Patent Application
20240228713
Hydrogen as an energy vector for grid balancing or power-to-gas and power-to-liquid processes plays an important role in the path toward a low-carbon energy structure that is environmentally friendly. Water electrolysis produces high quality hydrogen by electrochemical splitting of water into hydrogen and oxygen; the reaction is given by Eq. 1 below. The water electrolysis process is an endothermic process and electricity is the energy source. Water electrolysis has zero carbon footprint when the process is operated by renewable power sources, such as wind, solar, or geothermal energy. The main water electrolysis technologies include alkaline electrolysis, proton exchange membrane (PEM) water electrolysis (PEMWE as shown in
As shown in
Water electrolysis reaction:
2 H2O→2 H2+O2 (1)
Oxidation reaction at anode for PEMWE:
2 H2O→O2+4 H++4 e− (2)
Reduction reaction at cathode for PEMWE:
2 H++2 e−→H2 (3)
AEMWE is a developing technology. As shown in
Reduction reaction at cathode for AEMWE:
4 H2O+4 e−→2 H2+4 OH− (4)
Oxidation reaction at anode for AEMWE:
4 OH−→2 H2O+O2+4 e− (5)
AEMWE has an advantage over PEMWE because it permits the use of less expensive platinum metal-free catalysts, such as Ni and Ni alloy catalysts. In addition, much cheaper stainless steel bipolar plates can be used in the gas diffusion layers (GDL) for AEMWE, instead of the expensive Pt-coated Ti bipolar plates currently used in PEMWE. However, the largest impediments to the development of AEM systems are membrane hydroxyl ion conductivity and stability, as well as lack of understanding of how to integrate catalysts into AEM systems. Research on AEMWE in the literature has been focused on developing electrocatalysts, AEMs, and understanding the operational mechanisms with the general objective of obtaining a high efficiency, low cost and stable AEMWE technology.
Fuel cells, as a next generation clean energy resource, convert the energy of chemical reactions such as an oxidation/reduction redox reaction of hydrogen and oxygen into electric energy. The three main types of fuel cells are alkaline electrolyte fuel cells, polymer electrolyte membrane fuel cells, and solid oxide fuel cells. Polymer electrolyte membrane fuel cells may include proton exchange membrane fuel cells (PEMFC), anion exchange membrane fuel cells (AEMFC), and direct methanol fuel cells. PEMFC uses a PEM to conduct protons from the anode to the cathode, and it also separates the H2 and O2 gases to prevent gas crossover. AEMFC uses an AEM to conduct OH− from the cathode to the anode, and it also separates the H2 and O2 gases to prevent gas crossover.
The anode in an electrochemical cell is the electrode at which the predominant reaction is oxidation (e.g., the water oxidation/oxygen evolution reaction electrode for a water electrolyzer, or the hydrogen oxidation electrode for a fuel cell). The cathode in an electrochemical cell is the electrode at which the predominant reaction is reduction (e.g., the proton reduction/hydrogen evolution reaction electrode for a water electrolyzer, or the oxygen reduction electrode for a fuel cell). The membrane is one of the key materials that make up an electrolysis cell or a fuel cell and is an important driver for safety and performance. Some important properties for membranes for fuel cells and membrane electrolysis include high conductivity, high ionic permeability, high ionic exchange capacity (for ion-exchange membrane), high ionic/H2 and O2 selectivity (low H2 and O2 permeability/crossover), low price, low area resistance to minimize efficiency loss resulting from ohmic polarization, high resistance to oxidizing and reducing conditions, being chemically inert at a wide pH range, high thermal stability together with high proton conductivity, and high mechanical strength (thickness, low swelling).
Significant advances are needed in cost-effective, high performance, stable catalysts, membrane materials, as well as other cell stack components for AEM water electrolysis and AEMFCs with a wide range of applications in renewable energy systems.
Novel anion exchange polymers comprising a plurality of repeating units of formula (I)
were previously developed for the preparation of AEMs. The anion exchange polymers have stable hydrophobic polymer backbones comprising linear aromatic units, such as biphenyl and terphenyl, and polycyclic aromatic units, such as naphthalene and phenanthrene. Cationic groups, like piperidinium, quaternized carbazole derivative, quaternized phenothiazine derivative, or piperidinium salt, were covalently incorporated into the polymers for the preparation of novel AEMs. Therefore, these polymers provide high OH− conductivity, high chemical stability, low swelling in alkaline water at about 60-120° C., and high mechanical stability. The anion exchange polymers can be used for electrolysis, such as water or CO2 electrolysis, as well as other uses such as redox flow batteries, and fuel cell applications.
The anion exchange polymers were designed to achieve: high OH− conductivity by incorporating a piperidinium, or a piperidinium salt, or both into the polymer side chain; high chemical stability by having an polymer backbone free of ether bonds; and high mechanical strength due to high polymer backbone rigidity and molecular weight by incorporating both linear aromatic units, such as biphenyl and terphenyl, and polycyclic aromatic units, such as naphthalene and phenanthrene, into the polymer main backbone. The polymers have hydrophilic anion exchange functional groups such as piperidinium functional groups on the polymer side chains and stable hydrophobic polymer main backbones free of ether bonds comprising linear aromatic units, such as biphenyl and terphenyl, and polycyclic aromatic units, such as naphthalene and phenanthrene, which enable efficient and stable operation in water or CO2 electrolysis, redox flow battery, and fuel cell applications.
