WO2025232997A1

WO2025232997A1 - Method for producing a gas separation membrane containing a single-layer porous graphene film

Info

Publication number: WO2025232997A1
Application number: PCT/EP2025/052600
Authority: WO
Inventors: Kumar Varoon Agrawal; Mojtaba CHEVALIER; Ceren KOCAMAN
Original assignee: Ecole Polytechnique Federale de Lausanne EPFL
Current assignee: Ecole Polytechnique Federale de Lausanne EPFL
Priority date: 2024-05-06
Filing date: 2025-01-31
Publication date: 2025-11-13
Anticipated expiration: 2026-11-06

Abstract

Herein described is a method for producing a gas separation membrane precursor and optionally a gas separation membrane, in particular for CO₂ separation, containing a porous single-layer graphene film. The method comprises the following steps: (a) providing a metal foil substrate; (b) preparing a porous single-layer graphene film on the metal foil substrate; (c) depositing a gas-permeable support film on top of the porous single-layer graphene film; (d) applying a layer of transfer release tape on top of the gas-permeable support film; and (e) removing, in particular delaminating, the metal foil substrate to obtain a gas separation membrane precursor. The gas separation membrane can be obtained from the gas separation membrane precursor. Also described is a gas separation membrane obtainable by the method according to the invention.

Description

Method for producing a gas separation membrane containing a single-layer porous graphene film

TECHNICAL FIELD

The invention relates to a method for producing a gas separation membrane precursor, in particular for a gas separation membrane particularly for CO2 separation, containing a porous single-layer graphene film. The invention also relates to a gas separation membrane obtainable by the method according to the invention, which particularly contains the porous single-layer graphene film as the selective layer of the membrane.

BACKGROUND

Gas separation (e.g., H2 from CH4, N2, and hydrocarbons or CO2 from N2 and CH4) is one of the most energy-intensive processes in the chemical industry and in power plants mainly because most gas separation processes have a very low thermodynamic efficiency. Membrane-based separation improves upon the thermally driven separation of gas mixtures (i.e., distillation, absorption and adsorption) because, unlike these two processes, the membrane process operates in a continuous steadystate mode, does not require thermal energy but rather electrical energy, and results in higher efficiency for separation.

Among various classes of membrane materials, polymer-based membranes are the most mature technology. However, the performance of the polymeric membranes is limited by fundamental properties of polymeric materials. There is a fundamental trade-off between selectivity and permeability of polymers, arising from challenges in controlling the free volume elements between polymeric chains, which controls gas diffusivity through a polymeric film. Gas separation using membranes hosting a two- dimensional (2D) selective film, such as atom-thick porous single-layer graphene film, is highly promising as one can achieve extremely high flux combined with attractive selectivity based on molecular sieving from graphene pores (see e.g.: L. Wang et al., Nat. Nanotechnology 2017, 12, 509-522; L. F. Villalobos et al., Accounts Mater. Res. 2022, 3, 1073-1087).

While there has been considerable progress in engineering the porosity in single-layer graphene to incorporate molecular-selective pores, limited progress has been achieved in the scalable fabrication of porous single-layer graphene membranes for gas separation, which limits their prospect for commercial deployment (see e.g.: J. Wang et al., Nature 2023, 623, 956-963; C. Van Goethem et al., ACS Nano 2024, 18, 5730-5740; K. Zhao et al., ACS Nano 2024, 18, 5571-5580; M. T. Vahdat et al, Phys. Rev. Lett. 2023, 131, 168001; S. Huang et al., Adv. Mater. 2022, 34, 2206627). The challenge lies in the fact that porous graphene film is synthesized as a continuous sheet on a metal foil substrate (e.g., Cu foil) by chemical vapor deposition. It is challenging to peel off the porous graphene film from the metal foil substrate without inducing cracks and tears in the film especially when the film size significantly exceeds the length scale of 1 cm. Generally, such membranes are prepared by carefully scooping graphene film after the Cu foil is removed. For larger areas, avoiding transfer-related cracks and tears using the scooping method becomes challenging.

