Electrocatalytic reduction of Nitrate on copper single crystals in acidic and alkaline solutions.

Nitrate reduction on Cu (100) and Cu (111) surfaces in alkaline and acidic solutions was studied by electrochemical methods (cyclic voltammetry, rotating disc electrode) coupled with online and in situ characterization techniques (mass spectrometry, ion chromatography and Fourier transformed infra-red spectroscopy) to evaluate the reaction mechanism and products on the different surfaces. Electrochemical results show that reduction of nitrate in alkaline media on Cu is structure sensitive. The onset potential on Cu (100) is +0.1 V vs. RHE, ca. 50 mV earlier than on Cu (111). The onset potentials for nitrate reduction on Cu (100) and Cu (111) in acidic media are rather similar. Analytical techniques show a diverse product distribution for both surfaces and for both electrolytes. Whereas in acidic media both Cu electrodes show the formation of NO and ammonia, in alkaline media Cu reduces nitrate to nitrite and further to hydroxylamine. In alkaline media, Cu (100) is a more active surface for the formation of hydroxylamine than Cu (111).