Nickel-cobalt-selenium nano material for electrocatalytic oxidation of ethylene glycol

Abstract

The invention discloses a nickel-cobalt-selenium (Co1-xNixSe2) nano material for electrocatalytic oxidation of ethylene glycol as well as a preparation method and application of the nickel-cobalt-selenium (Co1-xNixSe2) nano material. The material is prepared by a hydrothermal method which comprises the following steps: (1) pouring 20mL of deionized water containing 475.9 mg of CoCl2. 6H2O into a 1mol / L NaOH solution containing 0.32 g of selenium powder to prepare a precursor solution; (2) placing in a stainless steel autoclave with a polytetrafluoroethylene lining, carrying out hydrothermal reaction at 180 DEG C for 18 hours, washing with absolute ethyl alcohol and deionized water, and carrying out vacuum drying at 60 DEG C to obtain a CoSe2 material; and (3) the molar feeding ratio of CoCl2. 6H2O to NiCl2. 6H2O is adjusted, so that the nickel / cobalt ratio x is 0.25, 0.50 or 0.75, and materials with different components, namely Co < 0.75 > Ni < 0.25 > Se < 2 >, Co < 0.50 > Ni < 0.50 > Se < 2 > and Co < 0.25 > Ni < 0.75 > Se < 2 >, are prepared. The series of materials are applied to ethylene glycol oxidation under the alkaline condition, the catalytic performance of Co < 0.50 > Ni < 0.50 > Se < 2 > is optimal, the current density reaches 111 mA cm <-2 > under the electric potential of 1.6 V vs.RHE, the total Faraday efficiency reaches up to 91.4%, and the application prospect in the field of PET plastic recovery is wide.

Description

Technical Field

[0001] This invention belongs to the fields of new energy materials and electrocatalysis technology, specifically relating to the preparation of a non-precious metal electrocatalytic material and its application in the study of ethylene glycol as a formate. Background Technology

[0002] Plastics are increasingly used in daily life and industrial production. Among them, polyethylene terephthalate (PET) is widely used in packaging, automotive, and textile industries due to its excellent properties. However, PET products are often discarded carelessly after use, resulting in a large amount of plastic waste entering the environment and posing a serious threat to ecosystems. From the perspective of resource recycling and environmental protection, converting waste PET plastics into high-value-added chemicals is of great value (Science. 2021, 373(6550), 61–65).

[0003] Currently, common plastic treatment methods mainly include two categories of technologies: separation and degradation. Separation technologies, such as adsorption, coagulation / flocculation, and filtration, are difficult to completely remove microplastics; while degradation technologies, such as biodegradation, advanced oxidation, electrochemical degradation, and photocatalytic degradation, often consume high energy, easily generate byproducts, fail to achieve resource recovery, and may even cause secondary pollution. In contrast, electrochemical plastic reforming technology provides a new path for achieving green, efficient, and controllable plastic recycling. In recent years, research on the electrochemical upgrading and recycling of PET has gradually increased. Its core process involves the catalytic hydrolysis of PET under alkaline conditions to produce ethylene glycol (EG) and terephthalic acid (PTA), followed by the selective electrochemical oxidation of EG (EG oxidation reaction, EGOR) to high-value chemicals such as formic acid and glycolic acid, while simultaneously generating green hydrogen gas at the cathode (Nat. Commun. 2021, 12, 4679). Among these, EGOR is the key to achieving the electrochemical resource recovery of PET plastics.

[0004] EGOR can occur on platinum group metal (PGM) based and non-PGM electrocatalysts, the latter of which has attracted much attention due to its cost and abundance advantages (ACS Catal. 2024, 14(7), 5366–5376). Among them, transition metal electrocatalysts, especially nickel- and cobalt-containing compounds, are promising platforms for EGOR. Nickel and cobalt are active but have different selectivities: single-metal nickel predominates on the C1 pathway, with higher formate yields than cobalt; in contrast, cobalt electrodes tend to follow the C2 pathway, with a Faradaic efficiency (FE) of approximately 43% for glycolic acid at RHE 1.60 V, which is much higher than that of nickel (Mater. Today Phys. 2023, 37, 101191). In summary, combining nickel and cobalt can maintain high EGOR currents and modulate product selectivity.

