Preparation method of Ag3PO4 nanospheres and application of Ag3PO4 nanospheres in electrocatalysis of CO2 reduction

Abstract

The invention discloses a preparation method of silver phosphate (Ag3PO4) nanospheres and application of the silver phosphate (Ag3PO4) nanospheres in electrocatalytic carbon dioxide reduction reaction (ECO2RR). The catalyst is synthesized by adopting a simple complexing-precipitation method, the process is simple and convenient, the condition is mild, and the catalyst is suitable for large-scale preparation. The obtained Ag3PO4 nanospheres show excellent catalytic performance in the CO2 electroreduction process, the activity of the nanospheres is mainly improved due to the fact that silver phosphate promotes generation of key intermediates COOH and COO, the adsorption capacity of the nanospheres to * CO2 intermediates is remarkably enhanced, and therefore the reaction selectivity and catalytic efficiency are effectively improved. The Ag-based electrocatalyst has the remarkable advantage of improving the problem of poor CO2 reduction selectivity of a traditional Ag-based electrocatalyst. Meanwhile, the technology is green and environment-friendly, the used raw materials are cheap and easy to obtain, the energy consumption in the synthesis process is low, and the method has good practicability and wide application prospects.

Description

Technical Field

[0001] The present invention relates to a preparation method of Ag3PO4 nanospheres and application thereof in an electrocatalytic carbon dioxide reduction reaction, belonging to the technical field of electrocatalytic material preparation, and is specifically applied to the electrocatalytic reduction of CO2 to generate CO. Technical Background

[0002] In recent years, global CO2 emissions have reached 36.3 Gt. The continued release of these massive quantities of CO2 has triggered a series of serious environmental problems, including ocean acidification, melting Arctic glaciers, and extreme climate change. Although CO2 reduction technology offers a viable path to carbon neutrality, existing approaches face numerous challenges: thermal catalytic CO2 reduction suffers from high energy consumption, poor product selectivity, and catalyst deactivation; photocatalytic CO2 reduction processes are limited by low light absorption efficiency and complex product distribution; and biocatalytic processes are limited in their widespread application due to low substrate affinity and slow reaction rates. Therefore, developing efficient, green, and sustainable CO2 conversion pathways has become a key research priority.

[0003] The electrocatalytic CO2 reduction reaction (ECO2RR) has become a research hotspot that has attracted much attention in recent years because it can be carried out at room temperature and pressure, and the required electricity can be provided by renewable energy sources such as solar energy, wind energy, and tidal energy. One of the target products, CO, is not only an important component of syngas and has a wide range of industrial applications, but is also one of the most economically viable products currently obtained through ECO2RR. However, due to the high bond energy of the C=O double bond in the CO2 molecule, which is as high as 750 kJ·mol -1 , and its activation process is very difficult. Although silver (Ag)-based catalysts are widely used in CO2 reduction reactions, their interaction with CO2 is weak, especially the poor adsorption capacity of the key intermediate *COO⁻ on its surface active sites, which seriously limits the efficiency of CO production. At the same time, the formation kinetics of CO2⁻ and COOH intermediates are slow, so that the initial activation process of CO2 is considered to be the rate-determining step of the overall reaction. At present, the structure and electronic properties of Ag-based catalysts are usually optimized by constructing nanostructures, introducing molecular regulation strategies, doping with foreign elements or constructing alloys, so as to improve their adsorption and activation ability for CO2 molecules, thereby improving the efficiency and selectivity of electrocatalytic reduction of CO2 to CO. Summary of the Invention

[0004] The present invention aims to address the numerous issues associated with Ag-based electrocatalysts in the electrocatalytic carbon dioxide reduction reaction (ECO2RR), including high overpotential, severe hydrogen evolution reaction, and slow reaction kinetics. These issues collectively result in generally low Faradaic efficiency and current density for the target product, CO. To this end, the present invention proposes an improved method for preparing Ag3PO4 nanospheres. During the synthesis process, silver ions first react with sodium citrate dihydrate to form a stable silver citrate complex. This complex exhibits strong intermolecular interactions, helping to control the release rate of silver ions in subsequent reactions. Subsequently, during the reaction with disodium hydrogen phosphate, the silver ion concentration in the system is maintained at a low level through the regulation of a complexing agent, avoiding localized oversaturation and enabling precise control of the crystal nucleation and growth processes. The initially formed silver phosphate nuclei are coated by the timely released citrate, significantly inhibiting internuclear aggregation and secondary growth, ultimately forming uniform, small-sized Ag3PO4 nanospheres.

