Anion Exchange Membrane Fuel Cells Research Articles

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.

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.

Carbazole-Based branched Poly(Aryl Piperidinium) membranes for Ultra-Stable anion exchange membrane fuel cells

In the technological development of anion exchange membrane fuel cells (AEMFCs), it is crucial to prepare anion exchange membranes (AEMs) with high conductivity and excellent dimensional stability. This study successfully developed highly branched poly(aryl piperidinium) AEMs by introducing 4,4′-bis(N-carbazolyl)-1,1′-biphenyl as branched linker unit into the poly(p-terphenyl piperidinium) backbone. With the introduction of the carbazole group, the plane-conjugated structure and non-rotatable properties are fully utilised, which effectively reduces the entanglement between the polymer backbones and increases the free volume of the AEMs, hence facilitates the construction of an efficient ion transport channel. The branched structure effectively reduces the water uptake of the membrane which leads to improved dimensional stability. The optimized QPCBP-TP-7 membrane exhibited high conductivity, reaching up to 151.88 mS cm−1 at 80 °C, along with excellent mechanical strength (TS = 42.51 MPa, EB = 13.32 %, wet state) and dimensional stability (SR of 22.9 % at 80 °C). Surprisingly, this membrane also exhibited favorable antioxidant properties (retaining over 97.28 % weight after 96 h in Fenton's reagent at 80 °C), and alkaline stability (retaining over 86.81 % efficacy after 1500 h in 5 M NaOH solution at 80 °C). In AEMFCs applications, the QPCBP-TP-7 membrane achieved peak power density (PPD) up to 616 mW cm−2 with the current density is 1330 mA cm−2 at 80 °C (H2-O2) and the QPCBP-TP-7 membrane remained stable and hardly degraded when operated at constant current of 0.1 A cm−2 (80 °C) over 100 h.

Temperature-Induced Interface Hybridization of WC Boosts NiCu Activity for Alkaline Hydrogen Oxidation Reaction.

The development of non-precious hydrogen oxidation reaction (HOR) catalysts is a major challenge for the commercialization of Pt-free fuel cells. Herein, a temperature-induced phase hybridization method is reported that greatly improves the catalytic performance of NiCu alloy for the HOR. The migration of W atoms hybridizes the interface of tungsten oxide (WOx) and tungsten carbide (WC) at the onset reduction temperature of WOx, leading to a greatly weakened H binding energy and an optimized OH binding energy, which endows NiCuW/WOx-WC@WC with favorable stability and CO resistance during HOR. The hybridization catalysts deliver a high mass activity of 29.37 mA mg-1 Ni and reach a peak power of 298 mW.cm-2 in H2-O2 anion exchange membrane fuel cells (AEMFCs).