Mechanistic study of the nitric oxide reduction on a polycrystalline platinum electrode

A systematic study was performed to determine the mechanism of the nitric oxide (NO) reduction on polycrystalline platinum. Both the reduction of NO in the presence of NO in the solution and the reduction of adsorbed NO in a clean electrolyte have been investigated. The adsorbate reduction takes place through a combined proton-electron transfer in equilibrium followed by a rate-determining chemical step. NH3 is the only product in the absence of NO in solution. The reduction in the presence of NO in the solution at potentials between 0.4 and 0.8 V versus RHE yields N2O as the only product. The mechanism of this reaction is not of the Langmuir-Hinshelwood type, but rather involves the combination of a surface-bonded NO molecule with an NO molecule from the solution and a simultaneous electron transfer. A protonation has to take place prior to this step. In alkaline solutions a chemical step appears to be partially rate determining. The continuous reduction of NO at potentials lower than 0.4 V yields mainly NH3. The mechanism of this reaction is the same as for the adsorbate reduction. (C) 2001 Elsevier Science Ltd. All rights reserve

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