Designing the next generation of proton-exchange membrane fuel cells

Microporous poly(aryl piperidinium) hydroxide exchange membranes with multi-directional branched structure for high performance fuel cells

Hydroxide exchange membranes (HEMs) are important materials for energy conversion devices in hydroxide exchange membrane fuel cells (HEMFCs). This study details a series of multi-directional branched HEMs containing octaphenylcyclotetrasiloxane (OCSi). The OCSi structure allows for the establishment of continuous OH- conducting channels within the membrane while addressing the prevailing trade-off between ionic conductivity and size/mechanical stability. Thanks to the formation of fine microphase-separated morphologies, the quaternized poly(octaphenylcyclotetrasiloxane-terphenyl-piperidinium) (QPOCSi-TP-2) membrane has high conductivity (152.9 mS cm-1 at 80 °C), excellent mechanical stability (tensile strength of 76.5 MPa) and outstanding chemical stability (1500 h in 5 M NaOH at 80 °C). In H2/O2 cell tests at 80 °C, the peak power density of the QPOCSi-TP-2 membrane reaches 1.26 W cm-2. During 120 h of operation at 100 m A cm-2, the voltage degradation rate of the cell is 1.02 mV h-1.

Optimizing ionomer distribution for constructing efficient Pt/ionomer interfaces: Research on improving the performance of low-platinum-loading hydrogen fuel cells

Reducing the platinum content within membrane electrode assemblies (MEAs) of proton exchange membrane fuel cells (PEMFCs) is a strategic approach to decrease their overall costs. Nevertheless, this approach can result in significant voltage losses which are primarily attributed to the increased impedance of oxygen through the Pt-ionomer interface. In this study, the local oxygen mass transfer resistance (RO2-local) is effectively reduced by doping sulfur onto the carbon supports. The surface hydrophilicity of the carbon supports is enhanced after sulfur doping, which intensifies the interaction between the polar side chains of the ionomers and the carbon supports. This results in a more uniform distribution of the ionomers within catalyst layers, thus enabling oxygen diffusion to the Pt surface without passing through a dense ionomer layer. Moreover, the uniform distribution of ionomers reduces the adsorption of sulfonic acid groups on Pt, thereby mitigating their toxic effect. In low Pt-loaded MEAs, i.e., 0.03 and 0.1 mg·cm-2 for anode and cathode, respectively, the sulfur-doped Pt/S-KB-1.0 catalyst demonstrates an effective Pt utilization of 0.098 gPt·kW-1 on the cathode side, and a 24.8 % decrease of RO2-local compared to the undoped sample. Additionally, it exhibits favorable low-humidity adaptability and superior durability performance.

Formation mechanism and morphology control of cracks in PEMFC catalyst layer during fabrication process: A review

The catalyst layer (CL) is susceptible to cracking during the fabrication process, which presents challenges to the performance and durability of proton exchange membrane fuel cell (PEMFC). This review systematically cascades mechanisms, factors, methods, and applications to provide the first all-encompassing analysis of CL cracking. To construct a research framework, this review comprehensively analyzes the formation mechanism of CL cracks and outlines various approaches for crack morphology optimization. By combining linear elastic fracture mechanics (LEFM) and related research on the drying of colloidal films, the causes of CL cracks can be attributed to structural defects and stress concentrations. On this basis, the means of crack regulation are illustrated from the perspective of ink components and drying conditions. In the end, the impact of cracks on the performance of CL is analyzed and some novel crack inhibition techniques are introduced. Although this review organizes and summarizes the results of related research, there is still a gap in the field of CL crack research. This is evidenced by the lack of a more accurate mechanism for CL crack formation, the unclarity on the effect of crack morphology on CL performance, and the fact that methods to regulate cracking by changing the drying pattern have yet to be further investigated.

Active-Sites-Integrated Hierarchical Porous Nanofibers for Improved Oxygen Reduction in Fuel Cells

M-N-C catalysts have emerged as a promising class of non-precious electrocatalysts for accelerating the kinetically sluggish oxygen reduction reaction (ORR). Nevertheless, their practical application in proton exchange membrane fuel cells (PEMFCs) faces significant challenges due to the complex reaction environment and stringent mass transport requirements, which place stringent demands on the structural design of electrocatalysts. Here, a strategy is proposed to construct a self-supporting membrane of zeolitic imidazolate framework-connected nanofibers, serving as an integrated substrate to cooperatively optimize active sites and mass transfer channels. The nanofiber-shaped electrocatalysts (FeSA/AC-N-PCNFs) with hierarchical porous structure can achieve the anchor of well-dispersion atomically Fe-N4 and Fe cluster. The FeSA/AC-N-PCNFs, as a catalyst layer of cathode, to assemble PEMFC and realized 43% enhanced maximum power density compared with traditional spraying. The finite element simulation proved that the self-supported porous fiber structure effectively reduced the oxygen diffusion resistance in the electrode. This work established an effective enhancement strategy for the M-N-C electrocatalysts from the structure engineering, which opens new avenues for the design and manufacture of high-performance fuel cell electrocatalysts.

Toward Molecular Simulation Guided Design of Next-Generation Membranes: Challenges and Opportunities

Membranes provide energy-efficient solutions for separating ions from water, ion-ion separation, neutral or charged molecules, and mixed gases. Understanding the fundamental mechanisms and design principles for these separation challenges has significant applications in the food and agriculture, energy, pharmaceutical, and electronics industries and environmental remediation. In situ experimental probes to explore Angstrom-nanometer length-scale and pico-nanosecond time-scale phenomena remain limited. Currently, molecular simulations such as density functional theory, ab initio molecular dynamics (MD), all-atom MD, and coarse-grained MD provide physics-based predictive models to study these phenomena. The status of molecular simulations to study transport mechanisms and state-of-the-art membrane separation is discussed. Furthermore, limitations and open challenges in molecular simulations are discussed. Finally, the importance of molecular simulations in generating data sets for machine learning and exploration of membrane design space is addressed.

Unraveling CO-Tolerance Mechanism in Proton Exchange Membrane Fuel Cells via Operando Infrared Spectroscopy

CO poisoning remains a critical challenge for proton exchange membrane fuel cells (PEMFCs). Current studies of CO tolerance primarily focus on solid/liquid interfaces (in situ conditions), which differ significantly from PEMFCs' solid/liquid/gas triple-phase interfaces (operando conditions) in microenvironment and mass transport. Herein, we developed an operando transmission infrared spectroscopy method that enables direct observation of CO tolerance mechanism on commercial PtRu/C catalysts in PEMFCs. Under in situ conditions, hydrogen oxidation reaction (HOR) activity is governed by CO mass transfer, and is insensitive to the availability of active sites, while it is highly sensitive under operando conditions due to enhanced mass transfer, thereby aggravating CO poisoning effects. Notably, 76% of HOR activity can recover upon switching to pure H2. Based on CO band evolution, we proposed a new pathway beyond the traditional bifunctional mechanism of CO tolerance: CO migrates from Pt to Ru sites, undergoing oxidation at potentials as low as 0.01 V versus reversible hydrogen electrode (RHE).

Nanocomposites from Polymer Brushes and Metal Oxide Clusters for Fabrication of High-Temperature Fuel Cell Proton Exchange Membranes

High-temperature proton exchange membranes (HT-PEMs) are highly desired for fuel cells with high energy density; however, the requirements in balanced anhydrous proton conductivity, mechanical/structural stability, processability and gas-barrier property impose great difficulty for molecular design. Herein, the supramolecular complexation of brush polymers and super acidic metal oxide cluster (H3PW12O40, abbreviation PW12) affords HT-PEMs with comprehensive performance that contributes to the robust performance of high energy density fuel cells. The polymers brush topology enables the decoupling of mechanical properties and proton conduction: the polyethylene glycol (PEG) side chains possess high affinity to PW12 for proton transport while the rigid backbones help maintain structural stability and mechanical strengths up to 250 °C. The PW12 clusters can be homogeneously dispersed in PEG with high loadings (≈80 wt.%) and it facilitates proton hopping among the crowded PW12 for promising anhydrous proton conduction, e.g., 2 × 10-3 S cm-1 at 200 °C. Their dense supramolecular bonds contribute to enhanced mechanical strength, flexibility and gas barrier property with mitigating hydrogen permeation current as 0.73 mA cm-2, enabling the feasible processability of PEMs and stable operation of fuel cells. The devices show high power density as 218 mW cm-2 at 180 °C with long-term stable operation.

