Green degradable hydrogel and solar charging zinc air battery

Abstract

The invention relates to a green polyacrylic acid hydrogel and a solar charging zinc air battery. The hydrogel material is obtained by crosslinking an acrylic monomer and cyclodextrin. The hydrogel has excellent stretchability, self-healing property and electrochemical stability, the assembled zinc-air battery shows stable charge-discharge cycle performance, the hydrogel zinc-air battery can be charged by using a solar battery, and light energy is converted into electric energy to be efficiently stored in the zinc-air battery; the influence of the intermittency and volatility of photovoltaic power generation on the operation stability of the power grid is reduced, and the challenge of the intermittency and volatility of photovoltaic power generation on the stable operation of the power grid is solved.

Description

Technical Field

[0001] The invention relates to a green degradable hydrogel and a solar-charged zinc-air battery, belonging to the technical field of zinc-air batteries. Background Art

[0002] Zinc-air battery is a type of metal-air battery, which uses oxygen in the air as the positive electrode active material, metal zinc as the negative electrode active material, and alkaline solution as the electrolyte. In recent years, zinc-air battery has attracted much attention due to its advantages such as high energy density, high safety and low cost.

[0003] Currently, the key challenge of zinc-air batteries lies in the electrolyte. Since zinc-air batteries are semi-open energy storage systems, the alkaline liquid electrolyte currently used is prone to leakage from the positive electrode, and the alkaline electrolyte is prone to absorb CO in the air. 2 , causing the electrolyte to deteriorate and fail. Therefore, the research and development and utilization of electrolytes in zinc-air batteries has always been a major challenge. Although some applications of hydrogel electrolytes in zinc-air batteries have been reported recently, most hydrogel electrolytes are still alkaline and lack excellent mechanical properties, degradability, self-healing properties and electrochemical stability, resulting in slow charging speed and low battery cycle life. Summary of the invention

[0004] The invention prepares a degradable PFD hydrogel electrolyte which can be used in solar-charged zinc-air batteries.

[0005] A hydrogel is composed of acrylic monomers, cyclodextrin, Fe 3+ Obtained by cross-linking.

[0006] The acrylic monomer is one or a mixture of acrylic acid, methyl acrylate, ethyl acrylate, methacrylic acid, allyl alcohol, hydroxyvinyl methacrylate or 2-hydroxyacrylic acid.

[0007] The cyclodextrin refers to one or a mixture of α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin or sulfate cyclodextrin.

[0008] The method for preparing the hydrogel comprises the following steps:

[0009] Step 1: Prepare an aqueous solution containing acrylic acid, then add iron salt and continue stirring to obtain PAA Fe 3+ Mixing solutions;

[0010] Step 2: Continue to add cyclodextrin and initiator to carry out polymerization reaction, and then obtain hydrogel after heat treatment.

[0011] In step 1, the volume ratio of acrylic acid to water is 50-70:100; the concentration of the iron salt in the aqueous solution containing acrylic acid is 0.05-0.5wt%, and the stirring time is 5-30h; the iron salt is FeCl 3 , FeBr 3 Or FeI 3 .

[0012] In step 2, cyclodextrin is added to PAA Fe 3+ The concentration in the mixed solution is 0.5-5wt%.

[0013] In step 2, the polymerization reaction time is 0.5-1 h, and the heat treatment condition is 50-70° C. for 1-10 h.

[0014] The initiator is K 2 S 2 O 8 .

[0015] A zinc-air battery, wherein the electrolyte material is the hydrogel mentioned above.

[0016] The hydrogel was pre-soaked in an electrolyte solution.

[0017] The electrolyte solution is NH 4 Cl and ZnCl 2 of mixed solution.

[0018] A photoelectric conversion and energy storage combined system comprises a polycrystalline silicon solar cell and the above-mentioned zinc-air battery, wherein the solar cell is used for charging the zinc-air battery.

[0019] The light intensity is 90-10mW / cm 2 Under the condition of 2 The light conversion efficiency of polycrystalline silicon solar cells reached 12.4%-12.8%.

[0020] The short-circuit current values ​​are 28-36 mA cm -2 , the output power is 45.0-56.0mW, which can be gradually increased with the increase of light intensity.

