Nitrite reduction over Ag nanoarray electrocatalyst for ammonia synthesis.

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 NO2-, such catalyst exhibits a maximum ammonia yield of 5,751 µg h-1 cm-2 (57,510 µg h-1 mgAg-1) and high Faradaic efficiency up to 97.7 %. Density functional theory calculations applied to uncover the catalytic mechanism of NO2- reduction reaction on Ag.

Ni2P nanosheet array for high-efficiency electrohydrogenation of nitrite to ammonia at ambient conditions.

Ammonia (NH3) 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 (NO2-) pollutants in the environment and convert it into more valuable NH3. Here, Ni2P nanosheet array on nickel foam is proposed as a 3D electrocatalyst for high-efficiency electrohydrogenation of NO2- to NH3 under ambient reaction conditions. When tested in 0.1 M phosphate buffer saline with 200 ppm NO2-, such Ni2P/NF is able to obtain a large NH3 yield rate of 2692.2 ± 92.1 µg h-1 cm-2 (3282.9 ± 112.3 µg h-1 mgcat.-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 NO2- achieves near 100%. The catalytic mechanism is further investigated by density functional theory calculations.

High-efficiency nitrate electroreduction to ammonia on electrodeposited cobalt-phosphorus alloy film.

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.