Search

In this work, a numerical approach is presented to reconstruct the ionomer three-dimensional distribution in the microstructure of the cathode catalyst layer (CCL) of a polymer electrolyte membrane fuel cell (PEMFC) from a 3D segmented image of the CCL obtained by focused ion beam-scanning electron microscopy (FIB-SEM). Three forms of ionomer are distinguished: the ionomer filaments, the coating ionomer and the inter-carbon grains ionomer. The ionomer filaments are identified by applying a filtering procedure to the size distribution in the segmented solid phase obtained via a maximum sphere inscription algorithm. The coating ionomer is reconstructed via a filtering procedure of the curvature distribution computed over the interface between the two segmented phases from the consideration that concave regions are preferential ionomer accumulation zones during the drying step of the CCL fabrication procedure. This procedure of coating controlled by the local curvature is applied until a desired value of coverage is reached. In a last step, catalyst nanoparticles, also not visible in the FIB-SEM image, are reconstructed in the image. • Ionomer coating is numerically reconstructed in a FIB-SEM image. • The ionomer coating is of variable thickness. • A small fraction of the ionomer forms protrusions in the pore space. • A significant fraction of the ionomer is in between the carbon grains. [ABSTRACT FROM AUTHOR]

The oxygen effective diffusion and proton effective conductivity tensors of a cathode catalyst layer (CCL) are computed using a two-scale approach on CCL microstructure three-dimensional images obtained by focused ion beam-scanning electron microscopy (FIB-SEM) after reconstruction of the ionomer distribution. The results show that the obtained tensors are not isotropic. It is also found that some off-diagonal components are not negligible in the case of the proton effective conductivity tensor. The simulations confirm that Knudsen diffusion has a significant impact on oxygen diffusion. The results are comparable to those obtained in previous works on synthetic images as regards the oxygen effective diffusion through-plane component but differ as regards the proton conductivity through-plane component. Contrary to previous works using synthetic images which tend to underestimate the proton conductivity, they are globally in better agreement with experimental data. The results also show that the effective proton conductivity is heterogeneous at the scale of the computational domains typically considered in several previous works due to the variability in the ionomer distribution at this scale. The impact of liquid water in the primary pores on the proton transport is explored and found to have a significant impact. • The oxygen effective diffusion tensor is computed from 3D digital images of a PEMFC catalyst layer (CL). • The proton effective conductivity tensor is computed from 3D digital images of the CL microstructure. • Liquid water in the primary pores has a noticeable impact on the proton transport. • Results on the proton transport validate the considered ionomer spatial distribution. [ABSTRACT FROM AUTHOR]

Relative humidity (RH), platinum-to-carbon (Pt/C) ratio, and ionomer content considerably affect the mass and proton transport of proton exchange membrane fuel cells (PEMFCs), thereby affecting their performance and gas distribution quality. This study is the first to investigate the combined effects of the Pt/C ratio and RH on the performance and oxygen distribution uniformity of a graded ionomer cathode catalyst layer (CCL) with different average ionomer contents. The results show that all graded ionomer CCLs outperform the uniform CCL at a high Pt/C ratio of 0.55, regardless of the RHs and average ionomer contents. However, whether the graded ionomer CCL enhances or weakens the performance is mainly determined by the RH and the average ionomer content when the Pt/C ratio is reduced to 0.35. Specifically, when the Pt/C ratio is 0.35, the graded ionomer distributions exhibit inferior performance to the uniform CCL at a lower average ionomer content and lower RH owing to the larger ohmic loss. However, the impact of the concentration loss outweighs that of the ohmic loss, which is the main factor responsible for the superior performance of the graded ionomer distributions when the average ionomer content and RH are high. Besides, both a reduction in the Pt/C ratio and an increase in RH deteriorate the oxygen distribution uniformity of the graded ionomer CCLs with different average ionomer contents at medium and high current densities of operations. Moreover, the graded ionomer CCLs with low upstream ionomer contents achieve more uniform oxygen distributions than the opposite CCL structures at high current densities of operations under different RH values and average ionomer contents. [Display omitted] • Joint effect of Pt/C ratio and relative humidity on graded ionomer CCL is studied. • Graded ionomer CCL outperform uniform CCL at high Pt/C ratio. • Impact of graded ionomer on performance rely on relative humidity at low Pt/C ratio. • Reduce in Pt/C ratio and rise in relative humidity reduce gas distribution quality. • Graded ionomer CCL with low upstream ionomer gets more uniform oxygen distribution. [ABSTRACT FROM AUTHOR]

Continuously improving performance and reducing cost targets for oxygen evolution reaction (OER) drive a growing interest in optimizing functionalities of ionomer binders in catalyst layer. The actual properties of catalysts significantly depend on the applied ionomers. Herein, we systematically examine five perfluorinated acid ionomers binders for OER on IrO x catalysts, including four Aquivion® short side chain ionomers and a long side chain Nafion™. Electrochemical measurements indicate that a combination of short side chain and increased equivalent weight can facilitate OER due to the optimized ionomer-catalyst interactions. Meanwhile, ionomers impact on OER by adjusting mass transport behaviors rather than reaction pathways. The accelerated durability tests further reveal that the long side chain and higher equivalent weight can decrease activity losses from 50% to 28%, implying enhancement of long-term electrochemical stability. Therefore, combining the advanced ionomer chemistry with the interfacial science provides a new opportunity to facilitate OER for energy conversion and storage. [Display omitted] • Illustrating ionomer-dependent oxygen evolution well from interface science. • Short side chain and high equivalent weight facilitate acidic oxygen evolution. • Long side chain and high equivalent weight improve electrochemical stability. • Ionomer greatly impacts on interfacial mass transport but not reaction pathways. [ABSTRACT FROM AUTHOR]

A cell with a superior performance and durable catalyst layer can be achieved by optimizing the catalyst ink formulation. A typical commercial catalyst layer for both proton exchange membrane fuel cells and water electrolyzers is prepared via dispersion-based catalyst inks. Generally, ink dispersion composed of supported catalyst, ionomer, and solvent. The ink formulation governs physical properties such as homogeneity, the interaction between ink components, ability to store the ink (shelf-life) for an extended period and reproducibility. This is pivotal in optimizing the catalyst ink formulation for high performance, extended durability, and reproducibility, particularly in large-scale industrial manufacturing in polymer electrolyte membrane (PEM) fuel cells and electrolyzers. Despite the substantial progress on synthesis of different catalysts and ionomers, there is a limited understanding of the colloidal stability of the catalyst ink. The novelty of this review is to provide a guide to understand the importance of catalyst ink dispersion stability for manufacturing MEAs at scale-up level. This is addressed through targeting fundamental interaction behavior and physical properties of the ink materials. Further, this review covers the effect of particle surface, effect of solvent composition, and the effect of ionomer concentration that ensures a homogenized catalyst ink. In addition, this review covers the influence of different dispersion methodologies and the relevant characterization techniques for better understanding the dispersion stability. • Reviewed the importance of ink constituents for PEM fuel cell and electrolyzer. • Elucidated the causation of ink agglomeration and the impact on the cell behavior. • Discussed the importance of ionomer adsorption on catalyst ink stability. • Reviewed the characterizing techniques to study the catalyst ink stability. [ABSTRACT FROM AUTHOR]

Carbon support has an important influence on the catalyst ink properties. The interaction between carbon support, solvent, and ionomer determines the dispersion of ink clusters. In this study, the effects of dispersion time, solvent, and ionomer on the cluster properties are studied. It is found that the shear time of 8 h is conducive to the fragmentation of catalyst particles, and isopropanol and ionomer D2020 has good dispersion for mesoporous carbon support with high specific surface area. The median diameter of catalyst clusters is effectively reduced from 1537 to 1014 nm, and 10 wt% solid content of ink is more conducive to slit coating. The increase of the ionomer content is helpful to reduce the catalyst layer cracks. When the mass ratio of dry ionomer to carbon(I/C) is larger than 0.85, the cracks of the catalyst layer are significantly reduced. The results of I–V curve tests show that when I/C = 0.85, the cell has the best polarization performance. The single cell voltage is 0.709 V at 1 A cm−2, and the power density is 1128.51 mW cm−2 at 2 A cm−2. The results of electrochemical impedance spectroscopy (EIS) are also consistent with the polarization curve test results. • The influence of ionomer on catalyst ink and fuel cell performance are analyzed. • The clusters size, Zeta potential and rheology of the ink are investigated. • The shear time, type of solvent and ionomer of the ink are optimized. • The I/C ratio and the solid content of the ink are optimized. • MEA with optimized parameters has good electrochemical performance. [ABSTRACT FROM AUTHOR]

