Microfluidic device for in-situ measurement of diffusion coefficient of carbon dioxide in electrochemical reduction reaction system and method and application thereof
By designing a T-shaped microfluidic device and a one-dimensional electrochemical diffusion model, the error in measuring the carbon dioxide diffusion coefficient under in-situ electrochemical reaction conditions was solved by traditional methods, and accurate measurement under in-situ electrochemical reaction conditions was achieved.
Patent Information
- Application Number
- CN202511167592.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-20
- Publication Date
- 2025-10-31
AI Technical Summary
Traditional devices struggle to accurately measure the carbon dioxide diffusion coefficient under in-situ electrochemical reaction conditions, especially in the carbon dioxide diffusion process under the influence of the potential difference between the cathode and anode.
A T-shaped microfluidic device was designed, including a gas supply and vacuum pumping component, a liquid supply and drainage component, and a data acquisition component. Combined with a Raman spectrometer, the ion distribution and potential distribution under in-situ electrochemical reaction conditions were simulated using the Nernst-Planck equation and the finite element method to obtain the carbon dioxide diffusion coefficient.
The carbon dioxide diffusion coefficient was accurately measured under in-situ electrochemical reaction conditions. The results were consistent with classical diffusion theory, which solved the measurement error of traditional methods and improved the measurement accuracy.
Smart Images
Figure CN120869890A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of chemical energy technology, specifically relating to a microfluidic device, method and application for in-situ measurement of the carbon dioxide diffusion coefficient in an electrochemical reduction reaction system. Background Technology
[0002] Carbon dioxide electrolysis driven by renewable energy power can reduce carbon dioxide emissions, synthesize renewable fuels, realize the high-value utilization of carbon dioxide, and store fluctuating renewable energy as chemical energy.
[0003] A typical carbon dioxide electrolyzer usually consists of two chambers: an anode and a cathode. Driven by voltage, carbon dioxide in the cathode chamber undergoes a series of processes, including dissolution in the electrolyte, diffusion to the electrode surface, adsorption and activation on the electrode surface, ultimately completing the carbon dioxide reduction reaction. In these complex physical and chemical processes, the diffusion coefficient of carbon dioxide in the electrolyte is one of the key physical properties.
[0004] Traditional methods or devices for measuring carbon dioxide diffusion coefficients are not suitable for in-situ measurements of electrochemical reactions. Traditional methods typically employ a chamber with a single-terminal structure, such as a capillary device, where the right end is closed. Carbon dioxide diffuses from the gas-liquid interface to the right, and Raman or fluorescence spectroscopy is used to measure the carbon dioxide concentration at different times at different diffusion distances downstream of the gas-liquid interface. The carbon dioxide diffusion coefficient is then obtained by fitting the experimental data to Fick's second law of diffusion. Therefore, it can be seen that traditional measuring devices are insufficient to construct in-situ electrochemical reaction conditions, i.e., the carbon dioxide diffusion process under the influence of the potential difference between the anode and cathode. Summary of the Invention
[0005] The purpose of this section is to outline some aspects of the embodiments of the present invention and to briefly describe some preferred embodiments.
[0006] The purpose of this invention is to provide a T-type microfluidic experimental device for measuring the carbon dioxide diffusion coefficient under in-situ electrochemical reaction conditions and a one-dimensional electrochemical diffusion model for accurately obtaining the carbon dioxide diffusion coefficient. This solves the problem that traditional devices struggle to accurately measure the carbon dioxide diffusion coefficient under in-situ electrochemical conditions. Before isolating the cation effect, the measured carbon dioxide diffusion coefficients under different in-situ electrochemical reaction conditions contradict conventional understanding: as the current density gradually increases, the measured value of the carbon dioxide diffusion coefficient gradually increases; as the electrolyte concentration increases, the measured diffusion similarity value gradually increases; however, after isolating the cation, the measured values of the carbon dioxide diffusion coefficient at different current densities and concentrations show results consistent with conventional understanding.
[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a microfluidic device for in-situ measurement of the carbon dioxide diffusion coefficient in an electrochemical reduction reaction system, characterized in that: it includes a T-shaped microfluidic component, the T-shaped microfluidic component includes a cover plate and a microchannel substrate that cooperates with the cover plate; the microchannel substrate is provided with an anode and a cathode, and the anode and the cathode are connected by a straight flow channel E provided on the surface of the microchannel substrate.
[0008] The surface of the microchannel substrate is also provided with a first microfluidic channel and a second microfluidic channel. Both the first and second microfluidic channels are parallel to the straight flow channel E. The first microfluidic channel is perpendicular to and connected to the flow channel A on the surface of the microchannel substrate. The second microfluidic channel is perpendicular to and connected to the flow channel C on the surface of the microchannel substrate. Flow channel A and flow channel C are connected by flow channel B. Flow channel B is arranged parallel to flow channel E. Flow channel B and flow channel E are connected by flow channel D, which is perpendicular to it.
