Nonaqueous LiFePO 4 reference electrode: probing potentials and Li-ion activity in Li-mediated ammonia synthesis Romain Tort , Ifan Stephens, Olivia Westhead, Matthew Spry, Bethan J.V. Davies, Mary P. Ryan, Maria-Magdalena Titirici Imperial College London, UK The Li-mediated ammonia synthesis delivers ever-increasing performance and selectivity since its reintroduction as the only unambiguous route for electrochemical N2 conversion to NH 3 . 1,2 However, a holistic understanding of the processes governing this complex reaction is still lacking. It is hindered by many variables impacting ammonia synthesis, whether they are known or not, controlled or not. 3 Here, we address one of these variables: electrochemical potentials. We demonstrate a true LiFePO 4 non-aqueous reference electrode with a stable and reproducible redox equilibrium from which to measure potentials against, in various environments. 4 Using this reference electrode, we demonstrate two issues. First, no further electrochemical process is limiting ammonia synthesis beyond lithium plating. Hence, no significant improvement can be done in energy efficiency without moving away from lithium as a catalyst. Second, the counter electrode potential increases linearly but dramatically with partial current density to ammonia, likely as a result of uncontrolled solvent oxidation: an anodic reaction that needs to be tuned down for a sustainable and continuous process. This reference electrode serves as a tool in this regard, probing electrolyte architecture in situ, and giving clues on potential electrolyte improvements to address the above issues. References 1. Du, H.-L.; Chatti, M.; Hodgetts, R. Y.; Cherepanov, P. V.; Nguyen, C. K.; Matuszek, K.; MacFarlane, D. R.; Simonov, A. N. Electroreduction of Nitrogen with Almost 100% Current-to-Ammonia Efficiency. Nature 2022, 609 (7928), 722–727. https:// doi.org/10.1038/s41586-022-05108-y. 2. Li, S.; Zhou, Y.; Li, K.; Saccoccio, M.; Sažinas, R.; Andersen, S. Z.; Pedersen, J. B.; Fu, X.; Shadravan, V.; Chakraborty, D.; Kibsgaard, J.; Vesborg, P. C. K.; Nørskov, J. K.; Chorkendorff, I. Electrosynthesis of Ammonia with High Selectivity and High Rates via Engineering of the Solid-Electrolyte Interphase. Joule 2022. https://doi.org/10.1016/J.JOULE.2022.07.009. 3. Westhead, O.; Spry, M.; Bagger, A.; Shen, Z.; Yadegari, H.; Favero, S.; Tort, R.; Titirici, M.; Ryan, M. P.; Jervis, R.; Katayama, Y.; Aguadero, A.; Regoutz, A.; Grimaud, A.; Stephens, I. E. L. The Role of Ion Solvation in Lithium Mediated Nitrogen Reduction. J. Mater. Chem. A 2023. https://doi.org/10.1039/D2TA07686A. 4. Tort, R.; Westhead, O.; Spry, M.; Davies, B. J. V.; Ryan, M. P.; Titirici, M.-M.; Stephens, I. E. L. Nonaqueous Li-Mediated Nitrogen Reduction: Taking Control of Potentials. ACS Energy Lett. 2023, 8, 1003–1009. https://doi.org/10.1021/ acsenergylett.2c02697.
P47
© The Author(s), 2023
Made with FlippingBook Learn more on our blog