Method for preparing formic acid by adding sulfuric acid into anode to promote electroreduction of carbon dioxide

Abstract

The invention relates to a method for improving the efficiency of preparing formic acid through CO2 electroreduction in a solid electrolyte (SSE) reactor by regulating and controlling the concentration of anode sulfuric acid. The method is characterized in that in a porous SSE reactor without a prefabricated anion exchange membrane (AEM), a sulfuric acid solution with the concentration of 0.01-0.1 M is used as an anolyte, preferably 0.05 M. According to the method, the hydrogen evolution side reaction caused by excessive migration of protons is inhibited by optimizing the anode microenvironment, and the formic acid selectivity (Faraday efficiency gt; 60%) and reducing the device voltage (the drop amplitude gt; 1.5 V). And by matching with a sandwich-structured gas diffusion electrode (GDE) and a filter paper interlayer, continuous and stable operation for 150 hours by passing through the formic acid with the concentration of 1.5 M at a time can be realized, and the electrode is suitable for efficient conversion from CO2 to formic acid in an electrochemical agricultural path.

Description

Technical Field

[0001] The invention belongs to the fields of electrochemistry, carbon dioxide utilization, bioengineering and modern agricultural technology, and particularly relates to a method for producing formic acid by promoting CO2 electroreduction by adding sulfuric acid to an anode. Background Art

[0002] Faced with the dual challenges of a global energy crisis and climate change, the efficient conversion of carbon dioxide (CO2) into chemicals or fuels has become a crucial path to achieving sustainable development. Among numerous technologies, the electrochemical carbon dioxide reduction reaction (CO2RR) shows significant potential due to its ability to be driven by renewable energy under mild conditions and its controllable product selectivity. However, the large-scale application of this technology is still limited by electrode performance bottlenecks, particularly the microenvironmental instability of gas diffusion electrodes (GDEs).

[0003] Conventional GDE can increase the current density to industrial level (>200mA / cm 2 ), which is significantly better than the immersed electrode. However, the gaseous CO2 feed will cause drastic changes in the local microenvironment: during the reduction reaction, the catalyst surface produces a strong alkaline microenvironment (pH>10) due to the rapid consumption of protons. When a high concentration of inorganic alkali metal cations (such as K + 、Cs + ) to suppress the hydrogen evolution reaction (HER), CO2 reacts with cations to form carbonate / bicarbonate precipitates (such as KHCO3 and K2CO3). These precipitates gradually clog the micropores within the GDE, hindering CO2 mass transfer and destroying the electrode's hydrophobicity, inducing "flooding" and leading to active site failure, current density decay, and decreased product selectivity.

[0004] To maintain reaction activity, existing technologies typically force the addition of 0.5–1M alkali metal electrolytes (such as KHCO3) to the cathode liquid. Although this can improve CO2 reduction efficiency in the short term, the irreversible accumulation of precipitates makes it difficult for the electrode stability to exceed 100 hours. More seriously, liquid products (such as formic acid and acetic acid) are mixed with alkali metal salts and need to be purified through energy-intensive downstream separation processes (such as distillation or electrodialysis), significantly increasing operating costs. In addition, an alkaline environment accelerates the degradation of anion exchange membranes, restricting the long-term operation of membrane electrode assemblies (MEAs).

[0005] In recent years, researchers have attempted to alleviate the precipitation problem through surface hydrophobic modification or pulse electrolysis strategies, but these efforts have failed to fundamentally eliminate the reliance on high-concentration alkali metal electrolytes. Therefore, innovative electrode structure designs are urgently needed to address the precipitation formation and mass transfer blockage issues through in situ microenvironmental manipulation, while also eliminating reliance on catholyte additives to achieve efficient, stable, and low-cost CO2 electrochemical reduction. Summary of the Invention

[0006] The present invention proposes a method for promoting the electroreduction of CO2 to produce formic acid by adding sulfuric acid at the anode. This method can effectively improve the efficiency of the electroreduction of CO2 to produce formic acid by regulating the anode sulfuric acid concentration in a porous solid electrolyte (SSE) reactor without a prefabricated anion exchange membrane.

[0007] In terms of reactor configuration, the anode is made of platinum-coated titanium felt, and the cathode is a sandwich-structured GDE, which includes a catalytic layer (Bi / C), a cationic layer (PDDA-GO), and a protective layer (Sustainion XA-9). The middle chamber is filled with H + Strong cation exchange resin (such as IRC120). By using a sulfuric acid solution with a concentration of 0.01-0.1M, preferably 0.05M, in the anolyte, the following synergistic effects can be achieved: inhibiting hydrogen evolution, reducing excessive proton migration, and maintaining a local alkaline environment at the cathode; reducing internal resistance; compared to 0.5M H2SO4, 0.05M H2SO4 can reduce the device voltage by more than 1.5V; and improving stability, avoiding electrode corrosion and resin contamination, supporting continuous stable operation for more than 150 hours.

[0008] In terms of operating parameters, the anolyte flow rate was controlled at 2 mL / min, the cathode CO2 ventilation rate was 50 sccm, and the operating current density was 25-250 mA / cm 2 The extraction solution uses deionized water at a flow rate of 0.05-0.26 mL / min. By optimizing these parameters and combining a sandwich-configured GDE with filter paper interlayers, a single-pass formic acid concentration of 1.5 M can be achieved, ensuring long-term stable operation of the device. This makes it suitable for the efficient conversion of CO2 to formic acid in electrochemical agricultural pathways, providing a stable and efficient formic acid supply pathway for downstream biomodules to utilize formic acid as a carbon source to produce high-value-added products, and is expected to play an important role in the field of green biomanufacturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 : Schematic diagram of the porous solid electrolyte (SSE) reactor structure.

