Method for improving performance of preparing formic acid by reducing carbon dioxide through electro-catalysis by wrapping tin sulfide nanoparticles with graphene oxide

Abstract

The invention relates to a method for preparing formic acid by wrapping tin sulfide (SnSx) with graphene oxide (GO) to improve reduction of carbon dioxide (CO2) through electro-catalysis, in particular to an efficient electro-catalysis carbon dioxide reduction system synthesized by wrapping the surface of SnSx with GO through a microwave-assisted method, and belongs to the technical field of catalytic energy. Amorphous SnSx nanoparticles are synthesized by adopting a solution method, and the surface of SnSx is coated with GO nanosheets by adopting a microwave-assisted method to form the SnSx / GO composite material. GO wrapping effectively inhibits crystallization growth of SnSx and loss of sulfur atoms in the electrochemical reduction process, and meanwhile GO is reduced into rGO in situ to optimize mass transfer. In a flow cell, the catalyst achieves a high current density of 126.25 + / -0.78 mA cm <-2 > and a formic acid Faraday efficiency (FE) of 99.9 + / -1.1%. The smooth implementation of the patent provides an efficient strategy for regulating and controlling the efficiency of reducing carbon dioxide into formic acid through electro-catalysis, solves the problem of unstable system structure in the prior art, and provides greater possibility for industrialization in the field of electro-catalysis carbon dioxide reduction.

Description

TECHNICAL FIELD

[0001] The application relates to a method for improving the performance of graphene oxide-wrapped tin sulfide nanoparticles in electrocatalytic carbon dioxide reduction to formic acid, in particular to a method for wrapping GO on the surface of SnS x The application relates to a method for improving the performance of graphene oxide-wrapped tin sulfide nanoparticles in electrocatalytic carbon dioxide reduction to formic acid, in particular to a method for wrapping GO on the surface of SnS BACKGROUND

[0002] The existing tin-based catalysts (such as SnS2) have two major bottlenecks: insufficient activity and selectivity; the traditional crystalline SnS2 is prone to generate large-size metal tin particles in electrochemical reduction, resulting in a formic acid FE of less than 50% (literature value), and a sharp decrease in selectivity under high current density; poor stability; a large amount of sulfur atoms are lost (S:Sn molar ratio decreases to 0.12) in the reduction process, and the catalyst structure collapses, making it difficult to maintain an industrial-level current (more than 100 mA cm -2 ). Although the existing improvement strategies (such as element doping and defect engineering) can improve the performance, they cannot simultaneously solve the problems of crystallization growth and sulfur loss, and therefore, a new structure regulation method needs to be developed. Based on this, the application adopts a solution method to synthesize amorphous SnS x nanoparticles, and GO nanosheets are wrapped on the surface of the SnS x nanoparticles through a microwave-assisted method to form SnS x / GO composite materials. In a flow cell, the catalyst achieves a high current density of 126.25+0.78 mA cm -2 and a formic acid Faraday efficiency (FE) of 99.9+1.1%. The method provides an efficient strategy for regulating the efficiency of electrocatalytic carbon dioxide reduction to formic acid, and solves the problem of unstable system structure in the prior art, thereby providing greater possibility for industrialization of the field of electrocatalytic carbon dioxide reduction. SUMMARY

[0003] The application solves the technical problems of the existing SnS x In the process of electrocatalytic carbon dioxide reduction, crystallization growth, serious loss of sulfur atoms, and the resulting decrease in catalytic activity, low product selectivity and insufficient stability are caused by the reduction environment in a timely manner.

[0004] To solve the above technical problems, the technical solution provided by the application is a method for improving the performance of graphene oxide-wrapped tin sulfide nanoparticles in electrocatalytic carbon dioxide reduction to formic acid, which adopts a solution method to synthesize amorphous SnS x nanoparticles, and GO nanosheets are wrapped on the surface of the SnS x nanoparticles through a microwave-assisted method to form SnS xThe method for preparing the / GO composite material is as follows: After the mixture of SnCl4 and Na2S is prepared, 0.9 mL of GO suspension (2 mg / mL) is added during the ultrasonic treatment. −1 The final product contained 1‰ graphene oxide by mass. The resulting mixture was microwaved for 5 minutes (output power = 800 W). The resulting product (SnS) x The mixture was washed five times with ultrapure water and then redispersed with a 10 mL water:ethanol mixture (1:1).

