Ultrasmall Ruthenium Nanoclusters Anchored on Thiol-Functionalized Metal–Organic Framework as a Catalyst for the Oxygen Evolution Reaction

The rational design of an efficient nanocatalyst is pivotal for catalyzing kinetically sluggish oxygen evolution reaction (OER). However, the uncontrolled nucleation and growth of nanostructures present significant challenges in the effectiveness and economic viability of implementing noble metal-based electrocatalysts. Functionalized metal–organic frameworks (MOFs) exhibit properties that can stabilize unstable nanoclusters in extremely small sizes by mitigating issues related to high surface energy and Ostwald’s ripening effect. In this study, we present the synthesis of ultrasmall Ruthenium nanoclusters stabilized through a thiol-functionalized Ni-MOF (RuNC/Ni-M-SH). The stabilization of ruthenium under reduced conditions on the MOF surface is facilitated by the lower electronegativity and increased orbital overlapping effect of sulfur, resulting in an average size of 1.5 nm. X-ray photoelectron spectroscopy and X-ray absorption spectroscopy studies confirm a perturbed electronic structure, providing a fundamental understanding of electronic redistribution. With this favorable electronic structure, the catalytic OER activity of RuNC/Ni-M-SH surpasses that of the state-of-the-art RuO₂, exhibiting a 3-fold increase in current density (242 mA cm^–2) and a 82 mV reduced overpotential. Furthermore, in situ FTIR and Raman analyses were performed to analyze the catalytically active sites and intermediates. With 95% faradaic efficiency, the turnover frequency (TOF) and mass activity of RuNC/Ni-M-SH are several orders of magnitude higher than RuO₂. Remarkably, unlike other Ru-based catalysts, RuNC/Ni-M-SH demonstrates exceptional high stability, as evidenced by over 24 h of chronoamperometry study. These attributes of RuNC/Ni-M-SH established it as an economically sustainable OER electrocatalyst.