CN114164450B

CN114164450B - MOFs derived bimetallic cathode, preparation method thereof and method for improving methane yield and quality by adopting MOFs derived bimetallic cathode

Info

Publication number: CN114164450B
Application number: CN202111128375.2A
Authority: CN
Inventors: 谢丽; 郑小梅; 周文静
Original assignee: Tongji University
Current assignee: Tongji University
Priority date: 2021-09-26
Filing date: 2021-09-26
Publication date: 2023-03-17
Anticipated expiration: 2041-09-26
Also published as: CN114164450A

Abstract

The invention provides a preparation method of MOFs derived bimetallic cathode and a method for improving the yield and quality of methane, wherein the preparation method comprises the following steps: synthesis of ZIF-67; synthesizing a Co-NC nanotube; synthesizing a Ni/Co-NC catalyst; and (4) preparing a cathode. The application of using the Ni/Co-NC catalyst modified carbon felt as a cathode to promote the methane production of the microbial electrolytic cell coupled anaerobic digestion system is realized, and the methane production rate is 1.5 times and 9.5 times that of a catalyst-free modified electrode system and an AD system respectively. According to the invention, the MOFs-derived bimetallic material modified carbon felt obtained by preparation is used as the cathode of the MEC-AD system obtained by coupling the single-chamber microbial electrolytic cell and the anaerobic digestion system, and the excellent hydrogen evolution activity and electrochemical performance of the carbon felt are utilized to promote the enrichment of hydrogen-consuming methanogens and the transfer of electrons from the electrode to the methanogens, so that the aim of improving the efficiency and quality of methanogenesis of the electrode is fulfilled.

Description

MOFs derived bimetallic cathode, preparation method thereof and method for improving methane yield and quality by adopting MOFs derived bimetallic cathode

Technical Field

The invention belongs to the technical field of carbon dioxide recycling, and particularly relates to a MOFs (metal-organic frameworks) derived bimetallic cathode, a preparation method thereof and a method for improving the yield and quality of methane by using the MOFs derived bimetallic cathode.

Background

With the rapid development of society, the problems of energy consumption and carbon emission become a dilemma faced by people at present. At present, the biogas generated by AD mainly contains 40-60% of CH4 and 60-40% of CO ₂ If it is possible to convert CO therein ₂ Conversion to methane, a leap from "zero carbon" to "negative carbon" can be achieved.

The coupled technology (MEC-AD) of the microbial electrolytic cell and the anaerobic digestion system can efficiently convert CO at lower applied voltage ₂ Conversion to CH ₄ The method overcomes the defects of transportation danger, low gas-liquid mass transfer efficiency, low solubility and the like of an exogenous hydrogen supply purification technology, and is a research hotspot in the field of methane purification. The core of the process is that a cathode with an electronic reservoir function and a microbial functional flora are separated out from the cathodeThe H2 and high conductivity of the microbial pool can promote the enrichment of functional flora, and are beneficial to the interaction of the functional flora and the formation of a biological membrane. Therefore, some special surface characteristics of the cathode material, such as surface roughness, biocompatibility, hydrogen evolution activity and the like, are directly related to the reduction of CO by the cathode ₂ Is the property of methane. The noble metal Pt-based catalyst is still the first electrode of the MEC-AD system at present due to the excellent hydrogen evolution catalytic activity, but the high price and the scarcity limit the large-scale application of the noble metal Pt-based catalyst. Although the non-noble metal cathode has excellent conductivity and corrosion resistance, the smooth surface and the lower specific surface area are not beneficial to the attachment of microorganisms, and the improvement effect on the methanogenesis performance of MEC-AD is small.

Disclosure of Invention

Aiming at the defects, the invention provides the MOFs-derived bimetallic cathode, the preparation method thereof and the method for improving the yield and the quality of methane by adopting the MOFs-derived bimetallic cathode, wherein the MOFs-derived bimetallic cathode is prepared by preparing a Ni/Co-NC nano composite material and modifying a carbon felt as a cathode, can obviously improve the hydrogen evolution activity and the conductivity of the electrode, and accelerates the enrichment of archaea and the electron transfer efficiency, so that the capability of reducing CO2 into CH4 by MEC-AD is improved, the capture and the conversion of CO2 are realized, and the effect of improving the yield and the quality of methane is achieved.

