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.

Table S1. Summary of Reported Heterogeneous Molecular Catalyst Performances. Data from graphs were extracted using WebPlotDigitizer [1] and should have an error less than 5%. Catalyst loading, current density, and TOF are related via Equation S1, allowing the calculation of unreported values if the other two values are reported. Catalyst loadings are listed as the amount deposited unless otherwise indicated. Potentials in aqueous solution are referenced to SHE rather than RHE since several studies have shown a pH-independent mechanism for ECR to CO on immobilized molecular catalysts. Please see the notes at the end of the table for definitions of acronyms and symbols. Catalyst Electrode Deposition Solvent Electrolyte Catalyst Loading (mol/cm 2 ) Voltage (V vs. SHE)

The mechanism for carbon dioxide reduction (CO 2 RR) to carbon monoxide (CO) at immobilized cobalt phthalocyanine (CoPc) in aqueous electrolytes has been widely debated. In this work, we investigated the mechanism of CO 2 RR to CO on CoPc via experimental reaction kinetics coupled with model fitting. Unexpectedly, reactant order dependences and Tafel slopes deviate from commonly expected values and change depending on the testing conditions. For example, (1) the effect of bicarbonate deviates from power law kinetics and transitions from inhibitory to promotional with increasingly reductive potential, and (2) the CO 2 order dependence deviates from unity at more-reductive potentials. We propose a kinetic model, chosen from more than 15 candidate models, that is able to quantitatively fit all of the experimental data. The model invokes (1) catalyst poisoning via bicarbonate electrosorption, (2) mixed control between concerted proton− electron transfer (CPET) and sequential electron transfer-proton transfer (ET-PT), and (3) both water and bicarbonate as kinetically relevant proton donors. The proposed model also predicts that the relative importance of the above factors changes depending on the reaction conditions, highlighting the potential downfalls of broadly applying reaction mechanisms that were inferred from kinetic data collected in a narrow range of testing conditions. This study emphasizes the importance of cohesively using kinetic data collected over a wide range of operating conditions to test and formulate kinetic models of electrocatalytic reactions.

We report a direct and efficient electrochemical carboxylation of benzylic C-N bonds with CO2 at room temperature. The reaction has been successfully applied to both primary and secondary benzylic C-N bonds with compatibility of a variety of functional groups. This procedure does not require stoichiometric metals, external reducing agents, or sacrificial anodes, making column chromatography unnecessary for product purification. Differential 2 electrochemical mass spectrometry (DEMS) was used to elucidate key intermediates of the electrocarboxylation reaction.