However, it was discovered that some poly(aryl piperidinium) anion exchange polymers derived from arenes and 4-piperidones tend to have low or very poor solubility in common organic solvents, even polar solvents such as dimethyl sulfoxide (DMSO) and N-methylpyrolidone (NMP), etc. As a result, it has proven to be challenging to dissolve the polymer with iodide counterions in organic solvents and to keep the solutions stable. In some cases, the polymer solutions were unstable and discolored easily due to oxidation. The poly(aryl piperidinium)-basedanion exchange polymers with OH− counterions were found to be unstable in the presence of O2. The poly(aryl piperidinium)-based anion exchange polymer with bicarbonate (HCO3−) counterions is insoluble in most of the organic solvents that are commonly used for membrane fabrication, such as NMP, dimethylformamide (DMF), DMSO, and dimethyl acetamide (DMAc), even though they are stable. In addition, the poly(aryl piperidinium)-based anion exchange polymer with HCO3− counterions is soluble in some alcohols such as ethanol. However, its solubility in alcohol results in a compatibility issue with the formulations used for catalyst coatings on the membrane comprising the polycylic-aromatic-hydrocarbon-based anion exchange polymer with HCO3− counterions, which is important for catalyst-coated membrane preparation. An ethanol or other alcohol solvent used in the catalyst ink formula could potentially damage or partially dissolve an anion exchange membrane that is prepared from the poly(aryl piperidinium)-based anion exchange polymer with HCO3− counterions.
The solubility and solution stability of the poly(aryl piperidinium)-based anion exchange polymers in common organic solvents such as DMSO can be improved by converting the original poly(aryl piperidinium)-based anion exchange polymers from their iodide (in which, iodide is the anionic counterion) to the acetate form (acetate anion as the counterion), for example. This is accomplished through ion exchange treatment.
The anion exchange polymers and polymer solutions containing them have a number of benefits. The unique solubility characteristics of the polymer make it a promising anion exchange polymer for the preparation of anion exchange membranes. The poly(aryl piperidinium)-based anion exchange polymers with the specified counterions have improved solubility in common organic solvents, for example, NMP, DMF, DMSO, and DMAc. Furthermore, the stability of the polymer solution for the preparation of anion exchange membranes is also improved. The poly(aryl piperidinium)-based anion exchange polymers with acetate (CH3COO−), trifluoroacetate (CF3COO−), propionate (CH3CH2COO−), or butanoate (CH3CH2CH2COO−) anions as the counterions also have a unique solubility profile, benefiting membrane casting and catalyst coating on membranes thereof.
One aspect of the invention is an anion exchange polymer. In one embodiment, the polymer comprises a plurality of repeating units of formula (I)
In some embodiments, Ar1 is selected from the group consisting of
and mixtures thereof.
In some embodiments, Ar1 is selected from the group consisting of
and mixtures thereof.
In some embodiments, Ar1 is selected from the group consisting of
and mixtures thereof;
In some embodiments, Ar1 is selected from the group consisting of
and mixtures thereof.
In some embodiments, Ar1 is selected from the group consisting of
and mixtures thereof.
In some embodiments, X1 is
In some embodiments, X1 is
In some embodiments, X1 is a mixture of
In some embodiments, the polymer comprising a plurality of repeating units of formula (I) is formed from a superacid catalyzed polyhydroxyalkylation reaction of monomers Ar1′ and X1′ followed by a Menshutkin reaction and an ion exchange reaction,
In some embodiments, Ar1′ is selected from the group consisting of:
and mixtures thereof.
In some embodiments, Ar1′ is selected from the group consisting of:
and mixtures thereof.
In some embodiments, Ar1′ is selected from the group consisting of:
and mixtures thereof;
In some embodiments, Ar1′ is selected from the group consisting of:
and mixtures thereof.
In some embodiments, Ar1′ is selected from the group consisting of:
and mixtures thereof.
In some embodiments, X1′ is
and wherein R30 is —H, —CH3, —CH2CH3, —CH(CH3)2, —C(CH3)3, —CH2—C6H5, or —CH2—CH(CH3)2.
In some embodiments, X1′ is
In some embodiments, X1′ is a mixture of
The anion exchange polymer comprising a plurality of repeating units of formula (I) may be synthesized by three steps: 1) a superacid catalyzed polyhydroxyalkylation reaction of monomers Ar1′ with X1′, such as a mixture of terphenyl and phenanthrene as Ar1′ with N-methylpiperidone as X1′, to form a neutral precursor polymer; 2) a Menshutkin reaction to convert the neutral precursor polymer with functional groups, such as piperidine-based groups, to the anion exchange polymer comprising a plurality of repeating units of formula (I) with anion-conducting functional groups, such as piperidinium-based cation groups, and halide-based counterions; and 3) an ion exchange reaction to convert the anion exchange polymer comprising a plurality of repeating units of formula (I) with halide-based counterions to acetate (CH3COO−), trifluoroacetate (CF3COO−), propionate (CH3CH2COO−), or butanoate anion (CH3CH2CH2COO−) counterions. Optionally, the anion exchange polymer comprising a plurality of repeating units of formula (I) with anion-conducting functional groups, such as piperidinium-based cation groups and negatively charged acetate (CH3COO−), trifluoroacetate (CF3COO−), propionate (CH3CH2COO−), or butanoate anion (CH3CH2CH2COO−) counterions is converted to an anion exchange polymer comprising a plurality of repeating units of formula (I) with anion-conducting functional groups, such as piperidinium-based cation groups and negatively charged hydroxide (HO−) ions by soaking in a base solution after the polymer is made into a membrane.
