Upgrading Li-Mediated Ammonia Synthesis Electrochemical Characterisation – A Battery-Inspired Cell Design
Romain Tort a, Olivia Westhead b, Matthew Spry b, Daisy Thornton b, Bethan Davies b, Mary P. Ryan b, Maria-Magdalena Titirici a, Ifan E. L. Stephens b
a Department of Chemical Engineering Imperial College London, South Kensington, Londres SW7 2AZ, Reino Unido, United Kingdom
b Department of Materials Imperial College London, South Kensington, Londres SW7 2AZ, Reino Unido, United Kingdom
Materials for Sustainable Development Conference (MATSUS)
Proceedings of Materials for Sustainable Development Conference (MAT-SUS) (NFM22)
#Suschem- Materials and electrochemistry for sustainable fuels and chemicals
Barcelona, Spain, 2022 October 24th - 28th
Organizers: Marta Costa Figueiredo and Raffaella Buonsanti
Contributed talk, Romain Tort, presentation 196
DOI: https://doi.org/10.29363/nanoge.nfm.2022.196
Publication date: 11th July 2022

Nitrogen fixation has shaped our society over the past two centuries, providing ammonia derived fertilizers through the Haber-Bosch process to now feed more than half the world population. However, its production is responsible for >1% of our greenhouse gases emissions.[1] It is therefore essential to find alternative synthesis methods sourced by renewable energies.

 

The electrochemical Li-mediated nitrogen reduction to ammonia (NRR) provides a more sustainable alternative to this challenging reaction.[2,3] This system, operating in a non-aqueous electrolyte analogous to the ones used in Li-ion batteries, provides tangible selectivity towards NH3.[3–5] Just like in Li-ion batteries, a passivating Solid-Electrolyte Interphase (SEI), made of electrolyte degradation products, forms at the cathode of the NRR system. This SEI likely plays a role in controlled proton activity at the electrode surface, limited hydrogen evolution and thus the observed selectivity.[6–8] Consequently, characterisation of this interface (and of the whole system) is vital.

 

The work presented here expresses guidance for reliable and in-depth electrochemical characterisation of the NRR system and its SEI, all through the lens of a new non-aqueous electrochemical cell design. Drawing further inspiration from batteries, considerations on the cell’s three-electrode geometry,[9–11] construction of a true reference electrode[10,12–14] (as opposed to quasi-reference electrodes in current setups in the field),[3,5,15] and cathode/anode processes separation will be under investigation. As a result, we propose and demonstrate an ideal setup for potential-controlled NRR electrochemistry, capable of measuring accurately the different electrochemical processes occurring over the course of this elusive reaction. Improvements in the accuracy, consistency and reproducibility of the electrochemical measurements resulting from this cell design will be illustrated through the study of a variety of electrolyte architectures.

[1] Lim, J., Fernández, C. A., Lee, S. W. & Hatzell, M. C. Ammonia and Nitric Acid Demands for Fertilizer Use in 2050. ACS Energy Lett. 6, 3676–3685 (2021).
[2] Tsuneto, A., Kudo, A. & Sakata, T. Lithium-mediated electrochemical reduction of high pressure N2 to NH3. J. Electroanal. Chem. 367, 183–188 (1994).
[3] Andersen, S. Z. et al. A rigorous electrochemical ammonia synthesis protocol with quantitative isotope measurements. Nature 570, 504–508 (2019).
[4] Andersen, S. Z. et al. Increasing stability, efficiency, and fundamental understanding of lithium-mediated electrochemical nitrogen reduction. Energy Environ. Sci. 13, 4291–4300 (2020).
[5] Lazouski, N., Schiffer, Z. J., Williams, K. & Manthiram, K. Understanding Continuous Lithium-Mediated Electrochemical Nitrogen Reduction. Joule 3, 1127–1139 (2019).
[6] Peled, E. & Menkin, S. Review—SEI: Past, Present and Future. J. Electrochem. Soc. 164, A1703–A1719 (2017).
[7] Gauthier, M. et al. Electrode-Electrolyte Interface in Li-Ion Batteries: Current Understanding and New Insights. J. Phys. Chem. Lett. 6, 4653–4672 (2015).
[8] Li, K. et al. Enhancement of lithium-mediated ammonia synthesis by addition of oxygen. Science (80). 374, 1593–1597 (2021).
[9] Ender, M., Illig, J. & Ivers-Tiffée, E. Three-Electrode Setups for Lithium-Ion Batteries. J. Electrochem. Soc. 164, A71–A79 (2017).
[10] Costard, J., Ender, M., Weiss, M. & Ivers-Tiffée, E. Three-Electrode Setups for Lithium-Ion Batteries. J. Electrochem. Soc. 164, A80–A87 (2017).
[11] Klink, S. et al. The importance of cell geometry for electrochemical impedance spectroscopy in three-electrode lithium ion battery test cells. Electrochem. commun. 22, 120–123 (2012).
[12] La Mantia, F., Wessells, C. D., Deshazer, H. D. & Cui, Y. Reliable reference electrodes for lithium-ion batteries. Electrochem. commun. 31, 141–144 (2013).
[13] Xiao, Y. et al. A Toolbox of Reference Electrodes for Lithium Batteries. Adv. Funct. Mater. 2108449, 1–19 (2021).
[14] Raccichini, R., Amores, M. & Hinds, G. Critical review of the use of reference electrodes in li-ion batteries: A diagnostic perspective. Batteries 5, 1–24 (2019).
[15] Cherepanov, P. V., Krebsz, M., Hodgetts, R. Y., Simonov, A. N. & MacFarlane, D. R. Understanding the Factors Determining the Faradaic Efficiency and Rate of the Lithium Redox-Mediated N 2 Reduction to Ammonia. J. Phys. Chem. C 125, 11402–11410 (2021).

I gratefully acknowledge the UK Royal Academy of Engineering for funding this work. My acknowledgements to the Chemical Engineering workshop at Imperial College London for their help in designing and manufacturing the electrochemical cell.

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