High-performance Proton Exchange Membranes Research Articles

High-performance proton-exchange membrane water electrolysis using a sulfonated poly(arylene ether sulfone) membrane and ionomer

Sulfonated poly(arylene ether sulfone) with degree of sulfonation of 50 mol.% (SPAES50) was synthesized for the preparation of a hydrocarbon-based membrane and ionomer, for application to proton-exchange membrane water electrolysis (PEMWE) as an alternative to Nafion™. The SPAES50 membrane showing the excellent physical and electrochemical properties as well as the SPAES50-based ionomer (P50) were prepared and applied to PEMWE to evaluate its performance. The effects of the membrane thickness and ionomer content were also investigated to realize high-performance SPAES-based PEMWE. The proposed SPAES-based PEMWE showed higher performance than that of commercial PEMWE with a Nafion™ membrane and ionomer. Additionally, this is the best performance reported to date, and it is attributed to the low ohmic resistance caused by the high proton conductivity of SPAES50 membrane and the small membrane thickness (20 μm). Therefore, we demonstrate the great potential of SPAES50 as a hydrocarbon-based membrane and ionomer in PEMWE.

Dendritic gold-supported iridium/iridium oxide ultra-low loading electrodes for high-performance proton exchange membrane water electrolyzer

The insufficient performance of current oxygen evolution reaction (OER) electrodes limits the realization of clean hydrogen production via proton exchange membrane water electrolyzers (PEMWEs). Herein, an innovative electrode design with an ultra-low Ir loading is proposed to achieve high catalytic OER performance, catalyst utilization, conductivity, and mass transfer. The microgram-scale loading of Ir on a highly roughened dendritic Au support is controlled by the number of Ir deposition pulses and, together with Ir coverage, which significantly affect the Ir electronic structure and intrinsic OER activity. Further control of the Ir electronic structure is achieved by forming Ir oxides via electrochemical and thermal oxidation to adjust the activity–stability balance. A PEMWE employing the fabricated electrode demonstrates substantially low ohmic and mass-transfer losses, especially in the higher-current-density region. As a result, superior cell performance with extremely high mass activity is achieved, significantly exceeding the mass activities of state-of-the-art Ir-based anodes.

Advancements in proton exchange membranes for high-performance high-temperature proton exchange membrane fuel cells (HT-PEMFC)

Abstract The high-temperature proton exchange membrane fuel cell (HT-PEMFC) offers several advantages, such as high proton conductivity, high CO tolerance, good chemical/thermal stability, good mechanical properties, and low cost. The proton exchange membrane (PEM) is the critical component of HT-PEMFC. This work discusses the methods of current PEMs development for HT-PEMFC including modifications of Nafion® membranes and the advancement in composite PEMs based on non-fluorinated polymers. The modified Nafion®-based membranes can be used at temperatures up to 140 °C. Nevertheless, the application of Nafion®-based membranes is limited by their humidification with water molecules acting as proton carriers and, thus, by the operation conditions of membranes under a relative humidity below 20%. To obtain PEMs applied at higher temperatures under non-humidified conditions, phosphoric acid (PA) or ionic liquids (ILs) are used as proton carriers in PEMs based on non-fluorinated polymers. The research discussed in this work provides the approaches to improving the physicochemical properties and performance fuel cell of PEMs. The effects of polymer blending, crosslinking, and the incorporation of inorganic particles on the membrane properties and fuel cell performance have been scrutinized. The incorporation of inorganic particles modified with ILs might be an effective approach to designing high-performance PEMs for HT-PEMFC.

Polymer grafted GO/sulfonated copolyimide proton exchange nanocomposite membrane: as a polymer electrolyte membranes fuel cell

Attaining a high performance proton exchange membrane as a suitable replacement for Nafion is one of the research priorities of fuel cell research. In this regard, we synthesized a copolyimide consisting of sulfonic acid substituents filled with different content of GO grafted sulfonated poly (urea-co-urethane) via in situ condensation polymerization. All nanocomposites showed a significant increase in thermal, mechanical properties, ion exchange capacity (IEC), water uptake (WU) and proton conductivity by incorporation of the modified GO nanosheets and the best results were found for membrane containing 1 wt% modified GO loading. The nanocomposite membrane with 1 wt% modified GO nanosheets exhibits 0.73 meq g−1 IEC and 7.3 mS cm−1 proton conductivity at room temperature. A single fuel cell test of this membrane demonstrates a maximum power density of 26.30 mW cm−2 at 0.26 V.