It is important to realize that tears and cracks in the graphene film allow at least three orders of magnitude faster transfer compared to gas-selective graphene pores. This is because gas transport from nanoscale cracks and tears, down to a gap size of 1 nm², takes place in the effusive transport regime, which is extremely rapid but nonselective. However, gas transport from selective pores takes place in the activated transport regime. Typical CO2 transport rates from the effusive (nonselective) regime and the activated transport (selective) regime are IO'¹⁹ and 10'²² mol s'¹ Pa'¹ pore'¹, respectively (see e.g.: K. Celebi et al., Science 2014, 344, 289-292; L. Wang et al., Nat. Nanotechnology 2017, 12, 509-522). So, even if tears and cracks with a size down to 1 nm² cover only 0.01% of the total surface area of graphene hosting a high density (IO¹² pores/cm²) of CO2 selective pores, one would lose CO2/N2 selectivity by a factor up to 20. In other words, a crack-free graphene film expected to yield a CO2/N2 selectivity of 100 would only yield a selectivity of 2 in the presence of cracks covering only 0.1% of the graphene area. This is a uniquely challenging aspect of gas separation membranes because, while several advances have been made in high-quality transfer of graphene onto smooth and flat wafers for applications other than gas separation (e.g., electronics, optoelectronics), none of these methods ensure crack-free transfer of graphene. In fact, these methods typically have a cracked area of at least up to 0.1% of the total area (see e.g.: A. Shivayogimath et al., Chem. Mater. 2019, 31, 2328-2336). These challenges are further compounded for membrane-based separation application where the substrate is not a smooth wafer but a porous support. In this scenario, graphene is not completely supported by the underlying porous support. As a result, it is essentially suspended over a porous matrix. During transfer, capillary forces exerted by the drying event of water residing in the support pores tend to crack the membrane (see e.g.: C.-K. Lee et al., ACS Nano 2014, 8, 2336-2344).

Attempts have been made towards crack-free graphene transfer (see e.g.: S. Huang et al., Nat. Commun. 2018, 9, 2632; G. He et al., Adv. Funct. Mater. 2020, 30, 2003979; W.- C. C. Lee et al.,/. Memb. Sci. 2021, 618, 118745). The approach of mechanical reinforcement of graphene by depositing a gas-permeable layer on top of graphene allowed the realization of a floating, substantially crack-free graphene film on a water bath after the removal of the metal foil substrate by dissolution of the latter in an acid bath. Ultimately, the floating film was scooped by a porous support substrate to form the membrane.

However, such a process is not scalable because the scooping of the floating film must be carried out with a lot of care and in a batch-wise manner, so as not to break the composite film consisting of the graphene layer and the gas-permeable layer, which is typically thinner than 1 pm. Increasing the thickness of this composite film to enhance the mechanical strength of the film decreases the permeance of the membrane, thus making it unattractive for gas separation processes. Membranes prepared by this method have been limited in size (i.e., 1 mm² or 1 cm² in area). Further, the success of this method is dependent on the operator’s skill in handling the fragile films. Such a process is unsuitable for continuous and/or large-scale manufacturing.

The metal foil substrate is typically removed via dissolution in an acid bath, which is lengthy, expensive, hazardous, and may adversely affect the properties of the gas- permeable support film. Electrochemical delamination of graphene has been reported before as an alternative (see e.g.: L. P. Ma et al., Small Methods 2019, 3, 1900049; M. C. Wang et al.,/. Mater. Chem. C 2017, 5, 11226-11232). However, several cracks and tears are typically formed in graphene due to mechanical stress generated during the electrochemical delamination step as the graphene layer is too fragile, rendering the method unsuitable. Further, the electrochemical solution is often quite harsh, either made of highly acidic or basic solution. This can easily degrade or change the gas permeation properties of the reinforcing support of graphene. Milder electrolytes have only been used in combination with sacrificial mechanical reinforcing support, where the gas permeation properties of said sacrificial support were not of interest.

In some of the prior art, transfer release tape (TRT) has been used to help with the transfer of graphene. However, it has been applied directly on top of the graphene layer, leading to crack formation in the graphene layer when TRT is removed after transfer. This happens because any portion of graphene that is not contacting the final support tends to break during this removal.

Thus, it is an object of the present invention to provide a method that addresses these and other needs in the state of the art, which method helps in manufacturing gas separation membranes containing porous graphene films. Preferably, the porous graphene films are large (more preferably hundreds of cm² in area) and substantially crack-free. This would allow to obtain large gas separation membranes with good selectivity and permeance. Other and further objects, features and advantages of the present invention will become apparent more fully from the following description.

SUMMARY OF THE INVENTION

Some or all of these objects are achieved with the present invention by the method according to claim 1 and the gas separation membrane according to claim 16.

It was surprisingly found that the method according to the invention allowed the production of a gas separation membrane precursor, in particular for CO2 separation, containing a porous single-layer graphene film. The gas separation membrane precursor can then be used for the manufacture of a gas separation membrane. In step

(a) of the method according to the invention, a metal foil substrate is provided. In step

(b), a porous single-layer graphene film is prepared on the metal foil substrate, for example by chemical vapor deposition. Suitable methods for preparing a porous single-layer graphene film are known to the skilled person and described in the literature (see e.g.: S. Huang et al., Adv. Mater. 2022, 34, 2206627; S. Huang et al., Sci.

