Albert Sung Soo Lee

Backbone isomer engineering regulates phase separation and ion-transport pathways, revealing a performance–stability trade-off and enabling a design strategy for balanced AEMs via copolymer and blend architectures.

Packing density critically influences the practical hydrogen storage capacity of metal-organic frameworks (MOFs), yet it is often overlooked in volumetric performance evaluations. In this study, we demonstrate that bimodal particle packing provides an effective route to enhance system-level volumetric hydrogen storage by reducing interparticle voids. A V₃(PET) MOF was synthesized in two distinct sizes (∼9 μm and ∼300 nm) to construct a bimodal particle system. Discrete element method (DEM) simulations were used to establish particle-packing design rules and to identify the optimal mixing composition for maximizing packing density. These simulation-guided predictions were then experimentally validated through tapping density measurements and high-pressure H₂ adsorption isotherms. The optimized bimodal mixture achieved a packing fraction of 0.56, compared to 0.42 for unimodal packing, leading to a 33-38% increase in volumetric excess hydrogen uptake at 77 K. Moreover, the bimodal system exhibited an enhanced working capacity of up to 37.7 g/L under pressure-temperature swing adsorption (PTSA) condition (160 K 5 bar to 77 K 100 bar). These results demonstrate particle-level packing engineering as a broadly applicable and experimentally accessible strategy for bridging intrinsic MOF properties with realistic, system-level hydrogen storage performance.

High‐temperature polymer electrolyte membrane fuel cells (HT‐PEMFCs) operating at 160°C on phosphoric acid‐doped polybenzimidazole membranes address the water management and CO poisoning challenges faced by conventional PEMFCs. However, phosphate anions adsorb strongly onto Pt active sites, hindering oxygen reduction kinetics (“phosphate poisoning”) and limiting long‐term performance. To address these challenges, we present PtFe nanoparticles encapsulated within a porous carbon shell engineered to impart molecular sieving of phosphate anions and protect against Pt degradation. Previously, the molecular‐sieving effect of carbon shell coatings has been studied in half‐cell evaluations; however, the reaction mechanism of carbon shell‐encapsulated catalysts remains under debate. Herein, we integrate the catalysts into membrane electrode assemblies and demonstrate high HT‐PEMFC performances (peak power density of 0.94 W·cm ⁻² and stability for 200 h). Furthermore, scanning electrochemical microscopy measurements demonstrate that O ₂ diffuses through the engineered porous carbon shell to the PtFe core rather than via uncontrolled defects, emphasizing the need for optimized mass transport. This single‐cell performance represents a significant step toward practical, high‐performance HT‐PEMFCs and underscores the importance of catalyst architectures that mitigate phosphate poisoning while maintaining catalytic activity under harsh, high‐temperature conditions.

The intrinsic trade‐off between ion conductivity and mechanical integrity in high‐ion exchange capacity (IEC) anion exchange membranes (AEMs) has remained a major challenge for the practical implementation of anion exchange membrane water electrolyzer (AEMWE) technology. Here, crosslinked AEMs (BP‐ cross ‐PDAA) is developed via free‐radical cyclopolymerization of diallylammonium‐functionalized poly(biphenyl alkylene), where the IEC ( n ) is precisely tuned from 2.32 meq g ⁻¹ to 3.39 meq g ⁻¹ by adjusting the content of diallyldimethylammonium comonomer. BP‐ cross ‐PDAA membranes exhibited excellent hydration characteristics, including hydroxide conductivity (up to 152.4 mS cm ⁻¹ at 80 °C), swelling ratio (24.2%), and alkaline stability (98.7% retention over 350 h), attributed to their robust crosslinked network structure without sacrificing their high IEC. Furthermore, membrane‐electrode assembly (MEA‐ n ) tests demonstrated remarkable AEMWE performance, with MEA‐3.39 achieving a peak current density of 12.39 A cm ⁻² at 2.0 V using a non‐platinum group metal anode, and 6.1 A cm ⁻² under pure water condition. MEA‐3.39 also exhibited excellent durability, with a minimal voltage degradation rate of 1.2 µV h ⁻¹ over 1,000 h at 1 A cm ⁻² in 1 M KOH at 50 °C.

