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Artificial ammonia synthesis is vital to modern life; however, the Haber-Bosch process, by which most ammonia is synthesized, is capital and carbon intensive. Zero-valent-metal-mediated ammonia synthesis is a promising alternative but requires a metal that is both a strong reductant and forms a stable nitride. Only a small number of metals, like lithium, can satisfy these constraints. Therefore, we developed an electrochemical paradigm enabling the use of different reductants by orthogonalizing the roles of the zero-valent metal between sodium metal and a Ti active site. These components are cheaper than lithium by two orders of magnitude. Using a sodium-naphthalene-titanium cascade, we achieved a rate of 475 nmol cm-2 s-1 and a Faradaic efficiency of 24% and found that the reaction rate depends primarily on current density. 

The lithium-mediated nitrogen reduction reaction (LiNRR) produces ammonia in ambient conditions. This electrochemical pathway is dependent on a catalytic solid–electrolyte interphase—a nanoscale passivation layer formed from reductive electrolyte decomposition on the surface of lithium metal. The catalytic solid–electrolyte interphase is a unique nanostructured environment that exists on reactive metal surfaces and intimately influences product selectivity. Here we explore recent progress made in the field of lithium-mediated nitrogen reduction to ammonia, especially in light of growing knowledge about the nature of the catalytic solid–electrolyte interphase. We systematically analyse the observed chemical species and reactions that occur within the solid–electrolyte interphase. We also summarize key developments in kinetic and transport models, as well as highlight the cathodic and complementary anodic reactions. Trends in ammonia selectivities and rates with varying electrolyte compositions, cell designs and operating conditions are extracted and used to articulate a path forward for continued development of lithium-mediated nitrogen reduction to ammonia. 

Abstract The Tafel slope is a key parameter often quoted to characterize the efficacy of an electrochemical catalyst. In this paper, we develop a Bayesian data analysis approach to estimate the Tafel slope from experimentally-measured current-voltage data. Our approach obviates the human intervention required by current literature practice for Tafel estimation, and provides robust, distributional uncertainty estimates. Using synthetic data, we illustrate how data insufficiency can unknowingly influence current fitting approaches, and how our approach allays these concerns. We apply our approach to conduct a comprehensive re-analysis of data from the CO 2 reduction literature. This analysis reveals no systematic preference for Tafel slopes to cluster around certain "cardinal values” (e.g. 60 or 120 mV/decade). We hypothesize several plausible physical explanations for this observation, and discuss the implications of our finding for mechanistic analysis in electrochemical kinetic investigations. 

Although electrocarboxylation reactions use CO 2 as a renewable synthon and can incorporate renewable electricity as a driving force, the overall sustainability and practicality of this process is limited by the use of sacrificial anodes such as magnesium and aluminum. Replacing these anodes for the carboxylation of organic halides is not trivial because the cations produced from their oxidation inhibit a variety of undesired nucleophilic reactions that form esters, carbonates, and alcohols. Herein, a strategy to maintain selectivity without a sacrificial anode is developed by adding a salt with an inorganic cation that blocks nucleophilic reactions. Using anhydrous MgBr 2 as a low-cost, soluble source of Mg 2+ cations, carboxylation of a variety of aliphatic, benzylic, and aromatic halides was achieved with moderate to good (34–78%) yields without a sacrificial anode. Moreover, the yields from the sacrificial-anode-free process were often comparable or better than those from a traditional sacrificial-anode process. Examining a wide variety of substrates shows a correlation between known nucleophilic susceptibilities of carbon–halide bonds and selectivity loss in the absence of a Mg 2+ source. The carboxylate anion product was also discovered to mitigate cathodic passivation by insoluble carbonates produced as byproducts from concomitant CO 2 reduction to CO, although this protection can eventually become insufficient when sacrificial anodes are used. These results are a key step toward sustainable and practical carboxylation by providing an electrolyte design guideline to obviate the need for sacrificial anodes.