When no hydrogen can reach the Pt catalyst in the anode for the hydrogen oxidation reaction (HOR) of an operating proton exchange membrane fuel cell (PEMFC), the anode potential increases and causes the cell potential to be reversed compared to normal operation conditions. During this reversal, the oxygen evolution reaction (OER) and carbon oxidation reaction (COR) will occur at the anode, where the COR has devastating consequences for the electrode. Introducing an OER catalyst limits the COR to occur, which makes a reversal tolerant anode (RTA). In this research, RTAs are differentiated by applying different ball milling times during catalyst layer processing, forming big and small OER (IrO x /TiO x) and HOR (Pt/C) catalyst particles. The two different particle sizes were electrochemically tested using a rotating disc electrode (RDE). Both catalyst sizes show a decrease in OER activity (mA cm−2) accompanied by loss of the ionomer in a self-developed accelerated stress test (AST). The small particle RTAs show higher OER activity as a result of increased surface area. However, during a chronopotentiometry measurement, which mimics a fuel cell reversal, the small particle coatings show a worse reversal tolerance. This phenomenon can be attributed to the increased difficulty in removing oxygen bubbles. [Display omitted] • Ball milling time influences the structure of a reversal tolerant anode. • The structure of the anode influences OER activity as well as reversal tolerance. • Loss of ionomer occurs during an accelerated stress test at fuel cell reversal potentials. [ABSTRACT FROM AUTHOR]

Durability problems are among the major obstacles that limit the large-scale application of polymer electrolyte membrane fuel cells (PEMFCs). Understanding the influence of metal cations on the performance of PEMFCs are of great significance for improving the durability. In this study, the membrane electrode assembly (MEA) is artificially contaminated using Cu2+ with different concentrations, and its influence as well as the mechanism on the activation, ohmic and mass-transport loss are systematically investigated upon 1200 h realistic driven cycle in combination with impendence analysis and physical characterization. In the beginning of life (BOL) tests, the rapid impact of Cu2+ is found by not only limiting the proton conductivity and oxygen transport in the ionomer, but also dramatically decreasing the activity of Pt/C on oxygen reduction reaction (ORR). After 1200 h durability tests (DT), those effects observed in BOL tests get significant and the degradation of membrane and carbon support come out. These insights into degradation behavior of various components in MEA in different time scales is instructive to understand the degradation mechanism and prolong the lifetime of PEMFCs. [Display omitted] • The impact and mechanism of Cu2+ contamination on PEMFC is investigated. • All of activation, ohmic and mass-transport loss are revealed to be responsible. • The limited proton conductivity and oxygen transport take effect at very beginning. • The oxygen reduction reaction kinetic dramatically decreases in the presence of Cu2+ on Pt/C. • The damage of membrane and carbon support is observed after 1200 h test. [ABSTRACT FROM AUTHOR]

The successful electrochemical reduction of CO 2 (eCO 2 R) into valuable fuels and chemicals relies on the development of low-cost, effective carbon-bonded metal catalysts. Carbon-bonded metal catalysts are crucial for efficient eCO 2 R due to their dual functionality—high electrical conductivity from carbon and catalytic activity from the metal. In this study, a facile hydrothermal method was used to synthesize carbon-derived bismuth oxide nanospheres (C-BiO x) on porous nickel foam (NF) electrodes as electrocatalysts for eCO 2 R. The eCO 2 R activity of this catalyst was evaluated in H-type cells and compared with commercially available Pd/C and Ag-nanoparticle catalysts. Our finding revealed that C-BiO x /NF exhibited a higher eCO 2 R activity (corresponding to the CO Faradaic efficiency (FE) of 16.2 % at −1 V vs. reversible hydrogen electrode (RHE) and HCOOH FE of 85.4 % at −0.7 V vs. RHE) than those of the Ag nanoparticle-based and Pd/C catalysts. Mechanistic insights from DFT-based studies further supported the enhanced catalytic activity of C-BiOx for HCOOH production over Ag catalysts. The fabricated catalyst was further utilized in a zero-gap CO 2 electrolyzer for gas-phase CO 2 reduction containing a self-supporting C-BiO x /NF gas diffusion layer (GDL). An anion exchange membrane-based CO 2 electrolyzer demonstrated a higher FE for CO formation (47.1%) with an energy efficiency (EE) of 29.5% as compared to those of a polymer electrolyte membrane-based CO 2 electrolyzer (FE: 25.2%, EE: 18.4%). Notably, the C-BiO x /NF catalyst exhibited remarkable stability (8 h) in the gas-phase GDL compared to that observed during the liquid-phase eCO 2 R. Our work provides new insights into utilizing improved catalyst designs in conjunction with flow cells for successful commercial implementation of this promising technology. Gas phase CO 2 electrolyzer with C-BiOx/NF gas diffusion layer for efficient and durable CO production. CO 2 electrolyzers are emerging as a promising route to convert CO 2 into fuel and alleviate the global worming problem. [Display omitted] • Carbon-derived bismuth oxide nanospheres (C-BiO x) on NF is fabricated. • High electrocatalytic activity and stability for eCO 2 RR are demonstrated. • Oxygen vacancies promote the transport of electrons for eCO 2 RR. • Self-standing ionomer free low loading C-BiO x /NF electrode for AEM and PEM reactors. • Demonstrated high catalytic stability during gas-phase CO 2 electrolysis on GDL. [ABSTRACT FROM AUTHOR]

In this study a one-dimensional transient isothermal model was implemented in MATLAB to conduct an in-depth evaluation of available modeling framework for cold start simulation of PEMFC. In this regard, several shortcomings were addressed and a combination of modifications introduced by other researchers and assumptions made in this study was used to improve modeling accuracy; reaction kinetics variation with temperature and ionomer water content was investigated and incorporated in the model; dynamics of nucleation and subcooling was described by Johnson-Mehl-Avrami-Kolmogorov (JMAK) and Classical Nucleation theories; effect of temperature on ECSA loss was examined and assumptions were made regarding electro-osmotic drag in catalyst layer under low load conditions. The results showed high fidelity to experiments in the early stage of cold start and the model was able to capture the effect of all three influential parameters, i.e. temperature, initial ionomer water content, and current density on performance evolution and failing time in isothermal cold starts with acceptable accuracy. Moreover, the linear performance drop at low subcooling and the nonlinear relation between cold start duration and initial ionomer water content were properly reproduced by the model. • In-depth examination of existing modeling framework for PEMFC cold start simulation. • Incorporating JMAK and Classical Nucleation theories in water freezing simulation. • Describing ORR kinetics variation with temperature and ionomer water content. • Capturing temperature effect on ECSA loss due to ice coverage. [ABSTRACT FROM AUTHOR]

The catalyst layers of proton exchange membrane water electrolyzer are generally made by coating ink mixtures of catalyst and ionomer to the membrane. The particle size and stability of such inks are crucial to the formation of the catalyst layer's microstructure and overall cost. In this paper, the characteristics and stability of iridium oxide inks are investigated. The effects of inks dispersed by sonication and ball-milling on the particle size distribution, zeta potential, and viscosity of the catalyst inks are investigated. For both dispersion methods, it is found that increasing the dispersion time and strength effectively reduces the average particle size as expected. The inks prepared by ball-milling tend to have narrower and smaller size distribution than those by sonication. The rheological behavior of these inks is found to be slightly non-Newtonian. Ball-milling appears to increase the ink viscosity. A dual-dispersion technique that combines both dispersion steps is developed in the present study. The inks made with this procedure yield smaller size distributions than those with single dispersion, thus a higher specific catalyst area that can reduce catalyst loading and cost. These inks are also found to have a long shelf life remaining homogeneous. • Fabrication methods for highly stable iridium oxide catalyst inks are developed. • Particle size distributions for inks dispersed by various methods are compared. • A dual-dispersion procedure is found to produce highly stable inks. [ABSTRACT FROM AUTHOR]

