Anion Exchange Membrane Fuel Cells Research Articles

Regulation Strategies for Fe-N-C and Co-N-C Catalysts for the Oxygen Reduction Reaction.

Proton exchange membrane fuel cells (PEMFCs) and alkaline membrane fuel cells (AEMFCs) have received great attention as energy devices of the next generation. Accelerating oxygen reduction reaction (ORR) kinetics is the key to improve PEMFC and AEMFC performance. Platinum-based catalysts are the most widely used catalysts for the ORR, but their high price and low abundance limit the commercialization of fuel cells. Non-noble metal-nitrogen-carbon (M-N-C) is considered to be the most likely material class to replace Pt-based catalysts, among which Fe-N-C and Co-N-C have been widely studied due to their excellent intrinsic ORR performance and have made great progress in the past decades. With the improvement of synthesis technology and a deeper understanding of the ORR mechanism, some reported Fe-N-C and Co-N-C catalysts have shown excellent ORR activity close to that of commercial Pt/C catalysts. Inspired by the progress, regulation strategies for Fe-N-C and Co-N-C catalysts are summarized in this Review from 5 perspectives: (1) coordinated atoms, (2) environmental heteroatoms and defects, (3) dual-metal active sites, (4) metal-based particle promoters, and (5) curved carbon layers. We also make suggestions on some challenges facing Fe-N-C and Co-N-C research.

Investigation of membranes-electrodes assemblies in anion exchange membrane fuel cells (AEMFCs): Influence of ionomer ratio in catalyst layers

Anion exchange membrane fuel cells (AEMFCs) have recently attracted significant attention as low-cost alternative fuel cells to traditional proton exchange membrane fuel cells because of the possible use of platinum-group metal-free electrocatalysts. Over the past decade, new materials dedicated to the alkaline medium, such as anion exchange membranes (AEMs) and anion exchange ionomers (AEIs), have been developed and studied in AEMFCs. However, only a few AEMs and AEIs are commercially available, and there are no ready-to-use membrane electrodes assemblies (MEAs) with the desired AEMs and AEIs. Consequently, the need to manufacture in-house CCMs or GDEs becomes a reality that we must face.This work deals with the influence of ionomer content on the prepared MEAs with the commercial anion exchange membrane and ionomer from Aemion™ Ionomr Innovations AF1–HNN8–2 and AP1–ENN8/HNN8 respectively and by varying the support (gas diffusion layer or membrane). The prepared MEAs were characterized morphologically by SEM and profilometry, as well as electrochemically by AEMFC polarization curves and cyclic voltammetry. In addition, an attempt to investigate water management was made with and without a reference electrode in the cell to understand the behavior of water in an operating AEMFC. Our results show that CCM-based MEAs can undergo deformation during the anion conversion step, leading to weakening of the membrane and hence faster degradation in the fuel cell. On the contrary, no deformation was observed for the GDEs during the anionic conversion, although the results are poorer due to (i) poor interface contact between membrane and GDE that depends on ionomer ratio in the ink and (ii) a high overpotential at the anode due to the production of water that cannot be effectively evacuated.

Synthesis of poly N-aryl piperidinium membrane and ionomer for anion exchange membrane fuel cell applications

Ether free backbones have recently attracted widespread attention in anion exchange membrane fuel cells (AEMFCs). Here we report the synthesis of two poly N-aryl piperidinium (PNAP) membranes from their monomers by the polycondensation method using trifluoromethanesulfonic acid as a catalyst. Density functional theory identifies the chemical reaction, and the radial distribution function represents the interactions between a water molecule and a functional group of PNAP membranes. The performance of the anion exchange membrane can be enhanced by varying the monomer ratios of PNAP. An optimized PNAP-2 membrane exhibits a hydroxide conductivity of 183 mS cm−1 at 90 °C and PNAP-2 ionomers with Pt/C catalysts display a greater half-wave potential (E1/2) of 0.81 V and a lower Tafel value of 65 mV dec−1. In fuel cell tests, a PNAP-2 ionomer alongside a 60% platinum-on-carbon (Pt/C) membrane electrode assembly achieved a peak power density of 2.07 W cm−2. The PNAP-2 remained stable for more than 230 h at a constant current density of 0.3 A cm−2. PNAP-2 also displays exceptional resistance to alkaline conditions, lasting for more than 1000 h in both 1 M and 5 M NaOH solutions at 60 °C.

