Anion Exchange Membrane Fuel Cells Research Articles

Single-Atomic Mn–N–C Catalyst with Hierarchical Pores for Anion Exchange Membrane Fuel Cells: A Mn Confinement Strategy

Single-Atomic Mn–N–C Catalyst with Hierarchical Pores for Anion Exchange Membrane Fuel Cells: A Mn Confinement Strategy

Solvation Effect-Determined Mechanisms of Cation Exchange Reactions for Efficient Multicomponent Nanocatalysts.

Cation exchange (CE) reaction is a classical synthesis method for creating complex structures. A lock of study on intrinsic mechanism limits its understanding and practical application. Using X-ray absorption spectroscopy, we observed that the evolution from Ru-Cl to Ru-O/OH occurs during the CE between K2RuCl6 and CoSn(OH)6 in aqueous solution, while CE between K2PtCl6 and CoSn(OH)6 is inhibited due to the failure of structural evolution from Pt-Cl to Pt-O/OH. Theoretical simulations imply that the interaction between Ru-O and CoSn(OH)6 with Co vacancy (CoVCoSn(OH)6) endows the electron transfer, as a result of strengthened adsorption on CoVCoSn(OH)6. Moreover, this mechanism is validated for CE between K2RuCl6 and ASn(OH)6 (A = Mg, Ca, Mn, Co, Cu, Zn), and CE between K2PdCl6/Na3RhCl6/K2IrCl6 and CoSn(OH)6. Impressively, the Pt-free CoRuSn(OH)x produced via CE displays a mass activity and a power density of 15.0 A mgRu-1 and 11.6 W mgRu-1, respectively, for anion exchange membrane fuel cell (AEMFC) exceeding the values of commercial PtRu/C (11.8 A mgRu+Pt-1 and 9.0 W mgRu+Pt-1). This work, for the first time, reveals the intrinsic mechanism of CE as structural evolution of target ion breaking through the traditional classic etch-adsorption mechanism and will promote fundamental research and practical application in various fields.

Solvation Effect‐Determined Mechanisms of Cation Exchange Reactions for Efficient Multicomponent Nanocatalysts

Cation exchange (CE) reaction is a classical synthesis method for creating complex structures. A lock of study on intrinsic mechanism limits its understanding and practical application. Using X‐ray absorption spectroscopy, we observed that the evolution from Ru−Cl to Ru−O/OH occurs during the CE between K2RuCl6 and CoSn(OH)6 in aqueous solution, while CE between K2PtCl6 and CoSn(OH)6 is inhibited due to the failure of structural evolution from Pt−Cl to Pt−O/OH. Theoretical simulations imply that the interaction between Ru−O and CoSn(OH)6 with Co vacancy (CoVCoSn(OH)6) endows the electron transfer, as a result of strengthened adsorption on CoVCoSn(OH)6. Moreover, this mechanism is validated for CE between K2RuCl6 and ASn(OH)6 (A = Mg, Ca, Mn, Co, Cu, Zn), and CE between K2PdCl6/Na3RhCl6/K2IrCl6 and CoSn(OH)6. Impressively, the Pt‐free CoRuSn(OH)x produced via CE displays a mass activity and a power density of 15.0 A mgRu−1 and 11.6 W mgRu−1, respectively, for anion exchange membrane fuel cell (AEMFC) exceeding the values of commercial PtRu/C (11.8 A mgRu+Pt−1 and 9.0 W mgRu+Pt−1). This work, for the first time, reveals the intrinsic mechanism of CE as structural evolution of target ion breaking through the traditional classic etch‐adsorption mechanism and will promote fundamental research and practical application in various fields.

Built-in electric field-driven electron transfer behavior at Ru-RuP2 heterointerface fosters efficient and CO-resilient alkaline hydrogen oxidation

Exploiting a cost-effective electrocatalyst for hydrogen oxidation reaction (HOR) with high-performance and CO poisoning resistance is essential for the widespread application of alkaline anion exchange membrane fuel cells (AEMFCs). Herein, we craft a unique Ru-RuP2 heterostructure within hollow mesoporous carbon sphere (Ru-RuP2@C) using phosphide-controlled phase-transition approach. Benefiting from the interfacial electron transfer from RuP2 to Ru, the Ru-RuP2@C electrocatalyst exhibits impressive HOR performance with a mass activity of 2.87 mA μgRu−1. Notably, Ru-RuP2@C demonstrates strong tolerance to 1000 ppm CO, a capability lacking in PtRu/C and Pt/C. When serves as an anode catalyst for AEMFC, it achieves a peak power density of 521 mW cm−2, comparable to Pt/C. Experimental and theoretical analyses reveal that the built-in electric field, resulting from work function differences, creates an asymmetric charge distribution that modulates the d-band center of Ru-RuP2@C. This optimizes the adsorption strength of hydrogen and hydroxide intermediates, thereby accelerating HOR catalytic kinetics.