[0005] Therefore, we used a simple hydrothermal method to prepare nickel cobalt selenide (Co) with adjustable composition. 1-x Ni x Se2) nanoparticles were used to achieve efficient ethylene glycol conversion at the anolyte. Preferably, the nickel / cobalt ratio was 0.5 (i.e., Co...). 0.50 Ni 0.50 When Se2), this catalyst can achieve 111 mA cm⁻¹ at a potential of 1.6 V vs. RHE. -2 It has a high current density and exhibits a Faraday efficiency of up to 94% and excellent stability. Summary of the Invention

[0006] To address the issues of low efficiency in the electrocatalytic conversion of ethylene glycol and the high cost of precious metal-based electrocatalytic materials, this invention provides a nickel-doped cobalt selenide (Co) solution. 1-x Ni x Se2) nanoparticle non-noble metal electrocatalytic materials, their preparation methods, and applications. These electrocatalytic materials are synthesized in one step via a hydrothermal method, exhibiting a controllable nickel doping ratio and optimized electronic structure. This allows for effective modulation of the spin state of cobalt active sites, thereby enhancing the adsorption behavior of reaction intermediates, promoting selective C / C bond cleavage, and achieving efficient formate conversion.

[0007] To achieve the above objectives, the technical solution adopted by the present invention to solve its technical problem is as follows:

[0008] (1) Preparation of precursor solution: Deionized water containing cobalt salt is poured into an alkaline solution containing selenium powder.

[0009] (2) Hydrothermal reaction: The precursor solution is subjected to a hydrothermal reaction at a temperature of 180°C for 18 hours.

[0010] (3) Preparation of CoSe2: After the reaction is completed, the solid product is naturally cooled to room temperature, collected, centrifuged, washed and vacuum dried to obtain CoSe2 material.

[0011] (4) Co 1-x Ni x Preparation of Se2: The nickel and cobalt salts from step (1) are added together to deionized water and then poured into an alkaline solution. Following steps (2) and (3), Co is obtained. 1-x Ni x Se2 NPs electrocatalytic materials.

[0012] Preferably, in step (1), the cobalt salt is 475.9 mg of CoCl2·6H2O, the deionized water is 20 mL, the alkaline solution is 1 mol / L NaOH solution, and the amount of selenium powder added is 0.32 g / 100 mL NaOH solution.

[0013] Preferably, in step (2), the hydrothermal reaction temperature is 180°C and the reaction time is 18 hours.

[0014] Preferably, in step (3), the product is washed with anhydrous ethanol and deionized water and dried in a vacuum drying oven at 60°C.

[0015] Preferably, in step (4), the nickel salt is NiCl2·6H2O, and the value of x is obtained by adjusting the molar ratio of CoCl2·6H2O to NiCl2·6H2O, which is 0.25, 0.50 or 0.75.

[0016] The above-mentioned Co 1-x Ni x Se2 (x = 0; 0.25; 0.50; 0.75) electrocatalysts were used as working electrode materials in the EGOR reaction. Through three-electrode system testing, in an electrolyte of 1M KOH and 1M EG, Co... 1-x Ni x Se2 (x = 0.50) material can achieve 111 mA cm⁻¹ at 1.6 V vs. RHE potential. -2 It has a high current density and exhibits a Faraday efficiency of up to 94% and excellent stability.

[0017] This study reveals a synthetic strategy for transition metal sulfides, providing an efficient and sustainable new approach for the value-added conversion of PET, particularly the EGOR reaction. Detailed Implementation

[0018] To facilitate further analysis, this invention employs the following four specific steps to describe Co in detail. 1-x Ni xPreparation of Se2 materials:

[0019] (1) Preparation of precursor solution: 20 mL of deionized water containing 475.9 mg CoCl2·6H2O was poured into a 1 mol / L NaOH solution containing 0.32 g selenium powder.

[0020] (2) Hydrothermal reaction: The precursor solution was placed in a stainless steel autoclave lined with polytetrafluoroethylene and the reaction temperature was 180℃ for 18 hours.

[0021] (3) Preparation of CoSe2: Wash with anhydrous ethanol and deionized water, and then dry in a vacuum drying oven at 60°C to obtain CoSe2 NPs.