The drying process of the membrane electrode assembly (MEA) has a significant impact on the structure of catalyst layer (CL) and the performance of proton exchange membrane water electrolysis (PEMWE). However, there is a lack of research on the relationship between drying temperature, CL structure, and performance. In this study, we investigated the drying process to regulate the CL microstructure, and the relationship between CL structure and water electrolysis performance was confirmed. As the drying temperature increased from 70 °C to 110 °C, the morphology of the CL changed from dense to loose due to differences in solvent evaporation rate. Specifically, the pore volume fractions of the CL (V v o i d ) increased from approximately 0 to 27%. Electrochemical tests revealed that the dense CL structure formed at lower drying temperatures increased activation and mass transfer losses, while the aggregated CL structure formed at higher drying temperatures resulted in high ohmic loss. Consequently, the MEA dried at 90 °C exhibited the best water electrolysis performance, achieving a voltage of 1.78V at a current density of 2.0 A cm−2. The V v o i d was found to 18%, while the wet ionomer volume fraction (V i o n , w e t ) was 50%. Furthermore, the durability test demonstrated that the MEA dried at 90 °C exhibited a voltage rate of −25 μV h−1 after 200 h of continuous current operation. The stable cell voltage was still observed even after 1000 intermittent start-stop operations, indicating excellent durability. This study provides valuable insights for optimizing the preparation process of MEA to enhance the structure of the CL and improve the PEMWE. It also presents a viable approach towards the commercialization of PEMWE. [Display omitted] • The impact of drying temperature on the CL structure was studied. • The evaporative cooling stage dominated the formation of CL structures. • The relationship between the CL structure and the cell voltage loss was studied. • MEA dried at 90 °C (V v o i d = 18%) exhibited great performance and durability. [ABSTRACT FROM AUTHOR]

As a critical electrochemical reaction region of the proton exchange membrane fuel cell (PEMFC), the cracking issue of the catalyst layer (CL) considerably affects the performance and durability of the PEMFC. However, the impact of chemical ionomer degradation on CL cracking has not been comprehensively revealed. This study investigates the effect of chemical ionomer degradation on CL cracking through accelerated stress tests, characterization, and theoretical analysis. The results indicate that the increasing chemical degradation degree facilitates CL cracking. The CL with the most severe chemical degradation has a single total crack length increment of 1.97 times for the novel CL under the same degree of mechanical degradation. CL fracture resistance analyses reveal that the decrease in interface fracture resistance is the predominant impulse in accelerating CL cracking. Furthermore, the cell voltage reduction of the CL with the most severe chemical degradation during mechanical degradation is 34.22 mV at the current density of 1800 mA cm−2, which is 1.82 times for the fresh CL. The increment of activation resistance and mass transfer resistance are the main causes of the larger cell performance loss. The above findings emphasize the significance of high interface fracture resistance in inhibiting CL cracking and offer theoretical support for analyzing post-operational CL cracking. • Accelerated crack propagation mechanism under joint chemical and mechanical degradations is revealed. • The interface fracture resistance is proved to be the most predominant. • The fracture resistance of the catalyst layer is characterized by a multi-scale measurement method. • Theoretical basis for post-operational catalyst layer cracking analysis is proposed. [ABSTRACT FROM AUTHOR]

Optimizing the structure of the membrane electrode assembly (MEA) is an effective strategy for improving the performance and durability of proton exchange membrane fuel cells. To prepare reinforced integrated MEAs, in this study, a wet ionomer solution coating with expanded polytetrafluoroethylene (ePTFE) reinforcement was deposited on a cathode gas diffusion electrode (GDE) surface and then wet-binding with the anode GDE. Reinforced integrated MEAs with different layers of ePTFE were prepared and their performance and mechanical durability were compared. The peak power densities of MEAs with single- and double-layer ePTFE reinforcements are 1.26 and 1.19 W cm−2, respectively, which are higher than that of conventional catalyst-coated membrane (CCM)-type MEA (1.04 W cm−2). The common defects in the direct membrane deposition-type MEA, including poor gas barrier ability and mechanical durability of the MEA, are essentially eliminated. The reinforced integrated MEAs have lower degradation than CCM-type MEA in humidity cycling conditions due to the restrictive effect of the ePTFE reinforcement in PEM and the supporting effect of the GDEs on both sides of the PEM. In addition, the double layers of the ePTFE reinforcement endow the MEAs with higher stability and further alleviated the mechanical degradation. The strategy of ionomer wet-binding and multilayered reinforcement provides a novel approach for fabricating MEAs with high performance and mechanical durability. [Display omitted] • The integrated MEAs with different layers ePTFE reinforcement are fabricated. • The reinforced integrated MEAs show higher performance and mechanical durability. • Double-layer ePTFE reinforced integrated MEA shows superior stability. [ABSTRACT FROM AUTHOR]

An in-depth understanding of the local mass transport process is essential for precisely regulating the catalyst layer structure in fuel cells. The ionomer on the Pt surface in the catalyst plays a crucial role in the local transport of oxygen and protons. While most models assume that Pt is completely covered by ionomer, experiments have indicated that Pt is partially covered by ionomer in some cause. In this paper, an improved local mass transport model is proposed to investigate the effect of ionomer coverage on internal mass transport process and fuel cell performance. The results show that the current density first increases and then decreases as the ionomer coverage rises from 10% to 90% under 0.6 V. The optimal performance is achieved with a coverage of 40%. Oxygen is more easily transported in water, while ionomer is a better proton conductor. Variations in ionomer coverage lead to different distances for oxygen and proton transfer, which have an important effect on reactant concentration. Furthermore, further study reveals that the current density is greatest at the interface between water and ionomer. Increasing the interface can effectively reduce the comprehensive transport distance of reactants in ionomer and water to improve performance, which is more pronounced than increasing the oxygen transfer coefficient in the ionomer. Overall, this study provides new ideas for the design of high-performance catalyst layers. • An improved fine-structure model of local mass transport in CCL is developed. • Simulate the effect of local oxygen and proton transport on cell performance. • The best cell performance is obtained with an ionomer coverage of 40% under 0.6 V. • Increasing the ionomer/water interface can significantly improve cell performance. • Increasing interface is more effective than enhancing oxygen diffusion in ionomer. [ABSTRACT FROM AUTHOR]

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. • PFSA ionomers of the various types of chemical structures and equivalent weights that serve as PEM materials for PEMEC are studied. • The relationships between the chemical structures of PFSA ionomers and the dispersion characteristics as well as the membrane properties were examined. • The membranes derived from shorter side-chain PFSA ionomers exhibited improved gas barrier and proton conductivity properties. [ABSTRACT FROM AUTHOR]

The development of new proton exchange membranes for PEM technology in fuel cells and electrolysers with increased durability is paramount to system's lifetime and scalability. In this work, new modified Nafion membranes doped with bisphosphonic acids are proposed with increased resilience to chemical degradation by H 2 O 2 /Fe2+, mimicking ex-situ radical attack to membrane structure. Relevant properties were evaluated throughout Fenton's test using fluoride ion release and gravimetry determinations, and by ATR-FTIR spectroscopy and SEM before and after the chemical degradation. The new membranes showed a very good chemical stability after oxidative degradation under Fenton's test conditions at 80 °C, with more durability than Nafion 115 commercial membrane. After chemical degradation, the proton conduction of the membranes was assessed through EIS which reveals a decrease in the proton conductivity of all membranes, with the new modified membranes showing a smaller decrease of their proton conduction properties than Nafion 115 membrane. Fluoride ion release, weight loss measurements and ATR-FTIR spectroscopy data analysis suggest degradation of the side chain of the ionomer. [Display omitted] · Chemical degradation was ensued by mimicking radical attack to membrane structure. · Membrane degradation was assessed through ATR-FTIR, SEM, fluoride ion and gravimetry. · New membranes show improved chemical stability vs Nafion after oxidative degradation. · Results indicated higher degradation of the side chain of the ionomer. · BP doped new membranes hold higher proton conductivity vs Nafion after Fenton's test. [ABSTRACT FROM AUTHOR]