Chitosan-based anion exchange membranes for fuel cell application: Enhanced hydration & durability to dry-wet cycling

Herein, a new type of anion exchange membranes (AEMs) based on chitosan (CS) and poly(4-vinylbenzyl chloride) (PVB) polymers is reported. Depending on whether the PVB side chains are mono-cationic (quaternized PVB, QPVB) or di-cationic (di-quaternized PVB, DQPVB), the AEMs are denoted as QPVB@CS and DQPVB@CS, respectively. Due to the lateral aggregation of chitosan chains assisted by hydrogen bonds, the in-plane expansion is limited (1.4–11.5 % at 80 °C), resulting in excellent mechanical properties of AEMs (dry tensile strength of 55.2–81.0 MPa). And after 10 dry-wet cycles, the AEMs maintain their appearance and show improved mechanical properties. Due to high through-plane swelling degree, AEMs effectively retaining water (water uptake of 272.5–501.5 % at 80 °C) in the AEMs. DQPVB@CS AEMs, with their higher ion content, exhibit superior ionic conductivity (74.2–116.5 mS cm−1 at 80 °C) compared to QPVB@CS (27.7–44.3 mS cm−1 at 80 °C) and achieve a peak power density of 729.6 mW cm−2 in an anion exchange membrane fuel cell (AEMFC), versus 128.1 mW cm−2 for QPVB@CS-2. To the best of our knowledge, the AEMs developed in this study represent the first example of AEMs prepared from chitosan gel membranes, achieving anisotropic swelling degree, high water uptake, and excellent dry-wet cycling resistance without the need for additional chemical cross-linking.

Conductivity-enhanced Poly(biphenyl piperidine) anion exchange membranes with organic tubes

Anion exchange membrane fuel cells (AEMFCs) present an economically efficient alternative to proton exchange membrane fuel cells because of the use of non-precious metals. The development of high-performance and durable AEMFCs necessitates the use of highly conductive and robust anion exchange membranes (AEMs). In this study, a novel organic-organic composite AEM was synthesized by preparing poly(arylene piperidinium) polymer through Friedel-Crafts acid condensation and incorporating one-dimensional organic tubes as reinforcing materials. The composite AEM exhibits high conductivity (235 mS cm−1 at 80 °C) due to the chain orientation within the organic tubes and the availability of abundant transport sites. Furthermore, in contrast to the incompatibility of inorganic materials with polymers, the flexible nature of organic tubes enhanced polymer entanglement, significantly boosting the mechanical strength (120 MPa) of the AEM. Crosslinking the polymer backbone with the organic tubes facilitated simultaneous swelling, effectively mitigating interfacial compatibility issues, result in high dimensional stability. The H2–O2 fuel cell employing the developed AEM demonstrated a peak power density of 1018 mW cm−2 at 80 °C. This study provides a comprehensive synthetic strategy for producing stable AEMs with high hydroxide ion conductivity and outstanding mechanical properties tailored for alkaline membrane fuel cell applications.

Weakening O-Intermediates Adsorption Strength Over the Pd Metallene via Lewis-Acidic Site Modulation for Enhanced Oxygen Reduction.

