Electrochemical Oxidation of Nitrogen towards Direct Nitrate Production on Spinel Oxides

Abstract

Nitrates are widely used as fertilizer and oxidizing agents. Commercial nitrate production from nitrogen involves high‐temperature‐high‐pressure multi‐step processes. Therefore, an alternative nitrate production method under ambient environment is of importance. Herein, an electrochemical nitrogen oxidation reaction (NOR) approach is developed to produce nitrate catalyzed by ZnFexCo2−xO4 spinel oxides. Theoretical and experimental results show Fe aids the formation of the first N−O bond on the *N site, while high oxidation state Co assists in stabilizing the absorbed OH− for the generation of the second and third N−O bonds. Owing to the concerted catalysis, the ZnFe0.4Co1.6O4 oxide demonstrates the highest nitrate production rate of 130±12 μmol h−1 gMO−1 at an applied potential of 1.6 V versus the reversible hydrogen electrode (RHE).

Electrochemical oxidation of molecular nitrogen to nitric acid – towards a molecular level understanding of the challenges

“…20 Recently, a few experimental reports emerged suggesting Pd-decorated MXenes and several oxides as potential electrocatalysts for nitrogen oxidative xation. [21][22][23][24] Fig. 1 Equations showing how nitric acid is manufactured on industrial scale by combining steam reforming, Haber-Bosch and Ostwald processes.…”

Protagonists and spectators during photocatalytic solar water splitting with SrTaOxNy oxynitride

“…This superficial CoO(OH) enriched surface layer has a beneficial effect on the OER for the oxides. 55,62 However, in the presence of surface nitrogen based species, the stabilised CoO(OH) contribute to both the NOR and OER. 62 Kato and Kudo 63 looked at numerous tantalate oxide photocatalysts, and the authors observed nitrate reduction under UV irradiation in an aqueous environment.…”

Rational design on photo(electro)catalysts for artificial nitrogen looping

“…The porous structure makes WO 3 to have more suspended bonds, activating high‐energy electrons to stimulate N≡N triple bond ( Figure 8A ) 117 . ZnFe x Co 2− x O 4 spinel oxides were also utilized as catalysts to carry out electrocatalytic NOR, 123 which achieved the direct synthesis of nitrate with high yield (130 ± 12 μmol/hr/g MO at 1.6 V vs RHE) by iron catalysts (Figure 8B,C). Besides, modified MXene electrocatalysts have also been utilized as electrocatalyst for NOR, which achieved 2.80 μg/hr/mg cat yield of nitrate (Figure 8D).…”

“…C, Relative energy diagram of NOR processes on ZnFe x Co 2‐ x O 4 spinel oxides ( x = 0, 0.4, and 2). Reproduced with permission: Copyright 2020, Wiley‐VCH 123 . D, Scanning electron microscopy, transmission electron microscopy, and high‐resolution transmission electron microscopy images of prepared Pd‐MXene, respectively.…”