Electrochemical reactions, especially electrocatalysis, involve complicated and rapid processes of proton-coupled electron transfer. However, conventional ensemble measurements can hardly allow insights into ultrafast surface and interface interactions. The urgent need for the development of in situ characterization techniques with high spatial and time resolution would offer great opportunities to an understanding and guidance of materials designing. We are developing in situ electrochemical molecular probes and demonstrating one can measure catalytic kinetic rates of individual active sites with high accuracy. This emerging technique is being coupled with other spectroscopies to permit more important quantitative information associated to electrocatalysis and materials chemistry.