Basic bismuth oxyiodide, anion exchange membrane and electrolytic cell

Abstract

The application discloses a basic bismuth oxyiodide, an anion exchange membrane and an electrolytic cell, and belongs to the ion exchange membrane field. 1‑x (OH) x Wherein, 0 The basic bismuth oxyiodide has anion exchange characteristics, and after the anion exchange membrane is prepared, the basic bismuth oxyiodide shows high ion conductivity and excellent stability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of ion exchange membranes, and more particularly relates to a basic bismuth oxyiodide material, a cation exchange membrane prepared from the basic bismuth oxyiodide material, and a battery. BACKGROUND

[0002] The increasing scarcity of fossil fuels has spurred the demand for fast ion conductors, especially anion exchange membranes (AEMs), which are crucial for advancing energy conversion and storage devices such as water electrolysis, fuel cells, and flow batteries. Previous research has focused on developing high-conductivity AEMs based on high-molecular-matrix substrates rich in hydrophilic groups to improve the efficiency of energy conversion devices.

[0003] Therefore, the prior art has the following problems: traditional polymers obtain high conductivity by increasing the concentration of ions in AEMs. However, this method usually causes excessive swelling of the membrane, resulting in poor mechanical properties of the membrane. In addition, polymeric alkaline anion exchange membrane materials also have the problem of relatively poor chemical stability. The quaternary ammonium groups in the high-molecular-chain structure are easily attacked by the strong alkaline nucleophile OH - , resulting in degradation of the quaternary ammonium groups and the main chain, destruction of the membrane, and loss of conductivity.

[0004] Metal-organic framework (MOF) materials can obtain relatively high ionic conductivity through molecular-level functional modification, so that they can maintain the mechanical properties of the membrane while increasing the concentration of ions in AEMs. However, the functional groups in the structure are also attacked by the strong alkaline nucleophile OH - , thereby degrading the stability of the membrane and the conductivity. At the same time, the complex preparation process also limits its further commercial application.

[0005] Aluminum-magnesium layered double hydroxide (LDH) can maintain stability at a certain alkali concentration, but the aluminum element therein will generate meta-aluminate with OH - , thereby degrading the stability of the membrane and the conductivity, and at the same time, the conductivity is relatively low (10 -2 S / cm), which is difficult to form an excellent AEM.

[0006] Therefore, how to improve the chemical stability of AEMs without losing conductivity is a difficult problem in the development of alkaline electrolysis hydrogen production technology. SUMMARY

[0007] 1. Problem to be solved

[0008] Therefore, the present application provides a new material, basic bismuth oxyiodide, for preparing an anion exchange membrane.

[0009] Further, the anion exchange membrane prepared by using the basic bismuth oxyiodide has significantly improved ionic conductivity and high chemical stability.

[0010] Further, the electrolytic cell comprising the anion exchange membrane prepared by using the basic bismuth oxyiodide has significantly improved electrolytic efficiency.

[0011] 2. Technical solutions

[0012] The technical solutions adopted by the present application are as follows:

[0013] [Basic bismuth oxyiodide]

[0014] The present application provides a basic bismuth oxyiodide in the first aspect, which has a chemical formula of BiOI 1-x (OH) x , wherein 0

[0015] The above-mentioned basic bismuth oxyiodide is obtained by partially exchanging OH - with I - on the basis of bismuth oxyiodide.

[0016] As a preferred embodiment of the basic bismuth oxyiodide according to any one of the embodiments of the first aspect of the present application, x has a value of 0.10-0.99; preferably, x has a value of 0.3-0.99; further preferably, x has a value of 0.3-0.7, or further preferably, x has a value of 0.7-0.99.

[0017] It should be noted that the larger the value of x, the better the anion exchange performance of the basic bismuth oxyiodide. As a preferred embodiment of the basic bismuth oxyiodide according to any one of the embodiments of the first aspect of the present application, the density of hydroxyl groups in the basic bismuth oxyiodide is 4.7-6.6 nm -2 . The density of hydroxyl groups is the number of OH - groups per unit area.

[0018] The higher the density of hydroxyl groups, i.e. the larger the value of x, the better the anion exchange performance of the basic bismuth oxyiodide.

[0019] As a preferred embodiment of the basic bismuth oxyiodide according to any one of the embodiments of the first aspect of the present application, the basic bismuth oxyiodide has a sheet structure, and at least 80% or more of the sheet structures with a lateral size greater than 50 nm in the AFM image have an aspect ratio of not less than 100, preferably an aspect ratio of not less than 200, more preferably an aspect ratio of not less than 400, more preferably an aspect ratio of not less than 500, and most preferably an aspect ratio of not less than 1000. It should be noted that, within the range that can be achieved by the prior art, the larger the aspect ratio of the basic bismuth oxyiodide, the more conducive to the improvement of its anion exchange performance.

[0020] [Preparation method of basic bismuth iodide]

[0021] The second aspect of this invention provides a method for preparing basic bismuth iodide according to any embodiment of the first aspect of this invention, comprising the step of exfoliating bismuth iodide crystals under hydrothermal conditions to obtain basic bismuth iodide, wherein the basic bismuth iodide has the chemical formula BiOI. 1-x (OH) x Where 0 < x < 1.0. Under hydrothermal conditions, the OH- in the solution... - I on bismuth iodide crystal - A partial exchange was performed to obtain basic bismuth iodide.

[0022] It is worth noting that the bismuth oxyiodide crystal is tetragonal.

