In-situ characterization of the electrical conductivity-structure-catalytic activity of an electrocatalyst

Abstract

The present application relates to a kind of in-situ characterization method of electric conductivity-structure-catalytic activity of electrocatalyst, the method includes the following steps: (1) preparation micro electrochemical cell;(2) the three-electrode system formed by counter electrode, working electrode and reference electrode forms in-situ electrical / electrochemical measurement circuit, constructs micro electrochemical environment;(3) in-situ electrical and electrochemical measurement: by source table at counter electrode electrocatalytic voltage is applied, simultaneously, small bias voltage is applied to micro-nano device between interdigital electrode array, respectively, the electrocatalytic signal and in-situ electric conductivity signal of micro-nano device are collected;(4) in-situ Raman spectrum characterization: by Raman spectrum, the in-situ Raman signal of reaction window during electrocatalytic reaction is collected, and the in-situ structure information of catalyst is obtained;(5) periodic catalytic voltage is applied, and the dynamic response characteristics of electrocatalytic signal and in-situ electric conductivity signal of catalyst are tested.The present application is convenient to test, can consider catalyst electrical property, actual reaction environment and structure information.

Description

Technical Field

[0001] This invention relates to the fields of electrochemical measurement and materials characterization, and in particular to an in-situ characterization method for the conductivity-structure-catalytic activity of an electrocatalyst. Background Technology

[0002] Electrocatalytic reactions involve charge transport between catalysts and transfer at the catalyst / electrolyte interface. Among these, charge transport is often overlooked compared to charge transfer, leading to inaccurate assessment of catalyst activity and hindering the design of highly efficient catalysts. Currently, most transition metal oxide (e.g., Co3O4 for the oxygen evolution reaction) and sulfide (e.g., MoS2 for the hydrogen evolution reaction) catalysts are semiconductors rather than metals, often exhibiting poor intrinsic conductivity. This necessitates the use of conductive additives (e.g., carbon nanomaterials) to enhance electrode conductivity in practical applications. However, the use of additives introduces several problems, such as covering active sites, hindering mass transfer, and increasing costs. Therefore, clarifying the relationship between catalyst conductivity, structural changes, and catalytic activity is crucial.

[0003] Currently, there are two main methods for studying the conductivity of catalysts: (1) two-electrode measurement, which involves measuring conductivity by placing a multimeter on the catalyst without adding electrolyte. This method is non-in-situ measurement and cannot reflect the in-situ conductivity information under actual reaction conditions; (2) electrochemical impedance spectroscopy, which extracts conductivity information from the fitting of equivalent circuits, resulting in a large error. Therefore, there is an urgent need to develop a new in-situ characterization technique that can take into account the electrical properties of the catalyst, the actual reaction environment, and structural information. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an in-situ characterization method for the conductivity-structure-catalytic activity of electrocatalysts that takes into account the electrical properties of the catalyst, the actual reaction environment and structural information.

[0005] To address the above problems, the present invention provides an in-situ characterization method for the conductivity, structure, and catalytic activity of an electrocatalyst, comprising the following steps:

[0006] (1) Preparation of micro-electrochemical cells:

[0007] (a) 32 electrodes were fabricated on a printed circuit board using electron beam lithography.

[0008] (b) Arbitrarily select two adjacent electrodes to create an interdigitated electrode array pattern on a printed circuit board using electron beam lithography, and then form an interdigitated electrode array through thermal evaporation.

[0009] (c) A series of polymethyl methacrylate windows were fabricated in the interdigitated electrode array region by electron beam lithography, and then a catalyst nanoparticle solution with a concentration of 5 mg / ml was dropped onto the printed circuit board and allowed to air dry naturally.

[0010] (d) The polymethyl methacrylate film was removed with acetone, allowing the catalyst nanoparticles to be precisely deposited on the windows of the interdigitated electrode array region, forming a micro / nano device chip assembled from the particles.