[0005] Preferred, amorphous SnS x Preparation process of nanoparticles: SnS was prepared by microwave-assisted method. x Nanocatalyst. First, Na₂S·9H₂O was dissolved in 20 mL of ultrapure water to obtain a 10 mM solution, and crystalline SnCl₄ was dissolved in 10 mL of ultrapure water to obtain a 5 mM solution. The SnCl₄ and Na₂S solutions were thoroughly mixed under ultrasound to form a suspension. The suspension was sonicated for 30 minutes, and then stirred at 600 rpm for 12 hours. Afterwards, the suspension was microwaved for 5 minutes (output power = 800 W). The resulting product (SnCl₄·9H₂O ... x Wash five times with ultrapure water, then redisperse with a 10 mL water:ethanol mixture (1:1).

[0006] Preferably, the working electrode is prepared by drop-coating the catalyst onto the surface of carbon paper. Typically, 10 mL of the prepared catalyst suspension is taken and 5 μL of a 5 wt% Nafion solution is added. After sonication for 30 minutes, a yellow suspension is obtained. Then, 50 μL of the suspension is drop-coated onto a 2 × 2 cm² gas diffusion electrode (GDE) and dried in air at 90°C for 15 minutes. This catalyst-coated carbon paper is used as the working electrode.

[0007] Preferably, the electrocatalytic CO2 reduction test procedure is as follows: using the working electrode described above, platinum foam and Ag|AgCl (stored in saturated KCl) are used as the counter electrode and reference electrode, respectively. Electrocatalysis is carried out in a flow cell. The counter electrode is separated from the GED and reference electrode by a proton exchange membrane (Nafion N117, DuPont). The potential is provided by an electrochemical cell (CHI 630E, CHInstrument). In this flow cell, 5 M KHCO3 is circulated at a flow rate of 5 mL min⁻¹, and CO2 gas is supplied at a flow rate of 30 mL min⁻¹.

[0008] Preferably, the gas phase product analysis process is as follows: analysis is performed using a gas chromatograph (GC-9860-5C, AGC, Nanjing, China), which is equipped with a thermal conductivity detector (TCD) for detecting H2 and a flame ionization detector (FID) for detecting CO, CH4, C2H4 and C2H6.

[0009] Preferably, the liquid phase product analysis process is as follows: the liquid phase product is quantified using a nuclear magnetic resonance (NMR) spectrometer (JNM-ECZ400S / L1, JEOL, Japan). The Faraday efficiency (FE) of the product is calculated using the following formula:

[0010] Where e is the number of electrons transferred. F It is the Faraday constant (96485 C mol⁻¹), n is the molar amount of product determined by GC or ¹H NMR, and Q total It is the total charge provided by the external circuit.

[0011] The beneficial effects of this invention are: 1. Improved structural stability: GO wrapper limits SnS x Crystallization growth (particle size after electrochemical treatment: 3.7 ± 0.9 nm vs. uncoated sample: 27.0 ± 8.4 nm); sulfur atom retention rate improved (S:Sn molar ratio: 0.7669 vs. uncoated sample: 0.1227).

[0012] 2. Breakthrough in catalytic performance: Formic acid FE reached 99.9±1.1% (-1.1 V vs. RHE), setting a new record high in the literature; formic acid partial current density was 126.25 mA cm⁻¹. -2 (Flow cell), 554.41 mA cm -2 (MEA); TOF improved by 62% (28.72 s⁻¹ vs. 17.72 s⁻¹ for unencapsulated samples).