Hydrogen production from the proton exchange membrane (PEM) water electrolysis process provides a promising solution for renewable energy storage. As the site where the electrochemical reactions occur in the PEM electrolyzer, the structure and performance of membrane electrode assembly (MEA) significantly affect the cell efficiency and device fabrication cost. In this paper, porous transport layers (PTLs) and catalyst coating membranes (CCM) that constitute MEA are studied. The use of platinum-coated titanium felt in the anode significantly reduces the cell voltage and ohmic resistance compared with uncoated PTL, while titanium felt works better than carbon paper in the cathode. Higher catalyst loading can provide sufficient active sites for electrode reaction, and 11.1 wt% ionomers provide the best proton and gas transport channel. After optimization, the cell voltage is reduced to 1.840 V at 2 A/cm2, and the efficiency reaches 79%. This paper provides insights for developing efficient and economical PEM electrolyzers. • CCM was first sprayed with anode Ir 0.6 Mn 0.4 O x and cathode Pt 1 Ni 3 /C catalysts. • The performance of PEM electrolyzer was largely affected by PTL materials. • Catalyst loadings in CLs were optimized to enhance performance and reduce costs. • MEA with 11.1 wt% ionomer provides the lowest cell voltage and resistance. [ABSTRACT FROM AUTHOR]

Proton exchange membrane fuel cells (PEMFCs) possess high energy and low power densities, while supercapacitors are characterized by high power and low energy densities. A hybrid PEMFC/supercapacitor device (HPSD) with high energy and power densities was proposed and fabricated for the first time using a reduced graphene oxide/Nafion/Pt electrode in this study. The reduced graphene oxide (rGO) was a capacitive material, and Pt was used as the electrocatalyst. Nafion ionomers adsorbed onto the rGO sheets surface and connected the rGO sheets and the electrolyte (Nafion membrane), thus increasing the utilization rate and specific capacitance of rGO. During the half-cell tests, the rGO/Nafion/Pt electrode exhibited better pulse discharge and galvanostatic discharge performance than the conventional Nafion/Pt electrode. Due to the unique synergy of electrochemical reaction current and capacitance current during the discharge process, the HPSD exhibited a higher power density (26.2 kW kg−1) than the PEMFC (23.9 kW kg−1). The energy density (12.7 kWh kg−1) exhibited by HPSD was close to that of the PEMFC (13.5 kWh kg−1). Therefore, the concept of HPSD is to create a new method for developing next-generation electrochemical devices with high energy and power densities. • A hybrid PEMFC/supercapacitor device (HPSD) was proposed and fabricated. • The HPSD possesses high energy (12.7 kWh kg−1) and power densities (26.2 kW kg−1). • The reduced graphene oxide/Nafion/Pt electrode was used to fabricated the HPSD. • Reduced graphene oxide (rGO) was capacitive material, and Pt was electrocatalyst. • Nafion ionomers could connect the rGO sheets and the electrolyte (Nafion membrane). [ABSTRACT FROM AUTHOR]

To improve the performance of anion exchange membrane fuel cells (AEMFCs) with platinum-group-metal (PGM)-free cathode, significant efforts are still needed. Herein, we prepare high oxygen reduction reaction activity FeNC catalyst and integrate such catalyst into AEMFCs with different ionomer/catalyst (I/C) ratios from 0.1 to 1.0. We show that suitable quaternary ammonia poly (methyl-piperidine-co-p-terphenyl) (QAPPT) ionomer content can provide better catalyst layers (CLs) microstructure, in which the transfer efficiency of electron and charge can be improved so as to decrease the active polarization. High ohmic resistance is caused by either low or excess ionomer which leads to inconsecutive ionic network of CLs or high coverage of non-electronic conductor. In addition, mass-transfer polarization is also brought out by excess QAPPT ionomer which fills up the gas–liquid transport pores inside FeNC/QAPPT aggregates. With the I/C ratio of 0.7, AEMFC with FeNC cathode exhibits the best cell performance achieving a peak power density of 660 mW cm−2 at 1500 mA cm−2 under H 2 /air (CO 2 -free). To verify the feasibility of FeNC cathode in realistic applications, an AEMFC stack with 29 cells of 270 cm2 MEAs was assembled with a power output of 508 W under H 2 /air. • High ORR activity FeNC catalyst was prepared and integrated into AEMFCs. • When ionomer/catalyst is 0.7, AEMFC exhibits the performance of 660 mW·cm−2@1500 mA·cm−2 under H 2 /air (CO 2 -free). • The first reported AEMFC stack with 29 cells of 270 cm2 MEAs was assembled with a power output of 508 W under H 2 /air. [ABSTRACT FROM AUTHOR]

The effect of ionomer content on the microstructures and multiphase transport properties of cathode catalyst layer (CCL) for polymer electrolyte membrane fuel cells is investigated via combining molecular dynamics simulations and single-cell experiments. The maximum electrochemical surface area (ECSA) is gained when the Pt/C surface is entirely covered by ionomer due to the established proton transport paths network. As the ionomer content increases in the CCL models, the diffusion coefficient of H 3 O+ increases by 2 times, while the O 2 diffusion coefficient shows decrease monotonously. Both charge transfer resistance and ohmic resistance exhibit U-shaped relationship to ionomer content. It is attributed to the coupling effect of increased ECSA, raised proton diffusion coefficient, and thickening CCL. The effect of ionomer on voltage loss in the low-to-high region is explained via a comprehensive understanding of structural interaction, transport dynamics, ECSA and impedance. It can guide the design of efficient three-phase boundary. • Effect of ionomer content on catalyst layer by combining MD simulation and experiment. • Maximum ECSA requires entire ionomer covered on the Pt/C surface. • Charge transfer resistance and ohmic resistance are U-shaped function to ionomer content. • Multiphase transport is impacted by ECSA, diffusion coefficient, and thickness. [ABSTRACT FROM AUTHOR]

Structure design is the primary strategy to acquire suitable ionomers for preparing proton exchange membranes (PEMs) with excellent performance. A series of comb-shaped sulfonated fluorinated poly(aryl ether sulfone) (SPFAES) membranes are prepared from sulfonated fluorinated poly(aryl ether sulfone) polymer (SPFAE) and sulfonated poly(aryl ether sulfone) oligomer (SPAES-Oligomer). Chemical structures of the comb-shaped membranes are verified by 1H nuclear magnetic resonance (NMR) and Fourier transform infrared (FT-IR) spectra. The comb-shaped SPFAES membranes display more continuous hydrophilic domains for ion transfer, because the abundant cations and flexible side-chains structure possess higher mobility and hydrophilicity, which show significantly improved proton conductivity, physicochemical stability, mechanical property compared to the linear SPFAE membranes. In a H 2 /O 2 single-cell test, the SPFAES-1.77 membrane achieves a higher power density of 699.3 mW/cm2 in comparison with Nafion® 112 (618.0 mW/cm2) at 80 °C and 100% relative humidity. This work offers a promising example for the synthesis of highly branched polymers with flexible comb-shaped side chains for high-performance PEMs. [Display omitted] • Long comb-shaped sulfonate side-chains were incorporated by a facile synthetic rout. • Enhanced water uptake and proton conductivity for comb-shaped PEMs. • Good antioxidative stability was obtained due to the existence of C–F bonds. • Highly branched ionomers for comb-shaped PEMs are beneficial to build continuous H+-channels. • SPFAES-1.77 exhibited higher cell performance than Nafion® 112 at 80 °C. [ABSTRACT FROM AUTHOR]