[0023] In a preferred embodiment of the preparation method of basic bismuth iodide according to the second aspect of the present invention, the hydrothermal temperature is 120-200°C.

[0024] In a preferred embodiment of the preparation method of basic bismuth iodide according to the second aspect of the present invention, the hydrothermal reaction time is 7 to 144 h.

[0025] As a preferred method for preparing basic bismuth iodide according to any embodiment of the second aspect of the present invention, in order to improve OH - to I - To achieve the desired exchange rate without sacrificing the aspect ratio of the basic bismuth iodide flaky structure, basic bismuth iodide BiOI was first obtained by exfoliation under hydrothermal conditions. 1-x1 (OH) x1 Where 0 < x1 < 1.0; then make the BiOI 1-x1 (OH) x1 Contact with alkaline solution yields basic bismuth iodide (BiOI). 1-x2 (OH) x2 , where 0 < x2 ≤ 1.0 and x1 < x2.

[0026] Preferably, the BiOI 1-x1 (OH) x1 Contact with alkaline solution includes BiOI 1-x1 (OH) x1 Soak in alkaline solution or spray with alkaline solution.

[0027] Typically, BiOI 1-x1 (OH) x1 The contact time with alkaline solution can range from several hours to several days or even tens of days, for example, from 1 hour to 30 days. Generally, the longer the contact time, the higher the OH content. - For the residual I- the more the exchange.

[0028] [BiOI 1-x (OH) x ]

[0029] The third aspect of the present application provides the BiOI 1-x (OH) x , wherein x is 1.0; the BiOI 1-x (OH) x is a sheet structure, and the sheet structure has a length-thickness ratio of not less than 100, preferably a length-thickness ratio of not less than 200, more preferably a length-thickness ratio of not less than 400.

[0030] [Application of the basic bismuth oxyiodide]

[0031] The fourth aspect of the present application provides the basic bismuth oxyiodide according to any one of the embodiments of the first aspect of the present application, or the basic bismuth oxyiodide prepared by the preparation method according to any one of the embodiments of the second aspect of the present application, or the BiOI 1-x (OH) x for use in preparing an anion exchange membrane. Experiments show that the basic bismuth oxyiodide is used in the anion exchange membrane, and the anion exchange membrane has excellent anion exchange characteristics and chemical stability.

[0032] [Anion exchange membrane]

[0033] The fifth aspect of the present application provides an anion exchange membrane, which comprises:

[0034] BiOI 1-x (OH) x , wherein 0

[0035] an adjuvant; preferably, the adjuvant is selected from one or more of nanocellulose, polyvinyl alcohol, perfluorosulfonic acid polymer (Nafion), quaternized poly(arylene ether sulfone) (QAPES), quaternized poly(phenylene oxide) (QAPPO), and polybenzimidazole (PBI).

[0036] As a preferred embodiment of the anion exchange membrane according to any one of the embodiments of the fifth aspect of the present application, the mass percentage of the basic bismuth oxyiodide in the anion exchange membrane is 70-99%, preferably the mass percentage of the basic bismuth oxyiodide in the anion exchange membrane is 75-90%.

[0037] As a preferred embodiment of the anion exchange membrane according to any one of the embodiments of the fifth aspect of the present application, the anion exchange membrane has a conductivity of not less than 80 mS cm -1cm-1 at 90℃. Preferably, the anion exchange membrane has an electrical conductivity of not less than 160 mS cm-1 at 90℃. -1

[0038] Preferably, the anion exchange membrane has an interlayer spacing of 0.80-0.95 nm, preferably 0.80-0.90 nm, calculated from the XRD diffraction pattern of the anion exchange membrane.

[0039] [Electrolytic cell]

[0040] The sixth aspect of the present application provides an electrolytic cell comprising the basic bismuth oxyiodide according to any one of the first aspect of the present application, or the basic bismuth oxyiodide prepared by the method according to any one of the second aspect of the present application, or the BiOI 1-x (OH) x , or the anion exchange membrane according to any one of the fifth aspect of the present application.

[0041] 3. Advantages

[0042] Compared with the prior art, the present application has the following advantages:

[0043] (1) The present application provides a new material, basic bismuth oxyiodide, in which part of the iodine in bismuth oxyiodide is replaced by hydroxyl. The basic bismuth oxyiodide has anion exchange characteristics, and after being prepared into an anion exchange membrane, it exhibits high ionic conductivity and excellent stability.

[0044] (2) Further, the basic bismuth oxyiodide (BiOI 1-x (OH) x , x has a value of 0.10-0.99, and in particular, x has a value of 0.30-0.70. When the basic bismuth oxyiodide is contacted with a base, the value of x increases, for example, to a value of 0.70-0.99. As the value of x increases, the ionic conductivity increases after the anion exchange membrane is prepared.

[0045] (3) The present application uses the basic bismuth oxyiodide (BiOI 1-x (OH) x ) to prepare an anion exchange membrane, which has significantly improved ionic conductivity.

[0046] ​(4) The present application first uses a hydrothermal reaction method to exfoliate bismuth oxyiodide from bismuth oxyiodide crystal materials, and during the reaction process, basic bismuth oxyiodide is unexpectedly obtained. After the basic bismuth oxyiodide is used to prepare an anion exchange membrane, it exhibits high ionic conductivity. Further, the basic bismuth oxyiodide obtained by hydrothermal reaction is contacted with an alkali solution to obtain basic bismuth oxyiodide with an increased x value. After the basic bismuth oxyiodide is used to prepare an anion exchange membrane, it has improved ionic conductivity.

