Efficient Nitrate Generation through Electrochemical N2 Oxidation with Nickel Oxyhydroxide Decorated Copper Hydroxide Driven by Solar Cells.

Electrocatalytic nitrogen oxidation reaction (NOR) into nitrate under ambient conditions, as an alternative to replace traditional industrial method, is a promising artificial N2 fixation strategy, especially powered by renewable energy. Here, through skillfully balancing competitive relationships between NOR and oxygen evolution reaction (OER), the nickel oxyhydroxide decorated Cu(OH)2 hybrid electrocatalyst with Cu:Ni molar ratio of 1:1 is developed, which achieves outstanding Faradaic efficiency (FE) of 18.7% and yield rate of 228.24 µmol h-1  gcat -1 at 2.0 V versus reversible hydrogen electrode (RHE) in the electrolyte of 0.1 m Na2 SO4 . Also, the hybrid catalyst maintained over five cycles (10 h each cycle) with negligible decay in performance. The synergetic effect between the components of nickel oxyhydroxide and Cu(OH)2 is found to remarkably activate N2 and suppress the activity of competitive OER, which enhances NOR performance eventually. Moreover, the conversion efficiency of solar-to-nitrate (STN) with 0.025% was obtained by coupling with a commercial solar cell. This work provides a novel avenue of rational catalysts design strategies and realizes solar-to-nitrate synthesis.

Electrochemical Nitrate Production via Nitrogen Oxidation with Atomically Dispersed Fe on N-Doped Carbon Nanosheets.

Electrocatalytic N2 oxidation (NOR) into nitrate is a potential alternative to the emerging electrochemical N2 reduction (NRR) into ammonia to achieve a higher efficiency and selectivity of artificial N2 fixation, as O2 from the competing oxygen evolution reaction (OER) potentially favors the oxygenation of NOR, which is different from the parasitic hydrogen evolution reaction (HER) for NRR. Here, we develop an atomically dispersed Fe-based catalyst on N-doped carbon nanosheets (AD-Fe NS) which exhibits an exceptional catalytic NOR capability with a record-high nitrate yield of 6.12 µ mol mg-1 h-1 (2.45 µ mol cm-2 h-1) and Faraday efficiency of 35.63%, outperforming all reported NOR catalysts and most well-developed NRR catalysts. The isotopic labeling NOR test validates the N source of the resultant nitrate from the N2 electro-oxidation catalyzed by AD-Fe NS. Experimental and theoretical investigations identify Fe atoms in AD-Fe NS as active centers for NOR, which can effectively capture N2 molecules and elongate the N≡N bond by the hybridization between Fe 3d orbitals and N 2p orbitals. This hybridization activates N2 molecules and triggers the subsequent NOR. In addition, a NOR-related pathway has been proposed that reveals the positive effect of O2 derived from the parasitic OER on the NO3- formation.

Electrocatalytic Hydrogenation of N2 to NH3 by MnO: Experimental and Theoretical Investigations.

NH3 is a valuable chemical with a wide range of applications, but the conventional Haber-Bosch process for industrial-scale NH3 production is highly energy-intensive with serious greenhouse gas emission. Electrochemical reduction offers an environmentally benign and sustainable route to convert N2 to NH3 at ambient conditions, but its efficiency depends greatly on identifying earth-abundant catalysts with high activity for the N2 reduction reaction. Here, it is reported that MnO particles act as a highly active catalyst for electrocatalytic hydrogenation of N2 to NH3 with excellent selectivity. In 0.1 m Na2SO4, this catalyst achieves a high Faradaic efficiency up to 8.02% and a NH3 yield of 1.11 × 10-10 mol s-1 cm-2 at -0.39 V versus reversible hydrogen electrode, with great electrochemical and structural stability. On the basis of density functional theory calculations, MnO (200) surface has a smaller adsorption energy toward N than that of H with the *N2 → *N2H transformation being the potential-determining step in the nitrogen reduction reaction.