Anion Exchange Membrane Fuel Cells Research Articles

Expediting the Volmer Step of Alkaline Hydrogen Oxidation with High-Efficiency and CO-Tolerance by Ru-O-Eu Bridge.

The quest for economical and highly efficient nanomaterials for the alkaline hydrogen oxidation reaction (HOR) is imperative in advancing the technology of anion exchange membrane fuel cells (AEMFCs). Efforts using Pt-based electrocatalysts for alkaline HOR are greatly plagued by their finitely intrinsic activities and significant CO poisoning, stemming from the difficulty of simultaneously optimizing surface adsorption toward different hydrogen-related adsorbates. Herein, Ru clusters coupled with Eu2O3 immobilized within N-doped carbon nanofibers (Ru/Eu2O3@N-CNFs) are developed toward drastically boosted electrocatalysis for HOR via a d-p-f gradient orbital coupling strategy. Theoretical calculations and in situ operando spectroscopy discover that the induction of Eu2O3 optimizes the Ru site electronic structure via constructing the gradient orbital coupling of Ru(3d)-O(2p)-Eu(4f), leading to optimal H intermediates, improved adsorption ability of OH and reduced energy barrier of water formation, and promoted CO oxidation, endowing the Ru/Eu2O3 as the promising catalyst alternative for fast alkaline hydrogen electrooxidation. As a result, the Ru/Eu2O3@N-CNFs reach an impressive kinetic current densities (jk) value of 156.3 mA cm-2 at 50 mV (38.4 times higher than Pt/C), and decent stability over 35000 s continuous operation. This comprehensive investigation featuring d-p-f gradient orbital coupling provides valuable insights for the strategic development of high-performance Ru-based materials for HOR and beyond.

MnO2 Nanowire Thin Mesh With Enhanced Mass Transfer as Hydroxide Exchange Membrane Fuel Cell Cathode

AbstractHydroxide exchange membrane fuel cells (HEMFCs) are promising due to the potential use of nonprecious metal catalysts. However, the performance of HEMFCs based on nonprecious catalysts is still unsatisfactory, and one reason for this is hindered mass transfer in the catalyst layer. In this study, we employ a hydrothermal method to grow in situ a MnO2 nanowire thin mesh (NTM) catalytic layer on the gas diffusion electrode. The HEMFC prepared with MnO2 NTM cathode achieves a peak power density of 425 mW cm−2, surpassing the performance of the HEMFC prepared using the traditional powder catalyst spraying method by four times. High‐frequency resistance and limiting current tests indicate that the MnO2 NTM reduces ohmic resistance and improves mass transfer, thereby enhancing the HEMFC performance. Furthermore, the peak power density of the HEMFC is increased to 626 mW cm−2 by depositing additional active Co3O4 nanoparticles on the MnO2 NTM. These findings demonstrate that an interconnected and porous catalyst layer structure is beneficial for improving mass transfer properties, which in turn enhances HEMFC performance.

Valorization of Sargassum spp. biomass as a promising source of electrocatalysts for energy generation based on life cycle assessment

This work presents the development of an S-doped biocarbon electrocatalyst, designed to address environmental and economic challenges posed by the proliferation of Sargassum spp. along the shores of Quintana Roo, Mexico. The synthesis involves a two-step process: hydrothermal treatment followed by pyrolysis at 900°C. This method produces a material with an exceptional surface area of 2142 m2g⁻1 and a high content of thiophene-type bonds (94.30%). The unique composition of S-doped biocarbon results in superior catalytic activity for the oxygen reduction reaction, evidenced by an onset potential of 0.981 V vs Reversible Hydrogen Electrode (RHE) and a half-wave potential of 0.878 V vs RHE. Additionally, the electrocatalyst demonstrates remarkable electrochemical stability, maintaining performance with negligible mass activity loss after 5000 cycles. A significant application of S-doped biocarbon is demonstrated in a self-breathing Anion Exchange Membrane Fuel Cell (AEMFCs), achieving 76.82% of the power density output compared to a commercial Pt electrocatalyst cathode. Furthermore, a life cycle assessment reveals that the synthesis of 1 g of S-doped biocarbon emits only 1.27 kg CO₂-eq, which is 3.84% of the emissions attributed to Pt. Thus, S-doped biocarbon is an environmentally friendly biocarbon and a high-performing electrocatalyst for AEMFCs, positioning it as a promising alternative to Pt for green energy applications.

