Anion Exchange Membrane Fuel Cells Research Articles

Development of highly conductive anion exchange membranes based on crosslinked PIM-SEBS with high free volume

x-PIM-SEBS membranes were developed by chemical crosslinking of PIM with SEBS. The developed membrane showed good phase separation and ion conductivity through free volume, and also showed high AEMWE performance of 1.905 A cm−2 at 2.0 V.

Atomically Dispersed Zn‐Pyrrolic‐N4 Cathode Catalysts for Hydrogen Fuel Cells

AbstractTo achieve practical application of fuel cell, it is vital to develop highly efficient and durable Pt‐free catalysts. Herein, we prepare atomically dispersed ZnNC catalysts with Zn‐Pyrrolic‐N4 moieties and abundant mesoporous structure. The ZnNC‐based anion‐exchange membrane fuel cell (AEMFC) presents an ultrahigh peak power density of 1.63 and 0.83 W cm−2 in H2‐O2 and H2‐air (CO2‐free), and also exhibits long‐term stability with more than 120 and 100 h for H2‐air (CO2‐free) and H2‐O2, respectively. Density functional calculations further unveil that the Zn‐Pyrrolic‐N4 structure is the origin of high activity of as‐synthesized ZnNC catalyst, while the Zn‐Pyridinic‐N4 moiety is inactive for oxygen reduction reaction (ORR), which successfully explain the puzzle why most Zn‐metal‐organic framework ‐derived ZnNC catalysts in previous reports did not present good ORR activity because of their Zn‐Pyridinic‐N4 moieties. This work offers a new route for speeding up development of AEMFCs.

Atomically Dispersed Zn-Pyrrolic-N4 Cathode Catalysts for Hydrogen Fuel Cells.

To achieve practical application of fuel cell, it is vital to develop highly efficient and durable Pt-free catalysts. Herein, we prepare atomically dispersed ZnNC catalysts with Zn-Pyrrolic-N4 moieties and abundant mesoporous structure. The ZnNC-based anion-exchange membrane fuel cell (AEMFC) presents an ultrahigh peak power density of 1.63 and 0.83 W cm-2 in H2 -O2 and H2 -air (CO2 -free), and also exhibits long-term stability with more than 120 and 100 h for H2 -air (CO2 -free) and H2 -O2 , respectively. Density functional calculations further unveil that the Zn-Pyrrolic-N4 structure is the origin of high activity of as-synthesized ZnNC catalyst, while the Zn-Pyridinic-N4 moiety is inactive for oxygen reduction reaction (ORR), which successfully explain the puzzle why most Zn-metal-organic framework -derived ZnNC catalysts in previous reports did not present good ORR activity because of their Zn-Pyridinic-N4 moieties. This work offers a new route for speeding up development of AEMFCs.

Assessment of the FAA3‐50 Polymer Electrolyte for Anion Exchange Membrane Fuel Cells

AbstractAEMFC is an attractive alternative to PEMFCs, due to the faster reaction kinetics that permits to use non‐platinum‐group metal catalysts and thanks to the high pH of the electrolyte allows less expensive metal hardware. In any case, the use of an alkaline exchange polymeric membrane as an electrolyte requires the development and optimization of the electrode structures and MEA. In this work, MEAs, based on FAA3‐50 commercial membrane, were developed and electrochemically characterized in single cell configuration. The hydroxylic exchange procedure of membrane and ionomer, was evaluated. The influence of different electrochemical activation procedures, and the presence of a microporous layer (MPL) in the electrodic structure were assessed. The developed MEAs were electrochemically characterized in a 25 cm2 single cell at different operative conditions. A maximum power density of 140 mW cm−2 at 60 °C was reached with the optimized MEAs.

Plasma-Assisted Synthesis of Metal Nitrides for an Efficient Platinum-Group-Metal-Free Anion-Exchange-Membrane Fuel Cell.