Designing a Maze-Structured Gas Diffusion Layer to Extend Water Transport Path for Enhancing the Performance and Stability of Air-Cooled Fuel Cells

The air-cooled fuel cell is a promising energy conversion device. However, the characteristics of forced convection often rapidly expel water from the gas diffusion layer (GDL) into the flow field, which reduces the humidity of the membrane electrode assembly (MEA). Under low-humidity conditions, the proton conductivity of the proton exchange membrane (PEM) decreases, thereby impairing the performance and durability of the air-cooled fuel cell. Inspired by the tortuous transport pathways in the maze model, we designed a GDL with a maze-like structure (M-GDL) to extend the water transport path, thereby increasing the internal humidity of the air-cooled fuel cell. We designed a water evaporation test to verify the water loss resistance of the GDL. The M-GDL exhibits remarkable resistance to water loss, with a rate of 0.35 mg min-1 cm-2, significantly lower than the 0.79 mg min-1 cm-2 observed for the commercial GDL. This extended water retention capability leads to a notable increase in the performance of the fuel cell, with a peak power density of 0.77 W cm-2, which is more than double that of the commercial GDL, where the peak power density is only 0.4 W cm-2. This work presents a strategy to mitigate the issue of low internal humidity in air-cooled fuel cells.

Polypyrrole-decorated Vulcan XC-72R support enables a low platinum content PtRu catalyst toward alkaline hydrogen oxidation reaction

PtRu alloys are promising catalysts for the hydrogen oxidation reaction (HOR) in alkaline hydroxide exchange membrane fuel cells (HEMFCs) for commercial application. However, there is a need to lower the loading of platinum while simultaneously increasing its activity. Herein, we successfully prepared a PtRu alloy catalyst featuring a precisely controlled Pt-to-Ru atomic ratio of 1:5, which is typically 1:1 or 1:3, supported on polypyrrole (Ppy) decorated Vulcan XC-72R (XC). The catalyst, named Pt1Ru5/Ppy-XC, exhibits a remarkable mass catalytic activity of 10.69 ± 1.40 mA μgPGM-1, which is 7.2-fold and 2.6-fold higher than those of commercial PtRu/C and Pt1Ru5 nanoparticles supported on raw XC, respectively. Moreover, the HEMFC with Pt1Ru5/Ppy-XC anode achieves a peak power density of 1.53 W cm-2 (0.15 mgPGM cmanode-2), outperforming that of Pt1Ru5/XC (1.26 W cm-2, 0.18 mgPGM cmanode-2). The combined experimental characterization and theoretical calculations reveal that Ppy significantly enhances the active site density due to the decrease in the proportion of micropores while optimizing the binding strength of *H and *OH species on Pt1Ru5/Ppy-XC, resulting in excellent catalytic performance even with a low Pt usage. This work provides a novel strategy for developing high-performance electrocatalysts by employing functionalized XC support to fine-tune catalyst/support interactions and control over the pore structure of carbon supports.

Electrocatalytic hydrogenation of alkynes and alkenes using a proton conductive graphene oxide membrane

Graphene-based membranes are emerging as promising materials for energy and chemical conversion due to their exceptional proton conductivity and stability. In this study, we report a graphene oxide (GO) nanosheet membrane for electrochemical hydrogenation reactions. The GO membrane demonstrates excellent proton conductivity, confirmed through concentration cell measurement and complex impedance spectroscopy, and efficiently facilitates proton transport when integrated with active platinum catalysts as the cathode and anode. This system enables selective hydrogenation of alkynes and alkenes into their corresponding alkanes, achieving selectivities of 82% to 93%. This work highlights the potential of graphene-based membrane reactors as cost-effective, scalable, and energy-efficient alternative to traditional hydrogenation methods.

Designing Flexible Carbon Nanofiber Membranes by Electrospinning and Cross-Linking for Proton Exchange Membrane Fuel Cells

Traditional carbon-based materials suffer from fragility, low mechanical strength, and electrical conductivity when they are used as a gas diffusion layer (GDL) in proton exchange membrane fuel cells (PEMFCs), resulting in low power density. In this study, a flexible carbon nanofiber membrane (CFM) was studied for use as a GDL, prepared by polyacrylonitrile (PAN) electrospinning with the incorporation of carboxylated multiwalled carbon nanotubes (MWCNTs), polyethylenimine (PEI) impregnation, glutaraldehyde (GA) cross-linking, and thermal treatment. The concentrations of MWCNTs in the electrospinning solution and PEI in the impregnation solution were investigated. Interestingly, the mechanical strength and electrical conductivity of CFM showed a triangle trend with the MWCNTs or PEI concentration. The optimal sample (CNT1.5/PEI7/GA-CFM) demonstrated good flexibility, with an in-plane resistivity of 18.60 mΩ cm, a tensile strength of 7.94 MPa, and a bending strength of 20.65 MPa. The peak power density and maximum current density were respectively 1169 mW cm-2 and 2720 mA cm-2, exceeding those of commercial Toray and Cetech GDLs under identical testing conditions. These results illustrate the potential of high-performance electrospun CFMs for GDL applications.

Suppressing Metal Dissolution in Multi-Grained Catalysts Through Intragrain Atomic Ordering for Stable Fuel Cells

Rational design of catalytic nanomaterials is essential for developing high-performance fuel cell catalysts. However, structural degradation and elemental dissolution during operation pose significant challenges to achieving long-term stability. Herein, the development of multi-grained NiPt nanocatalysts featuring an atomically ordered Ni3Pt5 phase within intragrain is reported. Ultrasound-assisted synthesis facilitates atomic transposition by supplying sufficient diffusion energy along grain boundaries, enabling unprecedented phase formation. The Ni3Pt5 embedded nanocatalysts exhibit outstanding proton exchange membrane fuel cell performance under both light-duty and heavy-duty vehicle conditions, with significantly reduced Ni dissolution. Under light-duty vehicle conditions, the catalyst achieves a mass activity of 0.94 A mgPt -1 and a 421 mA cm-2 current density (@ 0.8 V in air), retaining 78% of its initial mass activity after long-term operation. Under heavy-duty vehicle conditions, the multi-grained nanocrystal demonstrates only an 8% decrease in Pt utilization, a 5% power loss, and a 13 mV voltage drop, surpassing U.S. Department of Energy (DOE) durability targets. This study underscores the critical role of the atomically ordered Ni3Pt5 phase in stabilizing multi-grained NiPt nanocrystals, enhancing both durability and catalytic activity. These findings establish Ni3Pt5 embedded nanocatalysts as promising candidate for next-generation PEMFC applications, addressing key challenges in long-term operation.

