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.