In comparison to the well-developed proton-exchange-membrane fuel cells, anion-exchange-membrane fuel cells (AEMFCs) permit adoption of platinum-group-metal (PGM)-free catalysts due to the alkaline environment, giving a substantial cost reduction. However, previous AEMFCs have generally shown unsatisfactory performances due to the lack of effective PGM-free catalysts that can endure harsh fuel cell conditions. Here we report a plasma-assisted synthesis of high-quality nickel nitride (Ni3N) and zirconium nitride (ZrN) employing dinitrogen as the nitrogen resource, exhibiting exceptional catalytic performances toward hydrogen oxidation and oxygen reduction in an alkaline enviroment, respectively. A PGM-free AEMFC assembled by using Ni3N as the anode and ZrN as the cathode delivers power densities of 256 mW cm-2 under an H2-O2 condition and 151 mW cm-2 under an H2-air condition. Furthermore, the fuel cell shows no evidence of degradation after 25 h of operation. This work creates opportunities for developing high-performance and durable AEMFCs based on metal nitrides.

Water transport in anion and proton exchange membranes

Water balance in anion exchange membrane fuel cells (AEMFCs) is crucial because water not only is produced in the anode but also functions as a reactant in the cathode. Therefore, accurate measurement of AEM water transport properties is important for AEM design to improve AEMFC performance and durability. Very few studies report water transport properties of AEMs; even in those limited studies, interfacial transport rates were either not considered in data analysis or not given as a function of water activity. In this work, the liquid–vapor permeation method was used to determine the water flux across the Aemion® AH1-HNN8-50-X, Fumapem® FAA-3-30/50, and Versogen™ PiperION-A40. Using three numerical models, the results were analyzed to understand whether diffusion or interfacial transport resistances were limiting, and the values were estimated. Our results indicate that interfacial transport is limiting; therefore, the interfacial exchange rate and its activation energy were determined. Water desorption rate of AH1-HNN8-50-X is similar to Nafion® N115 and N117 (10−5–10−4 cm/s), and the activation energy for this process is also similar at 53.4 kJ/mol. On the other hand, FAA-3-30/50 and PiperION-A40 exhibit two to three times faster desorption and a lower activation energy: 46.0, 41.8, and 46.8 kJ/mol, respectively.

Cobalt-, iron- and nitrogen-containing ordered mesoporous carbon-based catalysts for anion-exchange membrane fuel cell cathode

Cobalt-, iron- and nitrogen-doped ordered mesoporous carbon (OMC)-based electrocatalysts are prepared, characterized, and used as cathode catalysts in anion-exchange membrane fuel cell (AEMFC). The OMC material is synthesized using a green and simple route via soft-template method and without the usage of harsh chemicals. To study the effect of porous structure of carbon support on the electrocatalytic properties, the OMC material is also mixed either with carbide-derived carbon (CDC) or carbon nanotubes (CNTs). Doping of carbon nanomaterials is done via high-temperature pyrolysis in the presence of cobalt and iron acetate as well as 1,10-phenanthroline. The physico-chemical characterization shows that the preparation of OMC and subsequent doping of nanocarbons has been successful, and the catalysts contain single-atom M-Nx centres. The initial assessment employing the rotating disc electrode method indicates that all three doped catalyst materials exhibit very high electrocatalytic activity toward the oxygen reduction reaction (ORR) in alkaline media and good stability after 10,000 potential cycles. In AEMFC testing with AEMION+ anion exchange membrane, the prepared cathode catalysts show good performance with CoFe-N-OMC/CNT obtaining the highest peak power density of 336 mW cm–2. Slightly lower AEMFC performance observed for CoFe-N-OMC and CoFe-N-OMC/CDC cathodes indicates that it is influenced by the catalyst's porous structure. It can be concluded that the OMC-based materials are promising cathode catalysts for AEMFC application.

Tuning the Hydrophobic Component in Reinforced Poly(arylimidazolium)-Based Anion Exchange Membranes for Alkaline Fuel Cells

A series of imidazolium-based aromatic copolymers were synthesized using fluorinated and non-fluorinated hydrophobic monomers. The quaternized copolymers were reinforced with the plasma-treated porous polyethylene substrate to provide flexible, homogeneous membranes. Cross-sectional SEM images revealed a triple-layer structure. The reinforced membranes exhibited phase-separated morphology as confirmed through TEM images. Among the membranes, QQP-MEIm-PE-containing quinquephenylene hydrophobic groups exhibited the most balanced properties (ion conductivity, mechanical strength, and alkaline stability). In particular, QQP-MEIm-PE exhibited excellent elongation properties with 24 MPa maximum stress and 205% elongation at break. A single H2/O2 fuel cell using the QQP-MEIm-PE membrane (1.26 meq g–1) and non-PGM-(Fe–N–C) cathode achieved 222 mW cm–2, which accounted for 888 mW mg–1Pt at 560 mA cm–2. Reasonable durability was confirmed with the membrane in the operating fuel cell.

