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.

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.

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.

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

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.

Balancing the Binding of Intermediates Enhances Alkaline Hydrogen Oxidation on D-Band Center Modulated Pd Sites.

Exploring efficient alkaline hydrogen oxidation reaction (HOR) electrocatalysts is of great concern for constructing anion exchange membrane fuel cells (AEMFCs). Herein, d-band center modulated PdCo alloys with ultralow Pd content anchored onto the defective carbon support (abbreviated as PdCo/NC hereafter) are proposed as highly efficient HOR catalyst. The as-prepared catalyst exhibits exceptional HOR performance compared to the Pt/C catalyst, achieving thermodynamically spontaneous and kinetically preferential reactions. Specifically, the resultant PdCo/NC demonstrates a marked enhancement in alkaline HOR performance, with the highest mass and specific activities of 1919.6 mA mgPd-1 and 1.9 mA cm-2, 51.1 and 4.2 times higher than those of benchmark of Pt/C, along with an excellent stability in a chronoamperometry test. In the analysis of in situ Raman spectra, it was discovered that tetrahedrally coordinated H-bonded water molecules were formed during the HOR process. This indicates that the promotion of interfacial water molecule formation and enhancement of HOR activities in PdCo/NC are facilitated by defect engineering and the turning of d-band center in PdCo alloy. The essential knowledge obtained in this study could open up a new direction for modifying the electronic structure of cost-effective HOR catalysts through electronic structure engineering.

Poly(ionic liquid) Ionomers Help Prevent Active Site Aggregation, in Single-Site Oxygen Reduction Catalysts.

Anion exchange membrane fuel cells (AEMFCs) can produce clean electricity without the need for platinum-group metals at the cathode. To improve their durability and performance, most research investigations so far have focused on optimizing the catalyst and anion exchange membrane, while few studies have been dedicated to the effect of the ionomer. Herein, we address this gap by developing a poly(ionic liquid)-based ionomer and studying its effect on oxygen transport and oxygen reduction kinetics, in comparison to the commercial proton exchange and anion exchange ionomers Nafion and Fumion. Our study shows that the choice of ionomer has a dramatic effect on the morphology of the catalyst layer, in particular on iron aggregation. We also observed that the quality of the catalyst layer and the degree of iron aggregation can be correlated to the rheological properties of the catalyst ink. Moreover, this work highlights the impact of the ionomer on the resistance to oxygen transport and reports improved oxygen diffusion compared to Nafion, for poly(ionic liquid)s with fluorinated anions. Finally, the performance of the catalyst-ionomer layer for oxygen reduction was tested with a rotating disc electrode (RDE) and a gas diffusion electrode (GDE). We observed dramatic differences between the two configurations, which we attribute to the different morphologies of the catalyst layer. In summary, our study highlights the dramatic and overlooked effect of the ionomer and the limitations of the RDE in predicting fuel cell performance.

Interlayer Polymerization to Construct a Fully Conjugated Covalent Organic Framework as a Metal-Free Oxygen Reduction Reaction Catalyst for Anion Exchange Membrane Fuel Cells.

Two-dimensional (2D) covalent organic frameworks (COFs) have a multilayer skeleton with a periodic π-conjugated molecular array, which can facilitate charge carrier transport within a COF layer. However, the lack of an effective charge carrier transmission pathway between 2D COF layers greatly limits their applications in electrocatalysis. Herein, by employing a side-chain polymerization strategy to form polythiophene along the nanochannels, a conjugated bridge is constructed between the COF layers. The as-synthesized fully conjugated COF (PTh-COF) exhibits high oxygen reduction reaction (ORR) activity with narrowed energy band gaps. Correspondingly, PTh-COF is tested as a metal-free cathode catalyst for anion exchange membrane fuel cells (AEMFCs) which showed a maximum power density of 176mWcm-2 under a current density of 533mAcm-2. The density functional theory (DFT) calculation reveals that interlayer conjugated polythiophene optimizes the electron cloud distribution, which therefore enhances the ORR performance. This work not only provides new insight into the construction of a fully conjugated covalent organic framework but also promotes the development of new metal-free ORR catalysts.

An all-metallic nanovesicle for hydrogen oxidation.

Vesicle, a microscopic unit that encloses a volume with an ultrathin wall, is ubiquitous in biomaterials. However, it remains a huge challenge to create its inorganic metal-based artificial counterparts. Here, inspired by the formation of biological vesicles, we proposed a novel biomimetic strategy of curling the ultrathin nanosheets into nanovesicles, which was driven by the interfacial strain. Trapped by the interfacial strain between the initially formed substrate Rh layer and subsequently formed RhRu overlayer, the nanosheet begins to deform in order to release a certain amount of strain. Density functional theory (DFT) calculations reveal that the Ru atoms make the curling of nanosheets more favorable in thermodynamics applications. Owing to the unique vesicular structure, the RhRu nanovesicles/C displays excellent hydrogen oxidation reaction (HOR) activity and stability, which has been proven by both experiments and DFT calculations. Specifically, the HOR mass activity of RhRu nanovesicles/C are 7.52 A mg(Rh+Ru)-1 at an overpotential of 50mV at the rotating disk electrode (RDE) level; this is 24.19 times that of commercial Pt/C (0.31mA mgPt-1). Moreover, the hydroxide exchange membrane fuel cell (HEMFC) with RhRu nanovesicles/C displays a peak power density of 1.62W cm-2 in the H2-O2 condition, much better than that of commercial Pt/C (1.18W cm-2). This work creates a new biomimetic strategy to synthesize inorganic nanomaterials, paving a pathway for designing catalytic reactors.

Ultralow-Loading Ruthenium-Iridium Fuel Cell Catalysts Dispersed on Zn-N Species-Doped Carbon.

Developing low-loading platinum-group-metal (PGM) catalysts is one of the key challenges in commercializing anion-exchange-membrane-fuel-cells (AEMFCs), especially for hydrogen oxidation reaction (HOR). Here, ruthenium-iridium nanoparticles being deposited on a Zn-N species-doped carbon carrier (Ru6Ir/Zn-N-C) are synthesized and used as an anodic catalyst for AEMFCs. Ru6Ir/Zn-N-C shows extremely high mass activity (5.87AmgPGM -1) and exchange current density (0.92mAcm-2), which is 15.1 and 3.9 times that of commercial Pt/C, respectively. Based on the Ru6Ir/Zn-N-C AEMFCs achieve a peak power density of 1.50Wcm-2, surpassing the state-of-the-art commercial PtRu catalysts and the power ratio of the normalized loading is 14.01WmgPGM anode -1 or 5.89W mgPGM -1 after decreasing the anode loading (87.49µgcm-2) or the total PGM loading (0.111mgcm-2), satisfying the US Department of Energy's PGM loading target. Moreover, the solvent and solute isotope separation method is used for the first time to reveal the kinetic process of HOR, which shows the reaction is influenced by the adsorption of H2O and OH-. The improvement of the hydrogen bond network connectivity of the electric double layer by adjusting the interfacial H2O structure together with the optimized HBE and OHBE is proposed to be responsible for the high HOR activity of Ru6Ir/Zn-N-C.