[0011] (e) A 1-2 μm thick polymethyl methacrylate film is used to cover the micro / nano device chip as an inert protective layer. Then, the region of interest is patterned on the polymethyl methacrylate by electron beam lithography to expose the surface of the catalyst particles as an electrochemical reaction window and a Raman spectroscopy acquisition window. The window size is 10-500 μm.

[0012] (2) Open the reaction window, use a carbon rod as the counter electrode, an interdigitated electrode array as the working electrode, and use silver / silver chloride or mercury / mercury oxide as the reference electrode. The three-electrode system consisting of the counter electrode, working electrode and reference electrode forms an in-situ electrical / electrochemical measurement circuit to construct a micro-electrochemical environment.

[0013] (3) In-situ electrical and electrochemical measurements:

[0014] Electrodes are led out by bonding wires to the printed circuit board and connected to the source meter. An electrocatalytic voltage of 0.5~2.0 V is applied to the electrodes through the source meter. At the same time, a small bias voltage of 0~100 mV is applied to the micro-nano device between the interdigital electrode array. The electrocatalytic signal and in-situ conductivity signal of the micro-nano device are collected respectively, realizing in-situ simultaneous electrical and electrochemical measurement.

[0015] (4) In-situ Raman spectroscopy characterization:

[0016] In-situ Raman signals were acquired through Raman spectroscopy at the reaction window during the electrocatalytic reaction to obtain in-situ structural information of the catalyst.

[0017] (5) Apply periodic catalytic voltages and test the dynamic response characteristics of the catalyst's electrocatalytic signal and in-situ conductivity signal.

[0018] In step (a), the printed circuit board refers to a SiO2 / Si, quartz, or sapphire substrate.

[0019] In step (b), the interdigitated electrode array consists of finger-shaped or comb-shaped electrodes with periodic patterns in their in-plane shape.

[0020] In step (c), the catalyst nanoparticles in the catalyst nanoparticle solution refer to any one of transition metal oxides, sulfides, nitrides, carbides, or phosphides, with a size ranging from nanometers to micrometers.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. This invention prepares an interdigitated electrode array, forming an in-situ electrical / electrochemical measurement circuit, and also incorporates in-situ Raman spectroscopy, constructing a three-dimensional integrated electrochemical environment encompassing conductivity, structure, and catalytic activity. Therefore, it can simultaneously acquire in-situ conductivity signals, electrocatalytic signals, and Raman signals of the electrocatalyst. Under actual electrocatalytic conditions, it can study the intrinsic conductivity of particulate catalysts and the interconnection conductivity mechanism between particles while monitoring the catalyst's conductivity, reaction current, and dynamic structural evolution. This allows for a comprehensive understanding of the relationship between the catalyst's conductivity mechanism and reaction mechanism, overcoming the shortcomings of traditional two-terminal electrode measurements and electrochemical impedance spectroscopy measurements.

[0023] 2. In this invention, the electrocatalytic voltage is dynamically applied by a voltage amplifier, which allows for the study of the time response characteristics of the catalyst performance and provides important information for understanding interparticle interface transport.

[0024] 3. This invention uses electron beam lithography to fabricate micro-nano devices, thus enabling the creation of miniaturized and integrated measurement platforms.

[0025] 4. The method of this invention requires less sample and is convenient to test. It can be widely used to study the conductivity mechanism and reaction mechanism of different types of electrocatalysts (metal oxides, sulfides, phosphides, etc.) and provides new ideas for catalyst screening. Attached Figure Description

[0026] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0027] Figure 1 This is a schematic diagram of the present invention.

[0028] Figure 2 This is a flowchart illustrating the fabrication process of the Co3O4 (left) and MoS2 (right) particle devices in the microelectrochemical cell of this invention.

[0029] Figure 3 The image shows a microelectrochemical cell of the present invention, displaying a microelectrochemical cell (left) and a device (right) located at the center of the cell. Individual Co3O4 or MoS2 particles are dispersed on an interdigitated electrode array, forming channels between the particles for measurement.