[0010] Figure 2 : Comparison of FE under different sulfuric acid concentrations (0.005M / 0.05M / 0.5M).

[0011] Figure 3 : Long-term stability curve under 0.05M H2SO4 (150h). DETAILED DESCRIPTION

[0012] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0013] This invention proposes a method for promoting the electroreduction of CO2 to formic acid by adding sulfuric acid to the anode. This method is used in a porous solid-state SSE reactor without a prefabricated anion exchange membrane. By regulating the sulfuric acid concentration at the anode, the efficiency of the electroreduction of CO2 to formic acid is effectively improved. The following is a specific implementation example of the invention.

[0014] Example 1

[0015] In this embodiment, combined with Figure 1 and Figure 2 , the present invention is subjected to sulfuric acid concentration optimization experiment, and the specific operation is as follows:

[0016] Conditional configuration:

[0017] Cathode structure: Sandwich GDE, Bi / C catalyst layer, PDDA-GO (PDDA degree of polymerization 400,000–500,000, loading 1 g L-1, PDDA:GO = 1:3), Sustainion XA-9 protective layer, GDL (200Sus) substrate, surface covered with No. 1 filter paper (3.2 × 3.2 cm -2 ).

[0018] Middle chamber: filled with 0.67g H + Strong cation exchange resin ( IRC120H, large particles). Anode: platinum-coated titanium felt (area 2.5×2.5cm -2 ).

[0019] Operating parameters:

[0020] Anolyte: 100 mL H2SO4 solution (concentration gradient: 0.005 M, 0.05 M, 0.1 M, 0.25 M, 0.5 M), flow rate 2 mL min -1 .

[0021] Extraction solution: deionized water, unidirectional flow rate 0.05 mL min -1 .

[0022] Cathode gas inlet: pure CO2, flow rate 50sccm.

[0023] Current density: 25–250 mA cm -2(corresponding to current 100–1000 mA), and each condition was run at constant current for 1 hour. Experimental results:

[0024] Focus on 100mA cm -2 Performance comparison of different sulfuric acid concentrations under current density:

[0025]

[0026] in conclusion

[0027] like Figure 2 (FE comparison chart under different sulfuric acid concentrations) as shown:

[0028] 0.05M H2SO4 has the best performance: the formic acid FE reaches 63.6%, and the device voltage is the lowest (4.8V), which is >1.5V lower than that of 0.5M H2SO4.

[0029] Both too low (0.005M) and too high (≥0.25M) concentrations deteriorate performance: the former intensifies hydrogen evolution at the cathode due to insufficient proton migration, while the latter increases voltage due to increased internal resistance and resin contamination.

[0030] Full current density verification: 0.05M H2SO4 at 25–250 mA cm -2 FE>60% is maintained within the range.

[0031] Although the present invention has been described in detail, modifications within the spirit and scope of the invention will be apparent to those skilled in the art. The foregoing description is intended only as an example and is not intended to limit the present invention.

[0032] The above are preferred embodiments of the present invention. Any changes made according to the technical solution of the present invention, as long as the resulting functions and effects do not exceed the scope of the technical solution of the present invention, shall fall within the scope of protection of the present invention.

Claims

1. A method for producing formic acid by promoting CO2 electroreduction by adding sulfuric acid to the anode, characterized in that: In a porous solid electrolyte (SSE) reactor without a prefabricated anion exchange membrane, the anolyte is a sulfuric acid solution with a concentration of 0.005–0.5 M. The excessive migration of protons is suppressed by regulating the concentration of sulfuric acid at the anode. Maintaining a local alkaline environment at the cathode achieves a formic acid Faradaic efficiency greater than 60% and a device voltage less than 5.0V.

2. The method according to claim 1, wherein: The sulfuric acid concentration is 0.01–0.1 M, 0.05M is preferred.

3. The method according to claim 1, wherein: The reactor comprises the following components: The anode is a platinum-coated titanium felt (thickness 0.25 mm, platinum coating thickness 0.5 μm). The cathode is a sandwich-type gas diffusion electrode (GDE), comprising: Catalytic layer: Bi / C nanocatalyst (particle size 50 nm) supported on hydrophobic carbon paper; Cationic layer: PDDA-GO composite layer (PDDA degree of polymerization 400,000–500,000, PDDA:GO mass ratio 1:3, loading amount 1 gL-1); Protective layer: anionic polymer Sustainion XA-9. The middle chamber is filled with H + Strong cation exchange resin (particle size 0.45–1.25 mm, such as IRC120H). The interface regulation layer is a filter paper (Whatman No. 1, area 3.2×3.2 cm) covering the cathode surface. -2 ).

4. The method according to claim 1, wherein: The anolyte flow rate is 1–3 mL / min. Preferably 2 mL / min; cathode CO2 ventilation rate is 40–60 sccm, preferably 50 sccm.

5. The method according to claim 1, wherein: Operating current density is 10–300 mA / cm 2 , preferably 25–250 mA / cm 2 ; The extraction solution is deionized water or contains ≤0.1MK + The electrolyte solution has a flow rate of 0.01–0.5 mL / min, preferably 0.05–0.26 mL / min.

6. The method according to claim 3, wherein: The packing density of the cation exchange resin is 0.6–0.8 g / cm 3 , preferably 0.67g / middle chamber.

7. The method according to claim 1, wherein: At a current density of 100 mA / cm 2 , under the conditions of sulfuric acid concentration of 0.05M, the formic acid Faraday efficiency is ≥63.6%, and the device voltage is ≤4.8V.

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