Cr-Doped FeC 2 O 4 Microrods Formed Directly on AISI 420 Stainless Steel to Enhance Electrochemical NO 3- Reduction to N 2 at Circumneutral pH.

We synthesized low-cost cathodes for use in the electrochemical NO ₃ ^- reduction reaction (NO ₃ RR) via the simple reconstruction of AISI 420 stainless steel (SS). Thermochemical treatment of the SS in oxalic acid generated iron oxalate (FeC ₂ O ₄ ) microrods (BL-SS), with further anodization affording Cr-doped Fe ₂ O ₃ (R-SS) or FeC ₂ O ₄ (G-SS). G-SS displayed supreme N ₂ selectivity during galvanostatic electrolysis at circumneutral pH. Electroanalysis and descriptor/scavenger analysis indicated that Fe sites were the primary active sites of NO ₃ ^- adsorption, with C ₂ O ₄ ^2- as the H-binding sites. The C ₂ O ₄ ^2- ligands and Cr dopants altered the electronic structures of the Fe sites. A parametric study of the current density, pH, [NO ₃ ^- ] ₀ , and [Cl ^- ] ₀ indicated an Eley-Rideal N ₂ generation mechanism, with NO ₂ ^- as an intermediate. Cl ^- elevated the N ₂ selectivity but reduced the NO ₃ RR efficiency. To demonstrate the practical applicability of G-SS with a proposed regeneration strategy, its durability was examined in synthetic and real wastewater matrices. Compared with that in synthetic wastewater, G-SS displayed more stable performance in real wastewater owing to the natural buffering capacity at the cathode, which reduced the corrosion rate. Cr-doped FeC ₂ O ₄ is viable for use in the low-cost, efficient electrochemical treatment of wastewater containing NO ₃ ^- .