Device and method for quantitatively detecting biochar electron transfer

Abstract

The invention belongs to the technical field of electrochemistry and materials, and particularly relates to a device and a method for quantitatively detecting biochar electron transfer. The invention provides a device for quantitatively detecting biochar electron transfer. The device comprises an electrolytic reaction tank, a sulfuric acid electrolyte, a carbon-containing film working electrode, a counter electrode, a reference electrode and an electrochemical workstation, the carbon-film-containing working electrode comprises a working electrode and a carbon film loaded on the surface of the working electrode; the preparation raw material of the carbon film comprises biochar. According to the device for quantitatively detecting biochar electron transfer, sulfuric acid serves as electrolyte, the surface of the working electrode is coated with the carbon film containing biochar, and the obtained device is stable in system and has good anti-interference capacity; by constructing a hydrogen / oxygen evolution reaction kinetic model, a quantitative relationship between biochar electron transfer and reaction kinetic parameters is established, so that the problems that the existing biochar electron gaining and losing capability test mode and technical operation are complicated, and the detection sensitivity and the detection accuracy are low are solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrochemistry and material technology, and particularly relates to a device and method for quantitatively detecting electron transfer of biochar. BACKGROUND

[0002] As a new and sustainable material, biochar has good redox performance and can act as an electron donor or acceptor to participate in the degradation of pollutants. However, the current testing method for the electron gain and loss ability of biochar is not mature, and the determination of the electron gain and loss ability mainly relies on traditional chemical methods and electrochemical methods. The traditional chemical method often uses Fe 3+ as an oxidizing agent to oxidize hydrogen, and then determines the reduced Fe 2+ or determines the hydrogen concentration in the system by gas chromatography to determine the electron gain and loss ability of biochar; this method needs to incubate chemical reagents with biochar for several days to ensure the complete redox reaction, and the testing time is long, the operation is complicated, and it needs to rely on redox chemical reagents for indirect determination.

[0003] The commonly used electrochemical method usually places biochar in a phosphate buffer solution (PBS) containing 2,2'-azino-bis(3-ethyl-benzothiazoline-6-sulfonic acid) diammonium salt (ABTS) mediator, establishes a three-electrode system including a working electrode, a counter electrode and a reference electrode in an electrolytic cell, changes the potential of the working electrode through an electrochemical workstation and records the current signal of the electrochemical reaction on the surface of the working electrode, and sets the working electrode to high and low potentials to determine the electron gain and loss ability of biochar. In this method, ABTS is easily oxidized at high potential, and after being over-oxidized, it generates products that are difficult to reduce, which reduces the reversibility of the redox cycle. This means that in the cyclic voltammetry test, the oxidation and reduction peak area of ABTS may gradually decrease or even disappear, thereby affecting the accuracy and repeatability of the test results. In addition, ABTS may generate other chemical substances such as ABTS· + or ABTS· 2+ during oxidation, and these degradation products not only reduce the effective concentration of ABTS, but also may have non-specific reactions with biochar or electrodes, generating additional electrochemical signals and interfering with the test results. SUMMARY

[0004] The purpose of the present application is to provide a device and method for quantitatively detecting electron transfer of biochar, by constructing a hydrogen / oxygen evolution reaction kinetic model and establishing a quantitative relationship between biochar electron transfer and reaction kinetic parameters, to solve the problems of complex operation, low detection sensitivity and low detection accuracy of the existing biochar electron gain and loss ability testing method.

[0005] In order to achieve the object of the present application, the present application provides the following technical solutions:

[0006] A device for quantitatively detecting electron transfer of biochar, comprising an electrolysis reaction tank, sulfuric acid electrolyte, a carbon film working electrode, a counter electrode, a reference electrode and an electrochemical workstation; the carbon film working electrode comprises a working electrode and a carbon film loaded on the surface of the working electrode; the raw material for preparing the carbon film comprises biochar.

[0007] Preferably, the concentration of the sulfuric acid electrolyte is 1-2 M, and the pH value is 1-3; the counter electrode is a CHL115 platinum wire electrode; and the reference electrode is a saturated calomel electrode.

[0008] Preferably, the preparation method of the carbon film working electrode comprises the following steps:

[0009] Mixing biochar, water, ethanol and a perfluorosulfonic acid resin solution to obtain a carbon film liquid;

[0010] Coating the carbon film liquid on the surface of the working electrode, drying to form a carbon film on the surface of the working electrode, and obtaining the carbon film working electrode.

[0011] Preferably, the biochar is obtained by burning biomass, and the biomass comprises one or more of corn straw, wheat straw and rice straw; the burning temperature is 350-700 DEG C, and the holding time is 1-4 h.