The reasonable design and modulation of the electronic properties of Pd metallene are acknowledged as a promising avenue for enhancing the oxygen reduction reaction (ORR) in anion exchange membrane fuel cells (AEMFCs), yet they remain a formidable challenge. Herein, a thin-sheet structure of Zr-doped Pd metallene (PdZr metallene) with abundant defects is proposed using a facile wet-chemical approach for efficient and highly durable ORR electrocatalysis. Multiple microstructural analyses uncover that orchestrated electronic and oxophilic regulation of PdZr metallene via Lewis-acidic Zr site modulation could concurrently optimize the electronic configuration of Pd, downshift the d-band center of Pd, and, thus, promote the intrinsic activity. Benefiting from the unique two-dimensional morphology and electronic structure optimization facilitated by the Zr coupling effect, the resultant PdZr metallene demonstrates significantly enhanced ORR electrocatalytic performance in basic solutions, with a high half-wave potential (E1/2) of 0.87 V and commendable stability for 30 000 s, surpassing those of Pd metallene and various advanced Pd-based catalysts reported in the literature. Encouragingly, the PdZr metallene-based AEMFC achieves an increased maximum power density (90.4 mW cm-2) and impressive robustness over 12 h in an alkaline environment, manifesting the practical application of PdZr metallene in AEMFCs. This study showcases the applicability of PdZr metallene via Lewis acid site regulation for fabricating highly active electrocatalysts for high-performance AEMFCs.

Robust branched Poly(p-terphenyl isatin) anion exchange membranes with enhanced microphase separation structure for fuel cells

Anion exchange membrane fuel cells (AEMFCs) are gradually becoming the focus of sustainable hydrogen energy research due to the advantages of clean by-products, faster oxidation-reduction dynamics and allowing cheap platinum-free base materials. As the key components of AEMFCs, anion exchange membranes (AEMs) are required to have high ionic conductivity and dimensional stability. This study focused on the design and preparation of branched AEMs for AEMFCs. The b-PTIN-x membranes were generated by incorporating 1,3,5-triphenylbenzene (TPB) units into rigid poly(p-terphenyl isatin) (PTI) polymer backbones. This innovative approach aimed to induce microphase separation structures by exploiting TPB with high FFV, as well as to enhance the tensile strength of AEMs with the help of branched structures. SAXS and AFM images revealed that the AEMs achieved enhanced microphase separation structures, resulting in the formation of ion transport channels with dimensions in the range of a few nanometers (3.36–3.70 nm). The branched b-PTIN-11 membranes displayed significant OH− conductivity (153.9 mS cm−1 at 80 °C) while having a low ion exchange capacity (IEC) (1.73 mmol g−1). The b-PTIN-11 membranes displayed improved tensile strength (56.69 MPa) and exceptional dimensional stability, with swelling ratio (SR) of 18.5 % at 80 °C. They also showed great chemical stability with 89.64 % conductivity remaining, lasting for more than 1200 h in 3 M NaOH solution at 80 °C. Ultimately, the b-PTIN-11 membrane underwent testing to evaluate its performance in a fuel cell using H2–O2. It demonstrated a peak power density (PPD) of 566 mW cm−2 when subjected to a current density of 1339 mA cm−2.

Synergistic effects of carbon nanotubes on α-MnO2 electrocatalysts for improved oxygen reduction in alkaline fuel cells

The Alkaline Membrane Fuel Cell (AMFC), is a device crucial for electrochemical energy production through the oxygen reduction reaction (ORR), conventionally relies on platinum catalysts. However, the challenges of excessive cost and inadequate stability in alkaline environments have hindered its widespread commercialization. Alpha manganese dioxide (αMnO2), with diverse applications in energy and environmental domains, has potential as an alternative catalyst due to its lower metal costs and comparable catalytic activity. This study focuses on the synthesis of αMnO2 nanotubes through controlled environment temperature, and integration with carbon nanotubes (CNTs). Optimizing the gas pressure and temperature during synthesis resulted in structural changes in αMnO2 nanotubes, with a notable increase in catalytic behavior at elevated temperatures. The sample treated at 450 °C and mixed with CNTs (CNT-MO450) demonstrated outstanding ORR performance and prolonged stability in an alkaline medium. Furthermore, the CNT-MO450 exhibited the highest current density of −5.2 mA/cm2 at a potential of 0.65 V vs RHE, a peak power density of 73 mW/cm2 (comparable to Pt/C at 95 mW/cm2), and a charge transfer resistance of 310 Ω. The temperature treatment affected the αMnO2 nanotubes, which resulted in increased length at an optimal temperature, leading to a larger surface area. This enhancement in surface area is crucial to improved catalytic activity, electrical conductivity, and extended stability during operation in alkaline media. The findings suggest that CNT-MO450 catalysts hold promise as a cost-effective and stable alternative catalyst for AMFCs.

