阅读说明：本技术 一种具有高质子电导率和离子选择性的pbi膜活化处理方法 (PBI membrane activation treatment method with high proton conductivity and ion selectivity ) 是由 赵天寿 范新庄 王振宇 于 2020-06-29 设计创作，主要内容包括：本发明涉及液流电池和燃料电池等领域,具体为一种具有高质子电导率和离子选择性的PBI膜活化处理方法。首先,将商业PBI膜浸泡在浓磷酸、浓硫酸或浓盐酸中使其充分的溶胀,使PBI膜中磷酸、硫酸或盐酸的掺杂含量不断增大,进而改善其质子电导率；然后,利用充分溶胀和掺杂后的PBI膜在溶液中自动收缩的特点,将此充分溶胀和掺杂后的PBI膜转移到使其自动收缩的溶液中,PBI膜外层收缩致密提高离子选择性。在全钒液流电池的测试中,该处理方法可以在100mA/cm<Sup>2</Sup>的电密下实现88.7％的能量效率,优于同等实验条件下Nafion212的能量效率(87.6％)；同时,该方法处理后的PBI膜稳定性较好,在100个循环内没有发生明显的性能衰减。(The invention relates to the fields of flow batteries, fuel cells and the like, in particular to a PBI membrane activation treatment method with high proton conductivity and ion selectivity. Firstly, soaking a commercial PBI membrane in concentrated phosphoric acid, concentrated sulfuric acid or concentrated hydrochloric acid to fully swell the PBI membrane, so that the doping content of the phosphoric acid, the sulfuric acid or the hydrochloric acid in the PBI membrane is continuously increased, and further the proton conductivity of the PBI membrane is improved; then, the fully swelled and doped PBI membrane is transferred into the solution which enables the PBI membrane to automatically shrink by utilizing the characteristic that the fully swelled and doped PBI membrane automatically shrinks in the solution, and the outer layer of the PBI membrane shrinks compactly to improve the ion selectivity. In the test of the all-vanadium flow battery, the treatment method can be 100mA/cm 2 The energy efficiency of 88.7 percent is realized under the electric density of the Nafion, which is superior to the energy efficiency (87.6 percent) of Nafion212 under the same experimental condition;meanwhile, the PBI membrane treated by the method has good stability, and no obvious performance attenuation occurs in 100 cycles.)

1. A PBI membrane activation processing method with high proton conductivity and ion selectivity is characterized in that firstly, a commercial PBI membrane is soaked in concentrated phosphoric acid, concentrated sulfuric acid or concentrated hydrochloric acid to fully swell the PBI membrane, so that the doping content of phosphoric acid, sulfuric acid or hydrochloric acid in the PBI membrane is continuously increased, and the proton conductivity of the PBI membrane is further improved; then, by utilizing the characteristic that the PBI membrane after full swelling and doping automatically shrinks in a dilute solution, the PBI membrane after full swelling and doping is transferred to the solution which enables the PBI membrane to automatically shrink for soaking, and the outer layer of the PBI membrane shrinks compactly, so that the ion selectivity is improved;

or heating and soaking the commercial PBI membrane in concentrated phosphoric acid, concentrated sulfuric acid or concentrated hydrochloric acid at the heating temperature of 30-60 ℃, and continuously increasing the doping content of phosphoric acid, sulfuric acid or hydrochloric acid in the PBI membrane while fully swelling the commercial PBI membrane, thereby improving the proton conductivity of the PBI membrane; the PBI membrane after full swelling and doping is directly cooled in concentrated phosphoric acid, concentrated sulfuric acid or concentrated hydrochloric acid, so that the outer layer of the PBI membrane shrinks and is compact, and the ion selectivity is further improved;

or, the commercial PBI membrane is soaked in concentrated phosphoric acid, concentrated sulfuric acid or concentrated hydrochloric acid to be fully swelled, so that the doping content of the phosphoric acid, the sulfuric acid or the hydrochloric acid in the PBI membrane is continuously increased, and the proton conductivity of the PBI membrane is further improved; then, natural air drying, vacuum drying or baking is adopted to fully swell and the PBI membrane after doping automatically shrinks.

