Non-noble metal-based paired electro-catalysis method for producing formic acid by coupling cathode dehalogenation with anode formaldehyde oxidation

Abstract

The invention relates to a non-noble metal-based paired electro-catalysis method for producing formic acid by coupling cathode dehalogenation with anode formaldehyde oxidation, which realizes efficient dehalogenation removal of pollutants and generation of high-value products. The Co-CuxO nanowire electrode with excellent catalytic performance is synthesized through a simple method and serves as a cathode and an anode at the same time, and the purpose that the cathode removes halogenated pollutants and the anode oxidizes formaldehyde to produce formic acid at the same time is achieved. Co-CuxO promotes generation of H *, the performance of electroreduction dehalogenation is improved, and the removal rate of trichloroacetic acid can reach 92.1% or above. And moreover, the reaction energy barrier is reduced, the selectivity of formic acid generated by oxidizing anode formaldehyde is improved, and the formic acid selectivity and Faraday efficiency can reach 100%. A paired electro-catalysis system shows extremely stable and outstanding electro-catalysis performance in the aspect of converting wastes into value-added products, and the problems of poor anode utilization rate and high energy consumption in the current electro-catalysis dehalogenation reaction are solved.

Description

Technical Field

[0001] The present invention relates to the fields of materials and environment, and in particular to a paired electrocatalytic method based on non-noble metal cathode dehalogenation coupled with anode formaldehyde oxidation to produce formic acid. Background Art

[0002] Halogenated pollutants, including halogenated aromatic hydrocarbons, halogenated olefins, halogenated alkanes, and halogenated acetic acids, such as trichloroacetic acid (TCA), a byproduct of chlorination disinfection. These pollutants pose potential health risks and represent a challenge in their management. Electrocatalytic reduction dehalogenation technology can convert halogenated pollutants into non-toxic products in a green and efficient manner, requiring no external reagents. This technology selectively removes chlorine atoms from TCA by generating reducing species such as atomic hydrogen (H*) at room temperature and pressure to produce acetic acid, a byproduct. It offers simple operation and high dehalogenation efficiency. However, electrocatalytic dehalogenation technology focuses solely on the dehalogenation performance of the cathode, while the anode, as a counter electrode, is not fully utilized, limiting the system's effectiveness. The kinetically slow oxygen evolution reaction at the anode, with a high thermodynamic overpotential (>1.23 V vs RHE), consumes significant electrical energy and results in energy waste.

[0003] Formaldehyde is not only a chemical raw material but also a common pollutant in wastewaters such as chemical, printing and dyeing, papermaking, pharmaceutical, and textile wastewater. Replacing the oxygen evolution reaction with the thermodynamically favorable formaldehyde oxidation reaction can produce formic acid at ultra-low potentials. Formic acid is widely used in industries such as rubber, chemicals, and printing and dyeing. The paired electrocatalytic reaction, consisting of cathodic electrocatalytic dehalogenation and anodic formaldehyde oxidation, not only removes pollutants but also produces high-value products such as formic acid, offering both environmental and economic benefits.

[0004] The construction of bifunctional catalysts for paired electrocatalytic reactions is a challenge. Such catalysts must achieve both efficient dehalogenation and be suitable for the anodic formaldehyde oxidation reaction. While noble metals offer excellent performance, their high cost limits their practical application. Non-noble metal catalysts, such as cobalt and copper, are gaining increasing attention. The design of efficient non-noble metal catalysts and the coupling mechanisms of paired electrocatalysis warrant further investigation. Summary of the Invention

[0005] In response to the problem that oxygen evolution reaction occurs at the anode in the current electrocatalytic dehalogenation process, resulting in energy waste and limiting the efficient development of the electrocatalytic dehalogenation process, the present invention proposes a paired electrocatalytic process in which anodes and cathodes are coupled to remove pollutants and produce high-value products. The process achieves simultaneous dehalogenation of halogenated pollutants at the cathode and oxidation of formaldehyde at the anode to produce formic acid. This not only provides an effective solution for pollution control, but also opens up a new method for resource recovery, with both environmental and economic benefits.

