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Ammonia (NH 3 ) plays an important role in agriculture and industry. The industry-scale production mainly depends on the Haber-Bosch process suffering from issues of environment pollution and energy consumption. Electrochemical reduction can degrade nitrite (NO 2 - ) pollutants in the environment and convert it into more valuable NH 3 . Here, Ni 2 P nanosheet array on nickel foam is proposed as a 3D electrocatalyst for high-efficiency electrohydrogenation of NO 2 - to NH 3 under ambient reaction conditions. When tested in 0.1 M phosphate buffer saline with 200 ppm NO 2 - , such Ni 2 P/NF is able to obtain a large NH 3 yield rate of 2692.2 ± 92.1 μg h -1 cm -2 (3282.9 ± 112.3 μg h -1 mg cat. -1 ), a high Faradic efficiency of 90.2 ± 3.0%, and selectivity of 87.0 ± 1.7% at -0.3 V versus a reversible hydrogen electrode. After 10 h of electrocatalytic reduction, the conversion rate of NO 2 - achieves near 100%. The catalytic mechanism is further investigated by density functional theory calculations., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Electrochemical synthesis of ammonia via nitrogen reduction reaction is a rational route to save energy and relieve pollution compared to the traditional Haber‐Bosch process. In this report, ZrO2 nanosphere derived from thermolysis of Zr‐based biphenyl‐4,4′‐dicarboxylic acid MOFs (ZrO2/C) as a non‐noble metal catalyst with large specific surface area and porous structure is proposed to fix nitrogen to ammonia at ambient conditions. Such catalyst achieves Faradaic efficiency of 11.86 % and a NH3 yield rate of 10.72 μg h−1 mg−1cat. at −0.6 V vs. the reversible hydrogen electrode in 0.1 M Na2SO4. First‐principles calculations confirm the alternating reaction at the catalyst surface. [ABSTRACT FROM AUTHOR]

Electrocatalytic nitrite reduction not only holds significant potential in the control of nitrite contamination in the natural environment, but also is an attractive approach for sustainable ammonia synthesis. In this communication, we report that a TiO2−x nanobelt array with oxygen vacancies on a titanium plate is able to convert nitrite into ammonia with a high faradaic efficiency of 92.7% and a large yield of 7898 μg h−1 cm−2 in alkaline solution. This monolithic catalyst also shows high durability with the maintenance of its catalytic activity for 12 h. Theoretical calculations further reveal the critical role of oxygen vacancies in nitrite electroreduction. [ABSTRACT FROM AUTHOR]

Electrocatalytic eight-electron nitrate (NO3−) reduction is a sustainable strategy to degrade NO3− and convert it into high value-added ammonia (NH3) but needs efficient catalysts with high activity and selectivity. Our study shows the use of Ti plate supported cobalt–phosphorus alloy film (Co–P/TP) as a highly active and selective electrocatalyst for ambient NO3−-to-NH3 conversion. In 0.2 M Na2SO4 with 200 ppm NO3−, Co–P/TP offers an NH3 yield rate of 416.0 ± 7.2 μg h−1 cm−2 and a high faradaic efficiency of 93.6 ± 3.3% at −0.6 V and −0.3 V vs. reversible hydrogen electrode, respectively, with good durability. Noticeably, a conversion rate of 86.9% is achieved after 10 h bulk electrolysis. [ABSTRACT FROM AUTHOR]

