Design Of Proton Exchange Membranes Research Articles

Designing continuous proton-conductive channels for direct methanol fuel cell through the sulfonated poly(ether ether ketone)/carbon quantum dot/graphitic carbon nitride nanosheet

In this research, new nanocomposite membranes were fabricated based on sulfonated poly(ether ether ketone)/carbon quantum dot/graphitic carbon nitride nanosheet (SPEEK/CQD/g-C3N4). It was found that anchoring CQD onto g-C3N4 provides a new proton transport pathway in the design of proton exchange membranes for high-performance fuel cell applications. The uniform distribution of CQDs on the nanosheets and the interaction of hydrophilic groups such as the –NH2 and CO with the -SO3H of the polymer matrix creates a hydrogen bond transfer network and facilitates the protons transfer based on the Grotthuss mechanism. The incorporation of CQD/g-C3N4 in the polymer matrix has increased the proton conduction from 0.023 S/cm for SPEEK at 20 °C and 100 % R.H. to 0.052 S/cm for the SPEEK/CQD/g-C3N4-3 %wt. The proton conduction for the nanocomposite membrane containing 3 wt% CQD/g-C3N4 improved at higher temperatures (0.128 S/cm at 80 °C) and also, this membrane showed better thermal properties (maximum Tg at 176 °C). Compared to the SPEEK membrane, the nanocomposite membrane with 3 wt% CQD/g-C3N4 had a better single-cell direct methanol fuel cell (DMFC) test performance.

Proton exchange membranes for polymer electrolyte fuel cells: An analysis of perfluorosulfonic acid and aromatic hydrocarbon ionomers

The design of proton-exchange membranes (PEMs) for high-performance, durable fuel cells and related electrochemical devices requires a delicate balance between high ion-exchange capacity and proton conductivity, while ensuring robust mechanical properties and preserving dimensional, chemical and thermal stability. In addition, low species crossover is desirable to reduce hydrogen peroxide formation. Ionomers used in PEMs can be classified into two main groups: (i) perfluorosulfonic acid (PFSA) polymers, and (ii) aromatic hydrocarbon (HC) polymers. In this work, an analysis of key characteristics of both PEM types is presented, including water uptake, proton conductivity, water transport properties, thermal conductivity, permeability, mechanical properties and chemical and thermal stability, among others. Comparatively, PFSA-based PEMs are undoubtedly the commercial standard due to its proven high proton conductivity and good chemical stability, even though PTFE-reinforced aromatic HC-based PEMs have also started to be commercialized recently. In the last decades, a growing trend is identified toward the development of hybrid and composite ultra-thin PEMs (5–20 μm in thickness) with tailored properties, e.g., incorporating microporous fillers to enhance water uptake and layered reinforced microstructures to improve mechanical properties and chemical stability. PEM design is to be accomplished in an environmentally friendly circular economy with facilitated recycling and re-utilization.

Design of proton exchange membranes with high durability for fuel cells: From the perspective of machine learning

Proton exchange membranes (PEMs)（） with high chemical durability have been generally researched in recent years. Free radical scavengers such as ceria can significantly suppress the chemical degradation of proton exchange membranes when added to proton exchange membranes. However, proton conductivity may decline in the presence of ceria. Thus, a trade-off between performance and durability in ceria-containing membranes emerges. To address this challenge, we developed a novel machine learning methodology called SPARK (Smart Prediction of Advanced Research on PEMs using Knowledge-based machine learning) to quickly predict the performance and durability of proton exchange membranes in fuel cell applications with high precision. Moreover, with the definition of the mixed index, the performance and durability were coupled, and the trade-off of performance and durability could be easily made. The SPARK methodology not only streamlines the design process for ceria-containing proton exchange membranes but also has broader implications for the development of other proton exchange membrane systems.

