Preparation process of modified porous carbon material catalyst

Abstract

The invention discloses a preparation process of a modified porous carbon material catalyst. The preparation process comprises the following steps: (1) mixing and calcining a biomass precursor and a template agent to prepare graded porous carbon; (2) low-frequency plasma pretreatment and high-frequency plasma fluorination modification are adopted; (3) introducing the pulse plasma into a nitrogen doping site; (4) spraying ionic liquid and activating H2 plasma to form a B / F co-doped layer; and (5) loading alloy nanoparticles such as PtRu through pulse electrodeposition. According to the obtained catalyst, biomass derived porous carbon serves as a carrier, a fluorine / nitrogen co-doped active layer is constructed on the surface of the carrier through multi-frequency plasma synergistic modification and ionic liquid auxiliary modification, superfine precious metal nanoparticles are loaded, the hydrogen evolution overpotential of the catalyst is smaller than or equal to 28 mV under the current density of 10 mA / cm < 2 >, the activity attenuation is smaller than 5% after 1000 times of circulation, and the catalyst has a good catalytic activity. The water electrolysis hydrogen production device is suitable for a large-scale water electrolysis hydrogen production device.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hydrogen production by water electrolysis, and particularly relates to a preparation process of a modified porous carbon material catalyst, in particular to a catalyst of a modified porous carbon material loaded with metal nanoparticles by multi-frequency plasma and a preparation process thereof, which is suitable for hydrogen evolution reaction (HER) in an alkaline / acidic electrolytic cell. BACKGROUND

[0002] Current hydrogen production catalysts by water electrolysis still rely heavily on noble metals (such as Pt / C), and their high cost restricts their large-scale application. Although non-noble metal catalysts have low cost, they have problems such as insufficient active sites and poor stability. Porous carbon materials have become ideal carriers due to their high specific surface area and electrical conductivity, but traditional chemical modification methods are difficult to precisely control the surface chemical properties, and metal nanoparticles are prone to agglomeration. Plasma technology can efficiently introduce active sites through physical-chemical interaction, but single-frequency plasma treatment has defects such as uneven modification and insufficient depth.

[0003] Therefore, it is of great significance to develop a multi-mode plasma modification process to realize the controllable construction of active sites on the surface of porous carbon and the uniform anchoring of metal nanoparticles, which can promote the industrialization of low-cost and efficient hydrogen production catalysts. SUMMARY

[0004] Therefore, the present application proposes a preparation process of a modified porous carbon material catalyst, which realizes the simultaneous improvement of catalyst activity and stability through multi-frequency plasma modification in combination with ionic liquid modification and pulse reduction technology.

[0005] The specific technical solution and process are as follows:

[0006] (1) Mix the low-ash biomass precursor and the template agent at a mass ratio of 1.5:1 to 4:1, calcine under an inert atmosphere at 800-1000℃, and obtain a hierarchical porous carbon carrier after acid washing;

[0007] (2) After pre-treatment by 10-50kHz low-frequency plasma, perform fluorination treatment by 100-500MHz high-frequency plasma to form a surface fluorination layer;

[0008] (3) Construct nitrogen-doped sites in an NH3 / H2 atmosphere by 1-10kHz pulse plasma;

[0009] (4) After spraying a 0.1-1.0mol / L fluorine-containing ionic liquid solution, form a B / F co-doped interface layer by 80-120W H2 plasma activation;

[0010] (5) Adopt t on / t off=5-20ms / 30-60ms pulse electrodeposition method load 2-5nm noble metal nanoparticles, ultimately obtain catalyst.

[0011] Preferably, the biomass precursor in (1) is coconut shell powder, bamboo charcoal or lignin with ash content <1%, crushed to 200-300 mesh. Preferably, coconut shell (cellulose content >60%) produced in tropical regions is selected; bamboo charcoal: requires pre-carbonization treatment (300℃ anaerobic calcination for 2h), removes volatile matter, and improves template penetration; lignin: choose the by-product of kraft pulping, needs to be washed with 0.1M HCl to pH=6.5 to avoid residual alkali affecting the pore structure. The template is ZnCl2 or KOH, the calcination heating rate is 3-5℃ / min, and the holding time is 2-4h. In the template ratio, ZnCl2 activation: mass ratio of 1.5:1 to 2.5:1, less than 1.5:1, the pore size distribution is large (>20nm), and more than 2.5:1, it is easy to cause micropore collapse; KOH activation: mass ratio of 3:1 to 4:1, the activation temperature needs to be accurately controlled within ±10℃ (optimal 800±10℃), to avoid the volatilization of KOH leading to the decrease of specific surface area.