The three-step reactions of monomers Ar1′ with monomer X1′ provides an anion exchange polymer with a polymer backbone free of ether bonds, which results in high chemical stability of the polymer. The incorporation of electron-rich monomer Ar1′ into the anion exchange polymer provides a hydrophobic polymer backbone free of ether bonds and the incorporation of monomer X1′ into the anion exchange polymer provides piperidinium derivative or piperidinium salt derivative anion-conducting functional groups, or both, that help achieve stable high OH− conductivity. The incorporation of monomer Ar1′ into the anion exchange polymer provides the polymer with high mechanical strength due to high polymer backbone rigidity and molecular weight. The incorporation of negatively charged acetate (CH3COO−), trifluoroacetate (CF3COO−), propionate (CH3CH2COO−), or butanoate anion (CH3CH2CH2COO−) counterions into the anion exchange polymer provides the polymer with improved solubility in common organic solvents, for example, NMP, DMF, DMSO, and DMAc. The anion exchange membrane prepared from the anion exchange polymer comprising a plurality of repeating units of formula (I) with anion-conducting functional groups, such as piperidinium-based cation groups, and negatively charged acetate (CH3COO−), trifluoroacetate (CF3COO−), propionate (CH3CH2COO−), or butanoate anion (CH3CH2CH2COO−)-based counterions has good compatibility with the catalyst inks coated on the surfaces of the membrane for the formation of catalyst-coated membrane. The combination of the hydrophobic polymer backbone with high mechanical strength, the hydrophilic polymer side chains, and alkaline stable hydrophilic piperidinium cationic groups provides the novel anion exchange polymer membrane with high OH− conductivity, high chemical stability, high mechanical strength, and long-term performance stability.
The superacid catalyzed polyhydroxyalkylation reaction can be carried out at −10° C. to 50° C., or at −5° C. to 30° C., or at −5° C. to 25° C. for 2 h to 72 h, or 10 h to 48 h, or 12 to 24 h. Suitable superacid catalysts include, but are not limited to, trifluoromethanesulfonic acid (CF3SO3H (TFSA)), methanesulfonic acid (MSA), fluorosulfuric acid (FSO3H), or mixtures thereof. Solvents for the polyhydroxyalkylation reaction are those that can dissolve one or more of the monomers. Suitable solvents include, but are not limited to, methylene chloride, chloroform, trifluoroacetic acid (TFA), or mixtures thereof.
The Menshutkin reaction is used to react the neutral precursor polymer with an alkyl halide, or with an alkyl amine first followed by an alkyl halide to convert the neutral precursor polymer to the anion exchange polymer comprising a plurality of repeating units of formula (I) with linear aromatic units, such as biphenyl and terphenyl, or polycyclic aromatic units, such as naphthalene and phenanthrene, and stable cationic ion-conducting functional groups, such as piperidinium, quaternized carbazole derivative, quaternized phenothiazine derivative, and piperidinium salt. Suitable alkyl halides include, but are not limited to, alkyl iodides or alkyl bromides. Suitable alkyl amines include, but are not limited to, trimethyl amine or triethyl amine. The Menshutkin reaction can be carried out at 10° C. to 80° C., or at 20° C. to 30° C. for 2 h to 72 h, or 10 h to 48 h, or 12 to 24 h. Solvents for the Menshutkin reaction are those that can dissolve the neutral precursor polymer. Suitable solvents include, but are not limited to, N-methylpyrrolidone (NMP), N,N-dimethyl acetamide (DMAC), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), 1,3-dioxolane, or mixtures thereof.
The ion exchange reaction is used to covert the anion exchange polymer comprising a plurality of repeating units of formula (I) with linear aromatic units, such as biphenyl and terphenyl, or polycyclic aromatic units, such as naphthalene and phenanthrene, stable cationic ion-conducting functional groups, and halide-based counterions to the anion exchange polymer comprising a plurality of repeating units of formula (I) with linear aromatic units, such as biphenyl and terphenyl, or polycyclic aromatic units, such as naphthalene and phenanthrene, stable cationic ion-conducting functional groups, and acetate (CH3COO−), trifluoroacetate (CF3COO−), propionate (CH3CH2COO−), or butanoate anion (CH3CH2CH2COO−) counterions. The ion exchange reaction can be carried out in an acidic aqueous solution, such as acetic acid, trifluoroacetic acid, propionic acid, or butanic acid aqueous solution, or an aqueous solution of a salt of an acid, such as potassium salt of acetic acid, with a concentration of 0.2 wt % to 10 wt %, or 0.5 wt % to 2 wt % at 20° C. to 60° C., or at 20° C. to 30° C. for 0.5 h to 72 h, or 0.5 h to 6 h, or 0.5 to 1 h.
The anion exchange polymer comprising a plurality of repeating units of formula (I) has a weight average molecular weight in a range of 10,000 to 1,000,000 Daltons, or in a range of 50,000 to 500,000 Daltons.