Ordered proton channels constructed from deoxyribonucleic acid-functionalized graphene oxide for proton exchange membranes via electrostatic layer-by-layer deposition

Based on the construction strategy of proton transport channels, we design a high-performance proton exchange membrane (PEM) with ordered deoxyribonucleic acid (DNA)-functionalized graphene oxide (GO) and Nafion matrix via the electrostatic layer-by-layer deposition (ELD) technique, which is a novel method of membrane formation aided by electrostatic force. The effects of different content rations of single-strand DNA (ss-DNA) molecules and GO (ss-DNA@GO) on the proton conductivity, methanol permeability, and single cell performance of composite PEMs are investigated. The composite membrane shows a high proton conductivity of 351.8 mS cm−1 (80 °C, 100%RH) but a low methanol permeability of 1.63 × 10−7 cm2 s−1 at room temperature. Furthermore, the composite membranes are assembled into direct methanol fuel cells at 60 °C, and Nafion/DNA@GO-2/5 exhibits a maximum power density of 255.33 mW cm−2, which is 2.42 times higher than that of pure Nafion. This work explores the application potential of DNA@GO in PEM and provides a bioinspired avenue to designing next-generation high-performance PEM for fuel cells.

Sulfonated poly(arylene ether sulfone) composite membrane having sulfonated polytriazole grafted graphene oxide for high-performance proton exchange membrane fuel cells

We investigated the effect of graphene oxide (GO) and sulfonated polytriazole grafted graphene oxide (SPTA-GO) on sulfonated poly(arylene ether sulfone) (SPAES) based polymer electrolytes for application in proton exchange membrane fuel cells. GO was fabricated by the chemical oxidation of graphite and SPTA-GO was prepared via the click reaction using copper (Ⅰ) catalyzed azide-alkyne 1,3-dipolar cycloaddition between ethynyl-terminated sulfonated polytriazole (E-SPTA) and azide functionalized GO (N3-GO). All the SPAES based composite membranes with GO and SPTA-GO revealed better physical/chemical stabilities and mechanical strength than the pristine SPAES membrane, while noticeable improvement of proton conductivity was only observed in the SPAES composite membrane with SPTA-GO since the SPTA moiety attached on GO has both sulfonic acid and triazole groups that can introduce the additional proton conducting channels into the SPAES matrix. The maximum power density of the membrane electrode assembly employing the SPAES composite membrane with SPTA-GO reached up to 1.58 W cm−2 at 80 °C and 100% RH condition, which is larger than that employing commercial Nafion 212 (1.33 W cm−2).

Systematic assessment of the anode flow field hydrodynamics in a new circular PEM water electrolyser

In this work, we investigated the key underlying flow characteristics of a circular unit cell proton exchange membrane (PEM) water electrolyser. In particular, we focused on investigating anode flow field design using computational fluid dynamics (CFD) tool. Transient, 3D single phase fluid flow simulation results were presented, and in-house experiments were conducted for validation against CFD simulation data identifying key performance parameters of the PEM water electrolyser: uniform water distribution, pressure drop and hydraulic retention time. The effects of the water flow rate, inlet and outlet sizing and different number of inlet and outlet configurations were considered. The main observation from the study was discussed to provide insight into the factors affecting the flow pattern. Among the studied flow field design cases, it was found that the average pressure drop decreased with increase in number of inlets, also flow profile can be grouped into different set, depending on number of inlets. The correlation between pressure drop and mean velocity profile for different inlet and outlet configurations provides a useful basis to properly design the high performance PEM water electrolyser.