[0021] The polycrystalline silicon solar cell charges the zinc-air battery with PFD hydrogel electrolyte under outdoor natural light irradiation, and stores the electricity generated by solar energy in the zinc-air battery efficiently and quickly.

[0022] Beneficial Effects

[0023] 1. PFD hydrogel can be gradually degraded by microorganisms in the soil under natural conditions.

[0024] 2. PFD hydrogel has excellent stretchability, self-healing properties and electrochemical stability, and the assembled zinc-air battery exhibits stable charge and discharge cycle performance (200 times).

[0025] 3. Solar cells can be used to charge PFD hydrogel zinc-air batteries, converting light energy into electrical energy and efficiently storing it in zinc-air batteries, reducing the impact of intermittent and volatile photovoltaic power generation on the stability of grid operation.

[0026] 4. In the preparation process of the hydrogel of this patent, Fe 3+ The ion exchange effect of the hydrogel and the hydrogen bond cross-linking effect of cyclodextrin make the material have a self-healing effect, thereby ensuring the stability of the hydrogel material when used as a zinc-air battery electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 :Schematic diagram of PFD hydrogel preparation

[0028] Figure 2 :PTD hydrogel tensile performance diagram and self-healing mechanical performance test diagram

[0029] Figure 3 :(a) SEM characterization of PFD hydrogel electrolyte; (b) EDS characterization of PFD hydrogel electrolyte

[0030] Figure 4 : Photocharging process of zinc-air batteries with PFD hydrogel electrolyte

[0031] Figure 5 :Gradual degradation process of PFD hydrogel electrolyte in natural environment

[0032] Figure 6 :(a) ORR catalytic activity of Co-MOFs; (b) ORR stability of Co-MOFs

[0033] Figure 7 :(a) OER catalytic activity of Co-MOFs; (b) OER stability of Co-MOFs

[0034] Figure 8 :Polarization curves of zinc-air batteries with PFD hydrogel electrolyte

[0035] Fig. 9 :Power density diagram of PFD hydrogel electrolyte zinc-air battery

[0036] Fig.10 :Rate performance of zinc-air batteries with PFD hydrogel electrolyte

[0037] Fig.11 :Specific capacity performance of zinc-air batteries with PFD hydrogel electrolyte

[0038] Fig.12 :Charge and discharge cycle test of zinc-air battery with PFD hydrogel electrolyte

[0039] Fig.13 :(a) Gas diffusion layer preparation process; (b) Homemade soft-pack zinc-air battery DETAILED DESCRIPTION

[0040] PFD hydrogel has excellent mechanical properties, degradability, self-healing and electrochemical stability. The assembled zinc-air battery has the ability to be charged by solar light, which reduces the energy consumption in the production process and achieves energy saving. In addition, the hydrogel has moisturizing properties because there are a large number of hydrogen bonds inside it, which can lock a part of the liquid water, thereby reducing the frequency of electrolyte replacement, improving the utilization rate of the electrolyte and reducing production costs. Finally, we successfully converted solar energy into electrical energy for storage and utilization in the photovoltaic joint application test, realizing the initial transformation from theory to practical application scenarios.

[0041] Example 1 Acrylic acid solution preparation:

[0042] Acrylic acid (M = 72.06 g / mol 60 mL) was dissolved in 100 mL of deionized water, and the mixture was then magnetically stirred at 60° C. for 3 to 4 days.

[0043] Example 2PAA Fe 3+ Mixed solution synthesis process:

[0044] Add FeCl 3 6H 2 O powder (0.1 g) was stirred for 12 to 24 h to obtain PAA Fe 3+ Mix the solution.

[0045] Example 3PAA Fe 3+ Synthesis process of β-CD hydrogel:

[0046] 1 g of β-cyclodextrin (β-CD) powder was added to the above mixed solution to form PAA Fe 3+ β-CD solution, and then ultrasonic for 30 min to make the solution more uniform. Next, a small amount of initiator K was added to the pre-gel solution under argon atmosphere. 2 S 2 O 8 The pre-gel solution was placed in a mold and heated at 60°C for 2-4 hours to obtain a PFD hydrogel. Figure 1 .