The invention provides the following technical scheme: the preparation method of the MOFs derived bimetallic cathode comprises the following steps:

1) Synthesis of ZIF-67: with 2-methylimidazole and Co (NO) ₃ ) ₂ ·6H ₂ Dissolving O serving as a raw material in deionized water respectively to form a first solution A and a second solution B, dropwise adding the second solution B into the first solution A, stirring at room temperature, centrifuging, washing and drying to obtain ZIF-67;

2) Synthesis of Co-NC nanotubes: putting the ZIF-67 obtained in the step 1) into a quartz container, and carbonizing at high temperature under nitrogen atmosphere to obtain Co-NC;

3) Synthesis of Ni/Co-NC catalyst: ultrasonically dispersing the Co-NC obtained in the step 2) into an HCl solution, and stirring, washing and drying to obtain acidified Co-NC; adding acidified Co-NC into a DMF solution, adding phthalocyanine nickel after ultrasonic dispersion, stirring, centrifuging, washing, drying, and finally annealing in a nitrogen atmosphere to obtain a Ni/Co-NC catalyst;

4) Preparing a cathode: mixing the Ni/Co-NC catalyst obtained in the step 3), carbon black, ethanol, deionized water and PTFE emulsion to prepare slurry, quickly coating the slurry on a carbon felt after oscillation, drying and calcining to obtain a Ni/Co-NC modified cathode, namely the MOFs-derived bimetallic cathode.

Further, 2-methylimidazole used in the step 1) is reacted with Co (NO) ₃ ) ₂ ·6H ₂ The mass ratio of O is 12.2.

Further, the carbonization process in the step 2) is carried out in a tubular furnace by introducing nitrogen, the treatment temperature is 900 ℃, the heating rate is 2 ℃/min, and the carbonization time is 2h.

Further, the concentration of the hydrochloric acid solution for acidification in the step 3) is 4M, the acidification time is 12 hours, the washing solvent is ethanol, the drying temperature is 80 ℃, and the drying time is 12 hours.

Further, the mass ratio of the acidified Co-NC to the nickel phthalocyanine in the step 3) is 10. The annealing temperature is 900 ℃, the heating rate is 5 ℃/min, and the annealing time is 1h.

Further, the size of the carbon felt in the step 4) is 4 multiplied by 4cm, and the surface area is 16cm ² The slurry comprises the following components: 0.025g of Ni/Co-NC catalyst, 0.04g of carbon black, 1080mL of ethanol, 600mL of deionized water and 120 mu L of PTFE.

Further, the calcining temperature of the step 4) is 360 ℃, and the calcining time is 1h.

The invention also provides the MOFs derived bimetallic cathode prepared by the preparation method.

The invention also provides a method for improving the yield and the quality of methane by adopting the MOFs derived bimetallic cathode, which comprises the following steps: constructing a single-chamber microbial electrolytic cell comprising an anode and a MOFs derived bimetallic cathode, and coupling the constructed single-chamber microbial electrolytic cell with an anaerobic digestion system to form an MEC-AD system, wherein the anode in the single-chamber microbial electrolytic cell is a carbon brush which is acclimated stably in advance and has the size of 3 x 6cm, and an Ag/AgCl electrode is used as a reference electrode; externally connecting a 10 omega resistor, applying an external voltage of 0.6V, inoculating sludge to be anaerobic granular sludge cultured in a laboratory, controlling the concentration of the anaerobic granular sludge in the inoculated single-chamber microbial electrolysis cell to be 8.4g/L, adding 0.5g of sodium acetate as a carbon source, and reacting at 37 ℃.

Further, ni/Co-NC modified cathodes increased methane production by 12.7% and 386% for MEC-AD system compared to anaerobic digestion system (AD) alone.

The invention has the beneficial effects that:

1. aiming at the defects of the prior art stated in the background art, the cathode is modified by adopting a Metal-organic frameworks (MOFs) and transition Metal composite material, so that the impedance and overpotential of the cathode can be reduced, the specific capacitance of the cathode can be improved, and H precipitation from the electrode can be accelerated ₂ And the enrichment of hydrogen consuming methanogens is promoted. In addition, the MOFs serving as a precursor can improve the specific surface area and biocompatibility of the electrode, provide more anchor points for microorganisms, and further accelerate the formation of a biological film, so that the methane generation and methane purification performance of the MEC-AD are improved.

2. The MOFs-derived bimetallic cathode prepared by the method has the characteristics of rough surface, higher specific surface area, good stability, excellent electrochemical performance and the like. Can be used in conjunction with MEC-AD systems for methane production.

3. The MOFs-derived bimetallic cathode prepared by the method has a good effect of promoting MEC-AD to produce methane, and can effectively reduce CO ₂ Is CH ₄ The biogas purification is carried out efficiently.

4. The MOFs-derived bimetallic cathode prepared by the method has high-efficiency hydrogen evolution activity, can shorten the methanogenesis lag time and the stabilization time of a system by promoting the enrichment of hydrogen-consuming methanogens, and is beneficial to the rapid preparation of methane and the improvement of the methane quality.