[0012] Preferably, in the optimization of the plasma modification process in (2), low-frequency pretreatment (10-50kHz): power gradient: increase by 20W every 5 minutes (such as 100W→120W→140W), gradually expand the carbon layer spacing (d002 increases from 0.34nm to 0.38nm through XRD detection); gas selection: adding 5% H2 in Ar can generate more defect sites (H free radical etching effect), but H2 ratio >10% will cause excessive damage to the carbon skeleton. High-frequency fluorination (100-500MHz): CF4 / Ar mixing ratio: 1:3 to 1:5 (volume ratio), CF4 flow rate is too high (>30sccm) will form inert CF x Polymer layer, hinder active site exposure; temperature control: the reaction cavity wall needs to be water-cooled to 25±2℃, to avoid local overheating (>80℃) leading to the desorption of fluorine element.

[0013] Preferably, the pulse plasma duty cycle in (3) is 10%-50%, the power is 150-300W, and the NH3 / H2 flow ratio is 1:1 to 1:3.

[0014] Preferably, the ionic liquid in (4) is fluorine-containing imidazole (such as [EMIM][PF6]) or pyrrolidine (such as [Py 14 ][TFSI]). H2 plasma activation pressure is 10-30Pa, and the treatment time is 5-15min.

[0015] Preferably, the metal nanoparticle anchoring in (5) is pulse electrodeposition: pulse waveform: square wave pulse (rise / fall time <1μs), ton / t off = 10ms / 50ms, metal ion diffusion is sufficient and the dendrite growth is inhibited; electrolyte additive: 5mM thiourea is added as a crystal face inhibitor to make the PtRu alloy preferentially expose the (111) crystal face. The metal nanoparticles are Pt-Co, Pt-Ni or Ru-Ir binary alloys, and the particle size is controlled at 2-5nm.

[0016] The beneficial effects of the present application are:

[0017] The present application adopts a three-stage plasma modification process of "low-frequency pretreatment-high-frequency fluorination-pulse nitridation": through multi-frequency plasma synergistic modification, combined with ionic liquid interface modification, the synergistic optimization of carbon carrier electronic structure regulation and metal particle anchoring is realized. And the ionic liquid interface modification: through ionic liquid spraying and H2 plasma activation, a uniform B / F co-doped layer is formed, further optimizing the surface structure and catalytic performance of the catalyst.

[0018] Compared with the prior art, the present application has the following advantages:

[0019] 1. Activity improvement: the fluorine / nitrogen co-doped surface constructed by multi-frequency plasma makes the intrinsic activity of carbon material increase by 3 times (compared with unmodified carbon), combined with ultrafine PtRu alloy, the overpotential is only 28mV (under alkaline conditions) at 10mA / cm 2 2. Stability optimization: the fluorination layer inhibits carbon corrosion, and the activity attenuation is less than 5% after 1000 cycles, which is better than the commercial Pt / C (attenuation 15%).

[0020] 2. Stability optimization: the fluorination layer inhibits carbon corrosion, and the activity attenuation is less than 5% after 1000 cycles, which is better than the commercial Pt / C (attenuation 15%).

[0021] 3. Cost advantage: the amount of noble metal is reduced by 60%, and mass production can be realized by adjusting the plasma parameters. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below in combination with specific examples.

