CN113193218A

CN113193218A - Proton exchange membrane applied to fuel cell and preparation method thereof

Info

Publication number: CN113193218A
Application number: CN202110478621.0A
Authority: CN
Inventors: 马海庆; 姚文东; 贺迪华
Original assignee: Shenzhen Hydrogen Age New Energy Technology Co ltd
Current assignee: Shenzhen Hydrogen Age New Energy Technology Co ltd
Priority date: 2021-04-29
Filing date: 2021-04-29
Publication date: 2021-07-30

Abstract

The invention discloses a proton exchange membrane applied to a fuel cell and a preparation method thereof, wherein the proton exchange membrane comprises the following raw materials: 0.005g-0.03g of functionalized cobalt titanate nano particles and 0.97g-0.995g of sulfonated polyether sulfone. The invention combines amine functionalized cobalt titanate nano particles with a sulfonated polyether sulfone polymer matrix to prepare a novel proton exchange membrane; grafting (3-aminopropyl) triethoxysilane is adopted to carry out surface modification on the cobalt titanate nano particles; the interface compatibility of the ACT nano particles after surface modification and the SPES is improved, and the ACT nano particles can be uniformly dispersed in the SPES film; the prepared nano composite film is characterized by adopting the technologies of Fourier transform infrared spectroscopy, thermogravimetric analysis, universal testing machine, field emission scanning electron microscope, atomic force microscope and the like; the obtained nano composite membrane shows better stability and good water retention performance.

Description

Proton exchange membrane applied to fuel cell and preparation method thereof

Technical Field

The invention relates to the technical field of fuel cells, in particular to a proton exchange membrane applied to a fuel cell and a preparation method thereof.

Background

Polymer electrolyte membranes are of great interest for their potential application in electric vehicles as well as in portable electronic devices such as fuel cells, batteries and electrolysis cells, desalination and separation of seawater. Fuel cells convert chemical energy directly into electrical energy, and Proton Exchange Membranes (PEM) are one of the important components of Polymer Electrolyte Membrane Fuel Cells (PEMFC); among them, the proton exchange membrane must satisfy certain application conditions: suitable water absorption, high proton conductivity and good thermal, mechanical and chemical stability.

The proton exchange membrane plays a role in electrode isolation and can simultaneously transmit protons from the anode to the cathode through the proton exchange membrane; sodium perfluorosulfonate ion exchange membranes, such as perfluorosulfonic acid (Nafion) membranes, are the most commercialized proton exchange membranes in PEMFC fuel cells due to their good proton conductivity, presence of pendant sulfonic acid chains, and good oxidative stability. However, such membranes are costly, have poor fuel barrier properties, and have operating temperature limitations.

Thus, many materials have been studied to date to replace Nafion membranes. For example, much research has been conducted on the development of sulfonated aromatic polymers such as Sulfonated Polyimide (SPI), Sulfonated Polyethersulfone (SPES), and sulfonated poly (phenoxide) (SPPO). SPES is reported in the literature as the most promising polymer in many polymers because it provides adjustable proton conductivity, is low cost, and has excellent chemical and thermal stability.

Proton conductivity of SPES can be readily manipulated by the Degree of Sulfonation (DS), which can be adjusted by sulfonation conditions such as reaction time, temperature, and sulfuric acid concentration. As DS increases, proton conductivity, water absorption, and membrane swelling all increase, however, excessive membrane expansion of SPES decreases the mechanical stability of the membrane due to high DS, thereby shortening the useful life of the membrane.

Therefore, in practical applications, it is desirable to modify a high DS (about 70%) SPES membrane to improve its mechanical and dimensional stability; the common modification method can be realized by blending SPES and inorganic filler, and the mechanical property of the composite membrane can be improved by adding inorganic nano particles into the SPES; however, when the nanoparticles are aggregated together, proton conductivity may be decreased. More recently, the authors have based on the use of BaZrO, containing benzenesulfonic acid or p-hydroxysulfonic acid₃The nanoparticles, sulfonated graphene oxide nanoplatelets, and cobalt titanate (IT) nanoparticles prepare a novel proton conductive composite membrane for a Polymer Electrolyte Membrane Fuel Cell (PEMFC). SPES based nanocomposite membranes have been studied in many ways. However, the synthesis and performance of a SPES/amine functionalized cobalt titanate (ACT) composite membrane for proton exchange membrane fuel cell electrolytes has not been reported.

In the research, ACT nanoparticles are used as fillers in the nano composite film, and the properties of the nano composite film, such as proton conductivity, water absorption, mechanical properties, oxidation stability, power density and the like, are evaluated.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a proton exchange membrane applied to a fuel cell and a preparation method thereof, wherein the hydrogen bond between ACT nano particles, hydroxyl (from free water molecules) and amino enhances the proton conductivity and mechanical property of the nano composite membrane; further, ANH in ACT₂Radicals and ASO in polymer matrices₃H groups form hydrogen bond action, and the mechanical stability of the nano composite film is improved. In addition, the existence of the aminated cobalt titanate nanoparticles can effectively reduce the aggregation of the nanoparticles in the polymer, improve the interface compatibility between the aminated cobalt titanate nanoparticles and the ACT, and simultaneously, the aminated cobalt titanate nanoparticles and the ACT nanoparticlesThe distance between the particles is shortened, thereby effectively improving the proton conductivity of the nano composite membrane. The hydroxyl groups of the cobalt titanate nanoparticles react with the alkoxy groups of 3-Aminopropyltriethoxysilane (APTES), improving the dispersion rate and compatibility of the cobalt titanate nanoparticles in the SPES matrix. The research investigates the chemical structure, the morphology, the membrane expansion, the water absorption, the mechanical properties, the thermal/oxidative stability and the proton conductivity of the nano composite membrane, and verifies the application of the nano composite membrane in the PEMFC.