[0047] (5) The electrolytic cell comprising the anion exchange membrane prepared by using the basic bismuth oxyiodide (BiOI 1-x (OH) x ) of the present application has significantly improved electrolytic efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 Characterization of BiOI crystals prepared by hydrothermal reaction. (a) BiOI crystal image under optical microscope. (b) Scanning electron microscope (SEM) image. (c) High-resolution transmission electron microscope (HRTEM) image. (d) Transmission electron microscope element mapping (TEM element mapping). (e) X-ray diffraction (XRD) pattern. (f) Crystal structure diagram of BiOI. Scale bar: (a) 10 microns; (b) 10 microns; (c) 2 nanometers, 5 nanometers -1 ; (d) 1 micron. The square shape of the BiOI crystal matches its tetragonal structure, which can also be confirmed by the (001), (002), (003) and (004) crystal planes in the XRD results.

[0049] Figure 2(a) Schematic of the preparation process of BiOIO nanosheets (x = 0.36), including two steps of hydrothermal intercalation and microfluidization, aiming to prepare BiOIO nanosheets (x = 0.36) from BiOI crystals. (b) Atomic force microscopy (AFM) image of BiOIO nanosheets (x = 0.36) synthesized in a hydrothermal exfoliation process at 160 °C for 24 h. The height profiles indicated by white lines show thicknesses of 3.89, 3.97, and 3.81 nm, respectively. (c) Size distribution and thickness distribution of BiOIO nanosheets (x = 0.36) synthesized in a hydrothermal exfoliation process at 160 °C for 24 h. (d) UV absorption intensity at 226 nm of the supernatant of BiOIO prepared at different hydrothermal times at 160 °C and the corresponding atomic ratio of Bi and I in BiOIO nanosheets. (e) Cross-sectional scanning electron microscopy (SEM) image of BiOIO (x = 0.36) film synthesized in a hydrothermal exfoliation process at 160 °C for 24 h. The inset shows the flexibility of BiOIO (x = 0.36) film. (f) O-H exchange ratio of BiOIO at different immersion times in 1 M NaOH aqueous solution, measured by EDS. The inset shows a schematic of BiOIO with different O-H exchange ratios. (g) X-ray diffraction (XRD) spectra of BiOIO at different O-H exchange times. The peaks at 9.6° and 10.8° are called peak I and peak II, respectively. Scale bars: (b) 5 μm, (e) 1 cm (inset) and 2 μm.

[0050] Figure 3 (a) Schematic of the preparation process of BiOIO nanosheets. First, the as-synthesized bulk BiOI crystals were hydrolyzed in water, and then microfluidization was performed to obtain BiOIO (x = 0.36) nanosheets. (b) Photograph of BiOIO (x = 0.36) nanosheets suspended in an ethanol-water mixture. (c) Lateral size of BiOIO nanosheets prepared at different hydrolysis times. (d) High-resolution transmission electron microscopy (HRTEM) image showing the (001) crystal plane of BiOIO (x = 0.36) nanosheets, with a (110) lattice distance of 0.282 nm. (e) Transmission electron microscopy (TEM) image and elemental mapping images of BiOIO (x = 0.36) nanosheets. (f) Maximum lateral size and minimum thickness of two-dimensional bismuth oxyhalides prepared by various methods. Our additive-free, hydrothermal exfoliation method is highly competitive in both top-down and bottom-up approaches. Scale bars: (d) 2 nm, 5 nm -1 ; (e) 2 μm.

[0051] Figure 4Effect of hydrolysis time on the formation of BiOI nanosheets: (a) UV absorption intensity of the supernatant after centrifugation of BiOI nanosheets prepared at different hydrolysis times. (b) XPS spectra of BiOI nanosheets prepared at different hydrolysis times. (c) Peak area ratio of O Bulk (oxygen in the crystal) and O v (oxygen vacancy) in BiOI nanosheets prepared at different hydrolysis times. (d) Peak area ratio of O Bulk and O O-H (hydroxyl oxygen) in BiOI nanosheets prepared at different hydrolysis times.

[0052] Figure 5 Effect of hydrolysis time on the formation of BiOI nanosheets: (a) Schematic illustration of the formation of BiOI nanosheets at different hydrolysis times. (b-f) Scanning electron microscope (SEM) images of BiOI nanosheets supported on AAO (anodic aluminum oxide) substrates. Scale bar: 2 micrometers. (g-k) Corresponding lateral size distribution of BiOI nanosheets.

[0053] Figure 6 Effect of hydrolysis temperature on the formation of BiOI nanosheets: (a, b) UV absorption intensity of the supernatant after 13 h hydrolysis and the atomic ratio of Bi and I in BiOI nanosheets prepared at different hydrolysis temperatures. (c) XPS spectra of BiOI nanosheets prepared at different hydrolysis temperatures. (d) Peak area ratio of O Bulk (oxygen in the crystal) and O v (oxygen vacancy) in BiOI nanosheets prepared at different hydrolysis temperatures.

[0054] Figure 7 Anion transport in BiOI films: (a) OH - Schematic illustration of the transport in BiOI 1-x (OH) x films at different OH 1-x (OH) x conductivity of BiOI 0.67 (OH) 0.33 (black line), BiOI 0.44 (OH) 0.56 (blue line) and BiOI0(OH)1(orange line). (d) Simulated calculation: OH -Mean square displacement (MSD) of ions; the slope of MSD represents the diffusion coefficient. (e) Simulated calculation: MSD of ions in BiOI 0.67 (OH) 0.33 , BiOI 0.44 (OH) 0.56 and BiOI0(OH)1under the influence of Grotthuss and vehicular mechanisms. (f) The relationship between ion conductivity and IEC of different materials. (g) Hardness and elastic modulus of BiOI0.36(OH)0.36film and commercial FAA HEM. (h) Radar chart of the performance comparison between BiOI0.36(OH)0.36film and commercial FAA in terms of conductivity, IEC, gas permeability, hardness, swelling ratio, etc.