2. The activation treatment method for PBI membrane with high proton conductivity and ion selectivity as claimed in claim 1, wherein the PBI membrane treated by the activation treatment method has an outer layer with a lower swelling and doping degree than the inner layer, the inner layer has a higher swelling and doping degree than the outer layer, the ion selectivity is enhanced by the outer layer, and the proton conductivity is improved by the inner layer.

3. The method for activating a PBI membrane with high proton conductivity and ion selectivity according to claim 1, wherein the mass concentrations of the concentrated phosphoric acid, the concentrated sulfuric acid and the concentrated hydrochloric acid are respectively 80-95 wt%, 80-98 wt% and 50-70 wt%, and the doping contents of the phosphoric acid, the sulfuric acid and the hydrochloric acid in the PBI membrane are respectively 1.5-12 mol%, 0.5-4 mol% and 0.5-2 mol%.

4. The method for activating a PBI membrane having high proton conductivity and ion selectivity according to claim 1, wherein the solution for causing the PBI membrane after swelling and doping to automatically shrink is: a low concentration acid solution, water or electrolyte, wherein: the low-concentration acid solution is phosphoric acid, sulfuric acid or hydrochloric acid, and the molar concentration ranges of the phosphoric acid, the sulfuric acid and the hydrochloric acid are 1-14 mol/L, 1-16 mol/L and 1-11 mol/L respectively; the electrolyte is a mixed solution of electrolyte containing vanadium ions and sulfuric acid, the vanadium ions are one or a combination of two of V (II), V (III), V (IV) and V (V), and the concentration ranges of the vanadium ions and the sulfuric acid are 0.1-2.0 mol/L and 0.5-3.5 mol/L respectively.

5. The method for the activation treatment of the PBI membrane having high proton conductivity and ion selectivity according to claim 1, wherein the specific steps are as follows:

(1) soaking a commercial PBI membrane in concentrated phosphoric acid with the mass fraction of 80-90 wt% for 1-7 days at room temperature to fully dope and swell the PBI membrane;

(2) and (2) taking the doped and swelled PBI membrane prepared in the step (1), transferring the PBI membrane into a dilute phosphoric acid solution with the molar concentration range of 1-13 mol/L, and soaking for 1-7 days at room temperature.

6. The activation treatment method for PBI membrane with high proton conductivity and ion selectivity according to claim 5, wherein preferably, in the step (1), the mass fraction of the concentrated phosphoric acid is 85 wt%, and the PBI membrane is soaked at room temperature for 2 days; in the step (2), the diluted phosphoric acid solution with the molar concentration of 11mol/L is soaked for 1day at room temperature.

Technical Field

The invention relates to the field of electrochemical energy storage, in particular to a PBI membrane activation treatment method with high proton conductivity and ion selectivity.

Background

In recent years, with the increase of greenhouse effect and global warming phenomenon, people have more urgent need for clean renewable energy sources such as wind energy and solar energy. The power generation of wind energy and solar energy is unstable, and only about 1000 hundred million degrees of wind energy and solar energy are abandoned in China every year. Therefore, it is necessary to establish a safe, economical and efficient energy storage system to store the electricity generated by wind energy and solar energy to the maximum. The all-vanadium redox flow battery shows a huge application prospect in a large energy storage system due to excellent safety, ultra-long service life and good battery performance. The proton exchange membrane plays a role in isolating positive and negative electrolytes in the all-vanadium redox flow battery and realizing hydrogen ion transmission, and has a decisive effect on the performance of the battery.

At present, a Nafion membrane of a dupont company, a hydrogen ion exchange membrane, is commonly used in all-vanadium flow batteries. However, Nafion membranes, while having good proton conductivity, are expensive and have relatively poor vanadium ion blocking capability. Therefore, it is important to find a proton exchange membrane with high hydrogen ion conductivity, lower price and stronger vanadium ion blocking capability. PBI (polybenzimidazole) membranes have received much attention because of their relatively low cost, good chemical stability, and high mechanical strength. However, PBI membranes hardly conduct hydrogen ions at room temperature, although some researchers use 3mol/L H₂SO₄And 6mol/L H₃PO₄The hydrogen ion conductivity of the alloy is greatly improved by soaking the alloy, but the energy efficiency is still very low (at 100 mA/cm)²The voltage efficiency at current density of (a) is 60% and 75%, respectively). Some researchers design porous PBI and compact PBI composite membranes to improve the proton conductivity of the composite membranes, but the control difficulty is high, the mechanical stability is relatively poor, and the batch production is difficult.