[0012] Preferably, the volume ratio of the water, ethanol and perfluorosulfonic acid resin solution is 3-5:1:0.4-1, and the mass concentration of the perfluorosulfonic acid resin solution is 0.2-0.5%.

[0013] Preferably, the total volume of the water, ethanol and perfluorosulfonic acid resin solution to the mass of the biochar is 0.35-0.9 mL:2-4 mg.

[0014] Preferably, the working electrode is a glassy carbon electrode; the coating amount of the carbon film liquid is 0.07-0.35 mg, and the coating area is 0.07065 cm 2 .

[0015] The device for quantitatively detecting electron transfer of biochar adopts the above technical solution, and the method comprises the following steps:

[0016] The carbon film working electrode, the counter electrode and the reference electrode are respectively electrically connected with the electrochemical workstation, and an electrolysis water reaction is carried out in the electrolysis reaction tank containing the sulfuric acid electrolyte.

[0017] The linear sweep voltammetry curve of the electron gaining and losing process of the biochar is obtained by using the linear sweep voltammetry method in a constant potential instrument, and the abscissa of the linear sweep voltammetry curve is electrode potential, and the ordinate is current; the Tafel curve of the electron gaining and losing process of the biochar is obtained by using the Tafel polarization method in a constant potential instrument, and the abscissa of the Tafel curve is electrode potential, and the ordinate is current density;

[0018] According to the linear sweep voltammetry curve and the Tafel curve, the electron gaining capacity and the electron losing capacity of the biochar are obtained.

[0019] Preferably, the reduction potential of the linear sweep voltammetry is that the low potential is-1V to-0.5V, and the high potential is 0V to +1V; the oxidation potential is that the low potential is 0V to +0.5V, and the high potential is +1V to +2V; and the scanning times are 2 to 200 times.

[0020] Preferably, the low potential of the Tafel polarization method is-0.4V to-0.1V, and the high potential is +0.1V to +0.8V.

[0021] The application discloses a device for quantitatively detecting electron transfer of biochar, which comprises an electrolytic reaction tank, sulfuric acid electrolyte, a carbon film working electrode, a counter electrode, a reference electrode and an electrochemical workstation; the carbon film working electrode comprises a working electrode and a carbon film loaded on the surface of the working electrode; and the raw material for preparing the carbon film comprises biochar.

[0022] The device for quantitatively detecting electron transfer of biochar provided by the application has stable system and good anti-interference capacity. The application provides a method for quantitatively detecting electron transfer of biochar, which tests the electron gaining and losing capacity of the biochar by electrocatalytic water decomposition, obtains a linear sweep voltammetry (LSV) curve and a Tafel (Tafel) curve by using the linear sweep voltammetry method and the Tafel polarization method in a constant potential instrument, and directly measures the rate, overpotential and current exchange density of a hydrogen evolution reaction (HER) and an oxygen evolution reaction (OER) catalyzed by the biochar. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 A flow chart for determining the electron gaining and losing capacity of biochar in the application;

[0024] Figure 2A linear sweep voltammetry (LSV) curve schematic diagram of a biochar electron gain hydrogen evolution reaction provided for Example 1;

[0025] Figure 3 A linear sweep voltammetry (LSV) curve schematic diagram of a biochar electron loss oxygen evolution reaction provided for Example 2;

[0026] Figure 4 A Tafel curve schematic diagram of a biochar electron gain and loss Tafel polarization method provided for the present application;

[0027] Figure 5 A biochar electron gain process (HER) hydrogen production and biochar electron gain capacity (EAC) correlation coefficient graph measured by a gas chromatograph used in the present application. DETAILED DESCRIPTION

[0028] The present application provides a device for quantitatively detecting biochar electron transfer, comprising an electrolysis reaction tank, a sulfuric acid electrolyte, a carbon film working electrode, a counter electrode, a reference electrode and an electrochemical workstation; the carbon film working electrode comprises a working electrode and a carbon film loaded on the surface of the working electrode; the raw material for preparing the carbon film comprises biochar.

[0029] In the present application, all raw materials are preferably commercially available products well known to those skilled in the art unless otherwise specified.

[0030] As an embodiment of the present application, the preparation method of the sulfuric acid electrolyte comprises the following steps:

[0031] The concentrated sulfuric acid is diluted with water to obtain the sulfuric acid electrolyte.

