Lignin multi-metal ordered carbonization interface quaternary electrocatalyst and application thereof in high-flow-density integral water decomposition

Abstract

The invention discloses a lignin multi-metal ordered carbonization interface quaternary electrocatalyst which is mainly composed of a FeNi alloy nano core, a MoCx gradient interface layer, a Ru ultra-small metal cluster and an N / O / P co-doped lignin derived carbon shell. The MoCx gradient interface layer tightly coats the surface of the FeNi alloy nano core, the Ru ultra-small metal clusters are distributed between the MoCx gradient interface layer and the N / O / P co-doped lignin derived carbon shell, and the N / O / P co-doped lignin derived carbon shell surrounds the outermost layer. Accordingly, a corresponding preparation method is also established. The quaternary electrocatalyst can be applied to high-flow-density integral water decomposition and used for preparing electrodes or alkaline integral water decomposition electrolytic cells, and a new path is provided for high-value utilization of biomass resources such as lignin in the field of high-flow-density electrolyzed water.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical hydrogen production and biomass-based functional materials technology, and particularly relates to a lignin-polymetallic ordered carbonized interface quaternary electrocatalyst and its application in high flow density integral water splitting. Background Technology

[0002] In alkaline water electrolysis systems, although noble metal-based electrocatalysts (such as RuO₂) and IrO₂ exhibit excellent kinetic performance in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), precious metal resources are scarce and expensive, making it difficult to meet the long-term operational needs of large-scale hydrogen production plants. Transition metal-based catalysts, represented by Fe and Ni, have significant advantages in resource reserves and cost, but problems such as metal dissolution, severe surface reconstruction, and carbon support corrosion often occur at high current densities above 100 mA cm⁻¹, causing the electrode potential to rise sharply over time, making stable operation on a scale of hundreds of hours difficult to achieve.

[0003] Lignin is widely available, inexpensive, and high in carbon content, making it the second most abundant aromatic polymer resource in nature after cellulose. With appropriate functionalization, lignin can not only serve as a precursor for porous carbon supports but also coordinate with metal ions through aromatic rings and various functional groups, thereby controlling the spatial distribution of metal precursors at the molecular scale. Although lignin is often considered a "passive carbon source" or a simple pore structure regulator in applications such as supercapacitors, water electrolysis, and batteries, its unique chemical structure and abundant functional groups make it a promising candidate for bio-based materials. Existing research has explored the application of lignin in the preparation of porous carbon-supported metal or alloy nanoparticles, but the ordered coordination and interfacial evolution of metal ions in the precursor still require systematic design. Modifications of lignin-based electrode materials, such as surface modification, functional group modification, and nanoparticle coating, have been shown to improve their electrochemical performance, which is crucial for optimizing the performance of supercapacitors.

[0004] On the other hand, carbide-alloy heterostructure catalysts exhibit significant advantages in enhancing electrode activity and stability through mechanisms such as synergistic effects, strain effects, and electronic interactions. For example, the combination of MoC and FeNi alloys can improve the adsorption energy of OER intermediates to some extent, while multi-metal alloys such as FeNiRu are beneficial for lowering the energy barrier of HER. However, existing works usually focus on optimizing single structures or finite element combinations, often employing physical mixing, incomplete coating, or simple series connection methods to stack multiple active phases on the electrode surface. This makes it difficult to construct an ordered, multi-level interface structure of "alloy core – carbide interface – noble metal cluster – multi-heteroatom-doped carbon shell." Within the same particle, multi-level structures can achieve multiple layers, leading to problems such as limited utilization of effective sites, uneven distribution of interfacial charges, and long-term instability.

[0005] Furthermore, many laboratory-scale multi-metal electrocatalyst preparation schemes are still at the stage of small-batch powder calcination. The morphology and rheological properties of the precursors are disconnected from the actual electrode forming process, making it difficult to balance the uniformity of the pyrolysis process and the construction of gas exhaust channels in the electrode layer. Electrode performance evaluation is also mostly limited to short-term tests at 10–50 mA·cm⁻² and room temperature, lacking systematic verification of long-term stability under high flow density conditions of 200–300 mA·cm⁻² and under heating conditions. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a lignin-based multimetallic ordered carbonized interface quaternary electrocatalyst and its application in high flow density integral water splitting.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: The lignin-based multimetallic ordered carbonized interface quaternary electrocatalyst mainly consists of FeNi alloy nanocores, MoCx gradient interface layers, Ru ultrasmall metal clusters, and N / O / P co-doped lignin-derived carbon shells. The MoCx gradient interface layer tightly coats the surface of the FeNi alloy nanocores, the Ru ultrasmall metal clusters are distributed between the MoCx gradient interface layer and the N / O / P co-doped lignin-derived carbon shells, and the N / O / P co-doped lignin-derived carbon shells surround the outermost layer.