Improving cell performance for anion exchange membrane fuel cells with FeNC cathode by optimizing ionomer content

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 H2/air (CO2-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 H2/air.

High-Performance FeCo/NC-Mo2TiC2/Carbon Nanotube Hybrid Support Catalyst toward Oxygen Reduction for Alkaline Anion Exchange Membrane Fuel Cell

High-Performance FeCo/NC-Mo₂TiC₂/Carbon Nanotube Hybrid Support Catalyst toward Oxygen Reduction for Alkaline Anion Exchange Membrane Fuel Cell

Chemically Folded Polyelectrolytes with Superior Alkaline Stability

In recent years, the development of anion-exchange membranes (AEMs) for anion-exchange membrane fuel cell (AEMFC) applications has been rapidly growing due to their numerous advantages over mainstream proton-exchange membrane fuel cells. However, a major challenge in the development of practical AEMs is the low chemical stability of the AEM quaternary ammonium (QA) functional groups in the strongly alkaline and the relatively dry environment produced during operation of the AEMFC. Herein, we investigate the effect of polymer chain folding on the chemical stability of the QA groups. While these polymers have virtually the same chemical composition, their molecular architectures are quite different, significantly affecting the kinetics of nucleophilic attacks on the QAs embedded inside the folded chains. The stability tests reveal a remarkable improvement in the stability of the folded chains compared to the linear (unfolded) control, resulting in polyelectrolytes that are two orders of magnitude more stable. We provide here a simple method for the preparation of chemically stable AEMs with different QA groups and polymer backbones. These folded architectures present a very promising family of polyelectrolyte membranes for AEMFCs and other electrochemical applications.

Physically and Chemically Stable Anion Exchange Membranes with Hydrogen-Bond Induced Ion Conducting Channels.

Anion exchange membranes (AEMs) with desirable properties are the crucial components for numerous energy devices such as AEM fuel cells (AEMFCs), AEM water electrolyzers (AEMWEs), etc. However, the lack of suitable AEMs severely limits the performance of devices. Here, a series of physically and chemically stable AEMs have been prepared by the reaction between the alkyl bromine terminal ether-bond-free aryl backbone and the urea group-containing crosslinker. Morphology analyses confirm that the hydrogen bonding interaction between urea groups is capable of driving the ammonium cations to aggregate and further form continuous ion-conducting channels. Therefore, the resultant AEM demonstrates remarkable OH- conductivity (59.1 mS cm-1 at 30 °C and 122.9 mS cm-1 at 90 °C) despite a moderate IEC (1.77 mmol g-1). Simultaneously, due to the adoption of ether-bond-free aryl backbone and alkylene chain-modified trimethylammonium cation, the AEM possesses excellent alkaline stability (87.3% IEC retention after soaking in 1 M NaOH for 1080 h). Moreover, the prepared AEM shows desirable mechanical properties (tensile stress > 25 MPa) and dimensional stability (SR = 20.3% at 90 °C) contributed by the covalent-bond and hydrogen-bond crosslinking network structures. Moreover, the resulting AEM reaches a peak power density of 555 mW cm-2 in an alkaline H2/O2 single fuel cell at 70 °C without back pressure. This rational structural design presented here provides inspiration for the development of high-performance AEMs, which are crucial for membrane technologies.