Constructing Asymmetric Fe-Nb Diatomic Sites to Enhance ORR Activity and Durability.

Iron-nitrogen-carbon (Fe-N-C) materials have been identified as a promising class of platinum (Pt)-free catalysts for the oxygen reduction reaction (ORR). However, the dissolution and oxidation of Fe atoms severely restrict their long-term stability and performance. Modulating the active microstructure of Fe-N-C is a feasible strategy to enhance the ORR activity and stability. Compared with common 3d transition metals (Co, Ni, etc.), the 4d transition metal atom Nb has fewer d electrons and more unoccupied orbitals, which could potentially forge a more robust interaction with the Fe site to optimize the binding energy of the oxygen-containing intermediates while maintaining stability. Herein, an asymmetric Fe-Nb diatomic site catalyst (FeNb/c-SNC) was synthesized, which exhibited superior ORR performance and stability compared with those of Fe single-atom catalysts (SACs). The strong interaction within the Fe-Nb diatomic sites optimized the desorption energy of key intermediates (*OH), so that the adsorption energy of Fe-*OH approaches the apex of the volcano plot, thus exhibiting optimal ORR activity. More importantly, introducing Nb atoms could effectively strengthen the Fe-N bonding and suppress Fe demetalation, causing an outstanding stability. The zinc-air battery (ZAB) and hydroxide exchange membrane fuel cell (HEMFC) equipped with our FeNb/c-SNC could deliver high peak power densities of 314 mW cm-2 and 1.18 W cm-2, respectively. Notably, the stable operation time for ZAB and HEMFC increased by 9.1 and 5.8 times compared to Fe SACs, respectively. This research offers further insights into developing stable Fe-based atomic-level catalytic materials for the energy conversion process.

Quantitative performance analysis of anion-exchange membrane fuel cells with in-plane and through-plane water transport

Effective water management is crucial in anion-exchange membrane fuel cells (AEMFCs) due to water's dual role as a reactant during alkaline oxygen reduction and a product of alkaline hydroxide oxidation. Meanwhile, both hydroxide conduction and water transport in polymer electrolytes are highly dependent on the hydration level. Therefore, a three-dimensional multi-physics model is developed to investigate the critical role of ionic and water transport parameters of the electrolyte on AEMFC performance. Additionally, detailed water distribution analysis is used to reveal its fundamental mechanism. The results reveal that extremely inhomogeneous water distribution and cathode water starvation are the main causes of the poor cell performance. Moreover, increasing membrane water diffusivity, water conversion, and decreasing the electro-osmotic drag coefficient all contribute to better cell performance through improved water balance and cathode water supply. Among these, cell performance is most sensitive to membrane water diffusivity, with a 40 % increase in peak power density when it is increased from 10−10 m2 s−1 to 10−9 m2 s−1. Although high ionic conductivity improves cell performance by directly reducing ohmic impedance, it also results in a more inhomogeneous distribution of water in the whole cell, so that a four-fold increase in ionic conductivity only yields a 62 % increase in peak power density.

Functionalized Triblock Copolymers with Tapered Design for Anion Exchange Membrane Fuel Cells.

Triblock copolymers such as styrene-b-(ethylene-co-butylene)-b-styrene (SEBS) have been widely used as an anion exchange membrane for fuel cells due to their phase separation properties. However, modifying the polymer architecture for optimized membrane properties is still challenging. This research develops a strategy to control the membrane morphology based on quaternized SEBS (SEBS-Q) by dual-tapering the interfacial block sequences. The structural and transport properties of SEBS-Q with various tapering styles at different hydration levels are systematically investigated by coarse-grained molecular simulations. The results show that the introduction of the tapered regions induces the formation of a bicontinuous water domain and promotes the diffusivity of the mobile components. The interplay between the solvation of the quaternary groups and the tapered fraction determines the conformation of polymer chains among the hydrophobic-hydrophilic subdomains. The strategy presented here provides a new path to fabricating fuel cell membranes with controlled microstructures.