[0013] 3. Long-term stability: Ampere-level current (~120 mA cm⁻¹) -2 After 50 hours of stable operation, the FE remains >99.7%.

[0014] 4. Universality verification: This strategy is applicable to catalysts such as MoS2 and Cu2S, and significantly improves the selectivity of formic acid. Attached Figure Description

[0015] The present invention will be further described below with reference to the accompanying drawings.

[0016] Figure 1 It is a GO package SnSx A schematic diagram illustrating the mechanism for inhibiting crystallization and sulfur loss.

[0017] Figure 2 It is SnS x Structural characterization of / GO. (a) SnS x TEM image of SnS. (b) SnS x High-resolution TEM image. (c) SnS x TEM image of / GO. (d) SnS x High-resolution TEM image of / GO.

[0018] Figure 3 It is SnS x Performance study of / GO and uncoated samples: (a) FE comparison. (b) Comparison of partial current densities. (c) TOF.

[0019] Figure 4 It is SnS x Stability testing of / GO.

[0020] Figure 5 It is SnS x and SnS x Comparison after the / GO reaction. (a) S:Sn ratio after activation. (b) XPS of the activated S 2p orbital.

[0021] Figure 6 It is SnS x TEM images and particle size distribution of / GO catalyst after electrochemical activation. Detailed Implementation Example

[0022] First, 5 mM SnCl4 and 10 mM Na2S·9H2O solution were mixed, and 2 mg / mL GO suspension (GO content 1‰) was added. The mixture was sonicated for 30 min, microwaved (800 W, 5 min), and washed to obtain SnS. x / GO composite materials.

[0023] Our electrocatalytic testing process is as follows: The SnS prepared above x / GO coated on GDE carbon paper was placed in a flowing electrolytic cell with 0.5 M KHCO3 as the electrolyte and CO2 was introduced at 30 mL / min. The eCO2RR was tested at −1.1 V vs. RHE. The results showed that the formic acid Faradaic efficiency reached 99.9%, and the current density reached 126 mA cm⁻¹. -2After 50 hours of continuous operation at −1.1 V vs. RHE, both the current density and formic acid Faraday efficiency remained stable without significant degradation. All test data were acquired in real time using an electrochemical workstation (CHI 760E, Shanghai Chenhua Instrument Co., Ltd.). like Figure 1 It is a GO package SnS x A schematic diagram illustrating the mechanism of inhibiting crystallization and sulfur loss. GO encapsulation effectively inhibits SnS during electrochemical reduction. x The crystallization growth and sulfur atom loss occur, while GO is reduced in situ to rGO to optimize mass transfer. like Figure 2 It is SnS x and SnS x Structural characterization of / GO. Synthetic SnS x High-resolution transmission electron microscopy (HRTEM) images of the nanocatalyst confirmed the presence of SnS. x The morphology of the nanocatalyst is as follows: it consists of amorphous and some ultrafine nanocrystals (2.3 ± 0.4 nm). A 0.314 nm interplanar spacing was observed, which can be attributed to the (001) plane of SnS2 (JCPDS No. 23-0677), indicating the presence of nanocrystalline SnS2. To reveal its crystallinity, selected area electron diffraction (SAED) was performed. The resulting SAED pattern showed a blurred ring structure, indicating that the synthesized SnS2 has amorphous or ultrafine nanocrystalline properties. x Irregular morphology was also observed in the / GO sample, and amorphous domains and some ultrafine nanocrystals were observed in the high-resolution TEM images. SnS2(001) planes were also observed in the TEM images, indicating the presence of the SnS2 phase. Furthermore, a more blurred SAED mode was observed, indicating that SnS... x / GO has poor crystallinity.

