Disclosure of Invention
The invention provides a Fe and Co bimetal doped ZIF-8 derived carbon-oxygen reduction catalyst and a preparation method and application thereof, 2-methylimidazole and zinc nitrate hexahydrate are used as raw materials to synthesize a ZIF-8 carrier precursor, and a hydrothermal method is adopted to synthesize the Fe and Co bimetal Co-doped ZIF-8 derived carbon-oxygen reduction catalyst, so that the problems of large amount of agglomeration and low single metal catalyst loading capacity of the catalyst precursor in the pyrolysis process are solved; the catalyst prepared by the invention has uniform particle size, high catalyst loading, good catalytic activity and stability, and a half-wave potential of 0.81V (vs. RHE) under an acidic condition, and 88.6 percent (the mass activity is only reduced by 11.4 percent and is far lower than the activity reduction (65.6 percent) of commercial Pt/C after a timing current test of 40000 s.
The catalyst of the invention is realized by the following technical scheme:
dissolving 2-methylimidazole in a methanol solution to obtain a solution named as A solution; dissolving zinc nitrate hexahydrate in a methanol solution to obtain a solution named as a solution B; adding the solution B into the solution A under the stirring condition, stirring at room temperature to obtain a white suspension ZIF-8, adding iron (III) acetylacetonate and cobalt (II) acetylacetonate into the suspension, stirring, transferring the mixture into polytetrafluoroethylene for hydrothermal reaction, centrifuging the obtained product, washing the product with ethanol for three times, and performing vacuum drying at 60 ℃; the precursor obtained is denoted as Fe1-x/Cox-ZIF-8(x ═ 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1). Transferring the product into a porcelain boat, and placing the porcelain boat into a tubular furnace for heat treatment to obtain Fe, Co bimetal doped ZIF-8 derived non-noble metal catalyst Fe1-x/Cox-NC(x=0、0.1、0.3、0.5、0.7、0.9、1)。
Preferably, the mixed solution A is prepared by adding 1.314g of 2-methylimidazole into 15mL of methanol, and the mixed solution B is prepared by adding 1.19g of zinc nitrate hexahydrate into 30mL of methanol;
preferably, the stirring time at room temperature after the solution B is added to the solution A is 24 hours;
preferably, the molar ratio of the iron (III) acetylacetonate to the cobalt acetylacetonate is (1-x)/x, wherein the molar ratio of the total amount of iron and cobalt to the zinc in the zinc nitrate hexahydrate is 1/6, i.e., (Fe + Co)/Zn ═ 1/6;
preferably, the heat treatment conditions are as follows: the temperature was raised to 900 ℃ at a rate of 5 ℃ per minute under nitrogen atmosphere and held for 3 h.
The invention also discloses Fe, Co bimetal doped Fe and Co bimetal doped ZIF-8 derived Fe prepared by the preparation method1-x/Cox-NC bimetallic oxygen reduction catalyst Fe1-x/Cox-NC (x ═ 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1), preferably Fe0.1/Co0.9-NC。
The invention also discloses Fe and Co bimetal doped ZIF-8 derived Fe prepared by the preparation method1-x/Cox-NC bimetallic oxygen reduction catalyst Fe1-x/Cox-NC (x ═ 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1) in proton exchange membrane fuel cells.
Compared with the prior art, the invention has the following advantages and effects:
the invention discloses a Fe and Co bimetal doped ZIF-8 derived carbon-oxygen reduction catalyst Fe1-x/Cox-NC and a process for its preparation. The method has low preparation cost and simple process, can be repeatedly operated, and overcomes the problem of agglomeration in the pyrolysis process of the catalyst; the influence of the doping amount of Fe and Co bimetal on the oxygen reduction activity of the catalyst is systematically researched, and the optimal catalyst Fe is obtained0.1/Co0.9the-NC has uniform particle size, high catalyst loading, good catalytic activity and stability, the half-wave potential reaches 0.81V (vs. RHE) under an acidic condition, and the half-wave potential is 88.6% after a timing current test of 40000 s.
