ИСТИНА

The process of nitrate electroreduction is attractive to researchers due to scientific (study of a multistage reaction, interest towards intermediates) and practical (water treatment) aspects. NO is one of the key intermediates in nitrate electroreduction. The electrochemical behaviour of NO on platinum electrodes represents an important part of the electrochemistry of nitrogen–containing compounds. The use of single crystal Pt electrodes with well-defined surfaces of different orientation allows establishing correlations between the structure of adsorption sites and their reactivity towards NO electroreduction that is characterized by strong adsorption on electrode surfaces. Previously, redox transformations of pre-adsorbed saturated NO layers were studied on different Pt(hkl) electrodes. In typical cyclic voltammograms of Pt(111) covered with a saturated NO adlayer, the potential sweep in the negative direction down to 0.05 V leads to reduction of the whole NO adlayer to NH4+. NH4+ is displaced by hydrogen adsorption, and the successive voltammetric cycle is nearly identical to that recorded on a clean Pt(111) electrode in the absence of NO. The potential sweep in the positive direction up to 1.10 V leads to oxidation of NOads to (NO2−)ads. As opposed to complete NO adlayer stripping, partial reduction of compact NO adlayers was studied in sufficient detail only for Pt(100) surfaces, but is as yet not described for the (111) plane. Partial reduction of NOads occurs in the course of a slow potential sweep to Ecat > 0.05 V. The further CVs recorded in the range, where no further NOads reduction occurs, display a new pair of stable redox peaks at ~0.6 V. These peaks are attributed to redox transformations between NH4+ (or NH3,ads) and intermediate (NxOyHz)ads species. The nature of NxOyHz on Pt(111) is under debate, though in the case of Pt(100) it was attributed to NOads. The pair of peaks at 0.72 V appears after reduction of a yet larger fraction of NOads and is attributed to adsorption/desorption of OH-species. Additional experiments are performed on stepped Pt(hkl) electrodes with (111) terraces and (111) or (100) steps. The increase in the concentration of the steps leads to a decrease in the intensity of the NH3,ads ↔ (NxOyHz)ads redox process, indicating that this process occurs on the (111) terraces. The nature of steps also plays a role in NH3,ads ↔ (NxOyHz)ads transformations: the intensity of this process is higher on stepped Pt electrodes with (100) steps. In our presentation we will attempt to elucidate the origin of this redox process.