[0005] Compared to traditional silver phosphate particles produced by the direct reaction of disodium hydrogen phosphate and silver nitrate, the Ag3PO4 nanospheres prepared in this invention have a smaller particle size and a higher specific surface area. This structural advantage not only enhances the adsorption capacity of the key intermediate *CO2⁻, but also significantly increases the number of exposed active sites on the catalyst surface, thereby improving the overall catalytic performance of the electrocatalytic reduction of CO2 to CO.

[0006] In order to achieve the above-mentioned purpose of the invention, the following technical solutions are mainly adopted: A method for preparing an Ag3PO4 nanosphere electrocatalyst material comprises the following steps: (1) Weigh a certain amount of silver nitrate, sodium citrate dihydrate, and disodium hydrogen phosphate respectively, add them to a beaker containing a certain volume of ethylene glycol, and stir vigorously for 30 minutes; (2) Add sodium citrate dihydrate solution dropwise to the silver nitrate solution to obtain a milky white mixed solution, and continue to stir vigorously for 30 minutes; (3) Then, disodium hydrogen phosphate solution was added dropwise to the milky white mixed solution and reacted for 1 hour; (4) After the reaction, the product was collected by centrifugation and washed with deionized water and ethanol three times each; (5) The obtained precipitate was vacuum dried at 60 °C for 12 h to obtain Ag3PO4 nanospheres.

[0007] The amount of each raw material used in the preparation method of the Ag3PO4 nanosphere electrocatalyst material described above is: 1-3 mmol of silver nitrate, 0-1 mmol of sodium citrate dihydrate, 1-2 mmol of disodium hydrogen phosphate, and a volume of 5-15 mL of ethylene glycol. The raw material ratio can be scaled up proportionally.

[0008] The method of the present invention prepares an Ag3PO4 nanosphere electrocatalyst material.

[0009] The beneficial effects of the present invention are: The electrode material prepared by the present invention adopts a simple complexation-precipitation method, which has the characteristics of simple operation steps, mild processing conditions, short reaction time, low energy consumption, and environmental friendliness. It is suitable for mass production and has certain application prospects.

[0010] Compared with the prior art, the present invention has significant advantages: the silver phosphate nanospheres prepared by the method are smaller in size than the silver phosphate obtained by direct precipitation of disodium hydrogen phosphate and silver nitrate, and can promote the reaction of *COOH and *COO - The generation of intermediates greatly promotes the production of *CO2 - The adsorption of the intermediate significantly improves the ECO2RR performance of Ag3PO4, effectively improving the poor selectivity of Ag-based electrocatalytic reduction of CO2. Furthermore, the complexation-precipitation method of the present invention is simple and easy to operate, has good reproducibility, strong controllability, is environmentally friendly, and has mild synthesis conditions, which is conducive to large-scale preparation and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is the XRD pattern of the Ag3PO4 nanocatalyst prepared by the complexation-precipitation method in Example 1.

[0012] Figure 2 This is the SEM image of the Ag3PO4 nanocatalyst prepared by the complexation-precipitation method in Example 1.

[0013] Figure 3 This is the electrocatalytic CO2 reduction activity diagram of the Ag3PO4 nanocatalyst prepared by the complexation-precipitation method in Example 1.

[0014] Figure 4 This is the total current density diagram of CO in the electrocatalytic reduction of CO2 over Ag3PO4 catalyst in Example 1.

[0015] Figure 5 This is the partial current density diagram of CO in the electrocatalytic reduction of CO2 over Ag3PO4 catalyst in Example 1.

[0016] Figure 6 This is the activity diagram of Ag electrocatalytic CO2 reduction in Example 2.

[0017] Figure 7 This is the total current density diagram of Ag electrocatalytic CO2 reduction in Example 2.

[0018] Figure 8This is the current density diagram of Ag electrocatalytic CO2 reduction in Example 2. DETAILED DESCRIPTION

[0019] The present invention is described in detail below with reference to specific embodiments, but is not intended to limit the present invention. Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0020] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0021] Example 1: 0.5096 g of silver nitrate, 0.2941 g of sodium citrate dihydrate, and 0.2839 g of disodium hydrogen phosphate were weighed and added to a beaker containing 15 mL of ethylene glycol. After vigorous stirring for half an hour, the sodium citrate dihydrate solution was added dropwise to the silver nitrate solution to obtain a milky white solution. After vigorous stirring for half an hour, the disodium hydrogen phosphate solution was added dropwise to the milky white solution. After reacting for one hour, the precipitate was centrifuged and washed three times with deionized water and ethanol, respectively. The precipitate was then dried in vacuo at 60°C for 12 hours to obtain the silver phosphate product.

