Transient Plasmonic Imaging of Ion Migration on Single Nanoparticles and Insight for Double Layer Dynamics

Single-nanoparticle electrochemistry offers electrochemical behaviors of individual entities beyond the ensemble system. An electric double layer (EDL) exists on any charged particle-liquid interface because of counter-ion accumulation, while direct measuring of the interfacial ion migration remains a challenge. Herein, a plasmonic-based transient microscopic method, with a temporal resolution of 1-2 μs, was demonstrated to directly track the ion migration dynamics on single charged nanoparticles. We found that the dynamics of EDL formation might deviate significantly from the prediction made by using the classical resistance-capacitance (RC) model under nanoscale and transient conditions. Under ultrafast charging, due to the limit migration rate of ions in the solution, the actual time scale of the EDL formation could be up to 5 times slower than the predicted value from the RC model. We then proposed a new theoretical model to describe the transient dynamics of EDL formation. These results may expand our current knowledge about nano-electrochemistry and transient electrochemistry.