Investigation of Gradient Platinum Loading and Porosity Distribution for Anion Exchange Membrane Fuel Cells

Abstract Anion exchange membrane fuel cells (AEMFCs) are in development as a low-cost alternative to proton exchange membrane fuel cells (PEMFCs). AEMFCs produce water at the anode side and consume it at the cathode side, resulting in no cathode water flooding like in PEMFCs. However, it brings complexity to water transportation behavior and requires appropriate water balance to avoid membrane drying out. In this study, a two-dimensional two-phase multi-physics model has been developed to investigate the impacts of three key electrode parameters (porosity, catalyst loading, and ionomer content) that are responsible for water production and transport as well as the performance of an AEMFC. A piecewise constant function along the x-direction (reactant diffusion direction) is used to apply the gradient on the porosity and platinum loading. The present results show that a larger porosity gradient near the cathode gas diffusion layer (GDL)/flow channel interface and lower near the GDL/microporous layer (MPL) interface can enhance mass transport and water removal, which is benefited the AEMFC performance. However, anode GDL porosity gradients show a lower AEMFC performance compared to the cathode porosity gradients. Moreover, it was confirmed that for both electrodes, the performance of AEMFC was significantly dependent on each electrode parameter.

Synthesis and ex‐situ evaluation of quaternized polysulfone as an anion exchange ionomer for AEM technologies

AbstractAnion exchange ionomer (AEI) is a critical component used on anion exchange membrane fuel cell (AEMFC) and alkaline water electrolyzer (AWE). In this work, quaternized polysulfone with different functionalization degree were used as an ionomer to evaluate the performance in the oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR), both implied in the operation of AEMFC and AWE. The synthesized ionomer exhibited a better performance in both reactions in comparison to the commercial AEI Aemion®. PSf‐130 exhibited better performance, since IEC and surface area increases twice regarding the same parameters in the PSf‐60. The PSf‐130 conductivity increases three times regarding the value exhibited by PSf‐60. Finally, the Jlim and Jk increases 67% and 100% for ORR. On the other hand, the same catalytic parameter increased 44% and 35% for HOR comparing both polysulfone‐based ionomers. The Tafel slope values do not showed drastically changes for different ionomers indicating the same rate determining step (RDS) and the same mechanism in both reactions for all the ionomers.

Understanding the effects of operating conditions on the water management in anion exchange membrane fuel cells

While water management in Anion Exchange Membrane Fuel Cells (AEMFCs) is seen as crucial for performance and durability, measurements of water management within operating cells remain few. In this work, we measured the performance of an H2/O2 AEMFC based on a low-density polyethylene membrane AEM, PtRu/C anode and Fe–N–C cathode for various combinations of inlet relative humidities, gas pressures and flow rates. Simultaneously, the anode and cathode outlet relative humidities were measured using humidity sensors, from which the amount of water removed from the cell could be quantified for each side. The data shows that back-diffusion of water from anode to cathode results in increasing outlet relative humidity with increased current density, both at anode and cathode. Water produced in the AEMFC was thus removed from both sides. The maximum current density was found to be strongly connected to anode flooding, which is also the main cause for hysteresis during potentiodynamic scans. However, under atypical operating conditions, the cell performance may also be limited by low humidity at the cathode, with associated low ionomer conductivity. Overall, it is concluded that water management of AEMFC with thin AEMs can be achieved by playing with both the anode and cathode operating conditions.

Preparation and Characterization of QPVA/PDDA Electrospun Nanofiber Anion Exchange Membranes for Alkaline Fuel Cells.

In recent years, there has been considerable interest in anion exchange membrane fuel cells (AEMFCs) as part of fuel cell technology. Anion exchange membranes (AEMs) provide a significant contribution to the development of fuel cells, particularly in terms of performance and efficiency. Polymer composite membranes composed of quaternary ammonium poly(vinyl alcohol) (QPVA) as electrospun nanofiber mats and a combination of QPVA and poly(diallyldimethylammonium chloride) (PDDA) as interfiber voids matrix filler were prepared and characterized. The influence of various QPVA/PDDA mass ratios as matrix fillers on anion exchange membranes and alkaline fuel cells was evaluated. The structural, morphological, mechanical, and thermal properties of AEMs were characterized. To evaluate the AEMs' performances, several measurements comprise swelling properties, ion exchange capacity (IEC), hydroxide conductivity (σ), alkaline stability, and single-cell test in fuel cells. The eQP-PDD0.5 acquired the highest hydroxide conductivity of 43.67 ms cm-1 at 80 °C. The tensile strength of the membranes rose with the incorporation of the filler matrix, with TS ranging from 23.18 to 24.95 Mpa. The peak power density and current density of 24 mW cm-2 and 131 mA cm-2 were achieved with single cells comprising eQP-PDD0.5 membrane at 57 °C.

