Anion Exchange Membrane Fuel Cells Research Articles

Quantum confinement-induced anti-electrooxidation of metallic nickel electrocatalysts for hydrogen oxidation

AbstractThe anion-exchange-membrane fuel cell (AEMFC) is an attractive and cost-effective energy-conversion technology because it can use Earth-abundant and low-cost non-precious metal catalysts. However, non-precious metals used in AEMFCs to catalyse the hydrogen oxidation reaction are prone to self-oxidation, resulting in irreversible failure. Here we show a quantum well-like catalytic structure (QWCS), constructed by atomically confining Ni nanoparticles within a carbon-doped-MoOx/MoOx heterojunction (C-MoOx/MoOx) that can selectively transfer external electrons from the hydrogen oxidation reaction while remaining itself metallic. Electrons of Ni nanoparticles gain a barrier of 1.11 eV provided by the QWCS leading to Ni stability up to 1.2 V versus the reversible hydrogen electrode (VRHE) whereas electrons released from the hydrogen oxidation reaction easily cross the barrier by a gating operation of QWCS upon hydrogen adsorption. The QWCS-catalysed AEMFC achieved a high-power density of 486 mW mgNi−1 and withstood hydrogen starvation operations during shutdown–start cycles, whereas a counterpart AEMFC without QWCS failed in a single cycle.

Aiming the water transport issues of anion exchange membrane fuel cells by introducing hydrophobic carbon nanotube diffusion layer

The gas diffusion layer (GDL) enhances the transport efficiency of reaction gases and facilitates the removal of accumulated liquid water, thereby improving water management in anion exchange membrane fuel cells (AEMFCs). Carbon nanotubes (CNTs) are recognized as one of the promising materials to optimize mass transport within GDLs. In this study, we successfully synthesized an abundance of CNTs on the surface of commercial gas diffusion media. The as-prepared CNT layer exhibits exceptionally high hydrophobic properties and forms a hierarchically hydrophobic structure combined with the gas diffusion media, effectively enhancing the mass transfer of the membrane electrode assembly (MEA) and reducing ohmic impedance. Under supersaturation conditions, the power density of the MEA containing CNTs reaches 1031.7 mW/cm2, significantly higher than the 760.64 mW/cm2 observed for the commercial GDL. Further testing demonstrates that the MEA containing CNTs exhibits a limiting current density of 2507.4 mA/cm2, which is much superior to the benchmark MEA with the commercial GDL (1591 mA/cm2). Electrochemical impedance spectroscopy analysis reveals that the mass transfer resistance of MEAs with CNTs is lower than that of MEAs with the commercial GDL. More importantly, the phase-field modeling is performed to simulate the transport of the liquid water in the hierarchical GDL.

In Situ-Grown Ultrathin Catalyst Layers for Improving both Proton Exchange Membrane Fuel Cell and Anion Exchange Membrane Fuel Cell Performances.

The mass transport and ion conductivity in the catalyst layer are important for fuel cell performances. Here, we report an in situ-grown ultrathin catalyst layer (UTCL) to reduce the oxygen mass transport and a surface ionomer-coated gas diffusion layer method to reduce the ion conducting resistance. A significantly reduced catalyst layer thickness (ca. 1 μm) is achieved, and coupled with the ionomer introduction method, the ultrathin catalyst layer is in good contact with the membrane, resulting in high ion conductivity and high Pt utilization. This ultrathin catalyst layer is suitable for both proton exchange membrane fuel cells and anion exchange membrane fuel cells, giving peak power densities of 2.24 and 1.11 W cm-2, respectively, which represent an increase of more than 30% compared with the membrane electrode assembly (MEA) fabricated by using traditional Pt/C power catalysts. Electrochemical impedance spectra and limiting current tests demonstrate the reduced charge transfer, mass transfer, and ohmic resistances in the ultrathin catalyst layer membrane electrode assembly, resulting in the promoted fuel cell performances.

Single atom catalyst induced by redox reaction between iron ion and aniline monomer

The effective design of a low-cost, efficient, and stable non-noble metal electrocatalyst to substitute the noble metal electrocatalyst for oxygen reduction reaction is highly significant. Even though atomically dispersed metal catalyst shows excellent catalytic activity with maximized atom efficiency, the challenge often lies in achieving uniform distribution for single-atom catalysts owing to their tendency to aggregate. In this work, we present a sequential method that involves the reduction of iron (Fe) mediated by aniline (anchored on support), followed by pyrolysis to fabricate the Fe-Nx moieties and achieve the high density of single atom active sites. The resulting Fe SA 900 catalyst exhibited a half-wave potential of 0.84 V vs. reversible hydrogen electrode (RHE) for oxygen reduction reaction and outstanding stability in alkaline condition. Using various analysis techniques and electrochemical analysis, we demonstrated that the electrocatalytic activity of the catalyst arises from Fe single atom. To validate the practical applicability of Fe-N-C catalysts, we conducted an anion exchange membrane fuel cell (AEMFC) test, which demonstrated a high performance of 212 mW cm−2 at maximum power density. This study proves that the effectiveness of a sequential strategy adopting redox reaction and following pyrolysis for precise synthesis of a single atom Fe catalyst.

