Mechanism of nitrate electroreduction on Pt(100)

Kinetics and mechanism of nitrate anion reduction on the Pt(100) electrode in perchloric and sulfuric acid solutions are studied. Analysis of the results of electrochemical measurements (combination of potentiostatic treatment and cyclic voltammetry) and the data of in situ IR spectroscopy allow suggesting the following scheme of the nitrate reduction process on Pt(100) differing from that in the literature. If the potential of 0.85 V is chosen as the starting potential for a clean flame-annealed electrode surface and negativegoing (cathodic) potential sweep is applied, then an NO adlayer with the coverage of about 0.5 monolayer is formed on Pt(100) in the nitrate solution already at 0.6 V. The further decrease in the potential results in NO reduction to hydroxylamine or/and ammonia, desorbing products vacate the adsorption sites for nitrate and hydrogen adatoms. At E < 0.1 V, adsorbed hydrogen is mostly present on the surface. During positive-going (anodic) potential sweep, the process of nitrate reduction starts after partial hydrogen desorption, the cathodic peak of nitrate reduction to hydroxylamine or ammonia is observed at 0.32 V on cyclic voltammograms. The process of nitrate anion reduction continues up to 0.7 V; at higher potentials, the surface redox process with participation of hydroxylamine or ammonia (the anodic peak at 0.78 V) and nitrate (the cathodic peak at 0.74 V is due to nitrate reduction to NO on the vacant adsorption sites) occurs.