[0008] N / O / P co-doped lignin-derived carbon shells are obtained by carbonizing lignin AO-L, which is activated by oxy-ammonia synergy, under an ammonia-containing inert atmosphere.

[0009] The thickness of the MoCx gradient interface layer is 0.6–3.0 nm, the average particle size of the Ru ultrasmall metal clusters is 0.5–1.8 nm, and the Raman spectrum of the N / O / P co-doped lignin-derived carbon shell has an intensity ratio of I_D / I_G of 0.8–1.2 for the D band to the G band.

[0010] The FeNi alloy nanocore has a Fe to Ni molar ratio of 3:1–2:1, the x in the MoCx gradient interface layer is 0.8–1.0, and the nitrogen content in the N / O / P co-doped lignin-derived carbon shell is 1–8 AT%, and the phosphorus content is 0.2–3 AT.

[0011] The preparation method of the above-mentioned quaternary electrocatalyst includes the following steps: S1, preparation of lignin AO-L activated by synergistic oxygen and ammonium; S2, dissolve the AO-L from step S1 in water or a water / alcohol mixture, and add metal salts of Fe, Ni, Mo and Ru in sequence to form an AO-L multimetal supramolecular precursor sol under alkaline conditions. S3, spray-dry or melt-extrude the sol from step S2 to obtain AM-P precursor microspheres or strip particles; S4. The AM-P precursor microspheres or strip particles from step S3 are subjected to a two-stage heat treatment of AO-L multi-metal ordered carbonization (AMOC) in an ammonia-containing inert atmosphere to obtain QIEC composite powder. S5. Selective dilute acid leaching, washing, and drying of QIEC composite powder yields the final product.

[0012] Step S1 is performed as follows: Weigh 10 g of enzymatically hydrolyzed lignin and add it to 200 mL of a 2 wt% NaOH aqueous solution, and stir magnetically at room temperature; then, under ice-water bath conditions, slowly add a 4.0 mol·L⁻¹ solution. 20 g of sodium hypochlorite solution was added, with the pH value controlled between 10 and 11, and the reaction was allowed to proceed for 1 h. Subsequently, the temperature was raised to 60 °C, and under continuous stirring, 15 g of urea and 5 g of ammonia solution with a mass fraction of 25-28 wt% were slowly added dropwise, and the reaction was continued for another 3 h. After the reaction was complete, the solution was cooled to room temperature and treated with 1.0 mol·L⁻¹ solution. The pH of the solution was adjusted to 7-8 with dilute hydrochloric acid, and then the solution was dialyzed using a dialysis bag with a molecular weight cutoff of 3.5 kDa for 48 hours. Finally, the solution was freeze-dried to obtain AO-L.

[0013] The molar ratio of Fe, Ni, Mo and Ru is 4:2:1:0.20. The AO-L multimetal ordered carbonization (AMOC) two-stage heat treatment involves pre-carbonization at 300–380 ℃ followed by high-temperature carbonization at 700–780 ℃.

[0014] The application of the aforementioned quaternary electrocatalyst in high flow density integral water splitting.

[0015] The aforementioned quaternary electrocatalyst is used to prepare electrodes or alkaline monolithic water splitting electrolyzers.

[0016] To address the problems of insufficient activity, simple interface structure, poor stability at high current densities, and difficulty in engineering scale-up of existing lignin-based electrocatalysts, the inventors have developed a quaternary electrocatalyst with a lignin multimetallic ordered carbonized interface. This quaternary electrocatalyst mainly consists of a FeNi alloy nanocore, a MoCx gradient interface layer, Ru ultrasmall metal clusters, and an N / O / P co-doped lignin-derived carbon shell. The MoCx gradient interface layer tightly coats the surface of the FeNi alloy nanocore, the Ru ultrasmall metal clusters are distributed between the MoCx gradient interface layer and the N / O / P co-doped lignin-derived carbon shell, and the N / O / P co-doped lignin-derived carbon shell surrounds the outermost layer. A corresponding preparation method has also been established. This invention achieves multi-level synergy of the FeNi alloy nanocore, MoCx gradient interface layer, Ru ultrasmall metal clusters, and N / O / P co-doped lignin-derived carbon shell in a single lignin precursor system, introducing E / Ion / gas, interface charge distribution index, three-flow network design, and Φ4 evaluation method. Accordingly, by developing heterostructure catalysts and high-entropy alloy nanoparticles, long-term stable operation of the electrode at current densities of 200–250 mA / cm, P ®, or even higher, can be achieved, significantly improving the energy efficiency and reliability of the overall alkaline water splitting system. Therefore, the quaternary electrocatalyst of this invention can be applied to high-fluid-density monolithic water splitting and used to prepare electrodes or alkaline monolithic water splitting electrolyzers.

