Bi–Sn nanoparticles for electrochemical denitrification: activity and selectivity towards N2 formation

Abstract Electrochemical denitrification is a promising approach to remove NO3− towards its conversion to innocuous N2. In this work, the electrocatalytic performance of Bi, Sn and BixSny carbon-supported nanoparticles (∼10 nm) was evaluated for the selective NO3− electroreduction (NER) to N2. The different electrocatalysts were synthesised using a simple chemical method, physicochemically characterised by TEM-EDS and XPS and, subsequently, air-brushed onto a Toray carbon paper to build electrodes. These electrodes were characterised by SEM-EDS and cyclic voltammetry. Electrolyses were carried out in a slightly alkaline media to find the most active electrocatalyst towards the NO3− removal. Among them, Bi60Sn40/C showed the best results with more than 50% of selectivity to N2 after exhaustive electrolyses, regardless of the cathode potential or the electric charge passed. Other detected non-desired secondary products were N2O, NO2− and NH4+/NH3. The results obtained point out that the combination of Sn and Bi gives rise to higher NER activity and selectivity to N2 than pure Bi and pure Sn. Therefore, these electrocatalysts are not only promising but also cost-effective for future practical applications like electrochemical denitrification of wastewater. Nevertheless, further investigation is still needed in order to assess the optimum operational conditions.