Selective Electrocatalytic Reduction of Nitrate to Ammonia with Nickel Phosphide

Abstract

Liquid ammonia is considered a sustainable liquid fuel and an easily transportable carrier of hydrogen energy; however, its synthesis processes are energy-consuming, high cost, and low yield rate. Herein, we report the electrocatalytic reduction of nitrate (NO3 –) (ERN) to ammonia (NH3) with nickel phosphide (Ni2P) used as a noble metal-free cathode. Ni2P with (111) facet was grown in situ on nickel foam (NFP), which was regarded as a self-supporting cathode for ERN to synthesis NH3 with high yield rate (0.056 mmol h–1 mg–1) and superior faradaic efficiency of 99.23%. The derived atomic H (*H), verified by a quenching experiment and an electron spin resonance (ESR) technique, effectively enhanced the high selectivity for NH3 generation. DFT calculations indicated that *NO3 was deoxygenated to *NO2 and *NO, and *NO was subsequently hydrogenated with *H to generate NH3 with an energy releasing process (ΔG < 0). OLEMS also proved that NO was the merely gas intermediate. NFP exhibited the unique superhydrophilic surface, metallic properties, low impedance, and abundant surface sites, favorable for adsorption of NO3 –, generation of *H, and then hydrogenation of NO3 –. Hence, NFP cathode showed high selectivity for NH3 (89.1%) in ERN. NFP with long-term stability and low energy consumption provides a facile strategy for synthesis of NH3 and elimination of NO3 – contamination.

Engineering Nitrogen Vacancy in Polymeric Carbon Nitride for Nitrate Electroreduction to Ammonia

“…11−15 Previous studies mainly focused on metal-based electrocatalysts. 16,17 Nevertheless, the scarcity and high price limited the wide application of noble metal-based catalysts. In contrast, transition metalbased electrocatalysts suffered from easy corrosion and second pollution.…”

“…Ammonia (NH 3 ) is considered as one of the most versatile chemicals in the agriculture, plastic, and textile industries. , Electrosynthesis of ammonia from water and nitrogen is an ideal alternative to the conventional Haber–Bosch process. − However, the advancement of this technique is significantly hindered by the inertness of the nonpolar NN bond (941 kJ mol –1 ) and the low solubility of nitrogen in water. , Simultaneously, vast numbers of nitrate (NO 3 – ) is discharged into the underground aquifer, threatening human health. − The electrochemical nitrate reduction to ammonia (NRA) offers a brilliant future landscape because of the much lower cleavage energy of NO (204 kJ mol –1 ) in nitrate and the significantly enhanced solubility in water. − Previous studies mainly focused on metal-based electrocatalysts. , Nevertheless, the scarcity and high price limited the wide application of noble metal-based catalysts. In contrast, transition metal-based electrocatalysts suffered from easy corrosion and second pollution .…”

Lattice-strain and Lewis acid sites synergistically promoted nitrate electroreduction to ammonia over PdBP nanothorn arrays

“…39,[53][54][55][56][57][58][59][60] On the other hand, the lattice strain induced by B and P co-doping makes some of the adsorbed hydrogen atoms (*H) survive, desorb away from the catalyst surface and ultimately evolve into hydrogen radicals ($H) existing in the reaction medium, which can reduce kinetic barriers in hydrogenating intermediates to ammonia. 43,44,50,61,62 Collectively, the modication of the Pd crystal structure with metalloid B and nonmetal P elements can modulate the electron conguration of the active center at the atomic level, thus inducing lattice strain and enabling the production of more moderate hydrogen adsorption/desorption intensities. Beneting from these advantages, the developed PdBP NAs/NF catalyst exhibits an excellent performance towards the NO 3 RR.…”

Electrochemical ammonia synthesisvianitrate reduction on perovskite LaxFeO3−δwith enhanced efficiency by oxygen vacancy engineering

“…Among them, the outstanding examples are Fe single-atom catalysts, 5 metal–organic framework-derived Co-doped Fe/Fe 2 O 3 , 6 and the metasequoia-like CuFe nanocrystals mentioned above. 4 Besides, transition metal elements such as Co 6–8 and Ni 9,10 have also been proved to have electrochemical NO 3 RR activities. In general, the above non-noble-metal based electrocatalysts are mainly in the form of single metal catalysts (single-atom catalysts, 5 nanoplate catalysts, 1 nanoarray catalysts, 7 etc.…”