Another aspect of the invention is an anion exchange membrane comprising the polymer described above. The anion exchange membrane may be used in a wide variety of applications including, but not limited to, fuel cells, electrolyzers, flow batteries, electrodialyzers, waste metal recovery systems, electrocatalytic hydrogen production systems, desalinators, water purifiers, waste water treatment systems, ion exchangers, or CO2 separators.
In some embodiments, the anion exchange membrane comprises a nonporous symmetric dense film membrane, an integrally-skinned asymmetric membrane, a reinforced composite membrane, or a thin film composite membrane. By “dense” we mean that the membrane does not have pores larger than 1 nm.
In some embodiments, the reinforced composite membrane or the thin film composite membrane comprises a porous substrate membrane impregnated or coated with the anion exchange polymer. The porous substrate membrane is prepared from a polymer different from the anion exchange polymer.
In some embodiments, the nonporous symmetric dense film membrane, the integrally-skinned asymmetric membrane, the reinforced composite membrane, or the thin film composite membrane may be a flat sheet membrane.
In some embodiments, the nonporous symmetric dense film anion exchange membrane is prepared using a method comprising: 1) dissolving the anion exchange polymer in a solvent to form a polymer casting solution; 2) casting the polymer casting solution on a nonporous substrate to form a uniform layer of the polymer casting solution; 3) drying the polymer casting solution layer to form a dried membrane on the nonporous substrate at 50° C. to 180° C., or at 50° C. to 120° C., or at 80° C. to 120° C.; and optionally 4) ion exchanging the acetate (CH3COO−), trifluoroacetate (CF3COO−), propionate (CH3CH2COO−), or butanoate (CH3CH2CH2COO−) anions of the anion exchange polymer in the membrane with hydroxide anion to form the nonporous symmetric dense film anion exchange polymer membrane. The nonporous substrate is removed from the membrane when the membrane is used in a desired application. The solvent used to dissolve the anion exchange polymer can be selected from, but is not limited to, NMP, DMAC, DMF, DMSO, 1,3-dioxolane, or mixtures thereof. The nonporous substrate used for the fabrication of the nonporous symmetric dense film membrane can be selected from, but is not limited to, glass plate, polyolefin film, polyimide film such as Kapton® film, polyester film such as Mylar® film, or fluorocarbon-based polymer film such as poly(tetrafluoroethylene) (PTFE) and poly(vinylidene fluoride) (PVDF) film.
In some embodiments, the integrally-skinned asymmetric anion exchange membrane is prepared using a method comprising: 1) making an anion exchange polymer membrane casting solution comprising the anion exchange polymer with formula (I), solvents which are miscible with water and can dissolve the anion exchange polymer, and non-solvents which cannot dissolve the anion exchange polymer; 2) casting a layer of the anion exchange polymer membrane casting solution onto a supporting substrate; 3) evaporating the solvent and non-solvent from the surface of the coated layer and then coagulating the coated polymer layer in a coagulating bath to form the integrally-skinned asymmetric membrane structure; 5) drying the membrane at 50° C. to 150° C., or at 50° C. to 120° C., or at 80° C. to 120° C.; and optionally 6) ion exchanging the acetate (CH3COO−), trifluoroacetate (CF3COO−), propionate (CH3CH2COO−), or butanoate (CH3CH2CH2COO−) anions of the anion exchange polymer in the membrane with hydroxide anion to form the integrally-skinned asymmetric anion exchange polymer membrane. In some embodiments, the supporting substrate is removed from the membrane when the membrane is used in a desired application. In some embodiments, the supporting substrate is part of the final integrally-skinned asymmetric anion exchange polymer membrane. The supporting substrate may comprise polyolefin such as polypropylene and polyethylene, polyester, polyamide such as Nylon 6 and Nylon 6,6, cellulose, or fluorocarbon-based polymer such as PTFE and PVDF. The solvents for the preparation of the integrally-skinned asymmetric membrane include, but are not limited to, NMP, DMAC, DMF, DMSO, dioxanes, 1,3-dioxolane, and mixtures thereof. The non-solvents for the preparation of the integrally-skinned asymmetric membrane include, but are not limited to, acetone, methanol, ethanol, tetrahydrofuran (THF), toluene, n-octane, n-decane, lactic acid, citric acid, isopropanol, and mixtures thereof. The integrally-skinned asymmetric membrane may have a thin nonporous dense layer less than 500 nm on a microporous support layer.
In some embodiments, the reinforced composite anion exchange membrane is prepared using a method comprising: 1) dissolving the anion exchange polymer in a solvent to form a polymer solution; 2) impregnating a porous matrix support membrane with the anion exchange polymer solution to fill the pores with the anion exchange polymer via dip-coating, soaking, spraying, painting, or other known conventional solution impregnating method; 3) drying the impregnated membrane at 50° C. to 150° C., or at 50° C. to 120° C., or at 80° C. to 120° C.; and optionally 4) ion exchanging the acetate (CH3COO−), trifluoroacetate (CF3COO−), propionate (CH3CH2COO−), or butanoate (CH3CH2CH2COO−) anions of the anion exchange polymer in the pores of the reinforced membrane with hydroxide anion to form the reinforced composite anion exchange membrane with interconnected anion exchange polymer domains in a porous matrix. The solvents for the preparation of the thin film composite anion exchange membrane include, but are not limited to, NMP, DMAC, DMF, DMSO, dioxanes, 1,3-dioxolane, and mixtures thereof. The porous matrix should have good thermal stability (stable up to at least 120° C.), high stability under high pH condition (e.g., pH greater than 8), high resistance to oxidizing and reducing conditions (insoluble and no performance drop under oxidizing and reducing conditions), high mechanical strength (no dimensional change under the system operation conditions), as well as other factors dictated by the operating conditions for electrochemical reactions. The porous matrix must be compatible with the electrochemical cell chemistry and meet the mechanical demands of cell stacking or winding assembly operations.
