Single-atom Fe engineered-PANI/AC/MXene composite flow electrode for sustainable water desalination and electroplating wastewater treatment

Developing high-performance flow electrodes is critical for advancing flow-electrode capacitive deionization (FCDI) toward practical water treatment. Here, we present a single-atom Fe engineered polyaniline/activated carbon/MXene (FeSA-PAM) composite electrode that achieves simultaneous brackish water desalination and treatment of real electroplating wastewater. Through advanced characterization including AC-TEM, XANES and EXAFS, we confirm that atomically dispersed Fe sites are anchored within the composite, serving as highly active centers which significantly enhance charge transfer kinetics and provide specific redox activity for Cr(VI) reduction. The optimized FeSA-PAM electrode delivers a high salt removal rate of 125 μg·cm$^{−2}$·min$^{−1}$ (60 % improvement over conventional AC electrode) and maintains exceptional Cr(VI) removal efficiency of 85–92 % across a broad concentration range (5–120 mg·L$^{−1}$), achieving drinking water standards (<0.01 mg·L$^{−1}$) with ultralow energy consumption (0.006–0.072 kWh·m$^{−3}$) and high charge efficiency (ca. 92 %). The removal mechanism involves synergistic effects of electrostatic adsorption, ion intercalation, and Fe-mediated reduction, while the electrode also enables effective chromium recovery (ca. ... mehr60 % in electrolyte phase). Techno-economic and environmental assessments confirm its cost-effectiveness (\$3.75 m$^{−3}$ treated water) and low carbon footprint (0.072 kg CO$_2$ m$^{−3}$), positioning FeSA-PAM as a scalable and environmentally sustainable flow electrode platform for water purification.