A proton exchange membrane applied to a fuel cell comprises the following raw materials: 0.005g-0.03g of functionalized cobalt titanate (ACT) nano-particles and 0.97g-0.995g of sulfonated polyether sulfone.

The invention also provides a preparation method of the proton exchange membrane applied to the fuel cell, which comprises the following steps:

the method comprises the following steps: synthesis of functionalized cobalt titanate (ACT) nanoparticles: firstly, 0.4mol of stearic acid is put into a beaker to be melted, and then 0.1mol of cobalt acetate is added into the melted stearic acid and dissolved to form a dark blue transparent solution; then, adding tetrabutyl titanate (0.1mol) in a stoichiometric ratio into the solution, stirring to form uniform light red brown sol, naturally cooling to room temperature, carrying out primary drying in an oven to obtain dry gel, and calcining by adopting a four-step method to prepare CT nanoparticles;

step two: activating CT nanoparticles in 10% (w/w) hydrochloric acid solution to rebuild hydroxyl, then drying 1g of activated IT (cobalt titanate) nanoparticles in a vacuum oven for the second time, and then putting the activated IT (cobalt titanate) nanoparticles into 100ml of toluene and performing ultrasonic dispersion for 30 min; then 0.3mL of triethylamine and 4mL of APTES were added dropwise to the mixture; finally, refluxing the solution in a nitrogen atmosphere at a certain temperature, washing the solution for several times by using toluene and ethanol to remove redundant reactants, and then drying the solution in an oven for the third time;

step three: preparation of sulfonated polyethersulfone sample: adding 20g of Polyethersulfone (PES) into 100ml of concentrated sulfuric acid (98%), and stirring for the first time at room temperature to form a uniform PES solution; transferring chlorosulfonic acid into a dropper, slowly dripping the chlorosulfonic acid into a PES solution, and stirring the solution for the second time to obtain a reaction mixture; stirring the obtained reaction mixture for the third time for several hours, reacting for a certain time, gradually precipitating the mixture into cooled deionized water under the stirring for the third time, recovering generated precipitates by filtering, and washing with the deionized water until the pH value is 6-7;

step four: preparing a SPES membrane and a SPES/ACT nano composite membrane by a solution casting method, and respectively naming the SPES membrane and the SPES/ACT nano composite membrane as Ms and MsACTx, wherein x represents the weight percentage of ACT nano particles in the nano composite membrane; the SPES membrane and the SPES/ACT nano composite membrane are prepared specifically: SPES (sulfonated polyethersulfone) 0.5g was dissolved in 2.5mL of DMAc to form a SPES suspension while stirring at room temperature; respectively dispersing ACT nano particles with different amounts in 2.5ml of DMAc by ultrasonic, then adding the DMAc into a SPES suspension, and stirring for 30min at room temperature to obtain uniform low-viscosity liquid; the resulting low viscosity liquid was cast directly onto a glass plate with a doctor blade at constant speed, dried at room temperature for 24h and then dried at 70 ℃ overnight; the thickness of the dried nano composite film is between 60 and 80 mu m.

Preferably, the stearic acid in step one is melted in a beaker at 73 ℃; the time for the first drying was 12 h.

Preferably, the four-step calcination in step one comprises a first stage: the xerogel is heated to 400 ℃ at a rate of 3 ℃/min, second stage: heating at 400 deg.C for 40min, and a third stage: the temperature of each sample was raised to 500 ℃, 550 ℃, 600 ℃ and 650 ℃, respectively, and the fourth stage: keeping the temperature in the air for 2 h.

Preferably, the activation time of the CT nanoparticles in the second step is 3 hours, and the ultrasonic dispersion time is 30 min; the second drying is carried out for 24 hours at the temperature of 100 ℃; the third drying was carried out at a temperature of 80 ℃ for 24 h.

Preferably, the time for the first stirring in the third step is 24 hours; the second stirring was carried out at 800rpm at 10 ℃.

Preferably, the different amounts of ACT nanoparticles in step four are selected from: 0.5 wt%, 1 wt%, 2 wt%, 3 wt%.

Preferably, the composite membrane prepared in the fourth step is pre-treated by soaking in 2mol of sulfuric acid solution for 24 hours before use.

By adopting the technical scheme of the invention, the invention has the following beneficial effects: combining amine functionalized cobalt titanate (ACT) nanoparticles with a Sulfonated Polyethersulfone (SPES) polymer matrix to prepare a novel proton exchange membrane; grafting (3-aminopropyl) triethoxysilane (APTES) is adopted to carry out surface modification on the cobalt titanate nano particles; the interface compatibility of the ACT nano particles after surface modification and the SPES is improved, and the ACT nano particles can be uniformly dispersed in the SPES film; the prepared nano composite membrane is characterized by adopting the technologies of Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), Universal Testing Machine (UTM), Field Emission Scanning Electron Microscope (FESEM), Atomic Force Microscope (AFM) and the like; the obtained nano composite membrane shows better stability (mechanical and oxidation) and good water retention performance; compared with a pure SPES membrane, the nano composite membrane added with the ACT nano particles has higher proton conductivity; the improved properties of the nanocomposite membranes are attributed to the fact that the different water transport channels at the polymer/nanoparticle interface are interconnected, which creates a better transport pathway for proton transport; in addition, the proton conductivity at 25 ℃ of the optimized SPES/ACT (2 wt.%) is 0.065s/cm¹The water absorption was 38%, the swelling ratio was 24%, and the proton conductivity at 80 ℃ was 0.12s/cm¹Maximum power density of 204mW/cm²For fuel cells and batteries.