[0032] As an embodiment of the present application, the water is deionized water with oxygen removed, and the volume ratio of the concentrated sulfuric acid to water can be 15-55:500-1000; the concentration of the sulfuric acid electrolyte can be 1-2M, and the pH value can be 1-3, specifically 1.5. The present application uses sulfuric acid as an electrolyte, which has the advantages of high conductivity, fast reaction kinetics and low overpotential in the process of biochar catalytic HER and OER, and is especially suitable for basic research that requires precise evaluation of the intrinsic activity of catalytic materials.

[0033] As an embodiment of the present application, the preparation method of the carbon film working electrode comprises the following steps:

[0034] Biochar, water, ethanol and perfluorosulfonic acid resin solution are mixed to obtain a carbon film solution;

[0035] The carbon film solution is coated on the surface of the working electrode, dried to form a carbon film on the surface of the working electrode, and the carbon film working electrode is obtained.

[0036] The present application mixes biochar, water, ethanol and perfluorosulfonic acid resin solution to obtain carbon film liquid. As an embodiment of the present application, the biochar is obtained by burning biomass, the biochar is obtained by burning biomass, the biomass includes one or more of corn stalks, wheat stalks and rice stalks, the burning temperature can be 350-700 DEG C, further can be 350-550 DEG C, and the holding time is 1-4 h. As an embodiment of the present application, the volume ratio of water, ethanol and perfluorosulfonic acid resin solution can be 3-5:1:0.4-1, and specifically can be 3:1:0.4; the mass concentration of perfluorosulfonic acid resin solution can be 0.2%-0.5%; the total volume of water, ethanol and perfluorosulfonic acid resin solution to the amount of biochar can be 0.35-0.9 mL:2-4 mg, and specifically can be 0.55 mL:4 mg. The present application mixes the biochar, water, ethanol and perfluorosulfonic acid resin solution, and then performs ultrasonic treatment to make the biochar powder fully dispersed, and the ultrasonic treatment time can be 2.5-3.5 h, and specifically can be 3 h.

[0037] After obtaining the carbon film liquid, the present application coats the carbon film liquid on the surface of a working electrode, dries to form a carbon film on the surface of the working electrode, and obtains the working electrode containing the carbon film. As an embodiment of the present application, the working electrode is a glassy carbon electrode; the present application further includes pretreatment and reversibility detection of the working electrode before coating. The pretreatment of the working electrode includes: sequentially performing first polishing treatment, first ultrasonic washing, second polishing treatment and second ultrasonic washing on the working electrode. The first polishing treatment and the second polishing treatment independently use Al2O3 polishing powder for polishing treatment, the particle size of the Al2O3 polishing powder used in the first polishing treatment is 0.3-0.5 μm; the particle size of the Al2O3 polishing powder used in the second polishing treatment is 0.05-0.1 μm; the present application performs polishing treatment to remove the surface oxide layer and impurities, and ensures that the polishing is smooth and mirror-like without obvious scratches. The first ultrasonic washing and the second ultrasonic washing are independently ultrasonic cleaning in deionized water and ethanol for 5-10 min. The method for reversibility detection of the working electrode includes: using K3Fe(CN)6 / K2Fe(CN)6 solution as electrolyte, platinum wire as counter electrode and saturated calomel electrode as reference electrode, and using cyclic voltammetry in a constant potential instrument to evaluate the reversibility of the working electrode after polishing treatment. The concentration of the K3Fe(CN)6 / K2Fe(CN)6 solution is 0.01-0.1 mol / L. If the ratio of the oxidation peak current (i_pa) to the reduction peak current (i_pc) is close to 1, it indicates that the electrode has good reversibility.

[0038] As an embodiment of the present application, the coating is drop coating, and the coating amount of the carbon film liquid can be 0.07-0.35 mg, specifically 0.07 mg, 0.14 mg, 0.21 mg, 0.28 mg or 0.35 mg; the coating area of the carbon film liquid on the working electrode is 0.07065 cm 2 The present application coats the carbon film liquid containing biochar on the surface of the working electrode, which can optimize the thermodynamic and kinetic processes of the electrocatalytic water splitting reaction, thereby realizing the high activity and stability of hydrogen and oxygen evolution, and providing direct electrochemical characterization basis for studying the electron transfer ability of biochar.

[0039] As an embodiment of the present application, the counter electrode is a CHL115 platinum wire electrode; the reference electrode is a saturated calomel (SCE) electrode; the top of the electrolysis reaction tank is provided with a feeding hole, a gas outlet hole, a working electrode insertion port, a counter electrode insertion port and a reference electrode insertion port; the electrolyte is injected into the electrolysis reaction tank from the feeding hole; the working electrode, the reference electrode and the counter electrode are sequentially inserted from the corresponding insertion ports and immersed in the electrolyte; the working electrode power line of the electrochemical workstation is connected with the working electrode; the auxiliary electrode power line of the electrochemical workstation is connected with the counter electrode; and the reference electrode power line of the electrochemical workstation is connected with the reference electrode.

