Ammonia Synthesis Under Ambient Conditions: Selective Electroreduction of Dinitrogen to Ammonia on Black Phosphorus Nanosheets

Abstract

Constructing efficient catalysts for the N 2 reduction reaction (NRR) is am ajor challenge for artificial nitrogen fixation under ambient conditions.H erein, inspired by the principle of "like dissolves like", it is demonstrated that am ember of the nitrogen family,w ell-exfoliated few-layer black phosphorus nanosheets (FL-BP NSs), can be used as an efficient nonmetallic catalyst for electrochemical nitrogen reduction. The catalyst can achieve ah igh ammonia yield of 31.37 mgh À1 mg À1cat. under ambient conditions.D ensity functional theory calculations reveal that the active orbital and electrons of zigzag and diff-zigzag type edges of FL-BP NSs enable selective electrocatalysis of N 2 to NH 3 via an alternating hydrogenation pathway.T his work proves the feasibility of using an onmetallic simple substance as an itrogen-fixing catalyst and thus opening an ew avenue towardst he development of more efficient metal-free catalysts. Ammonia (NH 3 )i sabasic raw chemical material used in modern industry and agriculture. [1] At present, the energyintensive Haber-Bosch process is the main artificial synthesis route for ammonia, and this process uses more than 1% of global annual energy consumption and produces carbon dioxide emissions. [2,3] In contrast, electrochemical reduction of nitrogen into ammonia under ambient conditions is ap otential strategy for sustainable ammonia production. [4][5][6] However,o wing to the strong dipole moment of the N N triple bond and the vigorous competing hydrogen evolution reaction (HER), [7][8][9][10][11] the development of highly effective catalysts with sufficient activity and selectivity is essential.According to available experimental and theoretical NRR data, an active center that can easily adsorb nitrogen molecules and sufficiently activate the N Nt riple bond is very desirable. [12][13][14][15] To this end, the search for an electrocatalytic NRR center in recent years has mainly focused on transition-metal-based materials. [8,[14][15][16][17][18][19][20][21][22][23] Specifically,b enefiting from the unoccupied and occupied dorbitals of transition metals,t he electron density from N 2 is synergically accepted with appropriate energy and symmetry,a nd then, the transition metal donates electrons to the p*o rbital of NN, strengthening N 2 adsorption and weakening the NNbond. [7] It is worthwhile to note that although an unoccupied nonbonding orbital and electron donor site with abundant electron cloud density are prerequisites for aN RR catalyst, the do rbital electrons in transition metals also benefit the formation of metal-hydrogen bonds,w hich will exacerbate the competitive hydrogen evolution reaction and limit the nitrogen reduction selectivity and catalytic efficiency. [24] Compared to transition metals,t he weak hydrogen adsorption of nonmetallic elements and their abundant valence electrons should provide am ore ideal nitrogen activation center. [25,26] Some recent studies have shown that the use of nonmetallic components as active centers may be an effective way to obta...

Nitrogen‐Doped NiO Nanosheet Array for Boosted Electrocatalytic N2 Reduction

“…The minor increased absorbance of the control experiments may stem from the trace amount of NH 3 in air [40] . In addition, the isotope-labelled 15 N 2 was used as the feeding gas for NRR on N-NiO/CC with the resultant products analyzed by 1 H nuclear magnetic resonance (NMR) [16,44] . As shown in Figure 2b, the 1 H NMR spectrum shows a distinguishable chemical shift of a doublet pattern with a coupling constant of 1 J NÀ H = 72.5 Hz, matching well with that of standard 15 NH 4 + sample.…”

Stable Confinement of Black Phosphorus Quantum Dots on Black Tin Oxide Nanotubes: A Robust, Double‐Active Electrocatalyst toward Efficient Nitrogen Fixation

“…To further exclude the influence of possible contamination, an isotopic labeling experiment was conducted. [29] At first, 15 detected (Supporting Information, Figure S25). This phenomenon basically excludes the false positives from serious contamination in 15 N 2 .T oq uantitatively determine the ammonia yields from 15 N 2 and 14 N 2 in the same setup,t he electrolysis was sequentially conducted in 15 N 2 and 14 N 2 at À0.4 Vvs.…”

“…[13,14] Therefore,B Pi se xpected to be an ideal electrocatalyst toward NRR. [15] Since the activity of an electrocatalyst is closely related to its size,B Pi sf urther downsized to quantum dots (QDs), which possess larger surface areas and thus more active sites than the bulk form. [16] However,B PQ Ds are prone to agglomeration, which inevitably results in the loss of active sites.B esides,t heir poor conductivity is not favorable for charge transport during electrolysis.Previously,weemployed reduced graphene oxide (RGO) as am atrix to support BP QDs,t hereby preventing their agglomeration and enhancing their conductivity.…”

Atomic Modulation, Structural Design, and Systematic Optimization for Efficient Electrochemical Nitrogen Reduction

“…Heteroatom doping also enables NRR by inducing defects as the active sites . Compared to the aforementioned carbon‐based materials, noncarbon materials have received less attention . Recently, black phosphorus nanosheets were prepared by exfoliation, which overcame van der Waals interactions and granted them abundant active sites for NRR on account of the generation of numerous zigzag and diff‐zigzag edges with concentrated electron densities.…”