Drawings

FIG. 1 is a schematic representation of the functionalization and distribution profile of CT nanoparticles in SPES according to the present invention;

FIG. 2(a) is a TGA profile of AIT nanoparticles of the present invention; FIG. 2(b) is a TEM image;

FIG. 3(a) is a graph of IT, ACT and APTES spectra in accordance with the present invention; FIG. 3(b) is a FTIR spectrum of a nanocomposite film;

FIG. 4(a) is XRD spectra of IT and ACT nanoparticles (a); FIG. 4(b) is an XRD spectrum of the nanocomposite film (b);

FIG. 5(a), FIG. 5(b), FIG. 5(c), FIG. 5(d) are end-face scanning electron microscopesPhotograph MSACT_0.5、 MsACT₁、MsACT₂、MsACT₃A schematic diagram;

FIG. 6 is EDX spectra of iron (red) and titanium (green) in the nanocomposite film of the invention: MsACT_0.5 (a)、MsACT₁(b)、MsACT₂(c) And MsACT₃(d) (upper panel is red, lower panel corresponds to green);

FIG. 7 shows Ms (a, a') of the present invention, MsACT_0.5(b，b’)，MsACT₁(c, c '), MsACT2 (d, d'), and MsACT₃(e, e') AFM 3D and 2D images of the composite film;

FIG. 8(a) is a graph showing water absorption and swelling for films with ACT nanoparticle content at various temperatures; FIG. 8(b) shows Ms and MsACT of the present invention₂Water absorption of the film; FIG. 8(c) shows Ms and MsACT₂Schematic swelling degree at different temperatures;

fig. 9(a) is a schematic of the proton conductivity of Ms and MsACTx membranes at different temperatures; FIG. 9(b) is an Arrhenius diagram of proton conductivity;

FIG. 10 is a schematic diagram of proton transfer pathways and proton transfer mechanisms in a nanocomposite membrane;

FIG. 11(a) is a TGA curve of Ms and nanocomposite films, and FIG. 11(b) is a stress-strain curve;

FIG. 12 is a graphical representation of oxidation resistance as a function of ACT nanoparticle content for films made according to the present invention;

FIG. 13 shows Ms and MsACT of the present invention₂Performance of the membrane at 80 ℃ and 90% relative humidity of the fuel cell: the Pt loading of the anode and the cathode are both 0.25mg/cm²，H₂And O₂The flow rates of (A) are 120 and 300ml/min, respectively.

Detailed Description

The invention is further described below with reference to the following figures and specific examples.

Example 1:

MsACT_0.5the preparation of (1):

referring to fig. 1, a SPES/ACT composite membrane is prepared by a solution casting method from a mixed solution of SPES and ACT nanoparticles, wherein a SPES membrane is prepared as a reference, and prepared membrane materials are respectively named Ms and MsACTx, wherein x represents the weight percentage of ACT nanoparticles in the nanocomposite membrane.

Stirring at room temperature, dissolving 0.995g of SPES in 2.5mL of DMAc to give a SPES suspension, ultrasonically dispersing 0.005g of ACT nanoparticles (0.5 wt.%) in 2.5mL of DMAc, then adding to the SPES suspension, and stirring at room temperature for 30min to give a homogeneous low viscosity liquid; the resulting low viscosity liquid was cast directly onto a glass plate at constant speed using a doctor blade, dried at room temperature for 24h, and then dried at 70 ℃ overnight; the prepared membrane needs to be soaked in a 2mol sulfuric acid solution for 24 hours for pretreatment before use.

Example 2:

MsACT₁the preparation of (1):

Stirring at room temperature, dissolving 0.99g of SPES in 2.5mL of DMAc to obtain a SPES suspension, ultrasonically dispersing 0.01g of ACT nanoparticles (1.0 wt.%) in 2.5mL of DMAc, then adding to the SPES suspension, and stirring at room temperature for 30min to obtain a uniform low-viscosity liquid; the resulting low viscosity liquid was cast directly onto a glass plate using a doctor blade at a constant speed, dried at room temperature for 24 hours, then dried at 70 ℃ overnight, and the prepared film was pre-treated by soaking in 2mol sulfuric acid solution for 24 hours before use.

Example 3:

MsACT₂the preparation of (1):

Stirring at room temperature, dissolving 0.98g of SPES in 2.5mL of DMAc to give a SPES suspension, ultrasonically dispersing 0.02g of ACT nanoparticles (2.0 wt.%) in 2.5mL of DMAc, then adding to the SPES suspension, stirring at room temperature for 30min to give a homogeneous low viscosity liquid, casting the resulting low viscosity liquid directly on a glass plate with a doctor blade at a constant speed, drying at room temperature for 24h, then drying at 70 ℃ overnight, and preparing a membrane that needs to be pre-treated by soaking in 2mol of sulfuric acid solution for 24h before use.

Example 4:

MsACT₃the preparation of (1):

Stirring at room temperature, dissolving 0.97g of SPES in 2.5mL of DMAc to give a SPES suspension, ultrasonically dispersing 0.03g of ACT nanoparticles (3.0 wt.%) in 2.5mL of DMAc, then adding to the SPES suspension, and stirring at room temperature for 30min to give a homogeneous low viscosity liquid; the resulting low viscosity liquid was cast directly onto a glass plate using a doctor blade at a constant speed, dried at room temperature for 24 hours, then dried at 70 ℃ overnight, and the prepared film was pre-treated by soaking in 2mol sulfuric acid solution for 24 hours before use.