[0022] (4) Co 1-x Ni x Se2 preparation: Add a certain amount of NiCl2·6H2O to the cobalt salt in step (1) so that the nickel / cobalt ratio x is 0.25, 0.50 or 0.75, and Co with different compositions can be prepared. 0.75 Ni 0.25 Se2, Co 0.50 Ni 0.50 Se2, Co 0.25 Ni 0.75 Se2 material.

[0023] The CoSe2 and Co obtained in steps (3) and (4) 0.75 Ni 0.25 Se2, Co 0.50 Ni 0.50 Se2, Co 0.25 Ni 0.75 For Se2 materials, the microstructure and morphology of the materials are analyzed first.

[0024] Figure 1 For the present invention (Co) 1-x Ni x Se2 (x = 0, 0.25, 0.50, 0.75) preparation process flow diagram. A simple hydrothermal method was used to add an alkaline NaOH solution containing CoCl2·6H2O, NiCl2·6H2O, and selenium powder to a high-pressure reactor. The temperature was set at 180℃ and the reaction time was 18 hours, yielding four materials.

[0025] Figure 2The image shows the XRD pattern of this invention. As shown, XRD analysis confirmed the crystal structure of CoSe2 nanoparticles in the synthesized material, and the characteristic peaks showed good agreement with the standard CoSe2 card (PDF#89-2003). It can be clearly seen that these peaks shift slightly to lower angles with increasing Ni content. The results indicate that Ni has been successfully doped into the crystal structure of CoSe2.

[0026] Figure 3-6 These are the SEM and EDS images of this invention. SEM characterization reveals Co... 1-x Ni x Se2(x=0 is Figure 3 x = 0.25 is Figure 4 x = 0.50 is Figure 5 x = 0.75 is Figure 6 The morphology of this series of nanoparticles is shown. Undoped CoSe2 exhibits well-dispersed nanoparticles, while increasing Ni doping leads to gradual particle aggregation. EDS spectra of this series of Co... 1- x Ni x The elemental ratios of Se2 agree well with the theoretical values. For ease of comparison, CoSe2 and Co are used. 0.75 Ni 0.25 Se2, Co 0.50 Ni 0.50 Se2, Co 0.25 Ni 0.75 Se2 is used to represent these samples.

[0027] Figure 7 For Co 0.5 Ni 0.5 TEM image of Se2, showing its morphology as nanoscale particles.

[0028] Figure 8 a is the HRTEM of CoSe2. This indicates that the nanostructure can be classified as a (cubic CoSe2 Pnnm phase, a = 4.84; b = 5.72; c = 3.60; α = β = γ = 90) phase. From the figure, the lattice fringe distances of CoSe2 are 0.1914 nm, 0.2059 nm and 0.1681 nm, respectively, located at 30.94° and 57.76°, which can be interpreted as cubic CoSe2, shown along its

[113] region axis. Figure 8 As shown in b, EM-EDS elemental mapping reveals the uniform distribution of Ni, Co, and Se throughout the nanoparticle structure.

[0029] Electrochemical properties were measured using a conventional three-electrode configuration. The working electrode (WE) was a standard glassy carbon electrode with an area of ​​0.196 square centimeters, the reference electrode (RE) was HgO / Hg, and the counter electrode (CE) was a platinum wire. The preparation of the working electrode included GC electrode surface treatment and catalyst electrode slurry preparation and coating. The main steps are as follows:

[0030] (1) First, the glassy carbon electrode was polished on a polishing pad with 0.05-micron alumina slurry for 1 minute, and then thoroughly rinsed with deionized water. Next, it was ultrasonically treated in anhydrous ethanol and deionized water for 1 minute in sequence to remove adsorbed impurities. Finally, the cleaned glassy carbon electrode was dried under a nitrogen flow.

[0031] (2) Preparation of the catalyst electrode slurry: 10 mg of nanomaterial catalyst powder with different compositions and 20 mg of carbon black (Vulcan XC-72) were added to a brown vial, along with a mixture containing 1.6 mL of deionized water, 1.6 mL of anhydrous ethanol, and 0.2 mL of 5% (w / v) Nafion solution. This dispersion was ultrasonically treated for 1 hour to form a uniform ink. Subsequently, 5 μL of the ink was drop-coated onto the surface of the pretreated glassy carbon electrode and dried at room temperature to obtain the final working electrode.