Mass Transport Based on Covalent Organic Frameworks

ConspectusMass transport is fundamental to biological systems and industrial processes, governing chemical reactions, substance exchange, and energy conversion across various material scales. In biological systems, ion transport, such as proton migration through voltage-gated proton channels, regulates cellular potential, signaling, and metabolic balance. In industrial processes, transporting molecules through solid, liquid, or gas phases dictates reactant contact and diffusion rates, directly impacting reaction efficiency and conversion. Optimizing these processes necessitates the design of efficient interfaces or channels to enhance mass transport.Crystalline porous materials, particularly covalent organic frameworks (COFs), offer an excellent platform for investigating and optimizing mass transport. With ordered, pre-engineered nano- or subnanometer pores, COFs enable confined substance transport and garnered significant attention for energy conversion, catalysis, drug delivery, adsorption, and separation applications. Deeper investigations into the mass transport mechanism in COFs at the molecular level are crucial for advancing materials science, chemistry, and chemical engineering.Our group focuses on COFs to explore multisubstance cooperative transport mechanisms and structure-activity relationships for ions, water, and gases. We have expanded the linker chemistry of COFs by developing irreversible α-aminoketone-linked COFs and introducing the irreversible Suzuki coupling reaction into COF preparation. We proposed strategies such as side-chain-induced dipole-facilitated stacking and prenucleation and slow growth to achieve record large pore sizes and highly oriented nanochannels. We implemented exfoliation and an interwoven strategy to accelerate ion transport at complex interfaces, refined gas permeability in molecular sieve-based membranes through precise pore size engineering, and elucidated the effects of pore size and hydrophobicity/hydrophilicity on water phase transition and diffusion. Building on these insights, we designed novel open framework ionomers to tailor the microenvironment of electrocatalytic interfaces and uncovered multiple substance transport mechanisms. The synergistically enhanced transport of ions, water, and gas across three-phase interfaces effectively modulates the electrochemical CO2 reduction reaction pathway and significantly boosts the power density of proton-exchange membrane fuel cells (PEMFCs).In this Account, we summarize recent advances in COF-based ion and molecular transport, emphasizing nanochannel construction strategies, including linkage, pore size, orientation, and function gradient modulations. We discuss the functional design of COFs, correlations between pore structure and transport properties, and their applications in gas separation, energy storage, and catalysis. Finally, we outline current challenges and future opportunities in synthetic chemistry, mass transport mechanisms, and applications. By understanding mass transport phenomena from microscopic particles to macroscopic scales, this Account aims to provide molecular design strategies for optimizing multisubstance transport across three-phase interfaces, aligning mass transport with reaction processes and offering insights to enhance catalytic efficiency and energy conversion performance.

pH-Dependent Structural Engineering of Sulfonate-Carboxylate Cu-MOFs for High Proton Conductivity

Metal-organic frameworks (MOFs) with free carboxylic acid (COOH) groups are promising for solid-state proton-conducting materials, owing to the Brønsted acidity, polarity, and the hydrogen-bonding ability of COOH groups. In this work, two Cu-MOFs with different dimensions were synthesized by adjusting the pH of the reaction solution using disodium-2,2'-disulfonate-4,4'-oxidibenzoic acid (Na2H2DSOA) and 4,4'-bipyridine (4,4'-bpy) as ligands to coordinate with Cu(II). The resulting compounds, CuDSOA-1 (([Cu(4,4'-bpy)2(H2O)2][Cu(H2DSOA)2(4,4'-bpy)(H2O)2]·12H2O)) and CuDSOA-2 ([Cu2(DSOA)(4,4'-bpy)2(H2O)2]·4H2O), have distinct dimensionalities and structures, mainly due to the pH's effect on carboxylic acid deprotonation. Notably, CuDSOA-1 with abundant COOH groups, uncoordinated sulfonate groups, and water molecules shows a significantly enhanced proton conductivity of 2.46 × 10-2 S cm-1 at 95 °C and 98% RH, surpassing CuDSOA-2 (3.40 × 10-5 S cm-1 at 85 °C and 98% RH). The conductivity mechanism was found to be a Grotthuss mechanism, confirmed by deuterium-hydrogen isotopic effects. This study offers a method to control the coordination of sulfonic-carboxylic acid ligands with Cu(II) by pH adjustment, aiming to create MOFs with ultrahigh proton conductivity.

Optimization analysis of air cooled open cathode proton exchange membrane fuel cell flow channel structure

The cathode channel of air-cooled open-cathode proton exchange membrane fuel cell (AO-PEMFC) is both a reactant supply channel and a cooling and heat dissipation channel, and its structural design is a key factor affecting its output performance. Firstly, the numerical study of AO-PEMFC with different cathode channel bending angles was carried out, and the results showed that the output performance of a single cell with a cathode bending angle of 2.5° was improved by 3.88% compared with that of a single cell with a cathode straight channel at rated point-density electricity, and the cathode voltage drop increased by only 1.5%. In addition, in order to further improve the power density of the fuel cell, two agent models, support vector regression and Gaussian process regression, are constructed and trained, and a genetic algorithm is used to find the parameter optimization for the bending angle, width and height of the cathode channel. Finally, the proposed ranges of width, height and bending angle of the optimal flow channel are obtained, which are w = 1.1-1.2 mm, d = 1.3-1.5 mm and θ = 2.23°-2.99°, respectively, and the output power density of a single cell within this range will be no less than 0.489 W/cm2.

Unlocking Proton Exchange Membrane Fuel Cell Performance with Porous PtCoV Alloy Catalysts

Carbon-supported Pt-based catalysts in fuel cells often suffer from sulfonate poisoning, reducing Pt utilization and activity. Herein, a straightforward strategy is developed for synthesizing a porous PtCoV nanoalloy embedded within the porous structures of carbon nanofibers. Incorporation of vanadium (V) atoms into the PtCo alloy optimizes the oxygen binding energy of Pt sites, while heightening the dissolution energy barrier for both Pt and Co atoms, leading to a significantly enhanced intrinsic activity and durability of the catalyst. By encapsulating the nanoalloys within porous nanofibers, a non-contact Pt-ionomer interface is created to mitigate the poisoning effect of sulfonate groups to Pt sites, while promoting oxygen permeation and allowing proton transfer. This rational architecture liberates additional active Pt sites, while the evolved porous nanostructure of the PtCoV alloy extends its exposed surface area, thereby boosting Pt utilization within the catalytic layer and overall fuel cell performance. The optimized catalyst demonstrates an exceptional peak power density of 29.0 kW gPt -1 and an initial mass activity of 0.69 A mgPt -1, which exceeds the U.S. Department of Energy 2025 targets. This study provides a promising avenue for developing highly active and durable low-Pt electrocatalysts for fuel cell applications.

Robust p-d Orbital Coupling in PtCoIn@Pt Core-Shell Catalysts for Durable Proton Exchange Membrane Fuel Cells

Pt-based catalysts are playing increasingly important roles in fuel cells owing to their high catalytic activity. However, harsh electrocatalytic conditions often trigger atomic migration and dissolution in these catalysts, causing rapid performance deterioration. Here, a novel L10-PtCoIn@Pt core-shell catalyst is introduced, where indium (In) is incorporated into a PtCo matrix. This integration promotes p-d orbital coupling, optimizing the electronic structure of Pt and causing additional lattice strain within PtCo. Impressively, L10-PtCoIn@Pt exhibits remarkable activity and durability, with only a 5.1% reduction in mass activity (MA) after 120 000 potential cycles. In H2-O2 fuel cells, this cathode achieves a peak power density of 1.99 W cm-2 and maintains a high MA of 0.73 A mgPt -1 at 0.9 V. After enduring 60 000 square wave potential cycles, the catalyst maintains its initial MA and sustains the cell voltage at 0.8 A cm-2, exceeding the U.S. Department of Energy (DOE) 2025 targets. Theoretical studies highlight the enhancements originating from the modulated electronic structures and shifted d-band center of Pt induced by In doping and increased vacancy formation energies in Pt and Co atoms, affirming the catalyst's superior durability.

Durable Proton Exchange Membrane Based on Polymers of Intrinsic Microporosity for Fuel Cells

High-temperature proton exchange membrane fuel cells (HT-PEMFCs) is regarded as a promising energy conversion system owing to simplified water management and enhanced tolerance to fuel impurities. However, phosphoric acid (PA) leaching remains a critical issue, diminishing energy density and durability, posing significant obstacle to the commercial development of HT-PEMFCs. To address this, composite membranes incorporating the carboxylic acid-modified polymer of intrinsic microporosity (cPIM-1) are designed as framework polymer, blended with polyvinylpyrrolidone (PVP) for HT-PEMFCs. The Lewis acid-base interactions between cPIM-1 and PVP created an extensive hydrogen-bonding network, improving membrane compatibility. The optimized microporous structure and multiple anchoring sites gave rise to "domain-limited" PA clusters, enhancing the capillary effect. Simultaneously, improved hydrophobicity synergistically optimizes catalytic interface, promoting continuous and stable proton transfer. The HT-PEMFCs based on PVP/cPIM-1 composite membrane achieved a peak power density of 1090.0 mW cm-2 at 160 °C, representing a 152% improvement compared to PVP/PES membrane. Additionally, it demonstrated excellent durability, with a voltage decay of 0.058 mV h-1 over 210 h of accelerated stress test corresponds to more than 5000 h of constant current density durability test. This study presents a promising strategy for the development of high-performance and durable novel membranes in various energy conversion systems.