Radiation-induced graft polymerization is introduced to effectively fabricate proton exchange membrane based on 12.5 μm fluorinated ethylene propylene (FEP) film. The graft side chains penetrate FEP film and distribute inside the bulk matrix evenly. The membranes exhibit hydrophilic/hydrophobic microphase-separated morphology as well as good thermal stability. The influences of irradiation parameters on the membrane property are investigated and the resulting membranes (named FEP-g-PSSA) exhibit excellent physicochemical properties. Membrane with 27.48% degree of graft and 130.1 mS cm−1 proton conductivity is employed for fuel cell performance measurement. Under optimized operate conditions (80 °C, 75% relative humidity), the power density could reach up to 0.896 W cm−2, inspiring for fuel cell application. The mass-transport-controlled polarization of membrane electrode assembly (MEA) based on FEP-g-PSSA membrane is higher than Nafion® 211 within the whole current density range and the gap is widening with increasing current density. At 2.0 A cm−2, the mass transfer polarization of FEP-g-PSSA reaches up to 0.204 V, far higher than Nafion® 211 (0.084 V). By promoting the compatibility between the ionomer in the catalyst layer and FEP-g-PSSA membrane and optimizing the membrane/catalyst layer/gas diffusion layer interfaces, the fuel cell performance could be significantly enhanced, making the FEP-g-PSSA membranes promising in fuel cell application. [Display omitted] • Side-chain type copolymers prepared by radiation-induced grafting on ultra-thin pristine FEP film. • FEP-g-PSSA membrane exhibited good combination of physicochemical properties. • FEP-g-PSSA membrane exhibited remarkable power density up to 0.896 W cm−2. • Mass-transport-controlled polarization is responsible for the performance inferiority of FEP-g-PSSA. • Fuel cell performance could be further enhanced by optimizing materials compatibility and MEA interfaces. [ABSTRACT FROM AUTHOR]

Cross-linked quaternised Poly(2,6-dimethyl-1,4-Phenylene Oxide) (QPPO)-based membranes were prepared via Friedel-Crafts reactions using SnCl 4 catalyst, 1,3,5-trioxane and chlorotrimethylsilane as environmentally-friendly chloromethylating reagents. New equations to calculate the degree of chloromethylation ( DC ) and cross-linking degree ( CLD ) were proposed. Ionic conductivity of 133 mS cm−1 at 80 °C was obtained, one of the highest reported for QPPO based membranes. We have compared QPPO to chloromethylated polystyrene- b -poly(ethylene/butylene)-b-polystyrene (SEBS) ionomer and report on the importance of ionomer-membrane interaction as well as the trade-off between swelling ratio and conductivity on performance and mechanical stability of AEM water electrolyser. Exsitu stability testing after 500 h in 1 M KOH showed membranes retained up to 94% of their original IEC . QPPO was employed as both membranes and ionomers in electrolyser tests. QPPO membranes exhibited area specific resistance of 104 mΩ cm−2 and electrolyser current density of 814 mA cm−2 at 2.0 V in 0.1 M NaOH solution at 40 °C. [Display omitted] • New equations to calculate the degree of chloromethylation (DC) and cross-linking degree (CLD). • Synthesis and fabrication of self-crosslinking PPO based AEM with ionic conductivity >0.13 S cm−1. • Electrolyser current density of 814 mA cm−2 at 2.0 V at 40 °C. • Area specific resistance of 104 mΩ cm−2 in 0.1 M NaOH solution at 40 °C. [ABSTRACT FROM AUTHOR]

The effect of polymeric architecture on the water uptake in ionomer membranes is modelled by Dissipative Particle Dynamics. We consider four polymers (a - d) of similar ion exchange capacity that contain hydrophobic A and hydrophilic C beads. For architecture a (A[A]C[A][A 2 ]) 5 and b (A[A]C[A 3 ]) 5 the C beads are located along the backbone that contain respectively 3 (a) and 2 (b) hydrophobic side chains per repeat unit. For architectures c ((A[C]A 4 ]) 5) and d ((A[C]A[A 3 ]) 5) each C bead represents a short hydrophilic side chain. Water is modelled by W beads. For ~20 nm thick membranes the water uptake is followed. The equilibrium water volume fraction varies between ~0.075 (architecture a) and ~0.4 (architecture d), and increases with (1) decreasing amount of C-A bonds per repeat unit and (2) the average number of bonds between hydrophobic beads and the nearest C bead, < N bond phob-phil>. The potential energy per bead at equilibrium decreases as function of < N bond phob-phil>. Water uptake is anticipated to show an increasing trend with increase of < N bond phob-phil> for various architecture families. Some supporting evidence from experiments in literature is discussed. These results are of relevance for the optimization of proton and hydroxide ion conducting pores in electrochemical devices. [Display omitted] • Water uptake for 4 model ionomers is modelled by dissipative particle dynamics. • The architectures share features with proton and anion exchange membranes. • The functional sites are pendent or located within the polymer backbone. • Water uptake increases with average hydrophobic-hydrophilic distance. • Similar trends are obtained from experimental results in literature. [ABSTRACT FROM AUTHOR]

A three-dimensional, multi-component, single-phase model is applied for analyzing the electrochemical performance of the proton exchange membrane fuel cell (PEMFC) with U-shaped channel using COMSOL Multiphysics software. To validate the numerical model, the results are compared with the experimental data available in the literature. This work numerically investigates the effects of convection and diffusion under the rib, membrane thickness, ionomer content, and current density distribution at an interface between the gas diffusion layer and the catalyst layer. These effects were not studied for a U-shaped single serpentine channel despite having several benefits such as uniform reactant distribution through convection and diffusion under the rib and the resulting uniform current generation. A total of three membranes with 2, 3.5, and 5 mil thicknesses are analyzed, and an improvement of 17% in PEMFC performance with 2 mil thickness is observed owing to a decrease in internal resistance compared to 3.5 and 5 mil. Furthermore, an ionomer volume fraction in the catalyst layer is varied from 0.3 to 0.6, and the performance enhancement of 7% is reported at 0.5 volume fraction. • PEMFC is numerically analyzed with a U-shaped channel. • Convection under the rib is found to be more prominent in anode. • Current density peak is observed near the channel – rib junction. • Improved flow channel design using current density distribution at multiple locations. • Performance comparison with optimal membrane thickness and ionomer volume fraction. [ABSTRACT FROM AUTHOR]

To increase the conductivity of proton exchange membranes in the membrane thickness direction, a novel mixed matrix membrane of Nafion ionomer and sulfonated graphene nanoplates (sGNP) with aligned proton channels is prepared with the assistance of an electric field. A high voltage alternative electric field is applied to a casting solution consisting of Nafion ionomer, sGNP, N, N-dimethylformamide (DMF), and p-xylene (PX) while evaporating the solvents. The sGNP, naturally attracting the ionic groups of Nafion ionomer to their vicinity, is polarized and rotated under the electric field, leaving aligned proton channels in the solidified membrane. The trans-plane proton conductivity of the mixed matrix membrane can reach 0.155 S cm−1 at 80 °C and 100% RH, an increase of 48% as compared with the conventional cast Nafion membrane. Accordingly, the peak power output of H 2 /O 2 fuel cell with the mixed matrix membrane increases by 15%, reaching 440 mW cm−2 at 80 °C. • sGNP-Nafion membrane with aligned ionic channels is fabricated under electric field. • Electrically aligned sGNP assists the trans-plane orientation of ionic channels. • sGNP-Nafion membrane shows 48% higher proton conductivity over cast Nafion membrane. • Peak power output of H 2 /O 2 fuel cell with sGNP-Nafion membrane increases by 15%. [ABSTRACT FROM AUTHOR]

Developing self-humidifying membrane electrode assembly (MEA) is of great significance for the practical use of proton exchange membrane fuel cell (PEMFC). In this work, a phosphoric acid (PA)-loaded Schiff base networks (SNW)-type covalent organic framework (COF) is proposed as the anode catalyst layer (CL) additive to enhance the PEMFC performance under low humidity conditions. The unique polymer structure and immobilized PA endow the proposed COF network with not only excellent water retention capacity but also proton transfer ability, thus leading to the superior low humidity performance of the PEMFC. The optimization of the additive content, the effect of relative humidity (RH) and PEMFC operating temperature are investigated by means of electrochemical characterization and single cell test. At a normal operation temperature of 60 °C and 38% RH, the MEA with optimized COF content (10 wt%) showes the maximum power density of 582 mW cm−2, which is almost 7 times higher than that of the routine MEA (85 mW cm−2). Furthermore, a preliminary durability test demonstrates the potential of the proposed PEMFC for practice operation under low humidity environment. • A COF network was proposed to develop MEA with self-humidifying ability. • The COF network possesses water retention and proton transfer abilities simultaneously. • The COF network has excellent compatibility with Nafion ionomer and membranes. • The MEA shows excellent low humidity performance at 60 °C and 38% RH. • Durability test reveals the good stability of the MEA for low humidity operation. [ABSTRACT FROM AUTHOR]