[0009] As a preferred embodiment of the microfluidic device for in-situ measurement of carbon dioxide diffusion coefficient in electrochemical reduction reaction system according to the present invention, it further includes a gas supply and vacuum pumping component, a liquid supply and drainage component, and a data acquisition component.
[0010] The gas supply and vacuum assembly includes a first channel, a second channel, and a porous medium gas buffer connected to the first channel and the second channel respectively; a high-pressure gas cylinder is connected to the first channel; and a vacuum pump is connected to the second channel.
[0011] The liquid supply and drainage assembly includes a third channel, and the syringe pump is connected to the third channel; the gas supply and vacuum assembly 100 and the liquid supply and drainage assembly are respectively connected to the T-type microfluidic assembly;
[0012] The data acquisition components include an electrochemical workstation and a Raman spectrometer; the anode and cathode pass through the microchannel substrate and are connected to the electrochemical workstation, and the Raman spectrometer is used to detect the relative concentration change of carbon dioxide in the flow channel E.
[0013] As a preferred embodiment of the microfluidic device for in-situ measurement of carbon dioxide diffusion coefficient in electrochemical reduction reaction system according to the present invention: the first microfluidic channel is connected to the gas supply and vacuum pumping components through its inlet, and the second microfluidic channel is connected to the liquid supply and drainage components through its inlet.
[0014] As a preferred embodiment of the microfluidic device for in-situ measurement of carbon dioxide diffusion coefficient in electrochemical reduction reaction system described in this invention: both the cover plate and the microchannel substrate are made of polymethyl methacrylate material with good light transmittance, and the cover plate and the microchannel substrate are sealed by thermo-press bonding.
[0015] As a preferred embodiment of the microfluidic device for in-situ measurement of carbon dioxide diffusion coefficient in electrochemical reduction reaction system according to the present invention: valve a, electronic pressure gauge for monitoring pressure, and valve b are sequentially provided on the first channel; valve c is provided on the second channel; and valve d is provided on the third channel.
[0016] This invention also provides a method for in-situ measurement of the carbon dioxide diffusion coefficient in an electrochemical reduction reaction system: Using the microfluidic device for in-situ measurement of the carbon dioxide diffusion coefficient in the electrochemical reduction reaction system, electrolyte is first filled into the first microfluidic channel, the second microfluidic channel, channel A, channel B, channel C, channel D, and channel E of a microchannel substrate. Then, carbon dioxide gas is slowly introduced through the first microfluidic channel to expel the electrolyte in channels A, B, and C. Next, the supply pressure from the high-pressure gas cylinder is increased, allowing carbon dioxide to enter channel D. Simultaneously, the electrolyte in channel D is completely introduced into channel E, ultimately forming a T-shaped gas-liquid interface between channels D and E. The anode and cathode are connected to an electrochemical workstation, a constant current is applied, voltage signals are acquired, and Raman spectroscopy is used to detect changes in the relative concentration of carbon dioxide to obtain the carbon dioxide diffusion coefficient.
[0017] As a preferred embodiment of the method for in-situ measurement of the carbon dioxide diffusion coefficient in an electrochemical reduction reaction system as described in this invention: Raman spectrometry is used to detect the Raman spectral signals at the T-shaped gas-liquid interface at the center point of the flow channel E and at locations 2 mm and 3 mm away from the cathode at the T-shaped gas-liquid interface, to obtain the characteristic peak signal intensity I of carbon dioxide. CO2 And the characteristic peak signal intensity of pure water I H2O Under in-situ electrochemical reaction conditions, the diffusion mass transfer process of carbon dioxide in the electrolyte satisfies the Nernst-Planck equation:
[0018]
[0019] In the formula, C i The concentration of substance i under in-situ conditions of electrochemical reaction (i = bicarbonate, carbonate, hydroxide, hydrogen ions and alkali metal cations M) + ), t is the diffusion time, R i The formation rate of substance i is controlled by the homogeneous reaction (Equations 1.3 to 1.5), J i Let i be the flux of substance i.
[0020]
[0021] In the formula, D i Let x be the diffusion coefficient of substance i, x be the distance in the diffusion direction, and z be the diffusion coefficient of substance i. iLet be the charge number of substance i, F be the Faraday constant, R be the ideal gas constant, T be the absolute temperature, and φ be the electric potential. The distance in the diffusion direction is from the gas-liquid interface at the T-junction (x = 0 mm) along the working electrode direction to the positions x = 2 mm and x = 3 mm.
[0022] As a preferred embodiment of the method for in-situ measurement of carbon dioxide diffusion coefficient in an electrochemical reduction reaction system as described in this invention: In order to accurately simulate the ion distribution and potential distribution under in-situ conditions of the electrochemical reaction, an electroneutrality assumption is considered in the diffusion model:
[0023]
[0024] The hydrogen evolution reaction and the oxygen evolution reaction occur at the cathode 301b-2 and the anode 301b-1, respectively.
