Unraveling Dynamic Structural Evolution of Single Atom Catalyst via In Situ Surface-Enhanced Infrared Absorption Spectroscopy

Metal–nitrogen-carbon (M–N-C) single-atom catalysts (SACs) have been widely applied in catalyzing electrochemical redox reactions. However, their long-term catalytic stabilities greatly limit their practical applications. This work investigates the dynamic evolution of two model Cu–N–C SACs with different Cu–N coordinations, namely the Cu1/Npyri-C and Cu1/Npyrr-C, in electrochemical CO reduction reaction (CORR), based on a collection of in situ characterizations including in situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy, in situ X-ray absorption spectroscopy, quasi-in situ electron paramagnetic resonance spectroscopy and in situ ultraviolet–visible spectroscopy, complemented by theoretical calculations. Our findings reveal that the Cu nanoparticle formation rate over Cu1/Npyrr-C is more than 6 times higher than that over Cu1/Npyri-C during the electrochemical CORR. Quasi-in situ electron paramagnetic resonance and in situ UV–vis spectroscopy measurements demonstrate that hydrogen radicals can be in situ produced during electrochemical CORR, which will attack the Cu–N bonds in the Cu–N–C SACs, causing leaching of Cu2+ followed by subsequent reduction to form Cu nanoparticles. Kinetic calculations show that Cu1/Npyri-C displays a better catalytic stability than Cu1/Npyrr-C resulting from the stronger Cu–Npyri bonds. This study deepens the understanding of the deactivation mechanism of SACs in electrochemical reactions and provides guidance for the design of next-generation SACs with enhanced durability.