An improvement on the electrocatalytic performance of ZIF-67 by in situ self-growing CNTs on surface

Efficient and robust oxygen reduction reaction (ORR) catalysts are essential for the development of high-performance anion-exchange membrane fuel cells (AEMFC). To enhance the electrochemical performance of metal–organic frameworks of cobalt-based zeolite imidazolium skeleton (ZIF-67), this study reported a novel ZIF-67-4@CNT by in situ growing carbon nanotubes (CNTs) on the surface of ZIF-67 via a mild two-step pyrolysis/oxidation treatment. The electrochemical results showed that the as-prepared ZIF-67-4@CNT after CTAB modification exhibited excellent catalytic activity with good stability, with Eonset, E1/2, and Ilimit, respectively were 0.98 V (versus RHE), 0.87 V (versus RHE) and 6.04 mA cm−2@1600 rpm, and a current retention rate of about 94.21% after polarized at 0.80 V for 10 000 s, which were all superior to that of the commercial 20 wt% Pt/C. The excellent ORR catalytic performance was mainly attributed to the large amount of the in situ growing CNTs on the surface, encapsulated with a wide range of valence states of metallic cobalt.

Hybrid high-performance oxygen reduction reaction Fe–N–C electrocatalyst for anion exchange membrane fuel cells

Atomically dispersed active sites and hierarchical porosity in Fe–N–C catalyst materials are essential for efficient oxygen reduction reaction (ORR) electrocatalysis and effective mass transport, respectively. However, the majority of these catalysts fail to deliver outstanding electrocatalytic activity and stumble when used as cathode materials in fuel cells. Herein, we developed a catalyst with partially transformed metallic Fe into Fe-Nx sites embedded in the carbonaceous matrix, and its excellent electrocatalytic performance is attributed to the hybrid nanoparticles and built-in Fe-Nx site structures. The optimized Fe@Fe–N–C catalyst was tested for ORR performance both ex-situ using the rotating (ring)-disk electrode technique and in an anion exchange membrane fuel cell (AEMFC). The Fe@Fe–N–C electrocatalyst exhibited remarkably enhanced ORR activity in alkaline media with a half-wave potential of 0.822 V vs. reversible hydrogen electrode (RHE) and showed the maximum power density (Pmax) of 242 mW cm−2 in an AEMFC test, surpassing the peak power density obtained from the Pt/C cathode catalyst (Pmax = 220 mW cm−2) under H2–O2 conditions. Therefore, the study provides a promising prospect for designing improved, cost-effective, and noble metal-free electrocatalysts for achieving high performance in AEMFCs.

High‐Performance Anion Exchange Membrane Fuel Cells Enabled by Nitrogen Configuration Optimization in Graphene‐Coated Nickel for Enhanced Hydrogen Oxidation

Anion exchange membrane fuel cell (AEMFC) technology is attracting intensive attention, due to its great potential by using non‐precious‐metal catalysts (NPMCs) in the cathode and cheap bipolar plate materials in alkaline media. However, in such case, the kinetics of hydrogen oxidation reaction (HOR) in the anode is two orders of magnitude sluggish than that of acidic electrolytes, which is recognized as the grand challenge in this field. Herein, we report the rationally designed Ni nanoparticles encapsulated by N‐doped graphene layers (Ni@NG) using a facile pyrolysis strategy. Based on the density functional theory calculations and electrochemical performance analysis, it is witnessed that the rich Pyridinic‐N within the graphene shell optimizes the binding energy of the intermediates, thus enabling the fundamentally enhanced activity for HOR with robust stability. As a proof of concept, the resultant Ni@NG sample as the anode with a low loading (1.8 mg cm−2) in AEMFCs delivers a high peak power density of 500 mW cm−2, outperforming all of those of NPMC‐based analogs ever reported.

