Preparation Method and Application of a Graphene Quantum Dot Composite Electrolytic Water Oxygen Evolution Catalytic Material

Abstract

Preparation method and application of a graphene quantum dot composite electrocatalytic material for water electrolysis oxygen evolution. The present invention aims to solve the problem that the activity of the OER electrocatalytic material without noble metals needs to be improved. Preparation method: First, ultrasonically clean nickel foam; Second, prepare a graphene quantum dot solution; Third, dissolve nickel chloride hexahydrate, iron nitrate nonahydrate, urea, and ammonium fluoride in deionized water to obtain a reaction solution, and place the nickel foam in the reaction solution for hydrothermal reaction; Fourth, place the nickel foam loaded with Fe-Ni(OH)2 in an aqueous solution of Co(OH)2 for potentiostatic electrodeposition; Fifth, immerse the Co(OH)2-Ni(OH)2 / nickel foam in the graphene quantum dot solution and perform electrodeposition using cyclic voltammetry to obtain the oxygen evolution catalytic material. The composite electrocatalytic material for water electrolysis oxygen evolution described in the present invention contains three transition metal elements of iron, cobalt, and nickel, and graphene quantum dots are electrodeposited on its surface, showing good electrocatalytic performance.

Description

Technical Field

[0001] The present invention relates to a preparation method and application of a Co(OH)2-Ni(OH)2 / nickel foam composite electrocatalytic material for water electrolysis oxygen evolution. Background Art

[0002] With the intensification of energy crisis and environmental pollution, it is crucial to develop new efficient and environmentally friendly energy conversion and storage technologies. Water electrolysis is considered an efficient hydrogen production method due to its abundant raw materials, high product purity, environmental friendliness, sustainability, etc. This reaction consists of two parts: hydrogen evolution reaction at the cathode and oxygen evolution reaction at the anode.

[0003] Among them, the oxygen evolution reaction is a complex process involving four electrons and requires a high overpotential. During water electrolysis, the OER exhibits slow reaction kinetics. Noble metal catalysts such as ruthenium, iridium, and platinum-based catalysts are currently widely considered to be efficient OER catalysts. However, due to their high prices, noble metal catalysts are not suitable for large-scale industrial applications.

[0004] The application of non-noble metal materials in electrocatalysis is becoming more and more extensive. For example, transition metal catalysts all exhibit good performance in electrocatalysis. Among them, oxides or hydroxides of transition metals have good OER catalytic activity, but the poor conductivity of pure oxides limits the further improvement of the catalytic performance of the materials. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems that the cost of existing noble metal-based electrocatalytic materials for water electrolysis oxygen evolution is relatively high and the catalytic activity of OER electrocatalytic materials without noble metals needs to be improved, and to provide a preparation method and application of a graphene quantum dot composite electrocatalytic material for water electrolysis oxygen evolution.

[0006] The preparation method of the graphene quantum dot composite electrocatalytic material for water electrolysis oxygen evolution of the present invention is realized according to the following steps:

[0007] Step 1: Ultrasonically clean nickel foam (NF) successively with hydrochloric acid, acetone, absolute ethanol, and deionized water, and obtain the cleaned nickel foam after drying.

[0008] Step 2: Ultrasonically disperse graphene oxide in deionized water, then add H2O2 with a mass fraction of 30%, heat and reflux for 15 - 20 h, and then perform dialysis treatment through a 3500 Da dialysis bag to obtain a graphene quantum dot (GQDs) solution.

[0009] Step 3: Dissolve nickel chloride hexahydrate, iron(III) nitrate nonahydrate, urea, and ammonium fluoride in deionized water to obtain a reaction solution. Place the cleaned nickel foam into the reaction solution and perform hydrothermal reaction at a temperature of 120 - 150 °C for 6 - 10 h to obtain nickel foam loaded with Fe-Ni(OH)₂;

[0010] Step 4: Place the nickel foam loaded with Fe-Ni(OH)₂ into an aqueous solution of Co(OH)₂. Using a three-electrode system, perform potentiostatic electrodeposition at -0.7 to -0.9 V to obtain Co(OH)₂-Ni(OH)₂ / nickel foam;

[0011] Step 5: Immerse the Co(OH)₂-Ni(OH)₂ / nickel foam as the working electrode into the graphene quantum dot solution. Using cyclic voltammetry, perform electrodeposition under a scanning potential window of 0 V - 1.0 V. After washing and drying, a graphene quantum dot composite electrocatalytic material for water electrolysis oxygen evolution is obtained;

[0012] Among them, the molar ratio of nickel chloride hexahydrate to iron(III) nitrate nonahydrate in the reaction solution described in Step 3 is (8 - 15):(1 - 4).