[0025] A constant blowing carbon dioxide source term was used to simulate the carbon dioxide concentration change at the T-type gas-liquid interface:
[0026]
[0027] In the formula, k l 'a' is the volumetric mass transfer coefficient at the gas-liquid interface, and 'C' is the mass transfer coefficient at CO2,aq C represents the saturated solubility in the electrolyte. CO2 This refers to the concentration of electrolyte solution.
[0028] The Nernst-Planck equations were solved using the finite element method, and then Raman spectroscopy principles and normalization were applied to obtain the simulated value of the diffusion coefficient.
[0029] As a preferred embodiment of the method for in-situ measurement of the carbon dioxide diffusion coefficient in an electrochemical reduction reaction system according to the present invention, the Raman spectroscopy principle and normalization process includes the conversion between the relative concentration of carbon dioxide and the Raman spectral signal intensity:
[0030]
[0031] In the formula, β is a proportionality coefficient that is independent of diffusion time t and diffusion distance x, and I is the Raman peak signal intensity, including characteristic peaks of carbon dioxide and water.
[0032] To improve the accuracy of the diffusion coefficient, relative concentration values are used for calculation, and the ratio of Raman peak intensities at a given diffusion distance and time is normalized to the ratio of Raman peak intensities at the gas-liquid interface:
[0033]
[0034] This allows the measured Raman signal intensity to be interconverted with the carbon dioxide concentration in the one-dimensional electrochemical diffusion model.
[0035] Preferably, in order to isolate the cation effect, 18-crown ether-6 is added to the electrolyte, and then the change of carbon dioxide diffusion coefficient under different current densities and different KHCO3 electrolyte concentrations is studied.
[0036] The beneficial effects of this invention: The microfluidic device for in-situ measurement of the carbon dioxide diffusion coefficient in an electrochemical reduction reaction system under in-situ electrochemical reaction conditions includes a gas supply and vacuum pumping assembly, a liquid supply and drainage assembly, a T-type microfluidic assembly, and a data acquisition assembly. This invention addresses the problem that traditional diffusion coefficient measurement devices are difficult to use for measuring the carbon dioxide diffusion coefficient under in-situ electrochemical reaction conditions. It designs a microfluidic device suitable for measuring the diffusion coefficient under applied current and potential conditions, and provides a one-dimensional electrochemical diffusion model for accurately obtaining diffusion coefficient results. When the KHCO3 electrolyte does not contain 18-crown ether-6, the measured carbon dioxide diffusion coefficient gradually increases with increasing current density before and after current application. Simultaneously, under constant current, the carbon dioxide diffusion coefficient in KHCO3 electrolytes of different concentrations increases with increasing concentration. The trends of the carbon dioxide diffusion coefficient measured under these two electrochemical conditions are inconsistent with classical diffusion theory. After adding 18-crown ether-6 to the KHCO3 electrolyte, the measured carbon dioxide diffusion coefficient remains constant at 1.42 × 10⁻⁶ under different current densities. -9 m 2 / s; meanwhile, as the electrolyte concentration decreased from 0.1M to 0.01M, the measured value of the carbon dioxide diffusion coefficient increased from 1.42 × 10⁻⁶. -9 m 2 / s increased to 1.51×10 -9 m 2 / s, the trend of the carbon dioxide diffusion coefficient measurement results after the addition of crown ether is consistent with the classical diffusion theory, indicating that the carbon dioxide diffusion coefficient measurement value obtained after adding 18-crown ether-6 is correct. Attached Figure Description
[0037] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below, wherein:
[0038] Figure 1 This is a schematic diagram of the microfluidic device for in-situ measurement of the carbon dioxide diffusion coefficient in an electrochemical reduction reaction system under in-situ conditions, as per the present invention.
[0039] Figure 2 This is a schematic diagram of the microfluidic device for in-situ measurement of the carbon dioxide diffusion coefficient in an electrochemical reduction reaction system under in-situ conditions according to the present invention.
[0040] Figure 3This is a schematic diagram of the process for constructing a T-shaped gas-liquid interface on a microchannel substrate according to the present invention.
[0041] Figure 4 This is a schematic diagram of diffusion measurement of the microchannel substrate of the present invention.
[0042] Figure 5 The image shows the Raman spectroscopy results of the microfluidic device for in-situ measurement of the carbon dioxide diffusion coefficient in an electrochemical reduction reaction system under in-situ conditions in 0.1 M KHCO3 at different times.
[0043] Figure 6 The graph shows the potential change over time of the microfluidic device for in-situ measurement of the carbon dioxide diffusion coefficient in an electrochemical reduction reaction system under in-situ conditions, as a constant current is applied in 0.1 M KHCO3.
