Non-aqueous gas diffusion electrodes for rapid ammonia synthesis from nitrogen and water-splitting-derived hydrogen

Abstract

The procedures and materials for nitrogen reduction outlined below have been optimized for reliable ammonia production. However, certain deviations from the procedure and material vendors, which are specifically called out in-text and in prior work, 1 may lead to poorer ammonia production. We recommend closely following the procedure for reproducibility and high yields. MaterialsTetrahydrofuran (THF, 99+%, stabilized with BHT) and molecular sieves (3Å, 4-8 mesh) were purchased from Acros Organics. Lithium tetrafluoroborate (LiBF4, 98%), dimethyl carbonate (DMC, ReagentPlus, 99%), propylene carbonate (PC, anhydrous, 99.7%), maleic acid (ReagentPlus, ≥99%), sodium salicylate (ReagentPlus®, ≥99.5%), sodium hypochlorite (NaOCl, 10-15%), nickel chloride hexahydrate (NiCl2•6H2O), hydrochloric acid (HCl, 37%), and ferrocenium hexafluorophosphate (FcPF6, 97%) were purchased from Sigma-Aldrich. Hexanes (C6H14), diethyl ether (Et2O), and sulfuric acid (H2SO4, 93-98%, trace metal grade) were purchased from Fisher Scientific. Platinum foil (Pt, 0.025 mm thick, 99.99%, trace metals basis) and sodium citrate (anhydrous) were purchased from Beantown Chemical. Ethyl alcohol (C2H5OH, Koptec, anhydrous, 200 proof), sodium hydroxide (NaOH, Macron Fine Chemicals, pellet form), and acetone (ACS, BDH Chemical) were purchased from VWR International. Sodium nitroprusside (99-102%), ferrocene (Fc, 99%, powder), boric acid (H3BO3, 99.99%, trace metals grade), nickel foil (annealed, 99+%, 0.05 mm), ammonium chloride (NH4Cl, anhydrous, 99.99%), and ammonium hexachloroplatinate (IV) ((NH4)2PtCl6, 43.4% min Pt) were purchased from Alfa Aesar. Isotope labelled nitrogen ( 15 N2, 98%+) was purchased from Cambridge Isotope Laboratories, Inc. Argon gas (UHP, 5.0 grade) and hydrogen gas (UHP, 5.0 grade) were purchased from Airgas. Nitrogen gas was available in-house; it is generated by boil-off of liquid nitrogen from Airgas. Milli-Q water was obtained by filtering deionized (DI) water through a Milli-Q purification system (Merck, Millipore Corporation). Steel cloth (304 stainless steel, 400x400 mesh) and steel foil (cold-worked 304 stainless steel, 0.002" thick) were purchased from McMaster-Carr. Platinum-coated carbon paper (0.5 mg cm -2 60% platinum on Vulcan, carbon paper) was purchased from FuelCellStore. Polyporous Daramic 175 separators were received as a sample from Daramic (Charlotte, NC). Electrolyte solution preparationDry THF was used as the solvent in THF-based experiments described below. It was obtained by drying as-purchased THF over 20% v/v of freshly dried molecular sieves for at least 48 hours in a round-bottom flask sealed with a rubber septum stopper. The sieves were prepared by washing with acetone and heating at 300 °C for 5 hours in a muffle furnace. The water content of dry THF was found to be 7.1±0.3 ppm (n = 3) via Karl-Fischer titration. As-purchased LiBF4, stored in an Ar glovebox, was dissolved in dry THF to obtain electrolyte solutions containing 1 M LiBF4. As discussed in previous work, 1 it is imperative for the LiB...

Identification and elimination of false positives in electrochemical nitrogen reduction studies

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Electrochemical oxidation of molecular nitrogen to nitric acid – towards a molecular level understanding of the challenges

“…A similar strategy has already been used successfully to increase the selectivity of electrochemical N 2 reduction (where the parasitic reaction is hydrogen evolution). [41][42][43][44] Limited access to holes can for instance be achieved by limiting conductivity to the surface. For TiO 2 this could be achieved by controlling the thickness of a non-conducting TiO 2 lm on the electrode surface.…”

Potential Viable Products Identified from Characterisation of Agricultural Slaughterhouse Rendering Wastewater

“…RCWW had high levels of NH 3 throughout the year, as seen in Figure 3. Lazouski et al demonstrated that the use of conventional gas diffusion electrodes can be used to produce NH 3 fertiliser from nitrogen and water-splitting-derived hydrogen, which could potentially be derived from wastewater [42]. However, this method is only capable of producing a NH 3 fertiliser, whereas the use of membrane distillation allows for the production of (NH 4 ) 2 SO 4 .…”