[0040] The present application provides a method for quantitatively detecting the electron transfer of biochar by using the device described in the above technical solution, which comprises the following steps:

[0041] The working electrode, the counter electrode and the reference electrode containing carbon film are respectively connected with the electrochemical workstation, and the water electrolysis reaction is carried out in the electrolysis reaction tank containing sulfuric acid electrolyte;

[0042] The linear sweep voltammetry curve of the electron gain and loss process of biochar is obtained by using the linear sweep voltammetry method in the constant potential instrument, and the abscissa of the linear sweep voltammetry curve is the electrode potential, and the ordinate is the current; the Tafel curve of the electron gain and loss process of biochar is obtained by using the Tafel polarization method in the constant potential instrument, and the abscissa of the Tafel curve is the electrode potential, and the ordinate is the current density;

[0043] According to the linear sweep voltammetry curve and the Tafel curve, the electron gain ability and the electron loss ability of biochar are obtained.

[0044] The carbon film working electrode, the counter electrode and the reference electrode are respectively connected with an electrochemical workstation, and an electrolytic water reaction is carried out in an electrolytic reaction tank containing sulfuric acid electrolyte.

[0045] The linear sweep voltammetry curve of the electron gain and loss process of the biochar is obtained by using the linear sweep voltammetry method in the constant potential instrument, and the abscissa of the linear sweep voltammetry curve is the electrode potential, and the ordinate is the current; the Tafel curve of the electron gain and loss process of the biochar is obtained by using the Tafel polarization method in the constant potential instrument, and the abscissa of the Tafel curve is the electrode potential, and the ordinate is the current density. As an embodiment of the present application, the reduction potential of the linear sweep voltammetry method is: the low potential is-1V to-0.5V, and the high potential is 0V to +1V; the oxidation potential is: the low potential is 0V to +0.5V, and the high potential is +1V to +2V, and specifically can be +1.8V; the scanning times are 2 to 200 times; the low potential of the Tafel polarization method is-0.4V to-0.1V, and specifically can be-0.35V, and the high potential is +0.1V to +0.8V.

[0046] According to the linear sweep voltammetry curve and the Tafel curve, the electron gain capacity of the biochar and the electron loss capacity of the biochar are obtained. As an embodiment of the present application, according to the linear sweep voltammetry curve and the Tafel curve, the data of the starting potential of the hydrogen evolution reaction and the cathode slope of the Tafel curve and the starting potential of the oxygen evolution reaction and the anode slope of the Tafel curve are obtained; the electron gain capacity of the biochar and the electron loss capacity of the biochar are calculated according to the data.

[0047] Figure 1 The flow chart for determining the electron gain and loss capacity of the biochar is provided. The reversibility of the working electrode is tested first, the carbon film liquid containing the biochar is prepared, the working electrode with good reversibility is selected to coat the carbon film liquid to prepare the carbon film working electrode, the prepared sulfuric acid electrolyte is injected into the reaction tank, and the device for quantitatively detecting the electron transfer of the biochar is prepared; the linear sweep voltammetry LSV curve and the Tafel polarization method Tafel curve in the constant potential instrument are used to obtain the electron gain capacity of the biochar and the electron loss capacity of the biochar; and the generated hydrogen is detected by the gas chromatography method to verify the feasibility and accuracy of the present application. In order to further illustrate the present application, the following will be described according to the following Figure 1The technical solutions in the present application are clearly and completely described in combination with the embodiments in the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the protection scope of the present application.

[0048] Embodiment 1

[0049] S1: Reversibility test of the working electrode: a glassy carbon electrode was used as the working electrode, the working electrode was vertically placed and polished with 0.3 μm Al2O3 polishing powder to remove the surface oxide layer and impurities, and then the working electrode was immediately placed in deionized water and ethanol for ultrasonic cleaning for 5 min, respectively, and then the working electrode was vertically placed and polished with 0.05 μm Al2O3 polishing powder, and then ultrasonic cleaning was performed in the above-mentioned manner, and then the working electrode was dried with a mirror paper.

