Effect of surface functionalization of Fe₃O₄ nano-enabled electrodes on the electrochemical reduction of nitrate

Nitrate is a noxious and persistent oxyanion in drinking waters. It is themed as one of the most common water quality violations worldwide. Nitrate electrocatalytic reduction appears to be a viable solution. However, the use of platinum group elements (PGEs) as electrocatalysts must be avoided due to their high cost and limited availability. In this study, earth-abundant nano-Fe₃O₄ electrodes were synthesized to surpass those implementation barriers. Surface functionalization has demonstrated to impact performance of inner sphere catalytic transformations but has been seldomly explored in the context of nitrate remediation. To understand the effect of the functionalization of Fe₃O₄ surfaces, Fe₃O₄ nano-enabled electrodes were functionalized with amine and carboxylic acids groups. After 360 min, the most promising results were obtained when the Fe₃O₄ surface was modified with carboxylic groups. The nitrate conversion obtained was ∼ 90%, selectivity towards ammonia of ∼ 55% and an electric energy per order (EE/O) of 37 kWh m⁻³ order⁻¹. This EE/O value is ∼ 2× lower, when compared to an experiment using a bare Fe-plate. Therefore, nano-Fe₃O₄ electrodes hold the potential of providing a green resource recovery process to treat nitrate pollution while recovering ammonia for its reuse as enriched water for crops irrigation.