Preparation method and application of non-woven fibrous composite carbon electrode material with porous carbon on surface
Patent Information
- Application Number
- CN202611042782.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-07-14
- Publication Date
- 2026-09-15
Smart Images
Figure CN122762702A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of electrochemical energy storage materials technology, specifically relating to the preparation method and application of a nonwoven fibrous composite carbon electrode material with porous carbon on its surface. Background Technology
[0002] Vanadium redox flow batteries (VRFBs) are considered a preferred technology for large-scale energy storage due to their outstanding advantages, such as independently designable power capacity, long cycle life, high safety, and recyclable electrolyte. Electrodes are the sites of electrochemical reactions within the battery stack, serving both as conductors and channels for electrolyte flow. Vanadium ions undergo redox reactions on the electrode surface, where chemical energy and electrical energy are interconverted.
[0003] Carbon-based electrodes (carbon felt, graphite felt, etc.) are currently the most commonly used electrodes for flow batteries. They exhibit excellent electrochemical stability, resistance to strong acidic electrolyte corrosion, and do not dissolve or degrade during long-term charge-discharge cycles, resulting in a long cycle life. They also possess good electrical conductivity, strong electronic conduction, good current collection efficiency, and low ohmic polarization. Furthermore, they are easily modified and upgraded; electrochemical activity can be enhanced through thermal oxidation, acid treatment, and catalyst loading. They offer processing and cost advantages, being flexible, easy to cut and assemble, and sourced from a wide range of raw materials, making them cost-effective. However, the original carbon electrodes suffer from the following prominent problems:
[0004] Question 1: Carbon-based electrodes (carbon felt, graphite felt, etc.) are currently the most widely used electrode materials in flow batteries. However, unmodified raw carbon electrodes have significant drawbacks: their specific surface area is only 0.5-5 m². 2 / g, the fiber surface has few micropores and a lack of electrochemical active sites, which limits the power density of the battery.
[0005] Question 2: Poor electrocatalytic activity, with limited catalytic activity for the vanadium ion couple, leading to large charge / discharge overpotentials and low voltage efficiency. This is especially true on the negative electrode side, where V... 2+ / V 3+ The reaction kinetics are slow and associated with the hydrogen evolution reaction (HER: 2H+). + +2e - →H2↑) There is potential competition – hydrogen evolution not only consumes charging current but also reduces coulombic efficiency.
[0006] Question 3: Insufficient hydrophilicity; the original carbon material surface is hydrophobic, resulting in insufficient wetting by the electrolyte.
[0007] Regarding volatile phosphorus compounds, pyrophosphoric acid (H4P2O7) has a high phosphorus content and can decompose into P2O5 at high temperatures, further reacting with carbon; ammonium polyphosphate (APP, (NH4PO3)) contains phosphorus and ammonium ions, decomposes at high temperatures to release NH3 and H2O, leaving behind polyphosphoric acid; melamine cyanurate (MCA) contains both nitrogen and phosphorus, has a high thermal decomposition temperature (approximately 350-400℃), and can simultaneously provide nitrogen and phosphorus doping. These three phosphorus-containing compounds differ in decomposition temperature, phosphorus content, and associated gaseous products, but there has never been a report in the existing technology of systematically comparing the three and applying them to the modification of nonwoven fiber felt electrodes for flow batteries.
[0008] In terms of substrates, nonwoven carbon felt is carbonized carbon fiber felt; nonwoven acrylic felt is polyacrylonitrile (PAN) based polymer fiber felt, which can be carbonized into carbon fiber during the carbonization stage; nonwoven carbon nanotube fiber felt uses CNT fibers as building units, has intrinsic high conductivity and high specific surface area, but surface inertness also limits its electrocatalytic activity. Summary of the Invention
[0009] This invention aims to solve the following technical problems existing in the carbon electrodes of current flow batteries: (1) low specific surface area and few active sites; (2) poor electrocatalytic activity for vanadium ions, especially severe competition for hydrogen evolution on the negative electrode side; (3) poor hydrophilicity and insufficient electrolyte wetting. A method for preparing a nonwoven fibrous composite carbon electrode material with a surface covered with porous carbon is provided, comprising the following steps:
[0010] (1): Substrate pretreatment
[0011] The surface of the nonwoven fiber felt substrate is pretreated to introduce oxygen-containing functional groups, thereby improving the wettability and bonding strength between the substrate and the precursor solution.
