The nature of chemisorbates formed from ammonia on gold and palladium electrodes as discerned from surface-enhanced Raman spectroscopy

The chemisorbates formed from ammonia-containing alkaline electrolyte on gold and palladium electrodes have been identified using surface-enhanced Raman spectroscopy (SERS). On gold, a potential-dependent band at ca. 365-385 cm(-1) is observed, consistent with the metal-nitrogen stretch for molecular adsorbed ammonia on the basis of the frequency redshift observed upon deuteration. A similar feature is also observed on palladium. at 440-455 cm(-1). again consistent with chemisorbed ammonia on the basis of the HID shift. On palladium. but not on gold, however. transfer of the electrode to ammonia-free electrolyte yielded a vibrational band at 455-465 cm(-1). The near-zero H/D frequency shift obtained for this irreversibly adsorbed component indicates the formation of chemisorbed atomic nitrogen on palladium. This finding is discussed in terms of the mechanism for ammonia electro-oxidation. (C) 2001 Elsevier Science B.V. All rights reserved.