Anion exchange membrane (AEM) water electrolysis (AEMWE) is considered an economical technology for producing green hydrogen energy. However, conventional AEMs comprising polymer backbones with anisotropically aligned cationic pendant groups exhibit unsatisfactory AEMWE performance and durability, limiting their practical implementation. Herein, a facile method for fabricating a durable high‐performance AEM via a one‐pot monomer‐level Menshutkin (m‐Men) reaction in a porous mechanical support is proposed. The rationally designed m‐Men reaction between multifunctional alkyl halide and tertiary amine monomers creates a highly crosslinked polymer network with isotropically interconnected, high‐density cationic groups. This unique structure is favorable for expediting anion conduction within the membrane and enhancing thermochemical robustness. The resultant membrane exhibits unprecedentedly high AEMWE performance with both non‐platinum‐group metal (PGM) and full‐PGM electrodes at 5 wt.% potassium hydroxide and 80 °C, outperforming commercial state‐of‐the‐art AEMs, with ensuring long‐term operation. The proposed strategy provides a breakthrough approach for fabricating advanced membranes for various energy applications.

State-of-the-art membranes derived from polymers of intrinsic microporosity offer promising alternatives to energy-intensive, thermally driven separation techniques but often suffer from reduced performance under condensable gases or physical aging. Here, extrinsically microporous polymer membranes (EMPMs) are introduced as a distinct class of microporous membranes, fabricated from perfluorinated aryl-ether-free aromatic polymers via defluorination-induced thermal cross-linking. This process generates extrinsic micropores, increases intersegmental distances, and significantly enhances gas permeability. EMPMs exhibit a Brunauer-Emmett-Teller surface area of 552 m² g⁻¹ and demonstrate exceptional plasticization resistance under equimolar CO₂/CH₄ mixed gas at pressures up to 40 bar. CO₂ permeability increases from 280 to 12,000 Barrer at 1 bar and 35 °C, while CO₂/N₂ selectivity reaches 46 at −20 °C, surpassing the 2019 polymeric upper bound. Furthermore, extrinsically microporous hollow fiber membranes prepared via dip-coating achieve a CO₂ permeance of 2174 gas permeation units and CO₂/N₂ selectivity of 30 at −20 °C, highlighting their industrial relevance. This study establishes a scalable method for fabricating high-performance microporous polymeric membranes with exceptional stability for sustainable energy and environmental applications.

Aqueous hydrofluoric acid (HF)‐based solutions are widely used for etching MAX phases to synthesize high‐purity 2D molybdenum carbides (MXenes). However, their applicability is limited to selected MAX phases, and the production of certain MXenes, such as Mo‐based MXenes, remains challenging owing to low quality, low yield, and the time‐intensive process, often requiring several days to weeks. In this study, a non‐aqueous etchant for faster and more efficient synthesis of high‐purity Mo‐based MXenes is introduced. This etchant, containing Cl⁻ and F⁻ ions, is adequately effective to etch the MAX phase using the F⁻ ions of moderate concentration regenerated from GaF₆³⁻ byproducts but only mildly caustic to prevent damage to the resulting MXene. Using this approach, the rapid production of Mo₂CT_x is demonstrated within 24 h at 100 °C, achieving up to 90% multilayer and 45% monolayer yields. Furthermore, the resulting monolayer Mo₂CT_x flake exhibits larger sizes and fewer defects, with an electrical conductivity of 5.9 S cm⁻¹, 6.5 times higher than that (0.9 S cm⁻¹) of aqueous HF‐Mo₂CT_x. This enhancement results in improved electrocatalytic activity of high‐purity Mo₂CT_x for hydrogen evolution reactions. These findings highlight the potential of non‐aqueous etching solutions to address the limitations of HF‐based MXene synthesis.