In Situ Surface-Enhanced Raman Spectroscopy of the Electrochemical Reduction of Carbon Dioxide on Silver with 3,5-Diamino-1,2,4-Triazole

The influence of 3,5-diamino-1,2,4-triazole (DAT) on the electrochemical reduction of carbon dioxide to carbon monoxide on a silver electrode was studied via in situ surface-enhanced Raman spectroscopy (SERS). SERS bands obtained in the absence of DAT indicate potential-dependent adsorption of the CO product to bridge and 3-fold hollow sites. With the addition of DAT, CO adsorption to less-coordinated surface sites was found, including a physisorbed or noncoordinating site that exhibited no significant Stark vibrational shift. Raman peaks associated with adsorbed DAT observed at the same potentials as this species suggest that the ligand promotes weaker CO adsorption, which may be responsible for the high efficiency of the AgDAT catalyst. The observation of potential-dependent methylene stretching vibrations indicates the presence of surface hydrocarbon species while the presence of C-D stretches in deuterated electrolyte confirm that these hydrocarbons are generated as a CO2 reduction byproduct.