[0032] Electrochemical tests were conducted in an electrolytic cell using 1M KOH and 1M KOH + 1M EG electrolytes prepared in deionized water. The results showed the presence of CoSe2 and Co. 0.75 Ni 0.25 Se2, Co 0.50 Ni 0.50 Se2, Co 0.25 Ni 0.75 The Se2 electrocatalytic material was used as the working electrode, the saturated Hg / HgO electrode as the reference electrode, and the platinum wire as the counter electrode. Electrochemical tests of the electrocatalytic material were performed at room temperature using a Koster electrochemical workstation.

[0033] Figure 9 a represents the CV values ​​of the four materials of this invention in 1M KOH alkaline solution. As can be seen from the figure, the CV curve of the CoSe2 electrocatalyst in 1M KOH exhibits smaller oxidation and reduction peaks, while its oxygen evolution reaction (OER) activity is low. Specifically, Co(OH)2 is oxidized to CoOOH at approximately 1.06 V compared to RHE, and then further oxidized to CoO2 near 1.4 V. During the reverse scan, cobalt oxide is reduced. 1-x Ni x In Se2 materials, Ni usually exists in the form of Ni(OH)2 in alkaline solution. Under certain voltage conditions, it is oxidized to NiOOH, and then reduced to Ni(OH)2 during reverse scanning. Figure 9b represents the coefficient of performance (CV) of the four materials in this invention in a 1M KOH + 1M EG solution. The figure shows that, compared to RHE, the current density of the four electrodes significantly increases at potentials above 1.3V after adding 1M EG to the 1M KOH electrolyte. At 1.4V, 1.5V, and 1.6V, Co... 0.50 Ni 0.50 The EGOR current densities on the Se2 electrode were 49.8, 86.5, and 111.3 mA cm⁻¹, respectively. -2 It is superior to the other three electrodes. Figure 9 c shows that after adding ethylene glycol at a potential of 1.5V, Co 0.50 Ni 0.50 The Se2 electrode has the highest current density.

[0034] To evaluate the selectivity of the catalyst for EGOR products at a constant potential, a chronoamperometry test was first employed. Figure 10 As shown in a, in a 1-hour test, Co 0.50 Ni 0.50 The Se2 electrode maintained a relatively stable current density at potentials of 1.3, 1.4, 1.5, 1.6, and 1.7 V. To analyze product selectivity and Faraday efficiency, electrolyte was collected after each chronoamperometry test and quantified using ion chromatography. Figure 10 b shows characteristic peaks at approximately 7.5 min and 9.1 min in the ion chromatography results, corresponding to glycolate and formate, respectively. The concentration and yield of the products were determined according to the standard calibration curve, and the Faradaic efficiency of ethylene glycol to glycolate and formate at different potentials was calculated. Figure 10 As can be seen in Figure c, Co 0.50 Ni 0.50 The Faraday efficiencies of the Se2 electrode materials were 81.5% (1.3V), 83% (1.4V), 82.2% (1.5V), 93.8% (1.6V), and 84.6% (1.7V), respectively. At all potentials and doping ratios, formate was the major product of EGOR, while glycolate was a minor product.

[0035] Figure 11 a represents the stability of the four electrodes under a 10-hour chronoampere test at 1.6V. It can be seen that Co... 0.5 Ni 0.5 The Se2 electrode exhibited the highest current density, stabilizing at 91.8 mA cm⁻¹. -2 .like Figure 11 As shown in b, CoSe2, Co 0.75 Ni 0.25 Se2, Co 0.5 Ni 0.5 Se2 and Co 0.25Ni 0.75 The formate Faradaic efficiencies of Se2 were 84.8%, 86.8%, 87.9%, and 88.9%, respectively, while those of glycolate were 5.4%, 4.4%, 3.5%, and 2.1%. The results indicate that with increasing Ni doping ratio, the catalyst's selectivity for formate gradually increases, while its selectivity for glycolate gradually decreases. In the tested electrodes, Co... 0.5 Ni 0.5 Se2 has the highest overall Faraday efficiency, reaching 91.4%.