[0006] The technical principle of the paired electrocatalytic process is as follows: The formaldehyde oxidation reaction occurs in the anode chamber of the paired electrocatalytic system using Co-Cu x The introduction of Co into the O nanowire electrode can reduce the energy barrier of C-H bond breaking and improve the selectivity of formic acid production. x The introduction of Co into the O electrode changes the Cu x The electronic structure of O enhances the electron-accepting ability of Co, promotes the generation of H*, and improves the performance of electroreduction.

[0007] The present invention relates to a paired electrocatalytic method for producing formic acid by coupling cathode dehalogenation with anode formaldehyde oxidation, which is characterized by: x O nanowires serve as cathode and anode. In a dual-chamber reactor, the cathode liquid is a solution containing halogenated pollutants, and the anode liquid is a potassium hydroxide solution containing formaldehyde. The anode potential is controlled to carry out paired electrocatalytic reactions.

[0008] The above-mentioned paired electrocatalytic method is characterized in that the pollutants treated at the cathode are halogenated pollutants, including halogenated aromatic hydrocarbons, halogenated olefins, halogenated alkanes, and halogenated acetic acids; the concentration of potassium hydroxide is controlled at 0.1 to 1 M, and the anode potential is set at 0.1 to 0.4 V vs RHE.

[0009] The above paired electrocatalytic method is characterized in that Co-Cu x The preparation method of the O nanowire electrode comprises the following steps: (1) The copper foam was placed in 3M HCl, deionized water and ethanol in turn, and ultrasonically treated for 15 minutes respectively to remove the oxide layer on the surface of the copper foam; (2) The treated copper foam was immersed in a solution of sodium hydroxide and ammonium persulfate, washed with water and ethanol, and dried at 60°C to obtain Cu(OH)2; (3) The prepared Cu(OH)2 was placed in a solution of cobalt chloride and urea, transferred to a reactor, and reacted at 120°C for 12 hours. After the reaction system was cooled to room temperature, the product was washed with water and ethanol to obtain Co-Cu x O.

[0010] The above-mentioned Co-Cu x The preparation method of the O nanowire electrode is characterized in that the concentration of sodium hydroxide is controlled at 1 to 3 M, the concentration of ammonium persulfate is controlled at 0.05 to 0.2 M, and the ratio of cobalt chloride to urea is controlled at 1:50 to 1:5.

[0011] The present invention has the following outstanding features: (1) Co-Cu x O preparation method is simple, Co-Cu xO is a nanowire structure, and Co exists in the Cu2O lattice in the form of doping, which has excellent activity and stability. x O reduces the reaction energy barrier, improves the selectivity of anodic formaldehyde oxidation to formic acid, and promotes the generation of H*, thereby enhancing the performance of electroreduction dehalogenation.

