In Situ Growth of Fe₂O₃ Nanorod Arrays on Carbon Cloth with Rapid Charge Transfer for Efficient Nitrate Electroreduction to Ammonia

Abstract

Electrochemical reduction of nitrate to ammonia (NH3), a green NH3 production route upon combining with renewable energy sources, is an appealing and alternative method to the Haber–Bosch process. However, this process not only involves the complicated eight-electron reduction to transform nitrate into various nitrogen products but simultaneously suffers from the competitive hydrogen evolution reaction, challenged by a lack of efficient catalysts. Herein, the in situ growth of Fe2O3 nanorod arrays on carbon cloth (Fe2O3 NRs/CC) is reported to exhibit a high NH3 yield rate of 328.17 μmol h–1 cm–2 at −0.9 V versus RHE, outperforming most of the reported Fe catalysts. An in situ growth strategy provides massive exposed active sites and a fast electron-transport channel between the carbon cloth and Fe2O3, which accelerates the charge-transport rate and facilitates the conversion of nitrate to NH3. In situ Raman spectroscopy in conjunction with attenuated total reflection Fourier transform infrared spectroscopy reveals the catalytic mechanism of nitrate to NH3. Our study provides not only an efficient catalyst for NH3 production but also useful guidelines for the pathways and mechanism of nitrate electroreduction to NH3.

Recent Advances in Electrocatalytic Nitrate Reduction to Ammonia: Mechanism Insight and Catalyst Design

“…Except for the above two in situ characterizations, the electrochemical in situ Raman spectroscopy can also provide sufficient evidence for the reaction pathway. As shown in Figure d, the peaks corresponding to the NO 3 – , NO 2 – , and NH 2 were observed on the Fe 2 O 3 nanorod arrays electrode . This indicated that NO 2 – was the key intermediate for electrocatalytic nitrate reduction.…”

“…(d) In situ Raman spectra in the range of 900–1800 cm –1 on Fe 2 O 3 NRs/CC. Reprinted with permission from ref . Copyright 2022 American Chemical Society.…”

“…As shown in Figure 4d, the peaks corresponding to the NO 3 − , NO 2 − , and NH 2 were observed on the Fe 2 O 3 nanorod arrays electrode. 52 This indicated that NO 2 − was the key intermediate for electrocatalytic nitrate reduction. Similar in situ Raman measurement results are also received on the Ag/ZnO electrocatalyst, indicating a similar reaction mechanism over Fe 2 O 3 nanorod arrays and Ag/ZnO electrode.…”

Self‐Supported Pd Nanorod Arrays for High‐Efficient Nitrate Electroreduction to Ammonia

“…[66] The peak at 3336 cm −1 is because of the creation of −NH 2 and the positive band at 1108 cm −1 is associated with the production of NH 3 . [14,67,68] Additionally, the positive peak at 1329 cm −1 and the band at 1470-1430 cm −1 correspond to NO − and monodentate nitrite (MONO). [66,69,70] Combined with the intermediates of in situ FTIR detection and theoretical calculations, we derived the possible NO 3 − RR reaction path on the surface of Pd/NF as shown in Figure 5b.…”

A strong metal–support interaction strategy for enhanced binder-free electrocatalytic nitrate reduction

“…[16][17][18][19][20] However, in order to reduce the cost and enhance the properties, numerous non-precious metal catalysts have been studied. [21][22][23][24][25] Fe-based electrocatalysts have stood out in replacing traditional noble metals due to their low cost, high reduction capacity, easy availability and recyclability. [26][27][28][29] However, the Fe-based nanoparticles are prone to being aggregated and oxidated.…”