Nitrogen reduction to ammonia at high efficiency and rates based on a phosphonium proton shuttle

Suryanto, Bryan H. R.; Matuszek, Karolina; Choi, Jaecheol; Hodgetts, Rebecca Y.; Du, Hoang-Long; Bakker, Jacinta M.; Kang, Colin S. M.; Cherepanov, Pavel V.; Simonov, Alexandr N.; MacFarlane, Douglas R.

doi:10.1126/science.abg2371

Cited by 377 publications

(384 citation statements)

References 45 publications

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“…The developed design principles in the form of above-threshold constraints on Kamlet–Taft α and β parameters provide a rationale not only for the promising candidates identified in this study but also others reported in the literature. For example, a concurrent work by Suryanto et al 48 reports a phosphonium-based proton shuttle with high Faradaic efficiency for a very similar scheme, the performance of which can be rationalized based on our design rule given that the phosphonium cation exhibits high KT parameter values as reported from other literature. 49 , 50 In light of this independent corroboration, we identify ionic liquids that exhibit high KT parameter values to be promising candidates for exploration in a subsequent effort.…”

Section: Discussionmentioning

confidence: 61%

Closed-Loop Electrolyte Design for Lithium-Mediated Ammonia Synthesis

et al. 2021

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Novel methods for producing ammonia, a large-scale industrial chemical, are necessary for reducing the environmental impact of its production. Lithium-mediated electrochemical nitrogen reduction is one attractive alternative method for producing ammonia. In this work, we experimentally tested several classes of proton donors for activity in the lithium-mediated approach. From these data, an interpretable data-driven classification model is constructed to distinguish between active and inactive proton donors; solvatochromic Kamlet–Taft parameters emerged to be the key descriptors for predicting nitrogen reduction activity. A deep learning model is trained to predict these parameters using experimental data from the literature. The combination of the classification and deep learning models provides a predictive mapping from proton donor structure to activity for nitrogen reduction. We demonstrate that the two-model approach is superior to a purely mechanistic or a data-driven approach in accuracy and experimental data efficiency.

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Section: Discussionmentioning

confidence: 61%

Closed-Loop Electrolyte Design for Lithium-Mediated Ammonia Synthesis

et al. 2021

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“…Future investigations should consider additional process arrangements for their ability to drive down the process energy demand. For example, increasing the faradaic efficiency of the process is key to achieving low energy demand due to the flow on effect observed here for the balance of plant energy demands and is likely to outweigh energy trade-offs such as high cell voltage as seen in recent breakthroughs in the electrochemical ammonia field (Suryanto et al, 2021). Understanding all process requirements for direct electrochemical ammonia can help direct research efforts and work outlined here should be expanded on for other electrochemical systems such as aprotic and redox mediated approaches.…”

Section: Optimised Performancementioning

confidence: 98%

“…Some evidence that increasing the temperature up to 60 °C can improve both faradaic efficiency and yield considerably has been presented (Qin et al, 2018) and therefore as a conservative estimate 60 °C has been used for both hydrogen and water fed cells since this is also the operational temperature of electrolysis and fuel cells and reduces process complexity. The majority of authors have not attempted to pressurise the cell, although Suryanto et al (2021) recently presented an interesting study with increased pressure on the cathode side showing high performance. Ambient pressure is assumed here however in keeping with most approaches for electrochemical ammonia formation.…”

Section: Electrochemical Ammonia Generationmentioning

confidence: 99%

“…Indeed the technology is early stage, very few authors progressing beyond bench scale and even half-cell reactions towards a full electrochemical synthesis with integrated in and out flows. Issues with experimental validity and reproduction of results have also been encountered, as outlined by MacFarlane et al (2020), although some recent breakthroughs in increased faradaic efficiency and ammonia production rate could point towards redox mediated approaches as being more promising moving forward (Suryanto et al, 2021).…”

Section: Introductionmentioning

confidence: 99%

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Electrochemical Ammonia: Power to Ammonia Ratio and Balance of Plant Requirements for Two Different Electrolysis Approaches