Adv. 2021, 7, eabf0116; US 11,559,772 B2; EP 3 888 777 Al). Subsequently, in step (c) a gas-permeable support film is deposited on top of the porous single-layer graphene film in order to serve as a mechanical reinforcement for the porous graphene and to protect the graphene surface from external particles and abrasion. In step (d), a layer of transfer release tape (TRT) is applied on top of the gas-permeable support film to allow easy handling of the entire assembly (e.g., by tweezers or fingers). In established methods of the prior art, TRT was typically directly applied on top of the porous graphene, which led to cracks in the porous graphene during removal of TRT. By depositing a gas-permeable support and then applying TRT on top of this support film instead, the porous graphene is protected from such damage. In step (e), the metal foil substrate is removed to obtain the gas separation membrane precursor.

Advantageously, the removal is achieved through delamination instead of conventional dissolution of the metal foil in an acid bath. The method according to the invention avoids the problems inherent in the methods of the prior art, thus enabling the production of much larger membranes. Conventional processes are typically limited to membranes with a size of 1 mm² to 1 cm² due to several limitations of the respective methods. Using the method according to the invention, in contrast, membranes with sizes of 250 cm² or more may be produced.

Fig. 1 shows the steps of the method according to the invention, beginning with the preparation of the porous single-layer graphene film on the metal foil substrate and ending with the removal of the TRT.

Fig. 2 shows the setup of the electrochemical delamination used in Example 2, with the Cu foil resting below graphene used as the working electrode and a platinum foil as the counter electrode.

Fig. 3 shows the effect of applied voltage on the delamination rate of graphene as described in Example 2 below.

Fig. 4 shows the effect of temperature on the Eh production rate and delamination rate of graphene as described in Example 2 below.

Fig. 5 shows photographs of various stages of electrochemical delamination of a 250 cm² sample as described in Example 3 below. The variable “t” in the photographs represents time in hours. Electrochemical delamination was performed at 4 V, at room temperature, and with 0.25 M NaHCOs electrolyte.

Fig. 6 shows a 250 cm² sized membrane prepared by the method according to the invention. Electrochemical delamination was performed at 4 V, at room temperature, and with 0.25 M NaHCOs. Smaller membrane coupons were cut from the large sample (Ml to M10), as described in Example 3 below. Ml to M8 have an area of 1 cm², while M9 and MIO have an area of 5 cm². The graph on the right shows the CO2 permeance and CO2/N2 selectivity of Ml to MIO.

Fig. 7a shows the parts of a custom-made module used in Example 3 for assessing the performance of the 1 cm² sized membrane coupons.

Fig. 7b shows the custom-made parts of the module in Fig. 7a after assembly.

Fig. 8 shows a custom-made membrane module (top) used for assessing the performance of a 50 cm² sized membrane coupon prepared by the method according to the invention, as described in Example 3 below. The CO2 permeance of the membrane over a course of 34 days of testing is shown on the bottom of Fig. 8.

Fig. 9 shows a 250 cm² sized Cu/porous graphene/PTMSP/TRT coupon before Cu foil delamination.

Fig. 10 shows two 250 cm² sized polyethersulfone (PES)/porous graphene/PTMSP membrane layers after electrochemical delamination of the Cu foil and removal of the TRT layer. The coupon size is larger than 25 cm in length with an area higher than 250 cm².

Fig. 11 shows a electron micrograph of a porous graphene/covalent organic framework (COF) on a silicon wafer.

Fig. 12 shows on the left a picture of a graphene membrane (using a composite COF/PTMSP support film with COF contacting graphene) and on the right a graph exhibiting Separation performances from three separate porous graphene/COF/PTMSP membranes. PREFERRED EMBODIMENTS OF THE INVENTION

The invention provides a method for producing a gas separation membrane precursor containing a porous single-layer graphene film, comprising the following steps:

(a) providing a metal foil substrate;

(b) preparing a porous single-layer graphene film on the metal foil substrate;

(c) depositing a gas-permeable support film on top of the porous single-layer graphene film;

(d) applying a layer of TRT on top of the gas-permeable support film;

(e) removing, in particular delaminating, the metal foil substrate to obtain the gas separation membrane precursor.

Further advantageous embodiments of the invention are specified in the dependent claims and are elucidated in detail herein below.