[0044] Figure 7 This is a typical result graph showing the fitting of experimental data and simulated data with time obtained by the microfluidic device for in-situ measurement of carbon dioxide diffusion coefficient in electrochemical reduction reaction system under in-situ conditions of the present invention in 0.1M KHCO3.
[0045] Figure 8 This figure shows the verification results of the microfluidic device for in-situ measurement of carbon dioxide diffusion coefficient in an electrochemical reduction reaction system under in-situ conditions, comparing the diffusion coefficient measured in pure water with the measured value in the literature.
[0046] Figure 9 The graph shows the diffusion coefficient results obtained by the microfluidic device of the present invention, which measures the diffusion coefficient of carbon dioxide in an electrochemical reduction reaction system under in-situ conditions, in 0.1M KHCO3 at different current densities.
[0047] Figure 10 The graph shows the diffusion coefficient results obtained by the microfluidic device of the present invention, which measures the diffusion coefficient of carbon dioxide in an electrochemical reduction reaction system under in-situ conditions, in different concentrations of KHCO3.
[0048] Figure 11 The microfluidic device for in-situ measurement of carbon dioxide diffusion coefficient in electrochemical reduction reaction system under in-situ conditions of electrochemical reaction of the present invention was prepared by adding 18-crown ether-6 to 0.1M KHCO3 electrolyte and obtaining carbon dioxide diffusion coefficient results at different current densities after isolating the cation effect.
[0049] Figure 12The microfluidic device for in-situ measurement of carbon dioxide diffusion coefficient in electrochemical reduction reaction system under in-situ conditions of electrochemical reaction is shown in the figure. 18-crown ether-6 was added to KHCO3 electrolyte of different concentrations to isolate the cation effect and obtain the carbon dioxide diffusion coefficient results. Detailed Implementation
[0050] To make the above-mentioned objectives, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to specific examples.
[0051] Example 1:
[0052] This embodiment provides a T-type microfluidic device for measuring the carbon dioxide diffusion coefficient under in-situ electrochemical reaction conditions, such as... Figure 1 and Figure 2 As shown, it specifically includes a gas supply and vacuum pumping assembly 100, a liquid supply and drainage assembly 200, a T-shaped microfluidic assembly 300, and a data acquisition assembly 400;
[0053] The gas supply and vacuum assembly 100 includes a first channel 101, a second channel 102, and a porous medium gas buffer 103 that is connected to the first channel 101 and the second channel 102 respectively. A high-pressure gas cylinder 101a is connected to the first channel 101 and is used to supply carbon dioxide to the microfluidic device. The first channel 101 is also provided with a valve a, an electronic pressure gauge (101b) for monitoring pressure, and a valve b in sequence. The vacuum pump 102a is connected to the second channel 102 and is used to evacuate the microfluidic device. The second channel 102 is provided with a valve c. The first channel 101 and the second channel 102 converge at the porous medium gas buffer 103 at the end.
[0054] The liquid supply and drainage assembly 200 includes a third channel 201, an injection pump 201a connected to the third channel 201, and a valve d is also provided on the third channel 201; the gas supply and vacuum assembly 100 and the liquid supply and drainage assembly 200 are respectively connected to the T-type microfluidic assembly 300.
[0055] The T-shaped microfluidic assembly 300 includes a cover plate 301a and a microchannel substrate 301b that mates with the cover plate 301a. The microchannel substrate 301b has an anode 301b-1 and a cathode 301b-2, which are connected by a linear flow channel E on the surface of the microchannel substrate 301b. The surface of the microchannel substrate 301b also has a first microfluidic channel 301b-3 and a second microfluidic channel 301b-4. The first microfluidic channel 301b-3 is connected to the gas supply and vacuum assembly 100 through its inlet. The control channel 301b-4 is connected to the liquid supply and drainage assembly 200 through its inlet. The first microfluidic channel 301b-3 and the second microfluidic channel 301b-4 are both parallel to the straight flow channel E. The first microfluidic channel 301b-3 is perpendicular to and connected to the flow channel A on the surface of the microchannel substrate 301b. The second microfluidic channel 301b-4 is perpendicular to and connected to the flow channel C on the surface of the microchannel substrate 301b. Flow channel A and flow channel C are connected through flow channel B. Flow channel B is parallel to flow channel E. Flow channel B and flow channel E are connected through flow channel D, which is perpendicular to it. Preferably, in this invention, both the cover plate 301a and the microchannel substrate 301b are made of polymethyl methacrylate (PMMA) material with good light transmittance, and the cover plate 301a and the microchannel substrate 301b are sealed by thermo-press bonding; more preferably, the sealing strength between the cover plate 301a and the microchannel substrate 301b can be improved by setting bolts around each channel and flow channel.