The polymers suitable for the preparation of the porous matrix can be selected from, but not limited to, polyolefins such as polyethylene and polypropylene, polyamide such as Nylon 6 and Nylon 6,6, polyester, cellulose acetate, polybenzimidazole, fluorocarbon-based polymer such as PTFE and PVDF, polycarbonate, cellulose, or combinations thereof. These polymers provide a range of properties such as low cost, high stability in alkaline water, good mechanical stability, and ease of processability for porous matrix fabrication.
The porous matrix can either a non-woven matrix or a woven matrix and have either a symmetric porous structure or an asymmetric porous structure. The porous matrix can be formed by an electrospinning process, a phase inversion membrane fabrication approach followed by direct air drying, or by phase inversion followed by solvent exchange methods. The porous matrix also can be fabricated via a dry processing of thermoplastic polyolefins or a wet processing of thermoplastic olefins. The dry processing of thermoplastic polyolefins utilizes extrusion to bring the polymer above its melting point and form it into the desired shape. Subsequent annealing and stretching processes may also be done to increase the crystallinity and orientation and dimension of the pores. The wet processing of polyolefin porous matrix is done with the aid of a hydrocarbon liquid or low molecular weight oil mixed with the polymer resin or a mixture of the polymer resin and inorganic nanoparticles in the melt phase. The melt mixture is extruded through a die similar to the dry processed separators. The thickness of the porous matrix can be in a range of 10-400 micrometers, or a range of 10-200 micrometers, or a range of 10-100 micrometers, or a range of 20-100 micrometers. The pore size of the porous matrix can be in a range of 1 micrometer to 500 micrometers, or a range of 10 micrometer to 200 micrometers, or a range of 50 micrometers to 100 micrometer.
In some embodiments, the thin film composite anion exchange membrane is prepared using a method comprising: 1) dissolving the anion exchange polymer in a solvent to form a polymer coating solution; 2) coating a layer of the anion exchange polymer coating solution on one surface of a microporous support membrane via dip-coating, meniscus coating, gravure coating, comma roll coating, spin coating, casting, soaking, spraying, painting, or other known conventional solution coating technologies; 3) drying the coated membrane at 50° C. to 150° C., or at 50° C. to 120° C., or at 80° C. to 120° C.; and optionally 4) ion exchanging the acetate (CH3COO−), trifluoroacetate (CF3COO−), propionate (CH3CH2COO−), or butanoate (CH3CH2CH2COO−) anions of the anion exchange polymer in the coating layer with hydroxide anions to form the thin film composite anion exchange membrane. The solvents for the preparation of the thin film composite anion exchange membrane include, but are not limited to, NMP, DMAC, DMF, DMSO, dioxanes, 1,3-dioxolane, and mixtures thereof. The microporous support membrane should have good thermal stability (stable up to at least 120° C.), high stability under high pH condition (e.g., pH greater than 8), high resistance to oxidizing and reducing conditions (insoluble and no performance drop under oxidizing and reducing conditions), high mechanical strength (no dimensional change under the system operation conditions), as well as other factors dictated by the operating conditions for electrochemical reactions. The microporous support membrane must be compatible with the electrochemical cell chemistry and meet the mechanical demands of cell stacking or winding assembly operations.
The polymers suitable for the preparation of the microporous support membrane can be selected from, but not limited to, polyolefins such as polyethylene and polypropylene, polyamide such as Nylon 6 and Nylon 6,6, polyester, cellulose acetate, polybenzimidazole, fluorocarbon-based polymer such as PTFE and PVDF, polycarbonate, cellulose, or combinations thereof. These polymers provide a range of properties such as low cost, high stability in alkaline water, good mechanical stability, and ease of processability for membrane fabrication.
The microporous support membrane can have either a symmetric porous structure or an asymmetric porous structure. The asymmetric microporous support membrane can be formed by a phase inversion membrane fabrication approach followed by direct air drying, or by phase inversion followed by solvent exchange methods. The microporous support membrane also can be fabricated via a dry processing of thermoplastic polyolefins or a wet processing of thermoplastic olefins. The dry processing of thermoplastic polyolefins utilizes extrusion to bring the polymer above its melting point and form it into the desired shape. Subsequent annealing and stretching processes may also be done to increase the crystallinity and orientation and dimension of the micropores. The wet processing of polyolefin separators is done with the aid of a hydrocarbon liquid or low molecular weight oil mixed with the polymer resin or a mixture of the polymer resin and inorganic nanoparticles in the melt phase. The melt mixture is extruded through a die similar to the dry processed separators. The thickness of the microporous support membrane can be in a range of 10-400 micrometers, or a range of 10-200 micrometers, or a range of 10-100 micrometers, or a range of 20-100 micrometers. The pore size of the microporous membrane can be in a range of 10 nanometers to 50 micrometers, or a range of 50 nanometers to 10 micrometers, or a range of 0.2 micrometers to 1 micrometer.