[0017] Compared with the prior art, the present invention has the following outstanding features: 1) Multi-level interface structure. On the one hand, this invention employs AO-L multi-metal coordination and AMOC processes to generate FeNi alloy nanonuclei, MoCx gradient interface layers, Ru ultra-small metal clusters, and N / O / P co-doped lignin-derived carbon shells in a predetermined order within a single particle, solving the problem of random aggregation of active phases and discontinuous interfaces in traditional multiphase materials. On the other hand, the thickness of the MoCx interface layer and the size of the Ru clusters are within a strictly controlled range, ensuring a balance between the continuity of electronic pathways and the exposure of active sites.

[0018] 2) Excellent electrocatalytic performance. Studies have shown that the QIEC electrode of this invention exhibits excellent electrocatalytic performance, especially in water electrolysis for hydrogen production. The electrode achieves a current density of 10 mA·cm⁻¹ in the hydrogen evolution reaction (HER) with an overpotential of only about 32 mV at P, while under standard conditions (1.0 mol, PKOH, 25 °C) the overpotential is approximately 210 mV in the oxygen evolution reaction (OER). Furthermore, at a temperature increased to 60 °C, the electrode achieves a current density of 50 mA·cm⁻¹ in the overall water splitting reaction. The required voltage is no more than 1.55 V, while at higher current densities of 200 mA·c At this voltage, the voltage is approximately 1.67 V. Compared with the control group without Ru, the control group without Mo, and the control group without AMOC two-stage process, the overpotential of HER and OER is reduced by an average of 35-60 mV, and the Tafel slope is significantly reduced.

[0019] 3) Excellent stability under high flow density. The QIEC electrode of this invention exhibits good stability at 60℃ and 250 mA·cm⁻¹. Under the same conditions, after 600 hours of continuous operation, the overall water splitting voltage increased by only about 40 mV, and the current retention rate exceeded 92%. Under the same conditions, the comparative electrode showed a voltage increase of over 80 mV within 400 hours, and some samples exhibited significant failure phenomena such as bubble retention and electrode peeling. In-situ and post-analysis characterization showed that the FeNi / MoCx / Ru multilevel interface in the QIEC of this invention remained highly intact after long-term operation, indicating that the multilevel interface structure has good self-support and anti-reconfiguration capabilities.

[0020] 4) Great potential for engineering and scale-up. The AO-L precursor has good solubility and rheological properties, making it suitable for various continuous processes such as spray drying, spray coating, and melt extrusion; the AMOC two-stage carbonization process can be implemented in conventional industrial furnaces without the need for additional template agents or expensive reaction atmospheres. The TPN electrode structure can be directly matched with the electrode clamping and electrolyte flow field design of existing alkaline electrolyzers, which is conducive to extending the technology of this invention to pilot-scale and industrial scale-up.

[0021] In summary, this invention establishes an effective link between microscopic interface control and macroscopic electrode engineering, providing a new path for the high-value utilization of biomass resources such as lignin in the field of high flow density water electrolysis. Attached Figure Description

[0022] Figure 1 is a comparison of the Ni 2p XPS spectra of different samples.

[0023] Figure 2 This is the HER polarization curve (LSV) plot.

[0024] Figure 3 This is the OER polarization curve (LSV) diagram.

[0025] Figure 4 is the overall decomposed water stability curve.

[0026] Figure 5 This is an electrochemical impedance spectroscopy (EIS) Nyquist plot.

[0027] Figure 6 It is an in-situ Raman spectrum.

[0028] Figure 7 This is a schematic diagram showing the relationship between the Φ4 exponent and overpotential. In the diagram, A represents the overpotential of Φ4 and HER (η@10 mA·cm). The relationship between Φ4 and OER overpotential (η@10 mA·cm) is shown; B is the relationship between Φ4 and OER overpotential (η@10 mA·cm). The relationship between ).

[0029] Figure 8 These are the XRD patterns of QIEC powder samples (including control samples).

[0030] Figure 9 The figures show the high-resolution structural characterization of the QIEC catalyst, including: (a) an HRTEM image of the QIEC catalyst, showing the core-layer-shell structure of the FeNi alloy core, MoCx interface layer, and N / O / P doped carbon shell, with the inset showing the lattice fringes of MoCx; (b) a HAADF-STEM image of the QIEC catalyst, showing the distribution of Ru ultraclusters in the interface region; (c) a statistical distribution diagram of the MoCx interface layer thickness; and (d) a statistical distribution diagram of Ru particle size. Detailed Implementation