[0056] The data acquisition component 400 includes an electrochemical workstation 401 and a Raman spectrometer 402. The anode 301b-1 and the cathode 301b-2 pass through the microchannel substrate 301b and are connected to the electrochemical workstation 401. The Raman spectrometer 402 is used to detect the change in the relative concentration of carbon dioxide in the flow channel E.
[0057] In this invention, valves a and b are used to control the supply or discharge of carbon dioxide in the first microfluidic channel 301b-3, and valve d is used to control the supply or discharge of electrolyte in the second microfluidic channel 301b-4.
[0058] This invention obtains the carbon dioxide diffusion coefficient by detecting the relative concentration change of carbon dioxide using Raman spectroscopy. Specifically, valves a and b are opened, and valves c and d are closed. The high-pressure gas cylinder 101a in the gas supply and vacuum assembly 100 continuously supplies carbon dioxide gas at a certain pressure to the device. The value of the electronic pressure gauge 101b is observed to perform an airtightness test. Then, valve a is closed, and valves c and d are opened. A vacuum pump 102a is used to evacuate the entire device to eliminate the influence of impurities in the pipeline and electrolyte on the measurement. Then, valve c is closed, and an injection pump 201a is used to inject electrolyte through the second microfluidic channel 301b-4. The electrolyte is observed through the cover plate 301a to ensure that the electrolyte fills the entire microchannel substrate 301b, including the first microfluidic channel 301b-3, the second microfluidic channel 301b-4, and channels A, B, C, D, and E. Figure 3 As shown in (a).
[0059] Then, valve a is slowly opened, and carbon dioxide gas is supplied at a low flow rate through the first microfluidic channel 301b-3 to remove the electrolyte present in channels A, B, and C of the microchannel substrate 301b. Figure 3 (b) and Figure 3 (c)
[0060] Close valve d, set the supply pressure of high-pressure gas cylinder 101a to the target gas pressure, and allow carbon dioxide gas in channel B to flow into channel D. Simultaneously, the electrolyte in channel D completely flows into channel E, ultimately forming a T-shaped gas-liquid interface between channels D and E. Figure 3 (d)
[0061] The electrochemical workstation 401 of the data acquisition component 400 is connected to the anode 301b-1 and cathode 301b-2 of the T-shaped microfluidic component 300 where gas diffusion occurs. A constant current is applied, and voltage signals are acquired. In the data acquisition component 400, a Raman spectroscopy focusing microscope is used perpendicular to the T-shaped flow channel component 300 to observe the specific location of the gas-liquid interface in the T-shaped region. The Raman shift platform is used to alternately measure the Raman spectral signals at the gas-liquid interface (0 mm) along the cathode 301b-2 at distances of 2 mm and 3 mm from the gas-liquid interface (where 0 mm refers to the center point of the flow channel E). Figure 4 During measurement, the laser parameters are adjusted to the optimal signal position to obtain the best spectral peak effect. The spectrum acquisition range is 1100-4000 cm⁻¹. -1 The individual spectra were taken over approximately 30 seconds and superimposed twice. The characteristic peak signal intensities of dissolved carbon dioxide and pure water were obtained using Labspec software. The characteristic peak of carbon dioxide was at 1381 cm⁻¹. -1 Nearby, the characteristic peak of pure water is at 3405 cm⁻¹. -1 nearby.
[0062] The intensity I of the carbon dioxide characteristic peak at the three locations (0 mm, 2 mm, and 3 mm) was obtained using Labspec software. CO2 And the characteristic peak signal intensity of pure water I H2O The ratio result is r = I. CO2 / I H2O The ratio results at 2mm and 3mm are normalized with the gas-liquid interface ratio results to obtain the experimental results of the carbon dioxide concentration at 2mm and 3mm changing with time.
[0063] In the microchannel substrate 301b, the ratio of the hydraulic diameter to the length of the microchannels is small, allowing the diffusion of carbon dioxide in the electrolyte of channel E to be approximated as one-dimensional diffusion. Under in-situ electrochemical reaction conditions, the diffusion mass transfer process satisfies the Nernst-Planck equation:
[0064]
[0065] In the formula, C i The concentration of substance i under in-situ conditions of electrochemical reaction (i = bicarbonate, carbonate, hydroxide, hydrogen ions and alkali metal cations M) + ), t is the diffusion time, R i The formation rate of substance i is controlled by the homogeneous reaction (Equations 1.3 to 1.5), J i Let i be the flux of substance i.
[0066]
[0067] In the formula, D i Let x be the diffusion coefficient of substance i, x be the distance in the diffusion direction, and z be the diffusion coefficient of substance i. i Let be the charge number of substance i, F be the Faraday constant, R be the ideal gas constant, T be the absolute temperature, and φ be the electric potential. The distance in the diffusion direction is from the gas-liquid interface at the T-junction (x = 0 mm) along the working electrode direction to the positions x = 2 mm and x = 3 mm.