Bio-analogue l-lysine lined arrangement on nanofibers with superior proton-conduction for proton exchange membrane

Manipulating nanophase-separation behavior and constructing ion-channels is of great challenge for optimizing proton transport. Herein, a novel strategy is demonstrated for constructing long-range and consecutive proton-conducting channels by immobilizing bio-analogue l-lysine onto surface of hydrolyzed polyacrylonitrile (PAN) nanofibers (L/P NFs), combing the superiority of the hydrophilicity 3D network structure (3DNWS) of hydrolyzed PAN NFs and the function of l-lysine as proton-conductors. The hybrid proton exchange membranes (PEMs) are fabricated by filling the inter-fiber voids of L/P NFs with Nafion matrix. The acid–base ion-channels formed between –SO3H of Nafion and –NH2 of L/P NFs may offer the abundant hydrogen-bonded networks for proton hopping. The results show L@Nafion hybrid PEMs can reach 0.263 S/cm (80 °C, 100% relative humidity) proton conductivity and 122.82 mW/cm2 power density for fuel-cell performance. Besides, the preponderance of 3DNWS of L/P NFs can considerably facilitate the thermal and dimensional stability as well as restrict methanol crossover for hybrid PEMs. This approach brings a unique vision for preparing high-performance PEMs for direct methanol fuel cells.

Preparation of Covalent-Ionically Cross-Linked UiO-66-NH2/Sulfonated Aromatic Composite Proton Exchange Membranes With Excellent Performance.

Metal-organic frameworks (MOFs), as newly emerging filler materials for polyelectrolytes, show many compelling intrinsic features, such as variable structural designability and modifiability of proton conductivity. In this manuscript, UiO-66-NH2, a stable MOF with -NH2 functional groups in its ligands, was selected to achieve a high-performance sulfonated poly(arylene ether nitrile)s (SPENs)/UiO-66-NH2-x covalent-ionically cross-linked composite membrane. Simultaneously, the obtained composite membranes displayed excellent thermal stability and dimensional stability. The as-prepared SPEN/UiO-66-NH2-x cross-linked membranes exhibited higher proton conductivity than recast SPENs, which can be attributed to the construction of ionic clusters and well-connected ionic nanochannels along the interface between UiO-66-NH2-x and SPEN matrix via molecular interactions. Meanwhile, the methanol permeability of the SPEN/UiO-66-NH2-x composite membrane had been effectively reduced due to the barrier effect of cross-linking and the addition of UiO-66-NH2-x. The SPEN/UiO-66-NH2-5 composite membrane had the highest selectivity of 6.42 × 105 S·s·cm−3: 14.3-times higher than that of Nafion 117. The preparation of cross-linked UiO-66-NH2/SPEN composite was facile, which provides a new strategy for preparing high performance proton exchange membrane.

Robust proton exchange membrane for vanadium redox flow batteries reinforced by silica-encapsulated nanocellulose

High ion selectivity and mechanical strength are critical properties for proton exchange membranes in vanadium redox flow batteries. In this work, a novel sulfonated poly(ether sulfone) hybrid membrane reinforced by core-shell structured nanocellulose (CNC-SPES) is prepared to obtain a robust and high-performance proton exchange membrane for vanadium redox flow batteries. Membrane morphology, proton conductivity, vanadium permeability and tensile strength are investigated. Single cell tests at a range of 40–140 mA cm−2 are carried out. The performance of the sulfonated poly(ether sulfone) membrane reinforced by pristine nanocellulose (NC-SPES) and Nafion® 212 membranes are also studied for comparison. The results show that, with the incorporation of silica-encapsulated nanocellulose, the membrane exhibits outstanding mechanical strength of 54.5 MPa and high energy efficiency above 82% at 100 mA cm−2, which is stable during 200 charge-discharge cycles.

Carbon nanocomposites self‐assembly UiO‐66‐doped chitosan proton exchange membrane with enhanced proton conductivity

