From silver nanoparticles to nanoclusters: enhanced oxygen evolution electrocatalysis through size reduction

Metal nanoclusters (MNCs) have attracted significant attention as emerging catalytic materials due to their ultrasmall size, discrete electronic states, high surface-to-volume ratio, and abundance of accessible active sites. MNCs are promising candidates for a wide range of catalytic applications; however, their application toward the oxygen evolution reaction (OER), a kinetically demanding half-reaction in water splitting, remains relatively less explored. In this work, fluorescent silver nanoclusters stabilized with L-Proline (L-Pro-AgNCs) that show blue fluorescence have been synthesized and systematically investigated as electrocatalysts for OER in alkaline medium. The electrocatalytic performance of L-Pro-AgNCs has been compared with that of larger silver nanoparticles (L-Pro-AgNPs) and commercial RuO₂ catalysts. The synthesized L-Pro-AgNCs exhibit superior OER activity with a low overpotential of ∼250 mV at 10 mA cm^-2 and a smaller Tafel slope of 116 mV dec^-1, outperforming L-Pro-AgNPs and RuO₂. Cyclic voltammetry (CV) studies revealed a larger electrochemically active surface area and improved charge-storage capability for L-Pro-AgNCs, while electrochemical impedance spectroscopy confirms faster interfacial electron-transfer kinetics with a low charge-transfer resistance of ∼0.56 Ω. Furthermore, chronoamperometric measurements demonstrate excellent stability over 16 h under alkaline conditions. This study highlights the strong size-dependent electrocatalytic advantages of silver nanoclusters and establishes them as efficient and stable catalysts for oxygen evolution reaction and sustainable energy conversion applications.