Another aspect of the invention is a membrane electrode assembly. In one embodiment, the membrane electrode assembly comprises: an anion exchange membrane comprising the polymer described above; a cathode comprising a cathode catalyst on a first surface of the anion exchange membrane; and optionally an anode comprising an anode catalyst on a second surface of the anion exchange membrane.
In some embodiments, the membrane electrode assembly further comprises: a cathode porous transport layer adjacent to the cathode; and an anode porous transport layer or an anode catalyst-coated anode porous transport layer adjacent to the anode. In some embodiments, the anode and the cathode catalysts are platinum group metal (PGM)-free electrocatalysts. The anode and the cathode catalysts are for oxygen evolution reaction and hydrogen evolution reaction, respectively. The anode and the cathode catalysts should have low cost, good electrical conductivity, and good electrocatalytic activity and stability. Suitable PGM-free cathode catalysts can be selected from, but are not limited to, Ni-based alloys such as Ni—Mo, Ni—Al, Ni—Cr, Ni—Sn, Ni—Co, Ni—W, and Ni—Al—Mo, metal carbides such as Mo2C, metal phosphides such as CoP, metal dichalcogenides such as MoSe2, and mixtures thereof. Suitable anode catalysts can be selected from, but are not limited to, Ni—Fe alloy, Ni—Mo alloy, spinel CuxCo3xO3, Ni—Fe layered double hydroxide nanoplates, immobilized metal catalyst on conductive supports, and mixtures thereof. In some embodiments, the anode and the cathode catalysts are PGM electrocatalysts. Suitable PGM cathode catalysts can be selected from, but are not limited to, platinum, ruthenium, osmium, rhodium, palladium, tin, tungsten, vanadium, cobalt, silver, gold, nickel, molybdenum, iron, copper, chromium, alloys thereof, oxides thereof, carbides thereof, phosphides thereof, or combinations thereof. Suitable PGM anode catalysts can be selected from, but are not limited to, iridium, platinum, ruthenium, osmium, rhodium, palladium, tin, tungsten, vanadium, cobalt, silver, gold, copper, nickel, molybdenum, iron, chromium, alloys thereof, oxides thereof, carbides thereof, phosphides thereof, or combinations thereof.
In some embodiments, the cathode comprising a cathode catalyst on a first surface of the anion exchange membrane is formed by coating a cathode catalyst ink on the first surface of the anion exchange membrane via meniscus coating, knife coating, spray coating, painting, gravure coating, comma roll coating, or other known conventional ink coating technologies, followed by drying the coated anion exchange membrane.
In some embodiments, the anode comprising an anode catalyst on a second surface of the anion exchange membrane is formed by coating an anode catalyst ink on the second surface of the anion exchange membrane via meniscus coating, knife coating, spray coating, painting, gravure coating, comma roll coating, or other known conventional ink coating technologies, followed by drying the coated anion exchange membrane.
In some embodiments, the anode catalyst ink comprises the anode catalyst, an OH− exchange ionomer as a binder, and a solvent. In some embodiments, the cathode catalyst ink comprises the cathode catalyst, an OH− exchange ionomer as a binder, and a solvent. The OH− exchange ionomer binder creates OH− transport pathways between the membrane and the reaction sites within the electrodes and thus drastically improves the utilization of the electrocatalyst particles while reducing the internal resistance. The OH− exchange ionomer binder can have a chemical structure similar to the anion exchange polymer described above, so that the binder will allow low interfacial resistance and similar expansion in contact with water to avoid catalyst delamination, but OH− conductivity and high oxygen and hydrogen permeance. The OH− exchange ionomer binder can have a chemical structure similar to the anion exchange polymer described above, but with different counterions such as bicarbonate (HCO3−) counterions. The solvent can be selected from, but is not limited to, water, alcohol, or a mixture thereof.
The anode porous transport layer and the cathode porous transport layer simultaneously transport electrons, heat, and products with minimum voltage, current, thermal, interfacial, and fluidic losses. The cathode porous transport layer can be made from, but is not limited to, stainless steel, titanium meshes, titanium felts, titanium foams, or carbon-based materials such as non-woven carbon paper, non-woven carbon cloth, or woven carbon cloth. The anode porous transport layer can be made from, but is not limited to, stainless steel, titanium meshes, titanium felts, or titanium foams.
The poly(terphenylene-co-phenanthrenylene piperidinium iodide) (abbreviated as PTPP-I) polymer with iodide counterions as described in Example 2 of U.S. patent application Ser. No. 17/823,975 was converted to poly(terphenylene-co-phenanthrenylene piperidinium acetate) (abbreviated as PTPP-OAc) via an ion exchange reaction as shown in
The poly(terphenylene-co-phenanthrenylene piperidinium iodide) (abbreviated as PTPP-I) polymer with iodide counterions as described in Example 2 of U.S. patent application Ser. No. 17/823,975 was converted to poly(terphenylene-co-phenanthrenylene piperidinium bicarbonate) polymer (abbreviated as PTPP-HCO3−) via an ion exchange reaction. 100 g of PTPP-I anion exchange polymer was dispersed in 4 L of 2.0 wt % sodium bicarbonate aqueous solution and stirred for 1 h at ambient temperature. The mixture was filtered, and the filter cake was resuspended in 4 L 2.0 wt % sodium bicarbonate aqueous solution to repeat the ion exchange and filtration procedure. The ion exchange and filtration steps were repeated several times to completely exchange the iodide anions to bicarbonate anions. The product was soaked in 4 L of reverse osmosis water under stirring for 1 h and filtered. The water soaking and filtration was repeated three times. The obtained filtered product was then dried at 60° C. for at least 24 h to produce PTPP-HCO3− polymer.
