Cr-Doped Fec2o4 Micro-Rods Directly Grown on Aisi 420 Stainless Steel for Enhanced Electrochemical Nitrate Reduction to N2 at Circum-Neutral Ph

Abstract

We synthesized low-cost cathodes for electrochemical NO3- reduction reaction (NO3RR) by simple reconstruction of AISI 420 stainless steel (SS). Specifically, thermochemical treatment of SS in oxalic acid generated FeC2O4 micro-rods (BL-SS), which further anodization afforded Cr3+-doped FeOOH (R-SS) or Cr3+-doped FeC2O4 (G-SS). G-SS displayed supreme N2 selectivity during galvanostatic electrolysis at circum-neutral pH. Electroanalysis and the experimental descriptor (Fe valency) effects indicated Fe2+/3+ as the primary active site for NO3- adsorption and C2O42- as the proton-binding site. The oxalate ligands and Cr dopants altered the electronic structure of the Fe-sites. Parametric study of the current density, pH, [NO3-]0, and [Cl-]0 indicated an Eley-Rideal N2 generation mechanism with NO2- as the intermediate. The chloride ion elevated N2 selectivity but reduced NO3RR efficiency. To demonstrate the practical applicability of G-SS with the proposed revivification strategy, its durability was examined in synthetic and real wastewater matrices. Compared with the repetition results using synthetic wastewater, G-SS showed a more stable performance in the real wastewater matrix, owing to the natural buffering capacity at the cathode, which reduced the corrosion rate. Overall, Cr-doped FeC2O4 is feasible for the low-cost and efficient electrochemical treatment of wastewater-containing NO3-.

Keywords: Electrochemical nitrate reduction, stainless steel, Cr-doped FeC2O4, N2 selectivity, Wastewater treatment