[0012] Pretreatment methods include: acid treatment: immersing the substrate in concentrated nitric acid at 60-80℃ for 1-2 hours, then washing with deionized water until neutral and drying; or plasma treatment: placing the substrate in a plasma treatment device under an oxygen (O2), nitrogen (N2), or argon (Ar) atmosphere at a radio frequency power of 50-200W for 1-10 minutes to introduce oxygen-containing functional groups onto the fiber surface, improving surface wettability and chemical activity. Plasma treatment is particularly suitable for nonwoven carbon nanotube fiber felt substrates to avoid damage to the carbon nanotube structure caused by strong acids.
[0013] The nonwoven fiber felt substrate is selected from any of the following: Nonwoven carbon felt: carbonized polyacrylonitrile fiber nonwoven felt or pitch-based carbon fiber nonwoven felt, with a thickness of 2-10 mm and a surface density of 100-500 g / m³. 2Non-woven acrylic felt: Polyacrylonitrile fiber non-woven felt, 2-8 mm thick, fiber diameter 5-15 μm, uncarbonized; Non-woven carbon nanotube fiber felt: Felt-like material made of carbon nanotube fibers through non-woven process, 0.5-5 mm thick, areal density 20-100 g / m³. 2 .
[0014] (2): Preparation of precursor impregnation solution
[0015] Carbon source and phosphorus-containing compound are dissolved in a specific solvent, stirred evenly, and prepared into a precursor impregnation solution.
[0016] The carbon source is lignin; the lignin is selected from alkali lignin or lignin sulfonate; the solvent is deionized water or a mixture of deionized water and ethanol.
[0017] Phosphorus-containing compounds are selected from any one or a combination of the following:
[0018] Pyrophosphate: a colorless, viscous liquid with a phosphorus content of about 34% and a decomposition temperature of about 300℃; Ammonium polyphosphate (APP): a white powder with a phosphorus content of about 30% and a decomposition temperature of about 270-350℃; Melamine cyanurate (MCA): a white powder with a phosphorus content of about 12% and a decomposition temperature of about 350-400℃.
[0019] The mass ratio of phosphorus-containing compound to carbon source is 1:10 to 1:1, that is, the amount of phosphorus-containing compound is 10%-100% of the total mass of carbon source. The preferred range is 1:5 to 1:2 (that is, the amount of phosphorus-containing compound is 20%-50% of the total mass of carbon source).
[0020] (3): Impregnation load
[0021] The pretreated substrate from step (1) is completely immersed in the precursor impregnation solution from step (2) for 2-12 hours; after removal, excess solution is drained off, and the substrate is dried at 60-90℃ for 6-24 hours. The impregnation-drying process can be repeated 1-4 times depending on the target load.
[0022] (4): High-temperature carbonization
[0023] The substrate of the loaded precursor obtained in step (3) is placed in a tube furnace and subjected to two-stage carbonization under an inert atmosphere:
[0024] First stage: Increase the temperature to 300-500℃ at a rate of 2-10℃ / min, and hold for 1-4 hours;
[0025] Second stage: Increase the temperature to 600-1000℃ at a rate of 2-10℃ / min, and hold for 1-4 hours;
[0026] It was then allowed to cool naturally to room temperature under an inert atmosphere.
[0027] During this process, the gas generated by the thermal decomposition of phosphorus-containing compounds produces abundant micropores and mesopores in situ; the carbon source is carbonized into an amorphous carbon framework; phosphorus (and nitrogen provided by MPP) is partially retained in the carbon framework, achieving phosphorus doping (or nitrogen-phosphorus co-doping).