Manipulating Oxygen Reduction Mechanisms of Platinum with Nonmetallic Phosphorus and Metallic Copper Synergistic Alloying

Alloying of platinum (Pt) nanostructures with heteroelements, commonly including transition-metals and nonmetals, is an effective strategy to improve the electrocatalytic performance for oxygen reduction reaction (ORR). However, the distinct mechanisms by which metal/nonmetal alloying improves ORR activity remain unclear. Herein, based on the successful alloying of porous network Pt nanospheres (NSs) with metallic copper (Cu) and non-metallic phosphorus (P) and systematically integrating the electrochemical tests, density functional theory calculations, and in situ electrochemical Raman spectroscopy, this study reveals that the internal Cu-alloying is responsible for modulating the binding strength of oxygenated intermediates to lower the free energy barrier of the potential-determining step (PDS) along the ORR associative mechanism, while the further surface P-alloying can transform the ORR pathway to dissociative mechanism, in which the PDS has a quite low barrier. As a result, the carbon-supported P/Cu co-alloyed porous network Pt nanospheres (P-PtCuNSs/C) catalyst synthesized by confinement growth and post-phosphorization demonstrates excellent electrocatalytic ORR activity and stability compared to the commercial Pt/C catalyst both in half-cells and proton exchange membrane fuel cells. In particular, the hydrogen (H2)-oxygen (O2) single cell with P-PtCuNSs/C as the cathode catalyst achieves a high mass activity of 0.52 A mgPt -1 at the voltage of 0.90 V, surpassing the U.S. Department of Energy's current activity target.

Asymmetrical Triatomic Sites with Long-Range Electron Coupling for Ultra-Durable and Extreme-Low-Temperature Zinc-Air Batteries

Reversible zinc-air battery (ZAB) is a promising alternative for sustainable fuel cells, but the performance is impeded by the sluggish oxygen redox kinetics owing to the suboptimal adsorption and desorption of oxygen intermediates. Here, hetero-trimetallic atom catalysts (TACs) uniquely incorporate an electron regulatory role beyond primary and secondary active sites found in dual-atom catalysts. In situ X-ray absorption fine structure (XAFS) and Raman spectroscopy elucidate Fe in FeCoNi SA catalyst (FCN-TM/NC) functions as the main active site, leveraging long-range electron coupling from neighboring Co and Ni to boost catalytic efficiency. The ZAB equipped with FCN-TM/NC exhibits ultra-stable rechargeability (over 5500 h at 1  mA cm-2 under -60 °C). The in-depth theoretical and experimental investigations attribute such superior catalytic activity to the asymmetric FeN4 configuration, long-distance electron coupling, modulated local microenvironment, optimized d orbital energy levels, and lower energy barrier for bifunctional oxygen electrocatalysis. This work provides a comprehensive mechanistic understanding of the structure-reactivity relationship in TACs for energy conversion.

Toward Hydrogen Mobility: Challenges and Strategies in Electrocatalyst Durability for Long-Term PEMFC Operation

Proton exchange membrane fuel cells (PEMFCs) are emerging as a key technology in the transition to hydrogen-based energy systems, particularly for heavy-duty vehicles (HDVs) that face operational challenges, such as frequent startup-shutdown cycles and fuel starvation. However, the widespread adoption of PEMFCs has been limited by their durability and long-term performance issues, which are crucial for heavy-duty applications. This Perspective focuses on recent advancements in PEMFC catalysts and supports, with an emphasis on strategies to enhance their durability. We introduce Pt-based intermetallic catalysts, including Pt transition metal (TM) alloys, which offer improved stability and activity through regular atomic arrangements and strengthened metal-support interactions. Hybrid catalysts combining Pt with M-N-C (M = Fe, Co) have shown promise in boosting performance by enhancing the catalytic activity while reducing the platinum content. Moreover, stringent conditions must be met to meet the HDV requirements. Consequently, alternative support materials, such as metal oxides and graphitized carbons, have been introduced to enhance both the corrosion resistance and the electrical conductivity, thereby addressing the limitations of conventional carbon supports. Structural innovations and material advancements are essential for optimizing catalysts and supports to achieve long-term PEMFC performance. This Perspective provides a comprehensive overview of key developments in catalyst and support design, offering insights into current challenges and future directions for achieving durable and cost-effective PEMFCs.

Harnessing Lithium-Mediated Green Ammonia Synthesis with Water Electrolysis Boosted by Membrane Electrolyzer with Polyoxometalate Proton Shuttles

Integrating water electrolysis (WE) with lithium-mediated nitrogen reduction (Li-NRR) offers a sustainable route for green ammonia production by directly utilizing protons from water oxidation, eliminating reliance on grey or blue hydrogen. Here, polyoxometalates (POMs) function as electron-coupled proton buffers (ECPBs) to seamlessly link WE with Li-NRR in a three-compartment flow reactor comprising an aqueous anode, an organic cathode, and a gas feed chamber. POMs serve as proton shuttles while suppressing the competing hydrogen evolution reaction (HER), facilitating efficient ammonia synthesis. The addition of polymethyl methacrylate (PMMA) enhances catholyte hydrophobicity, mitigating water contamination. By optimizing ECPB concentration, a dynamic balance is achieved between lithium nitride intermediates (LiNxHy) formation and consumption, yielding ammonia at 573.7 ± 5.2 µg h⁻¹ cm⁻2 with a Faradaic efficiency of 54.2%. This design advances flow reactor technology by uniquely utilizing water oxidation as a direct proton source, bypassing conventional hydrogen oxidation methods. The use of POMs as proton shuttles establishes a new benchmark for green ammonia production, reinforcing its potential in sustainable chemistry.

Atomic Symbiotic-Catalyst for Low-Temperature Zinc-Air Battery

Atomic-level designed electrocatalysts, including single-/dual-atom catalysts, have attracted extensive interests due to their maximized atom utilization efficiency and increased activity. Herein, a new electrocatalyst system termed as "atomic symbiotic-catalyst", that marries the advantages of typical single-/dual-atom catalysts while addressing their respective weaknesses, was proposed. In atomic symbiotic-catalyst, single-atom MNx and local carbon defects formed under a specific thermodynamic condition, act synergistically to achieve high electrocatalytic activity and battery efficiency. This symbiotic-catalyst shows greater structural precision and preparation accessibility than those of dual-atom catalysts owing to its reduced complexity in chemical space. Meanwhile, it outperforms the intrinsic activities of conventional single-atom catalysts due to multi-active-sites synergistic effect. As a proof-of-concept study, an atomic symbiotic-catalyst comprising single-atom MnN4 moieties and abundant sp3-hybridized carbon defects was constructed for low-temperature zinc-air battery, which exhibited a high peak power density of 76 mW cm-2 with long-term stability at -40 °C, representing a top-level performance of such batteries.

Linkage Microenvironment and Oxygen Electroreduction Reaction Performance Correlationship of Iron Phthalocyanine-based Polymers

Iron phthalocyanine-based conjugated polymers (PFePc) offer well-defined sites, rendering them ideal model systems to elucidate structure-property relationships towards oxygen reduction reaction (ORR), but have struggled to achieve improved catalytic activity due to uniform electron distribution of iron center and difficulty in molecular-level structure design. Although rationally linkage microenvironmental regulation is an effective approach to adjusting activity, the underlying fundamental mechanism is incompletely understood. Herein, systematic DFT calculations and experimental investigation of PFePc analogous reveal that the incorporation of the electron-withdrawing benzophenone linkage into the PFePc backbone (PFePc-3) drives the delocalization of Fe d-orbital electrons, downshifts the d-band energy level, thereby tailoring the key OH* intermediate interaction, demonstrating enhanced ORR performance with a half-wave potential of 0.91 V, a high mass activity of 21.43 A g-1, and a high turnover frequency of 2.18 e s-1 site-1. Magnetic susceptibility measurements and electron paramagnetic resonance spectroscopy reveal that linkage regulation can induce a 3d electron with high spin-state (t2g 3eg 2) of PFePc-3, significantly accelerating the ORR kinetics. In situ scanning electrochemical microscopy and variable-frequency square wave voltammetry further highlight the rapid kinetics of PFePc-3 to the high accessible site density (6.14×1019 site g-1) and fast electron outbound propagation mechanism.