Detailed Description
The present invention is described in further detail with reference to the following examples, which are only preferred embodiments of the present invention, but the present invention is not limited by the examples, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be regarded as equivalent substitutions and are included within the scope of the present invention.
The steps of this example are as follows:
dissolving 2-methylimidazole in a methanol solution to obtain a solution named as A solution; dissolving zinc nitrate hexahydrate in a methanol solution to obtain a solution named as a solution B; adding the solution B into the solution A under the stirring condition, stirring at room temperature to obtain a white suspension ZIF-8, adding an iron precursor and a cobalt precursor into the suspension, stirring, transferring the mixture into polytetrafluoroethylene for hydrothermal reaction, centrifuging the obtained product, washing the product with ethanol for three times, and performing vacuum drying at 60 ℃; the precursor obtained is denoted as Fe1-x/Cox-ZIF-8(x ═ 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1). Transferring the product into a porcelain boat, and placing the porcelain boat into a tubular furnace for heat treatment to obtain a non-noble metal catalyst derived from Fe and Co bimetal doped ZIF-8Agent Fe1-x/Cox-NC(x=0、0.1、0.3、0.5、0.7、0.9、1)。
Further, the iron precursor is iron (III) acetylacetonate.
Further, the cobalt precursor is cobalt (II) acetylacetonate.
Further, the mixed solution A is prepared by adding 1.313-1.315 g of 2-methylimidazole into 14.5-15.5 mL of methanol; the mixed solution B is prepared by adding 1.18-1.20 g of zinc nitrate hexahydrate into 29.5-30.5mL of methanol.
Further, the stirring time of the solution B after being added to the solution A at room temperature is 24 hours.
Further, the molar ratio of the added iron (III) acetylacetonate and cobalt (II) acetylacetonate is (1-x)/x, wherein the molar ratio of the total amount of iron and cobalt to the zinc in the zinc nitrate hexahydrate is 1/6, i.e., (Fe + Co)/Zn 1/6.
Further, the heat treatment conditions are as follows: the temperature was raised to 900 ℃ at a rate of 5 ℃ per minute under nitrogen atmosphere and held for 3 h.
Further, the vacuum drying temperature was 60 ℃.
The present invention will be described in further detail with reference to specific examples, but the embodiments of the present invention are not limited thereto, and may be carried out with reference to conventional techniques for process parameters not particularly noted.
Example 1
Preparation of Fe-NC catalyst:
dissolving 1.315g of 2-methylimidazole in 15.5mL of methanol solution to obtain a solution named as solution A; 1.18g of zinc nitrate hexahydrate is dissolved in 30.5mL of methanol solution, and the obtained solution is named as solution B; and then adding the solution B into the solution A under the stirring condition, stirring for 24 hours at room temperature to obtain a white suspension ZIF-8, adding 0.67mmol of iron (III) acetylacetonate and 0mmol of cobalt (II) acetylacetonate, stirring for 1 hour, transferring into polytetrafluoroethylene, carrying out hydrothermal reaction for 4 hours at 120 ℃, centrifuging and washing the obtained product with ethanol for three times, and carrying out vacuum drying at 60 ℃. And transferring the product into a porcelain boat, placing the porcelain boat into a tubular furnace, carrying out heat treatment for 3h at 900 ℃ in a nitrogen atmosphere, controlling the temperature rise rate of nitrogen to be 5 ℃/min, and recording the obtained product as Fe-NC.