Advantageously, in step (e) of the method according to the invention the metal foil substrate is removed by electrochemical delamination. Conventionally, the metal foil substrate must be removed through dissolution in an acid bath, which is lengthy, expensive, and hazardous. Electrochemical delamination has the advantage that the transferable assembly can simply be peeled off from the metal foil substrate. The metal foil substrate can then be recycled and/or reused. A distinct advantage of using electrochemical bubbling compared with the conventional acid dissolution approach is that the resulting transfer is environmentally friendly and can be carried out in continuous roll-to-roll protocols. Furthermore, electrochemical bubbling allows the removal of the metal foil substrate substantially without altering the properties of the gas-permeable support film.

According to an embodiment, the method according to the invention further comprises the additional step (f):

(f) placing the gas separation membrane precursor on top of a porous support substrate to obtain a supported gas separation membrane precursor. According to another embodiment, the method according to the invention further comprises the additional step (g):

(g) heating the supported gas separation membrane precursor to a temperature of from 100 to 180°C, preferably from 100 to 150°C, most preferably from 110 to 140°C, for a period of from 1 s to 1 h, preferably from 5 s to 30 min, more preferably from 1 min to 10 min, most preferably from 2 min to 5 min, followed by removing the TRT to obtain a gas separation membrane, in particular for CO2 separation.

According to another embodiment, the method according to the invention comprises the additional step (f) and (g) described herein.

If the method according to the invention comprises the additional step (g), it may also be referred to as a method for producing a gas separation membrane, in particular for CO2 separation.

The porous support substrate provides mechanical robustness for pressurizing the porous graphene membrane during operation. During step (g), the elevated temperature leads to the foaming of the adhesive in TRT, thus reducing the adhesive strength. TRT can then be removed from the supported gas separation membrane precursor, for example by hand. Importantly, all steps (a) to (g) can be performed in a roll-to-roll manner, thus making this process suitable for mass-manufacture of gas separation membranes and/or porous graphene membranes.

In a preferred embodiment, the gas-permeable support film has a thickness of from 10 nm to 10 pm, preferably from 500 nm to 2 pm, most preferably from 0.5 pm to 1.5 pm. The gas-permeable support film serves as a mechanical reinforcement for the porous graphene and protects the graphene surface from external particles and abrasion in the membrane module. Increasing the thickness of the gas-permeable support film to enhance the mechanical strength decreases the permeance of the resulting membrane, thus making it unattractive in gas separation processes. Therefore, a balance between permeance and mechanical strength has to be found.

Advantageously, the gas-permeable support film has a gas permeance of at least 100 GPU, preferably at least 1000 GPU, for at least one gas. In the context of this invention, “GPU” stands for “gas permeation unit”, wherein 1 GPU = 3.35 x 10'¹⁰ mol/(m² s Pa). The higher the permeance of the gas-permeable support film, the higher the overall permeance of the resulting membrane.

The gas-permeable support film is advantageously selected from the group consisting of porous inorganic films and highly permeable polymeric films. Among the inorganic films, particularly preferred films are porous carbon films, porous carbon films reinforced with carbon nanotubes, or porous silica films. Among the highly permeable polymeric films, particularly preferred films are polymers with intrinsic microporosity (P1M), polydimethylsiloxane (PDMS), poly(l-trimethylsilylpropyne) (PTMSP), porous organic polymers, porous aromatic frameworks, or covalent organic frameworks, or a combination of these. In a preferred embodiment, a highly permeable polymeric film is used as the gas-permeable support film, particularly preferably PTMSP. In another preferred embodiment, the gas-permeable support film is a covalent organic framework. A covalent organic framework may also be referred to as COF. In another preferred embodiment, the gas-permeable support film is a combination of a covalent organic framework and PTMSP. In this embodiment, the covalent organic framework is preferably in contact with the porous single-layer graphene film and the PTMSP is in contact with the covalent organic framework.

The skilled person knows many covalent organic frameworks. Covalent organic frameworks are for example described in the review article by Geng et al. Chem. Rev. 2020, 120, 16, 8814-8933. According to an embodiment, the covalent organic framework is based on an amine-functionalized molecule and an aldehyde- functionalized molecule. According to an embodiment, the porous single-layer graphene film acts as a selective layer, in particular of the gas separation membrane. The porous single-layer graphene film may also act as a selective layer of the gas separation membrane precursor.