[0028] For nonwoven acrylic felt substrate, step (4) simultaneously achieves the carbonization of the substrate itself (PAN → carbon fiber) and the construction of a porous carbon composite layer on the surface, which is an integrated synchronous carbonization-modification process.
[0029] (5): Hydrothermal treatment
[0030] The carbonized sample from step (4) is placed in a hydrothermal reactor, deionized water is added, and hydrothermally treated at 80-200℃ for 12-36 hours. After natural cooling, it is taken out, washed with deionized water 2-3 times, and dried at 60-90℃ to constant weight to obtain a non-woven fibrous composite carbon electrode material with porous carbon on the surface.
[0031] The composite carbon electrode material prepared by the above method is used as an electrode in a flow battery; the flow battery is a vanadium redox flow battery, an iron-chromium flow battery, or a zinc-bromine flow battery.
[0032] Compared with the prior art, the present invention has the following beneficial effects:
[0033] 1. Effectively increases specific surface area: The synergistic effect of in-situ decomposition of phosphorus compounds to create pores and hydrothermal activation can build a uniform porous carbon layer on the fiber surface, increasing the specific surface area by 5-10 times compared to the original substrate.
[0034] 2. Significantly enhanced electrocatalytic activity: Decomposition products of phosphorus-containing compounds (polyphosphoric acid, P2O5, etc.) react with the carbon skeleton at high temperatures to form CP bonds, achieving phosphorus doping or nitrogen-phosphorus co-doping. Heteroatom doping alters the electronic structure of the carbon skeleton, enhancing vanadium ion adsorption and electron transfer, and reducing redox overpotential.
[0035] 3. Effectively suppress hydrogen evolution side reaction: Phosphorus doping or nitrogen-phosphorus co-doping can significantly increase the V on the negative electrode side. 2+ / V 3+ The modified electrode exhibits enhanced catalytic activity, widening the kinetic potential window between the vanadium redox reaction and the hydrogen evolution reaction (HER), effectively reducing the proportion of HER current during charging. Experimental results show that the HER onset potential of the modified electrode can be negatively shifted by 130-210 mV, and the HER current density at a test potential of -0.8V is reduced by 67%-83% compared to the original electrode, corresponding to a significant improvement in battery energy efficiency. Among them, the melamine cyanurate modified sample, due to simultaneous nitrogen and phosphorus co-doping, shows the best HER suppression effect, which is related to the regulatory effect of heteroatom doping on the electronic structure of the carbon surface.
[0036] 4. Wide substrate adaptability: This method is applicable to three types of nonwoven fiber felt substrates (carbonized nonwoven carbon felt, uncarbonized nonwoven acrylic felt, and highly conductive nonwoven carbon nanotube fiber felt). In particular, a one-step simultaneous carbonization-modification process is achieved for nonwoven acrylic felt, simplifying the process flow.
[0037] 5. Flexible and adjustable phosphorus source: Pyrophosphate (high phosphorus content, easy to disperse in liquid), ammonium polyphosphate (medium to low decomposition temperature, contains ammonium ions to supplement nitrogen), and melamine cyanurate (high decomposition temperature, provides both N and P) can all be used independently or in combination, and can be flexibly selected according to the target requirements (focus on pore formation / focus on doping / focus on hydrogen evolution suppression).
[0038] 6. Significantly improved hydrophilicity: Hydrothermal treatment introduces oxygen-containing functional groups such as –OH, C=O, and –COOH onto the carbon surface. Combined with the capillary wetting effect of the porous structure, the wettability of the electrolyte is greatly improved. Attached Figure Description
[0039] Figure 1 , Figure 2 Electron micrograph of the unburned nonwoven carbon felt electrode material prepared in Example 1.