Screening of single-atomic catalysts loaded on two-dimensional transition metal dichalcogenides for electrocatalytic oxygen reduction via high throughput ab initio calculations

The design and screening of low cost and high efficiency oxygen reduction reaction (ORR) electrocatalysts is vital in the realms of fuel cells and metal-air batteries. Existing studies largely rely on the calculation of absorption free energy, a method established 20 years ago by Jens K. Nørskov. However, the study of electrocatalysts grounded solely on free energy calculation often lacks in-depth analysis, particularly overlooking the influence of solvent and electrode potential. In this regard, we here present a novel approach using constant-potential and ab initio molecular dynamics (AIMD) simulation to screen single-atom catalysts loaded on transition metal dichalcogenides (SA@TMDs) for ORR. An extensive investigation of 1584 SA@TMDs results in 20 high performing ORR catalysts with overpotential less than 0.33 V and high working stability. In addition, our study shows that the electrode potential has different effects on the adsorption energy of *OOH, *O and *OH, which leads to a reversal of the rate-determining step (RDS) of the ORR. This work presents not only credible, high-performance catalyst candidates for experimental exploration, but also significantly improves our understanding on the reaction mechanism of ORR under realistic reaction conditions.

Ferredoxin-Inspired Stereoisomeric Fe2CN-Bridge-S Dual Atom Catalyst for Enhanced Acid Oxygen Reduction Reaction

The bimetallic center catalyst (DMC) injects new vitality into the accelerated oxygen reduction reaction (ORR) due to its unique structure. The regulation of the coordination environment composition and spatial structure of metal active centers also provides opportunities for optimizing the performance. Herein, we have successfully constructed stereoisomeric Fe2CN-bridge-S (abbreviated as Fe2CN-b-S) catalysts based on the biomimetic Fe-S cluster structure of ferredoxin. Adjacent Fe dual atoms skillfully weaken the O-O bond, crafting a peroxide bridge-like adsorption configuration. The incorporation of S atoms meticulously constructs the stereo configuration of active Fe sites, thereby inducing greater structural deformation tension and a downward shift in the Fe d-band center. These factors collectively facilitate the release of the OH* intermediate. Meanwhile, the reasonable spatial configuration of S can promote the optimal rigid structure of Fe diatomic active centers, improving the stability of the ORR reaction process. Thus, the Fe2CN-b-S catalyst, which has a half-wave potential of 0.865 V, demonstrates superior ORR activity in comparison to Fe2CN. This study offers a perspective on the joint regulation of elemental composition and geometric arrangement for enhanced catalytic activity in oxygen reduction.

Unveiling the Catalytic Potential of Facet Heterojunctions in Platinum Alloys for Oxygen Reduction Reaction

Ensuring high-quality activity of proton exchange membrane fuel cells (PEMFCs) while mitigating the degradation of Pt-based alloy catalysts remains challenging. A platinum-skinned truncated octahedral PtNi alloy with (100)/(111) facet heterostructures is synthesized through a low-temperature thermally driven etching strategy, demonstrating exceptional oxygen reduction reaction (ORR) activity and stability. The heterostructure of the Ptskin-PtNi(111) facet destabilizes the *OOH intermediate and promotes the preferential O─O bond cleavage, leading to the optimization of ORR pathway. A linear correlation between the generalized coordination number (CN ¯ $\overline {{\mathrm{CN}}} $ ) and ΔG*OH demonstrates that the facet hetero-sites optimize the adsorption of *OH to the theoretically optimal state through ligand and geometric effects. The optimized PNZC-5A160 catalyst exhibits enhanced ORR activity (2.97 A mgPt -1 at 0.9 V vs. RHE) and superior H2-O2 single PEMFC performance [mass activity (MA) of 0.5 A mgPt -1 at 0.9 ViR-free; peak power density of 1.42 W cm-2, exceeding the U.S. Department of Energy 2025 targets. After accelerated stress tests, the loss in MA at 0.9 ViR-free and in potential at 0.8 A cm-2 is only 8% and 3.7 mV, respectively, due to the enhanced binding of subsurface Pt and Ni to surface Pt atoms through Pt skin, thereby inhibiting the dissolution of Pt and Ni.

Examining proton conductivity of metal-organic frameworks by means of machine learning

The tunable structure of metal-organic frameworks (MOFs) is an ideal platform to meet contradictory requirements for proton exchange membranes: a key component of fuel cells. Nonetheless, rational design of proton-conducting MOFs remains a challenge owing to the intricate structure-property relationships that govern the target performance. In the present study, the modeling of quantities available for hundreds of MOFs was scaled up to many thousands of entities using supervised machine learning. The experimental dataset was curated to train multimodal transformer-based networks, which integrated crystal-graph, energy grid, and global-state embeddings. Uncertainty-aware models revealed superprotonic conductors among synthesized MOFs that have not been previously investigated for the application in question, thus highlighting magnesium-containing frameworks with aliphatic linkers as high-confidence candidates for experimental validation. Furthermore, classifiers trained on the activation energy threshold effectively discriminated between well-known proton conduction mechanisms, thereby providing physical insights beyond the black-box routine. Thus, our findings prove high potential of data-driven materials design, which is becoming a valuable addition to experimental studies on proton-conducting MOFs.

Core/Shell-Structured Carbon Support Boosting Fuel Cell Durability

To enhance the lifetime of proton exchange membrane fuel cells, developing highly durable platinum-based cathode catalysts is essential. While two degradation pathways for the cathode catalyst-carbon corrosion and electrocatalyst (platinum nanoparticles) coarsening-have been identified, current approaches to enhance its durability are limited to addressing individual degradation pathways. Herein, the study develops a core/shell-structured carbon support that is designed to afford cathode catalysts capable of simultaneously inhibiting carbon corrosion and electrocatalyst coarsening. The core/shell structure is distinguished by its bifunctional nature: the core is made of highly graphitized carbon tailored to build a robust carbon skeleton, and the shell comprises heteroatom-doped amorphous carbon engineered to prevent electrocatalyst coarsening by chemical/physical anchoring of platinum nanoparticles. Thanks to this elaborate design, the catalyst surpasses the durability targets for carbon supports and electrocatalysts set by the U.S. Department of Energy, as supported by the achieved durability metrics after the square-wave/triangle-wave accelerated stress tests: electrochemical surface area loss at 13%/3%, mass activity loss at 27%/17%, and voltage loss of 29 mV (at 0.8 A cm- 2)/4 mV (at 1.5 A cm- 2).

Leveraging Long-Life Alkaline Redox Flow Batteries Using Durable and High-Hydroxide Exchange N-Bridged Triazine Framework Membranes

Fluorine-free organic framework polyelectrolyte membranes showing near frictionless ionic conductivities are gaining cognitive insights. However, the co-precipitation of COFs in the membranes often brings trade-offs to commission long-life electrochemical energy storage solutions. Herein, a durable and ionically miscible dual-ion exchange membrane based on triazine organic framework (TOF) is designed for alkaline redox flow batteries (RFB). Bearing dual ion-exchange architectures, the all-hydrocarbon TOF-based PEMs (sTOF's) surpass fluorinated Nafion in terms of energy efficiency (>80%), energy density, and peak power densities. The fabricated sTOF's evidenced the highest net ion-exchange of >2.1 meq g-1 which encourages electrolyte utilization with ≈100% and offers excellent capacities. Moreover, >97% efficiencies are preserved, and rate capability studies illustrate that, with sTOF-5, the RFB can operate at reduced overpotentials (η ≤200 mV) and can uplift batteries life. The sTOF's supports successful demonstrations of batteries at higher redoxolyte concentrations thereby multiplying the energy densities. The afterlife performance of sTOF-5 revealed efficiencies equivalent to fresh Nafion-117 and surpassed bearing >50% capacity after ≈3000 continuous cycles. With sTOF-5, the cell delivered a peak power (Pmax) of 2.3 W which is ≈60% higher than that of Nafion-117 (Pmax = 1.45 W).