[0047] like Figure 2In the present invention, the maximum stretching length of the PFD hydrogel based on the above-mentioned method reaches 15 cm, and it has good tensile properties and self-healing ability. The viscosity test shows that the hydrogel can be stretched between 3 cm and 15 cm and recover to 5 cm after release. The test results of the universal testing machine show that the 1 cm long hydrogel can be stretched to 15 cm, and its tensile strength reaches 25 kPa. These results fully demonstrate the excellent performance of PFD hydrogel in mechanical properties and self-healing ability.

[0048] Based on the above PFD hydrogel, Figure 3 a It can be seen that PFD hydrogel has PAA COO - key. Figure 3 b shows that the water range peak (including bound water and free water) appears in the range of 3200-3500, which shows that the water content of PFD hydrogel is very high. Figure 3 c, d show the morphology and element distribution of the pore structure of PFD hydrogel. Due to the large pore size and large number of pores, the ability to hold water is high, which also shows that the water content of PFD hydrogel is very high.

[0049] like Figure 4 The present invention is based on the use of polycrystalline silicon solar cells to charge the above zinc-air battery. When the light intensity is 90, 100, 110 mW / cm 2 Under the condition of 2 The light conversion efficiency of the polycrystalline silicon solar cells reached 12.5%, 12.6%, and 12.7% respectively. The short-circuit current values ​​were 28.6, 30.9, and 35.8 mA cm -2 , the output power can reach 45.0, 48.3, 55.7mW, and can gradually increase with the increase of light intensity. Within this light intensity range, the solar cell can stably provide an operating voltage of about 0.44V at the maximum light conversion efficiency, and stably convert solar energy into usable electrical energy for charging zinc-air batteries. Under outdoor daylight conditions, we used this polycrystalline silicon solar cell (specification: 2V 130mA) to charge the zinc-air battery with PFD hydrogel electrolyte, successfully storing the electricity generated by solar energy in the zinc-air battery efficiently, realizing the effective conversion and storage of solar energy, and the LED can be continuously lit for up to 10 hours after charging is completed.

[0050] like Figure 5 Based on the above-mentioned PFD hydrogel samples placed in two natural environments for degradation, it was demonstrated in different time periods and different weather that the PFD hydrogel electrolyte can be partially degraded 7 days after contacting the soil. After 30 days, the components of the PFD hydrogel electrolyte were almost completely decomposed by microorganisms and slowly released into the soil, promoting plant growth.

[0051] The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in zinc-air batteries are key electrochemical processes. Electrocatalysts can act as catalysts to reduce the activation energy of these reactions, thereby promoting the reaction rate and improving the performance of the battery. Figure 6 a We observed that the ORR performance of Co-MOFs showed an onset potential of 0.9 V, while the half-wave potential (E 1 / 2 ) can reach 0.81V, by Figure 6 b The stability of ORR was observed after 4 h, and 93% of the original current density was still maintained. Figure 7 In a, we found that its OER performance is 10 mA cm -2 Under the condition, it reached 1.73V, showing good OER performance. Figure 7 b shows the stability of OER after 10 h, which can still maintain 98.6% of the original current density.

[0052] like Figure 8 In the polarization curve, as the current density increases, the voltage usually decreases, causing the power density curve to show a peak. This is because at lower current densities, the polarization effect of the battery is smaller, but as the current density increases, the polarization effect gradually increases, causing the battery voltage to drop, ultimately limiting the battery's output power. Fig. 9 From the polarization curve, it can be calculated that the zinc-air battery with PFD hydrogel electrolyte has a current density of 26 mA cm -2 The highest power density is 18 mW cm -2 .

[0053] After observing that the zinc-air battery exhibited better polarization performance, we immediately connected it to the Xinwei battery test system for rate testing. We discharged the battery at different current densities to test its discharge voltage. Fig.10 It can be clearly observed that the zinc-air battery with PFD hydrogel electrolyte has a -2 The Zn-air battery can still maintain a voltage of 0.7 V under the discharge condition, showing excellent rate performance. After deep discharge, we further tested the battery capacity of the Zn-air battery. Therefore, we placed the Zn-air battery under 1 mA cm -2 The battery is discharged for a long time under the condition of , and the test is stopped when the battery voltage drops to 0.1V. Fig.11 It can be observed that after 20 hours of continuous discharge, the voltage of the battery dropped below 0.1 V. By calculating the specific capacity formula, we weighed the mass of the remaining zinc sheet and converted it to 350 mAh g -1 Specific capacity.