Recent Developments of Metal-N-C Catalysts Toward Oxygen Reduction Reaction for Anion Exchange Membrane Fuel Cell: A Review

<p>Metal-N-C (MNC) catalysts have been anticipated as promising candidates for oxygen reduction reaction (ORR) to achieve low-cost polymer electrolyte membrane fuel cells. The structure of the M-N<sub>x</sub> moiety enabled a high catalytic activity that was not observed in previously reported transition metal nanoparticle-based catalysts. Despite progress in non-precious metal catalysts, the low density of active sites of MNCs, which resulted in lower single-cell performance than Pt/C, needs to be resolved for practical application. This review focused on the recent studies and methodologies aimed to overcome these limitations and develop an inexpensive catalyst with excellent activity and durability in an alkaline environment. It included the possibility of non-precious metals as active materials for ORR catalysts, starting from Co phthalocyanine as ORR catalyst and the development of methodologies (e.g., metal-coordinated N-containing polymers, metal-organic frameworks) to form active sites, M-N<sub>x</sub> moieties. Thereafter, the motivation, procedures, and progress of the latest research on the design of catalyst morphology for improved mass transport ability and active site engineering that allowed the promoted ORR kinetics were discussed.</p>

Stabilizing the Catalyst Layer for Durable and High Performance Alkaline Membrane Fuel Cells and Water Electrolyzers.

Anion exchange membrane (AEM) fuel cells (AEMFCs) and water electrolyzers (AEMWEs) suffer from insufficient performance and durability compared with commercialized energy conversion systems. Great efforts have been devoted to designing high-quality AEMs and catalysts. However, the significance of the stability of the catalyst layer has been largely disregarded. Here, an in situ cross-linking strategy was developed to promote the interactions within the catalyst layer and the interactions between catalyst layer and AEM. The adhesion strength of the catalyst layer after cross-linking was improved 7 times compared with the uncross-linked catalyst layer due to the formation of covalent bonds between the catalyst layer and AEM. The AEMFC can be operated under 0.6 A cm-2 for 1000 h with a voltage decay rate of 20 μV h-1. The related AEMWE achieved an unprecedented current density of 15.17 A cm-2 at 2.0 V and was operated at 0.5, 1.0, and 1.5 A cm-2 for 1000 h.

Highly Active MoS2‐MXenes Hybrid Electrocatalysts Towards the Oxygen Reduction Reaction

AbstractIn this work, catalytic performance of MoS2 supported on Mo2TiC2 and Ti3C2 MXenes towards the oxygen reduction reaction (ORR) was studied. These materials were synthesised through an etching route of MAX phases as precursors of MXenes, followed by a hydrothermal treatment to coat them with MoS2. This procedure generated MoS2 nanospheres covering the MXenes, which were verified by SEM‐EDX mapping, Raman spectroscopy and XPS. Activity of these materials towards ORR was studied by RRDE, comparing its performance with that of individual MoS2 and MXenes. As main features, it was demonstrated that production of HOO− occurring on the composites decreases in comparison with individual materials. Long‐term stability tests performed in O2‐saturated electrolyte showed a drop in the activity of the materials due to the increase in the production of HOO−, although no morphological or compositional changes were observed. Despite this result, the improvement of the catalytic properties of the individual materials means that these composites can be considered as candidates to be used as supports of active non‐noble metal nanoparticles in the cathodes of anion exchange membrane fuel cells (AEMFCs).

Exploring the Potential of α-MnO<sub>2</sub>/ Carbon Nanotubes for Improved Oxygen Reduction Reaction Performance at the Cathode of Alkaline Fuel Cells