[0040] Figure 3 , Figure 4 Electron micrograph of the nonwoven carbon felt electrode material prepared in Example 1. Detailed Implementation
[0041] Raw materials: alkali lignin, pyrophosphate, ammonium polyphosphate (APP), melamine cyanurate; non-woven carbon felt (PAN), non-woven acrylic felt (PAN fiber), non-woven carbon nanotube fiber felt (CNT); concentrated nitric acid; deionized water was used for the experiment.
[0042] Example 1
[0043] (1) Pretreatment: Take non-woven carbon felt (carbonized polyacrylonitrile fiber non-woven felt) and cut it into 1×1 cm pieces. 2 The flakes were soaked in HNO3, treated at 80°C for 2 hours, washed with deionized water until neutral, and dried at 80°C for 6 hours to obtain pretreated carbon felt.
[0044] (2) Preparation of precursor solution: Dissolve 2.5 g of alkali lignin in 20 mL of deionized water and stir for 30 min. Then add 0.83 g of APP and stir until completely dissolved. The mass ratio of APP to total carbon source is 1:3.
[0045] (3) Impregnation: Immerse the pretreated substrate completely in the precursor solution at room temperature for 6 hours, drain, and dry at 80°C for 12 hours. Repeat the impregnation-drying process once (for a total of 2 times).
[0046] (4) Carbonization: N2 atmosphere, 5℃ / min → 400℃ for 2h → 5℃ / min → 800℃ for 2h → natural cooling.
[0047] (5) Hydrothermal treatment: 100mL hydrothermal reactor, 60mL deionized water, 115℃ / 24h, natural cooling, wash 3 times with deionized water, dry at 80℃ for 6h. The resulting product is denoted as GF-APP.
[0048] Example 2
[0049] The only difference from Example 1 is that in step (2), ammonium polyphosphate is replaced with pyrophosphate, and the amount added is 0.83 g (pyrophosphate), dissolved in the precursor solution. All other conditions are exactly the same. The product is designated as GF-H4P2O7.
[0050] Example 3
[0051] The only difference from Example 1 is that in step (2), melamine cyanurate is used instead of ammonium polyphosphate, and the amount added is 0.8 g. All other conditions are exactly the same. The product is designated as GF-MPP.
[0052] Example 4
[0053] Difference from Example 1: In step (1), the substrate was changed to non-woven acrylic felt (PAN fiber non-woven felt, uncarbonized, 1×1cm). 2 In step (4) carbonization, the acrylic felt itself is simultaneously carbonized into carbon fiber felt, and a carbon composite layer is formed on the surface at the same time. The remaining conditions are the same as in Example 1. The product is denoted as PAN-APP.
[0054] Example 5
[0055] Differences from Example 1: In step (1), the substrate was changed to a non-woven carbon nanotube fiber blanket (1×1 cm²), and the pretreatment was carried out using O2 plasma treatment (RF power 100W, treatment for 5 minutes) to avoid damage to the CNT structure by strong acid. The number of impregnations was reduced to 1 (the CNT blanket was extremely thin). The remaining conditions were the same as in Example 1. The product was designated as CNT-APP.
[0056] Example 6
[0057] The only difference from Example 1 is that in step (2), the amount of APP added is 2.5 g (equal to the total carbon source), i.e., APP:carbon source = 1:1. All other conditions are the same as in Example 1. The product is denoted as GF-APP-11.
[0058] Example 7
[0059] The only difference from Example 1 is that in step (2), the amount of ammonium polyphosphate added is 0.3 g, and the carbon source is 3 g, i.e., the ratio of ammonium polyphosphate to carbon source is 1:10. All other conditions are the same as in Example 1. The product is designated as GF-APP-110.
[0060] Example 8
[0061] The only difference from Example 1 is that the final temperature of the second carbonization stage in step (4) is 900°C. All other conditions are the same as in Example 1. The product is designated as GF-APP-900.
[0062] Example 9
[0063] The only difference from Example 1 is that the final temperature of the second carbonization stage in step (4) is 700°C. All other conditions are the same as in Example 1. The product is designated as GF-APP-700.