[0068]
[0069] To accurately simulate the ion and potential distribution under in-situ conditions of electrochemical reactions, the electroneutrality assumption was considered in the diffusion model:
[0070]
[0071] The hydrogen evolution reaction and oxygen evolution reaction are considered to occur at the working electrode (cathode 301b-2) and the counter electrode (anode 301b-1), respectively. In the model, the current density at the cathode and anode is equal to the current applied by the electrochemical workstation 401 to the T-type microfluidic component 300.
[0072] 2H2O+2e - →H2+2OH - (1.7)
[0073] 2H₂O→O₂+4H + +4e - (1.8)
[0074] A constant blowing carbon dioxide source term is used to simulate the carbon dioxide concentration change at the T-type gas-liquid interface. This term is incorporated as an additional generation term into the right-hand side R of equation (1.1). i As shown below:
[0075]
[0076] In the formula, k l 'a' is the volumetric mass transfer coefficient at the gas-liquid interface, and 'C' is the mass transfer coefficient at CO2,aq C represents the saturated solubility in the electrolyte. CO2 This represents the concentration dissolved in the electrolyte.
[0077] The Nernst-Planck equations were solved using the finite element method, and then Raman spectroscopy principles and normalization were applied to obtain a series of simulated values for the diffusion coefficient.
[0078] Initial conditions for the finite element method: (1) Before the carbon dioxide supply begins, the carbon dioxide concentration is 0 at all locations except the carbon dioxide source term region; (2) The concentrations of bicarbonate, carbonate, hydroxide, hydrogen ions, and M are calculated using electrolyte concentration and pH value. + The initial concentration. Boundary conditions: (1) The microchannels at both ends are in a zero-flux state because substance i cannot exceed the end position; (2) The anode potential is equal to 0 and the cathode potential is equal to the final potential value in the chronopotential test.
[0079] Interconversion between relative carbon dioxide concentration and Raman spectral signal intensity:
[0080] According to the principles of Raman spectroscopy, the concentration of carbon dioxide is directly proportional to the intensity of the carbon dioxide signal peak and the intensity of the water signal peak:
[0081]
[0082] In the formula, β is a proportionality coefficient that is independent of the diffusion time t and the diffusion distance x, and I is the Raman peak signal intensity, including the characteristic peaks of carbon dioxide and water.
[0083] To improve the accuracy of obtaining the diffusion coefficient, this invention uses relative concentration values for calculation. Therefore, the ratio of Raman peak intensities at a given diffusion distance and time is normalized to the ratio of Raman peak intensities at the gas-liquid interface (x = 0):
[0084]
[0085] According to equations (1.10) and (1.11), the Raman signal intensity measured in the experiment can be converted into the carbon dioxide concentration in the one-dimensional electrochemical diffusion model, and vice versa.
[0086] By comparing the simulated values corresponding to a series of diffusion coefficient values with the experimental values r(x,t), the diffusion coefficient value corresponding to the minimum standard deviation between the simulated and experimental values is the carbon dioxide diffusion coefficient obtained from the experiment.
[0087] like Figure 9-10 The figures represent the carbon dioxide diffusion coefficients obtained by this invention under different current densities and in KHCO3 electrolytes of different concentrations. The current densities are 0 mA / cm². 2 -3.85×10 -4 mA / cm and -3.85×10 -2 mA / cm 2 At that time, the diffusion coefficient increased from 1.49 × 10⁻⁶. -9 m 2 / s gradually increased to 1.59×10 -9 m 2 / s and 1.74×10 -9 m 2 / s; current density is -3.85×10 -2 mA / cm 2 When the electrolyte concentrations are 0.01M, 0.05M, and 0.1M, the diffusion coefficient increases from 1.63 × 10⁻⁶. -9 m 2 / s gradually increased to 1.67×10 -9 m 2 / s and 1.74×10 -9 m 2 / s. The influence of these two factors on the measured value of carbon dioxide diffusion coefficient is inconsistent with classical diffusion theory.
[0088] like Figure 11-12 This figure shows the carbon dioxide diffusion coefficients obtained at different current densities and in KHCO3 electrolytes of different concentrations after adding 18-crown ether-6 to the electrolyte to isolate the cation effect, according to the present invention. The current densities are 0 mA / cm². 2 With -3.85×10 -2 mA / cm 2 At that time, the carbon dioxide diffusion coefficient did not increase and remained at 1.42 × 10⁻⁶. -9 m 2 Approximately / s; current density is -3.85×10 -2mA / cm 2 When the electrolyte concentration decreased from 0.1M to 0.01M, the carbon dioxide diffusion coefficient decreased from 1.42 × 10⁻⁶. -9 m 2 / s increased to 1.51×10 -9 m 2 / s. After isolating the cation effect, the measured carbon dioxide diffusion coefficient shows a trend consistent with classical diffusion theory.
