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...

Electrochemical nitrogen reduction to ammonia is studied as a distributed and renewable alternative to Haber-Bosch. Most nitrogen reduction chemistries are performed in aqueous media, which suffer from low rates and selectivities. We present a lithium-mediated approach for producing ammonia in a non-aqueous medium that demonstrates high rates and yields. A coupled kinetic-transport model is developed to describe observed behaviors, which suggests that the process is limited by nitrogen diffusion to the electrode. HIGHLIGHTSLithium-metal-mediated approach for nitrogen electroreduction to ammonia is studied Ammonia production rate of (7.9 G 1.6) 3 10 À9 mol cm À2 s À1 is achieved Faradaic efficiency of 18.5% G 2.9% is obtained A kinetic-transport model incorporating observed diffusion limitations is developed Lazouski et al., SUMMARYAmmonia is a large-scale commodity chemical that is crucial for producing nitrogen-containing fertilizers. Electrochemical methods have been proposed as renewable and distributed alternatives to the incumbent Haber-Bosch process, which utilizes fossil fuels for ammonia production. Herein, we report a mechanistic study of lithium-mediated electrochemical nitrogen reduction to ammonia in a non-aqueous system. The rate laws of the main reactions in the system were determined. At high current densities, nitrogen transport limitations begin to affect the nitrogen reduction process. Based on these observations, we developed a coupled kinetic-transport model of the process, which we used to optimize operating conditions for ammonia production. The highest Faradaic efficiency observed was 18.5% G 2.9%, while the highest production rate obtained was (7.9 G 1.6) 3 10 À9 mol cm À2 s À1 . Our understanding of the reaction network and the influence of transport provides foundational knowledge for future improvements in continuous lithium-mediated ammonia synthesis.

Transforming carbon dioxide to carbon monoxide with electrochemical methods allows for small-scale, modular conversion of point sources of carbon dioxide. In this work, through the preparation of a well-dispersed cobalt phthalocyanine model catalyst immobilized on carbon paper, we revealed high turnover frequencies for reducing carbon dioxide at low catalyst loadings, which are obscured at higher loadings due to aggregation. The low catalyst loadings have also enabled mechanistic studies that provide a detailed understanding of the molecular-level picture of how cobalt phthalocyanine facilitates proton and electron transfers in the ratelimiting step. We are able to tune the rate-limiting step from electron transfer to concerted proton−electron transfer, enabling higher rates of carbon dioxide reduction. Our results highlight the significance of dispersion for understanding the intrinsic catalytic performance of metal phthalocyanines for electroreduction of CO 2 .

Epoxides are useful intermediates for the manufacture of a diverse set of chemical products. Current routes of olefin epoxidation either involve hazardous reagents or generate stoichiometric side products, leading to challenges in separation and significant waste streams. Here, we demonstrate a sustainable and safe route to epoxidize olefin substrates using water as the oxygen atom source at room temperature and ambient pressure. Manganese oxide nanoparticles (NPs) are shown to catalyze cyclooctene epoxidation with Faradaic efficiencies above 30%. Isotopic studies and detailed product analysis reveal an overall reaction in which water and cyclooctene are converted to cyclooctene oxide and hydrogen. Electrokinetic studies provide insights into the mechanism of olefin epoxidation, including an approximate first-order dependence on the substrate and water and a rate-determining step which involves the first electron transfer. We demonstrate that this new route can also achieve a cyclooctene conversion of ∼50% over 4 h.

Rapid bioorthogonal reactivity can be induced by controllable, catalytic stimuli using air as the oxidant. Methylene blue (4 μM) irradiated with red light (660 nm) catalyzes the rapid oxidation of a dihydrotetrazine to a tetrazine thereby turning on reactivity toward trans-cyclooctene dienophiles. Alternately, the aerial oxidation of dihydrotetrazines can be efficiently catalyzed by nanomolar levels of horseradish peroxidase under peroxide-free conditions. Selection of dihydrotetrazine/tetrazine pairs of sufficient kinetic stability in aerobic aqueous solutions is key to the success of these approaches. In this work, polymer fibers carrying latent dihydrotetrazines were catalytically activated and covalently modified by trans-cyclooctene conjugates of small molecules, peptides and proteins. In addition to visualization with fluorophores, fibers conjugated to a cell adhesive peptide exhibited a dramatically increased ability to mediate contact guidance of cells.