Hollow Pt‐Encrusted RuCu Nanocages Optimizing OH Adsorption for Efficient Hydrogen Oxidation Electrocatalysis

As one of the best candidates for hydrogen oxidation reaction (HOR), ruthenium (Ru) has attracted significant attention for anion exchange membrane fuel cells (AEMFCs), although it suffers from sluggish kinetics under alkaline conditions due to its strong hydroxide affinity. In this work, we develop ternary hollow nanocages with Pt epitaxy on RuCu (Pt‐RuCu NCs) as efficient HOR catalysts for application in AEMFCs. Experimental characterizations and theoretical calculations confirm that the synergy in optimized Pt8.7‐RuCu NCs significantly modifies the electronic structure and coordination environment of Ru, thereby balancing the binding strengths of H* and OH* species, which leads to a markedly enhanced HOR performance. Specifically, the optimized Pt8.7‐RuCu NCs/C achieves a mass activity of 5.91 A mgPt+Ru‐1, which is ~3.3, ~2.2, and ~15.0 times higher than that of RuCu NCs/C (1.38 A mgRu‐1), PtRu/C (1.83 A mgPt+Ru‐1) and Pt/C (0.37 A mgPt‐1), respectively. Impressively, the specific peak power density of fuel cells reaches 15.9 W mgPt+Ru‐1, significantly higher than those of most reported PtRu‐based fuel cells.

Hollow Pt-Encrusted RuCu Nanocages Optimizing OH Adsorption for Efficient Hydrogen Oxidation Electrocatalysis.

As one of the best candidates for hydrogen oxidation reaction (HOR), ruthenium (Ru) has attracted significant attention for anion exchange membrane fuel cells (AEMFCs), although it suffers from sluggish kinetics under alkaline conditions due to its strong hydroxide affinity. In this work, we develop ternary hollow nanocages with Pt epitaxy on RuCu (Pt-RuCu NCs) as efficient HOR catalysts for application in AEMFCs. Experimental characterizations and theoretical calculations confirm that the synergy in optimized Pt8.7-RuCu NCs significantly modifies the electronic structure and coordination environment of Ru, thereby balancing the binding strengths of H* and OH* species, which leads to a markedly enhanced HOR performance. Specifically, the optimized Pt8.7-RuCu NCs/C achieves a mass activity of 5.91 A mgPt+Ru-1, which is ~3.3, ~2.2, and ~15.0 times higher than that of RuCu NCs/C (1.38 A mgRu-1), PtRu/C (1.83 A mgPt+Ru-1) and Pt/C (0.37 A mgPt-1), respectively. Impressively, the specific peak power density of fuel cells reaches 15.9 W mgPt+Ru-1, significantly higher than those of most reported PtRu-based fuel cells.

Origin of Performance Decline in Carbonated Anion Exchange Membrane Fuel Cells.

Anion exchange membrane fuel cells (AEMFCs) have successfully eliminated anode carbonate precipitation through cation immobilization with the incorporation of alkaline polymer electrolytes (APEs). However, carbonation by CO2 in ambient air continues to induce significant AEMFC performance losses via mechanisms that remain unclear/elusive. In this multimodal investigation of AEMFC carbonation, we find that the increase in ionic resistance after carbonation accounts for only a small fraction of the cell voltage drop, especially at high current densities. Controlled anode and cathode carbonation tests indicated that the anode hydrogen oxidation reaction (HOR) was significantly impeded by carbonation. Hydrogen pump tests showed that the HOR kinetics were more than an order of magnitude lower after carbonation, thus accounting for the large decrease in the cell voltage. Further studies using the electrochemical quartz crystal microbalance (EQCM) revealed that there exists a large barrier to the rearrangement of the double layer at the Pt/ionomer interface in the hydrogen underpotential deposition (HUPD) region, which may explain the slower HOR kinetics after carbonation. These results provide fundamental insight into the unique properties of the catalyst/APE interface and suggest new directions for energy materials and technology developments.

Anion-Exchange Membranes’ Characteristics and Catalysts for Alkaline Anion-Exchange Membrane Fuel Cells

Anion-Exchange Membranes’ Characteristics and Catalysts for Alkaline Anion-Exchange Membrane Fuel Cells

Ligand Effect-Induced Electronic Structure Manipulation of Media-Entropy Alloy for Remarkable Stability over 50,000 Cycles in Oxygen Reduction.