Example 2
Fe0.9/Co0.1Preparation of NC catalyst:
1.315g of 2-methylimidazole is dissolved in 14.5mL of methanol solution, and the obtained solution is named as solution A; 1.20g of zinc nitrate hexahydrate is dissolved in 29.5mL of methanol solution, and the obtained solution is named as solution B; and then adding the solution B into the solution A under the stirring condition, stirring for 24h at room temperature to obtain a white suspension ZIF-8, adding 0.6mmol of iron (III) acetylacetonate and 0.07mmol of cobalt (II) acetylacetonate, stirring for 1h, transferring into polytetrafluoroethylene, carrying out hydrothermal reaction at 120 ℃ for 4h, centrifuging and washing the obtained product with ethanol for three times, and carrying out vacuum drying at 60 ℃. Transferring the product into a porcelain boat, placing the porcelain boat into a tubular furnace, carrying out heat treatment for 3h at 900 ℃ in nitrogen atmosphere, controlling the temperature rise rate of nitrogen to be 5 ℃/min, and recording the obtained product as Fe0.9/Co0.1-NC。
Example 3
Fe0.7/Co0.3Preparation of NC catalyst:
1.314g of 2-methylimidazole was dissolved in 15.0mL of a methanol solution, and the resulting solution was named solution A; 1.19g of zinc nitrate hexahydrate is dissolved in 30.0mL of methanol solution, and the obtained solution is named as solution B; and then adding the solution B into the solution A under the stirring condition, stirring for 24h at room temperature to obtain a white suspension ZIF-8, adding 0.47mmol of iron (III) acetylacetonate and 0.2mmol of cobalt (II) acetylacetonate, stirring for 1h, transferring into polytetrafluoroethylene, carrying out hydrothermal reaction at 120 ℃ for 4h, centrifuging and washing the obtained product with ethanol for three times, and carrying out vacuum drying at 60 ℃. Transferring the product into a porcelain boat, placing the porcelain boat into a tubular furnace, carrying out heat treatment for 3h at 900 ℃ in nitrogen atmosphere, controlling the temperature rise rate of nitrogen to be 5 ℃/min, and recording the obtained product as Fe0.7/Co0.3-NC。
Example 4
Fe0.5/Co0.5Preparation of NC catalyst:
1.313g of 2-methylimidazole was dissolvedIn 15.0mL of methanol solution, the obtained solution is named solution A; 1.20g of zinc nitrate hexahydrate is dissolved in 30.5mL of methanol solution, and the obtained solution is named as solution B; and then adding the solution B into the solution A under the stirring condition, stirring for 24h at room temperature to obtain a white suspension ZIF-8, adding 0.33mmol of iron (III) acetylacetonate and 0.33mmol of cobalt (II) acetylacetonate, stirring for 1h, transferring into polytetrafluoroethylene, carrying out hydrothermal reaction for 4h at 120 ℃, centrifuging and washing the obtained product with ethanol for three times, and carrying out vacuum drying at 60 ℃. Transferring the product into a porcelain boat, placing the porcelain boat into a tube furnace, carrying out heat treatment for 3h at 800 ℃ in a nitrogen atmosphere, controlling the temperature rise rate of nitrogen to be 6 ℃/min, and recording the obtained product as Fe0.5/Co0.5-NC。
Example 5
Fe0.3/Co0.7Preparation of NC catalyst:
1.314g of 2-methylimidazole was dissolved in 15.0mL of a methanol solution, and the resulting solution was named solution A; 1.19g of zinc nitrate hexahydrate is dissolved in 30.0mL of methanol solution, and the obtained solution is named as solution B; and then adding the solution B into the solution A under the stirring condition, stirring for 24h at room temperature to obtain a white suspension ZIF-8, adding 0.2mmol of iron (III) acetylacetonate and 0.47mmol of cobalt (II) acetylacetonate, stirring for 1h, transferring into polytetrafluoroethylene, carrying out hydrothermal reaction at 120 ℃ for 4h, centrifuging and washing the obtained product with ethanol for three times, and carrying out vacuum drying at 60 ℃. Transferring the product into a porcelain boat, placing the porcelain boat into a tubular furnace, carrying out heat treatment for 3h at 900 ℃ in nitrogen atmosphere, controlling the temperature rise rate of nitrogen to be 5 ℃/min, and recording the obtained product as Fe0.3/Co0.7-NC。
Example 6
Fe0.1/Co0.9Preparation of NC catalyst:
1.314g of 2-methylimidazole was dissolved in 15.0mL of a methanol solution, and the resulting solution was named solution A; 1.19g of zinc nitrate hexahydrate is dissolved in 30.0mL of methanol solution, and the obtained solution is named as solution B; adding the solution B into the solution A under stirring, stirring at room temperature for 24 hr to obtain white suspension ZIF-8, and adding 0.07mmol of iron (III) acetylacetonate and 0.6mmol of cobalt (II) acetylacetonate, stirring for 1h, hydrothermal reaction in polytetrafluoroethylene at 120 ℃ for 4h, centrifuging, washing with ethanol for three times, and vacuum drying at 60 ℃. Transferring the product into a porcelain boat, placing the porcelain boat into a tubular furnace, carrying out heat treatment for 3h at 900 ℃ in nitrogen atmosphere, controlling the temperature rise rate of nitrogen to be 5 ℃/min, and recording the obtained product as Fe0.1/Co0.9-NC。
Example 7
Preparation of Co-NC catalyst:
1.313g of 2-methylimidazole is dissolved in 14.5mL of methanol solution, and the obtained solution is named as solution A; 1.18g of zinc nitrate hexahydrate is dissolved in 30.0mL of methanol solution, and the obtained solution is named as solution B; and then adding the solution B into the solution A under the stirring condition, stirring for 24 hours at room temperature to obtain a white suspension ZIF-8, adding 0mmol of iron (III) acetylacetonate and 0.67mmol of cobalt (II) acetylacetonate, stirring for 1 hour, transferring into polytetrafluoroethylene, carrying out hydrothermal reaction for 4 hours at 120 ℃, centrifuging and washing the obtained product with ethanol for three times, and carrying out vacuum drying at 60 ℃. And transferring the product into a porcelain boat, placing the porcelain boat into a tubular furnace, carrying out heat treatment for 1h at 900 ℃ in a nitrogen atmosphere, controlling the temperature rise rate of nitrogen to be 5 ℃/min, and recording the obtained product as Co-NC.
Example 8
Characterization of the catalyst:
as can be seen from the SEM images of FIGS. 2(a-c), the synthesized precursors containing different metals, Fe-ZIF-8, Co-ZIF-8 and Fe0.1/Co0.9the-ZIF-8 has a complete rhombic dodecahedron structure, and after 3 hours of high-temperature 900 ℃ heat treatment in argon atmosphere, Fe-ZIF-8, Co-ZIF-8 and Fe0.1/Co0.9Conversion of-ZIF-8 to Fe-NC, Co-NC and Fe0.1/Co0.9NC while keeping Fe-ZIF-8, Co-ZIF-8, Fe intact0.1/Co0.9Morphology of ZIF-8 precursor, as shown in FIG. 2 (d-f). From FIG. 2g, Fe0.1/Co0.9The surface of the-NC catalyst is free from any agglomerated metal particles, clusters and the like, the morphology is very regular, and the four elements of Fe, Co, C and N in the catalyst are highly dispersed (as shown in figure 2i), and figure 2h also shows that Fe, C and N are dispersed in the catalyst,The distribution of two metals of Co is very uniform, and the metal content is high. According to Fe-ZIF-8, Co-ZIF-8 and Fe0.1/Co0.9XRD (FIG. 3a) of the precursor of ZIF-8 shows that the XRD peak shapes of the three are similar and the peak positions are basically the same, and comparing the XRD patterns of the ZIF-8 shows that Fe and Co metals are doped into the cavity of the ZIF-8 and the crystal structure of the ZIF-8 is not changed; according to Fe-NC, Co-NC and Fe0.1/Co0.9XRD (FIG. 3b) of NC catalyst shows that only two distinct carbon peaks, similar to NC after ZIF-8 carbonization, indicate that metal-doped carbon-oxygen reduction catalyst is successfully obtained, and no distinct metal particles and simple substances exist in the catalyst, which is consistent with TEM results. Fig. 4a is a Raman analysis of the catalyst, D for defect level and G for graphitization level, the ratio of which illustrates defect versus graphitization. According to the D/G value, the three catalysts Fe-NC, Co-NC and Fe0.1/Co0.9in-NC, Fe0.1/Co0.9Minimum D/G of-NC catalyst, thus indicating Fe0.1/Co0.9The NC catalyst has less defects and higher graphitization degree. The high graphitization degree can improve the oxidation corrosion resistance of the carbon carrier in the catalyst, so that Fe0.1/Co0.9The higher the stability of the NC catalyst. FIG. 4b is catalyst Fe0.1/Co0.9XPS analysis of NC, which indicates Fe0.1/Co0.9Five elements of C, N, O, Fe and Co exist in the NC catalyst, and the chemical states of the elements are different, wherein C, N, O is 1s, and the metals of Fe and Co are 2 p. Table 1 shows the analysis of the element content (ICP-MS) of the catalyst, and the higher the content of Fe and Co elements, the higher the metal loading of the catalyst is, and the better the catalytic activity is. According to the value, Fe0.1/Co0.9The total metal content of the-NC catalyst is 1.34%, and the metal content of the-NC catalyst is higher than that of the single metal catalysts Fe-NC (0.54%) and Co-NC (0.23%), which indicates that the metal loading of the catalyst is far larger than that of other single metals, and indicates that the catalyst prepared by the method is beneficial to improving the metal loading of the catalyst.