In the field of fuel cell technology, the development of cost-effective catalysts is crucial for the commercialization of Alkaline Membrane Fuel Cells (AMFCs). Platinum (Pt) has traditionally been employed as the catalyst in AMFCs, but its high cost poses a major barrier to widespread adoption. In this study, a new catalyst material was developed by incorporating Manganese Dioxide (α-MnO2) into Carbon Nanotubes (CNTs) using hydrothermal synthesis techniques. The synthesized catalyst was characterized using Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD), and its electrocatalytic activity was evaluated through Linear Sweep Voltammetry (LSV) and CV through Rotating Disc Electrode (RDE) experiments. The results showed that the α-MnO2-CNT composite displayed strong durability in the alkaline environment and high electrocatalytic activity for oxygen reduction reaction (ORR). The LSV measurements revealed a current density of -4.1 mA/cm2 and an overpotential of -0.3V relative to Standard Calomel Electrode (SCE) in a 0.1M KOH electrolyte. Additionally, the α-MnO2-CNT composite displayed high methanol tolerance and long-term stability compared to commercial Pt/C catalysts. This study demonstrates that the use of α-MnO2-CNT as a cost-effective alternative to Pt has the potential to facilitate the commercialization of AMFC technology.

Transient Distribution of Water in an Anion Exchange Membrane Fuel Cell Monitored by Operando Coherent Anti-Stokes Raman Scattering Spectroscopy

Transient Distribution of Water in an Anion Exchange Membrane Fuel Cell Monitored by Operando Coherent Anti-Stokes Raman Scattering Spectroscopy

A novel anion exchange membrane comprised of three aromatic units for fuel cells

Anion exchange membrane fuel cell (AEMFC) has made great progress recently due to the continuous improvement of anion exchange membrane (AEM). Aryl ether bond-free membranes are considered to be promising for improving the overall performance of AEMs. Here, we present a copolymer consisting of m-terphenyl, diphenyl ethane and biphenyl (PMDBP) to further enhance the microphase separation structure by introducing a third structural unit, biphenyl. Meanwhile, the more compact biphenyl structure enhances the mechanical strength of AEMs. Specifically, PMDBP AEMs possess superior OH- conductivity (up to 113 mS cm−1) and excellent mechanical properties (tensile strength up to 42 MPa). Furthermore, the PMDBP has an outstanding single-cell performance with a peak power density (PPD) of up to 95 mW cm−2 with a platinum-carbon (Pt/C) catalyst at 80°C in H2-air. In addition, PMDBP is provided with excellent durability, including NMR spectral consistency and over 90% ion conductivity retention in 1 M NaOH at 60°C for 720 h. This study provided a copolymer structure suitable for anion exchange membrane that can provide excellent performance for fuel cells and electrolyzers.

High-temperature inorganic anion exchange membranes based on layered double hydroxides for anion exchange membrane fuel cell applications

Anion-exchange membrane fuel cells (AEMFCs) have garnered substantial attention over the past two decades due to their numerous advantages, positioning them as promising alternatives to proton exchange membrane fuel cells (PEMFCs). However, their rapid development faces notable challenges, including the limited high-temperature and alkaline stability of anion-exchange membranes due to the incorporation of cationic functional groups, as well as intricate preparation processes. In this study, we propose a high-temperature inorganic anion exchange membrane based on layered double hydroxide doped with K2CO3 prepared by a simple process. This innovative approach optimizes the ionic transport pathway within the LDHs inorganic membrane and enhances water retention performance at elevated temperatures. The maximum cross-plane ionic conductivity of the membrane can reach up to 10−2 S cm−1. Remarkably, the peak power density attains an impressive level of 215.2 mW cm−2 at 110 °C and 200 kPa during the fuel cell testing.

Solvent Effects on the Catalyst Ink and Layer Microstructure for Anion Exchange Membrane Fuel Cells.

Understanding the complex solvent effects on the microstructures of ink and catalyst layer (CL) is crucial for the development of high-performance anion exchange membrane fuel cells (AEMFCs). Herein, we study the solvent effects within the binary solvent ink system composed of water, isopropyl alcohol (IPA), commercial anion exchange ionomer, and Pt/C catalyst. The results show that the Pt/C particles and ionomer tend to form large aggregates wrapped with a thick ionomer layer in IPA-rich ink and promote the formation of large mesopores within the CL. With the increase of the water content in the ink, Pt/C particles are more likely to bridge to each other through wrapped FAA to form a well-connected three-dimensional network. The CL fabricated using water-rich ink shows smaller pores, higher porosity, and a more homogeneous ionomer network without the formation of large aggregates. Based on these results, we propose that the properties of the solvent mixture, including dielectric constant (ε) and solubility parameter (δ), affect the coulomb interaction of charged particles and surface tension at interfaces, which in turn affects the microstructure of ink and CL. By leveraging the solvent effects, we optimize the CL microstructures and improve the performance of AEMFC. These results may guide the rational design and fabrication of AEMFCs.

