Attachment of molecular catalysts onto semiconductor or metal electrodes is a promising approach for rational design of efficient photoelectrochemical cells for solar water splitting and CO₂ reduction. The understanding and improvement of such devices requires fundamental understanding of the structure and dynamics of catalysts as well as the interfacial electrolyte environment at electrode-liquid interfaces. Vibrational sum frequency generation (VSFG) spectroscopy is an in situ interface specific technique for probing interfacial properties at the semiconductor electrode/electrolyte interface at the molecular level. In this talk, we discuss our recent efforts in developing and applying in situ time-resolved VSFG for studying structural and dynamics of rhenium bipyridyl and other molecular CO₂ reduction catalysts on semiconductor and metal electrodes. We have shown that by combining VSFG experiment with advanced computational modeling, catalyst adsorption geometry can be determined; through electrochemical Stark effect, local electric field and the potential profile in the electric double layer under light and dark conditions can be directly measured; using VSFG as a time-dependent probe, the interfacial charge transfer dynamics can be directly measured and key reactive intermediates can be identified.