Sangwon Kim

The long‐term durability of proton exchange membrane fuel cells (PEMFCs) remains a critical hurdle for their widespread commercialization, largely because of chemical degradation of the membrane electrode assembly (MEA) by unintentionally generated free radicals during operation. Defective ceria (CeO _2−x ) nanoparticles have emerged as promising radical‐scavenging additives through reversible Ce ³⁺ /Ce ⁴⁺ redox cycling. However, their radical scavenging efficiency is limited by the sluggish regeneration of surface Ce ³⁺ species, which are the active species for radical scavenging, leading to a gradual loss of their initial scavenging capability during long‐term cell operation. Here, we report a strategy to accelerate Ce ³⁺ regeneration kinetics by maximizing heterointerface‐derived interactions through simple seed‐mediated growth of defective ceria on the surface of a metal‐organic framework (MOF). In particular, UiO‐66‐NH ₂ undergoes partial amorphization and dissolution during the CeO _2−x nanoparticle growth, which enables intimate interfacial contact and enhanced electronic coupling with CeO _2−x . The resulting UiO‐66‐NH ₂ /CeO _2−x heterostructure exhibits improved redox cycling and higher Ce ³⁺ retention under oxidative conditions than commercial ceria nanoparticles. Moreover, when incorporated into the cathode catalyst layer of the MEA, the UiO‐66‐NH ₂ /CeO _2−x significantly suppressed the performance degradation, enabling stable single‐cell operation for over 500 h under an accelerated durability test.

Phosphonium ionic liquids are emerging electrolyte platforms for safer and more durable electrochemical energy‐storage systems because they combine low volatility, reduced flammability, thermal robustness, broad electrochemical stability windows, and highly tunable cation–anion chemistry. Their performance emerges from coupled cation–anion structure, salt concentration, electrolyte formulation, solvation environment, and electrode chemistry. This Review develops a structure–property–interphase framework for phosphonium‐based electrolytes in lithium, sodium, zinc, magnesium, and aluminum batteries, as well as supercapacitors and quasi‐solid‐state systems. For phosphonium‐based electrolytes, we analyze how alkyl chain length, branching, ether functionalization, and anion identity govern viscosity, conductivity, ion coordination, metal plating/stripping, corrosion, gas evolution, and solid–electrolyte and cathode–electrolyte interphase formation. The analysis shows that smaller, asymmetric, branched, or ether‐functionalized cations generally promote faster ion transport, whereas long‐chain hydrophobic cations are better suited for thermally robust, low‐volatility, gel, or deep‐eutectic‐type formulations. Finally, we propose practical design rules emphasizing low‐viscosity cation design, fluorine‐reduced anion chemistry, standardized benchmarking, full‐cell validation, and surface‐sensitive/operando interphase characterization.

Passive air-cooled polymer electrolyte membrane (PEM) fuel cell systems, recognized for their lightweight and simple design, are particularly suitable for drone and aircraft applications. Unlike their water-cooled counterparts, these systems utilize ambient air, facilitated by a fan, for both fuel and cooling purposes, which makes water and heat management crucial. This study aims to optimize such systems, focusing on cathode design variables, including gas diffusion layer thickness and gas channel dimensions. Employing a three-dimensional, multiscale, two-phase model, we analyze the impact of these variables on system performance and pressure drop to identify optimal configurations. Additionally, a neural network model helps in understanding design factor trends and pinpointing the best design setup. Our results indicate that specific optimal configurations for each design variable can significantly enhance system efficiency and stability, facilitating an effective design tailored for lightweight aviation applications.

Developing a time‐efficient, facile synthetic methodology for uniform and functionalized catalysts is essential to enhance the production efficiency and industrial applicability of heterogeneous catalysts. However, controlling the composition and structure without additional organic surfactants and complex multistep synthesis protocols remains challenging. Solution plasma process (SPP) is a promising strategy for the facile method to synthesize multimetallic nanocrystals embedded on surface‐engineered carbon supports. In this work, we report an in situ synthesis of bimetallic PtCo nanocrystals on a carbon support with tunable N‐doping levels via an SPP. Uniform sub‐2 nm PtCo nanocrystals were formed through a single‐step process within minutes. The optimized PtCo/N‐doped carbon catalyst exhibited enhanced activity and long‐term stability for the alkaline hydrogen evolution reaction compared to commercial Pt/C.

Intermetallic Pt ₅ Ce/C forms a Pt-skin with subsurface Ce, enabling rapid H ₂ O ₂ -scavenging, excellent oxygen reduction activity and durability.

Lithium-ion batteries (LiBs) represent a state-of-the-art electrochemical energy storage technology, enabling applications from portable electronics and electric transportation to large-scale grid energy storage systems. Despite their widespread adoption, LiBs face challenges like performance decrease, reduced lifespan, and safety risks, all closely tied to battery degradation. This review systematically examines the factors influencing LiB degradation, dividing them into intrinsic and extrinsic categories. Intrinsic factors include material chemistry, manufacturing inconsistencies, and design limitations, while extrinsic factors cover operational conditions such as temperature, charge–discharge rates, state of charge, and depth of discharge. The degradation factors influence the degradation mechanisms, and these correlations are discussed in detail. Additionally, this study highlights mitigation strategies and tradeoffs, including advanced electrode designs, surface modifications, and optimized battery management systems. By consolidating current research, this review provides insights into overcoming the challenges associated with LiB degradation, aiming to guide future developments in achieving safer, more durable, and efficient energy storage systems.