Ammonia is increasingly recognized as an important, sustainable fuel for global use in the future. Applications of ammonia in heavy transport, power generation, and distributed energy storage are being actively developed. Produced at scale, ammonia could replace a substantial fraction of current-day liquid fuel consumption. This ammonia-based economy will emerge through multiple generations of technology development and scale-up. The pathways forward in regard to current-day technology (generation 1) and immediate future approaches (generation 2) that rely on Haber-Bosch process are discussed. Generation 3 technology breaks this nexus with the Haber-Bosch process and enables direct reduction of dinitrogen to ammonia electrochemically. However, the roadmap toward scale in this technology has become obscured by recent research missteps. Nevertheless, alternative generation 3 approaches are becoming viable. We conclude with perspectives on the broader scale sustainability of an ammonia economy and the need for further understanding of the planetary nitrogen cycles of which ammonia is an important part.

Ammonia is of emerging interest as a liquefied, renewable-energy-sourced energy carrier for global use in the future. Electrochemical reduction of N2 (NRR) is widely recognised as an alternative to the traditional Haber–Bosch production process for ammonia. However, though the challenges of NRR experiments have become better understood, the reported rates are often too low to be convincing that reduction of the highly unreactive N2 molecule has actually been achieved. This perspective critically reassesses a wide range of the NRR reports, describes experimental case studies of potential origins of false-positives, and presents an updated, simplified experimental protocol dealing with the recently emerging issues.

Ammonia (NH3) is a globally important commodity for fertilizer production, but its synthesis by the Haber-Bosch process causes substantial emissions of carbon dioxide. Alternative, zero-carbon emission NH3 synthesis methods being explored include the promising electrochemical lithium-mediated nitrogen reduction reaction, which has nonetheless required sacrificial sources of protons. In this study, a phosphonium salt is introduced as a proton shuttle to help resolve this limitation. The salt also provides additional ionic conductivity, enabling high NH3 production rates of 53 ± 1 nanomoles per second per square centimeter at 69 ± 1% faradaic efficiency in 20-hour experiments under 0.5-bar hydrogen and 19.5-bar nitrogen. Continuous operation for more than 3 days is demonstrated.

No abstract

As research on sustainable ammonia synthesis via electrochemical and photochemical N 2 reduction progresses to include a wider variety of aqueous and aprotic electrolytes, 1 H NMR spectroscopy is increasingly adopted as a means for ammonium quantification. However, this method is highly sensitive to experimental parameters, as demonstrated herein using a highly versatile and robust NMR pulse program. We demonstrate the sensitivity of the measurement to the final pH of the analyzed solution and identify a [H + ] concentration range enabling robust quantification. We compare direct quantification versus calibration approaches to show that the former is highly sensitive to spin relaxation effects and identify the latter as the most reliable approach. This method, when optimized, enables direct, rapid quantification of both 14 NH 4 + and 15 NH 4 + within 12−22 min. The limit of detection of 5−10 μM, depending on the solvent, which meets the needs of current electrochemical and photochemical N 2 reduction research.

Previous theoretical work has predicted vanadium and niobium nitrides to be catalytically active toward the electrochemical reduction of dinitrogen to ammonia and inactive for the hydrogen evolution reaction. The present experimental study investigates the electrocatalytic activity of vanadium­(III) nitride, niobium­(III) nitride, and Nb4N5 for the nitrogen reduction reaction in aqueous electrolyte solutions of different pH under ambient conditions using a robust testing protocol and thoroughly controlled experimental conditions to exclude any contamination with adventitious sources of ammonia and nitrogen oxides. VN and Nb4N5 (supported on carbon cloth) were synthesized by annealing of hydrothermally produced hydroxide precursors in an NH3 atmosphere at 600–1100 °C; NbN was obtained by a solid-state reaction between niobium­(V) chloride and urea at 1000 °C. Comprehensive testing of the materials under a wide range of conditions unambiguously demonstrates their inability to catalyze the electrosynthesis of ammonia from dinitrogen, as well as the propensity of VN (synthesized at 600 °C) and Nb4N5 to release lattice nitride in a noncatalytic process, which leads to the formation of ammonia under reductive conditions. Thus, polycrystalline nitrides of vanadium and niobium are concluded to be catalytically inactive toward the ammonia electrosynthesis from N2 dissolved in water. The present work additionally emphasizes the compulsory requirement for the implementation of reliable testing and analysis procedures for the assessment of the catalytic properties of materials for the nitrogen reduction reaction.

The effective escape of nanocarriers from endosomal compartments of the cell remains a major hurdle in nanomedicine. The endosomal escape of pH-responsive, self-assembled, dual component particles based on poly[2-(diethylamino)ethyl methacrylate)(PDEAEMA) and poly(ethylene glycol)-b-poly[2-(diethylamino)ethyl methacrylate) (PEG-b-PDEAEMA) has been recently reported. Herein, we report that polymer molecular weight (M ) can be used to tune endosomal escape of nanoparticle delivery systems. PDEAEMA of M 7 kDa, 27 kDa, 56 kDa and 106 kDa was synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization and co-assembled with PEG-b-PDEAEMA (16 kDa) via nanoprecipitation. All particles had similar size, displayed pH-responsive behaviour, and low toxicity regardless of molecular weight. Ovalbumin was loaded in the particles to demonstrate loading and release capabilities and as a marker to study internalization and endosomal escape. Association and endosomal escape was found to depend on molecular weight, with enhanced escape observed for high M PDEAEMA: 42% of cells with particle induced endosomal escape for 106 kDa nanoparticles, compared to minimal escape for 7 kDa particles. The results show that a simple variation in molecular weight can enhance the endosomal escape of polymeric carriers, and thus improve their effectiveness for intracellular delivery of therapeutics.

The lithium mediated reduction of N 2 is one of the only available approaches to electrochemical ammonia production at significant yields under ambient conditions. However, much remains to be investigated about the various electrochemical processes and side reactions that are involved. Herein, we have examined the effects of parameters including electrode potential, convection, N 2 pressure, and water content to refine and control the process. We demonstrate that a closely linear ammonia yield can be maintained during experiments up to 60 h in length, with approximately constant faradaic efficiency. This steady state operation appears to be preceded by a coating of the electrode surface with the products of the reductive electrolyte decomposition, such as LiF. We demonstrate ammonia yield rates above 1 nmol s −1 cm −2 and faradaic efficiencies as high as 60% through the improved control of the reaction conditions.