[0055] Figure 8 . Water electrolysis performance of BiOI0.97(OH)0.03film. (a) Schematic diagram of experimental setup. (b) Polarization curves of BiOI0.97(OH)0.03film, FAA-PK-130 and PPS (electrolyte: 15% KOH, 60°C) assembled for water electrolysis. (c) EIS of each film material before stability experiment. (d) Stability test of water electrolysis of the film at 1000 mA cm -2 (60°C) conditions. (e) Stability performance comparison of BiOI0.97(OH)0.03film and other film materials.

[0056] Figure 9 Performance of BiOI0.97(OH)0.03film in water electrolysis: (a) Polarization curves of BiOI0.97(OH)0.03film at different temperatures in 3M KOH electrolyte. (b) Polarization curves of BiOI0.97(OH)0.03film in different concentrations of KOH electrolyte at 60°C. (c) Rohm (ohmic resistance) and Rct (ionic resistance) of the film before and after stability test at 1000 mA cm -2 (60°C) conditions. (d) Electrochemical impedance spectroscopy (EIS) of the film before and after stability test. (e) O2 purity at different test current densities in 3M KOH electrolyte at 60°C, determined by hydrogen sensor. (f) X-ray diffraction (XRD) of BiOI0.97(OH)0.03film before and after water electrolysis stability test. The test conditions were 120 hours, 3M KOH electrolyte and 60°C. The structure of BiOI0.97(OH)0.03can be demonstrated by the (001) peak at 10.8°, which proves that the layered structure of BiOI0.97(OH)0.03is not destroyed, and no structural change is observed after water electrolysis test, which proves its excellent stability. DETAILED DESCRIPTION

[0057] Unless otherwise defined, 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 application belongs; the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0058] Unless otherwise indicated, conventional methods or those modifications known to those of ordinary skill in the art were employed in the experiments of the examples. Unless otherwise indicated, the reagents or instruments used were commercially available and were used according to the manufacturer's instructions.

[0059] As used herein, the term "about" is used to provide flexibility to a numerical range endpoint by providing support for a somewhat greater or lesser inclusion of the values used in the endpoint - to within close proximity of the actual value - even if such values are not within the typical range while remaining within the claimed disclosure. One of skill in the art can readily determine the extent of flexibility of a particular variable.

[0060] Concentrations, amounts, and other numerical data can be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be construed as having been followed to following the principle of including and covering all the individual values of both the range extremes if it should contain such values. For example, amount of about 1 to about 4.5 should be interpreted to include not only the specifically recited amounts of 1 to about 4.5, but also individual amounts such as 2, 3, and 4 and sub-ranges such as 1 to 3, 2 to 4, etc. Likewise, the same applies to ranges reciting only one numerical value, such as "less than about 4.5", which should be interpreted to include all of the above values and ranges. In addition, this interpretation should apply regardless of the breadth of the range or the characteristics being described.

[0061] The application is further described below in connection with specific embodiments.

[0062] In this study, a HEM membrane based on BiOI nanosheet assembly was developed. By replacing iodide with hydroxide, the content of interlayer short hydrogen bond (SHB) was increased, providing a fast Grotthuss-type anion transport channel for confined water, resulting in a significant increase in ionic conductivity. With the promotion of SHB, BiOI HEM after full or partial replacement of hydroxide was applied to membrane electrode assemblies, showing high-efficiency and durable alkaline water electrolysis hydrogen production performance.

[0063] Material characterization and testing techniques

[0064] BiOI 1-x (OH) x The surface structure and morphology of BiOI 1-x (OH) xThe thickness of nanosheets was measured by AFM (Bruker Dimension ICON-PT). UV-Vis spectra were performed on a TU-1901 (Beijing Purkinje Instrument Co., Ltd.) spectrophotometer. TEM was tested using a Thermo Scientific Talos F200X electron microscope operating at 300 kV. Cu K α X-ray source (wavelength of ) in Bragg-Brentano geometry with an operating voltage of 40 kV and a current of 15 mA. X-ray photoelectron spectroscopy (XPS) analysis of the surface chemical state was performed on an AXIS Ultra DLD instrument using Al K α X-ray radiation. Low-field nuclear magnetic resonance (LF-NMR) measurements were performed on a 20 MHz NMR analyzer (A NMI20-Analyst NMR Analyzer, Suzhou Niumag Analytical Instruments Co., Ltd., China) with about 5 mg of well-hydrated membranes placed in a glass tube, and the NMR probe was inserted into the glass tube during testing. T2 was measured using the Carre-Purcelle-Meiboome-Gill (CPMG) sequence. Infrared spectroscopy (FT-IR) was performed on an infrared imaging microscope (iN10 MX Infrared Imaging Microscope, Thermo Scientific TM ,Nicolet TM ) using the attenuated total reflection (ATR) mode in an air environment. Nanoindentation tests were performed at room temperature using a triangular pyramid probe on a nanoindentation analyzer (NHT2 Nanoindentation Analyzer, Anton Paar Instruments GmbH, Austria) in a pressure control mode. The maximum pressure applied was 10 μN, and the results were obtained by repeating five times.