Ag/CNT Catalyst Synthesized by Plasma-Enhanced Atomic Layer Deposition for Anion Exchange Membrane Fuel Cells

Anion exchange membrane fuel cells (AEMFCs) have recently gained attention as a viable alternative to proton exchange membrane fuel cells (PEMFC), offering the potential for high output without relying on expensive platinum (Pt) catalysts. PEMFCs operate in an acidic environment characterized by a high concentration of H+, necessitating the use of platinum-based catalysts to ensure both performance and stability in such conditions. In contrast, AEMFCs operate in an alkaline environment (OH-), affording the use of high-performance catalysts like silver (Ag), which is sensitive to acidity. Moreover, the cost of Ag is approximately 1/50 of Pt, offering significant cost advantages for fuel cell commercialization. Atomic layer deposition (ALD) has garnered substantial attention as a valuable technique for crafting high-performance nano-catalysts. ALD's self-limiting nature, based on the sequential exposure of vaporized precursors and reactants, enables precise control over catalyst size and composition. In this study, we employed plasma-enhanced ALD (PEALD) to fabricate cutting-edge AEMFC cathodes comprised of carbon nanotubes (CNTs) adorned with Ag. This approach yielded impressive results, achieving an AEMFC output exceeding 300 mW cm-2 or more than 2 W mgAg -1 at 65 °C with a CNT cathode featuring an exceedingly low Ag loading of less than 0.15 mg cm-2. Notably, this represents the world's highest reported Ag-AEMFC performance to date. The Ag-decorated cathode created through ALD played a pivotal role in significantly reducing resistance in the polarization region, a major contributor to overall energy losses in AEMFCs. Additionally, when evaluating the durability of the Ag-decorated CNT anode in an alkaline environment, we observed excellent long-term stability. In this presentation, we will discuss a more detailed exploration of the relationship between AEMFC performance, featuring ALD-fabricated Ag-CNT catalysts, and the intricate catalyst structure.

(Invited) Efficient Ternary Nicuw Hydrogen Oxidation Catalysts for Anion Exchange Membrane Fuel Cells

Anion exchange membrane fuel cells (AEMFCs) offer prospective approaches to replace proton exchange membrane fuel cells via cost-effective catalysts and membranes. While significant progress has been made in efficient nonnoble electrocatalysts for oxygen reduction reaction in alkaline media, the hydrogen oxidation reaction (HOR) in the alkaline condition still relies on high platinum loadings to compensate for its sluggish kinetics. Therefore, developing efficient non-noble metal electrocatalysts with Pt-like HOR performances in alkaline electrolytes is highly desired but a great challenge.The hydrogen binding energy (HBE) has been identified as the primary descriptor for the HOR. Additionally, an unfavorable hydroxide binding energy (OHBE) is considered the rate-determining step in the Volmer reaction to generate water. Therefore, an ideal catalyst for HOR should achieve a balance between HBE and OHBE. However, despite being a promising non-noble metal, nickel exhibits excessively high HBE and lacks active sites for hydroxide adsorption, which hinders its further application in the real fuel cell.In this work, NiW was successfully deposited onto Cu to form a ternary Ni-Cu-W alloy catalyst by a chemical reduction method. Through XPS spectra, we found the charge transfer from Ni to W to give Ni a higher valence state, contributing to a weakened hydrogen binding energy. Electrochemical measurements observed Ni-Cu-W exhibit an kinetic activity with 117.9 mA/mgNi at η= 50 mV, which is the highest among the reported platinum group metal-free catalysts. Ni-Cu-W alloy showcased robust stability, with no activity degradation during an accelerated long-term durability test between a low overpotential (-0.1 ~ 0.1 V, vs RHE) with 10,000 cyclic voltammetry scans and only a 5.7% activity loss at η= 50 mV when applying more larger overpotential (-0.1 ~ 0.2 V) with the same cycles. When assembled with this catalyst as anode and Pt/C as cathode, it delivered a peak power density of 289 mW/cm2. Both experimental and theoretical studies were conducted to gain insights into the catalyst's enhanced performance. Our findings revealed that the incorporation of Cu into the catalyst significantly weakened the adsorption of hydrogen species, while simultaneously lowering the energy barrier required for the absorption of hydroxide ions. These key observations might shed light on the underlying mechanisms responsible for the catalyst's improved activity and stability.