Operando X-ray absorption spectroscopic investigation of electrocatalysts state in anion exchange membrane fuel cells

Capturing the active state of (electro)catalysts under operating conditions, namely operando, is the ultimate objective of (electro)catalyst characterization, enabling the unraveling of reaction mechanisms and advancing (electro)catalyst development. Operando insights advance our understanding of the correlations between electrochemical tests and device-level performances. However, operando characterization of electrocatalysts is challenging due to the complexity of electrochemical devices and instrumental limitations. As a result, the majority of electrocatalyst characterizations have been limited to half-cell in situ studies. Here, we present an operando X-ray absorption spectroscopic study of Mn spinel oxide electrocatalysts in an operating fuel cell employing a custom-designed cell. Our results reveal that in anion exchange membrane fuel cells, the Mn valence state, within spinel Mn3O4/C, increases to above 3+, adopting an octahedral coordination devoid of Jahn-Teller distortions. This structural change results in an AEMFC performance equivalent to that of Co1.5Mn1.5O4/C, a composition that outperforms Mn3O4/C in rotating disk electrode tests. Our results underscore the importance of operando characterizations in elucidating the active state of electrocatalysts and understanding the correlation(s) between electrochemical tests and device performance.

Platinum-based nanoalloys for the oxygen reduction reaction: exposing the true active phase via in situ/operando techniques

Platinum-based nanoalloys are efficient electrocatalysts for the oxygen reduction reaction (ORR). In situ/operando measurements have revealed that key properties including induced strain, chemical composition, coordination environment, evolve significantly during operation, which can hampertheir effective implementation in fuel cells. In fact, recent studies indicate that the impact of the early surface activation steps of Pt-based nanoalloys has been hitherto underestimated and is an important factor contributing to loss of their initial electroactivity. In this short perspective, we highlight the importance of in situ/operando characterization of Pt-based electrocatalysts during the initial operation steps in the ORR and discuss recent insights into their early degradation and evolution of their key properties during electrochemical characterization.

Symmetry Breaking of FeN4 Moiety via Edge Defects for Acidic Oxygen Reduction Reaction

Fe-N-C catalysts, with a planar D4h symmetric FeN4 structure, show promising as noble metal-free oxygen reduction reaction catalysts. Nonetheless, the highly symmetric structure restricts the effective manipulation of its geometric and electronic structures, impeding further enhancements in oxygen reduction reaction performance. Here, a high proportion of asymmetric edge-carbon was successfully introduced into Fe-N-C catalysts through morphology engineering, enabling the precise modulation of the FeN4 active site. Electrochemical experimental results demonstrate that FeN4@porous carbon (FeN4@PC), featuring enriched asymmetric edge-FeN4 active sites, exhibits higher acidic oxygen reduction reaction catalytic activity compared to FeN4@flaky carbon (FeN4@FC), where symmetric FeN4 is primarily distributed within the basal-plane. Synchrotron X-ray absorption spectra, X-ray emission spectra, and theoretical calculations indicate that the enhanced oxygen reduction reaction catalytic activity of FeN4@PC is attributed to the higher oxidation state of Fe species in the edge structure of FeN4@PC. This finding paves the way for controlling the local geometric and electronic structures of single-atom active sites, leading to the development of novel and efficient Fe-N-C catalysts.

Enhancement of Proton Conductivity in Water and Aqua-Ammonia Vapor by Incorporating Sulfonic Acid-Functionalized Polymer into MIL-101-SO3H

The design and preparation of super proton conducting metal-organic frameworks (MOFs) are of great significance for the advancement of proton exchange membrane fuel cells (PEMFCs). An effective approach to increase the sulfonic acid density and control the hydrogen bonding networks within MOFs involves incorporating polymer chains that contain sulfonic acid groups into their pore structures. In this work, we report the in situ synthesis of a polyvinyl sulfonic acid (PVS) cross-linked polymer within the nanopores of MIL-101-SO3H, resulting in the PVS@MIL-101-SO3H composite. This composite maintains high proton conductivity in pure water vapor, achieving a peak conductivity of 2.57 × 10-2 S·cm-1 at 85 °C and 98% relative humidity (RH). Significantly, the proton conductivity markedly increases in aqua-ammonia environments, reaching 1.21 × 10-1 S·cm-1 under 1.0 M aqua-ammonia vapor at 100 °C, approximately five times higher than that observed in pure water vapor. Moreover, the composite exhibits excellent stability. Therefore, this study offers an efficacious approach to enhancing the performance of aqua-ammonia-assisted solid-state proton-conducting materials.

Sandwiching intermetallic Pt3Fe and ionomer with porous N-doped carbon layers for oxygen reduction reaction

Proton exchange membrane fuel cells show great potential as power source for automobiles, yet are now facing technological challenges of low efficiency in the cathodic oxygen reduction reaction and severe degradation from Nafion ionomers. Herein, we report the design and construction of a core/shell nanoparticle, composing of Pt3Fe intermetallic nanoparticle as core and atomically-thin porous N-doped carbon layer as shell, to alleviate Nafion ionomer poisoning and local oxygen transport at the interfaces, thereby improving the performance of membrane electrode assemblies. Combining electrochemical, spectroscopic and calculation results verify that the sandwiching carbon layer can effectively prevent surface Pt active sites from poisoning by ionomers. Moreover, this deliberate design facilitates a more homogeneous distribution of ionomers in catalyst layer, and drives a H2-air fuel cell peak power density up to 1.0 W cm-2. Due to the configuration-induced strong Fe-N coordination, our unique catalyst efficiently preserves transition metals and consequently delivers a notable fuel cell durability at a constant potential of 0.5 V for 100 h.

Atomic Layer Thickness Modulated the Catalytic Activity of Platinum for Oxygen Reduction and Hydrogen Oxidation Reaction

Reducing platinum (Pt) usage and enhancing its catalytic performance in the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR) are vital for advancing fuel cell technology. This study presents the design and investigation of monolayer and few-layer Pt structures with high platinum utilization, developed through theoretical calculations. By minimizing the metal thickness from 1 to 3 atomic layers, an atomic utilization rate ranging from 66.66% to 100% is achieved, in contrast to conventional multilayer Pt structures. This reduction resulted in a unique surface coordination environment. These thinner structures exhibited nonlinear fluctuations in key electronic characteristics-such as the d-band center, surface charge, and work function-as the atomic layer thickness decreased. These variations significantly impacted species adsorption and the Pt-H2O interfacial structure, which in turn affected the catalytic activity. Notably, 1-layer Pt exhibited the best performance for HOR, while 3-layer Pt showed high activity for both HOR and ORR. The findings establish a clear relationship between atomic layer thickness, surface characteristics, adsorption behavior, electric double-layer structure, and catalytic performance in Pt systems. This research contributes to a deeper understanding of precision atomic-structured electrocatalyst design and paves the way for the development of highly effective, low-loading Pt-based catalytic materials.

Lattice-Confined Ru Electrocatalysts with Optimal Localized Interfacial Electrons for Efficient Alkaline Hydrogen Oxidation

The interfacial electronic structure has a significant influence on the electrocatalytic activity and durability of metal oxide-supported ruthenium (Ru) electrocatalysts for the alkaline hydrogen oxidation reaction (HOR). Herein, we optimize the interfacial electronic structure by tuning the Ru-O bonds within MnO lattice-confined Ru electrocatalysts, creating efficient and stable sites for alkaline HOR. The formed Ru-O bonds generate localized interfacial electrons and a downshifted d-band center of interfacial Ru atoms, which results in optimal adsorption ability of H* and OH* together with the reduced energy barrier of H2O formation. The mass activity achieves 1.26 mA μgRu-1 in 0.1 M KOH, which is 13.0-fold and 8.0-fold higher than that of the contrast Ru/C (0.097 mA μgRu-1) and commercial Pt/C (0.158 mA μgPt-1), respectively, while also exhibiting favorable durability and CO tolerance. This work highlights the rational design of Ru-O bonds in optimizing the interfacial electronic structure to enhance the alkaline HOR activity.