[0065] Commercial hydroxide ion exchange membrane (FAA-PK-130) was purchased from

[0066] Commercial hydroxide ion exchange membrane FA-500 (polyphenylene sulfide, PPS) was purchased from Hangzhou Huamo Co., Ltd. BiOI 1-x (OH) x content in BiOI -

[0067] BiOI 1-x (OH) x content in BiOI - ​The content of Bi was determined by EDS of SEM, specifically, the high efficiency rapid elemental energy spectrum (EDS) accessory of Carl Zeiss Merlin high resolution field emission scanning electron microscope (FE-SEM) was used to characterize at 15.0 kV.

[0068] Swelling ratio test

[0069] The swelling ratio (SR) of the membrane was determined by the difference in thickness of the membrane in wet state (d wet , in hydroxide form) and dry state (d dry , in hydroxide form) BiOI 1-x (OH) x and calculated according to the following equation:

[0070]

[0071] Ion exchange capacity (IEC) test

[0072] BiOI 1-x (OH) x The ion exchange capacity (IEC) of the membrane was determined by Mohr titration method. The dried BiOI membrane (in hydroxide form) was immersed in 50 ml of 0.5 M Na2SO4 standard solution for 4 hours at 25 °C, repeated three times. Then the solutions were titrated with standardized HC1 solution using a mixture of methyl red and methylene blue solution as indicator. The IEC was calculated according to the following equation:

[0073]

[0074] where c HCl is the concentration of HC1 solution; V HCl is the volume of HC1 solution; m BiOI is the dry weight of BiOI membrane (g). Conductivity test

[0075] Before the ion conductivity test, the membrane was treated in 1 M NaOH aqueous solution for 1 hour, then washed thoroughly with deionized water to adsorb the hydroxide ions. Electrochemical impedance spectroscopy (EIS) test was performed using two platinum electrodes with MFIA LCR (Zurich Instrument Inc.) in the range of 0.1 Hz to 1 M Hz. The x-axis intercept at high frequency was taken as the resistance of the sample. The ion conductivity (σ) was calculated according to the following equation:

[0076]

[0077] where R, S and L are the resistance, effective area and thickness of the membrane, respectively.

[0078] Electrolysis test

[0079] The membrane electrode assembly (MEA) was prepared by sandwiching a piece of ion exchange membrane with an active area of 1 cm2between an anode and a cathode. The preparation of the anode and cathode included spraying catalyst ink on the membrane (anode: Ir02 / FAA-3, cathode: Pt / C / FAA-3) with a loading of 6 mg cm-2and 3 mg cm-2, respectively. KOH solution was used as electrolyte and was fed to the cathode and anode at a flow rate of 5 mL min-1, respectively. The temperature was maintained at the specified value and was monitored by a thermocouple. The cell was held at 1 V to detect any pinholes or other short-circuiting in the MEA in the cell (the electrolysis current should decay to zero if the voltage is less than 1.23 V, if there is a short circuit current it will persist). Subsequently, the cell voltage was adjusted to 1.5 V and maintained for 15 min to reach steady state. Polarization curves were obtained by recording the current density over a voltage range of 1.4 to 2.0 V. Stability tests were performed at constant current density and the corresponding voltage data were collected.

[0080] Hydrogen permeability test

[0081] The hydrogen permeability was obtained from the alkaline water electrolysis setup mentioned earlier. The hydrogen volume flow rate was obtained by the drain method under the operating conditions. The hydrogen permeability (P) was calculated by the following equation: Hydrogen content in the generated oxygen The hydrogen content in the generated oxygen was determined by a hydrogen sensor (JEC-H2 hydrogen sensor from Jingxin Changtong Instruments, China). The hydrogen permeability (P) was calculated by the following equation:

[0082]

[0083] where, l is the BiOI 1-x (OH) x thickness of the membrane, Δp is the hydrogen pressure difference across the membrane, S is the active area, and t is the time.

[0084] Examples

[0085] I. Synthesis of alkali exchanged BiOI (BiOI) membranes

[0086] (1) Preparation of BiOI crystals

[0087] Ethanol (50 mL), bismuth nitrate pentahydrate (0.2 mmol) and sodium iodide (0.4 mmol) were mixed, stirred thoroughly in a 100 mL hydrothermal reactor and heated to 160 °C for 24 h. The product was a reddish-brown BiOI crystal. The characterization of the crystal is as follows: Figure 1 a-f. The product was washed with water and ethanol and dried at 60 °C for 12 h with a yield of 94.5%.

[0088] (2) Preparation of BiOIO nanosheets

[0089] As shown in Figure 2 a, the top-down exfoliation of BiOIO nanosheets was realized by intercalation of subcritical water and microfluidic homogenization-assisted exfoliation. BiOIO crystals (size about 30 μm, as shown in Figure 1 b) were used as raw materials, and BiOIO nanosheets were successfully exfoliated by intercalation of subcritical water (SCW) under hydrothermal conditions. Compared with previous studies, the exfoliation method of the present application does not need to use dangerous chemicals, such as butyllithium. The specific steps are as follows:

[0090] SCW intercalation: BiOIO crystals (50 mg) were mixed with ultrapure water (50 mL) and heated to 120-200 °C in a 100 mL hydrothermal reactor, and the protective atmosphere was N2, which lasted for 7-144 hours. In this embodiment, in order to reduce the side reaction of degradation in the XY direction during the intercalation of SCW, the hydrothermal reaction conditions of the intercalation process were optimized to 160 °C and 24 hours Figure 2 d).