[0024] like Figure 3 It is SnS x Performance study of / GO and uncoated samples, SnS at -1.0 vs. RHE potential. x The formic acid FE in the sample was 80.2 ± 1.8%, in SnS x In the / GO sample, the formic acid FE increased, achieving the highest FE (99.9 ± 1.1%) at a potential of -1.1 relative to RHE, indicating that GO encapsulation significantly contributes to the enhanced FE of formic acid in the CO2ER. To quantify the improvement in formic acid yield, we also calculated SnS x and SnS x Partial current density of formic acid at different potentials in the / GO system. xIn the GO / G system, the partial current density of formic acid increases, especially at more negative potentials, indicating that GO encapsulation makes a significant contribution to improving formic acid yield. At −1.1 vs. RHE potentials, a current density of 126.25 ± 0.78 mA cm⁻¹ was obtained. −2 The shunt current density is extremely high. At a potential of -1.3 vs. RHE, this shunt current density further increases to 259.00 ± 5.78 mA cm⁻¹. −2 SnS was calculated. x and SnS x / GO samples were analyzed for formic acid turnover times (TOFs) at -1.1V vs. RHE to quantify the improvement in formic acid production by CO2ER. SnS x The TOF of / GO further increased to 28.72 ± 0.26 s. −1 Compared to SnS x (17.72±0.23 s) −1 This indicates that SnS increased by 62%. x The catalytic activity of SnS was significantly higher than that of its crystalline counterpart, and the introduction of graphene oxide nanosheets further enhanced the catalytic activity of SnS. x Catalytic activity of formic acid production via CO2ER.

[0025] like Figure 4 It is SnS x / GO stability, SnS x / GO also exhibited high stability in CO2ER. The current density of −1.1 V vs. RHE remained stable at ~120 mA cm⁻¹ over a long reaction period of 50 h. −2 Furthermore, the electrocatalytic activity (FE) of formic acid remained stable at approximately 99.7% during a 50-hour reaction, further demonstrating its high electrocatalytic stability. like Figure 5 Yes, it is SnS x and SnS x Comparison after the / GO reaction, SnS before and after electrochemical activation was measured by ICP-OES. x and SnS x The elemental composition of / GO, further research on SnS x and SnS x Changes in / GO. SnS x and SnS x The S-Sn molar ratio of Sn / GO was approximately 1.675 ± 0.028. After electrochemical activation, SnS... x The molar ratio of S-to-Sn in Sn decreased significantly to 0.1227 ± 0.0002, confirming that SnS x A severe chemical reduction occurred, producing metallic Sn. SnS... xThe molar ratio of S-to-Sn in / GO decreased only to 0.7669±0.0095 after electrochemical activation, indicating that SnS x Partial electrochemical reduction occurred. SnS x The smaller decrease in the S-to-Sn molar ratio of the / GO catalyst indicates that graphene oxide nanosheets have a greater influence on SnS x It has a protective effect. XPS is also used to characterize electrochemically activated SnS. x and SnS x / GO surface state. In SnS x No S 2p peak was observed in the sample, indicating the absence of S atoms on the surface. (SnS) x The S 2p peak can be clearly observed in the / GO sample, indicating that the presence of GO / rGO nanosheets helps to confine S atoms.

[0026] like Figure 6 This visually reflects the microstructural evolution of the catalyst after electrochemical activation (reduction), providing crucial evidence for confirming the graphene oxide (GO) encapsulation effect. TEM images show that after undergoing a high-current-density electrochemical reduction process, SnS… x The / GO composite material retains its initial irregular fragmented morphology, without significant structural collapse. High-magnification images clearly show the presence of ultrafine SnS... x / GO nanoparticles were encapsulated layer by layer by thin GO / rGO nanosheets. In contrast, the unencapsulated sample under the same conditions exhibited large-area, coarse metallic tin crystals, while SnS x / GO effectively suppressed this phenomenon, indicating that the GO coating layer physically restricted the movement and recombination of the internal active components. Particle size statistics (Figure 6a) further confirmed that the activated SnS... x / GO nanoparticles have an average diameter of only 3.7 ± 0.9 nm and an extremely narrow distribution, successfully avoiding particle aggregation; while the uncoated sample rapidly crystallized and grew after activation, with the particle size increasing dramatically to 27.0 ± 8.4 nm, which is about 6.5 times the initial size.

