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.

is currently a doctoral student in the Chemical Engineering Department at MIT. An NSF Graduate Research Fellow and an MIT Presidential Fellow, he is studying applications of electrochemistry to the nitrogen cycle in the Manthiram Lab. Zachary received a B.S.E. from Princeton University in Chemical and Biological Engineering with minors in applications of computing and materials science. As an undergraduate, he worked in Dr. Craig Arnold's lab studying the coupling of mechanics and electrochemistry in lithium ion batteries. Karthish Manthiram is an Assistant Professor of Chemical Engineering at MIT. The Manthiram Lab develops technologies that enable modular and sustainable transformations of molecules. The lab is currently focused on the conversion of distributed feedstocks, such as air, water, carbon dioxide, and renewable electricity, into molecules that have an impact on our everyday lives. Examples include catalytic technologies through which farmers in developing countries can produce their own ammonia fertilizers and conversion of carbon dioxide into methanol to mitigate emissions that would otherwise contribute to global warming. Karthish received his bachelor's degree from Stanford University in 2010 and his Ph.D. from UC Berkeley in 2015, both in Chemical Engineering. Most recently, he was a postdoctoral researcher at the California Institute of Technology.

Understanding the function of nitric oxide (NO), a lipophilic messenger in physiological processes across nervous, cardiovascular and immune systems, is currently impeded by the dearth of tools to deliver this gaseous molecule in situ to specific cells. To address this need, we developed iron sulfide nanoclusters that catalyse NO generation from benign sodium nitrite in the presence of modest electric fields. Locally generated NO activates the NO-sensitive cation channel, transient receptor potential vanilloid family member 1 (TRPV1), and latency of TRPV1-mediated Ca 2+ responses can be controlled by varying the applied voltage. Integrating these electrocatalytic nanoclusters with multimaterial fibres allows NO-mediated neuronal interrogation in vivo . In situ generation of NO within the ventral tegmental area via the electrocatalytic fibres evoked neuronal excitation in the targeted brain region and its excitatory projections. This NO generation platform may advance mechanistic studies of the role of NO in the nervous system and other organs.

During battery use, electrode materials are known to expand and contract in repeatable patterns, and this strain has been previously correlated with battery properties such as state of charge and state of health. In this study, we show that the second derivative of strain, d 2 ε/dQ 2 , is mathematically proportional to dV/dQ within an electrode stage. We also experimentally quantify peaks in the strain curves for electrode stage transitions at practical charge rates of up to C/2 and confirm that transitions are visible in the practical scenario of discharging at the higher rate of 1C. Moreover, the location of the transition measured by d 2 ε/dQ 2 changes by less than 10% from 0.05 C to 0.5 C, but the transition measured with dV/dQ decreases by more than 15% from 0.05 C to 0.3 C, demonstrating the reliability of strain to measure electrode transitions at moderate charge rates. We also note that d 2 ε/dQ 2 exhibits similar peak shifts as those expected in dV/dQ as the cell ages. Our derivations for the model system of graphite and lithium cobalt oxide can be generalized to other battery systems and used to characterize materials at practical charge rates impossible with only voltage. Lithium ion batteries are a popular choice for energy storage due to their high ratio of energy capacity to size and their low rate of self-discharge.1 Unfortunately, batteries are difficult to characterize because they are essentially isolated systems with many reactions and processes occurring internally. Imaging the internal reactions and materials during battery operation is impractical, and very few tools exist that can provide information about material evolution during battery usage.Voltage is a common tool for characterizing battery materials during operation, particularly the derivative of voltage with respect to state of charge, dV/dQ. A cell's voltage is directly related to the chemistry of the materials, and many previous studies have investigated battery voltage and used it to identify phase transitions in materials, predict the effects of cell aging, and relate voltage to underlying chemical reactions. [2][3][4][5][6] In addition, many of these studies have resulted in the development of models to help understand battery material evolution by predicting voltage curves based on the fundamental physics in the battery. dV/dQ has proven to be an extremely useful tool and an accurate predictor of cell aging, but it is limited by physical constraints. Notably, electrode phase transitions are most easily viewed at slow charge rates, and the distinguishing features in a dV/dQ plot are nonexistent at high charge rates. Studies often cycle batteries at charge rates of C/20 or lower in order to glean information from dV/dQ curves.Recent battery research has focused on mechanical properties, such as strain, ε, as a novel tool to indicate underlying phenomena. 5,[7][8][9][10][11][12] This previous research relies on the fact that during battery operation, electrode materials are known to expand and contract in repeatable patterns. S...

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.

The hydrodynamics of electrochemical CO 2 reduction (CO 2 R) systems is an insufficiently investigated area of research that has broad implications on catalyst activity and selectivity. While most previous reports are limited to laminar and CO 2 -sparged systems, herein we address a wide range of hydrodynamics via electrolyte recirculation systems. We find that increased hydrodynamics at the electrode surface results directly in changes to the ethylene and methane Tafel slopes, demonstrating that mass transport is on equal footing with catalyst active sites in determining reaction mechanisms and the ensuing product distribution. Mass transport is traditionally considered to be in the purview of systems-level engineering, yet the present work shows that CO 2 R mechanistic work must be considered in the context of the mass transport conditions. We extend our analysis to organic coatings, demonstrating that the films shield the active sites from variability in hydrodynamics and increase the residence time of CO so that it may be further reduced to desirable products.

Decreasing costs of renewable sources of electricity will increase the viability of electrochemical processes in chemical manufacturing. To this end, improved understanding of electrochemical N-H bond activation is essential to develop electrochemical routes for nitrogen-containing chemicals. In this work, we investigate electrochemical ammonia activation in acetonitrile, a prototypical non-aqueous solvent for electro-organic syntheses. Non-aqueous environments are desirable for electroorganic syntheses due to large electrochemical stability windows and high solubility for organic products. We find that ammonia oxidation in acetonitrile proceeds through an outer-sphere mechanism involving an initial electron transfer as the rate-determining step, likely producing an ammonia radical cation. Density functional theory calculations explain a low transfer coefficient and suggest possible subsequent reaction steps. Structural factors involved in lowering of the transfer coefficient provide insights that are applicable to wider range of small-molecule activation chemistries.

Although lithium ion battery research often focuses on electrochemical properties, lithium ion intercalation materials are also mechanically active. Essentially, these materials exhibit a mechanical-electrochemical coupling such that when a stress is applied, the voltage of the battery increases. In this work, we develop a model to study and predict the effectiveness of intercalation materials as mechanical energy harvesters. Specifically, we show that a lithium ion battery harvester can be modelled as a simple circuit and that we can make both qualitative and quantitative predictions about the effectiveness of a battery material given its intrinsic mechanical and electrochemical properties. The measured efficiency of our system, calculated from the energy output and total work input, is 0.012 ± 0.004%, and our model predicts that the maximum theoretical efficiency of the system is 2.9 ± 0.5%. In the future, this model will help us develop and study other intercalation materials that will bring the measured efficiency closer to our proposed theoretical maximum.