Stabilizing ruthenium atom layer neighbors through molecular and metal support interactions for water electrolyzers

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.