We report on Ru-doped self-supported honeycomb nickel molybdate nanoflakes (Ru-NiMoO 4 /NF) with abundant OV on Ni foam and its application in both electrocatalytic NO 2 –RR and Zn-NO 2 – battery. The catalytic activity of Ru-NiMoO 4 /NF was significantly enhanced due to the Ru doping and the existence of oxygen vacancies, achieving high Faraday efficiency of 95.56 ± 0.72% and large ammonia yield of 17192.52 ± 1136.64 μg h−1 cm−2 at –0.6V vs. RHE in 0.5 M Na 2 SO 4 and 0.1 M NO 2 – solution, as well as preferable long-term stability. In addition, it was verified that Zn-NO 2 – battery with Ru-NiMoO 4 /NF as cathode delivers a good energy supply (13.87 mW cm−2), as well as simultaneously ammonium yield of 1524.74 μg h−1 cm−2 and Faradaic efficiency of 96.15% at 15 mA cm−2. [Display omitted] The electrocatalytic reduction of nitrite to recyclable ammonia (NH 3) is essential to maintain nitrogen balance and meet growing energy requirements. Herein, we report that Ru doped honeycomb NiMoO 4 nanosheet with copious oxygen vacancies grown on nickel foam substrate has been prepared by a facile hydrothermal synthesis and immersion process, which can act as an efficient electrocatalyst for NH 3 synthesis by reduction of nitrite. By optimizing the concentration of RuCl 3 solution, 0.01Ru-NiMoO 4 /NF possesses excellent NO 2 −RR performance with NH 3 yield of 20249.17 ± 637.42 μg h−1 cm−2 at −0.7 V and FE of 95.56 ± 0.72 % at −0.6 V. When assembled into a Zn–NO 2 − battery, it provides a remarkable level of power density of 13.89 mW cm−2, outperforming the performance of virtually all previous reports. The efficient adsorption and activation of NO 2 − over Ru-doped NiMoO 4 with oxygen vacancy have been verified by density functional theory calculations, as well as the possible reaction pathway. [ABSTRACT FROM AUTHOR]

Self-supported one-dimensional (1D) monoclinic nickel molybdate nanorods with abundant OVs on Ni foam (NiMoO 4 /NF) can achieve high Faraday efficiency of 94.49 ± 0.42% and a large ammonia yield of 18089.39 ± 227.98 μg h−1 cm−2 at –0.8V vs. RHE in 0.5 M Na 2 SO 4 and 0.1 M NO 2 – solution, together with preferable long-term stability. In addition, it was verified that Zn-NO 2 – battery with NiMoO 4 /NF as cathode delivers an ammonium yield of 1929.76 μg h−1 cm−2 and a Faradaic efficiency of 91.27% at 20 mA cm−2. [Display omitted] As an eco-friendly and sustainable strategy, the electrochemical reduction of nitrite (NO 2 –) can simultaneous generation of NH 3 and treatment of NO 2 – contamination in the environment. Herein, monoclinic NiMoO 4 nanorods with abundant oxygen vacancies self-supported on Ni foam (NiMoO 4 /NF) are considered high-performance electrocatalysts for ambient NH 3 synthesis by reduction of NO 2 −, which can deliver an outstanding yield of 18089.39 ± 227.98 μg h−1 cm−2 and a preferable FE of 94.49 ± 0.42% at −0.8 V. Additionally, its performance remains relatively stable during long-term operation as well as cycling tests. Furthermore, density functional theory calculations unveil the vital role of oxygen vacancies in promoting nitrite adsorption and activation, ensuring efficient NO 2 –RR towards NH 3. A Zn-NO 2 – battery with NiMoO 4 /NF as the cathode shows high battery performance as well. [ABSTRACT FROM AUTHOR]

Spinel-type MnCo 2 O 4 nanowire array grown on carbon cloth is highly active and stable for electrochemical NO 3 –-to-NH 3 conversion, capable of attaining a large NH 3 yield of 0.67 mmol h−1 cm−2 and the highest Faradaic efficiency of 97.1%. [Display omitted] Direct electrocatalytic reduction of nitrate (NO 3 –) is an efficient route to simultaneously synthesize ammonia (NH 3) and remove NO 3 – pollutants under ambient conditions, however, it is hindered by the lack of efficient and stable catalysts. Herein, a self-supported spinel-type MnCo 2 O 4 nanowire array is demonstrated for exclusively catalyzing the conversion of NO 3 – to NH 3 , achieving a high Faradic efficiency of 97.1% and a large NH 3 yield of 0.67 mmol h−1 cm−2. Furthermore, density functional analysis reveals that MnCo 2 O 4 (220) surface has high activity for NO 3 – reduction with a low energy barrier of 0.46 eV for *NO to *NOH. [ABSTRACT FROM AUTHOR]

