtaining the surface hole density of the photoelectrocatalyst according to the quasi-Fermi level change value specifically includes: Obtaining the surface hole density, Boltzmann constant, elementary charge, and preset temperature of the photoelectrocatalyst under dark equilibrium conditions; The surface hole density of the photoelectrocatalyst is obtained based on the quasi-Fermi level change value, the surface hole density of the photoelectrocatalyst under dark equilibrium conditions, the Boltzmann constant, the elementary charge, and the preset temperature.

6. The method for measuring the surface hole density of a photoelectrocatalyst according to claim 5, wherein: The surface hole density of the photoelectrocatalyst under dark equilibrium conditions is obtained in the following manner: Obtaining the valence band state density of the semiconductor photoanode, the valence band energy of the semiconductor photoanode, the formal electrochemical potential of the redox species, the reorganization energy of the solution, the Boltzmann constant, and the preset temperature; Based on the valence band state density of the semiconductor photoanode, the valence band energy of the semiconductor photoanode, the formal electrochemical potential of the redox species, the reorganization energy of the solution, the Boltzmann constant, and the preset temperature, the surface hole density of the photoelectrocatalyst under dark equilibrium conditions is obtained, wherein the redox species is a component of the solution in the semiconductor-solution-metal three-phase interface.

7. The method for measuring the surface hole density of a photoelectrocatalyst according to claim 1, wherein: After obtaining the surface hole density of the photoelectrocatalyst, the method further comprises: Based on the surface hole density of the photoelectrocatalyst, the reaction order and reaction rate constant of the photoelectrocatalytic reaction of the photoelectrocatalyst are determined by photocurrent-hole density kinetic analysis.

8. The method for measuring the surface hole density of a photoelectrocatalyst according to claim 7, wherein: The determining of the reaction order and reaction rate constant of the photoelectrocatalytic reaction of the photoelectrocatalyst by photocurrent-hole density kinetic analysis based on the surface hole density of the photoelectrocatalyst specifically includes: Measuring the photocurrent density of the photoelectrocatalyst during the photoelectrocatalytic reaction under different light intensities; The photocurrent density of the photoelectrocatalyst under the different light intensities during the photoelectrocatalytic reaction is fitted with the surface hole density of the photoelectrocatalyst by double logarithmic coordinates, and linear regression is performed based on the rate equation to obtain the reaction order and reaction rate constant of the photoelectrocatalytic reaction of the photoelectrocatalyst.

9. A device for measuring the surface hole density of a photoelectrocatalyst, characterized in that: The device comprises: A semiconductor photoanode, wherein a nanoporous gold film is provided on the surface of the semiconductor photoanode; an electrochemical workstation for controlling the short-circuit reaction state between the semiconductor photoanode and the counter electrode; A differential amplifier connected to the nanoporous gold film for real-time monitoring of the quasi-Fermi level change of holes on the surface of the semiconductor photoanode; The reference electrode is placed in the solution at the semiconductor-solution-metal triple-phase interface to provide a stable potential reference; A light source module, configured to provide excitation light of adjustable intensity, configured to excite the semiconductor photoanode to generate holes, so that the holes participate in a reaction to form a quasi-Fermi level change value of holes on the surface of the semiconductor photoanode; A data processing unit is used to calculate the surface hole density of the photoelectrocatalyst based on the measured quasi-Fermi level change value.

10. The device for measuring the surface hole density of a photoelectrocatalyst according to claim 9, characterized in that: The semiconductor photoanode includes an n-type semiconductor material and / or a p-type semiconductor material.

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