Immobilizing Ordered Oxophilic Indium Sites on Platinum Enabling Efficient Hydrogen Oxidation in Alkaline Electrolyte.

Addressing the sluggish kinetics in the alkaline hydrogen oxidation reaction (HOR) is a pivotal yet challenging step toward the commercialization of anion-exchange membrane fuel cells (AEMFCs). Here, we have successfully immobilized indium (In) atoms in an orderly fashion into platinum (Pt) nanoparticles supported by reduced graphene oxide (denoted as O-Pt3In/rGO), significantly enhancing alkaline HOR kinetics. We have revealed that the ordered atomic matrix enables uniform and optimized hydrogen binding energy (HBE), hydroxyl binding energy (OHBE), and carbon monoxide binding energy (COBE) across the catalyst. With a mass activity of 2.3066 A mg-1 at an overpotential of 50 mV, over 10 times greater than that of Pt/C, the catalyst also demonstrates admirable CO resistance and stability. Importantly, the AEMFC implementing this catalyst as the anode catalyst has achieved an impressive power output compared to Pt/C. This work not only highlights the significance of constructing ordered oxophilic sites for alkaline HOR but also sheds light on the design of well-structured catalysts for energy conversion.

Polyarylene-Based Anion Exchange Membranes for Fuel Cells.

Anion exchange membrane fuel cell (AEMFC) is an emerging and promising technology that can help realize a carbon-neutral, sustainable economy. Also, compared to the proton exchange membrane counterpart, AEMFC can achieve comparable cell outputs with lower costs due to the applicability of non-platinum group metal electrocatalysts for the reaction on the electrodes' surfaces. However, the wide application of the AEMFCs has been impeded by the unsatisfactory stability and performance of the hydroxide-conductive membranes in the past. Recently researchers have made breakthroughs using polyarylene (PA)-based AEMs. This article summarizes the recent advances of a class of AEMs with aromatic backbone without ether bonds, mainly synthesized by Friedel-Crafts polycondensation. Such PA-based AEMs showed high chemical/mechanical stabilities and ionic conductivity, and even the fuel cell with those AEMs showed impressive peak power density of up to 2.58 W cm-2. In this concept article, we classify major strategies for making PA-based AEMs to show the recent trends, highlight synthesis, characterization, and properties, and provide a brief outlook.

Partially PEG-Grafted Poly(Terphenyl Piperidinium) Anion Exchange Membranes with Balanced Properties for Alkaline Fuel Cells.

Poly(ethylene glycol) (PEG) or oligo (ethylene glycol) (OEG) grafted anion exchange membranes (AEMs) exhibit improved ionic conductivity, high alkaline stability, and subsequent boosted AEM fuel cell performance, but too much PEG/OEG side chains may can result in a reduction in the ion exchange capacity (IEC), which can have adverse effects on ion transport. Here, a series of partially PEG-grafted poly(terphenyl piperidinium) with different side chain length are synthesized using simple postpolymerization modification to produce AEMs with balanced properties. The polar and flexible PEG side chains are responsible for the controlled water uptake and swelling, superior hydroxide conductivity (122 mS cm-1 at 80 °C with an IEC of 1.99mmol g-1), and enhanced alkaline stability compared to the reference sample without PEG grafts (PTP). More importantly, the performance of AEM fuel cell (AEMFC) with the membrane containing partial PEG side chains surpasses that with PTP membrane, demonstrating a highest peak power density of 1110mW cm-2 at 80 °C under optimized conditions. This work provides a novel approach to the fabrication of high-performance AEM materials with balanced properties for alkaline fuel cell application.