2021

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Electrochemical ammonia generation allows direct, low pressure synthesis of ammonia as an alternative to the established Haber-Bosch process. The increasing need to drive industry with renewable electricity central to decarbonisation and electrochemical ammonia synthesis offers a possible efficient and low emission route for this increasingly important chemical. It also provides a potential route for more distributed and small-scale ammonia synthesis with a reduced production footprint. Electrochemical ammonia synthesis is still early stage but has seen recent acceleration in fundamental understanding. In this work, two different ammonia electrolysis systems are considered. Balance of plant (BOP) requirements are presented and modelled to compare performance and determine trade-offs. The first option (water fed cell) uses direct ammonia synthesis from water and air. The second (hydrogen-fed cell), involves a two-step electrolysis approach firstly producing hydrogen followed by electrochemical ammonia generation. Results indicate that the water fed approach shows the most promise in achieving low energy demand for direct electrochemical ammonia generation. Breaking the reaction into two steps for the hydrogen fed approach introduces a source of inefficiency which is not overcome by reduced BOP energy demands, and will only be an attractive pathway for reactors which promise both high efficiency and increased ammonia formation rate compared to water fed cells. The most optimised scenario investigated here with 90% faradaic efficiency (FE) and 1.5 V cell potential (75% nitrogen utilisation) gives a power to ammonia value of 15 kWh/kg NH3 for a water fed cell. For the best hydrogen fed arrangement, the requirement is 19 kWh/kg NH3. This is achieved with 0.5 V cell potential and 75% utilisation of both hydrogen and nitrogen (90% FE). Modelling demonstrated that balance of plant requirements for electrochemical ammonia are significant. Electrochemical energy inputs dominate energy requirements at low FE, however in cases of high FE the BOP accounts for approximately 50% of the total energy demand, mostly from ammonia separation requirements. In the hydrogen fed cell arrangement, it was also demonstrated that recycle of unconverted hydrogen is essential for efficient operation, even in the case where this increases BOP energy inputs.

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“…[12] Recently, Suryanto et al have reported even more promising results on electrochemical synthesis of NH 3 in a phosphonium salt in place of ethanol and achieved a high NH 3 production rate of roughly 53 × 10 À 9 mol cm À 2 s À 1 and a faradaic efficiency of around 69 % for 20 h under 0.05 MPa H 2 and 1.95 MPa N 2 . [20] Chemical methods for the nitrogen fixation with Li and the NH 3 synthesis have also been explored extensively. For example, McEnaney et al proposed a LiÀ Li 3 NÀ LiOH loop for NH 3 synthesis.…”

Section: Introductionmentioning

confidence: 99%

Lithium‐based Loop for Ambient‐Pressure Ammonia Synthesis in a Liquid Alloy‐Salt Catalytic System

et al. 2021

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The Haber‐Bosch process for ammonia (NH3) production in industry relies on high temperature and high pressure and is therefore highly energy intensive. In addition, the activity of the solid transition metal‐based catalysts used is typically limited by the scaling relation between activation barrier for N2 dissociation and nitrogen‐binding energy. Here, an innovative Li‐based loop in a liquid alloy‐salt catalytic system for ambient‐pressure NH3 synthesis from N2 and H2 was developed. The looping process consisted of three reaction steps taking place simultaneously. The first step was the nitrogen fixation by Li in the liquid Li−Sn alloy to form lithium nitride (Li3N), which floated up and dissolved into the molten salt. The second step was the hydrogenation of the Li3N to produce NH3 and lithium hydride (LiH) in the molten salt. The third step was the decomposition of the LiH to regenerate Li in the presence of Sn. An average NH3 yield rate of 0.025 μg s−1 was achieved in an 81 h test at 510 °C and ambient pressure. The floating and dissolution of Li3N realized in the liquid catalytic system enabled circumventing the scaling relation exerted on Li, and the remarkable properties of liquid alloy and molten salt offered extraordinary advantages for NH3 synthesis at ambient pressure.

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Nitrogen reduction to ammonia at high efficiency and rates based on a phosphonium proton shuttle

Cited by 377 publications

References 45 publications

Closed-Loop Electrolyte Design for Lithium-Mediated Ammonia Synthesis

Closed-Loop Electrolyte Design for Lithium-Mediated Ammonia Synthesis

Electrochemical Ammonia: Power to Ammonia Ratio and Balance of Plant Requirements for Two Different Electrolysis Approaches

Lithium‐based Loop for Ambient‐Pressure Ammonia Synthesis in a Liquid Alloy‐Salt Catalytic System

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