5. According to the invention, the Ni/Co-NC nano composite material is prepared and modified on the carbon felt as the cathode, so that the hydrogen evolution activity and the conductivity of the electrode can be obviously improved, the enrichment of archaea and the electron transfer efficiency are accelerated, and the reduction of CO by MEC-AD is improved ₂ Is CH ₄ Ability of (2) to realize CO ₂ The capture and conversion of the methane, and the effect of improving the yield and the quality of the methane is achieved.

Drawings

The invention will be described in more detail hereinafter on the basis of embodiments and with reference to the accompanying drawings. Wherein:

FIG. 1 is a simplified synthesis flow diagram of Ni/Co-NC.

FIG. 2 is a Gompertz model fit curve for methane production in Ni/Co-NC modified cathode systems, catalyst-free modified cathode systems, and AD systems.

FIG. 3 is a scanning electron microscope image of the electroactive biofilm on the cathode.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.

Example 1

As shown in fig. 1, the present implementation provides a MOFs-derived bimetallic cathode comprising the steps of:

1) Synthesis of ZIF-67: 5.5g of 2-methylimidazole and 0.45g of Co (NO) ₃ ) ₂ ·6H ₂ O was dissolved in 20mL of deionized water to form solution A and solution B, respectively. Then, the solution B was added dropwise to the solution a with stirring. Continuously stirring for 6h at room temperature, centrifuging to collect a sample (8000 rpm, 15 min), washing with deionized water for 3 times, and drying at 80 ℃ for 12h to obtain ZIF-67;

2) Synthesis of Co-NC nanotubes: putting the ZIF-67 obtained in the step 1) into a quartz container, carbonizing at 900 ℃ for 2h under nitrogen atmosphere at the heating rate of 2 ℃/min to obtain Co-NC;

3) Synthesis of Ni/Co-NC catalyst: ultrasonically dispersing 80mg of Co-NC obtained in the step 2) into 100mL of 4M HCl solution, stirring for 12 hours, washing with ethanol for a plurality of times, and drying at 80 ℃ for 12 hours to obtain acidified Co-NC. Adding 100mg of acidified Co-NC into 100mL of DMF, carrying out ultrasonic treatment for 30min, adding 10 mg of nickel phthalocyanine, stirring for 24h at room temperature, centrifuging (8000rmp, 10min), respectively washing with DMF and ethanol for three times, and finally annealing for 1h at 900 ℃ at the heating rate of 5 ℃/min under a nitrogen atmosphere to obtain the Ni/Co-NC.

4) Preparing a cathode: mixing 0.025g of Ni/Co-NC obtained in the step 3), 0.04g of carbon black, 1080mL of ethanol, 600mL of deionized water and 120 mu L of PTFE, shaking for 15s, and quickly coating on 16cm ² Drying at 80 ℃ for 12h and calcining at 360 ℃ for 1h on a (4 x 4 cm) carbon felt to obtain the Ni/Co-NC modified cathode, namely the MOFs derived bimetallic cathode.

Example 2

The method for improving the yield and quality of methane by using the MOFs-derived bimetallic cathode prepared by the preparation method provided in example 1 comprises the following steps:

operation of the microbial electrolysis cell: constructing a single-chamber microbial electrolytic cell comprising an anode and a MOFs derived bimetallic cathode, adopting the constructed single-chamber microbial electrolytic cell and an anaerobic digestion system to be coupled into an MEC-AD system, and adopting a carbon brush with the anode in the single-chamber microbial electrolytic cell being acclimated stably in advance

The cathode is a carbon felt modified by a Ni/Co-N catalyst and a carbon felt without the Ni/Co-N modification, an Ag/AgCl electrode is used as a reference electrode, and the effective working volume of the reactor is 160mL; connecting a 10 omega resistor externally, applying an external voltage of 0.6V, inoculating anaerobic granular sludge with VS of 8.4g/L and 0.5g of sodium acetate as a carbon source, reacting at the temperature of 37 ℃, and testing the volume and gas composition of the generated biogas every 12h.

Comparative example 1

In agreement with the operating conditions of the microbial cells of example 2, a set of conventional AD reactors was set as a control, and the conditions were in agreement with the MEC-AD system except for the absence of applied voltage. The results of the experiment are shown in fig. 2, and the morphology of the electrode surface after 5 batch cycles of the experiment is shown in fig. 3.

As can be seen from FIG. 2, the methane of MEC-AD system is rapidly accumulated within 48h of reaction, and Ni/Co-NC modifies the cathode systemThe lag phase was only 2h, indicating that the Ni/Co-NC catalyst can increase the methane production by shortening the methanogenic lag time of the system, and at the end of the experiment, the methane accumulation of the Ni/Co-NC modified cathode system reached 128.8mL, which was 12.7% and 386% greater than the catalyst-free modified cathode system (114.3 mL) and the AD system (26.5 mL), respectively. According to the Gompertz model, the methane production rate of the Ni/Co-NC modified cathode system was 0.608m ³ /(m ³ D), 1.5 and 9.5 times respectively for the non-catalyst modified cathode system and the AD system, demonstrating that the Ni/Co-NC modified cathode contributes to the rapid preparation of methane and the improvement of methane quality.

