Perfluorinated Sulfonic Acid Ionomers Research Articles

Selective Peptide Binders to the Perfluorinated Sulfonic Acid Ionomer Nafion (Adv. Funct. Mater. 20/2024)

Selective Peptide Binders to the Perfluorinated Sulfonic Acid Ionomer Nafion (Adv. Funct. Mater. 20/2024)

Fully solution-processed n-i-p type perovskite solar cells with efficiency over 19% enabled by a hydrophobic PEDOT:F interlayer and silver nanowire top electrode

Solution-processed top electrode is the key technology for the realization of fully solution-processed perovskite solar cells (PSCs). In this paper, we reported the preparation of fully-solution processed n-i-p type PSCs with spray-coated silver nanowires (AgNWs) top electrode. Experiment results demonstrated that low power conversion efficiency (PCE) of 16.00% with a low fill factor of 67.41% was obtained for the reference cell, when the AgNWs is directly coated on the 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD) layer. This result indicates a charge extraction barrier at the Spiro-OMeTAD/AgNWs interface, which could be attributed to the poor compatibility between Spiro-OMeTAD and AgNWs layers. By inserting a thin layer of poly(3,4-ethylenedioxythiophene):perfluorinated sulfonic acid ionomers (PEDOT:F), a modified PEDOT with lower surface energy, the interface connection between Spiro-OMeTAD/PEDOT:F and AgNWs was improved, leading to an enhanced PCE of up to 19.11%. In addition, the PEDOT:F-based cells retained 64% of the initial PCE after operating at the maximum power point for 1800 h, whereas the reference cells retained only 30% of the initial PCE. The current work proved that PEDOT:F/AgNWs could be an excellent option for fully-solution processed n-i-p type PSCs.

Recovery, Regeneration, and Reapplication of PFSA Polymer from End-of-Life PEMFC MEAs.

We have developed a recovery, regeneration, and reapplication process for Nafion, a perfluorinated sulfonic acid (PFSA) ionomer, from end-of-life (EoL) low-temperature proton-exchange membrane (PEM) fuel cells (FCs). Samples of PFSA PEM recovered from EoL membrane-electrode assemblies (MEAs) with a history of close to 19,000 h of operation were recycled by dissolving the polymeric material in ethanol and applying the dissolved PFSA ionomer for producing the ionomer phase of the catalyst layer of new PEMFC cathodes. Structural characterizations show a marginally lower abundance of sulfonic groups for the EoL PEM compared to a fresh sample. Sulfonation of the former was employed to regenerate sulfonic groups to compensate for the lost ones. New gas-diffusion electrodes (GDEs) were prepared with the recycled PFSA ionomer both with and without sulfonation, and MEAs with these GDEs as cathodes were assembled through a state-of-the-art procedure. Electrochemical characterizations of the GDEs and single-cell studies of the MEAs showed that the electrochemical performances of catalyst layers containing recycled PFSA ionomer were at least similar to those containing fresh. Durability studies of the GDEs and MEAs, performed through a three-electrode liquid cell and a single cell, respectively, show the highest durability for the GDE/MEA with PFSA ionomer recycled without applying the sulfonation step. However, the GDE with PFSA ionomer obtained from recycling a re-sulfonated PEM shows a durability comparable to that of the GDE with fresh PFSA ionomer. Hence, PFSA material aged during PEMFC operation may be employed to produce highly functional and durable regenerated PFSA ionomer for PEMFC catalyst layers. The studied process of PFSA ionomer recycling is highly attractive for industrial adoption.