[0031] I. Preparation of Functionalized Lignin AO-L (Example 1) Weigh 10 g of enzymatically hydrolyzed lignin and add it to 200 mL of a 2 wt% NaOH aqueous solution. Stir magnetically at room temperature until fully dissolved. Under ice-water bath conditions, slowly add 20 g of sodium hypochlorite solution (4.0 mol·L⁻¹, calculated as ClO₂). Simultaneously, the pH of the solution was controlled between 10 and 11, and the reaction was carried out for 1 hour to introduce some carboxyl groups and amidation sites. Subsequently, the temperature was raised to 60 °C, and under continuous stirring, 15 g of urea and 5 g of ammonia solution with a mass fraction of 25-28 wt% were slowly added dropwise, and the reaction was continued for 3 hours. After the reaction was completed, the solution was cooled to room temperature and treated with 1.0 mol·L⁻¹... The pH of the solution was adjusted to 7-8 with dilute hydrochloric acid, and then the solution was dialyzed using a dialysis bag with a molecular weight cutoff of 3.5 kDa for 48 hours. Finally, the solution was freeze-dried to obtain oxoammonia-activated lignin powder AO-L (denoted as AO-L).

[0032] The obtained AO-L exhibited enhanced intensity of the C=O stretching vibration of the carboxyl group at 1710 cm⁻ and enhanced intensity of the related peak of the amide bond in the range of 1550-1650 cm⁻ in the Fourier transform infrared spectrum, indicating that a large number of carboxyl and amide coordination sites were successfully introduced into the lignin skeleton, which is beneficial for the coordination of multi-metal ions.

[0033] II. Construction of AO-L multimetallic supramolecular precursors (Example 2) Weigh 2.0 g of AO-L and dissolve it in 100 mL of deionized water. Stir for 1 h to obtain a homogeneous brown solution. Add the following sequentially: The Fe:Ni:Mo:Ru ratio was controlled at 4:2:1:0.20, resulting in a total metal concentration of approximately 0.25 mol·L⁻¹. Slowly add 2.0 mol·L⁻¹ The pH of the system was adjusted to 9.5–10.0 with NaOH solution, and stirring was continued at room temperature for 4 h, during which a sol containing AO-L–Fe / Ni / Mo / Ru polymetallic complex was formed.

[0034] The above sol was transferred to a spray drying tower and spray dried under the conditions of inlet air temperature of 180 ℃, outlet air temperature of 90 ℃, and atomization pressure of 0.4 MPa to obtain AO-L multimetal supramolecular precursor microspheres (denoted as AM-P) with a particle size of 5-20 μm.

[0035] III. Preparation of QIEC Powder by AO-L Multimetal Ordered Carbonization (AMOC) Process (Example 3) AM-P microspheres were placed in a tubular furnace quartz boat, and air was introduced... (Volume ratio 4:1) gas mixture, at 2 °C·min The temperature was increased to 350 °C at a rate of [missing value], and held for 2 h to complete the pre-carbonization and initial formation of metal oxides / hydroxides; then increased at 5 °C·min [missing value]. The temperature was increased to 740 °C at a rate of 100°C and held for 3 h to reduce and alloy Fe and Ni to form FeNi nanonuclei. Mo species preferentially carbonized on the surface of the FeNi nuclei to form a MoCx gradient interface layer. Some Ru species migrated and nucleated at the MoCx / carbon interface to form Ru ultrasmall metal clusters. The QIEC composite powder was then naturally cooled to room temperature.

[0036] Further removal of uncoated large metal particles was achieved by dilute acid leaching: the above QIEC composite powder was dispersed in 0.1 mol·L⁻¹ The sample was stirred at room temperature for 2 h in dilute hydrochloric acid solution, centrifuged and washed until neutral, and then vacuum dried to obtain the final QIEC powder sample QIEC-1.

[0037] IV. Fabrication of QIEC Electrodes and Construction of TPN Architecture (Example 4) Take 80 parts by weight of QIEC-1 powder, 10 parts by weight of AO-LC binder (self-made: take the AO-L obtained in Example 1, dissolve it in a deionized water / ethanol mixed solvent (volume ratio 1:1) to prepare a binder solution with a solid content of 5–10 wt%, and ultrasonically disperse for 30 min; the binder is cured / carbonized during subsequent drying at 80 ℃ and short-path hot pressing at 280 ℃ to form AO-L derived carbonaceous binder phase AO-LC), and 10 parts by weight of conductive carbon black (Super P conductive carbon black, TIMCAL / Imerys, model Super P Li), add a small amount of isopropanol and deionized water to prepare a homogeneous slurry, and use ultrasonic dispersion for 30 min to remove large air bubbles. Place the pretreated nickel foam (2 cm × 3 cm, after acid washing and ultrasonic cleaning) on ​​a swing coating machine, and uniformly coat one side of the nickel foam with the above slurry, controlling the loading at 3.0–3.5 mg·cm⁻². After coating, the electrode is vacuum dried at 80 °C for 2 h, and then hot-pressed at 280 °C for 30 min to form a QIEC electrode with high mechanical strength and tight bonding with the substrate, denoted as QIEC-NF.

