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 reduction reaction (NORR) via the simple reconstruction of AISI 420 stainless steel (SS). Thermochemical treatment of the SS in oxalic acid generated iron oxalate (FeCO) microrods (BL-SS), with further anodization affording Cr-doped FeO (R-SS) or FeCO (G-SS). G-SS displayed supreme N selectivity during galvanostatic electrolysis at circumneutral pH. Electroanalysis and descriptor/scavenger analysis indicated that Fe sites were the primary active sites of NO adsorption, with CO as the H-binding sites. The CO ligands and Cr dopants altered the electronic structures of the Fe sites. A parametric study of the current density, pH, [NO], and [Cl] indicated an Eley-Rideal N generation mechanism, with NO as an intermediate. Cl elevated the N selectivity but reduced the NORR 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 FeCO is viable for use in the low-cost, efficient electrochemical treatment of wastewater containing NO.