The relationship between chemical structure of perfluorinated sulfonic acid ionomers and their membrane properties for PEMEC application

Polymer electrolyte membrane electrolyzer cells (PEMECs) has been confirmed as a prototype electrochemical system that is effective in converting water into hydrogen and oxygen under the application of electricity. Among the core components of PEMEC, the polymer electrolyte membrane (PEM) determines critically an overall electrochemical performance of the PEMEC. Ideally a PEM system should exhibit a complex transport behavior of small molecules (e.g., gases and ions) while mediating flows of ions in the cell; it should exhibit high proton selectivity while serving as a gas barrier to hydrogen and oxygen to increase current efficiency, which are in turn vital factors in determining an effectiveness when the electric energy is used for water electrolysis. Until now, perfluorinated sulfonic acid (PFSA) ionomers have been extensively used as PEM materials in water electrolysis while in generating hydrogen and oxygen gases simultaneously in high purity. In this study we have examined the chemical structure of PEM membranes derived from various types of PFSA ionomers by employing solid-state 19F MAS NMR. Subsequently, a structure-property-performance correlation was sought in accordance with the chemical structure, the dispersion characteristics, and membrane properties of PFSA ionomers. Furthermore, the effects of the membrane morphology as well as the ionomer packing characteristics on proton conduction and hydrogen transportation were investigated. Lastly, the membrane properties exerted by varying the chemical architectures and equivalent weight (EW) values of PFSA ionomers in PEMEC were confirmed. 3 M 725 membrane, which has the highest concentration of sulfonic acid groups in the hydrated state, has the highest proton conductivity. In addition, it showed the best water electrolytic cell performance via the synergistic effect with low gas permeability obtained as a result from the short side chain structure.

Effect of Blended Perfluorinated Sulfonic Acid Ionomer Binder on the Performance of Catalyst Layers in Polymer Electrolyte Membrane Fuel Cells.

In this study, blended perfluorinated sulfonic acid (PFSA) ionomers with equivalent weights (EWs, g/mol) of ~1000, 980, and 830 are prepared. Catalyst layers (CLs), using blended PFSA ionomers, with different side chain lengths and EWs are investigated and compared to CLs using single ionomers. The ion exchange capacity results confirm that blended ionomers have the target EWs. As a result, blended ionomers exhibit higher ion conductivity than single ionomers at all temperatures due to the higher water uptake of the blended ionomers. This implies that blended ionomers have a bulk structure to form a competent free volume compared to single ionomers. Blended ionomers with short side chains and low EWs can help reduce the activation energy in proton conduction due to enhanced hydrophobic and hydrophilic segregation. In addition, when using the blended ionomer, the CLs form a more porous microstructure to help reduce the resistance of oxygen transport and contributes to lower mass transfer loss. This effect is proven in fuel cell operations at not a lower temperature (70 °C) and full humidification (100%) but at an elevated temperature (80 °C) and lower relative humidity (50 and 75%). Blended ionomer-based CLs with a higher water uptake and porous CL structure result in improved fuel cell performance with better mass transport than single ionomer-based CLs.

An Efficient Solution‐Processed Interconnecting Layer for Large‐Area Tandem Organic Solar Cells

Interconnecting layer (ICL) is a key part of the tandem organic solar cells (OSCs) to achieve high efficiency. The ICLs of efficient inverted nonfullerene OSCs are complicated that comprise vacuum‐deposited MoO3, solution‐processed ZnO, and an additional thin silver (or PEDOT:PSS) film in between. Herein, an efficient fully solution‐processed ICL is first reported that comprises a PEDOT:F layer and a ZnO layer. The PEDOT:F is short for poly(3,4‐ethylenedioxythiophene):perfluorinated sulfonic acid ionomer that is alcohol dispersed and has a work function of 5.6 eV for hole collection. The ZnO is used for electron collection. The PEDOT:F/ZnO has a conductivity of 2.28 × 10−3 S cm−1 which can play a recombination zone. The solution‐processed ICL of PEDOT:F/ZnO has been validated in both two‐junction and triple‐junction solar cells. The tandem cells show high fill factor (FF) of 76–80% and high open‐circuit voltage (VOC) which is nearly the sum of the single‐junction OSCs. The PEDOT:F/ZnO ICL has also been used to fabricate large‐area tandem organic module (15.48 cm2) that shows a VOC of 10.25 V, FF of 75.1%, and a power conversion efficiency of 13.24%. The PEDOT:F/ZnO is a promising ICL for high‐performance tandem OSCs.