[0013] The application of the graphene quantum dot composite electrocatalytic material for water electrolysis oxygen evolution in the present invention is to use this graphene quantum dot composite electrocatalytic material as an OER electrocatalyst in the electrocatalytic water splitting reaction.

[0014] In the present invention, a graphene quantum dot-loaded Co(OH)₂-Ni(OH)₂ composite oxygen evolution catalytic material is prepared on the surface of nickel foam. Using nickel foam as the substrate, Fe-Ni(OH)₂ is loaded on the substrate by a hydrothermal method. The doping of Fe ions changes the local electronic structure of Ni(OH)₂, improves the conductivity of iron nickel hydroxide, and reduces the onset potential of OER. Co(OH)₂ is electrodeposited on the nickel foam loaded with Fe-Ni(OH)₂, making the composite oxygen evolution catalytic material contain three transition metal elements of iron, cobalt, and nickel at the same time. Both Co(OH)₂ and Ni(OH)₂ have good OER activity but relatively insufficient conductivity. Iron, cobalt, and nickel can enhance electron transfer with each other, promote the active center, and disperse the Co(OH)₂ particles. Finally, graphene quantum dots are electrodeposited on the composite oxygen evolution catalytic material. Graphene quantum dots have high electrocatalytic activity and excellent conductivity, ensuring the rapid transfer of ions / electrons, strengthening the transfer of electrons from the metal active center to the quantum dots. At the same time, the edge sites of graphene quantum dots can promote the reaction kinetics, thereby improving the OER activity of the composite electrocatalytic material for water electrolysis oxygen evolution.

[0015] The preparation method of the graphene-based composite electrocatalytic material for water electrolysis oxygen evolution in the present invention has the following beneficial effects:

[0016] 1. The graphene quantum dot composite electrolytic water oxygen evolution catalytic material prepared by the present invention is applied to the electrocatalytic decomposition of water for oxygen evolution reaction. This composite electrolytic water oxygen evolution catalytic material does not contain noble metal elements, has low cost, a simple synthesis method, and the electrodeposition method improves the stability of the composite oxygen evolution catalytic material;

[0017] 2. The graphene quantum dot composite electrolytic water oxygen evolution catalytic material prepared by the present invention contains three transition metal elements of iron, cobalt and nickel. Both Co(OH)2 and Ni(OH)2 have good OER activity and conductivity. Graphene quantum dots are electrodeposited on its surface, increasing the active sites and further improving the electron transfer efficiency;

[0018] 3. The graphene quantum dot composite electrolytic water oxygen evolution catalytic material prepared by the present invention has excellent electrocatalytic water oxygen evolution activity. Only 238 mV is required to drive a current density of 100 mA / cm 2 and the Tafel slope is 85 mV / dec, showing high OER electrocatalytic performance. Description of the Drawings

[0019] Figure 1 XRD test pattern of the graphene quantum dot composite electrolytic water oxygen evolution catalytic material obtained in Example 1;

[0020] Figure 2 SEM image of the graphene quantum dot composite electrolytic water oxygen evolution catalytic material obtained in Example 1;

[0021] Figure 3 Columnar bodies of the overpotentials required for the graphene quantum dot composite electrolytic water oxygen evolution catalytic materials obtained in Example 1 and Example 2 at a current density of 100 mA / cm 2 when; Detailed Embodiments

[0022] Detailed Embodiment 1: The preparation method of the graphene quantum dot composite electrolytic water oxygen evolution catalytic material in this embodiment is implemented according to the following steps:

[0023] Step 1. Ultrasonically clean nickel foam (NF) successively with hydrochloric acid, acetone, absolute ethanol, and deionized water, and obtain the cleaned nickel foam after drying;

[0024] Step 2. Ultrasonically disperse graphene oxide in deionized water, then add 30% by mass of H2O2, heat and reflux for 15 - 20 h, and then perform dialysis treatment through a 3500 Da dialysis bag to obtain a graphene quantum dot (GQDs) solution;

[0025] Step 3: Dissolve nickel chloride hexahydrate, iron(III) nitrate nonahydrate, urea, and ammonium fluoride in deionized water to obtain a reaction solution. Place the cleaned nickel foam in the reaction solution and perform hydrothermal reaction at a temperature of 120 - 150 °C for 6 - 10 h to obtain nickel foam loaded with Fe-Ni(OH)₂.