Ag nanoarray using NiO nanosheets array on carbon cloth as support behaves as a high-active and stable electrocatalyst for NO 2 – reduction into NH 3 with a remarkably yield up to 5,751 μg h−1 cm−2 (57,510 μg h−1 mg Ag -1) and a Faradaic efficiency as high as 97.7%. Density functional theory calculations was applied to uncover its catalytic mechanism. [Display omitted] Electrochemical reduction of nitrite to ammonia can simultaneously achieve ammonia synthesis and N -contaminant removal under mild conditions, which has attracted widespread attention but still lacks efficient catalysts. In this work, Ag nanoarray using NiO nanosheets array on carbon cloth as support is reported as an efficient electrocatalyst to selectively reduce nitrite to ammonia. In 0.1 M NaOH with 0.1 M NO 2 –, such catalyst exhibits a maximum ammonia yield of 5,751 μg h−1 cm−2 (57,510 μg h−1 mg Ag -1) and high Faradaic efficiency up to 97.7 %. Density functional theory calculations applied to uncover the catalytic mechanism of NO 2 – reduction reaction on Ag. [ABSTRACT FROM AUTHOR]

Electrocatalytic reduction of nitrite (NO 2 –) is an environmentally friendly method for ambient ammonia (NH 3) production, and the development of high–efficiency electrocatalysts is in urgent demand. Herein, we demonstrated that MoO 2 nanoparticles self–supported on a molybdenum plate (MoO 2 /MP) could act as an excellent catalyst for the conversion of NO 2 – to NH 3. The optimized catalyst can achieve an impressive NH 3 yield of 8678.4 ± 187.4 μg h–1 cm–2 with high Faradaic efficiency of 94.5 ± 0.2 % at −0.8 V in the solution of 0.5 M Na 2 SO 4 and 0.1 M NO 2 –, along with preferable durability. Additionally, density functional theory calculation reveals that the MoO 2 (1 ¯ 11) surface has a high activity for NO 2 – reduction, with 0.38 eV as the potential determining step (*NO 2 to NO 2 H), as well as severe suppress hydrogen evolution. [Display omitted] [ABSTRACT FROM AUTHOR]

Co 2 AlO 4 /CC achieves superb NO 3 − reduction performances with a large NH 3 yield of 7.9 mg h−1 cm−2 and a Faradaic efficiency of 92.6%. Furthermore, the Co 2 AlO 4 /CC-based Zn-NO 3 − battery offers a high power density and a large NH 3 yield. [Display omitted] • A Co 2 AlO 4 nanosheet array acts as a 3D electrocatalyst for NO 3 − electroreduction. • It exhibits a superior catalytic performances for selective NH 3 generation. • It attains a large NH 3 yield of 7.9 mg h−1 cm−2 and a Faradaic efficiency of 92.6%. • Zn-NO 3 − battery with Co 2 AlO 4 /CC cathode offers high power densities and NH 3 yields. • DFT reveals that Co 2 AlO 4 (2 2 0) inhibits HER but shows high NO 3 − reduction activity. A Co 2 AlO 4 nanosheet array on carbon cloth (Co 2 AlO 4 /CC) is proposed as a superb electrocatalyst for converting nitrate (NO 3 −) to ammonia (NH 3). In 0.1 M PBS solution with 0.1 M NO 3 −, it attains an NH 3 yield of 7.9 mg h−1 cm−2 with a Faradaic efficiency of 92.6%, with high durability. A Zn-NO 3 − battery with such Co 2 AlO 4 /CC as cathode offers a power density of 3.43 mW cm−2 with an NH 3 yield of 750 μg h−1 cm−2. Theoretical calculations reveal that Al ions reduce the electron cloud density on the surface of Co, making it highly conducive to NO 3 − adsorption at Co sites. Additionally, Co 2 AlO 4 (2 2 0) surface inhibits hydrogen evolution reaction but is highly active for NO 3 − reduction with a low energetically uphill pathway (ΔG of 0.42 eV) for the potential-determining step (*NO 3 to *NO 3 H), much smaller than that of Co 3 O 4 (2 2 0) (ΔG of 0.83 eV). [ABSTRACT FROM AUTHOR]