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Herein I describe Vibrational Sum Frequency Generation, a non-linear spectroscopy with vibrational specificity and high sensitivity for buried interfaces. I describe work to extend Vibration Sum Frequency Generation to electrochemical interfaces using Surface Plasmon Resonance. Using this method, I can detect molecules across the vibrational region at current densities greater than 1 mA/cm2 and with detection limits as low as 1% of a monolayer. During carbon dioxide reduction on gold electrodes I observe atop CO, a surface intermediate. Using Stark spectroscopy of the CO intermediate I measure the potential dependent interfacial electric field. I also prescribe a way to account for dipole-dipole and third order contributions to the SFG signal and comment on potential dependent intensity and coverage changes. Correlations between Stark field measurements and the SFG Intensity reveal potential dependent changes to the double layer structure that favor carbon dioxide reduction. I find that cite blocking by electrolyte cations lowers the steady state coverage of CO, but that its presence increases carbon dioxide reduction activity. Stark spectroscopy of several cations reveals that the increase in activity is not related to the magnitude of the interfacial electric field but is instead related to specific interactions of the hydrated cations with intermediates. Preliminary measurements of interfacial water also show differences between cations, which may corroborate these findings.