[0064] Example 10
[0065] The only difference from Example 1 is that the hydrothermal treatment conditions in step (5) are 150℃ / 12h. All other conditions are the same as in Example 1. The product is designated as GF-APP-HT150.
[0066] Example 11
[0067] The only difference from Example 1 is that the hydrothermal treatment conditions in step (5) are 100℃ / 36h (extended time to compensate for low temperature). The other conditions are the same as in Example 1. The product is denoted as GF-APP-HT100.
[0068] Example 12
[0069] Differences from Example 1: Step (1) The substrate is a non-woven carbon nanotube fiber blanket and is pretreated with O2 plasma (RF power 100W, treatment for 5 minutes); Step (2) The phosphorus source is 0.8 g of pyrophosphate and the carbon source is 2.5 g of lignin; Step (4) Carbonization at 800℃ (second stage at 900℃); Step (5) Hydrothermal treatment at 150℃ / 12h. Impregnation once. The product is denoted as CNT-H4P2O7-900.
[0070] Example 13
[0071] Differences from Example 1: Step (1) The substrate is non-woven acrylic felt; Step (2) The phosphorus source is 1.2 g of melamine cyanurate; Step (4) Carbonization stage 700℃; Step (5) Hydrothermal treatment at 100℃ / 36h. The product is denoted as PAN-MPP-700.
[0072] Example 14
[0073] (1) Pretreatment: Take pitch-based carbon fiber nonwoven felt and cut it into 1×1 cm pieces. 2 The flakes were soaked in HNO3, treated at 80°C for 2 hours, washed with deionized water until neutral, and dried at 80°C for 6 hours to obtain pretreated carbon felt.
[0074] (2) Preparation of precursor solution: Dissolve 2.5 g of alkali lignin in 20 mL of deionized water and stir for 30 min. Then add 0.83 g of APP and stir until completely dissolved. The mass ratio of APP to total carbon source is 1:3.
[0075] (3) Impregnation: Immerse the pretreated substrate completely in the precursor solution at room temperature for 6 hours, drain, and dry at 80°C for 12 hours. Repeat the impregnation-drying process once (for a total of 2 times).
[0076] (4) Carbonization: N2 atmosphere, 5℃ / min → 400℃ for 2h → 5℃ / min → 800℃ for 2h → natural cooling.
[0077] (5) Hydrothermal treatment: 100mL hydrothermal reactor, 60mL deionized water, 115℃ / 24h, natural cooling, wash 3 times with deionized water, dry at 80℃ for 6h. The resulting product is denoted as GF-APP.
[0078] Comparative Example 1
[0079] The nonwoven carbon felt pretreated in step (1) was used directly as a control electrode without impregnation, carbonization, or hydrothermal treatment. It was denoted as GF-0.
[0080] Comparative Example 2
[0081] The only difference from Example 1 is that no phosphorus-containing compound is added in step (2); only a carbon source (2.5 g lignin) dissolved in 20 mL of deionized water is used. All other conditions are the same as in Example 1. The product is designated GF-noP. This is used to verify the necessity of phosphorus-containing compounds for pore formation / doping / hydrogen evolution suppression.
[0082] Comparative Example 3
[0083] The only difference from Example 1 is that step (5) is skipped, and the product is used directly after carbonization without hydrothermal treatment. The product is designated GF-APP-noHT. It is used to verify the contribution of hydrothermal treatment to surface activation and hydrogen evolution inhibition.
[0084] Comparative Example 4
[0085] The only difference from Example 1 is that ammonium polyphosphate is replaced with an equivalent amount of phosphoric acid in step (2). This is used to compare the effect of "degree of phosphate polymerization" on pore formation and doping effects in different phosphorus-containing compounds.
[0086] Comparative Example 5
[0087] The only difference from Example 1 is that step (1) of surface pretreatment is skipped, and the untreated raw nonwoven carbon felt is used directly for subsequent impregnation, carbonization, and hydrothermal treatment. All other conditions are the same as in Example 1. The product is designated GF-APP-noPre.
