Boosting NH3 production from nitrate electroreduction via electronic structure engineering of Fe3C nanoflakes

• Published in: Green chemistry : an international journal and green chemistry resource : GC 2021-10, Vol.23 (19), p.7594-7608
• Main Authors: Wang, Yuanyuan, Zhang, Linlin, Niu, Yongjian, Fang, Dong, Wang, Jiao, Su, Qingxiao, Wang, Cheng
• Format: Article
• Language: English
• Subjects: Adsorption; Ammonia; Catalysts; Cementite; Chemical reduction; Electron transfer; Electronic structure; Green chemistry; Iron; Iron carbides; Kinetics; Mitigation; Nitrate reduction; Nitrates; Nitrogen dioxide; Reaction kinetics; Reaction mechanisms; Selectivity; Volcanoes
• ISSN: 1463-9262; 1463-9270
• DOI: 10.1039/d1gc01913a

Clear structure–performance relationships are helpful for the design of efficient catalysts and the understanding of reaction mechanisms. The electrocatalytic nitrate reduction reaction (NO3RR) offers a sustainable route to ammonia (NH3) synthesis and nitrate mitigation. However, it suffers from poor nitrate adsorption, low NH3 selectivity and sluggish reaction kinetics. Herein, N-doped carbon nanosheets supported Fe3C nanoflakes featuring large surface areas (860.024 m2 g−1) were prepared. Their NO3RR performances showed volcano-like relationships with the Fe3+/Fe2+ ratios and d-band centers. At −0.5 V, the NH3 yield, faradaic efficiency, selectivity and current density reached 1.19 mmol h−1 mg−1, 96.7%, 79.0% and 85.6 mA cm−2, respectively, exceeding most reported results. Such exceptional performances mainly originated from the optimized electronic structures that boosted nitrate adsorption and reaction kinetics (Tafel slope: 56.7 mV dec−1). Mechanistic investigations revealed a NO3− → NO2− → NH3 reaction pathway with the chemical process following the fast electron transfer process as the rate-determining step.