Chemical and structural characterization:

adopting Bru-ker point division method at 500-4000 cm^-1Fourier transform infrared spectroscopy (FTIR) of ACT nanoparticles and Attenuated Total Reflectance (ATR) of the film were measured over the wavelength range; the morphology and particle size of ACT nanoparticles were observed with a transmission electron microscope (TEM, Zeiss EM 10C); the amount of APTES grafted on the IT nano particle surface is quantitatively analyzed by using a thermogravimetric analysis method (TGA) to increase from room temperature to 700 ℃ at the temperature increase rate of 20 ℃/min; subjecting IT nanoparticles, original SPES and nanocomposites to an incident light angle in the range of 5-80 ° using an X-ray diffractometer (French INEL laboratory, model EQUINOX 3000)The film was subjected to X-ray diffraction (XRD) analysis; the morphology of the film was studied with a field emission scanning electron microscope (FESEM, TESCAN); the distribution of titanium and iron in the film is observed by an energy spectrometer (EDX); the surface roughness of the films was characterized at room temperature using an Atomic Force Microscope (AFM) from Seiko instruments model SPA-300 HV.

Characterization of physicochemical and electrical properties:

the water absorption (WU) of the prepared film was determined: soaking the membrane in distilled water at different temperatures of 25-70 ℃, and quickly weighing (Ww) after removing surface water; then, the wet film was dried in a drying oven at 80 ℃ for 12 hours and weighed again (Wd); finally, obtaining the final value of the water absorption rate by using the average value of three times of measurement, wherein the error is +/-5.0%; the water absorption (WU) calculation formula is as follows:

WU＝(Ww-Wd)/Wd×100

the swelling degree (MS) of the film was determined using the dry and wet length data of the film at different temperatures, denoted as Lw and Ld, respectively; the swelling degree MS is calculated as follows:

MS＝(Lw-Ld)/Ld×100

the proton conductivity of the membrane was measured with an Autolab potentiostat at a voltage amplitude of 50Mv at 0.1 hz-MHz. The self-made electric conduction battery consists of two current-carrying platinum sheets with platinum wires and is used for measuring potential, and the distance between the two current-carrying platinum sheets is 0.6cm in the measuring process.

The proton arrival rate is calculated as follows:

δ＝L/RWT

wherein δ is proton conductivity (S/cm), L is the distance between electrodes (0.6cm), and W and T are the width and thickness of the film, respectively; r is the ionic resistance of the membrane, derived from the lower intersection of the high frequency on the complex impedance plane and the actual axis.

Thermal stability and mechanical properties:

thermogravimetric analysis was performed on the sample under nitrogen atmosphere using a high resolution thermogravimetric analyzer (model TGA 2950, temperature range 50-600 ℃, heating rate 10 ℃/min).

The mechanical properties of the membranes were evaluated at room temperature using a universal test machine model STM-150 (UTM, SANTAM-DBBP, Iran) with an operating rate of 2 mm/min.

Oxidation resistance:

fenton reagent (containing 4ppm of FeSO) was used₄3% of H₂O₂Aqueous solution) the oxidation resistance of the film was investigated at 80 ℃. A small piece of the film was immersed in the Fenton reagent for 1h, after which the sample was taken out and washed several times with distilled water, then dried in a vacuum oven at 80 ℃ for 12h and weighed. The oxidation resistance was evaluated by measuring the residual weight of the film after 1h of soaking and the time at which the film started to crack without any mechanical force.

The battery performance is as follows:

membrane Electrode Assemblies (MEAs) water and glycerol were prepared using a Pt/C catalyst (20% platinum), 5 wt% Nafion solution as the electrode ionomer, isopropyl alcohol (IPA), and appropriate amounts of deionization. The catalyst ink was coated on a carbon cloth (E-tek, HT 2500-W), and then dried in an oven at 80 ℃ for 40min, followed by drying at 120 ℃ for 60 min. The catalyst loading of the anode and cathode electrodes were both 0.25mg/cm². The prepared film was sandwiched between two electrodes and then set at 135kg/cm²And hot pressing at 120 deg.C for 3 min.

Results and discussion:

and (3) characterization:

fig. 2a gives TGA curves for IT and ACT nanoparticles: the mass loss below 200 ℃ can be attributed to the loss of water and further condensation of APTE; the second weight loss in the temperature range of 250-; as the degradation temperature of the APTES grafted on the IT nano-particles is higher than the boiling point (217 ℃) of the APTES, we can speculate that chemical bonding exists between the IT nano-particles and the APTES, and the grafting rate is 6.46 percent, which is equivalent to 1.11 mmol/g; the morphology and size of ACT nanoparticles were studied using TEM (as shown in figure 2 b). The results show that the ACT nanoparticles have a particle size of 80nm or less and the silane thickness on the nanoparticle surface is close to 10 nm.

