Hydrogen and formic acid production method applied to single-chamber membrane-free electrolysis device

Abstract

The invention belongs to the field of hydrogen production through electro-catalytic hydrolysis, and particularly relates to a hydrogen and formic acid production method applied to a single-chamber membrane-free electrolysis device. The Pt-coated NiM-LDH catalyst is used for modifying the cathode and the anode at the same time, the two electrodes are placed in the single-chamber membrane-free electrolytic bath, the industrial-grade current density of 300 mA cm <-2 > can be obtained through the method of periodically changing the current direction and the ultra-low bath voltage, hydrogen production and formic acid production can be continuously achieved for 120 hours, and the Faraday efficiency of hydrogen production and formic acid production is close to 100%.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic water electrolysis for hydrogen production, specifically relating to a method for producing hydrogen and formic acid in a single-chamber electrolysis device. Background Technology

[0002] Hydrogen has high energy density and zero carbon emissions, making it an ideal energy carrier. Compared to hydrogen production technologies such as natural gas reforming and coal reforming, water electrolysis hydrogen production technology does not rely on fossil fuels and can be driven by green electricity, thus achieving zero carbon emissions throughout the entire process. Therefore, it has seen rapid development in recent years. Traditional electrolyzers exhibit hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at the cathode and anode, respectively. To avoid the risk of deflagration caused by the mixing of hydrogen and oxygen produced at the cathode and anode, a diaphragm or partition (CN113913844A) is typically used to separate the cathode and anode chambers. Therefore, hydrogen electrolyzers generally contain two electrode chambers and related sealing components such as a diaphragm (or partition). Taking the currently commonly used alkaline electrolyzer as an example, the diaphragm and related sealing components account for approximately 15-25% of the production cost, and the diaphragm needs to be replaced regularly, further increasing the maintenance cost of the electrolyzer. Furthermore, the kinetics of OER at the anode are slow, producing only low-value oxygen, resulting in high energy consumption for hydrogen production (cell voltage > 1.80 V, accounting for more than 85% of the total energy consumption of the electrolyzer) and low economic efficiency. To improve the economics of electrolytic hydrogen production, using a single-chamber membrane-free electrolyzer is an ideal solution (reducing the preparation and maintenance costs of the electrolyzer by approximately 20-30%). This means that the cathode and anode (or bipolar plates) of the electrolyzer share a single electrolysis chamber, requiring that the anode does not produce oxygen, and that hydrogen at the cathode is the only gaseous product.

[0003] The methanol oxidation (MOR) reaction is a typical anodic reaction that converts methanol into the value-added chemical formic acid under ambient temperature and pressure, thus offering both green and economic advantages. Replacing OER with HER-coupled hydrogen production (MOR‖HER) can simultaneously produce the value-added chemicals formic acid and H2, thus showing excellent application prospects. However, current MOR based on non-precious metal catalysts still requires relatively high electrode potentials (>1.3 V vs RHE) to achieve industrial-grade current densities (≥ 300 mA cm⁻¹). -2 ) (Li, J.; Li, L.; Wang, J.; Cabot, A.; Zhu, Y. Boosting hydrogen evolution bymethanol oxidation reaction on Ni-based electrocatalysts: From fundamental electrochemistry to perspectives. ACS Energy Letters 2024, 9(3), 853-879.), which leads to competition for OER at the anode and the generation of a small amount of oxygen, thus it cannot be used for hydrogen production in a single-chamber membraneless electrolyzer. As for noble metal catalysts, although their MOR electrode potential is very low (≤ 1.0 V vs RHE), which can avoid competition for OER, they face problems such as easy catalyst poisoning and poor long-term stability.

[0004] In summary, if the MOR‖HER system is applied to hydrogen production in a single-chamber membraneless electrolyzer, the low stability of the electrode pairs based on noble metal catalysts needs to be addressed. Summary of the Invention

[0005] To address the aforementioned technical problems, this application provides the following technical solution: This invention provides a method for producing hydrogen and formic acid in a single-chamber electrolysis unit, comprising the following steps: The cathode and anode are placed in a single-chamber membrane-free electrolytic cell, and hydrogen and formic acid are produced by electrolysis under the condition of periodically changing the direction of the current; wherein the cathode and anode are noble metal-based bifunctional electrodes Pt@NiM-LDH, and the electrolyte is an alkaline aqueous solution containing methanol.