[0026] Step 4: Place the nickel foam loaded with Fe-Ni(OH)₂ in an aqueous solution of Co(OH)₂, adopt a three-electrode system, and perform potentiostatic electrodeposition at -0.7 to -0.9 V to obtain Co(OH)₂-Ni(OH)₂ / nickel foam.

[0027] Step 5: Immerse the Co(OH)₂-Ni(OH)₂ / nickel foam as the working electrode in a graphene quantum dot solution, adopt cyclic voltammetry, and perform electrodeposition in a scanning potential window of 0 V to 1.0 V. After washing and drying, a graphene quantum dot composite electrocatalytic material for water electrolysis oxygen evolution is obtained.

[0028] Among them, the molar ratio of nickel chloride hexahydrate to iron(III) nitrate nonahydrate in the reaction solution described in Step 3 is (8 - 15):(1 - 4).

[0029] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that the ultrasonic cleaning time in Step 1 is 10 - 20 min each time.

[0030] Specific Embodiment 3: The difference between this embodiment and Specific Embodiment 1 or 2 is that the dialysis treatment time in Step 2 is 45 - 50 h.

[0031] Specific Embodiment 4: The difference between this embodiment and any one of Specific Embodiments 1 to 3 is that the concentration of the graphene quantum dot solution in Step 2 is 0.8 - 2 mg / L.

[0032] Specific Embodiment 5: The difference between this embodiment and any one of Specific Embodiments 1 to 4 is that in Step 3, the hydrothermal reaction is carried out at a temperature of 120 °C for 8 h.

[0033] Specific Embodiment 6: The difference between this embodiment and any one of Specific Embodiments 1 to 5 is that in Step 3, the molar ratio of nickel chloride hexahydrate to iron(III) nitrate nonahydrate is controlled to be (10 - 12):(2 - 4).

[0034] In this embodiment, the optimized molar ratio of nickel chloride hexahydrate to iron(III) nitrate nonahydrate is controlled to be 3 - 4:1.

[0035] Specific Embodiment 7: The difference between this embodiment and any one of Specific Embodiments 1 to 6 is that the concentration of the Co(OH)₂ aqueous solution in Step 4 is 0.6 - 0.9 mol / L.

[0036] In this embodiment, the concentration of the Co(OH)₂ aqueous solution is preferably 0.8 mol / L.

[0037] Embodiment 8: The difference between this embodiment and any one of Embodiments 1 to 7 is that in Step 5, cyclic voltammetry is used, with Ag / AgCl as the reference electrode and a Pt sheet as the counter electrode.

[0038] Embodiment 9: The difference between this embodiment and any one of Embodiments 1 to 8 is that in Step 5, electrodeposition is carried out under a scanning potential window of 0 V to 1.0 V, the scanning rate is controlled to be 20 to 30 mV / s, and continuous scanning is cycled 50 to 80 times.

[0039] Example 1: The preparation method of the graphene quantum dot composite electrolytic water oxygen evolution catalytic material in this example is implemented according to the following steps:

[0040] Step 1: Ultrasonically clean nickel foam (NF) with hydrochloric acid, acetone, absolute ethanol, and deionized water in sequence for 15 min each, and obtain the cleaned nickel foam substrate after drying.

[0041] Step 2: Ultrasonically disperse 100 mg of graphene oxide in 15 mL of deionized water, then add 12 mL of 30% by mass H2O2, heat and reflux for 20 h, and then perform dialysis treatment for 48 h through a 3500 Da dialysis bag to obtain a graphene quantum dot (GQDs) solution with a concentration of 1.2 mg / L.

[0042] Step 3: Dissolve nickel chloride hexahydrate, iron nitrate nonahydrate, urea, and ammonium fluoride in deionized water to obtain a reaction solution. Place the cleaned nickel foam in the reaction solution and perform a hydrothermal reaction at a temperature of 120 °C for 8 h to obtain nickel foam loaded with Fe-Ni(OH)2.

[0043] Step 4: Place the nickel foam loaded with Fe-Ni(OH)2 in an aqueous solution of Co(OH)2 with a concentration of 0.8 mol / L. The aqueous solution of Co(OH)2 contains 0.08 mol / L of NaNO3. Using a three-electrode system, perform potentiostatic electrodeposition at -0.8 V to obtain Co(OH)2-Ni(OH)2 / nickel foam.

