Seongbeen Kim

The development of active and durable acidic oxygen evolution reaction (OER) electrocatalysts is crucial for the commercialization of proton exchange membrane water electrolyzers (PEMWEs). Herein, we report a Ru‐substituted spinel Co ₂ MnO ₄ electrocatalyst (RuMnO), in which surface Co atoms are selectively replaced by Ru. This modification simultaneously tunes the reaction mechanism and interfacial water dynamics, synergistically enhancing OER kinetics. The formation of a short Ru─Ru bond length creates dual metal active sites that promote direct ^* OO ^* radical coupling, bypassing the conventional ^* OOH intermediate and suppressing lattice oxygen vacancy formation. Moreover, Ru substitution increases the fraction of free water molecules at the catalyst‐electrolyte interface, significantly accelerating the overall reaction kinetics. As a result, RuMnO achieves a low overpotential of 278 mV at 50 mA cm ⁻² and exhibits remarkable long‐term stability for 2500 h. Combined experimental and theoretical analyses reveal that RuMnO favors the oxide path mechanism (OPM) while simultaneously promoting the formation of interfacial free water. This study highlights the critical role of concurrently engineering the reaction mechanism and interfacial water dynamics to overcome the intrinsic limitations of acidic OER catalysis.

Designing catalysts that maximize both atomic efficiency and catalytic activity remains a central challenge in heterogeneous catalysis. While single-atom catalysts maximize noble metal utilization, their isolated structure limits the adsorption configurations of adsorbates, thereby diminishing their catalytic efficiency. We present a versatile platform based on atom-layer neighbors, where the proximity of Ru ensembles diversifies adsorption configurations while simultaneously enhancing adsorbate binding through ligand effects. By leveraging molecular interactions and strong metal-support interactions, we thermodynamically stabilize atomically thin structures comprising only a few Ru atoms, allowing the synthesis of size-tuned Ru atom-layer neighbors on WC _x supports. The optimized *H binding on size-tuned Ru ensembles, combined with *OH enrichment on WC _x supports, leads to competitive activity per unit noble metal cost in anion-exchange membrane water electrolyzers. Notably, our catalyst achieves the DOE 2026 performance target for PEMWE even at a lower temperature of 60 °C, with a Ru loading of 0.100 mg cm ⁻² , below the DOE’s ultimate noble metal loading threshold. This atom-layer neighbor platform offers a general strategy for enhancing catalyst efficiency while maintaining high noble metal utilization.

Dynamically stable oxidized surface states of sub-nanometer Ru clusters enhance interfacial hydrogen-bond connectivity, thereby enabling highly efficient alkaline water electrolysis.

Photoelectrochemical (PEC) performance of conventional 2D transition metal dichalcogenides (TMDs) in hydrogen evolution reaction (HER) is constrained by the limited selection of metal cations, predominantly MoS ₂ , whose inert basal planes and unstable 1T phases hinder PEC efficiency. High‐entropy TMDs, in which local lattice distortion and charge redistribution occur within a van der Waals layered structure, are expected to overcome these intrinsic limitations by improving catalytic activity, photocarrier dynamics, and phase stability. Here, we demonstrate a wafer‐scale 2D high‐entropy (MoWTaNbRu)S ₂ thin‐film catalyst with distorted 1T phase on p ‐Si photocathode for PEC‐HER. The high‐entropy effect induces substantial electronic redistribution, enhancing the contribution of d ‐orbitals near the Fermi level and optimizing hydrogen adsorption energetics. PEC kinetic analyses, including intensity‐modulated photocurrent spectroscopy, demonstrate that (MoWTaNbRu)S ₂ markedly suppresses the recombination of photogenerated charge carriers, enabling more efficient charge extraction and accelerated interfacial reaction kinetics. Furthermore, the high‐entropy‐driven stabilization of the metastable 1T phase ensures excellent durability of the photocathode. As a result, the (MoWTaNbRu)S ₂ /TiO ₂ / p ‐Si photocathode shows a remarkable photocurrent density and stability for over 100 h, outperforming single‐metal TMDs. This study demonstrates how configurational entropy enhances catalytic activity, photocarrier transport, and phase stability of TMDs, establishing a general design principle for next‐generation PEC catalysts.

Samples obtained via self-assembly-assisted dynamic placement exhibited outstanding mass activity among state-of-the-art AEMWE electrocatalysts.