Taehyun Kwon

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.

Doping Ru oxides with heteroatoms such as Pt can mitigate their intrinsic redox instability by redistributing charge at the interface during acidic OER conditions; however, achieving atomically intimate Pt–Ru configurations remains challenging because conventional synthesis routes cannot reliably juxtapose the two elements at structurally compatible catalytic sites. Here, we report a strain‐driven atomic migration strategy that enables controlled redistribution of Ru from the exterior to the interior of PtNi multiframe during thermal oxidation. Redox‐induced Ni oxidation generates lattice strain that drives inward Ru migration, leading to the formation of RuO ₂ /Pt mosaic heterointerfaces throughout the open framework. These heterointerfaces create a Pt‐biased redox environment that stabilizes Ru ⁴⁺ while strongly suppressing lattice oxygen participation. Operando XAFS and ¹⁸ O‐labeled DEMS reveal that this Pt–Ru redox asymmetry underpins the remarkable stability, while interfacial electronic modulation steers the reaction toward an adsorbate evolution mechanism‐dominated pathway with more favorable intermediate energetics. Consequently, the catalyst delivers an ultralow overpotential of 168 mV at 10 mA cm ⁻² and maintains stable operation for over 540 h. Overall, this work establishes strain‐directed atomic migration as a versatile post‐synthetic route for constructing redox‐stabilized heterointerfaces, providing a broadly applicable design principle for highly active and durable water‐splitting electrocatalysts.

This review explores recent advancements and challenges in the development of electrocatalysts for the electrochemical ozone production including mechanistic understanding, electrode preparation, and applications in practical wastewater treatment.

Research on polymer electrolyte membrane fuel cells (PEMFCs) has received great attention over the past few decades, leading to substantial advancements in their performance. However, their susceptibility to chemical degradation during the operation remains a great challenge, diminishing overall device longevity. This degradation is largely due to the unintended generation of reactive oxygen species (ROS), including free radicals, which break down the membrane polymers and catalyst layers. To address this issue, the incorporation of radical-scavenging additives has emerged as a promising strategy, as these materials can effectively react with ROS through various redox reactions. In particular, defective ceria (CeO_2−x) has shown great potential as a ROS scavenger in PEMFC devices due to its fast ROS scavenging reaction kinetics via reversible redox cycling between Ce³⁺/Ce⁴⁺ through oxygen vacancy formation and annihilation. This review highlights recent advancements in surface engineering strategies to improve the radical scavenging performance and surface regeneration kinetics of CeO_2−x-based additives. Furthermore, this review provides insights into developing highly active and stable radical scavenger additives, thereby enhancing the overall chemical stability of the PEMFC devices and paving the way for future research directions.

The success of proton exchange membrane water electrolysis (PEMWE) depends on active and robust electrocatalysts to facilitate oxygen evolution reaction (OER). Heteroatom-doped-RuO_x has emerged as a promising electrocatalysts because heteroatoms suppress lattice oxygen participation in the OER, thereby preventing the destabilization of surface Ru and catalyst degradation. However, identifying suitable heteroatoms and achieving their atomic-scale coupling with Ru atoms are nontrivial tasks. Herein, to steer the reaction pathway away from the involvement of lattice oxygen, we integrate OER-active Ir atoms into the RuO₂ matrix, which maximizes the synergy between stable Ru and active Ir centers, by leveraging the changeable growth behavior of Ru/Ir atoms on lattice parameter-modulated templates. In PEMWE, the resulting (RuIr)O₂/C electrocatalysts demonstrate notable current density of 4.96 A cm⁻² and mass activity of 19.84 A mg_Ru+Ir⁻¹ at 2.0 V. In situ spectroscopic analysis and computational calculations highlight the importance of the synergistic coexistence of Ru/Ir-dual-OER-active sites for mitigating Ru dissolution via the optimization of the binding energy with oxygen intermediates and stabilization of Ru sites.

The electrochemical production of sustainable hydrogen under neutral conditions is advantageous, as it allows for the use of wastewater or seawater without the need for pH adjustments. However, the low ion concentration in neutral electrolytes typically results in limited adsorption of reactants on the catalyst surfaces, leading to sluggish reaction kinetics. Therefore, enhancing absorption capacity is a key challenge in the development of neutral hydrogen evolution reaction (HER) catalysts. Hetero‐structured catalysts may improve surface adsorption through extensive interfacing between phases, enabling active transportation of reaction intermediates. Integrating metal sulfides and oxides, in particular, holds the potential for generating efficient electrocatalysts with improved HER activity and surface adsorption capacity. Herein, the synthesis of CrO_x‐doped Co₉S₈/CuCrS₂ mosaic hetero‐nanostructures is reported as a proficient HER catalyst. Facile Cr‐cation migration at the Co₉S₈/CuCrS₂ interface enables the preparation of Cr‐oxide sub‐nano domains within the sulfide matrix, boosting the HER catalysis in neutral media. The exceptional electrochemical performance is demonstrated in a pH 7.4 phosphate buffer solution, including low overpotential, small Tafel slope, and stability over 60 h. The formulation of catalyst design and synthetic approaches has the potential to pave the way for diverse catalytic applications utilizing metal oxide‐doped hetero‐nanostructures.

Highly active Ir electrocatalysts based on ultralow loading for proton exchange membrane water electrolysis (PEMWE) applications are desirable to achieve gigawatt production levels. However, no clear direction has been developed yet to achieve that scale. Here, newly‐synthesized Ir‐based jagged nanotubes (J‐IrNTs) with the ultrahigh electrode performance of 10 A mg_Ir⁻¹ at 1.6 V in a PEMWE cell at Ir loadings as low as 0.05 mg_Ir cm⁻² are reported, outperforming previously reported Ir‐based electrocatalysts. The Ir‐JrNT also exhibits only marginal degradation in stability tests. Notably, the resulting electrode of Ir‐JrNT provides enhanced intrinsic catalytic activity and high surface area for efficient electrocatalysis, with hierarchical branching composed of interconnected multiscale channels and highly corrugated surface textures, for facile mass transport. The findings demonstrate that the jagged nanotubular structure is a promising approach for overcoming the limitations associated with Ir‐based electrocatalysts and developing sustainable advanced PEMWE.