A PTPP-OAc anion exchange polymer membrane was prepared by dissolving the PTPP-OAc anion exchange polymer as described in Example 1 (5.0 g) in DMSO (20 g), casting the solution on a clean substrate, and drying at 60° C. overnight. The membrane was peeled off the substrate and further dried in a vacuum oven at 100° C. for 48 h. The PTPP-OAc membrane was ion exchanged in 1 M KOH aqueous solution for 10 h to convert PTPP-OAc anion exchange membrane with acetate anions to an anion exchange membrane with OH− anions (abbreviated as PAPP-OH membrane) to measure its in-plane hydroxide conductivity. The in-plane hydroxide conductivity of the PAPP-OH membrane was 126.8 mS/cm at room temperature.
A cathode catalyst ink was prepared by mixing 40% Pt/C catalyst, PAPP-HCO3− polymer as an ionomer as prepared in Example 2 in H2O and ethanol. The mixture was finely dispersed using an ultrasonication bath. The cathode catalyst ink was coated onto one surface of the PAPP-OAc anion exchange membrane as prepared in Example 3 via spray coating or Mayer Rod coating technique. The Pt loading was about 0.15 mg/cm2.
A PTPP-HCO3− anion exchange polymer membrane was prepared by dissolving the PTPP-HCO3− anion exchange polymer as described in Example 2 (5.0 g) in ethanol (30 g), casting the solution on a clean substrate, and drying at 50° C. overnight. The membrane was peeled off the substrate and further dried in a vacuum oven at 100° C. for 48 h.
A cathode catalyst ink was prepared by mixing 40% Pt/C catalyst, PAPP-HCO3− polymer as an ionomer as prepared in Example 2 in H2O and ethanol. The mixture was finely dispersed using an ultrasonication bath. The cathode catalyst ink was coated onto one surface of the PTPP-HCO3− anion exchange membrane as prepared in Comparative Example 1 via spray coating or Mayer Rod coating technique. The Pt loading was about 0.15 mg/cm2.
An anode catalyst ink was prepared by mixing a PGM anode catalyst IrO2, PAPP-HCO3− ionomer as prepared in Example 2 in H2O and ethanol. The mixture was finely dispersed using an ultrasonication bath. The IrO2 anode catalyst ink was spray coated onto one surface of a stainless steel porous transport layer to form IrO2 anode catalyst coated stainless steel porous transport layer (abbreviated as IrO2/PTL). The IrO2 anode catalyst loading was about 2.0 mg/cm2.
An anion exchange membrane (AEM) water electrolysis test station was used to evaluate the water electrolysis performance of (a) Pt/PAPP-OAc 2-layer MEA as prepared in Example 4 and (b) Pt/PTPP-HCO3− 2-layer MEA in a single electrolyzer cell with an active membrane area of 5 cm2. The test station included an integrated power supply, a potentiostat, an impedance analyzer for electrochemical impedance spectroscopy (EIS) and high-frequency resistance (HFR), and real-time sensors for product flow rate and cross-over monitoring. The Pt/PAPP-OAc 2-layer MEA or the Pt/PTPP-HCO3− 2-layer MEA was sandwiched between a carbon paper (as a cathode PTL) and the IrO2/PTL as prepared in Example 5. The testing was conducted at 80° C. and at atmospheric pressure. An ultrapure water feed was supplied to both the anode and cathode sides of the electrolyzer with a flow rate of 100 mL/min. The polarization curve was collected at 80° C., and the results are shown in
While the following is described in conjunction with specific embodiments, it will be understood that this description is intended to illustrate and not limit the scope of the preceding description and the appended claims.
