Single-Particle Insight into the Compression of Electrocatalytic Activity Distributions during Catalyst Poisoning

Electrocatalyst degradation is a major limitation in sustainable energy conversion, yet nanoscale insight into the interfacial processes governing activity and stability remain poorly understood. Here, controlled molecular poisoning is used as a perturbation to probe how surface blocking alters catalytic behavior across a population of gold nanoparticles. Specifically, we investigate inner-sphere 4-nitrophenol electroreduction on citrate-stabilized gold nanoparticles and use 6-mercaptohexanoic acid to progressively deactivate the gold surface. In macroscopic measurements, poisoning appears only as an average attenuation of current and does not reveal how catalytic activity is distributed. Single-particle measurements address this limitation by resolving catalytic turnover at the level of individual nanoparticles. Upon thiol exposure, increasing the 6-mercaptohexanoic acid concentration from 20 to 100 nM progressively shifts the nanoparticle population toward lower turnover per particle and a narrower activity distribution. Complementary Surface Enhanced Raman Spectroscopy and electrochemical stripping measurements verified surface-bound thiol formation, increasing poison coverage, and evolution of the Au-thiolate interfacial environment. Together, these results demonstrate that molecular poisoning redistributes catalytic activity nonuniformly across the nanoparticle population by compressing the accessible turnover range while increasing relative heterogeneity among the remaining active particles. More broadly, these findings establish nanoelectrochemistry as a direct tool for probing the nanoscale evolution of catalyst deactivation and activity heterogeneity, within experimentally accessible time scales.