As can be seen from FIG. 3, after 5 cycles, the cathode surface modified by Ni/Co-NC forms a biofilm with the main bacillus (the bacillus is found to be methanogen consuming hydrogen), and pili are observed among microorganisms, which can be used as a conductive bridge to accelerate electron transfer among cells and between cells and the electrode surface, thereby illustrating that Ni/Co-NC improves the electrode biocompatibility of the electrode and improves the methane yield and quality of the system by promoting the enrichment of methanogen consuming hydrogen.

The above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Moreover, those of skill in the art will appreciate that while some embodiments herein include some features included in other embodiments, not others, combinations of features of different embodiments are meant to be within the scope of the invention and form different embodiments. For example, in the claims above, any of the claimed embodiments may be used in any combination. The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

Claims

A method for improving the yield and quality of methane by a MOFs-derived bimetallic cathode, characterized by comprising the steps of: constructing a single-chamber microbial electrolytic cell comprising an anode and a MOFs derived bimetallic cathode, and coupling the constructed single-chamber microbial electrolytic cell with an anaerobic digestion system to form an MEC-AD system, wherein the anode in the single-chamber microbial electrolytic cell is a carbon brush which is acclimated stably in advance and has the size of 3 x 6cm, and an Ag/AgCl electrode is used as a reference electrode; externally connecting a 10 omega resistor, applying 0.6V external voltage, inoculating sludge into anaerobic granular sludge cultured in a laboratory, controlling the concentration of the anaerobic granular sludge in the inoculated single-chamber microbial electrolysis cell to be 8.4g/L, adding 0.5g of sodium acetate as a carbon source, and reacting at 37 ℃;

the preparation method of the MOFs derived bimetallic cathode comprises the following steps:

1) Synthesis of ZIF-67: with 2-methylimidazole and Co (NO) ₃ ) ₂ ·6H ₂ Dissolving O as a raw material in deionized water respectively to form a first solution A and a second solution B, dropwise adding the second solution B into the first solution A, stirring at room temperature, centrifuging, washing and drying to obtain ZIF-67;

2) Synthesis of Co-NC nanotubes: putting the ZIF-67 obtained in the step 1) into a quartz container, and carbonizing at high temperature under nitrogen atmosphere to obtain Co-NC;

3) Synthesis of Ni/Co-NC catalyst: ultrasonically dispersing the Co-NC obtained in the step 2) into an HCl solution, and stirring, washing and drying to obtain acidified Co-NC; adding acidified Co-NC into a DMF solution, adding phthalocyanine nickel after ultrasonic dispersion, stirring, centrifuging, washing, drying, and finally annealing in a nitrogen atmosphere to obtain a Ni/Co-NC catalyst;

4) Preparing a cathode: mixing the Ni/Co-NC catalyst obtained in the step 3), carbon black, ethanol, deionized water and PTFE emulsion to prepare slurry, quickly coating the slurry on a carbon felt after oscillation, drying and calcining to obtain a Ni/Co-NC modified cathode, namely the MOFs-derived bimetallic cathode.
2. The method according to claim 1, wherein the 2-methylimidazole used in step 1) is reacted with Co (NO) ₃ ) ₂ ·6H ₂ The mass ratio of O is 12.2.
3. The method according to claim 1, wherein the carbonization process in step 2) is performed in a tube furnace by introducing nitrogen, the treatment temperature is 900 ℃, the heating rate is 2 ℃/min, and the carbonization time is 2h.
4. The method as claimed in claim 1, wherein the concentration of the hydrochloric acid solution for acidification in the step 3) is 4M, the acidification time is 12h, the washing solvent is ethanol, the drying temperature is 80 ℃, and the drying time is 12h.
5. The method as claimed in claim 1, wherein the mass ratio of the acidified Co-NC to the nickel phthalocyanine used in the step 3) is 10.
6. The method of claim 1, wherein the size of the carbon felt in step 4) is 4 x 4cm and the surface area is 16cm ² The slurry comprises the following components: 0.025g of Ni/Co-NC catalyst, 0.04g of carbon black, 1080mL of ethanol, 600mL of deionized water and 120 mu L of PTFE.
7. The method according to claim 1, wherein the calcination temperature of step 4) is 360 ℃ and the calcination time is 1h.
8. The method of claim 1, wherein the Ni/Co-NC modified cathode increases methane production of the MEC-AD system by 12.7% and 386% over the anaerobic digestion system alone.