The Relationship between the Electronic State of Pt in Pt-Based Nanoparticle Catalysts and Their Electrochemical Catalytic Activity in the Oxidation of Small Organic Compounds

To examine the relationship between the electronic state of platinum (Pt) in Pt-based nanoparticle (NP) catalysts and their catalytic activities in the electrochemical oxidation of methanol (MeOH) and ethanol (EtOH) in alkaline aqueous solutions, Pt-based NP catalysts were synthesized; their electrocatalytic activities were evaluated by rotating electrode techniques; and the electronic state of Pt in Pt-based catalyst surfaces was analyzed via X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). Finally, plots of the electrocatalytic activity vs electronic state of the Pt atoms on the catalyst surface were obtained. The plots exhibited a so-called volcano-type correlation, indicating that there is an optimum electronic state of Pt atoms on the catalyst surface for maximizing the MeOH and EtOH oxidation activities. In addition, the existence of the optimum electronic state was confirmed with adatom-modified Pt electrodes with Pb, Bi, In, Co, and Cu.

Conductive Metal-Organic Frameworks and Their Electrocatalysis Applications

Recently, electrically conductive metal-organic frameworks (EC-MOFs) have emerged as a wealthy library of porous frameworks with unique properties, allowing their use in diverse applications of energy conversion, including electrocatalysis. In this review, the electron conduction mechanisms in EC-MOFs are examined, while their electrical conductivities are considered. There have been various strategies to enhance the conductivities of MOFs including ligand modification, the incorporation of conducting materials, and the construction of multidimensional architectures. With sufficient conductivities being established for EC-MOFs, there have been extensive pursuits in their electrocatalysis applications, such as in the hydrogen evolution reaction, oxygen reduction reaction, oxygen evolution reaction, N2 reduction reaction, and CO2 reduction reaction. In addition, computational modeling of EC-MOFs also exerts an important impact on revealing the synthesis-structure-performance relationships. Finally, the prospects and current challenges are discussed to provide guidelines for designing promising framework materials.

Elucidating the mechanistic synergy of fluorine and oxygen doping in boosting platinum-based catalysts for proton exchange membrane fuel cells

Proton exchange membrane fuel cells (PEMFCs) are recognized as promising next-generation energy sources for automotive applications. The development of efficient, durable, and low-cost electrocatalysts to enhance the oxygen reduction reaction (ORR) kinetics is crucial. Herein, we report the synthesis of Pt@C/F-COOH catalysts via the pyrolysis and HNO3 oxidation of the carbon support, followed by the growth of Pt nanoparticles through reduction. These catalysts demonstrate superior ORR activity with an increased half-wave potential (E1/2) by 70 mV compared to commercial Pt/C. Durability tests reveal that Pt@C/F-COOH catalysts exhibit only 1 % decay after 50,000 s, significantly lower than the 52 % decay observed for commercial Pt/C, outperforming most reported Pt-based catalysts. Theoretical calculations indicated that the interaction between the CF groups and the Pt nanoparticles leads to a unique electron redistribution, resulting in more positively charged Pt sites and optimized desorption of the reaction intermediates. Additionally, the exceptional durability is attributed to the appropriate degree of oxidation of the carbon support, yielding a high number of defect sites and optimal graphitization, enhancing Pt anchoring and antioxidant capacity.

Water Dynamics of Superacid Aromatic Proton Exchange Membranes for Fuel Cell Applications

Proton exchange membranes (PEMs) with high conductivity are of critical importance for the development of fuel cells, electrolyzers, and other electrochemical technologies. In this research, poly(1,1,2,2-tetrafluoro-2-phenoxyethane-1-sulfonic acid) (PTPS) with an aromatic polymer main chain and a perfluorinated superacidic polymer side chain was synthesized. The water dynamics of PTPS were characterized across various length scales using a combination of Fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) and compared with Nafion, a standard perfluorinated PEM, and sulfonated poly(ether sulfone) (SPES 40), an aromatic PEM without perfluorinated superacid side chains. The T 1 and T 2 relaxation times of water in the samples probed by NMR increase from SPES 40 to PTPS to Nafion, indicating that the local motion of the water molecules becomes faster. This trend corresponds well with the relative fraction of bulk-like water determined using FTIR. At larger length scales, the diffusion coefficient of water was characterized using pulsed-field gradient NMR (PFG-NMR). At a longer diffusion time (Δ = 100 ms), PTPS has a smaller diffusion coefficient compared with both Nafion and SPES 40, due to restricted diffusion, and this effect is also evident in the proton conductivity of the hydrated membranes. From this comparison, it is apparent that the aromatic backbone and side chain type greatly influence the water dynamics in PEMs at various length scales and the water dynamics significantly impact the bulk proton conductivity. These insights will lead to new designs for aromatic PEMs and help to identify bottlenecks in current materials.

Interfacial metal-coordinated bifunctional PtCo for practical fuel cells

Platinum (Pt) has been documented as the top-tier fuel cell catalyst, yet it faces a notable challenge regarding its poor CO tolerance and sluggish oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs), particularly when using CO-contaminated blue and gray H2. Here, we present an interfacial metal coordination strategy to design a bifunctional platinum-cobalt (PtCo) intermetallic catalyst integrated with a tin-nitrogen-carbon (Sn-N-C) support, which forms Pt-Sn-N bonds that substantially boost both ORR activity and CO tolerance. The PtCo/Sn-N-C-made fuel cell achieves a topmost peak power density of 2.11 watts per square centimeter in 100 parts per million (ppm) of CO-containing H2, surpassing all previously reported PEMFCs. In addition, it operates stably at a rated voltage for over 710 hours in 100 ppm of CO/H2-air. This work demonstrates the feasibility of fuel cells directly using CO-contaminated gray & blue H2, paving the way for PEMFC-driven energy vehicles.

Porous carbon-supported PtPdCu alloy heterostructures with a three-dimensional spatial network for efficient ethanol electro-oxidation

Rationalizing efficient and economical electrocatalysts for ethanol electro-oxidation (EOR) is crucial for the development of sustainable energy sources. Herein, porous carbon-supported PtPdCu ternary alloy heterostructures (PtxPdyCuz/C, x : y : z = atomic ratio) were constructed using Cu-BTC as the precursor. Benefiting from the advantages of its three-dimensional spatial network structure, flexible ternary alloy composition and strong metal-support interaction, the as-designed PtxPdyCuz/C catalyst presents impressive EOR performance. Specifically, it achieved an EOR specific activity of 37.89 mA cm-2 in alkaline electrolyte, which is 6 and 11.4 times higher than those of Pt/C (6.3 mA cm-2) and Pd/C (3.32 mA cm-2), respectively, and more than 90% of the initial activity was retained after 1000 consecutive CV cycles. In situ FTIR studies further reveal that the PtxPdyCuz/C catalyst requires a potential of only 0.45 V to oxidize poisonous CO intermediates in the EOR. This work provides valuable insights for the rationalization of MOF-derived ternary alloy electrocatalysts for ethanol electro-oxidation.

Constructing Hydrophilic Polymer Membranes with Microporosity for Aqueous Redox Flow Batteries

Ion selective membranes (ISMs) are key components of aqueous redox flow batteries (ARFBs), and their property in selective ion transport largely determines the energy storage efficiency of ARFBs. Traditional ISMs are based on microphase-separated structures and have been advanced for many years, but most of them show poor performance as membrane separators in ARFBs due to their conductivity-selectivity. In recent years, using confined micropores instead of dense hydrophilic regions as ion channels has been demonstrated to effectively break this tradeoff. We here summarize the synthetic strategies for constructing hydrophilic polymer membranes with microporosity and highlight the performance of some typical microporous ISMs in ARFBs. We also propose fundamental issues that remain to be addressed for the further development of ISMs.