In a preferred embodiment, the method according to the invention does not generate cracks or tears in the porous single-layer graphene film. Herein, cracks refer to nanoscopic tears with dimensions of greater than 1 nm and typically greater than 100 nm, which can be observed by electron and optical microscopy. Advantageously, the gas separation membrane containing the porous single-layer graphene film is substantially crack-free. Avoiding cracks and tears in the membrane is important because these large defects are not selective and compromise the selectivity of the membrane. In the prior art, crack-free transfer of porous single-layer graphene films with the help of TRT for gas separation applications has not been reported to date. This is because TRT is conventionally applied directly on top of the porous graphene. This leads to crack formation in the porous graphene when the TRT is removed because any portion of the porous graphene that is not contacting the final support tends to break during this removal.

In a preferred embodiment, the metal foil substrate is Cu foil or Ni foil.

In optional step (f) of the method described herein, the gas separation membrane is placed on top of a porous support substrate. According to an embodiment, the porous support substrate comprises or consists of a porous polymeric support, in particular porous polyethersulfone (PES). The porous polymeric support can either be used as a standalone, or in combination with a nonwoven fabric, or directly cast in a nonwoven fabric. Nonwoven fabric has the advantage of being relatively inexpensive and flexible.

According to an embodiment, the porous support substrate employed in step (f) of the method according to the invention has a thickness of from 25 pm to 500 pm, preferably from 50 pm to 200pm, most preferably from 90 pm to 110 pm. The porous support substrate preferably provides mechanical support as well as protection for the porous single-layer graphene film during the membrane module assembly and under operation.

According to an embodiment wherein step (e) of the method according to the invention comprises electrochemical delamination, the electrochemical delamination is advantageously carried out in an electrolyte solution with a pH of 6 to 10, preferably 7 to 9, most preferably 7.5 to 8.5. A pH value close to neutral serves to prevent damage (e.g., change in physical properties) of the gas-permeable support film. The highly permeable polymeric films that may be used as material for the gas- permeable support film are sensitive to the pH of electrolytic baths. While electrochemical bubbling can in principle also be carried out in acidic and basic baths, these generally affect the polymer chains of the highly permeable polymeric films, leading to the degradation of the highly permeable polymeric films. Therefore, according to a preferred embodiment of the method according to the invention, the pH of the electrolyte is designed to be close to neutral. This also makes the method according to the invention particularly suitable for large-scale operation.

Advantageously, the electrolyte solution should have a pH close to neutral pH compared to highly acidic or highly basic solution. According to a preferred embodiment, the electrolyte solution is an aqueous solution of a hydrogen carbonate salt, preferably selected from the group consisting of NaHCOs, KHCOs, and NH4HCO3, particularly preferably NaHCOs. In a preferred embodiment, the salt concentration is in the range of 0.01 to 5 M, preferably 0.1 to 2 M, preferably 0.1 to 1 M, most preferably 0.1 to 0.5 M. Hydrogen carbonate salt electrolytes have mild pH values and are thus easy to handle and environmentally friendly. Furthermore, they do not adversely affect the stability of the gas-permeable support film.

The electrochemical delamination may be carried out at a voltage of from 1 to 10 V, preferably from 2 to 8 V, more preferably from 3 to 5 V, most preferably from 3.5 to 4.5 V. The electrochemical delamination may be carried out at a temperature of from 0 to 100°C, preferably from 10 to 80°C, more preferably from 20 to 30°C. A higher delamination rate is beneficial for faster membrane fabrication. Without wishing to be bound by scientific theory, it is believed that an increase in applied voltage may also increase the current and the H2 production rate. The elevated H2 production rate may, in turn, increase the delamination rate due to the acceleration of bubble formation at the interface between the porous graphene and the metal foil substrate or the working electrode. Without wishing to be bound by scientific theory, it is also believed that another strategy to increase the delamination rate is to heat the electrolyte solution, as heating the electrolyte solution may increase the mobility of ions in the electrolyte solution and cause a H2O wicking effect due to the faster oxygen diffusion, which eventually enhances the H2 production kinetics and delamination rate.