[0091] Exfoliation (microfluidic homogenization technology): after cooling to room temperature, the mixture was transferred to a microfluidic homogenizer (model: NLM100, manufacturer: Retsch) and treated at a pressure of 800 bar for 50 cycles. Subsequently, the mixture was centrifuged (1000 rpm, 10 minutes) to obtain the supernatant (about 0.40 mg / mL); the supernatant was centrifuged at 14000 rpm for 10 minutes, and the precipitate was the BiOIO nanosheets with appropriate length-thickness ratio. According to the number of sheet structures with a lateral size greater than 50 nm in the AFM image, more than 80% of the BiOIO nanosheets had a length-thickness ratio greater than 100, and the characterization of the BiOIO nanosheets is shown in Figure 2 b-c.

[0092] It was measured by EDS that 36% of iodine in the BiOIO crystal was replaced by hydroxyl ions in water, that is, the obtained BiOIO was BiOIO 1-x (OH) x , wherein x is 0.36.

[0093] Under the same conditions, only BiOIO crystals successfully obtained BiOIO under hydrothermal conditions, while BiOCl and BiOBr did not intercalate successfully under the same conditions, and OH-substituted products could not be obtained.

[0094] In the above method, as shown in Figure 3As shown in Figure a, after SCW intercalation, the intercalated BiOI nanosheets (basic bismuth iodide nanosheets) were non-destructively exfoliated using microfluidic homogenization technology, and then prepared as a basic bismuth iodide nanosheet dispersion with a solid concentration of 0.4 ± 0.04 g / L. Figure 3 b). Among them, the 2D basic bismuth iodide nanosheets (x = 0.36) have an average thickness of 3.8 ± 0.49 nm and an average lateral dimension of 1.7 ± 1.01 μm. Figure 3 c) The average length-to-thickness ratio is approximately 450. Compared to previous studies (BiOX series materials), the length-to-thickness ratio is significantly improved. Figure 3 f). For example Figure 3 As shown in d, a high-resolution transmission electron microscope (HRTEM) image of basic bismuth iodide nanosheets is shown, revealing the (001) crystal plane and the (110) lattice distance of 0.282 nm. Figure 3 e indicates that the basic bismuth oxyiodide nanosheets contain Bi, O, and I elements.

[0095] In summary, this invention successfully synthesized well-dispersed basic bismuth iodide nanosheets with high aspect ratio through SCW intercalation and microfluidic homogenization techniques, and plans to use them to construct tunable 2D nanochannels—basic bismuth iodide membranes.

[0096] In some embodiments, the effect of different hydrolysis times on the formation of basic bismuth iodide nanosheets under the same conditions (160 °C) was also investigated, such as... Figure 4 and Figure 5 As shown.

[0097] In some embodiments, the effects of different hydrolysis temperatures on the formation of basic bismuth iodide nanosheets under the same conditions and the same hydrolysis time (13 h) were also investigated. Figure 6 As shown.

[0098] (2) Preparation of basic bismuth iodide (x = 0.36) film

[0099] Furthermore, the basic bismuth iodide dispersion (x = 0.36) obtained in (1) was vacuum filtered to prepare a semi-transparent membrane with certain flexibility, such as... Figure 2 e. Illustrations, specifically:

[0100] To enhance the mechanical strength of the basic bismuth iodide oxychloride membrane, approximately 20 wt% CNF (0.5 mg / mL CNF dispersion) was added in this embodiment and mixed with the exfoliated basic bismuth iodide oxychloride (x = 0.36) dispersion (0.4 ± 0.04 g / L, 10 mL). A basic bismuth iodide oxychloride (x = 0.36) membrane (thickness: 4.99 μm) was obtained using vacuum filtration. The basic bismuth iodide oxychloride nanosheets in the membrane formed long-distance ordered 2D channels. Figure 2e) Furthermore, the density of hydroxide in the basic bismuth iodide film is 2.30 nm. -2 x is 0.36.

[0101] (3) Alkali exchange treatment of basic bismuth iodide membrane

[0102] BiOI 0.64 (OH) 0.36 When the membrane is treated with alkali (NaOH, 1M), the hydroxyl content in the membrane gradually increases.

[0103] BiOI 0.35 (OH) 0.65 Membrane preparation: After 5 days of alkali exchange treatment, the hydroxide ion density in the basic bismuth iodide oxidase membrane was 4.35 nm. -2 x is 0.65;

[0104] BiOI 0.17 (OH) 0.83 Membrane preparation: After 10 days of alkali exchange treatment, the hydroxide ion density in the basic bismuth iodide oxychloride membrane was 5.56 nm. -2 x is 0.83;

[0105] BiOI 0.03 (OH) 0.97 Membrane preparation: After 20 days of alkali exchange treatment, the hydroxide ion density in the basic bismuth iodide oxychloride membrane can be increased to 6.08 nm. -2 x is 0.97 (e.g.) Figure 2 f);

[0106] Increasing the hydroxide ion density can be used to modulate the hydrophilicity of anion transport channels. In basic bismuth iodide membranes obtained after alkali exchange treatment for different durations (0-20 days), the 2D interlayer spacing of the untreated membrane (x = 0.36) was 0.91 nm (peak I). With increasing hydroxide ion exchange capacity, the interlayer spacing of the basic bismuth iodide membrane treated for 20 days (x = 0.36, then 0.97 after 20 days) decreased to 0.82 nm (peak II). Therefore, OH- ions in the basic bismuth iodide membrane can pass through the interlayer. - Content regulation of nanochannel spacing ( Figure 2 Therefore, 2D basic bismuth iodide films can provide 2D nanochannels with tunable confinement space and hydrophilic groups throughout for subsequent anion conduction.