Disclosure of Invention

The invention aims to provide a PBI membrane activation treatment method with high proton conductivity and ion selectivity, which can greatly improve the proton conductivity of a commercial PBI membrane to simultaneously obtain higher proton conductivity and ion selectivity, and has simple and easily-controlled preparation process and strong operability.

The technical scheme of the invention is as follows:

a PBI membrane activation processing method with high proton conductivity and ion selectivity, firstly, the commercial PBI membrane is soaked in concentrated phosphoric acid, concentrated sulfuric acid or concentrated hydrochloric acid to fully swell the PBI membrane, so that the doping content of phosphoric acid, sulfuric acid or hydrochloric acid in the PBI membrane is continuously increased, and further the proton conductivity of the PBI membrane is improved; then, by utilizing the characteristic that the PBI membrane after full swelling and doping automatically shrinks in a dilute solution, the PBI membrane after full swelling and doping is transferred to the solution which enables the PBI membrane to automatically shrink for soaking, and the outer layer of the PBI membrane shrinks compactly, so that the ion selectivity is improved;

or heating and soaking the commercial PBI membrane in concentrated phosphoric acid, concentrated sulfuric acid or concentrated hydrochloric acid at the heating temperature of 30-60 ℃, and continuously increasing the doping content of phosphoric acid, sulfuric acid or hydrochloric acid in the PBI membrane while fully swelling the commercial PBI membrane, thereby improving the proton conductivity of the PBI membrane; the PBI membrane after full swelling and doping is directly cooled in concentrated phosphoric acid, concentrated sulfuric acid or concentrated hydrochloric acid, so that the outer layer of the PBI membrane shrinks and is compact, and the ion selectivity is further improved;

or, the commercial PBI membrane is soaked in concentrated phosphoric acid, concentrated sulfuric acid or concentrated hydrochloric acid to be fully swelled, so that the doping content of the phosphoric acid, the sulfuric acid or the hydrochloric acid in the PBI membrane is continuously increased, and the proton conductivity of the PBI membrane is further improved; then, natural air drying, vacuum drying or baking is adopted to fully swell and the PBI membrane after doping automatically shrinks.

The PBI membrane treated by the activation treatment method has the advantages that the outer layer has lower swelling and doping degrees than the inner layer, the inner layer has higher swelling and doping degrees than the outer layer, the ion selectivity is improved through the outer layer, and the proton conductivity is improved through the inner layer.

According to the PBI membrane activation treatment method with high proton conductivity and ion selectivity, the mass concentration ranges of concentrated phosphoric acid, concentrated sulfuric acid and concentrated hydrochloric acid are 80-95 wt%, 80-98 wt% and 50-70 wt% respectively, and the doping content ranges of phosphoric acid, sulfuric acid and hydrochloric acid in the PBI membrane are 1.5-12 mol%, 0.5-4 mol% and 0.5-2 mol% respectively.

The PBI membrane activation treatment method with high proton conductivity and ion selectivity enables the swelled and doped PBI membrane to automatically shrink in the following solution: a low concentration acid solution, water or electrolyte, wherein: the low-concentration acid solution is phosphoric acid, sulfuric acid or hydrochloric acid, and the molar concentration ranges of the phosphoric acid, the sulfuric acid and the hydrochloric acid are 1-14 mol/L, 1-16 mol/L and 1-11 mol/L respectively; the electrolyte is a mixed solution of electrolyte containing vanadium ions and sulfuric acid, the vanadium ions are one or a combination of two of V (II), V (III), V (IV) and V (V), and the concentration ranges of the vanadium ions and the sulfuric acid are 0.1-2.0 mol/L and 0.5-3.5 mol/L respectively.

The PBI membrane activation treatment method with high proton conductivity and ion selectivity comprises the following specific steps:

(1) soaking a commercial PBI membrane in concentrated phosphoric acid with the mass fraction of 80-90 wt% for 1-7 days at room temperature to fully dope and swell the PBI membrane;

(2) and (2) taking the doped and swelled PBI membrane prepared in the step (1), transferring the PBI membrane into a dilute phosphoric acid solution with the molar concentration range of 1-13 mol/L, and soaking for 1-7 days at room temperature.