One-dimensional (1D) sodium ligninsulfonate functionalized carbon nanotubes (SCNT), two-dimensional (2D) graphene oxide (GO), and three-dimensional (3D) zirconium-based metal-organic frameworks (UiO-66) are self-assembled as filler materials for proton-exchange membranes (PEMs) because of their potential for extending proton transport pathways. Herein, UiO-66-SCNT and UiO-66-SCNT@GO were prepared by a facile solvothermal synthesis and then the nanohybrid chitosan (CS) PEMs were fabricated via solution casting. The hybrid PEMs with higher ion exchange capacity than the pure CS membrane displayed higher proton conductivity and selectivity. The proton conductivity of nanohybrid membrane doped with 7 wt% UiO-66-SCNT@GO (CS/U-S@GO-7) was enhanced to 64 mS cm−1 at 70°C. Simultaneously, the selectivity was reached 19.4 × 104 S s cm−3 and was much higher than the pristine CS membrane (0.13 × 103 S s cm−3). Moreover, the mechanical properties of all composite membranes were significantly enhanced compared with that of the pure CS membrane. The results showed that our research provided a valuable strategy for designing high-performance CS-based PEMs in direct methanol fuel cell (DMFC). Highlights A simple and facile solvothermal synthesis was used to prepare UiO-66-SCNT@GO. UiO-66-SCNT@GO was introduced into chitosan (CS) matrix to optimize proton transport channels. CS-based hybrid membranes exhibit high proton conductivity and selectivity. CS-based hybrid membranes show low methanol permeability.

Biofunctionalized nanofiber hybrid proton exchange membrane based on acid-base ion-nanochannels with superior proton conductivity

Regulating nanophase-separation behavior and constructing ion-nanochannels is of great importance for improving proton transport inside membrane. Herein, a novel strategy is proposed for constructing long-range and consecutive acid–base ion-nanochannels through embedding basic l-Arginine biofunctionalized hydrolyzed polyacrylonitrile nanofibers into acidic sulfonated polysulfone matrix, combing the superiority of the special three-dimensional network structure of nanofibers and the function of basic l-Arginine as proton-conductors. The formed acid–base ion-nanochannels between –SO3H of sulfonated polysulfone and –NH2 of l-Arginine biofunctionalized hydrolyzed polyacrylonitrile nanofibers may offer the abundant hydrogen-bonded networks for proton hopping. The results show nanofiber hybrid proton exchange membranes can achieve 0.216 S/cm (80 °C, 100% relative humidity) proton conductivity and 115.93 mW/cm2 power density for fuel-cell performance. Besides, the preponderance of three-dimensional network structure of nanofibers may considerably facilitate the thermal and dimensional stability as well as restrict methanol crossover for hybrid proton exchange membranes. This approach brings a unique vision for preparing high-performance proton exchange membranes for direct methanol fuel cells.

Zeolitic imidazolate framework decorated on 3D nanofiber network towards superior proton conduction for proton exchange membrane

Manipulating membrane nanophase-separation behavior to construct ion-nanochannels for optimizing proton transport was still a challenge. Herein, a novel strategy was proposed for constructing consecutive ion-nanochannels by combining zeolitic imidazolate framework (ZIF-8) and 3D network structure (3DNWS) of poly-m-phenyleneisophthalamide nanofibers (PMIA NFs) via a hydrothermal method. NF hybrid proton exchange membranes (PEMs) were fabricated by filling the inter-fiber voids of 3DNWS-PMIA/ZIF-8 (P/ZIF-8) NFs with Nafion matrix. The structures of P/ZIF-8 and performance of hybrid PEMs were evaluated. The construction of ZIF-8 on 3DNWS-PMIA NFs enabled channels on the basis of the acid–base pair between –SO3H (Nafion) and N–H (imidazole molecule of ZIF-8) to be longer and consecutive. Results showed that P/ZIF-8@Nafion could reach 0.258 S/cm (80 °C, 100% relative humidity) proton conductivity and 150.60 mW/cm2 power density for single-cell performance. In addition, the superiority of 3DNWS of PMIA NFs considerably promoted the thermal and dimensional stability, especially in methanol crossover for hybrid PEMs. This work provided a new approach for preparing high-performance PEMs for direct methanol fuel cells.

Ladder-type sulfonated poly(arylene perfluoroalkylene)s for high performance proton exchange membrane fuel cells.