[0044] Step 5: Immerse the Co(OH)2-Ni(OH)2 / nickel foam as the working electrode in the graphene quantum dot solution, use Ag / AgCl as the reference electrode and a Pt sheet as the counter electrode, and perform electrodeposition using cyclic voltammetry under a scanning potential window of 0 V to 1.0 V, control the scanning rate to be 20 mV / s, and continuously scan and cycle 60 times. After washing and drying (the drying temperature is 60 °C), obtain the graphene quantum dot composite electrolytic water oxygen evolution catalytic material.

[0045] Among them, the molar concentration of nickel chloride hexahydrate in the reaction solution described in step three is 0.05 mol / L, and the molar concentration of iron(III) nitrate nonahydrate is 0.013 mol / L.

[0046] This example optimizes the ratio of the three elements of iron, cobalt, and nickel in the graphene quantum dot composite electrolytic water oxygen evolution catalytic material.

[0047] The graphene quantum dot composite electrolytic water oxygen evolution catalytic material prepared in this example is a GQDs composite Co(OH)2-Ni(OH)2 / nickel foam material, and graphene quantum dots are loaded on the Co(OH)2-Ni(OH)2 / nickel foam electrode.

[0048] Example 2: The preparation method of the graphene quantum dot composite electrolytic water oxygen evolution catalytic material in this example is implemented according to the following steps:

[0049] Step 1: Ultrasonically clean nickel foam (NF) with hydrochloric acid, acetone, absolute ethanol, and deionized water for 15 min in sequence, and obtain the cleaned nickel foam substrate after drying.

[0050] Step 2: Ultrasonically disperse 100 mg of graphene oxide in 15 mL of deionized water, then add 12 mL of 30% by mass H2O2, heat and reflux for 20 h, and then perform dialysis treatment for 48 h through a 3500 Da dialysis bag to obtain a graphene quantum dot (GQDs) solution with a concentration of 1.2 mg / L.

[0051] Step 3: Dissolve nickel chloride hexahydrate, iron(III) nitrate nonahydrate, urea, and ammonium fluoride in deionized water to obtain a reaction solution. Place the cleaned nickel foam in the reaction solution and perform hydrothermal reaction at 120 °C for 8 h to obtain nickel foam loaded with Fe-Ni(OH)2, where the molar concentration of nickel chloride hexahydrate in the reaction solution is 0.085 mol / L, and the molar concentration of iron(III) nitrate nonahydrate is 0.013 mol / L.

[0052] Step 4: Place the nickel foam loaded with Fe-Ni(OH)2 in an aqueous solution of Co(OH)2 with a concentration of 0.7 mol / L. The Co(OH)2 aqueous solution contains 0.08 mol / L of NaNO3. Adopt a three-electrode system and perform potentiostatic electrodeposition at -0.8 V to obtain Co(OH)2-Ni(OH)2 / nickel foam.

[0053] Step 5: Immerse Co(OH)2-Ni(OH)2 / nickel foam as the working electrode into the graphene quantum dot solution, use Ag / AgCl as the reference electrode, and a Pt sheet as the counter electrode. Electro-deposition is carried out by cyclic voltammetry in a scanning potential window of 0 V to 1.0 V, with the scanning rate controlled at 20 mV / s, and continuously scanned for 30 cycles. After washing and drying (the drying temperature is 60 °C), a graphene quantum dot composite electrolytic water oxygen evolution catalytic material is obtained.

[0054] The electrochemical performance of the graphene quantum dot composite electrolytic water oxygen evolution catalytic material prepared in the example is tested:

[0055] The OER performance of the graphene quantum dot composite electrolytic water oxygen evolution catalytic material prepared in Example 1 was tested under the conditions of a three-electrode system in a 1 mol / L alkaline solution. Through linear sweep voltammetry testing, only 238 mV is required to drive a current density of 100 mA / cm 2 . For the graphene quantum dot composite electrolytic water oxygen evolution catalytic material prepared in Example 2, 263 mV is required to drive a current density of 100 mA / cm 2 . After a 15-hour constant potential (1.5 V) stability test in a 1 mol / L alkaline solution, the current density of the graphene quantum dot composite electrolytic water oxygen evolution catalytic material prepared in Example 1 decayed to 97.5% of the initial current density.