[0038] The QIEC-NF electrode utilizes a FeNi alloy-AN-LC carbon framework to form an electron conduction network, an AN-LC porous structure-MoCx / Ru active sites to synergistically construct an ion permeation network, and an NF cobalt porous structure-AN-LC mesopore / micropore parallel connection to form a good gas escape network. This effective combination of components achieves a three-permeation framework for energy storage.

[0039] V. Comparative Preparation Comparative Example C1 (without Ru): No Ru was added in Example 2. With all other conditions unchanged, FeNi / MoCx / AO-LC composite powder was obtained through spray drying and AMOC process. Electrodes were prepared according to the method in Example 4 and denoted as C1-NF.

[0040] Comparative Example C2 (without Mo): No Mo was added in Example 2. With all other conditions unchanged, FeNi / Ru / AO-LC composite powder was obtained through AMOC process, and the electrode was prepared and designated as C2-NF.

[0041] Comparative Example C3 (single-stage carbonization): AM-P microspheres were obtained entirely according to Example 2. In an atmosphere of 5 ℃·min The temperature was raised to 750 °C, held for 3 hours, and then cooled. Without setting a 350 °C pre-carbonization stage, the resulting powder was used to prepare an electrode according to Example 4, denoted as C3-NF.

[0042] VI. Electrochemical Performance Testing Two-electrode or three-electrode systems were used for testing in 1.0 mol / L KOH solution. In the three-electrode system, a prepared QIEC-NF or comparative electrode was used as the working electrode, a platinum sheet as the counter electrode, and HG / HGO as the reference electrode. In the two-electrode overall water splitting experiment, two QIEC-NF or comparative electrodes of the same area were used as the anode and cathode, respectively.

[0043] All potentials were compensated by IR and converted to RHE potentials (reversible hydrogen electrode). HER and OER polarization curves were obtained at a scan rate of 2 mV / s. Electrochemical impedance spectroscopy was performed near the open-circuit and operating potentials in the frequency range of 100 kHz – 0.1 Hz with an AC amplitude of 5 mV. Overall water splitting stability was tested at 25 °C and 60 °C, with current densities of 50, 100, 200, and 250 mA·cm⁻¹. The single-point constant current test time shall not be less than 100 hours, and the total test time shall not be less than 600 hours.

[0044] VII. Experimental Results and Discussion 1. Beyond performance differences, the applicant further used Ni 2p XPS to track the chemical state changes of Ni species and their relationship with interfacial regulation (see...). Figure 1 ).from Figure 1 It can be seen that the Ni 2p peak position and shape are not completely consistent among different samples, which usually means that the electronic environment around Ni has undergone measurable modulation during multi-metal synergy and interface construction. This spectroscopic feature is consistent with the electronic coupling effect brought about by the multi-level structure of "FeNi alloy core-MoCx graded interface layer-doped carbon shell", and also provides chemical state-level supporting evidence for the subsequent improvement of HER / OER kinetics.

[0045] 2. HER activity ( Figure 2The HER polarization curve of the QIEC-NF electrode at 25 °C is shown below. Figure 2 As shown. By Figure 2 It can be seen that at current densities of 10, 50, and 100 mA·cm⁻², the overpotentials η of QIEC-NF are approximately 32, 58, and 86 mV, respectively, all significantly lower than those of the comparative electrodes C1-NF, C2-NF, and C3-NF. This indicates that the FeNi alloy nanocore—MoC x The multi-level interface, consisting of a graded interface layer—Ru ultracluster—N / O / P co-doped carbon shell, effectively reduces the charge transfer resistance of the hydrogen evolution reaction and improves the utilization rate of active sites. Furthermore, at a temperature of 60 °C, the overpotential of QIEC-NF at 50 mA·cm⁻² is approximately 68 mV; compared to C1-NF and C2-NF at the same current density, this represents a decrease of approximately 40 mV and 55 mV, respectively. This indicates that the temperature rise condition and interface structure optimization have a synergistic effect, further improving the HER kinetics performance of the electrode.

[0046] 3. OER activity ( Figure 3 The OER polarization curve of the QIEC-NF electrode is shown below. Figure 3 As shown. At 25 °C, when the current density is 10, 50, and 100 mA·cm⁻¹ At these times, the overpotentials of QIEC-NF were approximately 210, 260, and 295 mV, respectively, all lower than those of the comparative electrode, indicating that this hierarchical interface structure can more effectively regulate the adsorption / desorption process of key OER intermediates and reduce the reaction driving force. Meanwhile, the Tafel slope of QIEC-NF was approximately 42 mV·dec. (See Figure 3 The corresponding fitting results further indicate that its reaction kinetics are faster and it has better potential growth suppression ability in the medium and high current density region.

