Ultrafine Ruthenium Nanoclusters Embedded in β-Ketoenamine Linked Nitrogen-Rich Covalent Organic Framework as a Stable Bifunctional Electrocatalyst for Overall Water Splitting

Developing robust and cost-effective bifunctional electrocatalysts is essential for advancing efficient overall water splitting. This study embodies a facile strategy for embedding ultrasmall ruthenium nanoclusters (Ru NC, size ∼ 1.25 nm) onto a chemically stable β-ketoenamine-linked covalent organic framework (TFG-TETA), forming RuNC/TFG-TETA. The interfacial crystallization of TFG and triethylenetetramine yields a highly porous COF with abundant nitrogen sites, enabling uniform dispersion and strong coordination of Ru NCs. Systematic variation of Ru loading revealed that an optimal 3.94 wt % Ru NC provided superior bifunctional electrocatalytic performance in alkaline media, requiring only 222 and 71 mV overpotential to achieve 10 mA cm –2 for the oxygen and hydrogen evolution reactions, respectively, while higher Ru loadings led to decreased activity. Enhanced performance is attributed to high surface area, strong metal–support interaction (Ru–N), and electronic modulation of Ru centers, as evidenced by XPS and XANES analyses. RuNC/TFG-TETA also delivers superior intrinsic activity and long-term durability over 40 h for both HER and OER. When applied as both anode and cathode, it achieves overall water splitting at a low cell voltage of 1.57 V at 10 mA cm –2 with sustained operation at higher current densities. This work presents a scalable method for fabricating COF-supported Ru nanoclusters and highlights their promise as efficient bifunctional catalysts for sustainable hydrogen production.