[0012] (2) The paired electrocatalytic system achieved the removal of pollutants while producing high-value products. The paired electrocatalytic system significantly promoted the formation of formic acid and dechlorination, reducing energy consumption by 17.0% and 99.6% compared to the individual formaldehyde oxidation and cathodic reduction reactions. The formic acid selectivity and Faradaic efficiency reached 100% at voltages of 0.1-0.4 V vs RHE. Good removal efficiencies (92.1% to 98.3%) and acetic acid selectivity (83.0% to 91.6%) were achieved for halogenated pollutants such as trichloroacetic acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Co-Cu prepared by the present invention x SEM image of O; Figure 2 Co-Cu prepared by the present invention x TEM image of O; Figure 3 Co-Cu prepared by the present invention x XRD pattern of O; Figure 4 Co-Cu prepared by the present invention x LSV curves of O under different reaction conditions; Figure 5 Co-Cu prepared by the present invention x O in a paired electrocatalytic system at different potentials for formaldehyde conversion, formic acid selectivity, and Faradaic efficiency; Figure 6 Co-Cu prepared by the present invention x O removal efficiency, rate constant, acetic acid selectivity, and acetic acid accumulation in a paired electrocatalytic system at different potentials; Figure 7 Comparison of energy consumption between the paired electrocatalytic system and the individual formaldehyde oxidation and trichloroacetic acid reduction reactions; Figure 8 Co-Cu prepared by the present invention x O formaldehyde conversion, formic acid selectivity, and Faradaic efficiency over 10 cycles in a paired electrocatalytic system; Figure 9 Co-Cu prepared by the present invention xO trichloroacetic acid removal efficiency, rate constant, acetic acid selectivity, and acetic acid accumulation in 10 cycles in the paired electrocatalytic system; Figure 10 Formic acid concentration and formaldehyde conversion rate of different catalysts prepared in the present invention in the anodic oxidation formaldehyde reaction; Figure 11 is the free energy of formaldehyde oxidation reaction; Figure 12 The removal efficiency, rate constant, acetic acid selectivity and acetic acid accumulation of trichloroacetic acid in cathode electrocatalytic dehalogenation of different catalysts prepared by the present invention; Figure 13 Co-Cu x O and Cu x EPR spectrum of O; Figure 14 Co-Cu prepared by the present invention x O removal efficiency of different halogenated pollutants in a paired electrocatalytic system. DETAILED DESCRIPTION

[0014] Implementation Case 1 The copper foam was placed in 3M HCl, deionized water and ethanol in turn, and ultrasonically treated for 15 minutes each to remove the oxide layer on the surface of the copper foam; the treated copper foam was immersed in a solution of sodium hydroxide and ammonium persulfate, washed with water and ethanol, and dried at 60°C to obtain Cu(OH)2; the prepared Cu(OH)2 was placed in a solution of 0.4 mM cobalt chloride and 2 mM urea, transferred to a reactor, and reacted at 120°C for 12 hours. After the reaction system was cooled to room temperature, the product was washed with water and ethanol to obtain Co-Cu x O. Figure 1 Co-Cu x O SEM image, we can find Co-Cu x O is in the form of interwoven nanowire structures and is evenly distributed. Figure 2 The TEM images further confirmed that Co-Cu x Nanowire structure of O. Figure 3 In the XRD spectrum of Co-Cu, significant diffraction peaks are observed at 43.3°, 50.4°, and 74.1°. These peaks correspond to the (111), (200), and (220) crystal planes of Cu, respectively (PDF#04-0836). In addition, diffraction peaks also appear at 37.0°, 42.6°, 62.4°, and 74.4°, which correspond to the (111), (200), (220), and (311) crystal planes of Cu2O, respectively (PDF#34-1354). xThe peak intensity corresponding to Cu2O in O increased. This phenomenon strongly confirms that the introduction of Co promotes the formation of Cu2O. Furthermore, no characteristic peaks associated with Co were detected. This suggests that Co does not exist in the form of nanoparticles but rather exists as a dopant within the Cu2O lattice structure.

[0015] Implementation Case 2 Co-Cu x The voltage-current density relationship for the coupled oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) was measured in a dual-chamber reactor with 1 M potassium hydroxide solution as both the catholyte and anolyte, using O as the cathode and anode. The voltage-current density relationship for the paired electrocatalytic reaction was measured in 30 mL of 1 M potassium hydroxide solution containing 0.1 mM trichloroacetic acid as the catholyte and 30 mL of 1 M potassium hydroxide solution containing 0.1 M formaldehyde as the anolyte. Figure 4 It shows that the current density of the coupled oxygen evolution and hydrogen evolution reactions reaches 100 mA cm -2 with 200 mA cm -2 When α-hydroxybenzoic acid (CHC) was added, the required voltages were 2.27 V and 2.64 V, respectively. After adding formaldehyde and trichloroacetic acid, the voltages required for the paired electrocatalytic reaction were significantly reduced by 1.59 V and 1.51 V, to 0.68 V and 1.13 V, respectively. This indicates that the paired electrocatalytic reaction can more efficiently utilize electrical energy and reduce energy waste.