[0030] Figure 4 The images show the polarization curves and in-situ conductivity curves of the Co3O4(a) and MoS2(b) catalysts of the present invention under different electrocatalytic voltages, as well as the in-situ Raman spectra of the Co3O4(c) and MoS2(d) catalysts under different electrocatalytic voltages. Detailed Implementation

[0031] like Figure 1 As shown, an in-situ characterization method for the conductivity-structure-catalytic activity of an electrocatalyst includes the following steps:

[0032] (1) Preparation of micro-electrochemical cells, such as Figure 2 As shown:

[0033] (a) 32 electrodes (i.e. gold electrodes) are fabricated on a printed circuit board using electron beam lithography; the printed circuit board refers to a SiO2 / Si, quartz or sapphire substrate.

[0034] (b) Two adjacent electrodes are randomly selected to form an interdigitated electrode array pattern on a printed circuit board using electron beam lithography, and then an interdigitated electrode array is formed by thermal evaporation.

[0035] (c) A series of polymethyl methacrylate windows were fabricated in the interdigitated electrode array region by electron beam lithography, and then a catalyst nanoparticle solution with a concentration of 5 mg / ml was dropped onto the printed circuit board and allowed to air dry.

[0036] The catalyst nanoparticles in the catalyst nanoparticle solution refer to any one of transition metal oxides, sulfides, nitrides, carbides, or phosphides, with a size ranging from nanometers to micrometers. Other substances with catalytic activity for electrocatalytic reactions can also be used.

[0037] (d) The polymethyl methacrylate film was removed with acetone, allowing the catalyst nanoparticles to be precisely deposited on the windows of the interdigitated electrode array region, forming a micro / nano device chip assembled from the particles.

[0038] (e) A 1-2 μm thick polymethyl methacrylate film is used to cover the micro / nano device chip as an inert protective layer. Then, the region of interest is patterned on the polymethyl methacrylate by electron beam lithography to expose the surface of the catalyst particles as an electrochemical reaction window and a Raman spectroscopy acquisition window. The window size is 10-500 μm.

[0039] (2) Open the reaction window, use a carbon rod as the counter electrode, an interdigitated electrode array as the working electrode, and use silver / silver chloride or mercury / mercury oxide as the reference electrode. The three-electrode system consisting of the counter electrode, working electrode and reference electrode forms an in-situ electrical / electrochemical measurement circuit, thus constructing a micro-electrochemical environment.

[0040] (3) In-situ electrical and electrochemical measurements:

[0041] Electrodes are led out by bonding wires to the printed circuit board and connected to the source meter. An electrocatalytic voltage of 0.5~2.0 V is applied to the electrodes through the source meter, and the measurement accuracy can reach 1 pA. At the same time, a small bias voltage of 0~100mV is applied to the micro-nano device between the interdigital electrode arrays, and the electrocatalytic signal and in-situ conductivity signal of the micro-nano device are collected respectively, realizing in-situ simultaneous electrical and electrochemical measurement.

[0042] Electrocatalytic voltage refers to the voltage at which an electrocatalytic reaction occurs. A small bias voltage is a voltage applied to the interdigitated electrodes that is much smaller than the electrocatalytic voltage, typically 0, 2, 5, 10, 20, or 50 mV.

[0043] (4) In-situ Raman spectroscopy characterization:

[0044] In-situ Raman signals were acquired during the electrocatalytic reaction by Raman spectroscopy to obtain in-situ structural information of the catalyst.

[0045] (5) Apply periodic catalytic voltages and test the dynamic response characteristics of the catalyst's electrocatalytic signal and in-situ conductivity signal.

[0046] In order to obtain a relatively strong Raman signal, the present invention places the micro-nano device in a polydimethylsiloxane mold and uses calcium fluoride as a transparent cover to better focus the Raman laser.

[0047] This invention uses a voltage amplifier to set the current, which can improve the accuracy of the time response to approximately 20 milliseconds.

[0048] This invention enables time-response measurement of electrocatalytic signals and in-situ conductivity signals by applying a periodic voltage with a controllable duty cycle to the counter electrode, thereby obtaining instantaneous information on charge transport and reaction activity at the start and end of the reaction.