Fuel Cell Types, Properties of Membrane, and Operating Conditions: A Review

Fuel cells have lately received growing attention since they allow the use of non-precious metals as catalysts, which reduce the cost per kilowatt of power in fuel cell devices to some extent. Until recent years, the major barrier in the development of fuel cells was the obtainability of highly conductive anion exchange membranes (AEMs). On the other hand, improvements show that newly enhanced anion exchange membranes have already reached high conductivity levels, leading to the suitable presentation of the cell. Currently, an increasing number of studies have described the performance results of fuel cells. Much of the literature reporting cell performance is founded on hydrogen‒anion exchange membrane fuel cells (AEMFCs), though a growing number of studies have also reported utilizing fuels other than hydrogen—such as alcohols, non-alcohol C-based fuels, and N-based fuels. This article reviews the types, performance, utilized membranes, and operational conditions of anion exchange membranes for fuel cells.

Anion exchange membranes and ionomer properties of a polyfluorene-based polymer with alkyl spacers for water electrolysis

Aryl ether-free polymers have attracted considerable attention in recent years for their application in anion exchange membrane (AEM) fuel cells (AEMFCs) and water electrolysis (AEMWE). Here, an aryl ether-free polyfluorene-based polymer bearing pendent ammonium groups in side chains and propyl spacers in its polymer backbone is synthesized through the Suzuki cross-coupling reaction. The propyl spacer introduced into the backbone improves the flexibility of the polymer and allows effective ionic cluster formation by the polymer. Compared to polyphenylene oxide (PPO), which has a similar molecular weight, quaternized poly[9,9-bis(6-bromohexyl)fluorene]–co-[4,4-bis((4-phenyl)propyl)biphenyl)] (PFPB-QA) polymers show significantly superior membrane-forming properties owing to the propyl spacers. The PFPB-QA membrane also exhibits high ionic conductivity (122 mS cm−1 at 80 °C) and excellent alkaline stability (1 M KOH at 80 °C for 720 h). Moreover, the AEMWE utilizing PFPB-QA exhibits a current density of 1.53 A cm−2 at 2.0 V in 1 M KOH at 70 °C. Therefore, the present study shows that an aryl ether-free polymer with an alkyl spacer has excellent mechanical properties, ionic conductivity, alkaline stability, and cell performance.

Templated Nitrogen-, Iron-, and Cobalt-Doped Mesoporous Nanocarbon Derived from an Alkylresorcinol Mixture for Anion-Exchange Membrane Fuel Cell Application

Templated Nitrogen-, Iron-, and Cobalt-Doped Mesoporous Nanocarbon Derived from an Alkylresorcinol Mixture for Anion-Exchange Membrane Fuel Cell Application

Activity Quantification of Fuel Cell Catalysts via Sequential Poisoning by Multiple Reaction Inhibitors.

The development of non-Pt or carbon-based catalysts for anion exchange membrane fuel cells (AEMFCs) requires identification of the active sites of the catalyst. Since not only metals but also carbon materials exhibit oxygen reduction reaction (ORR) activity in alkaline conditions, the contribution of carbon-based materials to ORR performance should also be thoroughly analyzed. However, the conventional CN- poisoning experiments, which are mainly used to explain the main active site of M-N-C catalysts, are limited to only qualitative discussions, having the potential to make fundamental errors. Here, we report a modified electrochemical analysis to quantitatively investigate the contribution of the metal and carbon active sites to ORR currents at a fixed potential by sequentially performing chronoamperometry with two reaction inhibitors, CN- and benzyl trimethylammonium (BTMA+). As a result, we discover how to quantify the individual contributions of two active sites (Pt nanoparticles and carbon support) of carbon-supported Pt (Pt/C) nanoparticles as a model catalyst. This study is expected to provide important clues for the active site analysis of carbon-supported non-Pt catalysts, such as M-N-C catalysts composed of heterogeneous elements.