Viscoelasticity Enhancement and Shear Thickening of Perfluorinated Sulfonic Acid Ionomer Dispersions in Water–Alcohol Solvent Mixtures

Viscoelasticity Enhancement and Shear Thickening of Perfluorinated Sulfonic Acid Ionomer Dispersions in Water–Alcohol Solvent Mixtures

Selective Peptide Binders to the Perfluorinated Sulfonic Acid Ionomer Nafion

AbstractFuel cells used for transport applications hold polymer membranes as a key element. Their efficiency can be significantly increased if structured ion channels are implemented at the molecular level into the proton‐conducting membrane. New functional molecules with selective affinity for ionomers are needed to obtain such a membrane design. This study presents a method to screen for selective peptide binders to perfluorinated sulfonic acid ionomers, e.g., Nafion using ultra‐high density peptide arrays with a spot size of up to 30 µm. First, the ionomer dispersion is incubated with the peptide chip containing 56014 randomly chosen 6‐mer peptides. Afterward, the peptide chip is washed. The peptide WIWHCW with the helix structure is identified as a selective binder to Nafion. The invariant amino acids responsible for binding are also determined using a peptide chip approach. The specific binding pocket of WIWHCW is formed by histidine and tryptophan. Its dissociation constant to the ionomer is measured at ≈140 µM.

Morphological transformation of perfluorinated sulfonic acid ionomer via ionic complex formation at a high entropy state

Proton exchange membranes (PEMs) act as conductors in PEM fuel cells (PEMFCs) to transport protons from the anode to the cathode in the membrane electrode assembly (MEA). Because protons are transported via the hydrophilic channels of the PEMs, the morphological control of these channels has been considered a key issue that influences their electrochemical performance. In this study, we propose a simple route that provides fast proton transport pathways via the morphological transformation of hydrophilic channels in a commercially available perfluorinated sulfonic acid (PFSA) ionomer, Nafion®. It is based on the formation of ionic complexes when metallic salts are added during the membrane fabrication process, instead of using PFSA ionomers with tuned chemical structures. The effectiveness of this strategy is theoretically verified by performing molecular simulations for the ionic cluster formation mechanism. The formation of the ionic complexes in a high entropy state is found to be advantageous in decreasing the distance between ionic clusters, improving proton transport efficiency resulting in higher proton conductivity and single cell performance without any additional chemical and processing step causing the production cost increase.

Ionomer immobilized onto nitrogen-doped carbon black as efficient and durable electrode binder and electrolyte for polymer electrolyte fuel cells

An implementation of the polymer electrolyte fuel cell (PEFC) electrode, composed of the perfluorinated sulfonic acid (PFSA) ionomer with unprecedented uniform distribution, has recently gained a great attention due to its positive impact on the cell performance as well as durability. However, an issue with the conventional electrodes is a stronger adsorption of sulfonate terminal groups specifically onto Pt catalyst than carbon black (CB) support, that accelerates an inhomogeneous distribution of the PFSA ionomer. In this work, we report a novel PEFC electrode by introducing the ionomer immobilized onto nitrogen-doped carbon black (I/NCB) as electrode binder as well as electrolyte. The carbon atoms adjacent to nitrogen allow a considerable attraction with sulfonated groups over the NCB surfaces, which creates more homogeneous distribution of ionomer when compared with Pt/CB in the conventional electrode. As compared with the conventional electrode, the electrode employing I/NCB presents a superior activity towards oxygen reduction reaction (Pt mass activity increased from 91.3 to 139.6 A g−1) and mass-transport characteristics (mass-transport resistance decreased from 65.9 to 45.5 mΩ cm2), with the cell current density enhanced by 23% at 0.6 V. The enhanced cell durability is confirmed by less degradation in the electrochemically available surface area after the accelerated stress test of carbon support, mainly attributed to the promoted stability of NCB over CB. Given the advances in both performance and durability, the proposed electrode architecture based on I/NCB may provide an alternative pathway in obtaining better electrode kinetics and O2 transport, along with an exceptional resistivity towards the carbon support degradation.

