Electrooxidation, Size Stability, and Electrocatalytic Activity of 0.9 nm Diameter Gold Nanoclusters Coated with a Weak Stabilizer

Abstract

AbstractWe describe the electrooxidation and size stability of 0.9 nm average diameter triphenylphosphine monosulfonate (TPPS)‐stabilized Au nanoclusters (NCs) as compared to 1.6 nm tetrakis(hydroxymethyl)phosphonium chloride (THPC)‐stabilized Au NCs and 4.1 nm citrate (Cit)‐stabilized Au nanoparticles (NPs). The potential for oxidative dissolution in KBr follows the order of TPPS Au0.9nm NCs (0.219 V)<THPC Au1.6nm NCs (0.452 V)<Cit Au4.1nm NPs (0.723 V)<bulk Au (ca. 0.932 V), whereas that for surface Au oxide reduction follows the order of TPPS Au0.9nm NCs (0.607 V)<THPC Au1.6nm NCs (0.679 V)<Au4.1nm NPs (0.808 V) vs. Ag/AgCl. TPPS Au0.9nm NCs and Cit Au4.1nm NPs convert to larger aggregates by fusing together in acidic pH, whereas THPC Au1.6nm NCs are highly stable from pH 2.4 to 11. Exposure of TPPS Au0.9nm NCs to ozone causes considerable size increase within 1–2 minutes, similar to previous results on THPC Au1.6nm NCs. THPC Au1.6nm NCs are stable against oxidation after exchange of THPC with 1‐butanethiol, whereas TPPS Au0.9nm NCs dissolve into solution during exchange. TPPS Au0.9nm NCs are inactive for the hydrogen evolution reaction and CO2 reduction reaction, whereas THPC Au1.6nm NCs exhibit excellent activity. The differences in oxidation potential, size instability, and electrocatalytic activity are attributed to the Au size as opposed to the different ligands, whereas the pH‐induced aggregation depends on the acidic or basic nature of the stabilizing ligand.