Modulating the "trade-off" between activity and durability of Pd-based alloys while eliminating the dissolution of the nonprecious metal element issue is highly significant for the advancement of commercializing anion-exchange membrane fuel cells (AEMFCs). Herein, by harmonizing composition and ligand effects and targeting the stability concerns of Pd-based alloys, we propose PdRhNi ternary medium-entropy-alloy (MEA) networks (PdRhNi ANs) as exceptionally efficient oxygen reduction reaction (ORR) electrocatalysts via ligand effect. The results of theoretical calculations provide compelling evidence that the ligand effect of Ni in PdRhNi ANs, which can endow an inductive effect to reshape the electronic configuration to induce a reduced energy barrier in the rate-determining steps, optimizes the adsorption energy of O-related intermediates and lowers the d-band center of metal species, collectively boosting the anti-CO capacity and the ORR efficiency. Consequently, the as-made PdRhNi ANs not only demonstrate significantly enhanced electrocatalytic properties with a half-wave potential of 0.85 V and excellent resistance to CO toxicity, in contrast to those of commercial Pt/C and binary counterparts, but also exhibit a negligible half-wave potential decline after 50,000 cycle stability examination. More excitingly, the homemade AEMFC with a PdRhNi AN air cathode delivers a higher power density of 109 mW cm-2, surpassing that of the PdRh AN-based battery, highlighting promising prospects for implementing MEA materials with ligand engineering in AEMFC environments.

MOF-199-Based Nitrogen-Doped Bimetal Cathode Catalyst for Anion Exchange Membrane Fuel Cells

MOF-199-Based Nitrogen-Doped Bimetal Cathode Catalyst for Anion Exchange Membrane Fuel Cells

Greatly Enhanced Oxygen Reduction Reaction in Anion Exchange Membrane Fuel Cell and Zn-Air Battery via Hole Inner Edge Reconstruction of 2D Pd Nanomesh.

Platinum group metals (PGM) have yet to be the most active catalysts in various sustainable energy reactions. Their high cost, however, has made maximizing the activity and minimizing the dosage become an urgent priority for the practical applications of emerging technologies. Herein, a novel 2DPd nanomesh structure possessing hole inner reconstructed edges (HIER) with exposed high energy facets and overstretched lattice parameters is fabricated through a facile room-temperature reduction method at gram-scale yields. The HIER enhances the catalytic performance of Pd in electrochemical oxygen reduction reaction (ORR), achieving superior mass activity (MA) of 2.672 A mgPd -1, which is 27.8 fold and 23.6 fold higher, respectively, than those of the commercial Pt/C (0.096 A mgPt -1) and Pd/C (0.113 A mgPd -1) at 0.9 VRHE. Most significantly, in H2-air anion exchange membrane fuel cell (AEMFC) and Zn-air battery (ZAB) applications, this unique Pd catalyst delivers a much-outperformed peak power density of 0.86 and 0.22W cm-2, respectively, compared with 0.54 and 0.13W cm-2 of the commercial Pt/C catalyst, indicating a novel pathway in electrocatalyst designs through HIER engineering.

Ni Nanoparticles Supported on Graphene-Based Materials as Highly Stable Catalysts for the Cathode of Alkaline Membrane Fuel Cells.

Ni nanoparticles supported on graphene-based materials were tested as catalysts for the oxygen reduction reaction (ORR) to be used in anion exchange membrane fuel cells (AEMFCs). The introduction of N into the graphene structure produced an enhancement of electrocatalytic activity by improving electron transfer and creating additional active sites for the ORR. Materials containing both N and S demonstrated the highest stability, showing only a 3% performance loss after a 10 h stability test and therefore achieving the best overall performance. This long-term durability is attributed to the synergetic effect of Ni nanoparticles and bi-doped (S/N)-reduced graphene oxide. The findings suggest that the strategic incorporation of both nitrogen and sulphur into the graphene structure plays a crucial role in optimising the electrocatalytic properties of Ni-based catalysts.

Exploring the impact of ionomer content and distribution on inkjet printed cathodes for anion exchange membrane fuel cells

Electrode composition optimization is critical to achieving high and stable anion exchange membrane fuel cell (AEMFC) performance. In this article, inkjet printing is pioneered as a method to fabricate AEMFC electrodes with varying and graded cathode ionomer loading in order to assess its impact on electrode electrochemical properties, cell performance and stability. Inkjet printed catalyst layers (CLs) exhibited decreasing porosity with increasing ionomer content, maintaining a constant active area at 50 °C under fully humidified conditions. The increase in active area and ionic conductivity with increasing ionomer content was detectable only at higher temperatures. At 60 °C with 90% relative humidity inlet gases, the AEMFCs with cathode electrodes with optimal 20 wt% uniform ionomer content achieved a highly repeatable and stable performance of 0.53 W/cm2 with a total loading of 0.3 mgPt/cmCL2. Grading the cathode ionomer content, with higher concentration near the membrane and lower near the gas diffusion layer (GDL), does not improve cell performance, indicating neither cathode conductivity nor mass transport limits performance. When tested at 80 °C, AEMFCs with a graded cathode ionomer structure (30 wt% near the membrane and 20 wt% near the GDL) demonstrated improved stability compared to those with a uniform 20 wt% ionomer content. This stability improvement is attributed to better water retention with more cathode ionomer content, as evidenced by the cell’s ability to maintain low resistance.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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