High conductivity and dimensional stability brominated poly (aryl piperidinium) anion exchange membranes: Synergistic interaction of hydrophilic and superhydrophobic fluorinated side chains

Anion-exchange membrane fuel cells (AEMFCs) is a promising renewable energy device for hydrogen production. Anion exchange membranes (AEMs), the key component of AEMFCs, is generally needed for excellent dimensional stability and conductivity. Here, we synthesised a variety of AEMs with different number of C–F bonds to enhance the hydrophilic/hydrophobic micro-phase separation structure while maintaining dimensional stability. At 80 °C, the QPBTTP-PEG-10-F9 shows high OH− conductivity (∼179.02 mS cm−1), excellent dimensional stability (swelling ratio <19 %), and mechanical properties (elongation at break: 37 %, tensile strength: 71 MPa). In addition, QPBTTP-PEG-10-F9 shows good alkaline stability (conductivity remaining of 92.52 %) in 3 M NaOH solution for 1800 h. The peak power density (PPD) of a single cell assembled with QPBTTP-PEG-10-F9 can reach 534.79 mW cm−2 with a current density of 951 mA cm−2.

Polycarbazole-based anion exchange membranes containing flexible side-chain linked piperidine pendants for alkaline fuel cells

In recent years, advancements in anion exchange membranes (AEMs) have notably enhanced the overall performance of anion exchange membrane fuel cells (AEMFCs). However, issues like limited alkali stability and low ionic conductivity of AEMs have become apparent. In this study, focusing on molecular design, a series of polycarbazole-based AEMs with flexible side chains, named PCP-n (where ‘n’ denotes the molar ratio of the newly synthesized monomer BHC in carbazole derivatives), were developed. The integration of long flexible side chains fosters chain movement and the clustering of piperidine cations, leading to distinct hydrophilic/hydrophobic nanoscale phase separation within the PCP-n membranes. Moreover, the PCP-n membranes demonstrate effective water management capabilities, with the PCP-90 membrane displaying a 32 % water uptake and an in-plane swelling ratio below 20 % at 80 °C. The introduction of an ether-free main chain based on carbazole derivatives along with the highly stable piperidine cationic group endows the PCP-n membranes with exceptional alkali resistance. Following a 1500-h immersion in 2 M KOH at 80 °C, the PCP-90 membrane successfully retains 79.92 % of its original ionic conductivity. Given its substantial thermal stability and mechanical strength, the PCP-90 membrane underwent testing in membrane electrode assembly and single-cell performance, achieving a notable peak power density of 275.64 mW cm−2 and an open-circuit voltage of 0.98 V. Overall, the impressive comprehensive performance of the PCP-n membranes suggests a promising future for their application.

Improving anion exchange membrane fuel cell performance via enhanced ionomer–carbon interaction in cathode catalyst layers with carbon-supported Pt catalyst using a pyrene carboxyl acid coating

While there have been substantial strides in anion exchange membrane and ionomer, engineering the catalyst layers (CLs) of anion exchange membrane fuel cells (AEMFCs) is still an unexplored domain despite its significance. Conventional anion exchange ionomers (AEIs) tend to be locally agglomerated in the CLs due to their weak interaction with the carbon support of catalyst, resulting in pore clogging in the CLs. Herein, we report that the coating of pyrene carboxyl acid (PCA) on the carbon surface increases ionomer–carbon interaction. PCA has a strong interaction with carbon surface via π–π interaction and with AEI via coulombic interaction. The use of PCA prevents the aggregation of ionomer chains, leading to homogeneous ionomer distribution and meso-porous CL structure. Due to the expanded catalyst/ionomer interface and promoted O2 transport, PCA coating improves the electrochemical performance of AEMFC. Controlling the ionomer–carbon interaction opens a new avenue for realizing high-performance AEMFCs.

Metal-free advanced energy materials for the oxygen reduction reaction in anion-exchange membrane fuel cells

The success of the next generation of anion-exchange membrane fuel cells (AEMFCs) depends on the development of active, reliable, and economical oxygen reduction reaction (ORR) catalysts. Here, we synthesize a series of ultra-low-cost metal-free ORR catalysts by doping a common pristine graphite precursor with chemically singular-type heteroatoms, namely I, S, N, or B, using single-step planetary ball milling technique. All doped-graphites show substantially enhanced ORR performance relative to the pristine (undoped) graphite. Among all the tested catalysts, N-graphite exhibited the highest ORR onset potential of 0.87 V vs. reversible hydrogen electrode. These results are supported by density functional theory calculations. The ORR catalysts also exhibit remarkable stability as evaluated through electrochemical tests. Most importantly, the AEMFCs prepared using these ultra-low-cost doped graphites deliver notable peak power densities with impressive voltage efficiencies, which further supports their efficacy in ORR catalysis and the broad implementation of this technology.

Iridium-Based Alkaline Hydrogen Oxidation Reaction Electrocatalysts.