FIG. 3a is an FTIR spectrum of APTES, IT nanoparticles, and ACT nanoparticles: at 540cm^-1And 665 cm^-1The peak at (A) is attributed to FeAO and FeATi groups in the nanoparticlesAnd (5) stretching and vibrating. The peaks at 1625cm-1 and 3448cm-1 in the spectrogram of IT nanoparticles were attributed to tensile and flexural vibrations of bound water in HAOAH, respectively. Characteristic groups of APTES include ACH₂Radicals and CAH radicals, in which ACH₂The radical is 2854cm^-1And 2854cm^-1Has symmetrical and asymmetrical characteristic absorption peak, and the CAH group is 1470cm^-1The SiOASi group in the ACT nano-particle is 1030 cm^-1And 1123cm^-1There is a characteristic absorption peak of the tensile vibration. The presence of these characteristic bands confirms the successful grafting of APTES onto the surface of IT nanoparticles. 810cm as shown in FIG. 3a^-1And 928cm^-1The peaks at (a) may be attributed to the vibrations of FeAOASi and TiAOASi, respectively. The ATR spectra of Ms and MsACTx membranes are given in fig. 3 b. All films were at 1020cm^-1、1078cm^-1And 1222cm^-1Three characteristic peaks appear, corresponding to asymmetric and symmetric tensile vibrations of O ═ S ═ O in the sulfonic acid group in SPES, and tensile vibrations of S ═ O, respectively, and the presence of the above characteristic absorption peaks confirms that the PES backbone successfully introduces the sulfonic acid group. After the ACT nanoparticles are introduced into the SPES, the intensity of the above characteristic peak is slightly decreased because hydrogen bonds and electrostatic forces can be formed between the sulfonic acid group of the SPES and the functional group of the ACT nanoparticles (for example, AS ═ O HAOA and AS ═ O HANA bonds). Similar results have been found in other SPES based composite membranes. At 1645cm^-1The absorption peak at (a) corresponds to the carbonyl of the SPES.

From the SEM images it can be concluded that ACT nanoparticles are well dispersed in the SPES matrix, indicating that there is an interaction between the sulfonic acid groups of the SPES and the amine groups of the ACT nanoparticles, thus improving the interfacial compatibility of the two.

Figure 4a is an XRD pattern of IT and ACT nanoparticles. Characteristic peaks at 2h 19.2, 26.4, 32.1, 37, 38.1, 40.1, 45.9 ° and 47.9 ° confirm the formation of IT nanoparticles. The peak intensity of ACT nanoparticles is lower than the peak intensity of IT nanoparticles. This is due to the reduction in crystallinity of IT nanoparticles caused by grafting of the amorphous coupling agent. Fig. 4b gives the XRD patterns of PES, pure SPES and nanocomposite membrane. The result shows that the polyether sulfone polymer is in a semi-crystalline structure, and peaks at 2 theta angles of 15-30 degrees correspond to (110), (111) and (200) planes. As PES is sulfonated, the crystallinity of PES is reduced, and a wider peak value appears at 2h (corresponding to 18-19 degrees). As can be seen in FIG. 4b, the amorphous nature of SPES increases with the addition of ACT nanoparticles, indicating an increased degree of structural disorder of the composite membrane. Additionally, as shown in the FESEM images, ACT nanoparticles are uniformly dispersed within the SPES matrix. This amorphous nature may simplify the ionic conductivity of the nanocomposite film.

Determining the crystallinity percentage (Xc) of the Ms and MsACTx nanocomposite membrane according to the relationship between Xc and beta in the formula (4),

β×(Xc)^1/3＝K_A (4)

in the formula, β is the full width at half maximum (FWHM) at 2 θ, and KA is a constant of 0.24.

Referring to table 1 below, table 1 shows the crystallinity of the Ms film and the MsACTx film. It can be seen that the crystallinity of the nanocomposite film decreases with increasing ACT content, with the lowest crystallinity at 2 wt.% addition, and then increases further with further increasing ACT content.

TABLE 1

FESEM and X-ray images:

the morphology and dispersion state of ACT nanoparticles in the membrane were studied with FESEM:

referring to fig. 5, a cross-sectional scanning electron microscope image of the nanocomposite film is shown: FESEM cross-sectional images show that the nanoparticles in the nanocomposite films at different ACT nanoparticle addition ratios are uniformly distributed in the polymer matrix. All films did not exhibit porosity and significant structural defects during the manufacturing process. The above results indicate that the interaction between the sulfonic acid groups of the polymer and the amine groups of the nanoparticles improves the interfacial compatibility of ACT nanoparticles and SPES matrix, thereby effectively improving the dispersibility of the nanoparticles in SPES. To prove ACT NaDispersion of rice particles in SPES matrix for MSACT_0.5、MSACT₁、 MSACT₂And MSACT₃The nano composite films are respectively subjected to electron energy spectrum analysis.

Referring to FIG. 6, iron and titanium are uniformly distributed within the membrane, with the distribution of titanium being consistent with that of iron, indicating that the nanoparticles are well incorporated into the SPES matrix.

Showing the appearance analysis:

the atomic force microscope is a high-resolution technology for researching the surface morphology of a thin film, which is developed in recent years. The surface topography (2D and 3D) of the Ms and MsACTx nanocomposite membranes were observed with an Atomic Force Microscope (AFM).

Referring to FIG. 7: the bright and dark areas in the figure reflect the difference in domain hardness. The dark areas in the image are designated as soft structures, corresponding to hydrophilic sulfonic acid groups, while the bright areas are designated as hydrophobic polymer backbones. Ms, MsACT were estimated by AFM images (FIGS. 7a-e)_0.5、MsACT₁、MsACT₂And MsACT₃The average surface roughness (Ra) of the nanocomposite film was 3.80, 4.69, 5.48, 6.58, and 7.46nm, respectively. The above studies indicate that the surface roughness of the nanocomposite film is similar to that of conventional PEMS. As is clear from the figure, the roughness of the membrane increases with increasing ACT content in the SPES matrix, and the water absorption and proton conductivity of the membrane can be increased due to the larger surface area. It can also be seen from the atomic force microscope image that ACT nanoparticles are uniformly dispersed in the nanocomposite film.

