Soil to society: Red-mud-derived iron oxide electrocatalysts for circular nitrogen upcycling via green ammonia production

Abstract

Red mud (bauxite residue) is a hazardous industrial solid waste generated in massive quantities by the alumina industry and is heavily enriched with iron oxides. Here we report a waste-to-wealth strategy for fabricating phase-controlled iron oxide electrocatalysts from red-mud/soil waste via a coordination-mediated tannic-acid route. Fe₂O₃ and Fe₃O₄ were selectively produced as a proof of concept, enabling sustainable upcycling of waste iron into value-added catalytic materials. On the other hand, nitrate (NO₃⁻) pollution in water bodies is a major environmental and public-health concern, whereas ammonia (NH₃) is indispensable for agriculture and emerging energy technologies. Electrochemical nitrate reduction to ammonia provides a sustainable route to close this nitrogen loop but is limited by the scarcity of efficient and scalable catalysts. The Fe₂O₃@C-TA catalyst achieves an ammonia production rate of 7.34 mg h⁻¹ cm⁻², which places it among the high-performing catalysts reported to date. These results identify the iron oxidation state and surface chemistry as decisive factors governing nitrate-to-ammonia conversion. This work establishes a scalable circular nitrogen-upcycling platform that transforms hazardous waste into functional electrocatalysts while enabling simultaneous water remediation and sustainable ammonia regeneration.