[0107] II. Anion Transport in Basic Bismuth Oxide Membranes

[0108] Basic bismuth iodide membranes possess tunable interlayer hydrogen bonds. Experiments show that the conductivity of basic bismuth iodide membranes increases with increasing alkali exchange. For example, the basic bismuth iodide membranes with x = 0.36, x = 0.65, x = 0.83, and x = 0.97 prepared in [I. Synthesis of Alkali-Exchanged BiOI (Basic Bismuth Oxide) Membranes] exhibit an increasing SHB network expansion in confined water as the x value increases (see...). Figure 7 a) The conductivity of the basic bismuth iodide film at 90 °C is 84.7 mS / cm. -1 (x=0.36) rapidly increased to 168 mS cm -1 (x = 0.97) (see) Figure 7 b) This value is higher than that of most reported polymer HEMs, such as o-PDQA (106 mS cm⁻¹). -1 Tec-PBI-60 (131.8mS cm) -1 ), QAPPT (137mS cm) -1 ), showing a difference from commercial PEMs (such as 83mS cm -1 It boasts performance comparable to other products.

[0109] Furthermore, the basic bismuth iodide membrane exhibits humidity-dependent ionic conductivity behavior, indicating the key influence of SHB in nano-confined water (see [link to article]). Figure 7 c). However, under 50% RH conditions, BiOI 1-x (OH) x The ionic conductivity at (x=0.97) still reaches 4.24 mS cm⁻¹. -1 This is three orders of magnitude higher than FAA (a typical commercial HEM). To investigate the ion selectivity of basic bismuth iodide oxide films, we used concentration diffusion to test them. BiOI 0.64 (OH) 0.36 The open-circuit voltage (V0) is +54.9mV, indicating that the 2D channel exhibits a positive charge. Based on the Nernst equation, OH is calculated... - The number of transmissions is 0.77 ( Figure 7 (d and e) indicate that the ionic conductivity of layered basic bismuth iodide is mainly attributed to OH. - Therefore, basic bismuth iodide membranes have the potential to become HEMs.

[0110] Interestingly, the ion exchange capacity (IEC) of our basic bismuth iodide oxychloride (x = 0.36) membrane is only 8.5 × 10⁻⁶. - 4 mmol / g, significantly lower than those of polymeric ion exchange membranes with similar or lower conductivity (see...). Figure 7f). While in most previous studies, the conductivity was elevated to 100 mS cm -1 Above, IEC is generally required to be higher than 2 mmol / g, therefore, people tried to increase the number of modification of charged functional groups. In this process, swelling and degradation of functional groups inevitably occurred, resulting in the decrease of ionic conductivity and other important physical properties (e.g. mechanical strength and gas permeability). In terms of anti-swelling performance, the BiOIx film (x = 0.36) increased by 24.7% compared to the commercial FAA, and the elastic modulus increased by 140% (see Figure 7 g and h). In addition, the H2permeability of the BiOIx film (x = 0.36) was 0.244 Barrer, which was 6.9% lower than that of FAA under experimental conditions. Therefore, it is speculated that the short hydrogen bond network formed in the confined space and the interfacial interaction can endow HEM with superior conductivity independent of IEC, thereby indirectly improving the mechanical and chemical stability of HEM (see Figure 7 h).

[0111] Three, application of BiOIx film in water electrolysis

[0112] To demonstrate the application potential of BiOIx film as a high-conductivity HEM, we applied the BiOIx film (x = 0.97) in alkaline membrane electrolysis of water (see Figure 8 a), and commercial hydroxide ion exchange membrane (FAA-PK-130) and FA-500 (polyphenylene sulfide, PPS) were used as comparison. Based on the polarization curve data at 60 °C, the current density of the membrane electrode (MEA) made of the BiOIx film (x = 0.97) with the highest conductivity was 1760 mA cm -2 , which was about 1200 mA cm -2 (see Figure 8 b) higher than that of FAA-PK-130 and PPS. After adjusting the temperature of the experiment to 80 °C, the current density can be further increased to 1986 mA cm -2 (see Figure 9 a and b). This excellent water electrolysis performance is mainly attributed to the extremely high hydroxide ion conductivity of the BiOIx film, which shows lower ohmic resistance (Rohm) and interfacial charge transfer resistance (Rct) (see Figure 8 c and 9c, d). In addition, the BiOIx (x = 0.97) HEM can run for more than 5 days at 1000 mA cm -2 , with a voltage loss of only 96 μV h -1 , which is lower than that of FAA-PK-130 and PPS (1049 μV h -1 and 2967 μV h -1) 31-fold and 11-fold (see Figure 8 d and Table 1), high current density and base concentration usually accelerate the degradation of HEMs, however, the voltage loss rate of BiOIx(x = 0.97) MEA is even lower than other reported HEMs, especially the highly conductive ones (see Figure 8 e), confirming its excellent durability under water electrolysis operating conditions. Moreover, the Rohm and Rct of BiOIx(x = 0.97) MEA are even decreased after the experiment (see Figure 9 c and d), indicating that the in-situ hydroxyl substitution further activates the ionic conductivity of BiOIxHEM. In contrast, the resistance of commercial MEA increases after the experiment, indicating that it has been degraded (see Figure 9 c). Furthermore, no obvious structural degradation of BiOIx(x = 0.97) HEM is observed by XRD characterization after 120 h of continuous operation (see Figure 9 f), making the MEA of the present application exhibit excellent stability. Due to its layered structure and sub-nanometer channels, BiOIx(x = 0.97) exhibits a low H2permeability, which is only 0.244 Barrer, four orders of magnitude lower than PPS (1095.7 Barrer) as previously described (see Figure 9 e). Therefore, the BiOIxHEM of the present application exhibits excellent performance on water electrolysis compared to other reported HEMs, with higher current density, lower voltage loss and good stability.

