Hydroxylamine electrochemistry at low-index single-crystal platinum electrodes in acidic media

The electrochemistry of hydroxylamine at low-index single-crystal platinum electrodes in acidic media has been studied by voltammetry and in-situ FTIRRAS. Hydroxylamine (HAM) reactivity at platinum is largely controlled by interaction of the other components of the solution or products of the HAM partial oxidation with the electrode surface. Reduction of HAM is a structure-sensitive reaction, at least through the structure sensitivity of the hydrogen adsorption on platinum. No formation of gaseous products was detected in the potential region corresponding to the H-upd region on Pt(l I I) and Pt(l 10). Voltammetric and spectroscopic data point to adsorbed nitric oxide (NO) as the main stable intermediate of the HAM oxidation. Being electrochemically stable in a wide potential region between ca. 0.5 and 0.8 V, adsorbed NO acts as a poison for further oxidation of HAM. The HAM oxidation to NO appears to be a structure-insensitive process, though somewhat affected by the anion coadsorption. The Tafel slope analysis suggests the second electron transfer to be the rate-determining step in HAM oxidation to adsorbed NO. The mechanism of the HAM oxidation to NOads proposed here is consistent with the mechanism of the NOads reduction we have proposed elsewhere. Voltammetric data for all three low-index surfaces indicates the possibility of the HAM reduction and oxidation (at moderate potentials) to occur simultaneously. This fact may be tentatively explained by the existence of an intermediate, which appears both in the reduction and oxidation process. Accordingly, the reduction of HAM would be activated by a dehydrogenation step.