Fluidic MXene Electrode Functionalized with Iron Single Atoms for Selective Electrocatalytic Nitrate Transformation...

The growth of renewable energy industries and the ongoing need for fertilizer in agriculture have created a need for sustainable production of ammonia (NH₃) using low-cost, environment-friendly techniques. The electrocatalytic nitrate (NO₃^-) reduction reaction (NO₃RR) has the potential to improve both the management of environmental nitrogen and the recycling of synthetic nutrients. However, NO₃RR is frequently hindered by the incomplete NO₃^- conversion, sluggish reaction kinetics, and suppression of the hydrogen evolution reaction (HER). Inspired by specific local electronic structures that are adjustable for single-atom catalysts, this work presents a nanohybrid electrocatalytic filter with iron single atoms (FeSA) immobilized on MXene. The fabricated FeSA/MXene filter exhibited maximum NH₃ Faradaic efficiency and selectivity (82.9 and 99.2%, respectively) that were higher than those for filters made of Fe nanoparticles anchored on MXene (FeNP/MXene) (69.2 and 81.3%, respectively) and MXene alone (32.8 and 52.4%, respectively), measured at an initial pH of 7 and an applied potential of -1.4 V vs Ag/AgCl. Density functional theory calculations revealed that, compared to the FeNP/MXene filter, the FeSA/MXene filter prevented the competition from the HER and reduced the activation energy of the potential-limiting step (*NO to *NHO) that made the NH₃ synthesis thermodynamically favorable . This work highlights an alternative strategy for achieving a synergistic NO₃^- removal and nutrient recovery with durable catalytic activity and stability.