Water Management in Anion Exchange Membrane Fuel Cells Via Distribution of Relaxation Times Analysis

In response to growing concerns regarding air pollution and energy scarcity, anion exchange membrane fuel cells (AEMFCs) have emerged as a promising technology for power generation due to their high efficiency, zero emissions, and the abundance of hydrogen resources. Within AEMFCs, water serves as a reactant, being consumed at the cathode, and generated at the anode, which can lead to an imbalance in the water content within the fuel cell. Maintaining an appropriate water distribution is essential for efficient charge transport and electrochemical reaction kinetics. Therefore, the development of a comprehensive water management strategy is crucial to ensure the stable operation and durability of AEMFCs.Characterizing the water condition of the anode and cathode in different operation conditions (normal, drying, or flooding) is a critical step that provides data foundation for devising effective water management control strategies. Electrochemical impedance spectroscopy (EIS) offers a means to investigate different resistances (kinetics, mass transport, and ohmic losses) over varying time scales during operation to assess water transport. The conventional interpretation of EIS data typically relies on equivalent circuit models, necessitating prior assumptions and initial component selections. In this study, we employed the distribution of relaxation times (DRT) methodology, known for its powerful ability to separate components, to conduct a more precise analysis of polarization processes. Initially, electrochemical impedance dynamics related to hydroxide transport, hydrogen oxidation reactions, and oxygen reduction reactions were effectively extracted. Subsequently, DRT was employed to investigate the loss and variation trends of each polarization process under conditions of anode and cathode water flooding and drying conditions, respectively. Furthermore, to gain a deeper understanding of the effects of water content on mass transport and electrochemical reaction kinetics, a three-dimensional multi-physics model for AEMFCs was developed. This model incorporated water phase transition, heat and mass transfer, liquid water and dissolver water transport, and electrochemical reactions. These endeavors represent a comprehensive and systematic approach to guide the utilization of the distribution of relaxation times in fuel cells.

Operando Characterization of Water Flux across Hydroxide-Exchange Membranes

The water balance in operating hydroxide-exchange-membrane fuel cells (HEMFCs) is a key challenge for improved performance and durability. For every 4 electrons produced in an HEMFC, 4 water molecules are generated in the anode, 2 water molecules are consumed in the cathode. Water is also transported from cathode to anode along with the hydroxide due to electroosmosis. Consequently, there is a concentration gradient of water that transport water from anode to cathode. Ineffective water management could lead to cathode dry-out, where insufficient water in the cathode limits the rate of reaction or causes ionomer degradation through alkaline instability, or to anode flooding, where excess liquid water in the anode limits gas diffusion. To address these issues, it is critical to measure the transport of water across the hydroxide-exchange membrane during cell operation. We built a water-flux station to measure the water in and out of the anode and cathode during cell operation with different inlet relative humidities and back pressures. Here, the effect of the membrane thickness and the effect of stacking hydroxide-exchange membranes on the water transport across the hydroxide exchange membrane is studied. The stacking of hydroxide-exchange membranes creates an interfacial ohmic resistance between membranes, measured from the high frequency resistance, but not an interfacial water transport resistance. This study shows that the water transport across the hydroxide-exchange membrane is sufficient for water consumption in the cathode and is not significantly affected by the membrane thickness or stacking. However, the added ohmic resistance from the increased membrane thickness or stacking membranes significantly affects the performance.

(Energy Technology Division Research Award) New Materials vs. Reaction Engineering in Anion Exchange Membrane Fuel Cells

In recent years, the desire to design, create and/or discover advanced functional nanomaterials has changed the way that faculty members and graduate students approach engineering research. Though materials can (and likely will) make a significant impact on most technologies, the truth is that in most disciplines, materials with highly complex structures remain on the fringes of realistic deployment. In some cases, even when so-called “advanced” materials are discovered there are significant difficulties in transitioning them from ex-situ tests to the real reacting environment. Therefore, we must be careful to understand that material chemistry and structure are only two variables in an extremely complex system and often times there are other fundamental (e.g. electronic mobility, thermodynamic barriers, diffusivity) and engineering (porosity, concentration, temperature) properties that drive behavior in such environments. Additionally, there are systems where materials are being sought without a clear understanding of what is truly limiting performance and durability or the properties that are required of a real engineered system to operate effectively.Anion exchange membrane fuel cells (AEMFCs) are an example system where the literature is littered with exotic materials that claim to improve activity and stability (presumed as performance and durability in real devices). However, it will be shown that for several years, such new materials had limited success (if any) in advancing performance and durability. This talk will summarize ~five years of work in AEMFCs where the performance and durability of AEMFCs were improved significantly without any new materials – just using traditional chemical engineering principles for reactor engineering. Only later – once device operation was well understood and controlled – were new materials helpful. On the operational side, the main discussion point will be the transport of water. On the materials side, new membranes and catalysts will be discussed. The talk will end with perspectives on transitioning AEMFCs to more realistic operating environments, including the mitigation of effects from CO2.

