Increasing Current Density of Li-Mediated Ammonia Synthesis with High Surface Area Copper Electrodes

Li, Katja; Shapel, Sarah G.; Hochfilzer, Degenhart; Pedersen, Jakob B.; Krempl, Kevin; Andersen, Suzanne Zamany; Sažinas, Rokas; Saccoccio, Mattia; Li, Shaofeng; Chakraborty, Debashis; Kibsgaard, Jakob; Vesborg, Peter Christian Kjærgaard; Nørskov, Jens K.; Chorkendorff, Ib

doi:10.1021/acsenergylett.1c02104

Cited by 80 publications

(113 citation statements)

References 41 publications

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“…This partial current density can be achieved by increasing the total current density, the Faradaic efficiency to ammonia, or both. At the moment, no nitrogen reduction chemistry has reported production rates of this magnitude, though approaches for increasing rates through pressurization and the use of high surface area electrodes, 70 as well as the use of gas diffusion electrodes 10 have been reported. This suggests that breakthrough improvements to the electrolyte and chemistry are critical for the lithium-mediated nitrogen reduction approach to be economically viable for large-scale centralized ammonia production using renewable resources.…”

Section: Discussionmentioning

confidence: 99%

Cost and Performance Targets for Fully Electrochemical Ammonia Production under Flexible Operation

et al. 2022

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Methods to produce ammonia from air, water, and renewable electricity are necessary to transition ammonia production away from the CO2-emitting Haber-Bosch process. In this vein, a fully electric process in which water-splitting-derived hydrogen and air-separation-derived nitrogen are reacted in an electrochemical process to produce ammonia is attractive. Such a process has the potential to be highly flexible and utilize intermittent renewable energy well. Here, we evaluated the cost-effectiveness of large-scale fully electric ammonia production relying on renewable electricity sources in conjunction with different types of storage and flexible operation, using a mixed-integer linear programming framework. The approach incorporates a first-principle, chemistry-independent representation of reactor power consumption and its dependence on reactor sizing and electrochemical parameters, the impact of product separation and recycling unconverted reactants, and plant dynamics in response to temporal variability in renewable energy availability. Given the emerging nature of electrochemical ammonia synthesis from nitrogen and hydrogen, we used the model to identify the reaction descriptors and their threshold values that enable cost parity between fully electric ammonia production with commercially viable production using thermochemical synthesis coupled with electrolytic hydrogen powered by renewable energy. We found that ammonia can be produced in an economically competitive manner, i.e. at costs <1 $/kg, at large scales if the electrochemical reactor can produce ammonia at partial currents exceeding 400 mA cm -2 , energy efficiencies exceeding 30%, and process lifetimes of several years. In light of this, novel chemistries that can reduce nitrogen at high rates and moderate (<2.5 V) overpotentials are necessary for economic, large-scale ammonia production.

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Section: Discussionmentioning

confidence: 99%

Cost and Performance Targets for Fully Electrochemical Ammonia Production under Flexible Operation

et al. 2022

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“…Thus, the “real” amount of byproducts would be different than assumed here because of nonmeasurable inorganic species. We have seen and reported several inorganic phases before by XRD and XPS, 8 , 10 , 16 , 24 and they are reproducible.…”

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confidence: 65%

“… 5 For an assembly of a typical LiMEAS cell, a noble metal anode, e.g., platinum (Pt), and a transition metal cathode which does not interact and alloy with Li, e.g., molybdenum (Mo) or copper (Cu), are employed. 6 − 8 The desired product, i.e., NH 3 , is synthesized when the electrodes are submerged in the nonaqueous organic electrolyte, which consists of a conducting salt, e.g., lithium perchlorate (LiClO 4 ); 9 an organic solvent, e.g., tetrahydrofuran (THF); 6 , 10 and a potential proton source, such as alcohol or hydrogen (H 2 ). 5 − 7 The charge is usually passed at high overall cell potentials (>5 V).…”

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confidence: 99%

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Oxygen-Enhanced Chemical Stability of Lithium-Mediated Electrochemical Ammonia Synthesis

Sažinas

Andersen

et al. 2022

J. Phys. Chem. Lett.

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Although oxygen added to nonaqueous lithium-mediated electrochemical ammonia synthesis (LiMEAS) enhances Faradaic efficiency, its effect on chemical stability and byproducts requires understanding. Therefore, standardized high-resolution gas chromatography–mass spectrometry and nuclear magnetic resonance were employed. Different volatile degradation products have been qualitatively analyzed and quantified in tetrahydrofuran electrolyte by adding some oxygen to LiMEAS. Electrodeposited lithium and reduction/oxidation of the solvent on the electrodes produced organic byproducts to different extents, depending on the oxygen concentration, and resulted in less decomposition products after LiMEAS with oxygen. The main organic component in solid-electrolyte interphase was polytetrahydrofuran, which disappeared by adding an excess of oxygen (3 mol %) to LiMEAS. The total number of byproducts detected was 14, 9, and 8 with oxygen concentrations of 0, 0.8, and 3 mol %, respectively. The Faradaic efficiency and chemical stability of the LiMEAS have been greatly improved with addition of optimal 0.8 mol % oxygen at 20 bar total pressure.

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“…These themes from battery science can provide insight for the Li-mediated nitrogen reduction system. Increasing the concentration of salt in the Tsuneto electrolyte could create a more stable, more inorganic SEI and prevent working electrode drift, which was briefly mentioned by Li et al 31 where the authors noticed an improvement in stability with a 2 M LiClO4 concentration. Du et al achieve excellent Faradaic efficiencies and stability using 1.5 M LiNTf in a THF and ethanol containing electrolyte, and note a change in Faradaic efficiency with increasing salt concentration, but do not link this rigorously to the properties of the SEI 16 .…”

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confidence: 91%

The Role of Ion Solvation in Lithium Mediated Nitrogen Reduction

Westhead

Spry

Bagger

et al. 2022

Preprint

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Since its verification in just 2019, there have been numerous high-profile papers reporting improved efficiency of the lithium-mediated electrochemical nitrogen reduction system to make ammonia. However, the literature lacks a cohesive investigation systematically linking bulk electrolyte properties to electrochemical performance and Solid Electrolyte Interphase (SEI) properties. In this study, we vary electrolyte salt concentration and observe a transition from an unstable working electrode potential to working electrode potential stability and peak in Faradaic efficiency of 7.8 ± 0.5 % at 0.6 M LiClO4. The behaviour is linked to the formation of Solvent Separated Ion Pairs in the electrolyte through Raman spectroscopy. Time of Flight Secondary Ion Mass Spectrometry and X-Ray Photoelectron Spectroscopy reveal a more inorganic, and therefore more stable, SEI layer with increasing salt concentration. A drop in Faradaic efficiency is seen at concentrations higher than 0.6 M LiClO4, which is attributed to a combination of a loss in nitrogen solubility and diffusivity as well as increased SEI conductivity as measured by Electrochemical Impedance Spectroscopy.

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Increasing Current Density of Li-Mediated Ammonia Synthesis with High Surface Area Copper Electrodes

Cited by 80 publications

References 41 publications

Cost and Performance Targets for Fully Electrochemical Ammonia Production under Flexible Operation

Cost and Performance Targets for Fully Electrochemical Ammonia Production under Flexible Operation

Oxygen-Enhanced Chemical Stability of Lithium-Mediated Electrochemical Ammonia Synthesis

The Role of Ion Solvation in Lithium Mediated Nitrogen Reduction

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