The hydroxide exchange membrane fuel cells (HEMFCs) are promising but lack of high-performance anode hydrogen oxidation reaction (HOR) electrocatalysts. The platinum group metals (PGMs) have the HOR activity in alkaline medium two to three orders of magnitude lower than those in acid, leading to the high required PGMs amount on anode to achieve high HEMFC performance. The mechanism study demonstrates the hydrogen binding energy of the catalyst determines the alkaline HOR kinetics, and the adsorbed OH and water on the catalyst surface promotes HOR. Iridium (Ir) has a unique advantage for alkaline HOR due to its similar hydrogen binding energy to Pt and enhanced adsorption of OH. However, the HOR activity of Ir/C is still unsatisfied in practical HEMFC applications. Further fine tuning the adsorption of the intermediate on Ir-based catalysts is of great significance to improve their alkaline HOR activity, which can be reasonably realized by structure design and composition regulation. In this concept, we address the current understanding about the alkaline HOR mechanism and summarize recent advances of Ir-based electrocatalysts with enhanced alkaline HOR activity. We also discuss the perspectives and challenges on Ir-based electrocatalysts in the future.

A Novel Side‐Chain Type Double‐Cation Grafted Poly (Binaphthyl Triphenyl Piperidine) Membranes for Anion Exchange Membrane Fuel Cells

AbstractRecent advancements in anion exchange membrane fuel cells (AEMFCs) have been primarily driven by improvements in anion exchange membranes (AEMs). Aryl ether bond‐free membranes have emerged as a promising avenue for enhancing the overall performance of AEMs. In this study, poly (binaphthyl triphenyl piperidine) with different side‐chain degree (PBTP‐s‐x), possesses double cationic groups, aiming at further enhancing overall performance for AEMs. The use of a twisted stereospecific backbone structure of polymerized binaphthyl and triple biphenyl monomer and grafted side chains of piperidine cationic groups not only improves the microphase separation structure of the membrane, but also improves the alkali resistance. Notably, the PBTP‐s‐100 AEMs exhibit exceptional OH− conductivity, reaching up to 138.21 mS cm−1, and show outstanding mechanical properties with a tensile strength of up to 28 MPa. Additionally, PBTP‐s‐100 displays excellent durability, proved by the NMR spectral consistency and over 80 % ion conductivity retention in 1 M NaOH at 60 °C for 4 weeks. And PBTP‐s‐100 exhibits a higher Lowest Unoccupied Molecular Orbital (LUMO) and a larger energy gap for LUMO and Highest Occupied Molecular Orbital (HOMO) by density functional theory calculation, which indicates it possesses sterling alkaline stability. These findings highlight the potential of PBTP‐s‐100 as a highly performing polymer structure suitable for anion exchange membranes, which is capable of significantly enhancing the performance of fuel cells.

Dilute RuCo Alloy Synergizing Single Ru and Co Atoms as Efficient and CO‐Resistant Anode Catalyst for Anion Exchange Membrane Fuel Cells

AbstractRuthenium (Ru) is considered a promising candidate catalyst for alkaline hydroxide oxidation reaction (HOR) due to its hydrogen binding energy (HBE) like that of platinum (Pt) and its much higher oxygenophilicity than that of Pt. However, Ru still suffers from insufficient intrinsic activity and CO resistance, which hinders its widespread use in anion exchange membrane fuel cells (AEMFCs). Here, we report a hybrid catalyst (RuCo)NC+SAs/N‐CNT consisting of dilute RuCo alloy nanoparticles and atomically single Ru and Co atoms on N‐doped carbon nanotubes The catalyst exhibits a state‐of‐the‐art activity with a high mass activity of 7.35 A mgRu−1. More importantly, when (RuCo)NC+SAs/N‐CNT is used as an anode catalyst for AEMFCs, its peak power density reaches 1.98 W cm−2, which is one of the best AEMFCs properties of noble metal‐based catalysts at present. Moreover, (RuCo)NC+SAs/N‐CNT has superior long‐time stability and CO resistance. The experimental and density functional theory (DFT) results demonstrate that the dilute alloying and monodecentralization of the exotic element Co greatly modulates the electronic structure of the host element Ru, thus optimizing the adsorption of H and OH and promoting the oxidation of CO on the catalyst surface, and then stimulates alkaline HOR activity and CO tolerance of the catalyst.

Dilute RuCo Alloy Synergizing Single Ru and Co Atoms as Efficient and CO-Resistant Anode Catalyst for Anion Exchange Membrane Fuel Cells.