In a preferred embodiment, the metal foil substrate and/or the porous single-layer graphene film and/or the gas separation membrane has an area of 50 cm² or more, preferably 100 cm² or more, more preferably 200 cm² or more, most preferably 250 cm² or more. While centimeter-scale membranes have been demonstrated in the prior art by scooping a floating graphene film, that process becomes extremely challenging for larger membrane areas as scooping becomes exponentially difficult to manage for large areas. Additionally, the risk of crack formation increases significantly for large areas, especially when the graphene film is scooped onto a porous support substrate. Thus, using conventional synthesis approaches, membranes have been limited in size (i.e., 1 mm² or 1 cm² in area) because the conventional approaches are not scalable, requiring careful handling and a batch-wise process. A distinct advantage of the method according to the invention is that the gas separation membrane precursor is relatively thick and thus extremely strong. The method according to the invention bypasses the need to float the graphene film after the removal of the metal foil substrate. For example, after removing the metal foil substrate, the gas separation membrane precursor may be simply handled by grasping an end of the TRT, which holds the graphene film rigidly. This allows for handling large sizes (e.g., 25 cm long pieces) without producing any cracks and tears in the membrane. Moreover, by applying the TRT on top of the gas-permeable support film, crack formation in the porous single-layer graphene film during removal of the TRT is avoided. The invention also relates to a gas separation membrane obtainable by the method according to the invention. The gas separation membrane may in particular be used for CO2 separation. Advantageously, the gas separation membrane shows a CO2/N2 selectivity greater than 10 and a CO2 permeance greater than 100 GPU, preferably greater than 1000 GPU. Selectivity and permeance of the membrane material determine the efficiency of the gas separation process. A high selectivity of CO2 over N2 is particularly important for a membrane intended for CO2 separation since the main component of air is N2. Cracks and tears are large, non-selective defects within the membrane and thus compromise the selectivity of the membrane. Consequently, the substantially crack-free nature of the gas separation membrane according to the invention is an important factor in providing a high selectivity.

In the following, the invention is further described by way of examples that are in no way meant to be limiting.

EXAMPLES

Materials

Poly(l-trimethylsilylpropyne) (PTMSP) was obtained from abcr GmbH. Transfer release tape (TRT) was obtained from Nitto. Cu foil was obtained from Carl Roth. Polyethersulfone (PES) with 0.2-0.8 pm-sized pores was obtained from Haining Zhongli Filtering Equipment Factory. NaHCOs was obtained from Chemie Brunschwig AG.

Analytical Methods

The porous graphene membrane coupon was placed inside a custom-made membrane module design for introducing the gas inlet (feed) in a cross-flow regime. The feed to the membrane module was connected to the gas flow system controlling the flow of various gases including CO2 and N2. A back pressure regulator valve at the retentate side was used to pressurize and control the pressure of the test. The permeate flow was measured using a bubble flow meter. For analysis of the mixture, gas chromatography was used to analyze the composition of the permeate.

The gas permeance (/V) was calculated as per Equation (1), derived from the ideal gas law: where T is the temperature of the permeate volume (room temperature), R is the universal gas constant, is the flow rate measured through bubble flow meter, and A is the membrane area. Permeate side pressure (P_p) is maintained close to one atmospheric pressure, and feed side pressure (PF) in the range of 2-3 bar. AP is the trans-membrane pressure difference across the membrane and is equal to PF - P_p.

For each membrane test, the membrane module was firstly heated to 130°C in the presence of CO2 for 1 h to desorb atmospheric contaminants from the membrane surface. After heating, the membrane was cooled down to the test temperature.

Example 1: Membrane preparation

In accordance with the preparation scheme provided in Figure 1, a porous single-layer graphene film was prepared on Cu foil by chemical vapor deposition following the procedure described in the Examples of EP 3 888 777 Al, in particular Example 1 of EP 3 888 777 Al. Then, 3 wt.-% PTMSP in toluene was spin-coated (1000 rpm for 1 min) as a gas permeable support film on the graphene surface. The film was dried overnight at room temperature. The resulting PTMSP film had a thickness of around 1 pm. Next, TRT was laminated on top of PTMSP as additional support. This allowed simply and conveniently lifting the sample by a pair of tweezers, making the transfer process simple to implement. In comparison, without TRT, lifting the sample with a pair of tweezers will destroy the film. Subsequently, the Cu foil was removed by electrochemical delamination, and the gas separation membrane precursor comprising porous graphene/PTMSP/TRT was washed with deionized water. Next, the gas separation membrane precursor was placed on the porous PES support using a pair of tweezers and dried under ambient conditions. In the last step, TRT was removed by heating to 130°C for 2 min.

Example 2: Electrochemical delamination

For removal of the metal foil substrate by electrochemical delamination, a water electrolysis cell was utilized where the Cu foil resting below graphene was used as the working electrode and a platinum foil was the counter electrode, as shown in Figure 2. A 0.25 M or saturated aqueous solution of NaHCOs was used as the electrolyte solution. The delamination experiments were performed at a constant 4 V bias voltage. During the delamination process, the electrolyte solution was kept under stirring to enhance the mass transfer of ions in the electrolyte solution. Complete delamination for a 250 cm² sized sample was achieved in 5 h at room temperature. It was determined that delamination was complete upon full detachment of the TRT- reinforced polymeric support layer from the metal substrate, and also by the sudden increase in the current recorded on the working electrode side.

