Operando Electrochemical Pump-Probe Spectroscopy for Resolving Electric Double Layer Formation Kinetics at Hydrogen Evolution Electrodes.

Nanoscale interfacial charge transfer regulates electrochemical kinetics via solid-liquid electric double layer (EDL) modulation on nanostructured electrodes. Direct probing of nanoscale charge dynamics remains limited by the lack of efficient operando techniques. Herein, we develop an electrochemical pump-probe spectroscopy platform to track transient nano-interfacial processes in real time. Featuring high spectral sensitivity and microsecond-to-millisecond resolution, this setup synchronously captures electrical and plasmonic signals to resolve charge relaxation and EDL dynamics of Au nanoparticle electrodes during hydrogen evolution. Correlated electrical and optical responses successfully decouple charge transport and accumulation in electrode and interfacial charge transfer on the electrode surface: the former is more closed to capacitive charging, while the latter is determined by ion diffusion. Such interfacial kinetics are precisely modulated by electrolyte concentration, applied bias, and cation hydration. This work elucidates intrinsic nanoscale EDL evolution under hydrogen evolution reaction (HER) conditions and provides a versatile operando tool for broad nanoelectrochemical studies.