A Simple Approach for Modulating the Active Site in Fe-Based Electrocatalysts

Proton Exchange Membrane Fuel Cells (PEMFCs) have garnered attention as a next-generation, environmentally friendly energy solution to address issues like the climate crisis and depletion of fossil fuels resulting from excessive usage. Nevertheless, the commercialization of PEMFCs faces challenges due to the use of expensive platinum catalysts for the Oxygen Reduction Reaction (ORR). In contrast, Anion Exchange Membrane Fuel Cells (AEMFCs) offer advantages by utilizing cost-effective non-platinum catalysts, making ongoing research on non-platinum catalysts for AEMFCs essential. Numerous studies have been conducted to develop M-N-C catalysts in nanoparticle units using transition metals such as Fe, Co, and Ni for AEMFCs. Notably, Fe-based catalysts with FeNx active sites are considered representative candidates for AEMFCs. Moreover, recent research aims to advance Fe catalysts by incorporating single-atom active sites to enhance mass transfer and improve reaction efficiency at the atomic level.We have developed a straightforward method for synthesizing an Fe catalyst. The catalyst, synthesized through a redox reaction between aniline and a metal ion, followed by pyrolysis, exhibited remarkable durability and activity for the Oxygen Reduction Reaction (ORR). Notably, it possesses an active FeNx site crucial for ORR. Furthermore, by simply altering the solvent during the synthesis process, we observed a variation in the Fe-to-N ratio. Particularly noteworthy was the synthesis of Fe4N, which demonstrated activity for the Oxygen Evolution Reaction (OER). This synthesis method allows for the controlled manipulation of the catalyst's chemistry by varying the solvent, resulting in the production of Fe-based catalysts with either FeNx or Fe4N active sites, active for ORR and OER, respectively. To understand the catalyst's characteristics based on the solvent used during synthesis, we conducted a comprehensive characterization using techniques such as Thermogravimetric Analysis (TGA), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The electrochemical activity was investigated through a half-cell test, and efforts were made to interpret the results based on the catalyst's properties.

Deep Eutectic Solvent Supported Polymer-Based High Performance Anion Exchange Membrane for Alkaline Fuel Cells

Alkaline anion exchange membrane fuel cells (AEMFC) have gained interest due to their potential as electrochemically energy conversion devices and a competitive alternative to the more extensively studied commercialized proton exchange membrane fuel cells (PEMFCs). Nevertheless, their development impedes the limited ion conductivity, chemical and mechanical stability in an alkaline medium of anion exchange membranes (AEMs). The ionic conductivity of AEM is lower than that of a proton exchange membrane (PEM) because the mobility of hydroxide ions is inherently lower than that of protons [1]. Deep eutectic solvents (DESs) as green solvents can overcome this issue.The main idea of this research is to fabricate a deep eutectic solvent-supported polymer-based AEM for alkaline fuel cell application by electrospinning technique. Poly(vinyl alcohol) (PVA) is one of the potential polymers for the development of AEM due to its water solubility, biodegradability, high fiber forming ability, non-toxicity, and high chemical and thermal stability [2]. This work aims to achieve high ionic conductivity, chemical and mechanical stability by two methods: swelling polyvinyl alcohol (PVA)-based nanofibers into DES and encapsulating DES inside the PVA-nanofibers together with optimizing fabrication methods.In this study, polymer electrolytes as potential AEMs were first prepared using the swelling method, where electrospun PVA nanofibers were fabricated via the electrospinning technique, followed by swelling in a series of DESs. To prepare the DES solutions, choline chloride (ChCl) and ethylene glycol (EG) were mixed at different molar ratios. The cross-linking of pure PVA fibers with glutaraldehyde in ethanol (see Figure 1B) and DES uptake and the presence of voids as channels for ion conduction (see Figure 1C) were successfully confirmed with a scanning electron microscopy (SEM, Crossbeam500, Zeiss). The ionic conductivity of swelled in DES PVA-based membranes were evaluated by electrochemical impedance spectroscopy (Metrohm Autolab) at room temperature and was equal to 0.336 mS/cm. The presence of DES in the membrane was confirmed with FTIR spectroscopy (FT-IR spectrometer, Nicolet iS10): a slight C-N+ peak at 953 cm-1 from ChCl has proven interaction between PVA and DES with FTIR spectroscopy, meaning that DES is present in the fiber. In addition, the nitrogen content in the obtained membrane was determined by CHNS elemental analysis (Elemental Vario micro cube) as 3.32 wt.%.In order to overcome high weight loss in the swelling method, the encapsulation method was suggested as an alternative option, which is based on the encapsulation of DES into the PVA solution by mixing them, varying the amount of DES added, and then preparing fibers using electrospinning. Observing the morphology of DES-encapsulated PVA nanofibers with a scanning electron microscope (SEM, Crossbeam500, Zeiss), as the content of DES in the solution increased, there was an observed rise in the average diameter of the nanofibers (see Figure 1D). Encapsulation of DES in PVA nanofibers was primarily confirmed by transmission electron microscope (TEM, JEM -1400 Plus, JEOL): PVA appears lighter due to its decreased density, proving that DES is present inside the fibers. Also, the same tendency was observed with the results of FTIR spectroscopy (FT-IR spectrometer, Nicolet iS10) as for the swelling method, meaning that DES is present in the fiber. According to CHNS elemental analysis (Elemental Vario micro cube), nitrogen content was lower than for the swelling method - 0.70 wt.%. The ionic conductivity was evaluated as 0.364 mS/cm by electrochemical impedance spectroscopy (Metrohm Autolab) at room temperature, which was almost the same as for the swelling method.As a result, very flexible and visually transparent electrospun DES-supported PVA-based AEMs were obtained via the swelling and encapsulation method.