[0089] Example 2:
[0090] In this invention, the T-shaped microfluidic component 300 is not connected to the electrochemical workstation 401 in the data acquisition component 400, and pure water is used as the working fluid to verify the reliability of the device in measuring the carbon dioxide diffusion coefficient.
[0091] The T-type gas-liquid interface was constructed using the same method as in Example 1. In determining the diffusion coefficient model, electromigration, homogeneous reactions, and redox reactions were not considered; only the effect of concentration changes over time was taken into account. The governing equation was simplified to:
[0092]
[0093] The solution is obtained using the finite element method. The initial conditions are: (1) Before the carbon dioxide is supplied, the carbon dioxide concentration is 0 in all locations except the carbon dioxide source region. The boundary conditions are: (1) Both ends of the microchannel are in a zero-flux state because the carbon dioxide cannot exceed the end position.
[0094] By comparing the simulated values corresponding to a series of diffusion coefficient values with the experimental values r(x,t), the diffusion coefficient value corresponding to the minimum standard deviation between the simulated and experimental values is the carbon dioxide diffusion coefficient obtained from the experiment.
[0095] like Figure 8 The diffusion coefficient of carbon dioxide in pure water, measured at 5.0 bar and 22°C, is 1.61 × 10⁻⁶. - 9 m 2 The diffusion coefficient of / s is close to that in literature under similar operating conditions (5.0 bar, 26℃), indicating that the device has good reliability in measuring the diffusion coefficient.
[0096] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.
Claims
1. A microfluidic device for in-situ measurement of the carbon dioxide diffusion coefficient in an electrochemical reduction reaction system, characterized in that: The T-type microfluidic assembly (300) includes a cover plate (301a) and a microchannel substrate (301b) that cooperates with the cover plate (301a). The microchannel substrate (301b) is provided with an anode (301b-1) and a cathode (301b-2), and the anode (301b-1) and the cathode (301b-2) are connected by a straight flow channel (E) provided on the surface of the microchannel substrate (301b). The surface of the microchannel substrate (301b) is also provided with a first microfluidic channel (301b-3) and a second microfluidic channel (301b-4). Both the first microfluidic channel (301b-3) and the second microfluidic channel (301b-4) are parallel to the straight flow channel (E). The first microfluidic channel (301b-3) is perpendicular to and connected to the flow channel (A) on the surface of the microchannel substrate (301b). The second microfluidic channel (301b-4) is perpendicular to and connected to the flow channel (C) on the surface of the microchannel substrate (301b). The flow channel (A) and the flow channel (C) are connected through the flow channel (B). The flow channel (B) is parallel to the flow channel (E). The flow channel (B) and the flow channel (E) are connected through the flow channel (D) which is perpendicular to it.
2. The microfluidic device for in-situ measurement of the carbon dioxide diffusion coefficient in an electrochemical reduction reaction system according to claim 1, characterized in that: It also includes a gas supply and vacuum pumping assembly (100), a liquid supply and drainage assembly (200), and a data acquisition assembly (400); The gas supply and vacuum assembly (100) includes a first channel (101), a second channel (102), and a porous medium gas buffer (103) that is connected to the first channel (101) and the second channel (102) respectively; and a high-pressure gas cylinder (101a) is connected to the first channel (101); and a vacuum pump (102a) is connected to the second channel (102). The liquid supply and drainage assembly (200) includes a third channel (201), and the syringe pump (201a) is connected to the third channel (201); the gas supply and vacuum assembly (100) and the liquid supply and drainage assembly (200) are respectively connected to the T-type microfluidic assembly (300); The data acquisition component (400) includes an electrochemical workstation (401) and a Raman spectrometer (402); the anode (301b-1) and the cathode (301b-2) pass through the microchannel substrate (301b) and are connected to the electrochemical workstation (401), respectively, and the Raman spectrometer (402) is used to detect the carbon dioxide diffusion coefficient in the flow channel (E).
3. The microfluidic device for in-situ measurement of the carbon dioxide diffusion coefficient in an electrochemical reduction reaction system according to claim 2, characterized in that: The first microfluidic channel (301b-3) is connected to the gas supply and vacuum assembly (100) through its inlet, and the second microfluidic channel (301b-4) is connected to the liquid supply and drainage assembly (200) through its inlet.
4. The microfluidic device for in-situ measurement of the carbon dioxide diffusion coefficient in an electrochemical reduction reaction system according to any one of claims 1 to 3, characterized in that: Both the cover plate (301a) and the microchannel substrate (301b) are made of polymethyl methacrylate material with good light transmittance. The cover plate (301a) and the microchannel substrate (301b) are sealed by thermo-press bonding.
5. The microfluidic device for in-situ measurement of the carbon dioxide diffusion coefficient in an electrochemical reduction reaction system according to claim 3, characterized in that: The first channel (101) is equipped with a valve (a), an electronic pressure gauge (101b) for monitoring pressure, and a valve (b) in sequence; the second channel (102) is equipped with a valve (c); and the third channel (201) is equipped with a valve (d).