A coupled-layer ion-conducting membrane using composite ionomer and porous substrate for application to vanadium redox flow battery

A thin ionomer layer composed of perfluorosulfonic acid (PFSA) polymer in composite with functionalized alkoxysilane (FAS) is prepared and coated onto one side of a porous polyethylene (PE) substrate for vanadium redox flow battery (VRFB) to produce a coupled-layer membrane. The approaches are: (1) suppression of permeation through membrane using additive component, (2) the use of thin ionomer layer for lowering the amount of costly PFSA, and (3) strengthening the thin ionomer layer by coating onto an inexpensive PE substrate. The membrane is easily prepared using automatic control coater. The observation of morphology and infrared spectroscopy at both sides of the coupled-layer membrane confirm the thin ionomer layer on only one side of the PE substrate, plus the addition of FAS helps achieve lower diffusion coefficient. After the unit cell cycling, the coupled-layer membrane shows the good cycling performance closing to Nafion 212 membrane level. Additionally, the morphology after cycling of the coupled layers between PFSA ionomer and PE substrate can remain the same as in initial state, indicating a stable combination from both layers. Based on the easy production and the good performance, the developed membrane can be readily adapted by membrane manufacturer for the wide application in VRFB. • A thin ionomer layer is coated on one side of porous polyethylene substrate. • The thin layer reduces amount of costly perfluorinated sulfonic acid ionomer. • VRFB cell performance was good by closing to that of Nafion 212 membrane. • Unchanged morphology between two layer was found after VRFB unit cell operation.

Influence of Ionomer Content in the Catalytic Layer of MEAs Based on Aquivion® Ionomer.

Perfluorinated sulfonic acid (PFSA) polymers such as Nafion® are widely used for both electrolyte membranes and ionomers in the catalytic layer of membrane-electrode assemblies (MEAs) because of their high protonic conductivity, σH, as well as chemical and thermal stability. The use of PFSA polymers with shorter side chains and lower equivalent weight (EW) than Nafion®, such as Aquivion® PFSA ionomers, is a valid approach to improve fuel cell performance and stability under drastic operative conditions such as those related to automotive applications. In this context, it is necessary to optimize the composition of the catalytic ink, according to the different ionomer characteristics. In this work, the influence of the ionomer amount in the catalytic layer was studied, considering the dispersing agent used to prepare the electrode (water or ethanol). Electrochemical studies were carried out in a single cell in the presence of H2-air, at intermediate temperatures (80–95 °C), low pressure, and reduced humidity ((50% RH). %). The best fuel cell performance was found for 26 wt.% Aquivion® at the electrodes using ethanol for the ink preparation, associated to a maximum catalyst utilization.

Study on Control of Polymeric Architecture of Sulfonated Hydrocarbon-Based Polymers for High-Performance Polymer Electrolyte Membranes in Fuel Cell Applications.