[0036] Experimental results show that Ni doping improves the EGOR performance of the CoSe2 catalyst. Specifically, the optimized Co... 0.5 Ni 0.5 The Se2 catalyst achieved 111 mA cm⁻¹ at a potential of 1.6 V (vs. RHE). -2 The catalyst exhibits high current density and an overall Faraday efficiency of 91.4%, along with excellent stability. This work provides EGOR with a highly efficient catalyst that can also be used for the resource recycling and utilization of PET plastics. Attached Figure Description

[0037] Figure 1 The four samples obtained in this invention (Co) 1-x Ni x Flowchart of Se2; x = 0, 0.25, 0.50, 0.75);

[0038] Figure 2 The four samples obtained in this invention (Co) 1-x Ni x XRD pattern of Se2);

[0039] Figure 3 The images shown are (a) SEM and (b) EDS images of CoSe2 obtained in this invention.

[0040] Figure 4 The Co obtained in this invention 0.75 Ni 0.25 SEM and EDS images of Se2;

[0041] Figure 5 The Co obtained in this invention 0.50 Ni 0.50 SEM and EDS images of Se2;

[0042] Figure 6 The Co obtained in this invention 0.25 Ni 0.75 SEM and EDS images of Se2;

[0043] Figure 7Co of the present invention 0.50 Ni 0.50 TEM image of Se2;

[0044] Figure 8 a is the Co of the present invention 0.50 Ni 0.50 HRTEM plot of Se2; Figure 8 b is the EELS mapping for Se, Co, and Ni.

[0045] Figure 9 a represents the CV curves of the four products of this invention in 1M KOH; b represents the CV curves of the four samples in 1M KOH and 1M EG; c represents the current density of the four samples at a potential of 1.5V (vs. RHE) in the two electrolytes.

[0046] Figure 10 a is Co 0.50 Ni 0.50 The CA curves of Se2 after continuous operation for 1 hour show potentials of 1.3, 1.4, 1.5, 1.6 and 1.7 V, respectively. Figure 10 b represents the corresponding IC curves under various applied voltages; Figure 10 c represents the corresponding FE diagram;

[0047] Figure 11 a is the 10-hour CA curve obtained using 1M KOH and 1MEG electrolyte under 1.6V vs. RHE conditions for four samples; Figure 11 b represents the FE values ​​of the four products after 10 hours of CA treatment.

Claims

1. A method for preparing a nickel cobalt selenium material for application in electrocatalytic oxidation of ethylene glycol, characterized by The method comprises the following steps: (1) Preparation of precursor solution: pour deionized water containing CoCl2·6H2O into an alkaline solution containing selenium powder. (2) Hydrothermal reaction: hydrothermal reaction of the precursor solution, reaction temperature is 180℃, reaction time is 18 hours. (3) Preparation of CoSe2 material: after the reaction is completed, it is naturally cooled to room temperature, the solid product is collected, centrifuged, washed and vacuum dried to obtain CoSe2 NPs material. (4) Co 1-x Ni x Se2 material preparation: the nickel salt and the cobalt salt in step (1) are added together into deionized water and poured into a basic solution, and then step (2) and step (3) are passed to obtain Co 1-x Ni x Se2 material.

2. The CoSe2, Co 1-x Ni x Se2 electrocatalytic material according to claim 1, characterized in that: In the step (1), the cobalt salt is 475.9 mg of CoCl2·6H2O, the deionized water is 20 mL, the alkaline solution is 1 mol / L NaOH solution, and the addition amount of selenium powder is 0.32 g / 100 mL NaOH solution.

3. The method for preparing a CoSe2 material according to claim 2, characterized in that: In the step (2), the hydrothermal reaction is carried out in a stainless steel autoclave with a polytetrafluoroethylene liner, the reaction temperature is 180℃, and the reaction time is 18 hours.

4. The method of claim 3, wherein the CoSe2 material is prepared by the following steps: In the step (3), the CoSe2 material is obtained by washing with anhydrous ethanol and deionized water and then drying in a vacuum drying box at 60℃.

5. A Co 1-x Ni x Method for producing a Se2 material, characterized in that: In the step (4), the nickel salt is NiCl2-6H2O, and by adjusting the molar feed of CoCl2-6H2O and NiCl2-6H2O, i.e. the value of the nickel / cobalt ratio x is 0.25, 0.50 or 0.75, Co 1-x Ni x Se2(x = 0.25; 0.50; 0.75) materials.

Images