[0023] Example 1:

[0024] (1) Carbon carrier preparation: 200 mesh coconut powder (ash content 0.8%) is mixed with ZnCl2 at a ratio of 1.5:1, heated to 800℃ at 3℃ / min and calcined for 2h

[0025] (2) Plasma modification: low-frequency pretreatment: 10kHz, 100W, Ar+5% H2, 10min (power gradient: 100→120W) high-frequency fluorination: 100MHz, 200W, CF4 / Ar=1:5, 15min (water cooling 25℃)

[0026] (3) Nitrogen doping: 1 kHz pulse, 150 W, NH3 / H2=1:1, duty cycle 10%, 15 min

[0027] (4) B / F co-doping: 0.1 mol / L [EMIM][PF6] spray, 80 W H2plasma activation for 10 min

[0028] (5) Metal loading: PtRu alloy (Pt:Ru=3:1), t on / t off = 5 ms / 60 ms, 10 mA / cm 2 , deposition amount 3 C / cm 2 (2) Multi-frequency plasma synergistic modification

[0029] Example 2:

[0030] (1) Carbon carrier preparation: 250 mesh pre-carbonized bamboo charcoal mixed with KOH at 3.5:1, heated at 4 ℃ / min to 900 ℃ for calcination for 3 h

[0031] (2) Plasma modification: low-frequency pretreatment: 30 kHz, 150 W, Ar+8% H2, 15 min (power gradient: 120→150→180 W); high-frequency fluorination: 300 MHz, 250 W, CHF3 / Ar=1:4, 20 min (water cooling at 25 ℃)

[0032] (3) Nitrogen doping: 5 kHz pulse, 220 W, NH3 / H2=1:2, duty cycle 30%, 20 min

[0033] (4) B / F co-doping: 0.5 mol / L [BMIM][BF4] spray, 100 W H2plasma activation for 10 min

[0034] (5) Metal loading: PtCo alloy (Pt:Co=4:1), t on / t off = 10 ms / 50 ms, 20 mA / cm 2 , deposition amount 5 C / cm 2

[0035] Example 3:

[0036] (1) Carbon carrier preparation: 300 mesh acid-washed lignin mixed with ZnCl2 at 4:1, heated at 5 ℃ / min to 1000 ℃ for calcination for 4 h

[0037] (2) Plasma modification: low-frequency pretreatment: 50 kHz, 200 W, Ar+10% H2, 20 min; high-frequency fluorination: 500 MHz, 300 W, CF4 / Ar=1:3, 25 min

[0038] (3) Nitrogen doping: 10 kHz pulse, 300 W, NH3 / H2 = 1:3, duty cycle 50%, 25 min

[0039] (4) B / F co-doping: 1.0 mol / L [Py 14 ][TFSI] spray, 120 W H2 plasma activation for 15 min

[0040] (5) Metal loading: RuIr alloy (Ru:Ir = 1:1), t on / t off = 20 ms / 30 ms, 30 mA / cm 2 , deposition amount 6 C / cm 2

[0041] Comparative Example 1 (without ionic liquid modification):

[0042] Compared with Example 1, steps (2)-(4) were omitted, and step (5) metal loading was directly performed, with the same PtRu alloy loading amount (4.3 wt%).

[0043] Comparative Example 2 (traditional chemical reduction method):

[0044] Compared with Example 1, step (5) therein was replaced by reducing the metal precursor with NaBH4.

[0045] Performance test:

[0046] 1. BET specific surface area test

[0047] Test standard: ISO 9277:2010 (gas adsorption method), instrument model: Micromeritics ASAP 2460; test procedure: sample pretreatment: vacuum degassing at 200°C for 6 hours to remove surface adsorbates; N2 adsorption-desorption test at liquid nitrogen temperature (77K); specific surface area calculated by BET model (relative pressure P / P0 = 0.05-0.30 interval); pore size distribution (micropore / mesopore ratio) analyzed by NLDFT model. Data verification: average value of 3 parallel tests (error ± 3%); instrument calibrated by comparison standard sample (NIST SRM 1898). The experimental results are shown in Table 1.

[0048] 2. Surface element content (fluorine / nitrogen) test

[0049] Test standard: ISO 15472:2010 (X-ray photoelectron spectroscopy, XPS), instrument model: Thermo Scientific K-Alpha+, test parameters: excitation source: Al K alpha ray (1486.6 eV); analysis area: 500 pm beam spot; binding energy calibration: internal standard with C1s (284.8 eV). Quantitative analysis: Fluorine content: integral F1s peak (688-690 eV) area, sensitivity factor correction; Nitrogen content: peak fitting N1s spectrum (pyridine-N 398.4 eV, graphitic-N 401.1 eV). Experimental results are shown in Table 1.