Polymer electrolyte membrane fuel cell (PEMFC) is an eco-friendly energy conversion device that can convert chemical energy into electrical energy without emission of harmful oxidants such as nitrogen oxides (NOx) and/or sulfur oxides (SOx) during operation. Nafion®, a representative perfluorinated sulfonic acid (PFSA) ionomer-based membrane, is generally incorporated in fuel cell systems as a polymer electrolyte membrane (PEM). Since the PFSA ionomers are composed of flexible hydrophobic main backbones and hydrophilic side chains with proton-conducting groups, the resulting membranes are found to have high proton conductivity due to the distinct phase-separated structure between hydrophilic and hydrophobic domains. However, PFSA ionomer-based membranes have some drawbacks, including high cost, low glass transition temperatures and emission of environmental pollutants (e.g., HF) during degradation. Hydrocarbon-based PEMs composed of aromatic backbones with proton-conducting hydrophilic groups have been actively studied as substitutes. However, the main problem with the hydrocarbon-based PEMs is the relatively low proton-conducting behavior compared to the PFSA ionomer-based membranes due to the difficulties associated with the formation of well-defined phase-separated structures between the hydrophilic and hydrophobic domains. This study focused on the structural engineering of sulfonated hydrocarbon polymers to develop hydrocarbon-based PEMs that exhibit outstanding proton conductivity for practical fuel cell applications.

Impact of the Composition of Alcohol/Water Dispersion on the Proton Transport and Morphology of Cast Perfluorinated Sulfonic Acid Ionomer Thin Films.

The dispersion of perfluorinated sulfonic acid ionomers in catalyst inks is an important factor that controls the performance of catalyst layers in membrane electrode assemblies of polymer electrolyte fuel cells. Herein, the effects of water/alcohol compositions on the morphological properties and proton transport are examined by grazing incidence small-angle X-ray scattering, grazing incidence wide-angle X-ray scattering, and electrochemical impedance spectroscopy. The thin films cast by a high water/alcohol ratio Nafion dispersion have high proton conductivity and well-defined hydrophilic/hydrophobic phase separation, which indicates that the proton conductivity and morphology of the Nafion thin films are strongly influenced by the state of dispersion. This finding is expected to further understand the morphology and proton transport properties of Nafion thin films with different water/alcohol ratios, which has implications for the performance of the Pt/Nafion interface.

Highly Ordered Ultrathin Perfluorinated Sulfonic Acid Ionomer Membranes for Vanadium Redox Flow Battery

In vanadium redox flow batteries (VRFBs), a perfluorinated sulfonic acid (PFSA) ionomer membrane plays a crucial role in transporting ions through hydrophilic channels. However, its randomly interc...

Characterizing Electrochemical and Thermal Properties of VDF Blended 3M PFSA Ionomer with Chemically Bonded Polyoxometalate Additives

Proton exchange membranes (PEMs) are considered as the most promising material for fuel cell automobile applications due to their high proton conductivity and power density. The radical attacks with peroxide formation cause lower durability, which is a major challenge to further commercialize fuel cell vehicles. Cerium and manganese cations and oxides have been implemented as radical scavenging agents to overcome the challenge from radical attacks. However, the additives tend to not stay on the initial location but move during the operation due to migration and diffusion. The migration results in cluster formation and eventually the additives may dissolve and leave the membrane system. Our previous work modifying commercial fluroelastomers with chemically bonded polyoxometalate resulted in a membrane with radical scavenging properties while inhibiting additive clustering. Advancement in PEM durability with additives has implications not only for the light-duty fuel cell vehicles but also for medium and heavy-duty vehicles applications, which would aid the widespread of commercialization of fuel cell vehicles.This work focuses on characterizing the blended perfluorinated sulfonic acid (PFSA) ionomer membrane with the chemically bound radical scavenger to enhance the durability of the membrane. Proton conductivity of the membrane was characterized under controlled relative humidity and temperature with electrochemical impedance spectroscopy (EIS). Ionic Exchange capacity of two or more proton conductive sites was measured using titration method. Correlation between water uptake and membrane properties is discussed and measuring using dynamic vapor sorption (DVS). Thermal stability was investigated through thermalgravimetric analysis (TGA).