[0027] Comparative Example 1: GO's packages can significantly affect SnS x To assess the catalyst's performance, we prepared SnS using a microwave-assisted method. xNanocatalyst. First, Na₂S·9H₂O was dissolved in 20 mL of ultrapure water to obtain a 10 mM solution, and crystalline SnCl₄ was dissolved in 10 mL of ultrapure water to obtain a 5 mM solution. The SnCl₄ and Na₂S solutions were thoroughly mixed under ultrasound to form a suspension. The suspension was sonicated for 30 minutes, and then stirred at 600 rpm for 12 hours. Afterwards, the suspension was microwaved for 5 minutes (output power = 800 W). The resulting product (SnCl₄·9H₂O ... x The sample was washed five times with ultrapure water and then redispersed with a 10 mL water:ethanol mixture (1:1). Amorphous SnS was prepared. x The catalyst, with a maximum FE content of 80.2%, is significantly lower than that of GO-encapsulated catalysts, demonstrating the important role of GO.

[0028] The present invention is not limited to the specific technical solutions described in the above embodiments. All technical solutions formed by equivalent substitutions are within the scope of protection claimed by the present invention.

Claims

1. A method for enhancing the electrocatalytic reduction of carbon dioxide to formic acid by encapsulating tin sulfide nanoparticles with graphene oxide, characterized in that: Tin source (SnCl4) and sulfur source (Na2S·9H2O) were mixed at a S:Sn molar ratio of 2:1, and a graphene oxide (GO) suspension (1‰ by mass) was added. SnS was synthesized by ultrasonic dispersion, stirring, and microwave treatment (800W, 5 min). x / GO composite material; the composite material was loaded onto a gas diffusion electrode (GDE) and electrocatalytically reduced CO2 in a flow cell or membrane electrolyzer. The electrolyte was 0.5 MkHCO3, and the CO2 flow rate was 30 mL / min. -1 .

2. The method for improving the electrocatalytic reduction of carbon dioxide to formic acid by encapsulating tin sulfide nanoparticles with graphene oxide according to claim 1, characterized in that: The GO package inhibits SnS x Crystallization growth during electrochemical reduction process, maintaining SnS x Particle size <4nm, and retains sulfur atoms (S:Sn molar ratio ≥0.7669 after electrochemical treatment).

3. The method for improving the electrocatalytic reduction of carbon dioxide to formic acid by encapsulating tin sulfide nanoparticles with graphene oxide according to claim 1, characterized in that: The GO is reduced in situ to hydrophobic rGO during the electrochemical process, which inhibits the hydrogen evolution reaction (HER) and promotes CO2 mass transfer.

4. The method for improving the electrocatalytic reduction of carbon dioxide to formic acid by encapsulating tin sulfide nanoparticles with graphene oxide according to claim 1, characterized in that: The SnS x The / GO catalyst achieved the following performance in a flow cell: formic acid FE up to 99.9 ± 1.1% (-1.1 V vs. RHE); formic acid partial current density 126.25 ± 0.78 mA cm⁻¹ -2 Stable operation for 50 hours at -1.1V vs. RHE with current density retention >95%.

5. The method for improving the electrocatalytic reduction of carbon dioxide to formic acid by encapsulating tin sulfide nanoparticles with graphene oxide according to claim 1, characterized in that: The method is applicable to the GO encapsulation modification of other amorphous / nanocrystalline catalysts (such as MoS2, Cu2S) to improve CO2 reduction selectivity.

6. The method for improving the electrocatalytic reduction of carbon dioxide to formic acid by encapsulating tin sulfide nanoparticles with graphene oxide according to claim 1, characterized in that: Add 5 μL of 5 wt% Nafion solution to 10 mL of the prepared catalyst suspension. After sonication for 30 min, a yellow suspension is obtained. Drop 50 μL of the suspension into a 2 × 2 cm⁻¹ column. 2 On the gas diffusion electrode (GDE), air-dry at 90°C for 15 min.

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