Water absorption and swelling analysis of the membrane:

water absorption is one of the most important parameters of Proton Exchange Membranes (PEMS) and plays an important role in the transport of protons from the anode to the cathode. The transport mechanism of protons in the composite membrane is achieved by the supply of proton carriers by water molecules and the formation of hydrogen bonds (see fig. 10). The water absorption and membrane expansion of the SPES and nanocomposite membrane at room temperature are shown in fig. 8 (a): the water absorption of the MS film was about 38% at 25 ℃. With the increase of the content of the ACT nano particles, the water absorption rate of the nano composite film is increased, because the cobalt titanate nano particles have water retention and hydrophilicity, and the IT nano particles respectively form hydrogen bonds with hydroxyl groups and free water on the surface of the ACT, so that the water absorption rate of the nano composite film is improved. Additionally, ACT nanoparticles may form water channels at the SPES/ACT interface. As the ACT content increases, the volume of the water channel increases and the ion channels (especially the closed ends) communicate with each other. When the addition amount of the ACT nano-particles is 2 wt%, the water absorption of the composite film can be increased by about 34%. However, with further increase in nanoparticle content, the water absorption begins to decrease due to the barrier effect of ACT nanoparticles in the polymer matrix.

The membrane swelling degree is another important parameter for researching the proton exchange membrane, and is used for characterizing the dimensional stability of the proton exchange membrane. Since the membrane has high expansibility, the membrane material itself has disadvantages of poor mechanical stability, poor durability, and the like, and the performance of the fuel cell may be degraded. As can be seen from fig. 8a, the swelling degree of the composite film decreased with the addition of ACT nanoparticles. After the ACT nanoparticles are added, hydroxyl and amine groups of the ACT can form hydrogen bonds with sulfonic acid groups of SPES, so that the swelling degree of the composite membrane is reduced from 24% to 16% (MsACT)₂). Furthermore, the interaction between SPES and functionalized nanoparticles limits the movement of the polymer chains, which is another reason for the good dimensional stability of the nanocomposite film.

Ms membranes and MsACT are studied herein₂The water absorption and expansion of the film are a function of temperature. As shown in fig. 8(b and c), the water absorption and swelling degree of the film increase with increasing temperature due to high chain mobility and water diffusivity. MsACT₂The water absorption rate of the film is improved from 51% to 69% within the range of 25-55 ℃, and the swelling rate is improved from 16% to 37%. At above 55 ℃, MsACT₂The water absorption of the film is increased from 69% to 145%, which is much lower than that of Ms film. Although the water absorption rate increases with an increase in temperature, dimensional instability due to expansion is not caused. This may be due to the incorporation of ACT nanoparticles that limit the movement of the polymer chains. The result shows that the structural stability of the nano composite membrane in water is improved. This is similar to the conclusions in other literature regarding the water absorption and expansion of SPES.

Analysis of proton conductivity:

proton conductivity of the SPES and nanocomposite membranes is shown in FIG. 9: the ACT nanoparticles have hygroscopicity, and the ACT nanoparticles have good dispersibility in the polymer matrix, so that the MSACTx film has higher proton conductivity than SPES. The aminated IT nano particles improve the dispersibility of the nano particles, and meanwhile, the distance between the ACT nano particles is shortened, so that an effective transmission path is provided for proton transmission, and the proton conductivity of the nano composite membrane is improved. ANH in functionalized IT nanoparticles₂The group serves as a proton transport site (as shown in FIG. 10).

As the number of ACT nanoparticles increased from 0.5 wt.% to 2 wt.%, the proton conductivity of the MSACTx membrane increased from 0.036s/cm to 0.065s/cm at 25 ℃ and from 0.080s/cm to 0.120s/cm at 80 ℃ (as shown in FIG. 9 a). This growth is due to the communication of water channels at the polymer/nanoparticle interface, making proton transport more direct. Thus, the addition of ACT nanoparticles can effectively increase the proton conductivity of the membrane. But as the ACT nanoparticle content increased, the proton conductivity of the membrane decreased. This may be related to the hindering effect of ACT nanoparticles, which may hinder and restrict the movement of protons in the membrane.

From FIG. 9b, it can be seen that the logarithmic proton conductivity of the SPES polymer is linear with 1/T, thus exhibiting Arrhenius-type temperature-dependent behavior. An arrhenius diagram of proton conduction is shown in fig. 9 b. The activation energy value (Ea) related to the proton conductivity of the membrane was calculated.

The Arrhenius equation r ═ r0 exp (Ea/kT), where ro refers to the pre-factor, k is the boltzmann constant, and T is the temperature in kelvin. The activation energy decreases with increasing ACT nanoparticles, from 15.61 kJ/mol for MS films to MSACT_0.5、MSACT₁、MSAT₂And 12.31, 10.60, 9.35, and 9.40kJ/mol of ACT nanoparticles. The results show that with increasing ACT nanoparticles, proton transfer of the membrane is easier.

As shown in Table 2, it can be seen that MsACT₂The proton conductivity and power density of the membrane are comparable to or higher than those of other membranes.The proton conductivity of the nano composite membrane is improved, mainly because the added nano particles have hydrophilicity and can be mutually connected with ion regions in a polymer matrix, so that communicated water channels are formed at the interface of the polymer/nano particles, and a more direct way can be created for proton transfer. The above results indicate that MsACTx membranes have sufficient proton conductivity and are therefore suitable as Proton Exchange Membranes (PEM) in PEMFCs. However, the cell performance of fuel cells using these membranes is still poor compared to Nafion, and there is a need for improvement.