[0113] Table 1 Water electrolysis performance of different AEMs

[0114]

[0115] In this work, we developed a HEM based on two-dimensional BiOIx, using SCW (supercritical water) intercalation and microfluidic exfoliation techniques to prepare high aspect ratio BiOIxnanosheets for constructing long-range ordered nanochannel confinement, and active groups on the inner wall of the channel can be replaced by hydrophilic groups, thus providing a simple method to adjust the interlayer hydrogen bond. With the replacement of iodine by hydroxyl, the short hydrogen bond (SHB) network can be extended in the two-dimensional nanochannel, creating more Grotthuss-type diffusion paths to facilitate fast ion transport. Benefiting from the SHB network in confined water, the hydrogen-oxide conductivity of the layered structure of BiOIx(x = 0.97) is improved to 168 mS cm -1This results in MEAs based on basic bismuth oxyiodide having excellent performance in alkaline water electrolysis. Moreover, the fast ion transport arising from the SHB network does not need to rely on increasing the ion exchange capacity (IEC) to be achieved, thus avoiding the side effects of higher IEC, such as reduced mechanical strength, decreased chemical stability, and reduced gas barrier properties. Thus, our work will open new ways for HEMs in sustainable energy conversion.

[0116] The above is a schematic description of the present application and its embodiments, which is not restrictive, and the embodiments shown in the examples are only one of the embodiments of the present application, and the actual embodiments are not limited thereto. Therefore, if a person skilled in the art is inspired by it, without departing from the purpose of the present application, similar embodiments and examples of the technical solution are not creatively designed, which should belong to the protection scope of the present application.

Claims

1. Application of basic bismuth oxyiodide in the preparation of anion exchange membranes, wherein the basic bismuth oxyiodide has the chemical formula BiOI. 1-x (OH) x ,in, 0.30＜x＜1.0。 2. The application according to claim 1, characterized in that, x takes values ​​from 0.70 to 0.

99.

3. The application according to claim 2, characterized in that, The hydroxide ion density in the basic bismuth iodide is 4.7~6.6 nm. -2 .

4. The application according to any one of claims 1 to 3, characterized in that, The basic bismuth oxyiodide has a sheet-like structure. Based on the number of sheet-like structures with a lateral dimension greater than 50 nm in the AFM image, at least 80% of the sheet-like structures have an aspect ratio of not less than 100.

5. A method for preparing basic bismuth oxyiodide, characterized in that, This includes exfoliating bismuth oxyiodide crystals under hydrothermal conditions to obtain BiOI. 1-x1 (OH) x1 Where 0.30 < x1 < 1.0; making the BiOI 1-x1 (OH) x1 Contact with alkaline solution yields the final product, basic bismuth iodide (BiOI). 1-x2 (OH) x2 , where 0.30<x2≤1.0, and x1<x2.

6. The application of the basic bismuth oxyiodide prepared by the method of claim 5 in the preparation of anion exchange membranes.

7. BiOI 1-x (OH) x Its application in the preparation of anion exchange membranes, among which, x takes a value of 1.0; the BiOI 1-x (OH) x It has a sheet-like structure, and the length-to-thickness ratio of the sheet-like structure is not less than 100.

8. Anion exchange membrane, characterized in that, The anion exchange membrane comprises: BiOI 1-x (OH) x Where 0.30 < x ≤ 1.0; and Excipients.

9. The anion exchange membrane according to claim 8, characterized in that, The excipients are selected from one or more of nanocellulose, polyvinyl alcohol, perfluorosulfonic acid polymer, quaternized poly(arylene ether sulfone), quaternized poly(phenylene ether oxide), and polybenzimidazole.

10. The anion exchange membrane according to claim 8, characterized in that, BiOI in anion exchange membrane 1-x (OH) x The mass percentage content is 70-99%.

11. The anion exchange membrane according to claim 8, characterized in that, The anion exchange membrane has a strength of not less than 80 mS / cm at 90°C. -1 The electrical conductivity.

12. The anion exchange membrane according to claim 8, characterized in that, The anion exchange membrane has a strength of not less than 160 mS / cm at 90°C. -1 The conductivity; or, the anion exchange membrane has an interlayer spacing of 0.80~0.95 nm, which is calculated based on the XRD diffraction pattern of the anion exchange membrane.

13. An electrolytic cell, characterized in that, Contains basic bismuth iodide; The basic bismuth iodide has the chemical formula BiOI. 1-x (OH) x Where 0.30 < x < 1.0; or The basic bismuth oxyiodide is the basic bismuth oxyiodide prepared according to the preparation method of claim 5.

14. An electrolytic cell, characterized in that, Includes BiOI 1-x (OH) x Where x takes the value 1.0; the BiOI 1-x (OH) x It has a sheet-like structure, and the length-to-thickness ratio of the sheet-like structure is not less than 100.

15. An electrolytic cell, characterized in that, It includes the anion exchange membrane according to any one of claims 8 to 12.

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