6. A method for in-situ measurement of the carbon dioxide diffusion coefficient in an electrochemical reduction reaction system, characterized in that: Using the microfluidic device for in-situ measurement of the carbon dioxide diffusion coefficient in an electrochemical reduction reaction system as described in claim 1, electrolyte is first filled into the first microfluidic channel (301b-3), the second microfluidic channel (301b-4), flow channel (A), flow channel (B), flow channel (C), flow channel (D), and flow channel (E) of the microchannel substrate (301b). Then, carbon dioxide gas is slowly introduced through the first microfluidic channel (301b-3) to remove the electrolyte from flow channels (A), (B), and (C). Electrolyte is applied, and then the supply pressure of the high-pressure gas cylinder (101a) is increased to allow carbon dioxide to enter the flow channel (D). At the same time, the electrolyte in the flow channel (D) is completely introduced into the flow channel (E), and finally a T-shaped gas-liquid interface is formed in the flow channels (D) and (E). The anode (301b-1) and cathode (301b-2) are connected to the electrochemical workstation (401) respectively, a constant current is applied, the voltage signal is collected, and the change in the relative concentration of carbon dioxide is detected by the Raman spectrometer (402) to obtain the carbon dioxide diffusion coefficient.
7. The method for in-situ measurement of the carbon dioxide diffusion coefficient in an electrochemical reduction reaction system according to claim 6, characterized in that: The Raman spectral signals at the T-shaped gas-liquid interface at the center of the flow channel (E) and at distances of 2 mm and 3 mm from the T-shaped gas-liquid interface along the cathode (301b-2) were detected using a Raman spectrometer (402) to obtain the characteristic peak signal intensity I of carbon dioxide. CO2 And the characteristic peak signal intensity of pure water I H2O Under in-situ electrochemical reaction conditions, the diffusion mass transfer process of carbon dioxide in the electrolyte satisfies the Nernst-Planck equation: In the formula, C i The concentration of substance i under in-situ conditions of electrochemical reaction (i = bicarbonate, carbonate, hydroxide, hydrogen ions and alkali metal cations M) + ), t is the diffusion time, R i The formation rate of substance i is controlled by the homogeneous reaction (Equations 1.3 to 1.5), J i Let i be the flux of substance i. In the formula, D i Let x be the diffusion coefficient of substance i, x be the distance in the diffusion direction, and z be the diffusion coefficient of substance i. i Let be the charge number of substance i, F be the Faraday constant, R be the ideal gas constant, T be the absolute temperature, and φ be the electric potential. The distance in the diffusion direction is from the gas-liquid interface at the T-junction (x = 0 mm) along the working electrode direction to the positions x = 2 mm and x = 3 mm.
8. The method for in-situ measurement of the carbon dioxide diffusion coefficient in an electrochemical reduction reaction system according to claim 7, characterized in that: To accurately simulate the ion and potential distribution under in-situ conditions of electrochemical reactions, the electroneutrality assumption is considered in the diffusion model: The hydrogen evolution reaction and the oxygen evolution reaction occur at the cathode (301b-2) and the anode (301b-1), respectively. A constant blowing carbon dioxide source term was used to simulate the carbon dioxide concentration change at the T-type gas-liquid interface: R CO2,feed =k l a(C CO2,aq -C CO2 ) In the formula, k l 'a' is the volumetric mass transfer coefficient at the gas-liquid interface, and 'C' is the mass transfer coefficient at CO2,aq C represents the saturated solubility in the electrolyte. CO2 This refers to the concentration of electrolyte solution. The Nernst-Planck equations were solved using the finite element method, and then Raman spectroscopy principles and normalization were applied to obtain the simulated value of the diffusion coefficient.
9. The method for in-situ measurement of the carbon dioxide diffusion coefficient in an electrochemical reduction reaction system according to claim 8, characterized in that: The process involves Raman spectroscopy principles and normalization, including the conversion between relative carbon dioxide concentration and Raman spectral signal intensity. In the formula, β is a proportionality coefficient that is independent of diffusion time t and diffusion distance x, and I is the Raman peak signal intensity, including characteristic peaks of carbon dioxide and water. To improve the accuracy of the diffusion coefficient, relative concentration values are used for calculation, and the ratio of Raman peak intensities at a given diffusion distance and time is normalized to the ratio of Raman peak intensities at the gas-liquid interface: This allows the measured Raman signal intensity to be interconverted with the carbon dioxide concentration in the one-dimensional electrochemical diffusion model.
10. The application of a microfluidic device for in-situ measurement of carbon dioxide diffusion coefficient in an electrochemical reduction reaction system according to claim 1 in the in-situ measurement of carbon dioxide diffusion coefficient under electrochemical reaction conditions.