Monitoring and Modeling of Compression Creep of Perfluorosulfonic Acid Membranes for Electrolyzers

Water-splitting electrolyzers are a key technology for enabling the hydrogen economy and reshaping the renewable energy landscape. Among the most viable candidates for the low-temperature electrolyzers is the proton-exchange membrane (PEM) water-splitting electrolyzers (PEMWEs), which uses an ion-conductive polymer solid-electrolyte. For PEMWEs to be commercially viable, PEMs must perform over long operational times in liquid environments under compression and therefore must exhibit good mechanical stability when hydrated. [1-2]. While a hydrated environment is an intrinsic result of the operation and membrane’s conductive function, it undermines PEM stability. [3] PEMs are under unique mechanical stresses due to differential pressure affecting the active area, and high sealing pressures to prevent off-board leaks, thus, high differential pressure in PEMWEs makes compressive creep a great concern. [4] However, mechanical stability of PEMs is commonly characterized by tensile testing [5], the applicability of which to electrolyzers or technologies with similar cell designs is unclear. Using compression and compression creep data of hydrated PEMs in situ and in controlled temperature [6], this work develops a material model to describe PEM under device-relevant operation.An important aspect of PEM design consideration is the stability of membrane, especially under conditions relevant to operation, such as, in a liquid environment with varying range of temperatures (50 to 80 °C). While hydration, pressure, and temperature are used as design parameters for optimizing electrolyzers performance, their role in durability is not established [5]. This creates a gap between performance and lifetime assessment of membranes for electrolyzers. Thus, there is need for a model that could capture membrane durability by accounting for performance operators. This study identifies compression creep as a potential material stability metric that can account for the operation-dependent variables, such as pressure, dehydration, and temperature, and provides guidance for better assessment of membrane lifetime in electrolyzers and similar electrochemical devices.Our results show compressive response of perfluorosulfonic acid (PFSA) membranes is significantly different than tensile behavior in both dry and hydrated states [6]. Moreover, PEMs exhibit creep response under compression with continuous decrease in its thickness over 24 hours, with a dependence on the applied pressure and temperature [6]. This work demonstrates the importance of studying the mechanical properties of PEMs under compression, which is more relevant to the stress-states the membrane undergoes during operation in an electrolyzer and similar electrochemical devices.

Optimization of Proton Exchange Membrane Electrolyzer Cell Design Using Machine Learning

We propose efficient multiple machine learning (ML) models using specifically polynomial and logistic regression ML methods to predict the optimal design of proton exchange membrane (PEM) electrolyzer cells. The models predict eleven different parameters of the cell components for four different input parameters such as hydrogen production rate, cathode area, anode area, and the type of cell design (e.g., single or bipolar). The models fit well as we trained multiple machine learning models on 148 samples and validated the model performance on a test set of 16 samples. The average accuracy of the classification model and the mean absolute error is 83.6% and 6.825, respectively, which indicates that the proposed technique performs very well. We also measured the hydrogen production rate using a custom-made PEM electrolyzer cell fabricated based on the predicted parameters and compared it to the simulation result. Both results are in excellent agreement and within a negligible experimental uncertainty (i.e., a mean absolute error of 0.615). Finally, optimal PEM electrolyzer cells for commercial-scaled hydrogen production rates ranging from 500 to 5000 mL/min were designed using the machine learning models. To the best of our knowledge, we are the first group to model the PEM design problem with such large parameter predictions using machine learning with those specific input parameters. This study opens the route for providing a form of technology that can greatly save the cost and time required to develop water electrolyzer cells for future hydrogen production.

