Electrodeposition of Ni Rh Alloys and their Use as Cathodes for Nitrate Reduction in Alkaline Solutions

Compact Ni-Rh alloys are electrodeposited potentiostatically on rotating disk and sheet electrodes; film compositions are adjusted by varying bath composition and deposition potential E-dep. SEM images of these alloys show a compact, globular morphology for Rh contents up to 30 at%, and a smoother aspect for films with a medium-to-high content of Rh. XRD spectra show the formation of a single crystalline phase, with diffraction peaks in intermediate positions between those of the constituent elements. Data analysis indicates that crystal lattice parameters vary with composition according to Vegard's law. Linear voltammetries of nitrate reduction in alkali highlight a maximum of activity, in terms of reduction current, for alloys in the range of 10-30 at.% Rh. Prolonged electrolysis at appropriate potential performed with Ni85Rh15 alloy shows, in comparison with pure Ni and pure Rh: much increased activity and faster abatement of nitrate; lower production of the undesired nitrite species; higher selectivity towards production of ammonia.