[0049] Using the method of the present invention, the following can be collected: (i) in-situ conductivity signals; (ii) electrocatalytic signals, revealing the charge transport behavior between adjacent catalysts and the reactivity during the reaction process; (iii) in-situ Raman signals, showing the dynamic structural changes of the catalyst during electrocatalysis; and (iv) the time response of in-situ conductivity and electrocatalytic activity.

[0050] The electrolyte can be any conventional electrolyte in the field, as long as it does not react with the catalyst.

[0051] In the following cases, the electrocatalytic voltage ranges from 0.93 V to 1.63 V (compared to the reversible hydrogen electrode) for the oxygen evolution reaction of the Co3O4 catalyst; and from 0.29 V to -0.431 V (compared to the reversible hydrogen electrode) for the hydrogen evolution reaction of the MoS2 catalyst.

[0052] Example 1: In-situ electrical / electrochemical / Raman characterization of Co3O4 catalyst

[0053] (1) Preparation of Co3O4 catalyst particles: 0.08 g of cobalt nitrate was dissolved in a mixture of 30 ml isopropanol and 6 ml glycerol by solvothermal method and reacted at 180 °C for 6 hours. The resulting product was calcined at 350 °C for 2 hours to obtain Co3O4 nanoparticles with an average diameter of 300~400 nm.

[0054] (2) Assembling Co3O4 catalyst micro / nano devices: Refer to Figure 2 The process described involves fabricating an interdigitated electrode array (Ti / Au 5 / 70 nm) on a printed circuit board. Then, a polymethyl methacrylate (PMMA) window is opened using electron beam lithography. A 5 mg / ml solution of Co3O4 nanoparticles is dropped in, and finally, a PMMA film is applied again. The reaction window is then opened again using electron beam lithography to obtain a micro / nano device deposited with Co3O4 particles. The particle-covered area serves as the reaction window, as shown in the diagram. Figure 3 As shown.

[0055] (3) In-situ electrical / electrochemical / Raman testing: The Co3O4 device was placed in a 1.0 M KOH electrolyte in a micro electrochemical cell. An electrocatalytic voltage of 0.93 to 1.63 V (compared to the reversible hydrogen electrode) was applied to the counter electrode, while a small bias voltage of 0 to 50 mV was applied to the interdigitated electrode array. The polarization curve and conductivity signal of the catalyst were collected, and the in-situ Raman spectral signals at different voltages were collected simultaneously.

[0056] (4) Data Analysis: From Figure 4 As can be seen, the Co3O4 catalyst exhibits significant conductive switching characteristics at the oxygen evolution reaction potential, with the in-situ conductivity current increasing by approximately four orders of magnitude compared to before the reaction. This is evident from Raman data (e.g., Figure 4 As shown in c), Co3O4 undergoes amorphization during the oxygen evolution reaction, but still maintains a high conductivity state, indicating that this conductivity behavior originates from the self-gating effect on the catalyst surface, rather than bulk conductivity.

[0057] Example 2 In-situ electrical / electrochemical / Raman characterization of MoS2 catalyst

[0058] (1) Preparation of MoS2 catalyst particles: Commercial MoS2 particles were filtered and classified to obtain MoS2 particles of 0.5~2 μm.

[0059] (2) Assembling MoS2 catalyst micro / nano devices: The fabrication process is similar to that of Co3O4 devices. An interdigitated electrode array (Ti / Au / Ti 5 / 50 / 20 nm) is fabricated on a printed circuit board. Then, a polymethyl methacrylate (PMMA) window is opened using electron beam lithography, and a 5 mg / ml MoS2 nanoparticle solution is dropped in. Finally, a PMMA film is applied again, and the reaction window is opened using electron beam lithography to obtain micro / nano devices deposited with MoS2 particles. The particle-covered area serves as the reaction window, such as... Figure 3 As shown.