[0022] Example 2: First, in a plastic beaker, dissolve 4.7286 g of sodium borohydride in 15 mL of deionized water (before use, purge the deionized water of dissolved oxygen with nitrogen) to prepare a 5 mol / L NaBH4 solution. Cool the solution to room temperature in an ice-water bath. Then, transfer the resulting solution to a 25 mL volumetric flask and dilute to volume with deionized water. Next, dissolve 0.4900 g of silver nitrate in 40 mL of deionized water and stir for 30 minutes in the dark. Then, add 5 mL of a prepared 0.5 mol / L NaOH solution dropwise to the silver nitrate solution. After stirring for 30 minutes, add 5 mL of freshly prepared 5 mol / L sodium borohydride solution dropwise to the solution. Finally, after stirring for an additional hour, the reaction mixture was centrifuged, and the precipitate was washed three times with deionized water and then with anhydrous ethanol. The final product was vacuum-dried at 60°C for 12 hours and ground to obtain the silver catalyst.

[0023] The structural test of the prepared samples was carried out on a Shimadzu X-ray diffractometer (XRD) (model XRD6100, Cu-Kα radiation, voltage of 40 kV) with a scanning range of 10°-80° and a scanning rate of 7 °min -1 .like Figure 1 As shown, in Example 1, the XRD spectrum shows that the prepared catalyst phase is Ag3PO4, indicating that the Ag3PO4 catalyst was successfully prepared.

[0024] Figure 2This is the SEM spectrum of the Ag3PO4 nanocatalyst prepared by the complexation-precipitation method in Example 1, which is a spherical and quasi-spherical catalyst material.

[0025] Electrocatalytic Activity Testing: Electrochemical tests were performed using an electrochemical workstation (Chenhua, CHI760E) equipped with a current amplifier. All potentials were measured relative to an Ag / AgCl reference electrode. CO and H₂ were analyzed using an online gas chromatograph (Shimadzu, GC-2014).

[0026] The Ag3PO4 electrocatalyst material prepared in the example was ground into a powder. A 4 mg sample was weighed using an analytical balance and placed into a 5 mL centrifuge tube. 800 µL of isopropanol, 200 µL of deionized water, and 10 µL of Nafion were added, and the solution was sonicated for 30 minutes to completely disperse the catalyst powder in the solution. A pre-cut gas diffusion electrode sheet (1 cm x 2.5 cm) was placed on a heating plate. After the temperature stabilized at 80°C, 500 µL of the catalyst suspension was evenly drop-coated onto the sheet. The prepared sheet served as the working electrode, with a saturated Ag / AgCl electrode and a Pt electrode serving as the reference and counter electrodes, respectively. Electrochemical measurements were performed using an electrochemical workstation using a 1.0 M KOH solution as the electrolyte. Before each electrochemical measurement, the working electrode was activated at a potential of -1 to -2 V vs. Ag / AgCl. The activity range was determined by linear sweep voltammetry (LSV) in 1.0 M KOH solution at a scan rate of 100 mV / s. Performance was measured in 1.0 M KOH electrolyte using current-time voltammetry over the range of -1.4 to -2.1 V vs. Ag / AgCl.

[0027] From the electrochemical performance test diagram above, it can be seen that the Ag3PO4 nanocatalyst prepared according to Example 1 exhibits excellent ECO2RR performance to CO.

[0028] The above disclosure is only a preferred embodiment of the present invention. Without departing from the above method concept of the present invention, replacements and improvements based on common technical knowledge and customary means in this field should be included in the scope of protection of the present invention.

Claims

1. A method for preparing Ag3PO4 nanosphere electrocatalyst material, characterized in that: The following steps are involved: (1) Weigh a certain amount of silver nitrate, sodium citrate dihydrate, and disodium hydrogen phosphate respectively, add them to a beaker containing a certain volume of ethylene glycol, and stir vigorously for 30 minutes; (2) Add sodium citrate dihydrate solution dropwise to the silver nitrate solution to obtain a milky white mixed solution, and continue to stir vigorously for 30 minutes; (3) Then, disodium hydrogen phosphate solution was added dropwise to the milky white mixed solution and reacted for 1 hour; (4) After the reaction, the product was collected by centrifugation and washed with deionized water and ethanol three times each; (5) The obtained precipitate was vacuum dried at 60 °C for 12 h to obtain Ag3PO4 nanospheres.

2. The method for preparing the Ag3PO4 nanosphere electrocatalyst material according to claim 1, characterized in that: The amount of each raw material used in step (1) is: 3 mmol of silver nitrate, 1 mmol of sodium citrate dihydrate, 2 mmol of disodium hydrogen phosphate, and the volume of ethylene glycol is 15 mL. The raw material ratio can be scaled up accordingly.

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