[0047] 4. Overall water splitting performance ( Figure 4 A symmetrical electrolyzer is assembled using two QIEC-NF electrodes of equal area as the anode and cathode, respectively. Its overall water splitting performance is as follows: Figure 4 As shown. At room temperature, the overall water splitting voltage is approximately 1.55 V; at 60 °C, when the current density is 50, 200, and 250 mA·cm⁻¹, the voltage is... At these times, the cell voltages were approximately 1.67, 1.67, and 1.72 V, respectively. For comparison, electrolytic cells assembled using C1-NF, C2-NF, and C3-NF cells operated at 200 mA·cm⁻¹. The time-cell voltages were approximately 1.76, 1.82, and 1.85 V, respectively. These results demonstrate that QIEC-NF exhibits lower energy consumption and better electrode matching under high-fluid-density overall water splitting conditions.

[0048] 5. Long-term stability ( Figure 4 ): at 60 ℃, 200 mA·cm Under the same conditions, the QIEC-NF electrode underwent constant current stability testing (total testing time not less than 600 h). Its cell voltage slowly increased from approximately 1.72 V to approximately 1.76 V, with a current retention rate greater than 92%, demonstrating excellent high current density durability. In contrast, the C3-NF electrode, after operating under the same conditions for approximately 400 h, had a cell voltage approaching 1.85 V and exhibited some fluctuations, indicating that its interface structure is more prone to reconstruction and instability. Combined with the ordered multi-level interface configuration of "alloy core – carbide interface layer – noble metal cluster – doped carbon shell" of this invention, performance degradation caused by metal dissolution and surface reconstruction can be effectively suppressed, thereby supporting long-term stable operation.

[0049] 6. Correlation between EIS / in-situ Raman and Φ4 index ( Figure 5 – Figure 7 To explain the performance differences and quantify the degree of quaternary interface synergy, electrochemical impedance spectroscopy (EIS) and in-situ Raman spectroscopy were used to characterize the interfacial charge and bonding state. The Nyquist curves are shown below. Figure 5 As shown, the interface charge transfer resistance R_ct can be obtained through equivalent circuit fitting; the in-situ Raman results are as follows. Figure 6 As shown, this reflects the displacement changes of characteristic peaks such as M–O / M–H during operation. After normalizing parameters such as R_ct, double-layer capacitance C_dl, and the M–O / M–H peak displacement, the Φ4 exponent is calculated. The results show that the Φ4 of QIEC-NF is approximately 0.93, while the Φ4 of C1-NF, C2-NF, and C3-NF are approximately 0.78, 0.81, and 0.74, respectively (see...). Figure 7 In addition, such as Figure 7 As shown, Φ4 is significantly negatively correlated with the HER / OER overpotential, indicating that Φ4 can be used as an effective indicator for evaluating the degree of synergy of the QIEC quaternary interface and its contribution to electrocatalytic performance. Figure 8 Characteristic diffraction signals associated with FeNi alloys were observed, along with diffraction features (or broad / weak peaks) associated with Mo-based carbides. This indicates that the alloying of Fe and Ni and the surface carburization of Mo species did indeed occur during heat treatment, providing a structural basis for subsequent mechanism discussion and stability analysis.

[0050] 7. To further verify the multi-level interfacial structure and size distribution characteristics of the QIEC catalyst described in this invention, the samples were characterized by high-resolution transmission electron microscopy and scanning transmission electron microscopy. The results are as follows: Figure 9 As shown.

[0051] like Figure 9 As shown in Figure a, the QIEC catalyst exhibits a clear core-layer-shell structure, in which a continuous MoCx interface layer with a thickness of about 3.0 nm is wrapped around the FeNi alloy core, and the outer layer is an N / O / P co-doped carbon shell; the MoCx lattice fringes can be observed in the inset, with a crystal plane spacing of about 0.21 nm.

[0052] like Figure 9 As shown in b, the Ru ultraclusters distributed near the interface can be clearly distinguished using the HAADF-STEM mode, with particle sizes in the nanoscale range.

[0053] Further statistical analysis was conducted on multiple areas. Figure 9 (c, 9d) The results show that the thickness of the MoCx interface layer is mainly distributed in the range of 0.5–2.5 nm, with an average thickness of about 1.8 nm; the Ru particle size is mainly distributed in the range of 0.5–1.6 nm, with an average particle size of about 1.1 nm.

[0054] The above results show that the method of the present invention can stably construct a multi-level ordered structure of FeNi alloy core—MoCx interface layer—Ru ultracluster—doped carbon shell, with its size distribution within a specific range.