Saline Water Electrolysis Membranes Prepared via the Simultaneous Irradiation of Electron-Beam

Polymer electrolyte membrane water electrolysis is a representative electrochemical process to produce both hydrogen and oxygen gases by applying electricity. Perfluorinated sulfonic acid (PFSA) ionomers have been widely used as electrode binder materials owing to their high proton conductivity and excellent compatibility with membrane materials with identical or similar chemical architectures. Different in the membrane materials, PFSA binder materials should have fast gas permeation behavior to minimize mass flux resistance. It makes it difficult to use the same ionomer dispersion for both applications. In this study, the average size of dispersed PFSA ionomer particle was controlled via a supercritical technique. The relationship between ionomer dispersion characteristics and electrochemical performances was systematically investigated.

Tunable aggregation of short-side-chain perfluorinated sulfonic acid ionomers for the catalyst layer in polymer electrolyte membrane fuel cells

We control the aggregation of short-side-chain (SSC) perfluorinated sulfonic acid (PFSA) ionomers for catalyst-layer (CL) inks by using a dispersion solvent of dipropylene glycol (DPG) and water. By increasing the fraction of PFSA backbone preferable DPG content in a dispersion solvent, the size of SSC-PFSA aggregates decreases exponentially from microscale to nanoscale, affecting the catalyst-ionomer agglomerates’ size and distribution in the CL inks. The surface morphology and porosity properties of the resulting CL are investigated, and the fuel cell performances are studied at two different humidity conditions (50 and 100% RH). Compared to the previous study with long-side-chain (LSC) PFSA ionomers, the SSC-PFSA ionomers show the optimized performance at higher DPG content, where the solvating power is intermediate for SSC-PFSA ionomers having shorter hydrophilic side chain than LSC-PFSA ionomers.

Rational design of perfluorinated sulfonic acid ionic sieve modified separator for high-performance Li-S battery

Practical application of Li-S battery is limited by the fast capacity decay and low coulombic efficiency caused by the shuttling phenomenon. Modification of the battery separator to impart the separator with ionic sieving property is an effective strategy to alleviate the shuttling phenomenon. In this study, perfluorinated sulfonic acid (PFSA) ionomers with different equivalent weight (EW) values are used to modify the commercial polyethylene separator, and the electrochemical performance of these separators is systematically investigated. Our results show that the separator modified using PFSA ionomer with a low EW value of 830 shows optimal battery performance owing to its unique structure of the ionic cluster. The Li-S battery with this modified separator shows an initial discharge capacity of 1352 mAh g−1 and a retained capacity of 931.6 mAh g−1 after cycling 100 times at 0.2 C, which demonstrates the effectiveness of this modification strategy. Furthermore, the correlation between the properties of PFSA ionomers and the electrochemical performance of the modified separator unveiled in this study may provide insight for the rational design of advanced separator for battery applications.

Comparative investigation into the performance and durability of long and short side chain ionomers in Polymer Electrolyte Membrane Fuel Cells

Perfluorinated sulfonic acid (PFSA) ionomers have high proton conductivity and excellent mechanical-chemical stability under humid conditions in low temperature Polymer Electrolyte Membrane Fuel Cell (PEMFC) application. In this work, we compare performance and durability between long side chain (LSC) and short side chain (SSC) PFSA ionomers as a solid electrolyte membrane and as ionomer-additive in the electrodes. Membrane electrode assemblies (MEAs) are prepared combining the LSC/SSC membrane with the corresponding LSC/SSC ionomer in the catalyst layer. Thereby, their chemical compatibility could be determined. MEAs are tested in single cell test benches with segmented bipolar plate for long term degradation test with dynamic load-cycling. While maintaining uniform conditions, we have experienced that different MEAs show different behavior in short-term to long-term application. Owing to its stability in lower equivalent weight; SSC ionomer provides favorable proton conductivity leading to higher power density of the cell. Nevertheless, faster degradation of SSC than the LSC ionomer are encountered in this study likely due to the higher gas permeation of thinner SSC membranes and lower polytetrafluoroethylene content. This study contributes a significant insight in the behavior of ionomers in FC as function of time, and shows avenues for further improvement of durability.