[0056] The Tafel slope reflects the reaction rate and kinetic performance of the electrocatalyst. After testing, the Tafel slope of the graphene quantum dot composite electrolytic water oxygen evolution catalytic material obtained in Example 1 is 85 mV / dec. The smaller Tafel slope reflects that this graphene quantum dot composite electrolytic water oxygen evolution catalytic material has a faster reaction kinetics and exhibits excellent OER electrocatalytic performance.

Claims

1. Preparation method of graphene quantum dot composite electrolytic water oxygen evolution catalytic material, characterized in that The preparation method of the graphene quantum dot composite electrolytic water oxygen evolution catalytic material is realized according to the following steps: Step 1: Ultrasonically clean nickel foam with hydrochloric acid, acetone, absolute ethanol, and deionized water in sequence, and obtain the cleaned nickel foam after drying; Step 2: Ultrasonically disperse graphene oxide in deionized water, then add H2O2 with a mass fraction of 30%, heat and reflux for 15 - 20 h, and then perform dialysis treatment through a 3500 Da dialysis bag to obtain a graphene quantum dot solution; Step 3: Dissolve nickel chloride hexahydrate, ferric nitrate nonahydrate, urea, and ammonium fluoride in deionized water to obtain a reaction solution. Place the cleaned nickel foam in the reaction solution and perform hydrothermal reaction at a temperature of 120 - 150 °C for 6 - 10 h to obtain nickel foam loaded with Fe-Ni(OH)2; Step 4: Place the nickel foam loaded with Fe-Ni(OH)2 in an aqueous solution of Co(OH)2, adopt a three-electrode system, and perform potentiostatic electrodeposition at -0.7 - -0.9 V to obtain Co(OH)2-Ni(OH)2 / nickel foam; Step 5: Immerse the Co(OH)2-Ni(OH)2 / nickel foam as the working electrode in the graphene quantum dot solution, adopt cyclic voltammetry, and perform electrodeposition under a scanning potential window of 0 V - 1.0 V. After washing and drying, obtain the graphene quantum dot composite electrolytic water oxygen evolution catalytic material; Among them, the molar ratio of nickel chloride hexahydrate to ferric nitrate nonahydrate in the reaction solution described in Step 3 is (8 - 15):(1 - 4).

2. The preparation method of the graphene quantum dot composite electrolytic water oxygen evolution catalytic material according to claim 1, wherein In Step 1, the ultrasonic cleaning time each time is 10 - 20 min.

3. The preparation method of the graphene quantum dot composite electrolytic water oxygen evolution catalytic material according to claim 1, wherein In Step 2, the dialysis treatment time is 45 - 50 h.

4. The preparation method of the graphene quantum dot composite electrolytic water oxygen evolution catalytic material according to claim 1, characterized in that In Step 2, the concentration of the graphene quantum dot solution is 0.8 - 2 mg / L.

5. The preparation method of the graphene quantum dot composite electrolytic water oxygen evolution catalytic material according to claim 1, wherein In Step 3, perform hydrothermal reaction at a temperature of 120 °C for 8 h.

6. The preparation method of the graphene quantum dot composite electrolytic water oxygen evolution catalytic material according to claim 1, characterized in that In Step 3, control the molar ratio of nickel chloride hexahydrate to ferric nitrate nonahydrate to be (10 - 12):(2 - 4).

7. The preparation method of the graphene quantum dot composite electrolytic water oxygen evolution catalytic material according to claim 1, characterized in that In Step 4, the concentration of the aqueous solution of Co(OH)2 is 0.6 - 0.9 mol / L.

8. The preparation method of the graphene quantum dot composite electrolytic water oxygen evolution catalytic material according to claim 1, wherein In Step 5, adopt cyclic voltammetry, use Ag / AgCl as the reference electrode and a Pt sheet as the counter electrode.

9. The preparation method of the graphene quantum dot composite electrolytic water oxygen evolution catalytic material according to claim 1, wherein In Step 5, perform electrodeposition under a scanning potential window of 0 V - 1.0 V, control the scanning rate to be 20 - 30 mV / s, and continuously scan and cycle 50 - 80 times.

10. Use of the graphene quantum dot composite electrolytic water oxygen evolution catalytic material prepared as claimed in claim 1, characterized in that Apply this graphene quantum dot composite electrolytic water oxygen evolution catalytic material as an OER electrocatalyst to the electrocatalytic water splitting reaction.

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