Sulfonated poly(arylene perfluoroalkylene)s containing a sulfone-bonded ladder structure (SPAF-P-Lad) were synthesized by treating the precursor SPAF-P polymers with oleum as a novel proton exchange membrane for fuel cells. SPAF-P-Lad membranes had excellent solubility in polar organic solvents and high molecular weight (Mn = 145.4–162.9 kDa, Mw = 356.9–399.1 kDa) to provide bendable membranes with ion exchange capacity (IEC) ranging from 1.76 to 2.01 meq. g−1. SPAF-P-Lad membranes possessed higher proton conductivity than that of the precursor SPAF-P membranes because of the stronger water affinity. Compared with SPAF-P membranes (Tg: 72–90 °C, Young's modulus: 0.08–0.42 GPa; yield stress: 5.7–15.1 MPa), SPAF-P-Lad membranes showed better mechanical stability to humidity and temperature and improved tensile properties (Young's modulus: 0.51–0.59 GPa; yield stress: 23.9–29.6 MPa). The selected membrane, SPAF-mP-Lad, exhibited improved fuel cell performance, in particular, under low humidity with air; the current density at 0.5 V was 0.56 A cm−2, while that for SPAF-pP was 0.46 A cm−2. The SPAF-mP-Lad membrane endured an open circuit voltage hold test for 1000 h with average decay of as small as 70 μV h−1. A series of post-analyses including current–voltage characteristics, molecular structure, molecular weight, and IEC suggested very minor degradation of the membrane under the accelerated testing conditions.

Application based multi-objective performance optimization of a proton exchange membrane fuel cell

Abstract An application-based multi-objective optimization approach is presented to acquire the best operation condition for a proton-exchange membrane fuel cell. The optimization is done for propulsion, power station, and portable applications, in which the recommended range for decision variables and importance level of the objective functions are taken into consideration for optimization to obtain more accurate and practical results. In the multi-objective optimization, from each important aspect of the performance, i.e., technical, economic, dimensional, and environmental aspects, one objective is selected. The effect of the maximum allowable (threshold) current density on both optimum decision variables and objective functions are also investigated to find the best value for that. The results reveal that increasing the maximum allowable current density leads to improvements in optimized values of all the objective functions. Moreover, the conducted sensitivity analyses determine that the best value for threshold current density for the propulsion and power station applications is 1.3 A cm−2 and for the portable application is 1.5 A cm−2. Furthermore, comparison of the results to the base case condition shows that values of the temperature, pressure, and voltage in power station are not affected by optimization, whereas substantial decrease in both propulsion and portable applications brings more level of safety. Similarly, objective functions, i.e., efficiency, levelized cost, size, and greenhouse emission are averagely improved by 9.93, 16.95, 37.13, and 7.77%, respectively. The proposed procedure helps to design and manufacture the high-performance proton-exchange membrane fuel cells based on the employed application and users’ preference.

Polyaromatic Perfluorophenylsulfonic Acids with High Radical Resistance and Proton Conductivity.

We report on the straightforward metal-free synthesis of poly(p-terphenyl perfluorophenylsulfonic acid)s by efficient superacid-catalyzed Friedel-Crafts polycondensations of commercially available perfluoroacetophenone and p-terphenyl, followed by sulfonation of the pendant pentafluorophenyl groups via a selective and quantitative thiolation-oxidation procedure. The stiff and well-defined polymer structure with precisely sequenced and highly acidic units induces efficient ionic clustering, restricted water uptake and swelling, excellent resistance against radical attack, and very high proton conductivity. At 120 °C, the conductivity reaches 40 and 232 mS cm-1 at 50 and 90% relative humidity, respectively, which very closely matches the benchmark Nafion NR212 membrane. The properties are further tuned by copolymerizations. Overall, the results demonstrate that these materials possess a very attractive combination of characteristics for use as high-performance proton-exchange membranes for fuel cells and water electrolyzers.

Towards High-Performance Proton Exchange Membrane Fuel Cells Using Polymer Coated Heteroatom Doped Partially Unzipped Carbon Nanotubes As Catalyst Support