Advanced Architectures of Air Electrodes in Zinc-Air Batteries and Hydrogen Fuel Cells.

The air electrode is an essential component of air-demanding energy storage/conversion devices, such as zinc-air batteries (ZABs) and hydrogen fuel cells (HFCs), which determines the output power and stability of the devices. Despite atom-level modulation in catalyst design being recently achieved, the air electrodes have received much less attention, causing a stagnation in the development of air-demanding equipment. Herein, the evolution of air electrodes for ZABs and HFCs from the early stages to current requirements is reviewed. In addition, the operation mechanism and the corresponding electrocatalytic mechanisms of ZABs are summarized. In particular, by clarifying the air electrode interfaces of ZABs at different scales, several approaches to improve the air electrode in rechargeable ZABs are reviewed, including innovative electrode structures and bifunctional oxygen catalysts. Afterward, the operating mechanisms of proton-exchange-membrane fuel cells (PEMFCs) and anion-exchange-membrane fuel cells (AEMFCs) are explained. Subsequently, the strategies employed to enhance the efficiency of the membrane electrode assembly (MEA) in PEMFCs and AEMFCs, respectively, are highlighted and discussed in detail. Last, the prospects for air electrodes in ZABs and HFCs are considered by discussing the main challenges. The aim of this review is to facilitate the industrialization of ZABs and HFCs.

Construction of Heterostructure between Ni17W3 and WO2 to Boost the Hydrogen Oxidation Reaction in Alkaline Medium.

The inferior intrinsic performance of Ni-based catalysts for the hydrogen oxidation reaction (HOR) in an alkaline medium seriously restricts the utilization of emerging anion-exchange membrane fuel cells (AEMFCs). This is because the hydrogen and hydroxyl binding energies on Ni need to be optimized. Although electrocatalysts obtained by alloying Ni with Mo or W reportedly exhibit enhanced activity, they are still far from industrial requirements based on unbalanced HBE and OHBE. Herein, we report to further enhance alkaline HOR activity by constructing a heterostructure between NiW alloy and metal oxide (Ni17W3/WO2), which is synthesized through solvothermal treatment combined with annealing. The as-fabricated reduced graphene oxide (rGO)-supported Ni17W3/WO2 (Ni17W3/WO2/rGO) exhibits state-of-the-art catalytic activity (current density of 2.9 mA cm-2 at 0.1 V vs RHE), faster kinetics (geometric kinetics current density of 4.0 mA cm-2 that can be comparable to Pt/C), and high stability (maintaining the current density for more than 80 h) toward HOR in alkaline media. The detailed characterizations reveal that the charge transfer across the boundary arising from constructing the as-prepared heterostructure tunes the electronic structures, ultimately facilitating the HOR process.

"Fishbone" Design of Amino/N-Spirocyclic Cations toward High-Performance Poly(triphenylene piperidine) Anion-Exchange Membranes for Fuel Cells.

N-Spirocyclic cations have excellent alkali resistance stability, and precise design of the structure of N-spirocyclic anion-exchange membranes (AEMs) improves their comprehensive performance. Here, we design and synthesize high-performance poly(triphenylene piperidine) membranes based on the "fishbone" design of amino/N-spirocyclic cations. The "fishbone" design does not disrupt the overall stabilized conformation but promotes a microphase separation structure, while exerting the synergistic effect of piperidine cations and spirocyclic cations, resulting in a membrane with good conductivity and alkali resistance stability. The hydroxide conductivity of the QPTPip-ASU-X membrane reached up to 133.5 mS cm-1 at 80 °C. The QPTPip-ASU-15 membrane was immersed in a 2 M NaOH solution at 80 °C for 1200 h, and the conductivity was maintained at 91.02%. In addition, the QPTPip-ASU-5 membrane had the highest peak power density of 255 mW cm-2.