[0050] 3. Metal nanoparticle characterization

[0051] Particle size statistics: instrument: JEOL JEM-2100F TEM; method: take >5 pictures of different areas, measure 300 particle diameters, Gaussian fitting to get average particle size ± standard deviation (e.g. 3.2 ± 0.8 nm). Experimental results are shown in Table 1.

[0052] 4. Loading determination: ICP-OES (PerkinElmer Avio 500): sample digestion: aqua regia (HC1:HNO3=3:1) microwave digestion; detection of Pt (214.423 nm) and Ru (240.272 nm) characteristic lines; mass percentage calculation by standard curve method. Experimental results are shown in Table 1.

[0053] 5. Hydrogen evolution overpotential (η 10 ) test

[0054] Test standard: IEC 62607-3-1:2020, test system: electrochemical workstation: Bio-Logic VMP3; three-electrode system: working electrode (catalyst-coated glassy carbon electrode), counter electrode (Pt mesh), reference electrode (Hg / HgO, 1 M KOH). Test procedure: activation: 20 cycles of cyclic scanning in the range of -0.8 ~ 0 V (vs. RHE) (scan rate 50 mV / s); linear sweep voltammetry (LSV): scan rate 2 mV / s, iR compensation (85%);

[0055] Overpotential calculation: take the potential corresponding to a current density of 10 mA / cm 2 , and the theoretical potential (0 V vs. RHE). Quality control: repeat the test 5 times for each sample, and exclude data with deviation >5%; use commercial Pt / C (20 wt%, Johnson Matthey) as a reference. Experimental results are shown in Table 2.

[0056] 6. Tafel slope test

[0057] Data processing: extract Tafel region (usually 20-100 mA / cm 2 ) from LSV curves; fit equation: η = a + b log |j|, where b is Tafel slope; require correlation coefficient R 2 > 0.995. Mechanistic correlation: slope 30-40 mV / dec indicates Heyrovsky step (H* + H2O + e - → H2 + OH-) is rate determining; compare to commercial Pt / C (30 mV / dec) to verify reaction path consistency. Experimental results are shown in Table 2.

[0058] 7. Cycle stability test

[0059] Accelerated aging test: cycling condition: -0.2 ~ 0.1 V (vs. RHE), scan rate 100 mV / s; LSV test (2 mV / s) every 200 cycles; decay rate calculation: Δη 10 = (η 10 , 1000 - η 10 , initial) / η 10 , initial x 100%. Experimental results are shown in Table 2.

[0060] 8. Electrochemical active surface area (ECSA) test

[0061] Hydrogen adsorption / desorption method: scan -0.2 ~ 0.1 V (vs. RHE) in 0.5 M H2SO4 saturated with N2; integrate hydrogen desorption peak charge (assuming 210 μC / cm 2 corresponds to monolayer adsorption); calculation equation: ECSA = Q H / (210 x Pt loading mass). Experimental results are shown in Table 2.

[0062] Table 1. Physical-chemical property characterization of catalysts

[0063]

[0064] Table 2. Electrochemical performance test (1 M KOH, 25 °C)

[0065]

[0066] Data analysis:

[0067] Table 1 Physical-chemical property characterization:

[0068] Example 1: with higher specific surface area 1820 m 2 / g, fluorine content 8.7 at%, nitrogen content 4.2 at%, small and uniform metal particle size (3.2±0.8 nm), moderate metal loading (4.5 wt%), which together provide a basis for good catalytic performance. Example 2: Specific surface area slightly higher (1890 m 2 / g), fluorine content and nitrogen content slightly higher than Example 1, but metal particle size smaller (2.8±0.6 nm), and loading lower (4.1 wt%), to some extent, by optimizing the precursor and metal loading, the cost is reduced while the good physical and chemical properties are maintained. Example 3: Specific surface area 1750 m 2 / g, fluorine content and nitrogen content moderate, metal particle size and loading similar to Example 1, and the physical and chemical properties of the catalyst are good. Comparative Example 1: No ionic liquid modification was performed, resulting in severe metal particle agglomeration, large particle size (5.1±1.2 nm), and no fluorine and nitrogen doping, which makes the catalytic performance poor. Comparative Example 2: The traditional chemical reduction method was used, and the metal particle size distribution was uneven, and the active area was small, indicating that this method is difficult to achieve uniform dispersion and effective loading of metal nanoparticles.

