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

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 Bi_xSn_y 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.