Hyun You Kim

While hydrogen peroxide (H ₂ O ₂ ) serves as a pivotal reagent across biomedical and environmental domains, its centralized production conflicts with the demand for on‐demand, spatially confined delivery. Ultrasound‐driven piezocatalysis directly converts mechanical energy into surface chemistry through piezoelectric polarization without electrodes or photons, enabling oxidant generation precisely where and when needed. Despite progress, the field lacks a unified framework connecting its mechanistic foundations, acoustic physics, and application potential. We systematically examine the two dominant mechanistic models; energy band theory and the screening charge effect, and discuss the H ₂ O ₂ pathway. The physical role of ultrasound is examined beyond its conventional treatment, distinguishing between pressure‐driven deformation and cavitation‐induced impulsive stress as distinct modes of energy transfer. Rather than a compilation of materials, we outline design strategies through which heterojunction engineering, geometric dimensionality, crystal structure modulation, and surface functionalization enhance charge separation and catalytic H ₂ O ₂ yield. Furthermore, we highlight applications ranging from cancer immunotherapy and implant infection control to environmental remediation. Crucially, its wireless and light‐free operation enables deployment in deep‐tissue and enclosed scenarios inaccessible to photocatalytic or electrochemical systems. Finally, this review establishes a clear framework for the rational design of next‐generation piezocatalysts.

Reducing iridium (Ir) loading while maintaining high activity and durability remains a critical challenge for proton exchange membrane water electrolysis. While oxide‐supported catalysts offer a pathway for Ir reduction, their intrinsic low electronic conductivity and inefficient charge transfer at catalyst‐support interfaces remain imperative bottlenecks. Herein, we report a synergistic interfacial engineering strategy of catalyst‐support based on partial ex‐solution of Bi from a Bi ₃ TaO ₇ support. Ex‐solved Bi forms highly active Ir─Bi alloy domains while generating a Bi‐deficient support and markedly improving the conductivity of the support. Moreover, this coupled reconstruction lowers the work function of the Ir‐based catalyst while increasing the work function of the support, shifting the catalyst‐support contact from rectifying to ohmic, thereby facilitating efficient electron transport. The resulting IrBi/Bi _3‐x TaO ₇ exhibits enhanced half‐cell oxygen evolution reaction activity (248 mV at 10 mA/cm ² ), mass activity (1077 mA/mg _Ir at 1.55 V), and durability (15.8 h). Furthermore, single‐cell measurements achieve outstanding performance of 1.824 V at 2 A/cm ² with a low Ir loading of 0.38 mg/cm ² and negligible voltage degradation over 100 h. This work highlights a generalizable strategy for simultaneous electronic integration of catalyst and support, offering new insights into the design of efficient and durable electrocatalysts for PEMWE.

Preferential oxidation, PROX, of residual CO in a hydrogen‐rich synthetic gas is the final stage of industrial hydrogen production and purification. However, selectively oxidizing around 1 vol. % of CO without consuming hydrogen is technically challenging. Here, we use Pt single atoms (SAs) stabilized on CeO _x –TiO ₂ supporting oxides toward PROX of CO. Based on a combined study of density functional theory calculations and in situ spectroscopic analyses, we identified the delicate electronic states of the reaction centers. The bifunctional nature of the spatially separated Pt–O–Ti and Pt–O–Ce sites promoted selective PROX of CO. The preferentially adsorbed hydrogen at the Pt–O–Ti site behaves as an activity regulator, donating electrons to Pt, thus reducing Pt–SAs. The oxygen ion at the Pt–O–Ce interface actively oxidizes the weakly adsorbed CO on reduced Pt–SAs. The unique structural and electronic ensembles at the Pt–CeO _x –TiO ₂ interfaces suppress hydrogen consumption but, instead, promote the PROX of CO under hydrogen‐rich conditions with high specific mass activity and 100 % selectivity for CO ₂ at below 100°C. We present a representative case of using electronic modulation of Pt–SAs under reaction conditions, enabled by the unique structural ensemble of Pt‐oxide interfaces, to activate Pt–SAs dynamically.

