Surface Engineering of Hydrophobic Ag-Polyhedral Nanocrystals for Electrochemical Water Splitting

Electrochemical water splitting is fundamentally constrained by the sluggish kinetics of the oxygen evolution reaction (OER), which is a counter reaction at the anode that occurs along with the hydrogen evolution reaction (HER) at the cathode. Noble-metal oxides, such as IrO2 and RuO2, exhibit exceptional catalytic efficiency and are considered benchmark catalysts for the OER; nevertheless, their scarcity and high cost limit their widespread industrial application in water electrolysis, motivating the development of alternative electrocatalysts. Here, we report a strategy for synthesizing highly monodisperse, well-faceted polyhedral silver (Ag0) nanocrystals via a facile heating method with a controlled high heating rate. In contrast, conventional heating rates lead to irregular morphologies and ill-defined particle shapes. The silver (Ag0) polyhedral nanocrystals were further systematically surface functionalized using hydrophobic thiol, carboxylate, hydroxide, and sulfide-based ligands with different steric hindrance, binding strength, and polarity, which enable precise modulation of the local electronic structure, interfacial charge accumulation, and electrochemically accessible active sites to assess how the electrochemical OER behavior of Ag0 nanocrystal varies with the surface chemistry of Ag0 polyhedra. It was found that the sulfide-based surface ligands on Ag0 nanocrystals exhibit significantly enhanced OER activity, together with improved operational stability during the electrocatalysis, in comparison to the pristine oleylamine-capped hydrophobic Ag0 counterparts. In contrast, when the same strategy was extended to the HER using differently surface-functionalized Ag0 polyhedral nanocrystals, the hydrophobic thiol-functionalized Ag0 nanocrystals outperformed those capped with other surface ligands, exhibiting a trend completely different from that observed for the OER. Correlating surface chemistry with electrochemical metrics reveals a clear impact of the nanocrystals’ surface nature on electrochemical activity, demonstrating how ligand-induced interfacial engineering can overcome the intrinsic activity limitations of hydrophobic silver nanoparticles. This work presents a generalizable design framework for surface-engineering cost-effective Ag0-based nanocatalysts through molecular-level surface control and consequent advancement of their viability for high-performance electrochemical water-splitting applications.