Revealing Enhanced Size Uniformity of the Electrochemical Deposition of Palladium Nanoparticles via Single-Particle Dark-Field Scattering Imaging

Electrochemical deposition of palladium nanoparticles provides ligand-free surfaces that enhance the catalytic activity for various chemical reactions. However, achieving controllable density and uniform size distribution of electrodeposited palladium nanoparticles remains challenging due to the complexity of nucleation and growth mechanisms. In this study, we employ single-particle dark-field scattering microscopy to monitor the growth of thousands of palladium nanoparticles during electrochemical deposition in situ. The nanoparticle size is accurately determined using a calibration curve, correlating the scattering intensity with their sizes characterized by scanning electron microscopy. A dual-pulse sequence, consisting of a short pulse at −0.74 V vs Pt for nucleation and a long pulse at −0.21 V vs Pt for growth, enables the separation of nucleation and growth processes. The results of single-particle dark-field scattering microscopy demonstrate that the nucleation pulse controls nanoparticle density, while the growth pulse increases size and size uniformly over time. Growth exponent analysis reveals that smaller palladium nanoparticles grow faster than larger ones, resulting in a more homogeneous size distribution. This dual-pulse strategy offers a robust method for controlling nanoparticle density and achieving homogeneous size distribution, while dark-field scattering microscopy provides a noninvasive, high-accuracy approach for in situ size characterization with substantial statistics.