In the drawings of the invention:
FIG. 1 is Fe1-x/Cox-NC bimetallic oxygen reductionSchematic synthesis of the catalyst.
FIG. 2 a) SEM picture of Fe-ZIF-8; b) SEM picture of Co-ZIF-8; c) fe0.1/Co0.9SEM picture of ZIF-8; d) SEM picture of Fe-NC; e) SEM image of Co-NC; f) fe0.1/Co0.9-SEM picture of NC; g. h) are each Fe0.1/Co0.9-TEM and high angular ring dark field images of the NC; i) fe0.1/Co0.9Distribution diagram of Fe, Co, C, N elements of NC.
FIG. 3a shows Fe-ZIF-8, Co-ZIF-8 and Fe0.1/Co0.9-XRD pattern of ZIF-8 precursor;
FIG. 3b shows Fe-NC, Co-NC and Fe0.1/Co0.9-XRD pattern of NC catalyst.
FIG. 4a shows Fe-NC, Co-NC and Fe0.1/Co0.9-a raman map of the NC;
FIG. 4b is Fe0.1/Co0.9XPS plots of NC.
TABLE 1Fe-NC, Co-NC, Fe0.1/Co0.9ICP-MS of-NC catalyst
Example 9
Electrochemical oxygen Reduction (RDE) test:
5mg of Fe are weighed1-x/CoxDispersing NC catalyst and 20% commercial Pt/C catalyst into 1mL mixed solution of ethanol and Nafion (2.5 wt%), ultrasonically dispersing uniformly, transferring 20 muL (5 ul Pt/C) onto the surface of a glassy carbon electrode, and airing at room temperature to obtain the catalyst electrode, wherein the loading capacity of the catalyst electrode is 0.510mg/cm2. Fe obtained by using the Pine electrochemical workstation of the United states1-x/CoxNC samples and Pt/C catalysts were tested for oxygen reduction activity. The oxygen reduction scanning rate is 10mV/s, and the electrolyte is O2And N2Saturated 0.1M HClO4An aqueous solution, the potential window is 1.0-0V (vs. RHE). With the resultant Fe1-x/Coxthe-NC catalyst and Pt/C catalyst electrodes are working electrodes, the Pt net is a counter electrode, the Ag/AgCl is a reference electrode,separate testing of different catalysts at O2And N2Saturated 0.1M HClO4Oxygen reduction activity of aqueous solution, wherein in N2The test in (1) was to subtract out the other background of the catalyst.
Example 10
Rotating Disk Electrode (RRDE) test:
5mg of Fe are weighed0.1/Co0.9Dispersing NC catalyst and 20% commercial Pt/C catalyst into 1mL mixed solution of ethanol and Nafion (2.5 wt%), ultrasonically dispersing uniformly, transferring 20 muL (5 ul Pt/C) onto the surface of a glassy carbon electrode, and airing at room temperature to obtain the catalyst electrode, wherein the loading capacity of the catalyst electrode is 0.510mg/cm2. Fe obtained by using the Pine electrochemical workstation of the United states0.1/Co0.9The NC samples and the Pt/C catalyst were subjected to the RRDE test. The oxygen reduction scanning rate is 10mV/s, and the electrolyte is O2And N2Saturated 0.1M HClO4An aqueous solution, a potential window of 1.0 to 0V (vs. RHE), and an applied ring voltage of 1.2V (vs. RHE). With the resultant Fe0.1/Co0.9The electrodes of the-NC catalyst and the Pt/C catalyst are working electrodes, the Pt net is a counter electrode, the Ag/AgCl is a reference electrode, and different catalysts are respectively tested in O2And N2Saturated 0.1M HClO4Oxygen reduction activity of aqueous solution, wherein in N2The test in (1) was to subtract out the other background of the catalyst.