[0016] Implementation Case 3 Co-Cu x O served as the cathode and anode in a dual-chamber reactor. The catholyte was 30 mL of a 1 M potassium hydroxide solution containing 0.1 mM trichloroacetic acid, and the anolyte was 30 mL of a 1 M potassium hydroxide solution containing 0.1 M formaldehyde. The paired electrocatalytic reaction was carried out at a controlled anode potential of 0.1–0.4 V vs. RHE. Figure 5 The results show that during the anodic oxidation of formaldehyde to formic acid, the formaldehyde conversion rate increases from 69.9% to 100% with increasing potential. Furthermore, at an anodic voltage of 0.1-0.4 V vs RHE, both the formic acid selectivity and Faradaic efficiency reach 100%, demonstrating the excellent catalytic performance of the paired electrocatalytic reaction, which selectively converts formaldehyde to formic acid. Figure 6 This indicates that paired electrocatalysis also achieves the directional removal of halogenated pollutants. The electrocatalytic dehalogenation reaction dechlorinates trichloroacetic acid and converts it into acetic acid. At different potentials, the removal rate of trichloroacetic acid can reach more than 92.1%, and the selectivity of acetic acid is between 83.0% and 91.6%. With the increase of voltage, the cumulative concentration of acetic acid increases from 0.079 mM to 0.09 mM, and the rate constant is 0. k From 0.059 min -1 Increased to 0.126 min-1 . Figure 7 It shows that the paired electrocatalytic system (0.195kWh kg -1 ) significantly reduced energy consumption compared to the single formaldehyde oxidation reaction (0.235 kWh kg -1 ) and trichloroacetic acid reduction reaction (48.86 kWh kg -1 ) decreased by 17.0% and 99.6% respectively.

[0017] Implementation Case 4 Co-Cu x O was used as cathode and anode in a dual-chamber reactor. The cathode liquid was 30 mL of 1 M potassium hydroxide solution containing 0.1 mM trichloroacetic acid, and the anode liquid was 30 mL of 1 M potassium hydroxide solution containing 0.1 M formaldehyde. The anode potential was controlled at 0.4 V vs RHE for 10 consecutive paired electrocatalytic reactions. Figure 8 and Figure 9 As shown, Co-Cu x O exhibited excellent stability. Over 10 cycles, the formaldehyde conversion, formic acid selectivity, and Faradaic efficiency of the anodic formaldehyde oxidation reaction all exceeded 90%. The trichloroacetic acid removal efficiency and acetic acid selectivity of the cathodic electrocatalytic dehalogenation reaction also remained above 83.7%.

[0018] Implementation Case 5 Cu was prepared without adding cobalt chloride. x O, and the other preparation conditions were the same as those of Co-Cu x O is consistent. Figure 10 As shown in the figure, in the anodic oxidation formaldehyde reaction, with the doping of Co, the formaldehyde conversion rate increased from 57.5% to 99.4%. At the same time, the concentration of the generated formic acid also increased from 57.5 mM to 97.1 mM, indicating that the introduction of cobalt helps to improve the selectivity of formaldehyde to formic acid. Figure 11 is the Gibbs free energy of the formaldehyde oxidation reaction. In an alkaline environment, formaldehyde is converted to HOCH2O by spontaneous hydrolysis and deprotonation. - Afterwards, HOCH2O - Adsorbed onto the catalyst surface to form HOCH2O* intermediate. Next, HOCH2O* undergoes a C-H bond cleavage step to generate HCOOH*. Finally, HCOOH* desorbs from the catalyst surface to form formic acid. The C-H bond cleavage of HOCH2O* is the rate-determining step in the entire oxidation process. x The Gibbs free energy of O is 1.67 eV, which is lower than that of Cu without Co doping. x O (2.35 eV) is even lower. The introduction of Co can effectively promote the breaking of C-H bonds, thereby accelerating the reaction rate.