[0054] Long cycle life can extend the service life of the battery and reduce the cost per unit of energy. Especially for large-scale applications such as energy storage systems or electric vehicles, the length of the cycle life directly affects the economics of the battery system. Fig.12 As shown, the PFD hydrogel electrolyte zinc-air battery has a -2 Under the discharge conditions, it exhibits a cycle life of up to 200 times, indicating that the PFD hydrogel zinc-air battery exhibits excellent cycle stability.

[0055] Example 4 Preparation of PFD hydrogel zinc-air battery:

[0056] First, prepare the positive electrode. Cut the nickel mesh and carbon cloth according to the size of the soft-pack battery and stack them together. Then, drop 5 mg of the catalyst (Co-MOFs) in the middle of the carbon cloth to form an area of ​​1 cm. 2 The catalyst layer is wrapped with tin foil on the smooth side and then hot pressed to obtain the oxygen electrode ( Fig.13 a); containing 2.5 M NH 4 Cl + 0.2M ZnCl 2 The PFD hydrogel was used as the electrolyte to assemble the oxygen electrode and the negative zinc sheet to prepare a solar-charged green biodegradable hydrogel zinc-air battery ( Fig.13 b).

Claims

1. A hydrogel, characterized in that: It is composed of acrylic monomer, cyclodextrin, Fe 3+ Obtained by cross-linking.

2. The hydrogel according to claim 1, characterized in that The acrylic monomer is one or a mixture of acrylic acid, methyl acrylate, ethyl acrylate, methacrylic acid, allyl alcohol, hydroxyvinyl methacrylate or 2-hydroxyacrylic acid.

3. The hydrogel according to claim 1, characterized in that The cyclodextrin refers to one or a mixture of α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin or sulfate cyclodextrin.

4. The method for preparing the hydrogel according to claim 1, characterized in that: The steps include: Step 1: preparing an aqueous solution containing acrylic acid, then adding iron salt, and stirring to obtain PAA Fe 3+ Mix the solution; Step 2: Continue to add cyclodextrin and initiator to carry out polymerization reaction, and then obtain hydrogel after heat treatment.

5. The method for preparing the hydrogel according to claim 4, characterized in that: In step 1, the volume ratio of acrylic acid to water is 50-70:100; the concentration of the iron salt in the aqueous solution containing acrylic acid is 0.05-0.5wt%, and the stirring time is 5-30h; the iron salt is FeCl3, FeBr3 or FeI3.

6. The method for preparing the hydrogel according to claim 4, characterized in that: In step 2, cyclodextrin is added to PAA Fe 3+ The concentration in the mixed solution is 0.5-5wt%.

7. The method for preparing the hydrogel according to claim 4, characterized in that: In step 2, the polymerization reaction time is 0.5-1 h, and the heat treatment condition is 50-70° C. for 1-10 h.

8. A zinc-air battery, characterized in that: The electrolyte material is the hydrogel described in claim 1; the hydrogel has been pre-soaked in an electrolyte solution; and the electrolyte solution is a mixed solution of NH4Cl and ZnCl2.

9. A photoelectric conversion and energy storage system, characterized in that: It comprises a polycrystalline silicon solar cell and the zinc-air battery as claimed in claim 1, wherein the solar cell is used for charging the zinc-air battery.

10. The photoelectric conversion and energy storage system according to claim 9, characterized in that: The light intensity is 90-10mW / cm 2 Under the condition of 2 The light conversion efficiency of polycrystalline silicon solar cells reached 12.4%-12.8% and the short-circuit current values ​​were 28-36mA cm -2 The output power is 45.0-56.0mW, which can be gradually increased with the increase of light intensity; the polycrystalline silicon solar cell charges the zinc-air battery with PFD hydrogel electrolyte under outdoor natural light irradiation, and stores the electricity generated by solar energy in the zinc-air battery efficiently and quickly.

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