Table 2 shows a comparison of MsACTx membrane proton conductivity to maximum power density with Nafion117 nanoparticles added.

a dopamine modified silica nanoparticles;

b, modifying graphene oxide by a sulfonated polymer brush;

c, sulfonating porous benzene silicon oxide;

d sulfonated montmorillonite;

e organic montmorillonite;

f, sulfonating porous benzene silicon oxide;

g polyvinyl alcohol;

h, modifying the graphene oxide sulfonated chitosan;

i sulfonated polyether sulfone.

Analysis of thermal and mechanical stability:

thermal stability and mechanical stability are key parameters for ensuring long life of proton exchange membrane fuel cells. As shown in fig. 11(a), the thermal stability of the prepared film at 50 to 600 ℃ was analyzed by thermogravimetric analysis (TGA). In all films, the TGA curve shows similar three main weight loss phases. Initial weight loss at about 80-100 ℃ is mainly adsorption of water and residual solvent. From about 250The weight loss starting at C is mainly the decomposition of the sulfonic acid groups in SPES. The weight loss during the third phase, starting at 450 ℃, is primarily the degradation of the SPES matrix. The TGA curve of MsACTx film slightly shifts to higher temperatures compared to Ms film due to ANH in ACT nanoparticles₂And AOH groups with ASO in SPES matrices₃Hydrogen bonding between H groups.

The mechanical properties of each film were tested by UTM and the stress-strain curves are shown in fig. 11 (b).

Reference is made to table 3 below for the mechanical properties of the individual films: table 3 summarizes the tensile strength, elastic modulus and elongation at break of the films. Notably, MsACTx membranes have higher tensile strength than MS membranes.

TABLE 3

membrane	Tensile strength Mpa	Elongation at break%	Modulus of elasticity Mpa
				MS	32.6	12.7	700
MSACT_0.5	35.1	8.7	743
				MSACT₁	36.7	7.8	779
MSACT₂	41.8	6.9	836
				MSACT₃	43.4	6.1	885

The results in table 3 show that as the ACT nanoparticle content in the SPES film increases, the interaction between ACT and SPES polymer increases, the film structure becomes denser, and the tensile strength of the film increases. In previous work, the effect of the addition of nano IT on the mechanical properties of the membrane was investigated. The results indicate that when IT content exceeds 1 wt.%, the agglomeration of IT nanoparticles in the polymer matrix reduces the tensile strength and modulus of the nanocomposite film. Surface modification of IT nanoparticles with APTE increases the dispersibility of the nanoparticles in the SPES matrix (fig. 1), thereby allowing the transfer of stress from the polymer matrix to ACT nanoparticles. Thus, as the ACT nanoparticles increased, the tensile strength of the MsACTx film increased to 3%. However, the MsACTx membrane has a lower elongation at break than the MS membrane due to the hydrogen bonding between the nanoparticles and the SPES matrix, which reduces the flexibility of the polymer chains.

Oxidation resistance analysis:

the durability of the proton exchange membrane is an important factor in the practical application of fuel cells. And (3) placing the MS membrane and the MsACTx membrane into a Fenton reagent for 2h, and observing the dissolution conditions of the MS membrane and the MsACTx membrane to characterize the antioxidant performance of the MS membrane and the MsACTx membrane. As shown in fig. 12, all nanocomposite films have higher oxidation resistance than the Ms film, with the oxidation resistance of the film increasing slightly with increasing ACT content. The improved oxidation resistance may be due to the good dispersibility of the ACT nanoparticles in the SPES matrix and the interaction of the ACT nanoparticles with the sulfonic acid groups, to some extent preventing the diffusion of hydroxyl and hydrogen peroxide radicals (OHH and HOOH) generated by the Fenton reagent.

Performance analysis of Fuel cells

In order to accurately demonstrate that the prepared membrane can be used as a proton exchange membrane of a Proton Exchange Membrane Fuel Cell (PEMFC), the power density of the fuel cell was studied. MsACT₂Has good proton conductivity and structural stability, and is selected as a representative nano composite film. FIG. 13 shows current density-potential (I-V) and the use of H at 80 ℃ and 90% relative humidity₂Fuel and O₂Oxidant use of Ms and MsACT in a single cell₂Power density-current density curve of the film measurement. MsACT₂The open circuit voltage of the membrane (0.89V) is higher than the Ms membrane (0.84V). As shown in FIG. 13, the maximum current density of the PEMFC based on the Ms film was 515mA/cm²Maximum power density of 123mW/cm²Using MsACT₂The maximum current density of the PEMFC of the membrane was 855mA/cm²Maximum power density of 204mW/cm². MsACT compared to Ms film₂The high water absorption and proton conductivity of the membrane improves the performance of the PEMFCs.