Preferably, in the step (1), the mass fraction of the concentrated phosphoric acid is 85 wt%, and the PBI membrane is soaked for 2 days at room temperature; in the step (2), the diluted phosphoric acid solution with the molar concentration of 11mol/L is soaked for 1day at room temperature.

The design idea of the invention is as follows:

1. the invention takes commercial PBI as raw material, and realizes high proton conductivity and high ion selectivity of the PBI membrane at normal temperature by a simple post-treatment method of the PBI membrane without changing the existing manufacturing mode. The method is simple to operate, does not increase the manufacturing cost, has no additional requirement on the processing environment, obtains the diaphragm with high proton conduction and high ion selectivity, and has great application prospect in the fields of flow batteries, hydrogen fuel batteries and the like.

2. The invention aims to obtain the high proton conductivity and ion selectivity, and realizes the functions through a structure with low phosphoric acid doping degree on the surface layer and high phosphoric acid doping degree inside. For commercial PBI membranes, high phosphoric acid doping is achieved by a concentrated phosphoric acid soak, followed by a dilute phosphoric acid soak to achieve a relatively low phosphoric acid doping of the PBI surface layer. The doping concentration of phosphoric acid in the PBI membrane can be increased and the doping time can be shortened by heating and soaking the PBI membrane with concentrated phosphoric acid or relatively low-concentration phosphoric acid. Similarly, the PBI film with high doping level can be diluted by phosphoric acid or sulfuric acid with different concentration, or the formation of the surface layer with low doping level can be accelerated by low temperature dilution. The treatment method is simple and suitable for large-scale application.

The invention has the following advantages and beneficial effects:

1. the method comprises the steps of soaking the PBI membrane in concentrated phosphoric acid at normal temperature, heating and soaking the PBI membrane in concentrated phosphoric acid or heating and soaking the PBI membrane in relatively dilute phosphoric acid to obtain the PBI membrane doped with high phosphoric acid, and soaking in dilute phosphoric acid, low-temperature soaking in dilute phosphoric acid or low-temperature soaking in concentrated phosphoric acid to obtain PBI with a low doping degree on the surface layer. The preparation method is simple, high in yield and easy for large-scale application.

2. The PBI membrane after swelling and doping is soaked by dilute phosphoric acid to obtain the PBI membrane with a denser outer layer and higher ion selectivity, and the method for shrinking the PBI membrane is suitable for low-concentration phosphoric acid but not limited to dilute phosphoric acid, and is also suitable for other solutions (such as dilute sulfuric acid, water, electrolyte and the like) and methods (such as natural air drying, vacuum drying, drying and the like) which can shrink the PBI membrane after swelling and doping.

3. In the invention, the PBI membrane in a concentrated phosphoric acid environment is fully doped and swelled and then transferred into a dilute phosphoric acid solution to shrink the surface of the PBI membrane so as to improve the selectivity of ions, but any combination of any other treatment method capable of doping and swelling the PBI membrane and a treatment method capable of shrinking the PBI membrane is suitable for the invention.

4. The operation method can greatly improve the proton conductivity of the PBI membrane and has excellent ion selectivity, and in the test of the all-vanadium redox flow battery, the treatment method can be at 100mA/cm²The energy efficiency of 88.7 percent is realized under the electric density of the Nafion, which is superior to the energy efficiency (87.6 percent) of Nafion212 under the same experimental condition; meanwhile, the PBI membrane treated by the method has good stability, and no obvious performance attenuation occurs in 100 cycles.

5. The invention mainly adopts a mode of firstly swelling and then shrinking to realize high proton conductivity and high ion selectivity; similarly, the acid with the same concentration can be doped by firstly increasing the temperature to increase the doping degree and then reducing the temperature to shrink the surface.

6. The method can obtain the PBI membrane with high proton conductivity and ion selectivity, has simple operation, easy control, no requirement on the operation environment, extremely low cost and easy industrialization, and can be widely used in the fields of flow batteries, hydrogen fuel batteries and the like.

Drawings

Fig. 1 is a cross-sectional view of a PBI membrane before and after activation treatment. Wherein, (a) the cross section before the PBI membrane activation treatment, and (b) the cross section after the PBI membrane activation treatment.