Compressive Creep of Perfluorosulfonic Acid Membranes in Controlled Environments

For proton-exchange membrane (PEM) water-splitting electrolyzers (PEMWEs) to be commercially viable, PEMs must perform over long operational times in liquid environments under compression and therefore must exhibit good mechanical stability when hydrated [1], [2]. While a hydrated environment is an intrinsic result of the operation and membrane’s conductive function, it undermines PEM stability [3]. They are under unique mechanical stresses due to differential pressure affecting the active area, and high sealing pressures to prevent off-board leaks, thus, high differential pressure in PEMWEs makes compressive creep a great concern [4]. However, mechanical stability of PEMs is commonly characterized by tensile testing [5], the applicability of which to electrolyzers or technologies with similar cell designs is unclear. In this study, a compression setup was developed to monitor creep response of hydrated PEMs in situ and in controlled temperature.Water-splitting electrolyzers are a key technology for enabling the hydrogen economy and reshaping the renewable energy landscape. Among the most viable candidates for the low-temperature electrolyzers is the proton-exchange membrane (PEM) water-splitting electrolyzers (PEMWEs), which uses an ion-conductive polymer solid-electrolyte. Stability, in liquid environments at temperatures ranging from 50 to 80 °C, is an important aspect of PEM design considerations. While hydration, pressure, and temperature are used as design parameters for optimizing electrolyzer performance, their role in durability is not established [5]. This creates a gap between performance and lifetime assessment of membranes for electrolyzers. Thus, there is need for a metric that could capture membrane durability by accounting for performance operators. This study identifies compression creep as a potential material stability metric that can account for the operation-dependent variables, such as pressure, dehydration, and temperature, and provides guidance for better assessment of membrane lifetime in electrolyzers and similar electrochemical devices.Our results show compressive response of perfluorosulfonic acid (PFSA) membranes is significantly different than tensile behavior in both dry and hydrated states [6]. Moreover, PEMs exhibit creep response under compression with continuous decrease in its thickness over 24 hours, with a dependence on the applied pressure and temperature [6]. This work demonstrates the importance of studying the mechanical properties of PEMs under compression, which is more relevant to the stress-states the membrane undergoes during operation in an electrolyzer and similar electrochemical devices.

Research Progress of Proton Exchange Membrane Failure and Mitigation Strategies.

Proton exchange membrane (PEM) is critical for the efficient, reliable and safe operation of proton exchange membrane fuel cells (PEMFC). The lifetime of PEM is the main factor restricting the commercialization of PEMFC. The complexity of operating conditions, such as open-circuit/idling, dynamic load and startup-shutdown under automotive conditions, on PEMFC will cause the mechanical and chemical degradation of PEM and affect the service life of PEMFC. In order to understand the degradation behavior and durability of PEM, this paper presents an overview of the degradation failure mechanism and mitigation strategies of PEM. The mechanical and chemical degradation behavior of PEM and its causes, as well as the mitigation strategies are discussed in order to give a direction for PEM design and fuel cell system control strategy. It is proposed as a primary principle in order to further develop and promote the durability of PEM, to focus on the material improvement and system engineering.

Theoretical Understanding of Mechanisms of Proton Exchange Membranes Made of 2D Crystals with Ultrahigh Selectivity

Recent reports on proton conduction across pristine graphene and hexagonal boron nitride (h-BN) provide a new avenue for the design of proton exchange membranes. The uniform pores formed by the electron clouds of two-dimensional (2D) crystals can effectively block the undesired transportation of other species thus ultrahigh selectivity can be achieved. With the aid of first-principles calculations, we investigate the proton conduction process across six kinds of intact 2D crystals, namely graphene, h-BN, β12 boron sheet, χ3 boron sheet, phosphorene, and silicene. To clarify the proton conduction mechanism, three proton penetration modes are proposed: dissociation-penetration, adsorption-penetration, and direct penetration. Based on our calculation results, for graphene and h-BN without atomic defects, they are unlikely to provide sufficient proton conductivity at room temperature when no bias potential is applied. By contrast, the β12 boron sheet, χ3 boron sheets, and silicene exhibit relatively lower proton penetration energy barriers, making them prospective candidates for future proton exchange membrane applications.

Building block candidates for the design of proton exchange membranes: Maleimide and its homologues

Density functional theory (DFT) calculations are applied to the study of proton transport in maleimide and its homologues, succinimide and phthalimide. The calculations reproduce correctly their structural characteristics and reveal the hydrogen bonding and proton hopping properties. Specifically, the calculations show that the potential barrier for proton transfer between two maleimide molecules is about 30.60 kcal mol−1 mediated by one or two water molecules with correction of solvation effect by water, and will decrease to about 13.22 kcal mol−1 if ethylphosphonic acid molecule is used as mediator with correction of solvation effect by phosphoric acid. In addition, the calculations also show that succinimide and phthalimide possess similar characteristics compared to maleimide. Finally, it is concluded that maleimide and its homologues are building block candidates for the design of high-temperature proton exchange membranes.