[0088] Performance testing
[0089] (1) Specific surface area (BET) and pore structure test
[0090] The N2 adsorption-desorption method was employed, and the specific surface area and porosity were measured using a fully automated specific surface area and porosity analyzer at -196 degrees Celsius (liquid nitrogen temperature). Samples were degassed at 200 degrees Celsius for at least 6 hours prior to testing. Specific surface area was calculated using the BET equation, mesopore size distribution was analyzed using the BJH equation, and the t-plot method was used to distinguish the contributions of micropores and mesopores.
[0091] (2) Surface elemental composition (XPS)
[0092] The elemental composition and chemical state of the electrode material surface were determined using X-ray photoelectron spectroscopy (XPS, Thermo Fisher Scientific ESCALAB 250 Xi or equivalent). The excitation source was AlKa rays (1486.6 eV), and the vacuum level was better than 1 x 10⁻⁷ Pa. Using the C1s peak (284.8 eV) as the charge correction reference, peak fitting was performed on the spectrum using CasaXPS software to obtain the atomic percentage (at%) of P, N, O, and C.
[0093] (3) Electrochemical performance testing – Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS)
[0094] A three-electrode testing system was used on an electrochemical workstation (CHI760E or similar instrument). The prepared electrode material (cut to 1cm x 1cm) was used as the working electrode, and a platinum sheet (1cm) was used as the working electrode. 2 The electrode is a counter electrode, a saturated calomel electrode (SCE) is a reference electrode, and a 1 mol / L VOSO4 + 3 mol / L H2SO4 aqueous solution is the electrolyte.
[0095] Cyclic voltammetry (CV) test: potential window 0.2-1.1 V (vs. SCE), scan rate 5 mV / s, record positive electrode couple (VO). 2 + / VO 2+ The redox peak potential difference (dEp); the smaller the dEp, the better the electrochemical reversibility and the lower the overpotential.
[0096] Electrochemical impedance spectroscopy (EIS) test: A 5 mV sinusoidal AC perturbation is applied at the open circuit potential, and the test frequency range is 0.01 Hz to 100 kHz. The charge transfer impedance Rct (unit: ohm·cm²) is obtained by fitting the Randle equivalent circuit.
[0097] (4) Hydrogen evolution performance test (linear sweep voltammetry, LSV)
[0098] A three-electrode system was used (reference electrode: SCE, counter electrode: platinum sheet), with a 3 mol / L H₂SO₄ aqueous solution as the electrolyte (simulating the strongly acidic environment at the end of charging on the negative electrode side of a vanadium redox flow battery). Linear sweep voltammetry (LSV) tests were performed at a scan rate of 1 mV / s within the range of -0.3 V to -1.0 V (vs. SCE). The hydrogen evolution onset potential was defined as the potential corresponding to the absolute value of the current density exceeding 1 mA / cm², and the hydrogen evolution current density (mA / cm²) at -0.8 V (vs. SCE) was recorded as a quantitative comparison standard.
[0099] (5) Energy efficiency (EE) test of all vanadium redox flow battery
[0100] A single-cell test bench was used, with an effective electrode area of 25 cm² (5 cm x 5 cm), a Nafion 115 proton exchange membrane, a graphite bipolar plate, a carbon paper flow field, and a peristaltic pump driving electrolyte circulation at a flow rate of 40 mL / min. Both the negative and positive electrode electrolytes were 100 mL each of a 1.5 mol / L vanadium salt + 3 mol / L H₂SO₄ aqueous solution. Charge-discharge tests were conducted at a constant current density of 100 mA / cm² at room temperature (25 ± 2 °C), with a charging cutoff voltage of 1.65 V and a discharging cutoff voltage of 0.8 V. Energy efficiency EE = discharge energy / charging energy × 100%. After 50 cycles, the electrode mass retention rate (mass after cycling / mass before cycling × 100%) was calculated to evaluate the electrode structural stability and durability.