[0060] (3) In-situ electrical / electrochemical / Raman testing: The MoS2 device was placed in a 0.5 M H2SO4 electrolyte, and an electrocatalytic voltage of 0.29 to -0.431 V (compared to the reversible hydrogen electrode) and a small bias voltage of 0-50 mV were applied to collect the electrocatalytic current, in-situ conductivity current signal and Raman spectrum signal.

[0061] (4) Data Analysis: The MoS2 catalyst also exhibits obvious conductive switching characteristics at the hydrogen evolution reaction potential, such as... Figure 4 As shown in b, the in-situ conductivity current increases by approximately three orders of magnitude. However, its Raman spectrum shows no significant change during the hydrogen evolution reaction, as... Figure 4 As shown in d, the improved conductivity of the MoS2 catalyst mainly stems from the surface self-gating effect rather than changes in the bulk structure.

Claims

1. An in-situ characterization method for the conductivity-structure-catalytic activity of an electrocatalyst, comprising the following steps: (1) Preparation of micro-electrochemical cells: (a) 32 electrodes were fabricated on a printed circuit board using electron beam lithography. (b) Arbitrarily select two adjacent electrodes to create an interdigitated electrode array pattern on a printed circuit board using electron beam lithography, and then form an interdigitated electrode array through thermal evaporation. (c) A series of polymethyl methacrylate windows were fabricated in the interdigitated electrode array region by electron beam lithography, and then a catalyst nanoparticle solution with a concentration of 5 mg / ml was dropped onto the printed circuit board and allowed to air dry naturally. (d) The polymethyl methacrylate film was removed with acetone, allowing the catalyst nanoparticles to be precisely deposited on the windows of the interdigitated electrode array region, forming a micro / nano device chip assembled from the particles. (e) A 1-2 μm thick polymethyl methacrylate film is used to cover the micro / nano device chip as an inert protective layer. Then, the region of interest is patterned on the polymethyl methacrylate by electron beam lithography to expose the surface of the catalyst particles as an electrochemical reaction window and a Raman spectroscopy acquisition window. The window size is 10-500 μm. (2) Open the reaction window, use a carbon rod as the counter electrode, an interdigitated electrode array as the working electrode, and use silver / silver chloride or mercury / mercury oxide as the reference electrode. The three-electrode system consisting of the counter electrode, working electrode and reference electrode forms an in-situ electrical / electrochemical measurement circuit to construct a micro-electrochemical environment. (3) In-situ electrical and electrochemical measurements: Electrodes are led out by bonding wires to the printed circuit board and connected to the source meter. An electrocatalytic voltage of 0.5~2.0 V is applied to the electrodes through the source meter. At the same time, a small bias voltage of 0~100 mV is applied to the micro-nano device between the interdigital electrode array. The electrocatalytic signal and in-situ conductivity signal of the micro-nano device are collected respectively, realizing in-situ simultaneous electrical and electrochemical measurement. (4) In-situ Raman spectroscopy characterization: In-situ Raman signals were acquired through Raman spectroscopy at the reaction window during the electrocatalytic reaction to obtain in-situ structural information of the catalyst. (5) Apply periodic catalytic voltages and test the dynamic response characteristics of the catalyst's electrocatalytic signal and in-situ conductivity signal.

2. The in-situ characterization method for the conductivity-structure-catalytic activity of an electrocatalyst as described in claim 1, characterized in that: In step (a), the printed circuit board refers to a SiO2 / Si, quartz, or sapphire substrate.

3. The in-situ characterization method for the conductivity-structure-catalytic activity of an electrocatalyst as described in claim 1, characterized in that: In step (b), the interdigitated electrode array consists of finger-shaped or comb-shaped electrodes with periodic patterns in their in-plane shape.

4. The in-situ characterization method for the conductivity-structure-catalytic activity of an electrocatalyst as described in claim 1, characterized in that: In step (c), the catalyst nanoparticles in the catalyst nanoparticle solution refer to any one of transition metal oxides, sulfides, nitrides, carbides, or phosphides, with a size ranging from nanometers to micrometers.

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