Example 11
And (3) stability testing:
5mg of Fe are weighed0.1/Co0.9Dispersing NC catalyst and 20% commercial Pt/C catalyst into 1mL mixed solution of ethanol and Nafion (2.5 wt%), ultrasonically dispersing uniformly, transferring 20 muL (5 ul Pt/C) onto the surface of a glassy carbon electrode, and airing at room temperature to obtain the catalyst electrode, wherein the loading capacity of the catalyst electrode is 0.510mg/cm2. Fe obtained by using the Pine electrochemical workstation of the United states0.1/Co0.9NC samples and Pt/C catalysts were subjected to stability tests. Before and after 5000 circles of test, the oxygen reduction activity of the catalyst is respectively tested, wherein the oxygen reduction scanning rate is 10mV/s, and the electrolyte is O2And N2Saturated 0.1M HClO4An aqueous solution with a potential window of 1.0-0V (vs. RHE); the scanning speed of 5000-circle potential cycle test is 100mV/s, and the electrolyte is O20.1M HClO of4The potential window of the aqueous solution is 1.0-0.6V (vs. RHE). With the resultant Fe0.1/Co0.9the-NC catalyst and Pt/C catalyst electrodes are working electrodes, the Pt net is a counter electrode, and the Ag/AgCl is a reference electrode.
Example 12
Testing the timing current:
5mg of Fe are weighed0.1/Co0.9Dispersing NC catalyst and 20% commercial Pt/C catalyst into 1mL mixed solution of ethanol and Nafion (2.5 wt%), ultrasonically dispersing uniformly, transferring 20 muL (5 ul Pt/C) onto the surface of a glassy carbon electrode, and airing at room temperature to obtain the catalyst electrode, wherein the loading capacity of the catalyst electrode is 0.510mg/cm2. Fe obtained by using the Pine electrochemical workstation of the United states0.1/Co0.9The NC sample and the Pt/C catalyst were subjected to chronoamperometric test in which the test voltage was fixed at 0.7V (vs. RHE), the number of revolutions was 400rpm, the test time was 40000s, and the electrolyte was O2Saturated 0.1M HClO4Aqueous solution of Fe0.1/Co0.9the-NC catalyst and Pt/C catalyst electrodes are working electrodes, the Pt net is a counter electrode, and the Ag/AgCl is a reference electrode.
FIG. 5a is a graph of various bis-non-noble metal oxygen reduction catalysts prepared at 0.1M HClO4Oxygen reduction profile in solution; FIG. 5b shows the best Fe0.1/Co0.9NC bimetallic oxygen reduction catalyst and commercial Pt/C at 0.1M HClO4Oxygen reduction profile in solution.
FIG. 6 shows the best Fe0.1/Co0.9NC bimetallic oxygen reduction catalyst and commercial Pt/C catalyst at 0.1M HClO4Hydrogen peroxide (H) in solution2O2) Yield and electron transfer number.
FIG. 7a is Fe0.1/Co0.9-oxygen reduction profiles before and after 5000 cycles for NC oxygen reduction catalysts and commercial Pt/C catalysts; FIG. 7b is Fe0.1/Co0.9Current-time for NC oxygen reduction catalyst and for commercial Pt/C catalyst(i-t) diagram.
It should be understood that the above detailed description of the embodiments of the present invention with reference to the preferred embodiments is illustrative and not restrictive, and it should not be considered that the detailed description of the embodiments of the present invention is limited thereto, and it should be understood that those skilled in the art to which the present invention pertains that modifications may be made to the embodiments described in the embodiments or that equivalents may be substituted for some of the features thereof without departing from the spirit of the present invention and the scope of the patent protection is defined by the claims to be filed with the present invention.
The above examples of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.