[0050] The working electrode reversibility was evaluated by cyclic voltammetry in a constant potential instrument with a K3Fe(CN)6 / K2Fe(CN)6 solution with a concentration of 0.01-0.1 mol / L as an electrolyte, a platinum wire as a counter electrode, and a saturated calomel (SCE) electrode as a reference electrode. The obtained oxidation peak current (i_pa) was 1.684 μA, the obtained reduction peak current (i_pc) was 1.666 μA, and the ratio of the oxidation peak current (i_pa) to the reduction peak current (i_pc) was 1. If the ratio of the oxidation peak current (i_pa) to the reduction peak current (i_pc) is greater than or equal to 0.9 and less than or equal to 1.1, it indicates that the working electrode has good reversibility.

[0051] S2: Preparation of H2SO4 electrolyte: 27 mL of concentrated H2SO4 was slowly added to 500 mL of pre-deaerated deionized water to prepare a H2SO4 electrolyte with a concentration of 1 M.

[0052] S3: Preparation of carbon film solution: 0.375 mL of water, 0.125 mL of ethanol and 50 μL of Nafion solution with a mass fraction of 0.5% were mixed in a centrifuge tube; 4 mg of biochar was added, the biochar was corn straw burned at 350 ℃ for 4 h; the mixed system was ultrasonically treated for 3 h to prepare a carbon film solution.

[0053] S4: Preparation of carbon film-containing working electrode: the working electrode with better reversibility evaluated by cyclic voltammetry in S1 was sequentially ultrasonically cleaned in deionized water and ethanol solution for 5 min, and then the water was absorbed with a mirror paper; 0.07 mg, 0.14 mg, 0.21 mg, 0.28 mg and 0.35 mg of carbon film liquid was dropped on the working electrode respectively by drop coating method, and then carbon film was formed on the surface of the working electrode after natural drying, thereby obtaining a carbon film-containing working electrode.

[0054] S5: Preparation of device for quantitative detection of electronic transfer of biochar: 100 mL of 1 M H2SO4 electrolyte was injected into the electrolysis reaction cell, and the carbon film-containing working electrode, the reference electrode and the counter electrode were sequentially inserted into the electrolysis reaction cell and immersed in the H2SO4 electrolyte, the working electrode power line of the electrochemical workstation was connected with the working electrode; the auxiliary electrode power line of the electrochemical workstation was connected with the counter electrode; the reference electrode power line of the electrochemical workstation was connected with the reference electrode, and the open circuit potential was tested, when the reaction current was stable, the linear sweep voltammetry in the constant potential instrument was used, the low potential of the reduction potential was set to-1 V, the high potential was set to 0 V, and the scanning number was set to 2 times, then the running was started, and the LSV curve of the electron gain process of biochar was generated.

[0055] Example 2

[0056] The steps of S1-S4 were the same as those in Example 1.

[0057] S5: 100 mL of 1 M H2SO4 electrolyte was injected into the electrolysis reaction cell, and the carbon film-containing working electrode, the reference electrode and the counter electrode were sequentially inserted into the electrolysis reaction cell and immersed in the H2SO4 electrolyte, and then the electrochemical workstation was connected, the open circuit potential was tested, when the reaction current was stable, the linear sweep voltammetry in the constant potential instrument was used, the low potential of the oxidation potential was set to 0 V, the high potential was set to +1.8 V, and the scanning number was set to 2 times, then the running was started, and the LSV curve of the electron loss process of biochar was generated.

[0058] Example 3

[0059] The steps of S1-S4 were the same as those in Example 1.

[0060] The steps of S5 were basically the same as those in Example 1, except that in Example 3, when the reaction current was stable, the Tafel polarization method in the constant potential instrument was used, the low potential of the redox potential was set to-0.35 V, the high potential was set to +0.8 V, then the running was started, and the Tafel curve of the electron gain and loss process of biochar was generated.

[0061] Test Example 1

[0062] The device for quantitative detection of electron transfer in biochar prepared in this invention uses a saturated calomel electrode (SCE) as a reference electrode. To eliminate the influence of solution pH and the potential shift of the SCE, the potential is converted relative to the standard hydrogen electrode (RHE) using formula (1):

[0063] E RHE =E SCE +0.0591×pH+E OSCE (1);

[0064] Among them, E RHE E is the potential relative to the standard hydrogen electrode (RHE). SCE E represents the potential recorded in the experiment relative to the saturated calomel electrode (SCE), pH represents the pH value of the solution, and E represents the potential. OSCE This is the potential offset of the SCE, which is typically +0.241V at 25°C.

[0065] Data processing was performed on the LSV and Tafel curves of the biochar electron gain process, and the electron gain capacity (EAC) of biochar was obtained using formula (2):

[0066] EAC (μmol / mg) = k HER ×|ΔE HER |×C Biochar (2);

[0067] Where, k HER It is the electron transfer coefficient (calibrated using standard substances) of the hydrogen evolution reaction (HER) process, ΔE HER It is the difference between the initial potential and the theoretical equilibrium potential, C Biochar This refers to the mass concentration of biochar.