Ruthenium (Ru) is considered a promising candidate catalyst for alkaline hydroxide oxidation reaction (HOR) due to its hydrogen binding energy (HBE) like that of platinum (Pt) and its much higher oxygenophilicity than that of Pt. However, Ru still suffers from insufficient intrinsic activity and CO resistance, which hinders its widespread use in anion exchange membrane fuel cells (AEMFCs). Here, we report a hybrid catalyst (RuCo)NC+SAs/N-CNT consisting of dilute RuCo alloy nanoparticles and atomically single Ru and Co atoms on N-doped carbon nanotubes The catalyst exhibits a state-of-the-art activity with a high mass activity of 7.35 A mgRu -1. More importantly, when (RuCo)NC+SAs/N-CNT is used as an anode catalyst for AEMFCs, its peak power density reaches 1.98 W cm-2, which is one of the best AEMFCs properties of noble metal-based catalysts at present. Moreover, (RuCo)NC+SAs/N-CNT has superior long-time stability and CO resistance. The experimental and density functional theory (DFT) results demonstrate that the dilute alloying and monodecentralization of the exotic element Co greatly modulates the electronic structure of the host element Ru, thus optimizing the adsorption of H and OH and promoting the oxidation of CO on the catalyst surface, and then stimulates alkaline HOR activity and CO tolerance of the catalyst.

Lignin-Derived Precious Metal-Free Electrocatalysts for Anion-Exchange Membrane Fuel Cell Application

Lignin-Derived Precious Metal-Free Electrocatalysts for Anion-Exchange Membrane Fuel Cell Application

Advancements in electrocatalyst architecture for enhanced oxygen reduction reaction in anion exchange membrane fuel cells: A comprehensive review

This comprehensive review explores recent advancements in electrocatalyst architecture to enhance the oxygen reduction reaction (ORR) in anion exchange membrane fuel cells (AEMFCs). It examines strategies such as nanostructuring, alloying, and heteroatom doping to improve catalytic activity, stability, and durability properties. Key findings reveal the importance of optimizing catalyst morphology, composition, and interface engineering to mitigate challenges such as sluggish kinetics and electrode degradation. Additionally, insights into mechanistic aspects and performance metrics are discussed, highlighting the crucial role of electrocatalysts in advancing AEMFC technology. Overall, this review provides valuable perspectives for researchers and engineers in designing efficient and durable electrocatalysts for next-generation AEMFCs, thereby facilitating the transition towards sustainable energy solutions.

Polyaniline 합성 시 단량체와 산화제 비율이 음이온 교환막 연료전지에 대한 산소 환원 촉매의 활성에 미치는 영향

Polyaniline 합성 시 단량체와 산화제 비율이 음이온 교환막 연료전지에 대한 산소 환원 촉매의 활성에 미치는 영향

Anion Exchange Membrane with Pendulous Piperidinium on Twisted All-Carbon Backbone for Fuel Cell.

As a central component for anion exchange membrane fuel cells (AEMFCs), the anion exchange membrane is now facing the challenge of further improving its conductivity and alkali stability. Herein, a twisted all-carbon backbone is designed by introducing stereo-contorted units with piperidinium groups dangled at the twisted sites. The rigid and twisted backbone improves the conduction of hydroxide and brings down the squeezing effect of the backbone on piperidine rings. Accordingly, an anion exchange membrane prepared through this method exhibits adapted OH- conductivity, low swelling ratio and excellent alkali stability, even in high alkali concentrations. Further, a fuel cell assembled with a such-prepared membrane can reach a power density of 904.2 mW/cm2 and be capable of continuous operation for over 50 h. These results demonstrate that the designed membrane has good potential for applications in AEMFCs.

Atomically dispersed Iridium on Mo2C as an efficient and stable alkaline hydrogen oxidation reaction catalyst

Hydroxide exchange membrane fuel cells (HEMFCs) have the advantages of using cost-effective materials, but hindered by the sluggish anodic hydrogen oxidation reaction (HOR) kinetics. Here, we report an atomically dispersed Ir on Mo2C nanoparticles supported on carbon (IrSA-Mo2C/C) as highly active and stable HOR catalysts. The specific exchange current density of IrSA-Mo2C/C is 4.1 mA cm−2ECSA, which is 10 times that of Ir/C. Negligible decay is observed after 30,000-cycle accelerated stability test. Theoretical calculations suggest the high HOR activity is attributed to the unique Mo2C substrate, which makes the Ir sites with optimized H binding and also provides enhanced OH binding sites. By using a low loading (0.05 mgIr cm−2) of IrSA-Mo2C/C as anode, the fabricated HEMFC can deliver a high peak power density of 1.64 W cm−2. This work illustrates that atomically dispersed precious metal on carbides may be a promising strategy for high performance HEMFCs.