An Efficient H2S-Tolerant Hydrogen Oxidation Electrocatalyst Enabled by a Lewis Acid Modifier for Fuel Cells

Industrial hydrogen fuel typically comprises about 5 ppm of hydrogen sulfide (H2S), incurring irreversible poisoning of platinum on carbon (Pt/C) catalyst in fuel cells. For realistic use, H2S should be removed to below 4 ppb; this process, however, is challenging and costly. We describe an exceptional H2S-tolerant yet high-performing hydrogen oxidation reaction (HOR) catalyst prepared by chemical grafting of chromic oxide (Cr2O3) onto a molybdenum-nickel (MoNi4) alloy. Cr2O3 as a Lewis acid enhances the specific adsorption of hydroxyl ions, which in turn prevents from S2- diffusing to the catalyst surface via electrostatic repulsion. Meanwhile, the adsorbed hydroxyl species boost HOR kinetics through improving the hydrogen-bond networks in electrical double layers. The composite catalyst achieved HOR performance comparable to that of commercial Pt/C in an alkaline electrolyte. Moreover, a fuel cell using this catalyst as anode can survive 5 ppm of H2S without deactivation, compared with rapid degradation observed over the Pt/C counterpart.

Integrating PtCo Intermetallic with Highly Graphitized Carbon Toward Durable Oxygen Electroreduction in Proton Exchange Membrane Fuel Cells

Exploiting robust and high-efficiency electrocatalysts for sluggish oxygen reduction reaction (ORR) is essential for proton exchange membrane fuel cells (PEMFCs) toward long-term operation for practical applications, yet remains challenging. Herein, the ordered PtCo intermetallic is reported with a Pt-rich shell loaded on a highly graphitized carbon carrier (O-PtCo@GCoNC) prepared by an impregnation annealing strategy. Systematic X-ray spectroscopic, operando electrochemical techniques and theoretical calculations reveal that thanks to the synergistic interaction of the core-shell PtCo intermetallic structure with a tailor-made Pt electronic configuration and highly graphitized carbon, O-PtCo@GCoNC exhibits significantly enhanced activity and stability toward ORR. Crucially, O-PtCo@GCoNC delivers a much-enhanced mass activity of 0.83 A mgPt -1 at 0.9 V versus reversible hydrogen electrode (RHE) in 0.1 m HClO4, which only drops by 26.5% after 70 000 cycles (0.6-1.0 V vs RHE), and 10.8% after 10 000 cycles (1.0-1.5 V vs RHE), apparently overmatching Pt/C (0.19 A mgPt -1, 73.7%, and 63.1%). Moreover, O-PtCo@GCoNC employed as the cathode catalyst in H2/air PEMFC achieves a superb peak power density (1.04 W cm-2 at 2.06 A cm-2), outperforming that of Pt/C (0.86 W cm-2 at 1.79 A cm-2). The cell voltage loss at 0.8 A cm-2 is 28 mV after 30 000 cycles, outstripping the United States Department of Energy 2025 target.

Double Confinement Design to Access Highly Stable Intermetallic Nanoparticles for Fuel Cells

Maintaining the stability of low Pt catalysts during prolonged operation of proton exchange membrane fuel cells (PEMFCs) remains a substantial challenge. Here, a double confinement design is presented to significantly improve the stability of intermetallic nanoparticles while maintaining their high catalytic activity toward PEMFCs. First, a carbon shell is coated on the surface of nanoparticles to form carbon confinement. Second, O2 is introduced during the annealing process to selectively etch the carbon shell to expose the active surface, and to induce the segregation of surface transition metals to form Pt-skin confinement. Overall, the intermetallic nanoparticles are protected by carbon confinement and Pt-skin confinement to withstand the harsh environment of PEMFCs. Typically, the double confined Pt1Co1 catalyst exhibits an exceptional mass activity of 1.45 A mgPt -1 at 0.9 V in PEMFCs tests, with only a 17.3% decay after 30 000 cycles and no observed structure changes, outperforming most reported PtCo catalysts and DOE 2025 targets. Furthermore, the carbon confinement proportion can be controlled by varying the thickness of the coated carbon shell, and this strategy is also applicable to the synthesis of double-confined Pt1Fe1 and Pt1Cu1 intermetallic nanoparticles.

Proton Exchange Membrane with Dual-Active-Center Surpasses the Conventional Temperature Limitations of Fuel Cells

High temperature-proton exchange membrane fuel cells (HT-PEMFC) call for ionomers with low humidity dependence and elevated-temperature resistance. Traditional perfluorosulfonic acid (PFSA) ionomers encounter challenges in meeting these stringent requirements. Herein, this study reports a perfluoroimide multi-acid (PFMA) ionomer with dual active centers achieved through the incorporation of sulfonimide and phosphonic acid groups into the side chain. The fluorocarbon skeleton and multi-acid side chain structure facilitate the segregation of hydrophilic and hydrophobic microphases, augmenting the short-range ordering of hydrophilic nanodomains. Furthermore, the introduction of a rigid segment-benzene ring is employed to decrease side chain flexibility and raise the glass transition temperature. Notably, the prepared membrane exhibits a conductivity of 41 mS cm-1 at 40% relative humidity, showcasing a 1.8 times improvement over that of PFSA. Additionally, the power output of the H2-air fuel cell based on this membrane reaches 1.5 W cm-2 at 105 °C, marking a substantial 2.3 times enhancement compared to the PFSA. This work demonstrates the unique advantages of perfluorinated ionomers with multiple protogenic groups in the development of high-performance high-temperature electrolyte materials.

Turn the Harm into A Benefit: Axial Cl Adsorption on Curved Fe-N4 Single Sites for Boosted Oxygen Reduction Reaction in Seawater

Seawater electrocatalysis is urgently needed for various energy storage and conversion systems. However, the adsorption of chloride ions (Cl-) to the active sites can degrade the oxygen reduction reaction (ORR) activity and stability, thus reducing the catalytic performance. In this paper, a curved FeN4 single atomic structure is designed by utilizing curvature engineering, which can turns the harmful Cl adsorption into a benefit on the Fe single site that changes the rate determining step of ORR and reduces the overall energy barrier according to density functional theory (DFT) calculation. Experimental studies reveal the prepared highly-curved single-atom iron catalyst (HC-FeSA) exhibits excellent ORR activity in different electrolytes, with half-wave potentials of 0.90 V in 0.1 M KOH, 0.90 V in simulated seawater, and 0.75 V in natural seawater, respectively. This work opens up an avenue for the synthesis of high-performance seawater-based single-atom ORR catalysts through regulating the local atomic curvature.

New Morphology Modifier Enables the Preparation of Ultra-Long Platinum Nanowires Excluding Mo Component for Efficient Oxygen Reduction Reaction Performance

The structural tailoring of Pt-based catalysts into 1D nanowires for oxygen reduction reactions (ORR) has been a focus of research. Mo(CO)6 is commonly used as a morphological modifier to form nanowires, but it is found that it inevitably leads to Mo doping. This doping introduces unique electrochemical signals not seen in other Pt-based catalysts, which can directly reflect the stability of the catalyst. Through experiments, it is demonstrated that Mo doping is detrimental to ORR performance, and theoretical calculations have shown that Mo sites that are inherently inactive also poison the ORR activity of the surrounding Pt. Therefore, a novel gas-assisted technique is proposed to replace Mo(CO)6 with CO, which forms ultrafine nanowires with an order of magnitude increase in length, ruling out the effect of Mo. The catalyst performs at 1.24 A mgPt -1, 7.45 times greater than Pt/C, demonstrating significant ORR mass activity, and a substantial improvement in stability. The proton exchange membrane fuel cell using this catalyst provides a higher power density (0.7 W cm-2). This study presents a new method for the preparation of ultra-long nanowires, which opens up new avenues for future practical applications of low-Pt catalysts in PEMFC.