Material Changes of Bimetallic Ag–Cr, Fe, Co, Ni, Cu, Sn Electrocatalysts during Alkaline Oxygen Reduction in Fundamental Versus Alkaline Membrane Exchange Fuel Cell Conditions

The more apparent challenges of climate change drastically increase the global demand for sustainable fuel production and usage.1 In this context, hydrogen fuel cells (FCs) powered by renewable electricity are among the promising technologies.2 Addressing the sluggish cathode reaction in FCs, the oxygen reduction reaction (ORR), these devices hold immense potential for sustainable energy conversion and storage. An alkaline environment allows for the utilization of more abundant and cost-effective metals in contrast to current platinum-based catalysts. Silver (Ag), for instance, exhibits high selectivity for the ORR, i.e., forming hydroxide instead of peroxide.3 When combined with secondary metals, bimetallic Ag catalysts show enhanced activity, making them viable alternatives to platinum-group materials for ORR.In our highly collaborative research, we investigated the material transformations of bimetallic Ag thin films with chromium (Cr), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), and tin (Sn) as secondary metals for ORR electrocatalysis in fundamental rotating disk electrode (RDE) setups and the application device, anion-exchange membrane FC (AEMFC). Grazing-incidence X-ray diffraction (GI-XRD) conducted prior to electrochemical testing reveals no evidence of alloying except for the Ag-Sn bimetallic thin film. However, X-ray photoelectron spectroscopy (XPS) indicates a shift of the Ag 3d peaks to higher binding energies for all catalysts, suggesting a hybridization of Ag and the secondary metals. The composition of the metal surface, native oxide formation, ORR performance, and material changes post-RDE testing vary distinctly among the Ag bimetallic catalysts depending on the secondary metal. Intriguingly, performance is either enhanced (Ag-Co, Ag-Sn), maintained with reduced Ag content (Ag-Fe, Ag-Cr), or falls in between the two monometallic materials (Ag-Ni) compared to monometallic Ag thin films. Density functional theory (DFT) calculations offer insights into the catalyst performances and changes in metal oxidation states and surface composition prior and post electrocatalysis. AEMFC tests reveal promising performances under device conditions contradicting our fundamental RDE measurements. The integration of fundamental and application device tests, along with material characterization and DFT calculations, enables a comprehensive exploration of material changes under varying electrochemical conditions. This underscores the complexity of bimetallic catalysts and the importance of testing under device conditions, positioning Ag-bimetallic catalysts as highly promising alternatives to platinum-group metal catalysts for alkaline ORR.