With the wide use of platinum alloy electrocatalysts proton exchange membrane fuel cells, the dissolution of transition metal in the acid environment of catalyst layer becomes a major concern due to the decreased catalytic activity during long-term operation. Although great efforts have been done, few attention is paid to the effect of transition metal ion contamination of Nafion ionomer that wrapped around catalyst particles within catalyst layer which might greatly influence the proton conduction. To elucidate such effect, ultrathin Nafion film on SiO 2 model substrate is prepared via self-assembly method to represent the ionomer in fuel-cell catalyst layers, and the ultrathin film with specific thickness is further equilibrated in Co(NO 3) 2 /HNO 3 solutions with different Co2+ concentration to achieve different doping level. Conductivity measurements demonstrate that the non-precious metal contamination severely worsens proton conduction of Nafion ionomer, but it is always ignored before. In addition, when the occupation of H+ in Nafion ionomer is less than 50%, the activation energy shows a sharp increase, indicating a possible change in proton conduction mechanism. Image 1 • 40 and 120 nm Nafion thin films with different cobalt doping levels are prepared. • Effect of cobalt doping level on proton conduction of Nafion ionomer is tested. • The increase of cobalt doping level seriously reduces the proton conductivity. [ABSTRACT FROM AUTHOR]

Crosslinkable poly (arylene ether sulfone) block copolymers (bSPAES (x/y)) containing pendant butanesulfonic acid and ethanedione groups were prepared from a new side-chain difluoro aromatic monomer 1-(2,6-difluorophenyl)-2-(3,5-dimethoxyphenyl)-1,2-ethanedione via block copolycondensation, demethylation, and further nucleophilic substitution of 1,4-butane sultone. Meanwhile, quinoxaline-based crosslinked block copolymers (C-bSPAES (x/y)) were obtained via cyclocondensation. The corresponding block copolymer membranes have high mechanical properties and anisotropic membrane swelling for either crosslinked or uncrosslinked ones. bSPAES (5/10) with ion exchange capacity (IEC) of 2.05 mequiv. g−1 has low water uptake (WU) of 59.1% at 80 °C but relatively high conductivity of 225 mS cm−1, which is ascribed to its good microphase separation. Meanwhile, the crosslinked C-bSPAES (5/10) with IEC of 1.76 mequiv. g−1 exhibits a decreased WU by half, an improved oxidative stability by 200% and a reduced membrane swelling by 40% than the uncrosslinked bSPAES (5/10). The results suggest that quinoxaline-based crosslinking can obviously improve properties of bSPAES (x/y). In addition, even though maximum power density of C-bSPAES (5/10) is lower than that of Nafion 212, C-bSPAES (5/10) still has an acceptable good single-cell performance, indicating a possible fuel cell application. Image 1 • Crosslinkable and crosslinked SPAE block copolymers are developed. • DFDMED-based side-chain block ionomer membranes exhibit good microphase separation. • Crosslinking contributes to enhance oxidative stability and restrain PEM swelling. • Good performance is joint result of crosslinking, side-chain and block copolymer. [ABSTRACT FROM AUTHOR]

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. • The size of SSC-PFSA aggregations was tuned in binary solvents of DPG and water. • The size of ionomers and Pt/C-ionomers was investigated by DLS. • The morphology of CLs is presented by DPG content in the catalyst inks. • Total oxygen transport resistance of the CLs with the DPG contents was investigated. [ABSTRACT FROM AUTHOR]

In spite of significant achievements in alkaline exchange membrane fuel cells (AEMFCs) in recent years, they are still lagging behind proton exchange membrane fuel cells (PEMFCs) due to performance instability. Among the relevant operational parameters of AEMFC, the researchers have found that poor water management within the cell was the main reason for failure of the system. In the past five years, numerous modeling and experimental works were reported proposing different strategies to improve water management of AEMFC. With proper water management, the achievable power output in AEMFCs is comparable with that of PEMFCs or even more. Efforts have to be continued, but AEMFCs can become a strong competitor in the market place. This review paper discusses the strategies and developments impacting water management of AEMFCs providing knowledge source for upcoming studies. • Water dynamics are more complex in AEMFC than PEMFC. • PTFE in GDL plays crucial role in water management. • Pt and ionomer loading in the electrode strongly impacts water management. • AEM with low diffusion resistance mitigates anode flooding. • Operating conditions (RH, T) should be optimized for stable AEMFC performance. [ABSTRACT FROM AUTHOR]

Designing polymer chains which contain building blocks with well-defined dimension is an efficient method to induce microphase separation and regulate the ionic channels of polymer electrolyte membranes (PEMs). In this study, a Wells-Dawson-type polyoxometalate (POM) is synthesized and chemically bonded to a norbornene derivative to prepare poly (POM) blocks. Then the block copolymer poly (POM) 10 - b -poly (COOH) 300 is fabricated using poly (POM) and poly (COOH) blocks. Finally, the block copolymer is blended with sulfonated polysulfone (SPS). The electrostatic interactions between the block copolymer and SPS confer the blend membrane with enhanced mechanical and dimensional stabilities. Due to the homogenous distribution of POM clusters and the hydrophilic-hydrophobic interactions between POMs and polymer backbones, the adjacent hydrophilic domains are connected and continuous proton-transfer channels are induced. As a result, the blend membrane displays proton conductivity of 0.053 S cm−1 (25 °C, 100% RH) and 1.5 × 10−2 S cm−1 (80 °C, 40% RH), which are 2.52 and 6.25 times higher than those of the plain SPS membrane. Furthermore, SPS/POM-BC-30 shows a maximum power density of 164.9 mW cm−2, which is 54.7% higher than SPS. Image 1 • POM is chemically bonded to a norbornene derivative to prepare block copolymer. • Blend membrane containing poly (POM) 10 - b -poly (COOH) 300 is fabricated. • The proton-transfer channels are regulated and optimized by POM clusters. • The blend membrane exhibits a 6.25-fold proton conductivity enhancement. [ABSTRACT FROM AUTHOR]

A novel anion-conducting ionomer binder, quaternized polybenzimidazoles (QPBIs) with 4-methyl-4-glycidylmorpholin-4-ium chloride (MGMC) in the main-chain and/or in the side group were synthesized for solid alkaline fuel cells (SAFCs). Crosslinking of the polybenzimidazole derivatives using a crosslinker containing epoxy groups formed ionomer binder in electrodes, and the crosslinked QPBIs showed better mechanical stability than non-crosslinked QPBIs. During the electrode drying process, on-site crosslinking was introduced to form thermally crosslinked ionomer binder in catalyst layers. A bench-scale SAFC with the crosslinked QPBI (CQPBI) containing 35 wt% of ionomer binder showed higher peak power density (35.3 mW cm−2) than the SAFC with 2,2′(m -phenylene)-5,5′bibenzimidazole (m -PBI) with 35 wt% of ionomer binder (20.9 mW cm−2). The membrane-electrode assembly (MEA) with CQPBI (35 wt% binder) showed two times higher chemical stability than that with m -PBI (35 wt% of ionomer binder) in load cell tests. On-site crosslinking formation of thermally crosslinked quaternized polybenzimidazole occurs at the electrodes of membrane-electrode assemblies during their drying process. Image 1 • The anion conducting PBI membranes were prepared by a grafting method. • The crosslinked QPBI showed higher chemical stability than non-crosslinked QPBI. • Two-way anionic conduction by PBI as well as quaternized functional groups of PBI. • Mitigation of a decrease in ionic conductivity by crosslinking. [ABSTRACT FROM AUTHOR]