[0068] The electron loss capacity (EDC) of biochar is obtained using formula (3):

[0069] EDC (μmol / mg) = k OER ×ΔE OER ×C Biochar (3);

[0070] Where, k OER It is the electron transfer coefficient (calibrated using standard substances) of the oxygen evolution reaction (OER) process, ΔE OER It is the difference between the initial potential and the theoretical equilibrium potential, C Biochar This refers to the mass concentration of biochar.

[0071] For the HER reaction, the electron transfer coefficient can be calculated from the cathode slope of the Tafel curve. The electron transfer coefficient (k) for the HER reaction process is obtained using formula (4). HER ):

[0072]

[0073] where R is the gas constant (8.314 J / (mol K)), T is the absolute temperature (K), b is the Tafel curve cathodic slope, n is the number of electrons transferred in the reaction (n = 2 for the HER reaction), and F is the Faraday constant (96485 C / mol).

[0074] For the OER reaction, the electron transfer coefficient can be calculated from the Tafel curve anodic slope, using equation (5) to obtain the electron transfer coefficient (k OER ) for the OER reaction process:

[0075]

[0076] where R is the gas constant (8.314 J / (mol K)), T is the absolute temperature (K), b is the Tafel curve anodic slope, n is the number of electrons transferred in the reaction (n = 4 for the OER reaction), and F is the Faraday constant (96485 C / mol).

[0077] Equation (6) is used to obtain the |AE HER | for the HER reaction process:

[0078] AE HER = E 起始 - E 平衡 (6) ;

[0079] where E 起始 is the onset potential obtained in the experiment, and E 平衡 is the theoretical equilibrium potential (for the HER, typically close to 0 (V vs. RHE).

[0080] Equation (7) is used to obtain the |AE OER | for the OER reaction process:

[0081] AE OER = E 起始 - E 平衡 (7) ;

[0082] where E 起始 is the onset potential obtained in the experiment, and E 平衡 is the theoretical equilibrium potential (for the OER, typically close to 0 (V vs. RHE).

[0083] According to Example 1 and Example 2, the data is processed and calculated to generate the LSV curves for the biochar electron gain hydrogen evolution reaction and electron loss oxygen evolution reaction processes, as shown in Figure 2 and Figure 3 . Figure 2Linear sweep voltammetry (LSV) curve schematic diagram of the biochar electron gain hydrogen evolution reaction (HER) provided for example 1. Figure 3 Linear sweep voltammetry (LSV) curve schematic diagram of the biochar electron loss oxygen evolution reaction (OER) provided for example 2. Figure 2 and Figure 3 In the abovementioned linear sweep voltammetry (LSV) curve schematic diagram, the abscissa is electrode potential (E) with unit of volt (V), and the ordinate is current density (j) with unit of milliampere per square centimeter (mA / cm 2 ). Different curves represent different mass of biochar dropped on the carbon-containing film working electrode with unit of mg. According to the abovementioned linear sweep voltammetry (LSV) curve schematic diagram, it can be seen that the EAC and EDC of the biochar prepared at 350℃ are evaluated based on the HER and OER, and the EAC and EDC are linearly related to the mass of the biochar. The device and method can reduce overpotential and accelerate hydrogen production rate. Compared with the ABTS method, the interference of the mediator is eliminated, and the device and method can be used for synchronous detection and have self-calibration function. Figure 2 and Figure 3 In the abovementioned linear sweep voltammetry (LSV) curve schematic diagram, the abscissa is electrode potential (E) with unit of volt (V), and the ordinate is current density (j) with unit of milliampere per square centimeter (mA / cm 2 ). Different curves represent different mass of biochar dropped on the carbon-containing film working electrode with unit of mg. According to the abovementioned linear sweep voltammetry (LSV) curve schematic diagram, it can be seen that the EAC and EDC of the biochar prepared at 350℃ are evaluated based on the HER and OER, and the EAC and EDC are linearly related to the mass of the biochar. The device and method can reduce overpotential and accelerate hydrogen production rate. Compared with the ABTS method, the interference of the mediator is eliminated, and the device and method can be used for synchronous detection and have self-calibration function.