[0006] Preferably, the working cell voltage of the noble metal-based bifunctional electrode is 0.1 ~ 1.23 V, and the current is 1 ~ 300 mA cm⁻¹. -2 .

[0007] Preferably, during the electrolysis of hydrogen and formic acid, the direction of the current is changed every 1 to 15 minutes.

[0008] Preferably, the electrolyte is an aqueous solution of sodium hydroxide or potassium hydroxide containing methanol.

[0009] Furthermore, in the electrolyte, the concentration of sodium hydroxide or potassium hydroxide is 0.8 ~ 1.2 mol / L, and the concentration of methanol is 1 ~ 4 mol / L.

[0010] Preferably, the method of periodically changing the direction of the current is to exchange the cathode and the anode.

[0011] Preferably, the preparation method of the noble metal-based bifunctional electrode Pt@NiM-LDH includes the following steps: S11: Add nickel foam to the mixed solution and perform a hydrothermal reaction at 90-100℃ for 5-7 hours to obtain nickel foam with a supported precursor; the mixed solution contains nickel salt, metal salt, urea, ammonium fluoride and water; the metal salt is selected from cobalt salt, manganese salt, copper salt or iron salt; S12: Add the nickel foam of the supported precursor to water containing platinum salt, and heat at 90~100℃ for 2~12 hours to obtain the noble metal-based bifunctional electrode Pt@NiM-LDH.

[0012] Furthermore, the molar ratio of the nickel salt, metal salt, urea, and ammonium fluoride is 3~5:1:500:80~100.

[0013] Furthermore, the concentration of the nickel salt in the mixed solution is 2 to 3 mmol / L.

[0014] Further, in step S12, the concentration of platinum in the water containing platinum is 13.3 ~ 80.0 mg / L.

[0015] Preferably, the nickel salt is selected from nickel nitrate, the metal salt is selected from cobalt nitrate, manganese nitrate, copper nitrate or ferric nitrate, and the platinum salt is selected from chloroplatinic acid.

[0016] The technical solution of the present invention has the following advantages compared with the prior art: The technical problems to be solved by this invention include: the susceptibility to poisoning and low operational stability of noble metal catalysts when used as anodes under MOR conditions. To address these problems, this invention provides a method for the continuous electrolysis of hydrogen and formic acid (or formate) in a single-chamber membrane-free electrolyzer based on a strategy of periodically changing the current direction. Using a synthesized Pt-based composite catalyst (Pt@NiCo-LDH) as both anode and cathode, an ultra-low cell voltage of only 1.02 V is required to achieve 300 mA cm⁻¹ in a single-chamber electrolyzer. -2 The invention achieves industrial-grade current density; by periodically changing the current direction, continuous electrolytic hydrogen and formic acid production for up to 120 hours can be realized, with a formic acid production Faraday efficiency approaching 100%. Therefore, this invention is expected to provide a process route suitable for large-scale, economical, green, rapid, and safe hydrogen and formic acid (or formate) production.

[0017] The MOR‖HER system based on the Pt@NiCo-LDH electrode pair provided by this invention can be applied to a single-chamber membraneless electrolyzer to produce hydrogen and formic acid because the working cell voltage of this system is lower than 1.23 V and no oxygen is generated at the anode.

[0018] The method of periodically changing the current direction provided by this invention can effectively prevent the noble metal catalyst at the anode from being rapidly poisoned under MOR conditions. Therefore, the two-electrode system based on the Pt-based composite catalyst Pt@NiCo-LDH can achieve 300 mA cm⁻¹ in a single-chamber electrolyzer and at a cell voltage of 1.02 V. -2 The current density is high, and hydrogen and formic acid are produced continuously for up to 120 hours, with the anodic formic acid production Faraday efficiency approaching 100%. Attached Figure Description

[0019] Figure 1 The following are performance graphs of the Pt@NiCo-LDH electrode pair and Pt / C(-)||RuO2(+) electrolysis for MOR-assisted electrolytic hydrolysis to produce hydrogen and formic acid and water electrolysis to produce hydrogen: (a) polarization curve, (b) Faraday efficiency graph. Figure 2 These are the stability test curves of the MOR-assisted water electrolysis for hydrogen production and formic acid electrolyzer in Comparative Example 1, Examples 1 to 3 of the present invention; (a) is Comparative Example 1, (b) is Example 2, (c) is Example 1, and (d) is Example 3. Figure 3 These are morphology images of the cathode (a) and anode (b) catalysts Pt@NiCo-LDH after stabilization in Example 1 of this invention; Figure 4 This is a schematic diagram of the single-chamber membraneless electrolytic cell used in Embodiment 1 of the present invention and an electrolysis method that periodically changes the direction of the current. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0021] Example 1:

[0022] This embodiment relates to a method for producing hydrogen and formic acid in a single-chamber membraneless electrolysis device, specifically including the following steps: The preparation steps of the composite catalyst are as follows: (1) Weigh 0.08 mmol of nickel nitrate hexahydrate, 0.02 mmol of cobalt nitrate hexahydrate, 10.00 mmol of urea and 1.80 mmol of ammonium fluoride, add 30 mL of deionized water and stir continuously for 30 minutes to fully dissolve them to obtain a mixed solution. (2) Transfer the above mixed solution to a 50 mL hydrothermal reactor and place in a piece of nickel foam (2×4 cm) that has been ultrasonically washed successively with 2 M hydrochloric acid, alcohol and deionized water. 2 The reaction was carried out at 100 °C for 6 hours and then naturally cooled to room temperature. After the reaction was completed, the nickel foam supported on the precursor was removed and the surface of the nickel foam was rinsed three times with deionized water and alcohol. Then it was dried at 60 °C for later use and labeled as NiCo-LDH. (3) Add 6 mg of chloroplatinic acid to a round-bottom flask containing 150 mL of deionized water (chloroplatinic acid concentration is 40.0 mg / L), stir until completely dissolved, and then add a piece of NiCo-LDH modified nickel foam (NF). Then, heat the reaction at 95 °C for 6 hours. After the reaction is complete, take out the sample, rinse it repeatedly with deionized water and alcohol, and finally dry it under vacuum at 60 °C to obtain the composite catalyst (Pt-based catalyst), named noble metal-based bifunctional electrode Pt@NiM-LDH.

[0023] The noble metal-based bifunctional electrode Pt@NiM-LDH (1×0.5 cm) 2 Simultaneously serving as both anode and cathode, a two-electrode system was constructed in a single-chamber electrolyzer. Using a 1 M KOH + 3 M CH3OH aqueous solution as the electrolyte, the stability of the methanol oxidation-assisted water electrolysis hydrogen production system was tested using a chronopotential method, with a set current of 300 mA cm⁻¹. -2 Change the current direction every 5 minutes and replace the electrolyte every 10 hours.

[0024] Example 2:

[0025] In this embodiment, the time interval for changing the current direction is adjusted to 15 minutes, and the remaining steps and conditions are the same as in Embodiment 1.

[0026] Example 3:

[0027] In this embodiment, the time interval for changing the current direction is adjusted to 1 minute, and the remaining steps and conditions are the same as in Embodiment 1.

[0028] Comparative Example 1: In this comparative example, the current direction is kept constant, and the remaining steps and conditions are the same as in Example 1.

[0029] Effect Evaluation 1: The noble metal-based bifunctional electrode Pt@NiM-LDH (1×0.5 cm) 2 A two-electrode system was constructed, serving as both the anode and cathode. An aqueous solution of 1 M KOH + 3 M CH3OH was used as the electrolyte, and its catalytic activity for methanol oxidation-assisted water electrolysis to produce hydrogen was tested using a Donghua 7000C electrochemical workstation. Within a voltage range of 0.1 ~ 2.5 V (for various oxidation reactions), the catalytic activity was tested at 5 mV s⁻¹. -1 A linear voltammetric scan is performed at a scan rate that yields the corresponding polarization curves (none of which have been adjusted to account for the ohmic potential drop caused by the electrolyte).

[0030] like Figure 1As shown, the noble metal-based bifunctional Pt@NiM-LDH electrode pair exhibits excellent MOR-assisted water and formic acid electrolysis performance, significantly outperforming the commercial RuO2||Pt / C electrode pair in water electrolysis hydrogen production systems. This electrode pair maintains a Faradaic efficiency of over 93% for formic acid production, and requires only an ultra-low cell voltage of 1.02 V to achieve 300 mA cm⁻¹. -2 The industrial-grade current density, as demonstrated, is between 1 and 300 mA cm⁻¹. -2 Within the current density range, the MOR-assisted hydrogen production system based on Example 1 can completely avoid the generation of oxygen, and the use of a membraneless electrolyzer and the significant reduction in energy consumption will lead to a significant reduction in the cost of the hydrogen production system.