Maleimide: a potential building block for the design of proton exchange membranes studied by ab initio molecular dynamics simulations

Ab initio molecular dynamics (AIMD) simulations are applied to the study of proton transport in solid state maleimide.

Considerations of the morphology in the design of proton exchange membranes: Cross-linked sulfonated poly(ether ether ketone)s using a new carboxyl-terminated benzimidazole as the cross-linker for PEMFCs

A novel benzimidazole trimer (alkyl-BI) was synthesized using 3,3′-diaminobenzidine and succinic acid as monomers, and then a series of cross-linked membranes (c-SPEEK-Xs) were prepared by a heating method using the alkyl-BI as the cross-linker. We systematically studied the water uptake and swelling ratio, thermal and chemical stability, mechanical properties, proton conductivity, and methanol permeability of the cross-linked membranes as a function of different loading ratios of the alkyl-BI trimer. All of the properties of the cross-linked membranes were significantly improved over membranes consisting of unmodified SPEEK. In particular, the performance of the c-SPEEK-Xs membranes was compared to that of a cross-linked membrane, c-SPEEK-BI7, which was prepared by using rigid-BI as the cross-linker. The latter cross-linker was synthesized by using 3,3′-diaminobenzidine and isophthalic acid as monomers in order to investigate how cross-linkers with different structures affect the morphology and properties of the membranes. Transmission electron microscopy (TEM) analysis showed that c-SPEEK-BI7 and the c-SPEEK-6.5% possess different hydrophilic/hydrophobic two-phase separation morphologies, which have dramatic effects on the proton conductivity and methanol permeability.

Mechanisms of Morphology Development and Water Motion in Proton Exchange Membranes

Two critical parameters of nanophase morphology and water motion are discussed in the design of proton exchange membranes (PEMs). While much has been learned about the function of proton exchange membranes by studying poly(perfluorosulfonic acid) and sulfonated aromatic polymers, new generations of electrolytes for aqueous applications are being developed that push the limits of ion conductivity and small molecule transport rates in water-absorbing polymers. The utility of employing block copolymers has been demonstrated to concentrate and affect long-range connectivity of ionic domains, but the details of how ions arrange in these systems are still to be explored. Examples of block copolymer proton exchange membranes and their usefulness in understanding membrane function will be reviewed. Additionally, water motion in PEMs is critical to achieving sufficient proton conductivity. The relationship between water motion and conductivity can be used to design new materials with insight of the water-polymer interactions in the system.

Synthesis and performance evaluation of a polymer mesh supported proton exchange membrane for fuel cell applications

Abstract A novel approach to the design and fabrication of proton exchange membrane (PEM) has been developed whereby a non-structural polymer fabricated with high proton exchange capacity was bound to an inert polymer matrix. The patented fabrication techniques used here allow greater flexibility in PEM design. Results related to proton exchange performance of these novel PEMs are presented here. The proton exchange material described herein is a ter-polymer composed of various ratios of monomers. These materials were bound to an inert ethylene–tetrafluoroethylene (ETFE) copolymer mesh that had been rendered adhesive using patented hydroxylation technique in a two-step water-borne process. The basic characteristics of the new membranes were compared to those of Nafion ® 212. An aqueous two-cell testing unit is utilized by which the rate of protons transferred from one cell through the membrane into the other cell was determined by monitoring the change in pH of the cells. Results indicated that the new membrane could transfer protons approximately 10 times faster per unit area compared to Nafion ® 212 under the test conditions utilized at 80 °C. In addition to improvement in induction time and reduced resistance, the new membrane conducts protons at reduced membrane water content compared to Nafion ® 212.