[0084] According to example 3, the data is processed and calculated to generate the biochar electron gain and loss process Tafel curve, as shown in Figure 4 . Figure 4 Tafel polarization method Tafel curve schematic diagram of the biochar electron gain and loss provided by the present application. Figure 4 In the abovementioned Tafel polarization method Tafel curve schematic diagram, the abscissa is electrode potential (E) with unit of volt (V), and the ordinate is the logarithm of current density (log(j)) with unit of ampere per square centimeter (A / cm 2 ). Different curves represent different mass of biochar dropped on the carbon-containing film working electrode with unit of mg. According to the abovementioned Tafel polarization method Tafel curve schematic diagram, it can be seen that the EAC and EDC of the biochar prepared at 350℃ are evaluated based on the HER and OER, and the EAC and EDC are linearly related to the mass of the biochar. The device and method can reduce overpotential and accelerate hydrogen production rate. Compared with the ABTS method, the interference of the mediator is eliminated, and the device and method can be used for synchronous detection and have self-calibration function. Figure 4 According to the abovementioned Tafel polarization method Tafel curve schematic diagram, it can be seen that increasing the biochar loading can optimize the kinetics of the HER and OER processes, including reducing overpotential and adjusting the reaction mechanism.

[0085] In order to eliminate the influence of some non-specific reactions or background current, the electrode potential range of the abovementioned biochar electron gain and loss process LSV curve is greater than +1.23V positive potential region, the side reaction is isolated through the thermodynamic threshold, the oxidation reaction dominated electron transfer process is focused, and the current signal of the LSV curve more purely reflects the oxidation reaction biochar electron loss ability (EDC); the electrode potential range of the LSV curve is less than 0V negative potential region to evaluate the reduction reaction biochar electron gain ability (EAC).

[0086] Test example 2

[0087] In order to prove the accuracy and feasibility of the quantitative detection of biochar electron transfer method based on hydrogen / oxygen evolution reaction kinetics in Example 1, the present application detects the hydrogen generated under the electrochemical redox reaction of the carbon-containing film working electrode with different biochar contents obtained in Example 1 by gas chromatography. The principle is based on the different retention times of hydrogen and other gas components in the chromatographic column to realize separation. Specifically, the carrier gas (nitrogen) carries the hydrogen sample into the chromatographic column. Due to its unique physical and chemical properties, the retention time of hydrogen in the chromatographic column is significantly different from that of other components, thereby realizing separation. The separated hydrogen passes through the flame ionization detector (FID), and an electrical signal is generated according to the change in the thermal conductivity of hydrogen. After amplification and processing, the signal is converted into a measurable peak area, and then the concentration of hydrogen is calculated through the calibration curve.

[0088] Using high-purity nitrogen as the balance gas, 10% methane, 10% carbon monoxide, 10% carbon dioxide, and 5% hydrogen were injected into the gas bag according to the volume percentage. The standard samples were prepared according to the dilution ratios of 0.2, 0.1, 0.05, 0.025, and 0.01, respectively. A 1 mL microsyringe was used to inject the standard sample into the gas chromatograph. The sampling time was set to 2 min, and the peak area of the H2 component in each diluted sample was measured and recorded in turn. The concentration of H2 in each standard sample was linearly fitted with the corresponding peak area to obtain the hydrogen standard curve equation.

[0089] The main purpose of determining the hydrogen standard curve is to realize the quantitative analysis of hydrogen, and to establish an accurate correspondence between the hydrogen concentration or content and the detection signal, providing a reliable basis for the determination of hydrogen content in subsequent actual samples.

[0090] 100 mL of 1 M H2SO4 electrolyte was injected into the electrolysis reaction cell. The carbon-containing film working electrode, saturated calomel reference electrode, and platinum wire counter electrode were inserted into the electrolysis reaction cell in turn and immersed in the electrolyte. The electrochemical workstation was connected, the open circuit potential was tested, and when the reaction current was stable, the linear sweep voltammetry in the constant potential instrument was used. The low potential of the redox potential was set to 0 V, the high potential was set to +1.8 V, the scan number was set to 200 times, and then the operation was started. After the reaction was completed, 1 mL of sample gas was manually extracted from the gas outlet of the electrolysis reaction cell using a 1 mL microsyringe. The electrolysis reaction cell was sealed throughout the reaction process.

[0091] The sample gas is injected into the gas chromatograph, and the sample measurement time is set to 2 min. The peak area of the H2 component in each sample gas is measured and recorded in turn. According to the chromatographic peak area of the sample, combined with the calibration curve, the hydrogen production amount of each sample in the electron acquisition process (HER reaction) is calculated. The calculated hydrogen production amount of the biochar in the electron acquisition process (HER reaction) is correlated with the electron acquisition capacity (EAC) of the biochar to understand the linear correlation between the two variables, as shown in Figure 5

[0092] Figure 5 The correlation coefficient graph of the hydrogen production amount of the biochar in the electron acquisition process (HER) measured by the gas chromatograph and the electron acquisition capacity (EAC) of the biochar is used in the present application. Figure 5 R 2 = 0.90786 > 0.9, indicating a strong linear relationship, further verifying the accuracy and feasibility of the electron acquisition and loss test method for the biochar.