Enhancing the durability and reducing the cost of Proton Exchange Membrane Fuel Cells (PEMFC) are the bottlenecks for the commercialization. Platinum is reported as the best electrocatalyst for both anode and cathode due to its optimum binding energy towards hydrogen, oxygen atoms and products during the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR). The electrocatalyst loading at the anode and the cathode can be minimized by dispersing Pt nanoparticles (NPs) on high surface area and conductive carbon support material. The durability and performance of PEMFC depend on the interaction between the support and Pt NPs as well as the number of active sites available for the reactions, which can be enhanced by selective coating of proton conducting polymer on the hetroatom doped supporting material. In the present work, we have synthesized highly proton conducting polymer polyvinyl phosphonic acid (PVPA) coated heteroatom doped partially unzipped carbon nanotubes (H-PECNT) and used as the catalyst support material for Pt NPs. The heteroatom doping increases the ORR activity of the support material and the PVPA coating adhere Pt NPs to the support during cycling and also increases the active sites. Moreover, we have coated PVPA on H-PECNT by varying different ratios of PVPA to H-PECNT and to find the optimum PVPA percentage on H-PECNT, which enhances the performance of PEMFC. The single cell measurements deliver a high power density with 6% of PVPA than the commercial Pt/C as well as other PVPA ratios wherein both electronic conductivity of the support material and proton conductivity of PVPA contribute significantly to the performance.

Control of Edge/in-Plane Interactions toward Robust, Highly Proton Conductive Graphene Oxide Membranes.

Graphene oxide (GO) membrane, bearing well-aligned interlayer nanochannels and well-defined physicochemical properties, promises fast proton transport. However, the deficiency of proton donor groups on the basal plane of GO and weak interlamellar interactions between the adjacent nanosheets often cause low proton conduction capability and poor water stability. Herein, we incorporate sulfonated graphene quantum dots (SGQD) into GO membrane to solve the above dilemma via synergistically controlling the edge electrostatic interaction and in-plane π-π interaction of SGQD with GO nanosheets. SGQD with three different kinds of electron-withdrawing groups are employed to modulate the edge electrostatic interactions and improve the water swelling resistant property of GO membranes. Meanwhile, SGQD with abundant proton donor groups assemble on the sp2 domain of GO via in-plane π-π interaction and confer the GO membranes with low-energy-barrier proton transport channels. As a result, the GO membrane achieves an enhanced proton conductivity of 324 mS cm-1, maximum power density of 161.6 mW cm-2, and superior water stability when immersed into water for one month. This study demonstrates a strategy for independent manipulation of conductive function and nonconductive function to fabricate high-performance proton exchange membranes.

Proton-exchange membrane CO2 electrolyzer for CO production using Ag catalyst directly electrodeposited onto gas diffusion layer

Carbon monoxide is an important product of electrochemical CO2 reduction because its syngas mixture with H2 can be used to synthesize hydrocarbons via the Fischer-Tropsch process. Herein, a hierarchical dendritic Ag catalyst for electrochemical CO2 reduction is prepared through pulse electrodeposition onto functionalized carbon paper. To gain the hydrophilicity required for contact with the deposition electrolyte, carbon paper is acid-treated to induce oxygen-containing functional groups on the surface. Among the acids tested, H2SO4 significantly enhances the morphological characteristics, such as population and size, of Ag clusters during pulse electrodeposition. This leads to lower charge transfer resistance and 1.6 times higher current density for CO production during CO2 electrolysis in a bath-type cell than those for Ag on pristine carbon paper. This superior activity is maintained in a membrane-electrode-assembly-type cell employing a proton-exchange membrane, which is desirable for mass production of CO. Thus, pulse electrodeposition of Ag onto H2SO4-treated carbon paper is a beneficial strategy to fabricate an electrode for a high-performance proton-exchange membrane CO2 electrolyzer.

Facile fabrication of nanostructured NiMo cathode for high-performance proton exchange membrane water electrolyzer

Clean hydrogen production via water electrolyzer connected with renewable energies is an essential technology for a sustainable energy in future. To realize the system, development of high-performance electrode remains a challenge. In this study, simple cathodic electrodepositions allow for the facile fabrication of a nanostructured non-noble metal cathode. Under optimized deposition condition, the NiMo catalyst supported by Cu foam exhibits overpotential of 68.7mV at −10mA/cm2 for hydrogen evolution reaction in acidic medium. The proton exchange membrane water electrolyzer employing the cathode demonstrates a remarkable current density of ˜2.0A/cm2 at 2.0V, which is the highest performance among state-of-the-art non-noble cathodes reported to date. The results presented herein indicate a promising cost-effective cathode for practical applications.