A first embodiment of the invention is a composition comprising a plurality of repeating units of formula (I)
wherein Ar1 is selected from the group consisting of
and mixtures thereof; X1 is selected from the group consisting of
optionally
and mixtures thereof; wherein Y1− or Y2− or both are
wherein R1-R28 are each independently hydrogen, a halide, an alkyl group, an alkenyl group, an alkynyl group, or an aryl group, and the alkyl, alkenyl, alkynyl, or aryl groups are optionally substituted with a halide or a positively charged functional group; wherein R29-R31 are each independently hydrogen, an alkyl group, an alkenyl group, an alkynyl group, or an aryl group, and the alkyl, alkenyl, alkynyl or aryl groups are optionally substituted with a halide or a positively charged functional group; wherein R32 is an alkyl group, an alkenyl group, an alkynyl group, or an aryl group, and the alkyl, alkenyl, alkynyl or aryl group is optionally substituted with a halide or a positively charged functional group; wherein R50 is CH3, CF3, CH3CH2, or CH3CH2CH2; wherein A is O, S, or NR100; wherein R100 is hydrogen, an alkyl group, an alkenyl group, an alkynyl group, or an aryl group, and the alkyl, alkenyl, alkynyl, or aryl groups are optionally substituted with a halide or a positively charged functional group; wherein n is an integer from 10 to 1000; wherein p is 1, 2, 3, or 4; wherein q is 0, 1, 2, or 3; and wherein t is 1, 2, 3, 4, 5, or 6. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein Ar1 is selected from the group consisting of
and mixtures thereof; wherein R25, R26, R27, and R28 are each independently —H or —CH3; wherein p is 1 or 2; and wherein q is 0 or 1. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein Ar1 is selected from the group consisting of
and mixtures thereof. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein Ar1 is selected from the group consisting of
and mixtures thereof. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein X1 is
wherein R30 and R31 are each independently —H, —CH3, —CH2CH3, —CH(CH3)2, —C(CH3)3, —CH2—C6H5, or —CH2—CH(CH3)2, wherein Y1− is
and wherein R50 is CH3, CF3, CH3CH2, or CH3CH2CH2. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein X1 is
wherein t is 1, 2, 3, 4, 5, or 6, wherein Y2− is
and wherein R50 is CH3, CF3, CH3CH2, or CH3CH2CH2. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein X1 is a mixture of
wherein R30 and R31 are each independently —H, —CH3, —CH2CH3, —CH(CH3)2, —C(CH3)3, —CH2—C6H5, or —CH2—CH(CH3)2; wherein t is 1, 2, 3, 4, 5, or 6; wherein Y1− and Y2− are
and wherein R50 is CH3, CF3, CH3CH2, or CH3CH2CH2. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the anion exchange polymer is synthesized from monomers Ar1′, and X1′ wherein Ar1′ is selected from the group consisting of
and mixtures thereof; and X1′ is selected from the group consisting of
optionally
and mixtures thereof; wherein Y2− is
wherein R50 is CH3, CF3, CH3CH2, or CH3CH2CH2; wherein R1-R28 are each independently hydrogen, a halide, an alkyl group, an alkenyl group, an alkynyl group, or an aryl group, and the alkyl, alkenyl, alkynyl, or aryl groups are optionally substituted with a halide or a positively charged functional group; wherein R29 and R30 are each independently hydrogen, an alkyl group, an alkenyl group, an alkynyl group, or an aryl group, and the alkyl, alkenyl, alkynyl or aryl groups are optionally substituted with a halide or a positively charged functional group; wherein R32 is an alkyl group, an alkenyl group, an alkynyl group, or an aryl group, and the alkyl, alkenyl, alkynyl or aryl group is optionally substituted with a halide or a positively charged functional group; wherein A is O, S, or NR100; wherein R100 is hydrogen, an alkyl group, an alkenyl group, an alkynyl group, or an aryl group, and the alkyl, alkenyl, alkynyl, or aryl groups are optionally substituted with a halide or a positively charged functional group; wherein p is 1, 2, 3, or 4; wherein q is 0, 1, 2, or 3; and wherein t is 1, 2, 3, 4, 5, or 6. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein Ar1′ is selected from the group consisting of
and mixtures thereof; wherein R25, R26, R27, and R28 are each independently —H or —CH3; wherein p is 1 or 2; and wherein q is 0 or 1. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein Ar1′ is selected from the group consisting of
and mixtures thereof. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein Ar1′ is selected from the group consisting of
and mixtures thereof. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein X1′ is
and wherein R30 is —H, —CH3, —CH2CH3, —CH(CH3)2, —C(CH3)3, —CH2—C6H5, or —CH2—CH(CH3)2. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein X1′ is
wherein t is 1, 2, 3, 4, 5, or 6, wherein Y2− is
wherein R50 is CH3, CF3, CH3CH2, or CH3CH2CH2. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein X1′ is a mixture of composition wherein t is 1, 2, 3, 4, 5, or 6, wherein Y2− is
and wherein R50 is CH3, CF3, CH3CH2, or CH3CH2CH2. A system comprising the anion exchange polymer. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the anion exchange membrane is used in a fuel cell, an electrolyzer, a flow battery, an electrodialyzer, a waste metal recovery system, an electrocatalytic hydrogen production system, a desalinator, a water purifier, a waste water treatment system, an ion exchanger, or a CO2 separator. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the anion exchange membrane comprises a nonporous symmetric dense film membrane, an integrally-skinned asymmetric membrane, a reinforced composite membrane, or a thin film composite membrane. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the integrally-skinned asymmetric membrane, the reinforced composite membrane, or the thin film composite membrane comprises a porous substrate material impregnated or coated with the anion exchange polymer.
A second embodiment of the invention is a membrane electrode assembly, comprising an anion exchange membrane comprising the anion exchange polymer; a cathode comprising a cathode catalyst on a first surface of the anion exchange membrane; and optionally an anode comprising an anode catalyst on a second surface of the anion exchange membrane. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph wherein the assembly further comprises a cathode porous transport layer adjacent to the cathode; and an anode porous transport layer or an anode catalyst-coated anode porous transport layer adjacent to the anode.
Without further elaboration, it is believed that using the preceding description that one skilled in the art can utilize the present invention to its fullest extent and easily ascertain the essential characteristics of this invention, without departing from the spirit and scope thereof, to make various changes and modifications of the invention and to adapt it to various usages and conditions. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limiting the remainder of the disclosure in any way whatsoever, and that it is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.
In the foregoing, all temperatures are set forth in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.