Additionally, the effect of varying the applied voltage and temperature were investigated. As the applied voltage was increased from 4 to 8 V, the current and the H2 production rate at the Cu/graphene interface increased. The elevated H2 production rate also increased the delamination rate of the samples. The delamination rate could be increased by a factor of 6 by increasing the bias voltage from 4 to 8 V, as shown in Figure 3. Upon heating the electrolyte solution from room temperature to 50, 60, and 80°C at a constant 4 V bias voltage, the H2 production rate increased gradually from 0.11 to 0.23 mmol/h, along with the delamination rate of the samples, as shown in Figure 4.

Right after the delamination of the graphene/PTMSP/TRT stack from the metal foil substrate, the membrane stack was moved to a deionized water bath and kept for at least 1 h for removal of possible electrolyte residues. Example 3: Membrane performance

Two 1 cm² sized porous graphene membranes prepared by the method according to the invention yielded an average CO2 permeance of 880 GPU at 25°C, with an average CO2/N2 selectivity of 21.5 at 25°C. Before testing, the membranes were heated to 120°C for 1 h in the presence of CO2 to remove contaminants on the graphene.

Additionally, a 250 cm² sized porous graphene membrane was prepared by the method according to the invention. This sample is shown in Figure 5 at various stages during the electrochemical delamination.

As shown in Figure 6, eight 1 cm² sized membrane coupons (Ml to M8) were prepared by cutting pieces from the 250 cm² membrane. They showed an average CO2 permeance of 1502±130 GPU and an average CO2/N2 selectivity of 14±1.6 at 25°C. Further, two 5 cm² sized membrane coupons (M9 and MIO) prepared from the 250 cm² membrane also showed comparable performance. The CO2 permeance and CO2/N2 selectivity of the membranes are also shown in Figure 6. For testing the performance of the coupons Ml to M8, a custom-made apparatus was used comprising a module parts of which are depicted in Figures 7a (disassembled) and 7b (assembled).

A 50 cm² sized membrane was also prepared by the method according to the invention. The membrane yielded a stable gas separation performance over the course of 34 days of testing. A slight decrease in CO2 permeance could be attributed to the slow accumulation of contaminants on the graphene pores. This effect was reversible by heating the membrane to 130°C for 1 h, restoring the original permeance, as shown by the results presented in Figure 8.

Moreover, a 250 cm² sizes supported gas separation membrane precursor coupon consisting of a Cu foil, a porous graphene film, a PTMSP film and a TRT film as shown in Figure 9 was prepared using the method described in Example 1. Finally, two 250 cm² sized gas separation membrane layers on porous polyethersulfone supports as shown in Figure 10 were prepared using the method described in Example 1 and subsequently delaminated using the method described in Example 2 (0.25 M aqueous electrolyte, 4 V, 25°C) followed by transfer to the porous polyethersulfone supports (each about 100 pm thick) using tweezers and removal of the TRT film by heating to about 130°C for 2 minutes and manually pealing the TRT off.

As elucidated in the given examples, the method according to the invention allows the easy and robust synthesis of large porous graphene membranes with high CO2 permeance and high CO2/N2 selectivity.

Example 4: Preparation of COF-based gas permeable support film

Acetonitrile and dioxane are mixed in a 5:1 volume ratio to obtain a solvent mixture. Two separate solutions are prepared. A 0.3 mM concentration of amine precursor to COF is added to 10 mL of the solvent mixture. The solution is then sonicated for 20 minutes to ensure proper dissolution and dispersion. Second, a 0.45 mM concentration of aldehyde precursor to COF is added to a 10 mL of the solvent mixture. This solution is also sonicated for 20 minutes under the same conditions.

Following sonication, both solutions are separately filtered using a 0.2-micron PTFE filter to remove any undissolved particles or impurities. Immediately after filtration, the two solutions are mixed, leading to the development of a pale-yellow color, indicating the formation of the desired intermediate. The combined solution is sonicated again for 10 minutes to further promote uniform mixing and reaction progression.

The prepared solution is spin-coated onto a graphene/Cu substrate using a two-step spin-coating process: The solution is spin-coated at 1000 rpm for 30 seconds, repeated for two cycles, to ensure uniform film formation. Then, the spinning speed is reduced to 500 rpm for 30 seconds, also repeated for two cycles, to optimize film thickness.

Following the spin-coating process, the coated samples are transferred to an oven and dried at 70 °C for 30 minutes to facilitate solvent evaporation and enhance film stability. Finally, the coated samples are left to dry at room temperature overnight to allow complete solvent evaporation and proper film stabilization before further analysis or use. A covalent organic framework on a porous graphene membrane was subsequently imaged by electron microscopy as shown in Figure 11.

