High-Efficiency Electrosynthesis of Ammonia with Selective Reduction of Nitrate in Neutral Media Enabled by Self-Supported Mn₂CoO₄ Nanoarray

Abstract

Ambient ammonia synthesis by electroreduction of nitrate (NO3 –) provides us a sustainable and environmentally friendly alternative to the traditional Haber–Bosch process. In this work, Mn2CoO4 nanoarray grown on carbon cloth (Mn2CoO4/CC) serves as a superior electrocatalyst for efficient NH3 synthesis by selective reduction of NO3 –. When operated in 0.1 M PBS with 0.1 M NaNO3, Mn2CoO4/CC reaches a high Faraday efficiency of 98.6% and a large NH3 yield up to 11.19 mg/h/cm2. Moreover, it exhibits excellent electrocatalytic stability. Theory calculations show that the Mn2CoO4 surface has strong interaction with NO3 –, which can effectively inhibit the occurrence of hydrogen evolution, beneficial for NO3 –-to-NH3 conversion.

High-Efficiency Electrochemical Nitrate Reduction to Ammonia on a Co3O4 Nanoarray Catalyst with Cobalt Vacancies

“…Co 3 O 4 , as one of the typical spinel oxides, has been used as a catalyst for NO 3 RR. , However, its performance is still not as good as expected due to the inherently large band gap, resulting in low electrical conductivity and poor NO 3 – binding ability on active sites. Recently, remarkable progress in our group has been made to improve the catalytic performance of the cobalt-based spinel for NO 3 RR by constructing bimetallic spinel oxide catalysts. − The introduction of another metal atom can regulate the electron cloud distribution at the Co active sites and further enhance the adsorption ability of NO 3 – on the Co sites, thus promoting the performance of NO 3 RR. In view of catalytic reactions that occur on the surface of the catalyst, the relatively stable coordination environment and electronic structure of atoms on the surface for catalysts limit the catalytic active sites.…”

Durable Electrocatalytic Reduction of Nitrate to Ammonia over Defective Pseudobrookite Fe2TiO5Nanofibers with Abundant Oxygen Vacancies

“…Until now, a series of electrocatalysts including noble metals [10–12] and transition metals [13–18] have been attempted to reduce nitrate to ammonia. Among all the catalysts, spinel oxides with a typical formulation of AB 2 O 4 exhibit excellent catalytic activity due to its advantages of versatility, flexible ion arrangement, multivalence structure and high electronic conductivity [19–21] . TiO 2 with vacant oxygen is found to realize impressive electrochemical performance, [22, 23] and Iron (Fe) as an active substance of the Haber–Bosch process is a potential catalyst for nitrate reduction [24–26] .…”

“…Among all the catalysts, spinel oxides with a typical formulation of AB 2 O 4 exhibit excellent catalytic activity due to its advantages of versatility, flexible ion arrangement, multivalence structure and high electronic conductivity. [19][20][21] TiO 2 with vacant oxygen is found to realize impressive electrochemical performance, [22,23] and Iron (Fe) as an active substance of the Haber-Bosch process is a potential catalyst for nitrate reduction. [24][25][26] Thus, inspired by the double-cation structure, we propose defective Fe 2 TiO 5 (FTO) as a new electrocatalyst to reduce nitrate and nitrite to ammonia, where iron is able to modulate oxygen vacancy (Vo) in FTO due to its relatively high reducibility of randomly displacing Ti 4 + .…”

In Situ Derived Co2B Nanosheet Array: A High-Efficiency Electrocatalyst for Ambient Ammonia Synthesis via Nitrate Reduction

“…A negligible NH 3 content can be observed under the open-circuit potential (OCP) conditions, similar to those detected in pure PBS and fresh electrolyte, excluding the influence of contaminations from experimental instruments and reagents. Moreover, a 15 N labeling experiment was conducted and 15 NH 4 + was determined by proton nuclear magnetic resonance ( 1 H NMR) spectroscopy. As shown in Figure 2e, the 1 H NMR spectra of ammonia using 15 NO 3 − and 14 NO 3 − as reactants display typical triple peaks of 14 urations are considered.…”

“…Nitrate (NO 3 – ) is a common nitrogen source and widely exists in wastewater, , which is much more easily reduced to NH 3 than N 2 . − Thus, NH 3 production via the electrochemical NO 3 – reduction reaction (eNO 3 RR) can not only effectively alleviate the energy crisis but also help control NO 3 – pollution in water. Since the electroreduction of NO 3 – is very complex and involves many intermediates (NO 2 – , NO, HNO, H 2 NO, NH 2 OH, NO, N 2 O, etc.…”