Coherent anti-Stokes Raman scattering spectroscopy system for observation of water molecules in anion exchange membrane

Anion exchange membrane fuel cells (AEMFCs) provide one of the most feasible remedies to fuel cells’ dependency on the dwindling Pt group catalysts. Nevertheless, AEMFCs still suffer reduced durability, which requires an in-depth understanding of their membranes. The low thermal endurance of the anion exchange membranes (AEMs) usually limits the direct application of powerful techniques, such as Raman spectroscopy. We sought to establish a system for coherent anti-Stokes Raman scattering (CARS) spectroscopy capable of taking measurements inside an AEM rapidly and accurately without photodamage. A 785 nm CARS system was newly developed to study the water species in an AEM (QPAF-4) located vertically in a fuel cell. From the results of water measurement in a QPAF-4 membrane, the OH-related region was deconvoluted into nine Gaussian peaks: Five H-bonded OH peaks, non-H-bonded OH, OH–, and two CH peaks. The H-bonded species increased with increasing relative humidity, but the other species remained constant. These results open unlimited possibilities for studying and comparing different AEMFCs, enabling more rapid technology optimization.

Selective Glycerol‐to‐glycerate Electro‐oxidation on Cerium‐modified Pt/C Nanocatalyst in an Alkaline Direct Alcohol Fuel Cell: Cogeneration of Energy and Value‐added Products

AbstractGlycerol electro‐oxidation reaction was performed in an alkaline environment with an anion exchange membrane fuel cell (AEMFC) operating in bath mode at low Pt‐loadings. BAE‐synthesized Pt/C and PtCe/C nanostructured catalysts were used as anode materials during 4‐hour operation to selectively obtain 65 % and 41 % of glycerate as main product, respectively. The modification of Pt with Ce improved the catalytic activity of the Pt/C catalyst generating 30 % more energy density after 4‐hour operation by achieving a higher degree of glycerol oxidation in cogeneration with added‐value products confirmed by spectroelectrochemical (in situ FTIR) and liquid chromatography coupled with mass spectrometry (LC–MS) analyses. The bifunctional mechanism generated by the presence of Ce is used to explain the improvement in the catalytic activity of Pt/C, due to the properties of this rare earth element to adsorb oxygenated species (OH−) and promote oxidation. The cathode material was a polyol‐synthesized PdFe/C electro‐catalyst for ORR that presented impressive stability and tolerance to glycerol.

Oligo (ethylene glycol)-grafted poly(terphenyl indole piperidinium) with high water diffusivity for anion exchange membrane fuel cells

The water diffusivity of polymeric anion exchange membranes (AEMs) plays a critical role in determining the AEM fuel cells (AEMFCs) performance because it generates an imbalance in the amount of water at the anode and cathode. However, the correlation between water diffusivity and the chemical structure of AEMs remains unclear. This study focuses on a series of oligo(ethylene glycol) (OEG) functionalized poly(arylene indole piperidinium) AEMs, in which OEG grafts are directly attached onto the polymer backbones. The polar and flexible OEG side chains afford a microphase-separated morphology, close polymer-chain packing, and extra sites for water–ion transport, resulting in high ion-exchange-capacity (IEC)-normalized conductivity, improved water diffusivity, and dimensional stability. Moreover, these side chains provide excellent ex-situ stability in a 1 M NaOH solution (80 °C) for 1080 h, surpassing the stability of its alkyl side chain counterpart (PITP-C10Q85) by a significant margin. The resultant PITP-OEG-85 with the highest water diffusivity exhibits a highest peak power density of 1.23 W cm−2 at 80 °C despite its low IEC value and conductivity. In-situ durability tests of this membrane at 0.2 A cm−2 for 24 h revealed the degradation of piperidinium under harsh conditions (70 % anode relative humidity at 60 °C). This work opens a new avenue for designing highly conductive and alkali-stable AEM materials with high water diffusivity to realize high-performance AEMFCs.