[0055] , To clarify a more suitable preparation route and electrode configuration for high-fluid-density integral water splitting, the applicant prepared AO-L-CM, QIEC-CM, and electrodes with different substrates based on Examples 1–4 and compared them (Table 1). The results show that the QIEC system obtained by "multi-metal precursor sol-forming-AMOC ordered carbonization" exhibits better overall performance when combined with a three-dimensional conductive framework / TPN architecture, and is therefore identified as the basic route for subsequent optimization.

[0056] , Under the condition that the precursor construction and AMOC process remain unchanged, the applicant only adjusted the Fe:Ni:Mo:Ru molar ratio and prepared a series of QIEC powders for comparison of HER / OER activity and stability (Table 2). The comprehensive results determined the preferred range to be 4:2:1:0.10–0.30, and a further preferred range is 4:2:1:0.20.

[0057] , The applicant screened combinations of pre-carbonization temperature T1 and high-temperature carbonization temperature T2 and compared their effects on interface structure and electrochemical performance (Table 3). Based on comprehensive comparison, the preferred temperature windows were determined to be T1 = 300–380 ℃ and T2 = 700–780 ℃.

[0058] , Under the same heat treatment procedure, the applicant only changed the NH3:N2 volume ratio and compared the doping / wetting effect with performance stability (Table 4). Accordingly, the preferred range is NH3:N2 = 1:4–2:3, and more preferably 1:3–2:3.

[0059] , The applicant prepared AO-L with different functionalization levels and constructed corresponding QIEC samples for comparison (Table 5) to evaluate its impact on multi-metal anchoring and interface uniformity. Based on the overall results, "medium to high functionalization" was selected as the preferred precursor region for the stable acquisition of highly synergistic QIEC interfaces.

[0060] , The applicant categorized and screened catalyst areal density and coating thickness, and verified their impact on the high flow density operation of the TPN three-flow network electrode (Table 6). The optimal areal density was determined to be approximately 3.0–3.5 mg·cm³. The coating thickness is approximately 20–40 μm.

[0061] In summary, this invention first proposes the concept of a "quadra-interface electrocatalyst (QIEC)". QIEC uses functionalized lignin AO-L, activated by oxy-ammonia synergistic reaction, as the sole organic framework. It simultaneously introduces multiple metals—Fe, Ni, Mo, and Ru—into a single precursor system. Through AO-L multi-metal ordered carbonization (AMOC) processing, a four-level interface structure unit is formed within the same particle, consisting of a FeNi alloy nanocore, a MoCx gradient interface layer, a Ru ultra-small metal cluster, and an N / O / P co-doped lignin-derived carbon shell. Among these, The FeNi alloy nanocore provides a continuous electronic conduction framework and reconfigurable transition metal active centers; the MoCx graded interface layer maintains metallic conductivity while modulating the electronic structure of Fe / Ni through d-orbital coupling, and serves as a stable adsorption platform for OER intermediates; Ru ultrasmall metal clusters preferentially distribute between the MoCx interface layer and the outer carbon layer, forming highly dispersed active rings. Therefore, it is beneficial for adsorption and desorption in HER and overall water splitting, as it can effectively weaken the binding strength of H and OH intermediates during water molecule breakage, playing a decisive role in HER and overall water splitting. Meanwhile, the AOLC porous carbon shell can provide high conductivity, highly hydrophilic sites, and multi-scale pore structures for electrolyte ions and gaseous products through N / O / P co-doping.

[0062] To precisely control the formation process of QIEC, this invention designs a two-stage AO-L multi-metal ordered carbonization (AMOC) process: In the first stage of pre-carbonization at 300–380 ℃, the AO-L framework undergoes partial dehydration condensation and aromatization, and Fe, Ni, Mo, and Ru metal precursors are gradually transformed into oxide or hydroxide nanoclusters and firmly bonded to the AO-L framework; In the second stage of high-temperature carbonization at 700–780 ℃, the reduction and carbonization rates are controlled by an ammonia-containing inert atmosphere, Fe and Ni ions are reduced and alloyed to form FeNi nanonuclei, Mo species preferentially carbonize on the core surface to obtain a MoCx gradient interface layer, and Ru species nucleate and grow in the interface region and are partially covered by a porous carbon shell to form Ru ultra-small cluster active rings.

[0063] At the macroscopic electrode level, this invention uses AO-LC / FeNi / MoCx / Ru composite powder as a base and employs a combination of spray coating and short-range hot pressing to construct a three-percolation network (TPN) on a porous conductive substrate (such as nickel foam, porous stainless steel plate, conductive carbon paper, etc.). This TPN connects an electron conduction network, an ion percolation network, and a gas expulsion network. The electron conduction network consists of a FeNi alloy core and a highly graphitized AO-LC framework; the ion percolation network consists of hydrophilic AO-LC and exposed MoCx / Ru active sites; and the gas expulsion network relies on the synergistic matching between the multi-scale porous structure of the AO-LC and the pore size of the substrate.