Carbon-supported Pt catalysts (Pt/Cs) for use of cathode catalyst layers (CLs) for PEFCs were covered with silica layers in order to improve performance. CLs with low ratio of ionomer to carbon (I/C) for Pt/C and silica-coated Pt/C were fabricated using an inkjet printing (denoted as Pt/C(IJ) and SiO 2 -Pt/C(IJ)) to reduce oxygen diffusion resistance. Compared to Pt/C(IJ), SiO 2 -Pt/C(IJ) ink maintained good dispersion and high stability under the lower I/C. The performance of SiO 2 -Pt/C(IJ) was significantly higher than Pt/C(IJ) at 0.6 V under all humidity conditions. In particular, the performance of SiO 2 -Pt/C(IJ) under low humidity conditions showed noticeable improvement regardless of current density area. From FIB-SEM, it was confirmed that the morphologies and porosities of both catalysts were the same. Thus, these results indicate that oxygen diffusion resistance, related to structure of CLs, hardly affects the performance, whereas improved performance is attributed to increased proton conductivity by silica layers containing hydrophilic groups. • CL for silica-coated catalysts with low ionomer are prepared by inkjet method. • The coverage of Pt with silica layers improves dispersion in the catalyst ink. • The silica-coated Pt catalysts with low ionomer show high performance on MEA. • Silica coating of Pt catalysts enhances performance under RH below 60% conditions. [ABSTRACT FROM AUTHOR]

Perfluorosulfonic acids (PFSA) are the most widely used ionomers in Polymer electrolyte membrane fuel cells as both membrane and catalyst layer support. This study presents an electrochemical based analysis of using long-side-chain Nafion® and short-side-chain Aquivion® PFSA ionomers as binders in the catalyst-layers of PEMFC. Membrane electrode assemblies were designed with consistent components, varying only the catalyst ink's ionomer type from 28 wt% Aquivion® to 28 wt% Nafion®. The durability and performance profile of the resulting catalyst-coated-membranes made from using these PFSA ionomers as binders in the catalyst layers was investigated. Semi-empirical modeling shows that the Nafion® ionomer based binders give a catalyst-coated-membrane with a 46.6% higher ohmic resistance compared to using Aquivion® ionomers as binders. The power density analysis also showed that catalyst-coated-membranes made with Aquivion® ionomer based binder gives an output power that is 22.33% higher than catalyst-coated-membranes made with Nafion® ionomers as binders in the catalyst layers. The Aquivion® ionomer binder also shows higher catalyst utilization compared to the Nafion® ionomer binders. The Electrochemical Impedance Spectroscopy– Equivalent Circuit Model analysis showed that the membrane electrode assembly degradation is more pronounced in the Nafion® ionomer based binder compared to its Aquivion® counterpart. It is thus shown that Aquivion® ionomers are better catalyst binders compared to the Nafion® ionomers as they result in catalyst-coated-membranes that are better performing and more durable. • Aquivion® based catalyst-binder showed lower ohmic resistance compared to Nafion®. • Aquivion® ionomer-based catalyst-binder showed higher ECSA compared to Nafion®. • MEA degradation is more pronounced in the Nafion® ionomer compared to Aquivion®. • Catalyst utilization was higher for Aquivion® compared to Nafion® ionomer. [ABSTRACT FROM AUTHOR]

Abstract Previously, nanofiber-nanoparticle electrodes produced via a simultaneous electrospinning and electrospraying (E/E) process (E/E electrodes) resulted in polymer electrolyte membrane fuel cells with high power densities at ultra-low platinum (Pt) loadings (<0.1 mg Pt cm−2). In this study, E/E electrodes were fabricated at various Nafion contents to investigate the impact of ionomer content on catalyst layer transport resistances and fuel cell power density at ultra-low Pt loadings. Regardless of the Nafion content in the electrospray, the Nafion nanofiber diameters and catalyst aggregate particle sizes are constant in the E/E electrodes evidenced by electron microscopy. Therefore, this study allows for the exclusive investigation of the effect of transport resistances on fuel cell performances at different ionomer contents at a constant catalyst layer morphology, which differs from conventional electrodes. At higher magnifications, changes are evident in the micrographs around the catalyst aggregate particles, where an increase in ionomer thin film thickness is observed with increasing ionomer content. The maximum fuel cell performance and a minimum in catalyst layer resistance for E/E electrodes is observed at a total Nafion content of 62 wt%, which differs from conventional electrodes (ca. 30 wt%). Graphical abstract Image 1 Highlights • Nanofiber-nanoparticle electrodes via simultaneous electrospinning/electrospraying. • High fuel cell power densities at ultra-low platinum loadings. • Ability to maintain similar catalyst layer morphology at different Nafion contents. • Exclusive investigation of transport resistances at different Nafion contents. • Optimum Nafion content at 62 wt percent. [ABSTRACT FROM AUTHOR]

Abstract Oxygen can only be reduced at the quadruple phase boundary (catalyst, carbon support, ionomer and oxygen) of the cathode catalyst layer with non-conducting electrocatalyst. To maximize the quadruple phase boundary sites is crucial to increase the peak power density of each membrane electrode assembly. The quadruple phase boundary is depending on the ratio of catalyst, carbon support and ionomer. The loading of catalyst layer is also crucial to the fuel cell performance. In this study, non-stoichiometric α-MnO 2 manganese dioxide nanorod material has been synthesized and the ratios of carbon, ionomer and catalyst loadings were optimized in alkaline membrane fuel cell. In total, ten membrane electrode assemblies have been manufactured and tested. Taguchi design method has been applied in order to understand the effect of each parameter. The conclusion finds out the ionomer has more influence on the alkaline membrane fuel cell peak power performance than carbon and loading. Highlights • Oxygen vacancy imbedded α-MnO 2 catalyst as the cathode for alkaline fuel cell. • Optimize the carbon:catalyst:ionomer ratios for cathode catalyst layer. • Taguchi design method was used to determine the effect factor of each parameter. [ABSTRACT FROM AUTHOR]

Abstract Nanocomposite membranes incorporating electrospun nanofibers of SPEEK, blended with 30 wt% PVB within a water-based matrix of SPEEK with 35 wt% PVA using water as solvent, were prepared and characterized for their application as Polymer Electrolyte Membrane Fuel Cells (PEMFCs) in H 2 /O 2 operating at low temperatures. Compared with a dense bulk phase, an improvement of proton conductivity in the SPEEK-30PVB nanofiber framework was observed. The incorporation of the SPEEK-30PVB nanofibers provides mechanical improvement while the matrix phase of SPEEK-35PVA emphasizes the proton conductivity at crosslinking temperatures up to 140 °C. PEMFC performance tests showed promising results for the use of these novel low cost membranes. The nanocomposite membrane reached a power density which is 25% higher than that of Nafion117 membranes with MEAs constructed with Pt loading in anode and in cathode. However, when the Pt of the cathode is substituted by Ru 3 Pd 6 Pt, the power density is lower in Nafion117 MEAs than in the nanocomposite. When used commercial Pt-carbon cloth (Pt-ETEK) for the electrodes, the power density achieved is 1.4 times higher for the Nafion117 MEAs than SPEEK nanocomposites. The differences observed in performance is attributed to the large polarization losses found in the composite membranes because of the interfacial phenomena associated with the use of commercial Nafion-based electrodes. Highlights • Nanofiber morphology with the SPEEK-30PVB system improves proton conductivity. • Membranes mechanical properties are adequate for application in PEMFC and DMFCs. • Results show that the composite membranes represent a viable alternative to Nafion®. [ABSTRACT FROM AUTHOR]

A modified Loschmidt cell was used to measure the relative gas diffusivity ( D ∗ ) of the porous catalyst layers (CLs) of polymer electrolyte membrane fuel cells as a function of CL ionomer/carbon weight ratio (I/C) (0.5, 1.1, and 1.5) and operating temperature (20, 40, and 72 °C). D * decreased by 80% when I/C was increased from 0.5 to 1.5. While the effective gas diffusivity of CL increased with temperature, D * decreased because binary diffusion increases more rapidly than Knudsen diffusivity with temperature. The structure of CL was modeled through considering a packed-sphere model for carbon particles within agglomerates, and a network of overlapped spherical agglomerates forming the CL. The gas diffusion problem was solved analytically for the CL structure considering both Knudsen and molecular mechanisms, and, results were validated. Using the model, the effect of porosity, pore size distribution and ionomer coverage on gas diffusivity was evaluated. [ABSTRACT FROM AUTHOR]