[0019] Implementation Case 6 The preparation of the catalyst in Example 6 is basically the same as that in Example 1. Figure 12 It shows that in the electrocatalytic dehalogenation reaction, Co-Cu x O showed the best dechlorination effect, which could increase the removal efficiency of trichloroacetic acid to 97.7%. k 0.11 min -1 The concentration of acetic acid produced reached 0.088 mM, and its selectivity was as high as 89.8%. x O has significant advantages in improving dechlorination efficiency and selective conversion. Figure 13 It shows that Co-Cu x The DMPO-H* signal of O is significantly stronger than that of Cu x O, which indicates that the incorporation of Co enhances the generation of H*. Further experiments show that in Co-Cu x After the pollutant trichloroacetic acid was added to the O electroreduction system, the DMPO-H* signal was significantly weakened. H* plays a crucial role in the reduction process of trichloroacetic acid.

[0020] Implementation Case 7 The catalyst preparation of Example 7 is basically the same as that of Example 1. The cathode function of the paired electrocatalytic system is extended to the degradation of various chlorine-containing pollutants, including chloramphenicol (CAP), thiomycin (TAP) and florfenicol (FLO). Figure 14 As shown, the paired electrocatalytic system achieved excellent removal effect, with removal efficiency ranging from 87.9% to 99.1%, which was 10.4% to 27.9% higher than that of single cathode reduction.

[0021] The above is only an embodiment of the present invention and does not limit the present invention in any form. Any ordinary technician in this industry can successfully implement the present invention as shown in the drawings and above. However, any technician familiar with this profession can make some changes, modifications and evolutions of the contents shown above without departing from the scope of the technical solution of the present invention, which are all equivalent embodiments of the present invention. At the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are within the scope of protection of the technical solution of the present invention.

Claims

1. The present invention relates to a paired electrocatalytic method for producing formic acid by coupling cathode dehalogenation with anode formaldehyde oxidation using a non-noble metal, characterized in that: Co-Cu x O nanowires serve as cathode and anode. In a dual-chamber reactor, the cathode liquid is a solution containing halogenated pollutants, and the anode liquid is a potassium hydroxide solution containing formaldehyde. The anode potential is controlled to carry out paired electrocatalytic reactions.

2. The paired electrocatalytic method according to claim 1, characterized in that: The pollutants treated at the cathode are halogenated pollutants, including halogenated aromatics, halogenated alkenes, halogenated alkanes, and halogenated acetic acids; the concentration of potassium hydroxide is controlled at 0.1 to 1 M, and the anode potential is set at 0.1 to 0.4 V vs RHE.

3. The paired electrocatalytic method according to claim 1, characterized in that Co-Cu x The preparation method of the O nanowire electrode comprises the following steps: (1) The copper foam was placed in 3M HCl, deionized water and ethanol in turn, and ultrasonically treated for 15 minutes respectively to remove the oxide layer on the surface of the copper foam; (2) The treated copper foam was immersed in a solution of sodium hydroxide and ammonium persulfate, washed with water and ethanol, and dried at 60°C to obtain Cu(OH)2; (3) The prepared Cu(OH)2 was placed in a solution of cobalt chloride and urea, transferred to a reactor, and reacted at 120°C for 12 hours. After the reaction system was cooled to room temperature, the product was washed with water and ethanol to obtain Co-Cu x O.

4. The Co-Cu according to claim 3 x The preparation method of O nanowire electrode is characterized in that The concentration of sodium hydroxide is controlled within a range of 1 to 3 M, the concentration of ammonium persulfate is controlled within a range of 0.05 to 0.2 M, and the ratio of cobalt chloride to urea is controlled within a range of 1:50 to 1:5.

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