And (4) conclusion:

preparing a functionalized cobalt/titanium composite membrane by adopting a cast-infiltration method; due to the hydrogen bond action between the SPES and ACT nano particles and the uniform dispersion of the nano particles in the SPES, the MsACTx nano composite membrane is superior to the Ms membrane in the aspects of swelling property, mechanical stability, thermal stability, oxidation resistance and the like; particularly, the interconnection of ACT nano particles and an ion area in a polymer matrix and a water channel of a polymer/ACT interface form a continuous proton transfer path, so that the proton conductivity of the nano composite membrane is improved. Wherein, when 2 wt% of ACT nano particles are added, the proton conductivity of the obtained nano composite membrane is maximum (0.12S/cm), which is 106.9% higher than that of the Ms membrane. The extremely high conductivity of the nanocomposite membrane (equivalent to Nafion117, 0.09S/cm) at 80 ℃ shows its potential application in proton exchange membrane fuel cells. Due to the fact thatThus, the developed SPES/amine functionalized cobalt titanate nanocomposite membrane can be used as a potential material for PEMFC applications. Due to MsACT₂The membrane has good proton conductivity and water absorption, and has appropriate dimensional stability, so MsACT is selected₂The membrane was subjected to experiments relating to fuel cells. When the battery voltage is 0.5V and the temperature is 80 ℃, MsACT₂The film showed higher performance than Ms (current density and power density of 320 mA/cm, respectively)²And 160mW/cm²). Therefore, the introduction of the amino-functionalized cobalt titanate improves the overall performance of the nanocomposite membrane. The MsACTx nano composite membrane has good proton conductivity and stability, and is an ideal choice for fuel cell membranes.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention, and all modifications and equivalents of the present invention, which are made by the contents of the present specification and the accompanying drawings, or directly/indirectly applied to other related technical fields, are included in the scope of the present invention.

Claims

1. A proton exchange membrane applied to a fuel cell is characterized by comprising the following raw materials: 0.005g-0.03g of functionalized cobalt titanate nano particles and 0.97g-0.995g of sulfonated polyether sulfone.

2. The method for preparing a proton exchange membrane for a fuel cell according to claim 1, comprising the steps of:

the method comprises the following steps: synthesis of functionalized cobalt titanate nanoparticles: firstly, 0.4mol of stearic acid is put into a beaker to be melted, and then 0.1mol of cobalt acetate is added into the melted stearic acid and dissolved to form a dark blue transparent solution; then, adding tetrabutyl titanate with a stoichiometric ratio into the solution, stirring to form uniform light red brown sol, naturally cooling to room temperature, carrying out primary drying in an oven to obtain dried gel, and calcining by adopting a four-step method to prepare CT nanoparticles;

step two: activating CT nano particles in a 10% (w/w) hydrochloric acid solution to rebuild hydroxyl, then drying 1g of activated IT nano particles in a vacuum oven for the second time, and then putting the IT nano particles into 100ml of toluene and carrying out ultrasonic dispersion; then 0.3mL of triethylamine and 4mL of APTES were added dropwise to the mixture; finally, refluxing the solution in a nitrogen atmosphere at a certain temperature, washing the solution for several times by using toluene and ethanol to remove redundant reactants, and then drying the solution in an oven for the third time;

step three: preparation of sulfonated polyethersulfone sample: adding 20g of polyether sulfone into 100ml of concentrated sulfuric acid, and stirring for the first time at room temperature to form a uniform PES solution; transferring chlorosulfonic acid into a dropper, slowly dripping the chlorosulfonic acid into a PES solution, and stirring the solution for the second time to obtain a reaction mixture; stirring the obtained reaction mixture for the third time for several hours, reacting for a certain time, gradually precipitating the mixture into cooled deionized water under the stirring for the third time, recovering generated precipitates by filtering, and washing with the deionized water until the pH value is 6-7;

step four: preparing a SPES membrane and a SPES/ACT nano composite membrane by a solution casting method, and respectively naming the SPES membrane and the SPES/ACT nano composite membrane as Ms and MsACTx, wherein x represents the weight percentage of ACT nano particles in the nano composite membrane; the SPES membrane and the SPES/ACT nano composite membrane are prepared specifically: stirring at room temperature, dissolving 0.5g SPES in 2.5mL DMAc to make a SPES suspension; respectively dispersing ACT nano particles with different amounts in 2.5ml of DMAc by ultrasonic, then adding the DMAc into a SPES suspension, and stirring at room temperature to obtain uniform low-viscosity liquid; the resulting low viscosity liquid was cast directly onto a glass plate with a doctor blade at constant speed, dried at room temperature for 24h and then dried at 70 ℃ overnight; the thickness of the dried nano composite film is between 60 and 80 mu m.

3. The method for preparing a proton exchange membrane for a fuel cell as claimed in claim 2, wherein the stearic acid in the first step is melted in a beaker at 73 ℃; the time for the first drying was 12 h.

4. The method for preparing a proton exchange membrane for a fuel cell as claimed in claim 3, wherein the four-step calcination in the first step comprises a first stage: the xerogel is heated to 400 ℃ at a rate of 3 ℃/min, second stage: heating at 400 deg.C for 40min, and a third stage: the temperature of each sample was raised to 500 ℃, 550 ℃, 600 ℃ and 650 ℃, respectively, and the fourth stage: keeping the temperature in the air for 2 h.

5. The method for preparing the proton exchange membrane applied to the fuel cell as claimed in claim 2, wherein the time for activating the CT nanoparticles in the second step is 3 hours, and the time for ultrasonic dispersion is 30 min; the second drying is carried out for 24 hours at the temperature of 100 ℃; the third drying was carried out at a temperature of 80 ℃ for 24 h.

6. The method for preparing a proton exchange membrane for a fuel cell according to claim 2, wherein the time for the first stirring in the third step is 24 hours; the second stirring was carried out at 800rpm at 10 ℃.

7. The method according to claim 2, wherein the different amount of ACT nanoparticles in step four are selected from the group consisting of: 0.5 wt%, 1 wt%, 2 wt%, 3 wt%.

8. The method for preparing a proton exchange membrane for a fuel cell as claimed in claim 6, wherein the composite membrane prepared in the fourth step is pre-treated by soaking in 2mol of sulfuric acid solution for 24h before use.