Deciphering Site-Specific Kinetics on Shaped Pd Nanocrystals via Single-Particle Electrocatalysis

Particle size plays a critical role in governing catalytic activity and selectivity due to the distinct behaviors of different surface sites. However, direct experimental probing of site-specific electrocatalytic activity remains formidably challenging. Here, we employ a correlated scanning electrochemical cell microscopy-transmission electron microscopy (SECCM-TEM) approach to precisely analyze the intrinsic electrocatalytic activities of specific surface atoms (edge versus plane) on individual palladium nanocubes down to 8 nm, using the hydrogen evolution reaction (HER) as a model process. Our measurements reveal that the edge sites exhibit a HER turnover frequency approximately four times higher than that of (100) plane sites. Density functional theory calculations and additional single-particle studies of edge-covered Pd-Au nanocubes further confirm the pivotal role of edge atoms in catalysis. This SECCM-TEM methodology provides unambiguous insights into the distinct catalytic properties of edge and plane sites and can be extended to decipher catalytic active sites in more structurally complex electrocatalysts.