The degradation of perfluorinated sulfonic acid ionomer (PFSA) binder in catalyst layer of Proton Exchange Membrane Fuel Cell (PEMFC) was investigated on Membrane-Electrode-Assemblies (MEA) operated up to 10400 h in base load conditions for telecom relay. Soxhlet extractions in water media were performed on the catalyst layer deposited on the Gas Diffusion Layer (GDL). The Soxhlet solutions for anode and cathode sides were analyzed by 19 F NMR spectroscopy showing degradation products originating from the ionomer in the catalyst layer. At the cathode side, 1,2,2-tetrafluoro-2-(1,2,2,2-tetrafluoroethoxy)ethanesulfonic acid were clearly identified. This suggests that PFSA binder degradation originated from an H• and/or •OH radical attack of the side chain. The NMR quantification of the degradation products allows a fruitful comparison with the literature. The degradation mechanism of the PFSA binder is different from that of the membrane. [ABSTRACT FROM AUTHOR]

Block poly(arylene ether sulfone) copolymers caring pendent benzyl-quaternary ammonium groups were prepared through multiple-step reaction pathways that involve pre-polycondensation, block copolycondensation, bromomethylation and Menshutkin reactions. The copolymer ionomer based anion exchange membranes (AEMs) with ion exchange capacity (IEC) from 0.75 to 1.10 mequiv g −1 display relatively large hydroxide conductivities of 45.9–66.1 mS cm −1 at 80 °C, which are ascribed to the distinct hydrophobic/hydrophilic microphase separation resulted from the block copolymer structures and side-chain type hydrophilic segments. Compared to the corresponding random copolymer based AEM, the block ones have obviously higher stability and larger hydroxide conductivity due to the well-connected ionic nanochannels. Among the AEMs, bQPAE-x7y32 with IEC of 1.10 mequiv g −1 gives the best performance with high hydroxide conductivity of 66.1 mS cm −1 , low methanol permeability of 4.9 × 10 −7 cm 2 s −1 , large φ of 4.6 × 10 4 Scm −3 s, as well as good alkaline stability, respectively. [ABSTRACT FROM AUTHOR]

Fatigue-induced membrane fracture due to dynamic stresses is an important lifetime-limiting failure mode in automotive fuel cell applications. Here, a series of ex situ experiments are first conducted to measure the rate of crack growth in Nafion NRE211 membranes for a range of stress, temperature (23–70 °C), and relative humidity (50–90%) conditions relevant to automotive fuel cell operation. The crack growth rate is found to be ∼1–10 nm per load cycle and strongly depends on the stress intensity: the rate increases by an order of magnitude for a mere 10–30% increase in stress, which suggests that improved stress uniformity and avoidance of high stress points is important for durability. Moreover, the sensitivity to applied stress doubles from room conditions to fuel cell conditions, where the temperature has 2–3x stronger impact on the fracture propagation than the relative humidity. Microstructural analysis indicates that plastic deformation (60% localized thinning) at the crack tip accompanies crack growth. A semi-analytical model based on Paris law is then developed to simulate crack growth as a function of cyclic loading. The model incorporates elastic-viscoplastic mechanical behaviour of ionomer membranes and provides crack growth predictions in agreement with ex situ data up to 100% strain. [ABSTRACT FROM AUTHOR]

The last advances on the application of INCA (Ionomer Nc Analysis) methodology for a better understanding of perfluorinated ionomers are reported and discussed. It was found that INCA is a very suitable technique for the determination of the melting temperature (Tm) of un-crystallized and semi-crystalline perfluorinated ionomers. Furthermore, for these determinations, it is even more precise than dynamic mechanical analysis, a method essentially developed for polymers in which the water-uptake is negligible. Of interest, it is the information that INCA methodology gives on the phenomenon of the water-uptake memory of perfluorinated ionomers. [ABSTRACT FROM AUTHOR]

The effect of ionomer/carbon (I/C) ratio on proton exchange membrane (PEM) fuel cell cold start is investigated experimentally with theoretical water transport analysis. The scanning electron microscope (SEM) images show larger agglomerates and smaller effective reaction area by increasing the I/C ratio from 0.7 to 1.7. For normal operation, increasing the I/C ratio can improve the humidity tolerance, especially in the cathode. For cold start >−10 °C, a lower I/C ratio leads to better performance because the core reaction area is shifted towards the membrane, leading to more membrane water absorption and slower ice formation. For <−15 °C, the total water production is low and almost the same for the different I/C ratios because the ice formation takes place before effective membrane water absorption; and although the cathode catalyst layer (CL) and micro-porous layer (MPL) can provide sufficient space to store all the ice, higher I/C ratios (e.g. 1.2) still cause more ice formation in GDL and flow channel because the core reaction area becomes closer to GDL. The results show that the CL design has significant effect on the cold start performance, and there is a potential for further improvement. [ABSTRACT FROM AUTHOR]

In this study, crosslinked poly(vinyl alcohol)/sulfosuccinic acid (PVA/SSA) ionic polymer and Nafion ® N-115 membranes are used as electrolytes to fabricate different types of membrane electrode assemblies (MEAs) for proton exchange membrane fuel cells (PEMFC). Each MEA is fabricated with various crosslinked PVA/SSA ionomer loadings (0.04–1.5 mg cm −2 ) in catalyst layer based on volumetric ratio between catalyst and ionomer. Properties of each catalyst layer are evaluated using scanning electron microscopy, cyclic voltammetry, and hydrogen pumping technique. I–V characteristics, impedance, and incubation behaviour of each cell are evaluated in fuel cell testing fixture. Incubation of cell is effective when ionomer loadings are below 0.1 mg cm −2 . At ionomer loading of 0.04 mg cm −2 , PEMFC demonstrates highest power densities than that observed with other loadings of ionomer due to higher electrochemical active surface area of the electrode. Hydrogen pumping studies reveals that the PVA/SSA ionic polymer is a potential anode material for PEMFC electrodes while ionomer loadings are below 0.1 mg cm −2 . [ABSTRACT FROM AUTHOR]

In order to elucidate a porous structure consisting of carbon aggregate and ionomers, the agglomeration mechanism of carbon black in CL is examined based on the experimental results of particle diameter distribution of carbon black in CL ink with or without an ionomer and the transmission electron microscopy image of carbon black dispersion. A theoretical model of the attraction and repulsion between carbon particles is also discussed, and compared with experimental results. From this model and the measured particle distribution data, it is supposed that the structure with large isolated pores results from carbon black dispersion in CL slurry, and the interaction phenomenon of each carbon black particle depends on the weight ratio of ionomer and carbon. Furthermore, the carbon black aggregate and the agglomerate structure in CL are reproduced numerically, and the effects of the heterogeneous structure on gas diffusion performance are examined by simulations. These results suggest that gas diffusion performance depends on pore size and ionomer adhesion. In particular, ionomer migration near large pores strongly affects gas diffusion performance because of the existence of isolated pores. In addition, better gas diffusion needs a certain amount of pores of non-uniform sizes. [ABSTRACT FROM AUTHOR]

Recent development on new anionic exchange membranes for alkaline membrane fuel cells has led to an increase on electrocatalyst testing measurements in three-electrode half-cells in alkaline media. However, there is not yet any commercial alkaline ionomer widely used, comparing to Nafion ® in acidic media. In this work, two different commercial alkaline ionomers (I2 from Acta and Fumion ® FAA-3 from Fumatech) are tested. Different catalyst: ionomer ratios are employed in order to adjust the ink composition for a correct evaluation of the catalyst activity. For this purpose, a commercial 20 wt.% Pt/C catalyst was tested for CO electrooxidation and oxygen reduction reaction in thin layer RDE configuration. [ABSTRACT FROM AUTHOR]

Proton and water transport properties as well as water sorption, thermomechanical properties, and morphology of a new series of semi-Interpenetrating Polymer Network (semi-IPN) combining perfluorosulfonated ionomer (Aquivion ® ) with a neutral fluorinated network of composition ranging between 10 and 50 wt% have been studied. When less than 20 wt% of neutral fluorinated network are included, water and proton transport properties of semi-IPNs are enhanced compared to that of Aquivion ® , despite of their decrease of ion exchange capacity and their capacity to absorb water. Thermal and chemical stabilities are maintained very close to those of Aquivion ® . In addition, these new materials show similar performances in fuel cell operation at 105 °C compared to those of Aquivion ® . That evidences that perfluorosulfonated ionomer can be strengthened by association with a neutral fluorinated network. [ABSTRACT FROM AUTHOR]