In addition, a covalent organic framework on a porous graphene membrane with a PTMSP film on top of the covalent organic framework was prepared (see Fig. 12, left) and subsequently its CO2 performance as well as its CO2/N2 selectivity were determined (see Fig. 12, right).

Claims

C l a i m s

1. A method for producing a gas separation membrane precursor containing a porous single-layer graphene film, comprising the following steps:

(a) providing a metal foil substrate;

(b) preparing a porous single-layer graphene film on the metal foil substrate;

(d) applying a layer of transfer release tape on top of the gas-permeable support film;

2. The method according to any one of the preceding claims, characterized in that in step (e) the metal foil substrate is removed by electrochemical delamination.

3. The method according any one of the preceding claims, comprising the further step

(f) and optionally the further step (g):

(f) placing the gas separation membrane precursor on top of a porous support substrate to obtain a supported gas separation membrane precursor;

(g) heating the supported gas separation membrane precursor to a temperature of from 100 to 180°C, preferably from 100 to 150°C, most preferably from 110 to 140°C, for a period of from 1 s to 1 h, preferably from 5 s to 30 min, more preferably from 1 min to 10 min, most preferably from 2 min to 5 min, followed by removing the transfer release tape to obtain a gas separation membrane, in particular for CO2 separation.

4. The method according to any one of the preceding claims, characterized in that the gas-permeable support film has a thickness of from 10 nm to 10 pm, preferably from 500 nm to 2 pm, most preferably from 0.5 pm to 1.5 pm.

5. The method according to any one of the preceding claims, characterized in that the gas-permeable support film has a gas permeance of at least 100 GPU, preferably at least 1000 GPU, for at least one gas.

6. The method according to any one of the preceding claims, characterized in that the gas-permeable support film is selected from the group consisting of porous inorganic films, in particular porous carbon films, porous carbon films reinforced with carbon nanotubes or porous silica films, and highly permeable polymeric films, in particular polymers with intrinsic microporosity (P1M), polydimethylsiloxane (PDMS), poly(l-trimethylsilylpropyne) (PTMSP), porous organic polymers, porous aromatic frameworks, or covalent organic frameworks, or a combination of these, preferably a highly permeable polymeric film, most preferably PTMSP or a covalent organic framework or a combination of a covalent organic framework and PTMSP.

7. The method according to any one of the preceding claims, characterized in that the metal foil substrate is Cu foil or Ni foil.

8. The method according to any one of the preceding claims, characterized in that the porous support substrate comprises or consists of a porous polymeric support, in particular porous polyethersulfone (PES).

9. The method according to any one of the preceding claims, characterized in that the porous support substrate has a thickness of from 25 pm to 500 pm, preferably from 50 pm to 200pm, most preferably from 90 pm to 110 pm.

10. The method according to any one of claims 2 to 9, characterized in that step (e) is carried out in an electrolyte solution with a pH of 6 to 10, preferably 7 to 9, most preferably 7.5 to 8.5.

11. The method according to claim 10, characterized in that the electrolyte solution is an aqueous solution of a hydrogen carbonate salt, preferably selected from the group consisting of NaHCCU, KHCOs, and NH4HCO3, particularly preferably NaHCOs, in particular with the salt concentration in the range of 0.01 to 5 M, preferably 0.1 to 2 M, more preferably 0.1 to 1 M, most preferably 0.1 to 0.5 M.

12. The method according to any one of claims 2 to 11, characterized in that step (e) is carried out at a voltage of from 1 to 10 V, preferably from 2 to 8 V, more preferably from 3 to 5 V, most preferably from 3.5 to 4.5 V , and/or at a temperature of from 0 to 100°C, preferably from 10 to 80°C, more preferably from 20 to 30°C.

13. The method according to any one of the preceding claims, characterized in that the porous single-layer graphene film acts as a selective layer, in particular of the gas separation membrane.

14. The method according to any one of the preceding claims, characterized in that the method does not generate cracks or tears in the porous single-layer graphene film and/or that the gas separation membrane containing the porous single-layer graphene film is substantially crack-free.

15. The method according to any one of the preceding claims, characterized in that the metal foil substrate and/or the porous single-layer graphene film and/or the gas separation membrane has an area of 50 cm² or more, preferably 100 cm² or more, more preferably 200 cm² or more, most preferably 250 cm² or more.

16. Gas separation membrane obtainable by the method according to any one of claims

3 to 15, in particular for CO2 separation, with CO2/N2 selectivity greater than 10, and CO2 permeance greater than 100 GPU, preferably greater than 1000 GPU.