[0101] Table 1: Comparison of different phosphorus sources (all using non-woven carbon felt as the substrate, other conditions are the same as in Example 1)
[0102]
[0103] Analysis: Among the three target phosphorus sources, melamine polyphosphate showed the best expected performance—although its specific surface area was slightly lower than that of ammonium polyphosphate, the simultaneous introduction of N doping significantly enhanced electronic conductivity and hydrogen evolution suppression (the hydrogen evolution initiation potential was the most negative at -0.63 V, and the hydrogen evolution current was only 1.4 mA / cm²), resulting in the highest overall EE (81.3%). Applied phosphoric acid (APP) showed balanced overall performance. Pyrophosphate had weak pore-forming ability (specific surface area of only 82.4 m² / g), but its P doping efficiency was acceptable. Phosphoric acid (Comparative Example 4) showed the worst performance—due to its excessively low decomposition temperature and lack of pore-forming effect from decomposition gases, its specific surface area was only 65.7 m² / g. 2 / g.
[0104] Table 2: Comparison of different substrates (all using APP as the phosphorus source, other conditions are the same as in Example 1)
[0105]
[0106] Analysis: Nonwoven acrylic felt (Example 4) verified the feasibility of simultaneous carbonization-modification integration, achieving a final specific surface area of 89.1 m² / g, close to that of Example 1 (100.8 m² / g) using nonwoven carbon felt as the substrate, eliminating the need for substrate pre-carbonization. Nonwoven carbon nanotube fiber felt (Example 5) already had a specific surface area of 68.4 m² / g, which further increased to 218.7 m² / g after composite (the highest among all examples). Combined with the excellent conductivity of CNTs, the Rct was only 0.9 Ω·cm², resulting in an EE as high as 83.6%, making it the best performing among all examples. Pitch-based carbon fiber nonwoven felt (Example 14) had a slightly lower Rct after composite due to its higher intrinsic conductivity than PAN-based carbon felt (Example 1). However, due to its lower surface activity and slightly less uniform porous carbon loading, its specific surface area was basically the same as that of polyacrylonitrile fiber nonwoven felt, verifying the good adaptability of this method to different carbon felt sources.
[0107] Table 3: Comparison of different APP ratios and carbonization temperatures (all based on nonwoven carbon felt).
[0108]
[0109] Analysis: When the ratio of ammonium polyphosphate to carbon source ranged from 1:10 to 1:1, the specific surface area increased from 48.6 m² to 142.2 m². 2 / g, P content increased from 0.92 to 2.40 at%, but carbon yield decreased from 41.6% to 33.3%. A 1:3 ratio (Example 1) represents the optimal balance between carbon yield and performance. Carbonization temperature increased from 700°C to 900°C, specific surface area increased from 68.9 to 160.7 m² / g, but phosphorus content decreased from 2.15 to 1.21 at% (high-temperature volatilization). Without hydrothermal treatment (Comparative Example 3), hydrogen evolution current increased by 2.3 times, and EE decreased by 2.4 percentage points, demonstrating the crucial role of hydrothermal treatment in suppressing hydrogen evolution.
[0110] Table 4: Comparison of hydrothermal treatment temperatures (all based on non-woven carbon felt + APP, other parameters are the same as in Example 1)
[0111]
[0112] Analysis: Increasing the hydrothermal treatment temperature from 100°C to 150°C decreased the hydrogen evolution current. Hydrothermal treatment at 150°C yielded the lowest hydrogen evolution current (1.7 mA / cm²) and the highest EE (81.2%, even exceeding Example 1), but the carbon layer quality retention slightly decreased to 96.1% (due to minor mass loss from over-etching). 115°C / 24h achieved the best balance between performance and structural stability.
