Hyunjoo Lee

Reducing the use of precious metals is essential for the commercialization of proton exchange membrane water electrolysis (PEMWE). The Schottky contact formed between the catalyst layer and Ti porous transport layer (PTL) at the anode significantly degrades cell performance and necessitates high Ir loading or Pt coating. IrO ₂ catalysts with various crystallite sizes (1.7‒11.0 nm) were synthesized, and their membrane electrode assembly (MEA) performance was evaluated at a low Ir loading of 0.3 mg _Ir cm ⁻² using Pt‐coated Ti PTL and bare Ti PTL. The MEA performance exhibited opposite trends depending on the type of PTL, primarily due to variation in the work function, which is determined by the surface oxygen configuration of the IrO ₂ catalyst. Smaller crystallites exhibited a larger work function, resulting in a greater performance discrepancy between the two PTL types. To overcome the suboptimal performance of IrO ₂ , we utilized the crystalline 7.1 nm‐sized IrO ₂ as an electron pathway and deposited highly active amorphous IrO _x on its surface. This mixed‐phase Ir oxide exhibited good cell performance and durability even with a bare Ti PTL. This study highlights that the Schottky contact problem of IrO ₂ catalysts can be overcome through surface engineering, enabling low Ir use for PEMWE.

Water electrolyzers are key technologies for enabling a carbon-neutral society by facilitating sustainable hydrogen production. Despite extensive efforts to develop highly active catalysts, a persistent gap remains between catalyst performance evaluated in rotating disk electrode (RDE) systems and that achieved in practical membrane electrode assembly (MEA) configurations. In this perspective, we highlight the origins of this discrepancy and emphasize that intrinsic catalytic activity alone is insufficient to predict electrolyzer performance. Using the acidic hydrogen evolution reaction (HER) as a model system, we demonstrate that apparent activity metrics such as mass activity and Tafel slope can be significantly influenced by catalyst loading, composition, and measurement conditions in RDE, often leading to misleading conclusions. In contrast, MEA performance is governed by complex interfacial phenomena including mass, electron, and charge transport. A similar behavior was also observed for alkaline HER and acidic oxygen evolution reaction (OER). We further present case studies illustrating the critical roles of electron transfer and durability in water electrolyzers. In addition, recent advances in proton-exchange-membrane water electrolyzer commercialization are discussed, highlighting the importance of system-level optimization, including ionomer distribution control and scalable manufacturing via slot-die coating, which enabled the deployment of a 2.5 MW system. Overall, bridging the gap between laboratory catalyst research and industrial water electrolyzer applications requires a shift from catalyst-centric design toward integrated system-level engineering.

Precise stabilization of atomic structures under reaction environments remains a central challenge in heterogeneous catalysis. Here, we demonstrate that ammonia (NH ₃ ) serves as a chemically active nitrogen source to derive the selective migration of ruthenium (Ru) atoms onto ceria (CeO ₂ ) domains, forming a durable atomically dispersed structure. During ammonia decomposition, nitrogen-containing intermediates promote atomic redistribution of Ru and anchor the atoms selectively at CeO ₂ , yielding stable Ru-ceria interfaces. The resulting catalyst exhibits high activity in high-pressure ammonia decomposition for hydrogen production, attributed to its lowered activation energy and mitigated hydrogen poisoning. Furthermore, both the catalytic performance and the atomic Ru structure are preserved during long-term high-pressure operation, confirming the exceptional structural stability of the designed configuration. This study establishes active-nitrogen-driven migration as an effective strategy for constructing robust and reaction-friendly catalyst surface.

Atomically dispersed Pt on defect-rich ceria-carbon enables highly selective glycerol electrooxidation toward C3 products, particularly glycerate. It favors single-carbon adsorption, suppressing C–C cleavage.

Efforts to improve C₂₊ selectivity in CO₂ electroreduction have increasingly focused on strategies that deliberately induce catalyst surface reconstruction to create and maintain active sites. Among these, approaches using anodic pulses have gained particular attention for their ability to modulate the copper catalyst surface in situ. However, the underlying Cu surface reconstruction mechanisms triggered by anodic polarization still remain unclear. Here, we show that applying anodic potentials to copper can lead to two distinct surface reconstructions: surface oxide formation or metal dissolution, each defining a different reconstruction pathway with contrasting impacts on product selectivity. Oxide-derived reconstruction transiently enhances C₂ over C₁ selectivity but gradually loses effectiveness during operation, while dissolution-redeposition reconstruction continuously forms C₂-selective sites, resulting in a progressive increase in C₂ selectivity over time. Leveraging this mechanistic understanding, we implement electrolyte engineering by introducing trace Cu²⁺ ions under cathodic conditions to directly activate the dissolution-redeposition pathway without anodic bias. This strategy drives a dynamic electrochemical interface that sustains active-site regeneration and enables controllable selectivity, offering an energy-efficient alternative.

Electrochemical CO ₂ reduction reaction (CO ₂ RR) in neutral or alkaline environment suffers from carbonate formation, leading to low CO ₂ utilization. Acidic operation can mitigate this issue, but is hampered by the dominant hydrogen evolution reaction (HER). Here, we report a cavitated carbon particle (CCP)–supported Au catalyst featuring abundant inner cavities that sustain elevated local alkalinity. These cavities could be formed by inducing interfacial instability in block copolymer particles. A solid carbon particle (SCP)‐supported Au catalyst, which does not possess any cavities, was also synthesized, and the effect of the cavity for the CO ₂ RR was evaluated in 5 wt.% Au/CCP and Au/SCP catalysts at pH 2. Flow cell data and multi‐physics simulation results confirm that a confined cavity geometry (diameter ∼130 nm) could increase local alkalinity significantly, suppressing HER and enhancing CO ₂ reduction. The microenvironment was further modulated by changing the binder type, cation identity, and cation concentration. These findings establish cavity confinement as a powerful strategy to modulate the local reaction environment and enable selective CO ₂ RR under highly acidic conditions, providing a viable pathway for efficient CO ₂ electrolysis.

Reducible metal oxides are widely used in surface reactions, primarily due to their ability to activate and transfer oxygen. Ceria, known for its rapid Ce³⁺/Ce⁴⁺ redox property, is well-known to follow Mars van Krevelen mechanism. In this study, we prepare Pt/CeO₂-Al₂O₃ catalysts with different ceria domain sizes of 3.7, 5.6, and 7.3 nm to understand oxygen transfer, mainly O₂ activation and lattice oxygen transfer. The ceria domains are isolated on the alumina, preventing oxygen transfer between the ceria. Pt single atomic structures are meticulously prepared to exclude O₂ activation on Pt nanoparticles and provide uniform active sites. Interestingly, the activity trend for CO oxidation is reversed in O₂-rich and O₂-deficient conditions. O₂ activation occurs efficiently in small ceria domains of 3.7 nm. In contrast, larger ceria domains exhibit less O₂ activation but significant lattice oxygen transfer. This behavior is also modeled using large-scale molecular dynamics simulations with a neural network potential trained on first-principles data. Based on these understanding, the catalyst for methane oxidation is proposed by accelerating O₂ activation in O₂-rich condition. This work provides an impactful platform for understanding metal oxide catalysts.