[0093] In summary, the device and method provided by the present application test the electron acquisition and loss capacity of biochar by electrocatalytic water decomposition, which has a stable system and enhanced anti-interference capability. The method uses H2SO4 as an electrolyte, and directly measures the rate, overpotential and current exchange density of hydrogen gas (HER reaction) and oxygen gas (OER reaction) released by biochar catalytic water decomposition using linear sweep voltammetry (LSV curve) and Tafel polarization method (Tafel curve) in a constant potential instrument. Compared with traditional chemical methods and conventional electrochemical methods, the operation method is simple, the experimental conditions are easy to control, efficient and makes the biochar reaction fully proceed, which can complete the evaluation of the electrochemical activity of biochar in a short time, does not depend on chemical mediation reagents such as ABTS, can realize the rapid quantification of the electron acquisition and loss capacity of biochar, and the test results are accurate and reliable.

[0094] The principles and implementation modes of the present application are described by applying specific examples in this paper, and the above examples are only used to help understand the method and core idea of the present application; at the same time, for those skilled in the art, according to the idea of the present application, the specific implementation mode and application range will be changed. In summary, the content of the specification should not be understood as a limitation of the present application.​

Claims

1. A device for quantitatively detecting electron transfer of biochar, comprising an electrolysis cell, a sulfuric acid electrolyte, a carbon film working electrode, a counter electrode, a reference electrode and an electrochemical workstation; the carbon film working electrode comprises a working electrode and a carbon film loaded on the surface of the working electrode; the raw material for preparing the carbon film comprises biochar.

2. The apparatus of claim 1, wherein, The concentration of the sulfuric acid electrolyte is 1-2 M, and the pH value is 1-3; the counter electrode is a CHL115 platinum wire electrode; and the reference electrode is a saturated calomel electrode.

3. The apparatus of claim 1, wherein, The preparation method of the carbon film working electrode comprises the following steps: mixing biochar, water, ethanol and a perfluorosulfonic acid resin solution to obtain a carbon film solution; coating the carbon film solution on the surface of the working electrode, drying to form a carbon film on the surface of the working electrode, and obtaining the carbon film working electrode.

4. The apparatus of claim 1 or 3, wherein, The biochar is obtained by burning biomass, and the biomass comprises one or more of corn stalks, wheat stalks and rice stalks, and the burning temperature is 350-700℃, and the holding time is 1-4 h.

5. The apparatus of claim 3, wherein, The volume ratio of the water, ethanol and perfluorosulfonic acid resin solution is 3-5: 1: 0.4-1, and the mass concentration of the perfluorosulfonic acid resin solution is 0.2-0.5%.

6. The apparatus of claim 3, wherein, The total volume of the water, ethanol and perfluorosulfonic acid resin solution to the mass of the biochar is 0.35-0.9 mL: 2-4 mg.

7. The apparatus of claim 3, wherein, The working electrode is a glassy carbon electrode; the coating amount of the carbon film liquid is 0.07-0.35 mg, and the coating area is 0.07065 cm 2 . 8.A method for quantitatively detecting electron transfer of biochar by using the device according to any one of claims 1-7, comprising the following steps: connecting the carbon film working electrode, the counter electrode and the reference electrode with the electrochemical workstation respectively, and performing an electrolytic water reaction in the electrolysis cell containing the sulfuric acid electrolyte; obtaining a linear sweep voltammetry curve of the electron gain and loss process of the biochar by using a linear sweep voltammetry method in a constant potential instrument, wherein the abscissa is the electrode potential, and the ordinate is the current; obtaining a Tafel curve of the electron gain and loss process of the biochar by using a Tafel polarization method in a constant potential instrument, wherein the abscissa is the electrode potential, and the ordinate is the current density; obtaining the electron gain capacity and the electron loss capacity of the biochar according to the linear sweep voltammetry curve and the Tafel curve.

9. The method of claim 8, wherein, The reduction potential of the linear sweep voltammetry method is: the low potential is-1 V to-0.5 V, and the high potential is 0 V to +1 V; the oxidation potential is: the low potential is 0 V to +0.5 V, and the high potential is +1 V to +2 V; and the scanning times are 2-200 times.

10. The method of claim 8, wherein, The low potential of the Tafel polarization method is-0.4 V to-0.1 V, and the high potential is +0.1 V to +0.8 V.

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