FIG. 2 is a graph comparing Electrochemical Impedance Spectroscopy (EIS) with Nafion212 (inset) after PBI membrane activation treatment in the examples. In the figure, the abscissa Re (Z)/Ohm represents the real impedance part Z' (Ω), and the ordinate-lm (Z)/Ohm represents the imaginary impedance part Z "(Ω).

FIG. 3 shows battery performance tests of the all-vanadium redox flow battery under different working conditions in the example, (a), (b), and (c) are respectively Coulombic Efficiency (CE), Voltage Efficiency (VE), and Energy Efficiency (EE) corresponding to different densities, and (d) is 200mA/cm of the all-vanadium redox flow battery²Energy Efficiency (EE) and variation over 100 cycles. In the figure, the abscissa Cycle number is the Cycle number, and Nafion212 represents a proton exchange membrane (Dupont, USA)212, PBI (proton exchange membrane) concentrated H₃PO₄2days+11M H₃PO₄1day represents that the PBI membrane is soaked in concentrated phosphoric acid with the mass fraction of 85 wt% for two days and then soaked in a dilute phosphoric acid solution with the mass fraction of 11mol/L for 1 day.

FIG. 4 is the change in PBI mass before and after soaking. Wherein the ordinate Weight represents Weight (mg). In the figure, beforeming represents the weight of the PBI membrane before being soaked in phosphoric acid, and After being soaked in concentrated phosphoric acid with the mass fraction of 85% wt for two days, After being soaked in the aromatic polycarbonate resin; after the PBI membrane is soaked in concentrated phosphoric acid with the mass fraction of 85% wt for two days, the membrane is soaked in dilute phosphoric acid solution with the mass fraction of 11mol/L for 1 day.

FIG. 5 shows the content of phosphorus in XPS test at different etching times. Wherein the abscissa Etch time represents the etching time(s) and the ordinate PThe 2p mass centered represents the mass fraction of phosphorus element characteristic of the 2p electron orbital of the XPS test. In the figure, centralized H₃PO₄doping represents the PBI membrane after two days of soaking in 85 wt% concentrated phosphoric acid. This method process represents the PBI membrane after soaking in 85 wt% concentrated phosphoric acid for two days and then soaking in 11mol/L dilute phosphoric acid solution for 1 day.

Detailed Description

In the specific implementation process, the raw material of the PBI membrane with high proton conductivity and ion selectivity is a common commercial PBI membrane, and the molecular formula of the PBI membrane is as follows:

the selected concentrated phosphoric acid is 85 percent phosphoric acid by mass fraction, and the dilute phosphoric acid is diluted by deionized water to different degrees. The preparation method comprises the following steps: first, a commercial PBI film was obtained, which had a thickness of about 55 μm. The membrane is soaked in concentrated phosphoric acid at room temperature for 2 days and then taken out, the doping content of the phosphoric acid in the PBI membrane is about 4 mol%, the proton conductivity is 40.42mS/cm, and the proton conductivity of Nafion212 under the same test conditions is 27.91 mS/cm. Then, the PBI membrane is put into 11mol/L diluted phosphoric acid solution to be continuously soaked for 1day, so that the outer layer of the PBI membrane shrinks and is compact, and the ion selectivity is further improved. And taking out the PBI membrane after soaking treatment, and then washing with deionized water to remove phosphoric acid adhered to the surface of the PBI membrane, thereby obtaining the PBI membrane with high proton conductivity and ion selectivity.

As shown in fig. 1, it can be seen from the cross-sectional views before and after the PBI membrane activation treatment, the proton conductivity of the PBI membrane can be greatly improved by soaking the PBI membrane in concentrated phosphoric acid, but the ion selectivity of the PBI membrane is poor, and the swelling of the PBI surface layer can be reduced by soaking the PBI membrane soaked in concentrated phosphoric acid in a dilute phosphoric acid solution, so that a thin layer which is denser than the inside of the PBI is formed on the surface of the PBI membrane, and further the ion selectivity of the PBI is improved. The method finally realizes that the doping degree of phosphoric acid on the surface of the PBI membrane is lower so as to obtain higher ion selectivity, the doping amount of internal phosphoric acid is higher so as to obtain higher proton conductivity, and further realizes the PBI membrane with high proton conductivity and high ion selectivity.

In order that the invention may be more fully understood, reference will now be made to the following description. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.