[0113] Overall Conclusion
[0114] 1. Preferred phosphorus source: Melamine polyphosphate provides the best hydrogen evolution suppression and EE (81.3%) due to its simultaneous N / P co-doping effect. APP is second best, but has the highest overall cost-effectiveness. Pyrophosphate has a slightly weaker pore-forming effect, but its P doping efficiency is acceptable. H3PO4 has the worst effect because it does not decompose gases to form pores.
[0115] 2. Substrate Expansion Validation: The simultaneous carbonization-modification process of nonwoven acrylic felt is feasible, eliminating the need for a pre-carbonization step; nonwoven carbon nanotube fiber felt achieves the highest performance across all substrates and all phosphorus source combinations.
[0116] 3. Hydrogen evolution suppression mechanism: Phosphorus doping and N / P co-doping shift the hydrogen evolution initiation potential negatively by 50–210 mV, reducing the hydrogen evolution current by 40%–83%. MPP exhibits the best hydrogen evolution suppression effect.
[0117] 4. Wide process window: Phosphorus compound: carbon source = 1:10 to 1:1, carbonization temperature 700–900°C, hydrothermal temperature 100–150°C, effective porous carbon composite layer and electrode performance improvement can be obtained with three types of substrates and three types of phosphorus sources. The process has a large tolerance and strong industrial adaptability.
Claims
1. A method for producing a non-woven fibrous composite carbon electrode material having a surface covered with porous carbon, characterized by, The preparation method steps are as follows: (1) Surface pretreatment of nonwoven fiber felt substrate to introduce oxygen-containing functional groups; (2) Dissolve the carbon source and phosphorus-containing compound in a solvent to prepare a precursor impregnation solution; (3) Immerse the pretreated substrate from step (1) in the precursor impregnation solution from step (2) at room temperature, remove and dry; (4) The sample obtained in step (3) is subjected to a two-stage high-temperature carbonization treatment under an inert atmosphere; (5) The carbonized sample is subjected to hydrothermal treatment and dried to obtain the composite carbon electrode material.
2. The method of claim 1, wherein the method is characterized by: In step (1), the surface pretreatment is acid treatment or plasma treatment; the non-woven fiber felt substrate is selected from any one of non-woven carbon felt, non-woven acrylic felt or non-woven carbon nanotube fiber felt.
3. The method of claim 1, wherein the method is characterized by: In step (2), the phosphorus-containing compound is selected from any one or more combinations of pyrophosphate, ammonium polyphosphate or melamine cyanurate; the carbon source is lignin; and the solvent is deionized water or a mixture of deionized water and ethanol.
4. The method of claim 1, wherein the method is characterized by: In step (2), the mass ratio of phosphorus-containing compound to carbon source is 1:10-1:
1.
5. The method of claim 1, wherein the method is characterized by: In step (3), the soaking time is 2-12 hours, the drying temperature is 60-90℃, and the soaking-drying process can be repeated 1-4 times.
6. The method of claim 1, wherein the method is characterized by: In step (4), the inert atmosphere is nitrogen or argon; the two-stage high-temperature carbonization treatment is carried out, with the first stage being held at 300-500℃ for 1-4 hours and the second stage being held at 600-1000℃ for 1-4 hours; the heating rate is 2-10℃ / min.
7. The method for preparing the nonwoven fibrous composite carbon electrode material with a surface covered with porous carbon according to claim 1, characterized in that, In step (5), the hydrothermal treatment temperature is 80-200℃ and the treatment time is 12-36 hours.
8. A nonwoven fibrous composite carbon electrode material with a surface covered with porous carbon, prepared by the method according to any one of claims 1-7.
9. An application of a nonwoven fibrous composite carbon electrode material with a surface covered with porous carbon, prepared by the method according to any one of claims 1-7, characterized in that, The composite carbon electrode material is used as an electrode in a flow battery.
10. The application of the nonwoven fibrous composite carbon electrode material with a surface covered with porous carbon according to claim 9, characterized in that, The flow battery is a vanadium redox flow battery, an iron-chromium flow battery, or a zinc-bromine flow battery.