[0064] To quantitatively characterize the degree of synergy at the QIEC quaternary interface, this invention also proposes a "quaternary synergistic interface charge distribution index Φ4" to quantitatively evaluate the contribution of multi-level interfaces to charge transport. Φ4 is calculated using an empirical model based on data such as the open-circuit potential versus time curve, interfacial resistance obtained from electrochemical impedance spectroscopy fitting, double-layer capacitance C_dl, and characteristic peak shifts of M–O / M–H in in-situ Raman spectroscopy. The closer the Φ4 value is to 1, the more uniform the charge distribution at the FeNi / MoCx / Ru / AO-LC quaternary interface, and the more significant the synergistic catalytic effect on HER and OER.

Claims

1. A lignin-based multimetallic ordered carbonized interface quaternary electrocatalyst, characterized in that... It is mainly composed of FeNi alloy nanocore, MoCx gradient interface layer, Ru ultrasmall metal clusters and N / O / P co-doped lignin-derived carbon shell; the MoCx gradient interface layer is tightly coated on the surface of FeNi alloy nanocore, the Ru ultrasmall metal clusters are distributed between the MoCx gradient interface layer and the N / O / P co-doped lignin-derived carbon shell, and the N / O / P co-doped lignin-derived carbon shell surrounds the outermost layer.

2. The quaternary electrocatalyst according to claim 1, characterized in that: The N / O / P co-doped lignin-derived carbon shell is obtained by carbonizing lignin AO-L, which is activated by oxy-ammonia synergy, under an ammonia-containing inert atmosphere.

3. The quaternary electrocatalyst according to claim 2, characterized in that: The thickness of the MoCx gradient interface layer is 0.6–3.0 nm, the average particle size of the Ru ultrasmall metal clusters is 0.5–1.8 nm, and the ratio of the D band to the G band peak intensity (I_D / I_G) in the Raman spectrum of the N / O / P co-doped lignin-derived carbon shell is 0.8–1.

2.

4. The quaternary electrocatalyst according to claim 3, characterized in that: The FeNi alloy nanocore has a Fe to Ni molar ratio of 3:1–2:1, the x in the MoCx gradient interface layer is 0.8–1.0, and the nitrogen content in the N / O / P co-doped lignin-derived carbon shell is 1–8 AT% and the phosphorus content is 0.2–3 AT%.

5. The method for preparing the quaternary electrocatalyst according to claim 1, characterized in that... Includes the following steps: S1, preparation of lignin AO-L activated by synergistic oxygen and ammonium; S2, dissolve the AO-L from step S1 in water or a water / alcohol mixture, and add metal salts of Fe, Ni, Mo and Ru in sequence to form an AO-L multimetal supramolecular precursor sol under alkaline conditions. S3, spray-dry or melt-extrude the sol from step S2 to obtain AM-P precursor microspheres or strip particles; S4, the AM-P precursor microspheres or strip particles from step S3 are subjected to AO-L multi-metal ordered carbonization two-stage heat treatment in an ammonia-containing inert atmosphere to obtain QIEC composite powder. S5. Selective dilute acid leaching, washing, and drying of QIEC composite powder yields the final product.

6. The preparation method according to claim 5, characterized in that... Step S1 was performed as follows: 10 g of enzymatically hydrolyzed lignin was weighed and added to 200 mL of a 2 wt% NaOH aqueous solution, and magnetically stirred at room temperature. Then, under ice-water bath conditions, 20 g of a 4.0 mol·L⁻¹ sodium hypochlorite solution was slowly added dropwise, while controlling the pH value of the solution between 10 and 11, and the reaction was carried out for 1 h. Subsequently, the temperature was raised to 60 ℃, and under continuous stirring, 15 g of urea and 5 g of a 25-28 wt% ammonia solution were slowly added dropwise, and the reaction was continued for 3 h. After the reaction was completed, the solution was cooled to room temperature, and the pH value of the solution was adjusted to 7-8 with 1.0 mol·L⁻¹ dilute hydrochloric acid. The solution was then dialyzed using a dialysis bag with a molecular weight cutoff of 3.5 kDa for 48 h. Finally, the solution was freeze-dried to obtain AO-L.

7. The preparation method according to claim 5, wherein the characteristic is: The molar ratio of Fe, Ni, Mo and Ru is 4:2:1:0.

20.

8. The preparation method according to claim 5, characterized in that: The AO-L multi-metal ordered carbonization two-stage heat treatment involves pre-carbonization at 300–380 ℃ followed by high-temperature carbonization at 700–780 ℃.

9. The application of the quaternary electrocatalyst of claim 1 in high flow density integral water splitting.

10. The quaternary electrocatalyst of claim 1 is used to prepare electrodes or alkaline monolithic water splitting electrolyzers.

Images