Unlocking Synergistic Electrothermal Catalysis on Defective Carbon for On-Demand Ammonia Production

Closing the anthropogenic nitrogen loop demands innovative technologies that can simultaneously remediate nitrate pollution and produce valuable ammonia (NH₃) in a decentralized and sustainable manner. Herein, we establish a metal-free catalytic framework for the nitrate reduction reaction (NO₃RR) by synergistically integrating vacancy-defect engineering with a mild electrothermal coupling strategy (<100 °C). The defective carbon nanotubes (d-CNTs) create localized electron-rich pockets that optimize the adsorption of NOx intermediates and facilitate proton-coupled electron transfer. Under electrothermal coupling at 50 °C, the d-CNTs achieve a Faradaic efficiency of 64.4% and an NH₃ yield rate of 2.54 mg h⁻¹ cm⁻² at a nitrate concentration of 10 mM. A combination of in situ spectroscopic techniques and density functional theory calculations unravels a dual-channel acceleration mechanism: defect-induced electronic redistribution enhances NO₃⁻ activation, while thermally promoted atomic hydrogen (H*) mediates the sequential hydrogenation steps. This synergy not only suppresses the competing hydrogen evolution but also enables remarkable stability over 20 cycles in simulated wastewater. Beyond the laboratory performance, we demonstrate a practical product recovery route via gas stripping and acid absorption, and a comparative life-cycle assessment confirms a >90% reduction in carbon footprint relative to conventional industrial routes. The significance of this work lies in the conceptual integration of defect engineering and electrothermal operation within a metal-free NO₃RR system, offering a generalizable strategy for low-carbon nitrate remediation and nitrogen valorization.