[0031] Effect Evaluation 2: like Figure 2 As shown, the stability of the electrode pair composed of Example 1 for catalytic methanol oxidation to formic acid-assisted water electrolysis was tested. The current set was 300 mA cm⁻¹, industrial grade. -2 .like Figure 2 As shown in (a), when tested using the conventional chronopotential method, the catalyst is poisoned because the MOR at the anode produces formic acid and a trace amount of CO adsorbs onto the active sites of the catalyst. Comparative Example 1 was completely deactivated after only about 2.2 hours. Figure 2 As shown in (b) to (d), by using the method of periodically changing the current direction, with a time interval of 1 to 15 minutes between changes in the current direction, the stability of Examples 1 to 3 was significantly improved, and the catalyst CO poisoning phenomenon was mitigated. In particular, Example 1 could achieve a stability at 300 mA cm⁻¹. -2 It operated stably for 120 hours at industrial-grade current density, and the nanosheet morphology of the anode and cathode catalysts remained intact after the stability test. Figure 3 Meanwhile, the required cell voltage in Example 1 is all below 1.23 V, which completely avoids the generation of oxygen and can only obtain the single gaseous product hydrogen. The required electrolytic cell does not need to use a diaphragm. Therefore, the various application examples of the present invention can be applied to the large-scale, rapid, green and safe production of formic acid and hydrogen.

[0032] like Figure 4 The diagram shows the membraneless single-chamber electrolyzer used in Example 1 and the electrolysis strategy of periodically changing the current direction.

[0033] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for producing hydrogen and formic acid in a single-chamber electrolysis unit, characterized in that, Includes the following steps: The cathode and anode are placed in a single-chamber membrane-free electrolytic cell, and hydrogen and formic acid are produced by electrolysis under the condition of periodically changing the direction of the current; wherein the cathode and anode are noble metal-based bifunctional electrodes Pt@NiM-LDH, and the electrolyte is an alkaline aqueous solution containing methanol.

2. The method for producing hydrogen and formic acid in a single-chamber electrolysis unit as described in claim 1, characterized in that, The working cell voltage of the noble metal-based bifunctional electrode is 0.1 ~ 1.23 V.

3. The method for producing hydrogen and formic acid in a single-chamber electrolysis unit as described in claim 1, characterized in that, When producing hydrogen and formic acid by electrolysis, the direction of the current is changed every 1 to 15 minutes.

4. The method for producing hydrogen and formic acid in a single-chamber electrolysis unit as described in claim 1, characterized in that, The electrolyte is an aqueous solution of sodium hydroxide or potassium hydroxide containing methanol.

5. The method for producing hydrogen and formic acid in a single-chamber electrolysis unit as described in claim 4, characterized in that, The electrolyte contains sodium hydroxide or potassium hydroxide at a concentration of 0.8 to 1.2 mol / L and methanol at a concentration of 1 to 4 mol / L.

6. The method for producing hydrogen and formic acid in a single-chamber electrolysis unit as described in claim 1, characterized in that, The method of periodically changing the direction of the current is to exchange the cathode and anode.

7. The method for producing hydrogen and formic acid in a single-chamber electrolysis unit as described in claim 1, characterized in that, The method for preparing the noble metal-based bifunctional electrode Pt@NiM-LDH includes the following steps: S11: Add nickel foam to the mixed solution and perform a hydrothermal reaction at 90-100℃ for 5-7 hours to obtain nickel foam with a supported precursor; the mixed solution contains nickel salt, metal salt, urea, ammonium fluoride and water; the metal salt is selected from cobalt salt, manganese salt, copper salt or iron salt; S12: Add the nickel foam of the supported precursor to water containing platinum salt, and heat at 90-100°C for 2-12 hours to obtain the noble metal-based bifunctional electrode Pt@NiM-LDH.

8. The method for producing hydrogen and formic acid in a single-chamber electrolysis unit as described in claim 7, characterized in that, The molar ratio of the nickel salt, metal salt, urea, and ammonium fluoride is 3~5:1:500:80~100.

9. The method for producing hydrogen and formic acid in a single-chamber electrolysis unit as described in claim 7, characterized in that, The concentration of the nickel salt in the mixed solution is 2 to 3 mmol / L.

10. The method for producing hydrogen and formic acid in a single-chamber electrolysis unit as described in claim 7, characterized in that, In step S12, the concentration of platinum in the water containing platinum is 13.3 ~ 80.0 mg / L.

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