In our group, we focus on employing the 2nd order nonlinear optical spectroscopy, mostly vibraitonal sum frequency generation (SFG) to study various fundamental processes at the electrochemical interfaces. These include the adsorption of solvent and ions on the single crystal electrodes, the reaction intermediates for important electrochemical catalytic reactions (i.e. ORR, HER, electrochemical oxidation of small organic molecules), and also the structure of the charge carrier during the heterogeneous charge transfer processes (i.e. solvated electron, hydronium and anions). As a compensation of the optical probing method, we also detect the nonlinear electrical signal, i.e. photo current/voltage, that induced by two sequential ultra-shot laser pulses with desired frequencies for ultra-fast electrochemical processes.