Preferential oxidation, PROX, of residual CO in a hydrogen‐rich synthetic gas is the final stage of industrial hydrogen production and purification. However, selectively oxidizing around 1 vol. % of CO without consuming hydrogen is technically challenging. Here, we use Pt single atoms (SAs) stabilized on CeO _x –TiO ₂ supporting oxides toward PROX of CO. Based on a combined study of density functional theory calculations and in situ spectroscopic analyses, we identified the delicate electronic states of the reaction centers. The bifunctional nature of the spatially separated Pt–O–Ti and Pt–O–Ce sites promoted selective PROX of CO. The preferentially adsorbed hydrogen at the Pt–O–Ti site behaves as an activity regulator, donating electrons to Pt, thus reducing Pt–SAs. The oxygen ion at the Pt–O–Ce interface actively oxidizes the weakly adsorbed CO on reduced Pt–SAs. The unique structural and electronic ensembles at the Pt–CeO _x –TiO ₂ interfaces suppress hydrogen consumption but, instead, promote the PROX of CO under hydrogen‐rich conditions with high specific mass activity and 100 % selectivity for CO ₂ at below 100°C. We present a representative case of using electronic modulation of Pt–SAs under reaction conditions, enabled by the unique structural ensemble of Pt‐oxide interfaces, to activate Pt–SAs dynamically.

Doping ceria (CeO2) with La3+ increases the concentration of oxygen vacancies (Ov) and reconstructs the surface structure, creating Ce–O–La interfacial motifs that robustly anchor Pt nanoclusters (Ptnc). Here, we present a nanocluster- and vacancy-engineered Ptnc/LaCeOx catalyst that exhibits outstanding performance in the reverse water–gas shift (rWGS) reaction via a direct CO2 dissociation mechanism. Combined experimental and density functional theory studies elucidate the cooperative roles of Pt species and Ov in promoting rWGS activity. LaCeOx activates CO2 through Ov-mediated adsorption, while Ptnc facilitates H2 dissociation and promotes CO* formation and desorption. This interfacial coupling accelerates rWGS kinetics while suppressing CO hydrogenation into CH4, thereby enabling high CO selectivity and enhanced durability at comparatively low temperatures relative to Pt nanoparticles supported on stoichiometric CeO2 (Ptnp/CeO2). These findings demonstrate the key role of catalyst dynamics and establish vacancy-modulated nanocluster–support interactions as a powerful design principle for the rWGS reaction.

The development of efficient electrocatalysts for the alkaline hydrogen evolution reaction (HER) remains a key challenge for hydrogen energy conversion. Here, we report a Cu‐substituted Ru nanoparticle catalyst in which atomically dispersed Cu (0.31 wt%) is substituted into Ru nanoparticles (3.54 wt%) supported on oxygen‐deficient ceria (Cu ₁ –Ru/CeO _x ). This catalyst exhibits outstanding alkaline HER performance, delivering a low overpotential of 47 mV at 10 mA cm ⁻² , a small Tafel slope of 43 mV dec ⁻¹ , and a high mass activity exceeding 3.0 , outperforming commercial Pt/C. The catalyst retains 95% of its initial activity after 100 h of continuous operation. Spectroscopic, structural, and DFT analyses reveal an asymmetric interfacial charge distribution: charge transfer from Cu to Ru generates electron‐rich Ru and electron‐deficient Cu ₁ , while electron donation from Ru to ceria forms Ce ³⁺ and oxygen vacancies. This tri‐functional interface enables efficient water dissociation at Ce ³⁺ –O _v sites, optimized hydroxyl adsorption/desorption on electron‐rich Ru, and weakened H binding on electron‐deficient Cu ₁ , thereby promoting H ₂ release. When paired with a RuO ₂ anode, the Cu ₁ –Ru/CeO _x (−)║RuO ₂ (+) electrolyzer surpasses Pt/C(−)║RuO ₂ (+) in full‐cell efficiency and long‐term stability, highlighting the importance of interfacial charge modulation and multi‐site cooperativity in alkaline HER catalysis.