[0069] Table 2 Electrochemical performance test:

[0070] Example 1: In 1M KOH electrolyte, η 10 31 mV, Tafel slope 35 mV / dec, η 10 attenuation rate 5.2% after 1000 cycles, electrochemical active area 79.3 m 2 / g pt

[0071] Example 2: The hydrogen evolution overpotential (η 2 ) at 10 mA / cm 10 is only 28 mV, Tafel slope 32 mV / dec, η 10 attenuation rate as low as 4.8% after 1000 cycles, electrochemical active area larger (85.6 m 2 / g pt ), showing excellent catalytic activity and stability.

[0072] Example 3: η 10 30 mV, Tafel slope 33 mV / dec, η 10 attenuation rate only 4.5% after 1000 cycles, electrochemical active area 82.1 m 2 / g pt , and also shows good performance in highly corrosive electrolyte.

[0073] Commercial Pt / C: As a comparison, its η 1035 mV, Tafel slope 30 mV / dec, but after 1000 cycles, η 10 attenuation rate up to 15.0%, electrochemical active area 72.4 m 2 / g pt , which shows that the catalyst of the application has obvious advantages in stability. Comparative Example 1: due to metal particle agglomeration and lack of doping, η 10 up to 58 mV, Tafel slope 67 mV / dec, after 1000 cycles, η 10 attenuation rate 22.3%, electrochemical active area 41.2 m 2 / g pt , the performance is far lower than that of the examples. Comparative Example 2: using the traditional reduction method, η 10 41 mV, Tafel slope 48 mV / dec, after 1000 cycles, η 10 attenuation rate 12.7%, electrochemical active area 63.5 m 2 / g pt , the performance is also not as good as that of the catalyst of the application. Through the three groups of examples and comparative experiments, the combined advantages of multi-frequency plasma synergistic modification and pulse electrodeposition process are fully proved.

[0074] The defects on the surface of carbon materials are generated by radio frequency plasma, which provides active sites for subsequent fluorination and nitrogen doping, helps to improve the intrinsic activity of carbon materials, and gradually expands the carbon layer spacing, which is beneficial to the loading and dispersion of metal nanoparticles. Microwave plasma can uniformly combine fluorine atoms with the carbon surface to form a fluorinated layer. The fluorinated layer not only can improve the surface energy of carbon materials and enhance the interaction with metal nanoparticles, but also can inhibit the corrosion of carbon materials during water electrolysis, thereby improving the stability of the catalyst. The introduction of fluorine elements can also change the electronic structure of carbon materials, further improving their catalytic activity. Pulsed plasma introduces nitrogen doping sites: pulsed plasma can introduce nitrogen doping sites on the surface of carbon materials to form pyridine-N active sites. The electronegativity of nitrogen is different from that of carbon, and its doping can adjust the electronic structure of carbon materials, increase the electron density, and thus improve the ability of carbon materials to adsorb and desorb hydrogen, and enhance the catalytic activity. After the ion liquid is sprayed and activated by H2 plasma, a B / F co-doped layer can be formed on the surface of carbon materials. This co-doped layer can further optimize the surface chemical properties of carbon materials, enhance the interaction between metal and support, improve the dispersion and stability of metal nanoparticles on the surface of carbon materials, and prevent metal particles from agglomerating during the reaction, thereby maintaining high catalytic activity. Pulsed electrodeposition method can precisely control the size and dispersion of metal nanoparticles. By precisely controlling the pulse parameters, small and uniformly distributed noble metal nanoparticles can be obtained. Smaller particle size can increase the number of active sites of metal nanoparticles and improve the catalytic activity; uniform dispersion can avoid particle agglomeration, fully exert the catalytic effect of each particle, and also help to improve the stability of the catalyst. Biomass-derived porous carbon is used as a carrier, which is widely available and low-cost, reducing the overall cost of the catalyst. At the same time, by optimizing the treatment of biomass precursors and the ratio of templates, porous carbon materials with high specific surface area and appropriate pore size distribution can be prepared, providing a material basis for high performance of the catalyst.

[0075] It should be understood by those of ordinary skill in the art that the above discussion of any embodiment is merely exemplary and is not intended to suggest that the scope of the present application is limited to these examples; under the idea of the present application, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other changes of different aspects of the present application as described above. In order to be brief, they are not provided in detail.

Claims

1. A process for preparing a modified porous carbon material catalyst, characterized in that: The following steps are involved: (1) A low-ash biomass precursor and a template are mixed in a mass ratio of 1.5 to 4:1, calcined at 800-1000°C in an inert atmosphere, and acid-washed to obtain a hierarchical porous carbon support; (2) After pretreatment with a 10-50 kHz low-frequency plasma, a 100-500 MHz high-frequency plasma is used for fluorination treatment to form a surface fluorination layer; (3) constructing nitrogen-doped sites in an NH3 / H2 atmosphere by 1-10 kHz pulsed plasma; (4) spraying a 0.1-1.0 mol / L fluorine-containing ionic liquid solution and then activating it with 80-120 W H2 plasma to form a B / F co-doped interface layer; (5) Using t on / t off =5-20ms / 30-60ms pulse electrodeposition method to load 2-5nm noble metal nanoparticles and finally obtain the catalyst.

2. The preparation process of a modified porous carbon material catalyst according to claim 1, characterized in that: The biomass precursor in (1) is coconut shell powder, bamboo charcoal or lignin with an ash content of less than 1%; the template is ZnCl2 or KOH, the calcination heating rate is 3-5°C / min, and the holding time is 2-4h.

3. The process for preparing a modified porous carbon material catalyst according to claim 1, characterized in that: The low-frequency plasma pretreatment power in (2) is 100-200W, using Ar or a mixed gas containing ≤10% H2; the fluorination treatment power is 200-300W, using a CF4 / Ar or CHF3 / Ar mixed gas with a volume ratio of 1:3 to 1:

5.

4. The process for preparing a modified porous carbon material catalyst according to claim 1, characterized in that: The pulse plasma described in (3) has a duty cycle of 10% to 50%, a power of 150-300W, and an NH3 / H2 flow ratio of 1:1 to 1:

3.

5. The process for preparing a modified porous carbon material catalyst according to claim 1, characterized in that: The fluorine-containing ionic liquid in (4) is an ethanol solution of [BMIM][BF4] or [EMIM][PF6]; the H2 plasma activation pressure is 10-30 Pa, and the treatment time is 5-15 min.

6. The process for preparing a modified porous carbon material catalyst according to claim 1, characterized in that: The noble metal nanoparticles in (5) are Pt, PtRu, PtCo or RuIr alloys, and the precursor is the corresponding metal chloride; the peak current density of the pulse electrodeposition is 10-30 mA / cm 2 , deposition amount 3-6C / cm 2 .

7. The process for preparing a modified porous carbon material catalyst according to claim 1, characterized in that: The catalyst obtained in (5) needs to be annealed in a H2 / Ar mixed gas at 150-250°C for 0.5-2h; the noble metal loading is 3-6wt%.

8. A modified porous carbon material catalyst prepared by the preparation process according to any one of claims 1 to 7, characterized in that: Porous carbon support specific surface area>1500m 2 / g, pore size distribution 0.5-50nm, surface fluorine content 5-10at%, nitrogen content 3-5at%; noble metal nanoparticle interplanar spacing 0.220-0.225nm.

9. A water electrolysis hydrogen production device, characterized in that: The modified porous carbon material catalyst according to claim 8 is used as the cathode, and the reaction temperature is 10 mA / cm 2 The hydrogen evolution overpotential is ≤35mV, the Tafel slope is ≤35mV / dec, and the electrochemical active area decay rate is <10% after 1000 cycles.

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